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MOOAC02 | A Short-Pulse Hard X-ray Source with Compact Electron LINAC Via Laser-Compton Scattering for Medical and Industrial Radiography | laser, electron, scattering, cathode | 121 | |||||
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An intense, quasi-monochromatic hard X-ray beam has been generated via the laser-Compton scattering of a picosecond electron bunch with an intense femtosecond TW laser. A s-band linear accelerator of 40 MeV and Ti:Sa femtosecond TW laser were used to generate X-rays. We plan to increase the X-ray yield up to two-orders than the current one until FY2008. Our recent R&D for that purpose are generation of multi-pulse electron beam using a photo-cathode rf-gun, and multi-pulse laser cavity for Compton scattering. We briefly describe the specifications of the electron accelerator and the laser systems, together with the developments and modifications being undergone.
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MOZBC02 | Status of the Hadrontherapy Projects in Europe | proton, ion, cyclotron, synchrotron | 127 | |||||
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Several new facilities for cancer therapy based on light ion accelerators are being designed and constructed in European countries (France, Germany, Italy). This talk will cover the current status of these facilities.
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MOOBC01 | Electron Accelerator Options for Photo-Detection of Fissile Materials | electron, target, linac, laser | 137 | |||||
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Funding: Work supported by DNDO of US Government |
For national security, it is important to detect the presence of Special Nuclear Materials (SNM), especially Highly-Enriched Uranium (HEU). Generally used methods for such detection include interrogation by photons and neutrons. For example, photofission in HEU can be initiated with 14-MeV photons. The resulting delayed neutrons and photons from the fission fragments are clear signatures of the presence of HEU. One can generate high-energy photons using electron accelerators via various mechanisms. In this paper, we will describe two of them, namely electron bremsstrahlung and Compton-backscattered photons. We focus on these two mechanisms because they cover a wide range of accelerator requirements. Electron bremsstrahlung can be generated using a compact low-energy electron linac while the generation of Compton-backscattered photons requires a high-energy electron accelerator of a few hundred MeV. We review these two options, describe their accelerator requirements, and compare their relative merits. |
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MOPAN024 | Commissioning of the ELETTRA Fast Orbit Feedback System | feedback, electron, controls, power-supply | 203 | |||||
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A fast orbit feedback system has been installed at ELETTRA. It globally corrects the closed orbit at 10 kHz rate using all the BPMs and corrector magnets of the storage ring. The Libera Electron device has been used to upgrade the original detectors in order to provide micrometric accuracy and fast data rate of the beam position measurements. The article reports the experience gained during the commissioning of the system and the first operational results.
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MOPAN041 | Design of a Movable Synchrotron Radiation Mask with SiC Absorber for the Photon Factory Advanced Ring (PF-AR) | synchrotron, synchrotron-radiation, factory, klystron | 248 | |||||
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We have six rf cavities in the Photon Factory Advanced ring (PF-AR) at KEK. Three years ago, one of them was seriously damaged by the Synchrotron Radiation (SR) from the upstream of the cavity. In order to protect the cavities from SR, we intend to install SR masks nearby the cavities. The masks have to be positioned as close as possible to the beams in order to block the SR completely during the beam storage, and as far as possible during the beam injection. Therefore SR masks should be movable. Since it is placed under strong HOM power from the cavities, careful design is necessary for power dissipation. The basic structure of the movable masks is a coaxial wave-guide with cylindrical SiC absorber whose power capability is designed to be more than 1kW. We report the design of the movable SR masks and the result of rf power test.
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MOPAN060 | Compensation of BPM Chamber Motion in PLS Orbit Feedback System | feedback, vacuum, electron, controls | 290 | |||||
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The false BPM reading resulting from the BPM vacuum chamber motion due to thermal load change by synchrotron radiation is compensated by the real-time monitoring of the chamber position in the PLS orbit feedback system. The BPM chamber moves up to 20 μm during the beam refill and the chamber motion has a time constant of about one and half hour, which is related to thermal equilibrium of the vacuum chamber. To monitor the BPM chamber motion, LVDTs with 0.2 μm reading accuracy were installed on all BPM chambers, and the measured data are used in the orbit feedback every 1 minute. In this paper, we will describe how serious the BPM chamber motion are and how well it is compensated.
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MOPAN113 | The P0 Feedback Control System Blurs the Line between IOC and FPGA | feedback, controls, storage-ring, monitoring | 431 | |||||
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The P0 Feedback System is a new design at the APS with the main intent to stabilize a single bunch in order to operate at a higher accumulated charge. The algorithm for this project required a high-speed DSP solution for a single channel that would make adjustments on a turn-by-turn basis. An FPGA solution was selected that not only met the requirements of the project, but far exceeded the requirements. By using a single FPGA, we were able to adjust up to 324 bunches on two separate channels with a total computational time of ~6x109 multiply-accumulate operations per second. The IOC is a Coldfire CPU tightly coupled to the FPGA, providing a dedicated control and monitoring of the system through EPICS process variables. One of the benefits of this configuration is having a four-channel scope in the FPGA that can be monitored on a continuous basis. |
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MOPAS025 | Conceptual Design of ILC Damping Ring Wiggler Straight Vacuum System | wiggler, quadrupole, vacuum, damping | 488 | |||||
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Funding: U. S. Department of Energy, Contract No. DE-AC02-05CH11231. |
The positron and electron damping rings for the ILC (International Linear Collider) will contain long straight sections consisting of twenty wiggler/quadrupole pairs. The wigglers will be based upon the CESR-C superconducting design* . There are a number of challenges associated with the design of the wiggler straight vacuum system, in particular, the absorption of photon power generated by the wigglers. This paper will present the overall conceptual design of the wiggler straight vacuum system developed for the ILC RDR. Particular emphasis will be placed on photon power load calculations and the absorber design.
* A. Mihailichenko, Optimized Wiggler Magnet for CESR, Proceedings of PAC2001, Chicago, Il, June 18-22, 2001 |
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TUOBC01 | Synchronizable High Voltage Pulser with Laser-Photocathode Trigger | laser, gun, electron, vacuum | 862 | |||||
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Funding: Work supported by DOE SBIR grant no. DE-FG02-03ER83878. |
High-gradient electron guns can suppress space-charge induced transverse emittance growth when the electron beam is still in the low-energy injection stage. A synchronizable, high-voltage pulser can be used to power up a high-gradient gun. We propose to build a 200 kV pulser using a special trigger that utilizes a laser-photocathode sub-system. A laser trigger beam will first energize a spark gap, and then provide a second trigger signal from a photocathode using its leftover energy, to further close the gap. This system will not only raise the utilization efficiency of the laser beam energy, but also enhance the reliability of the trigger circuit. Our preliminary analysis shows that the proposed system will significantly improve the performance of the laser trigger pulse with the jitter on the order of hundreds of picoseconds. It is expected that the pulser can be used in the applications of high gradient guns as well as in other devices that need high precision trigger such as short pulse lasers, streak cameras, impulse radiating antennas, etc. |
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TUPMN016 | Upgrade of the BESSY Femtoslicing Source | laser, undulator, background, electron | 950 | |||||
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The BESSY femtoslicing source as the first undulator-based source has succesfully demonstrated its capabilities of providing ~100 fs x-ray pulses in an energy range from 300 to 1400 eV with linear and circular polarisation. With this type of slicing source exhibiting an excellent signal-to-noise ratio, the number of detected photons at the user frontend is still limited to ~103 / sec. Several improvements are underway to increase the photon flux and to improve the stability of the source. An upgrade of the present laser system will increase the pulse repetition rate from 1 to 3 kHz. Furthermore, a new evacuated laser beam path will be implemented to provide higher pointing stability and an automated postion feedback. The benefits and limitations of these improvements will be discussed, and new measurements will be presented.
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TUPMN037 | Power Tests of a PLD Film Mg Photo-cathode in a RF Gun | cathode, laser, gun, target | 995 | |||||
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Metallic film photo-cathodes are rugged, have a fast response and good emission uniformity. Mg has also a relevant Quantum Efficiency in the near UV. A cathode suitable for a 1.5 cells S-band RF gun has been produced by depositing an Mg film on Cu by Pulsed Laser Deposition technique. After different optimizations, stable good results have been reached in the low field measurement scenario. A sample was deposited on a gun flange and tested in the 1.6 cell injector at UCLA Pegasus facility to prove cathode resistence in a high field environment. The results are described.
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TUPMN038 | Coherent Cherenkov Radiation as a Temporal Diagnostic for Microbunched Beams | radiation, diagnostics, electron, vacuum | 998 | |||||
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Cherenkov radiation of a relativistic e-beam traversing a thin section of aerogel is analized, putting the stress on the coherent contribution due to the intra-beam, transverse and longitudinal structure. The use of this tool as a temporal diagnostic for micro-bunched beams makes possible to improve the amount of collected power at the microbunching frequency several orders of magnitude more respect to the uncoherent Cherenkov contribution. The non-idealities of a real beam are taken in account, and some techniques aimed on enhancing the coherent part of radiation are proposed and analized analitically and through simulation codes.
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TUPMN045 | PF-Ring and PF-AR Operational Status | injection, undulator, insertion, insertion-device | 1019 | |||||
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In KEK, we have two synchrotron light sources which were constructed in the early 1980s. One is the Photon Factory storage ring (PF-ring) and the other is the Photon Factory advanced ring (PF-AR). The PF-ring is usually operated at 2.5 GeV and sometimes ramped up to 3.0 GeV to provide photons with the energy from VUV to hard X-ray region. The PF-AR is mostly operated in a single-bunch mode of 6.5 GeV to provide pulsed hard X-rays. Operational performances of them have been upgraded through several reinforcements. After the reconstruction of the PF-ring straight sections from March to September 2005, two short-gap undulators were newly installed. They allow us to produce higher brilliant hard X-rays even at the energy of 2.5 GeV. At present we are going to prepare a top-up operation for the PF-ring. In the PF-AR, new tandem undulators have been operated in one straight section since September 2006 to generate much stronger pulsed hard X-rays for the sub-ns resolved X-ray diffraction experiments. In this conference, we report operational status of the PF-ring and the PF-AR including other machine developments.
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TUPMN047 | W-band Electromagnetic Wave Undulator for AIST 800 MeV Electron Storage Ring TERAS | undulator, electron, storage-ring, synchrotron | 1025 | |||||
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An electromagnetic-wave undulator based on a quasi-optical resonator operated in higher order TE mode is proposed to generate monochromatic X-rays. We plan to install it to an 800MeV electron storage ring TERAS of AIST. Mode propagation in the resonator was analysed with an electromagnetic-wave simulation code MAFIA and HFSS. Design parameters for the undulator operated in W-band (95 GHz) was presented. The peak electric field along the electron orbit was estimated to be 130 kV/m when we fed 1 kW of 95 GHz electromagnetic wave. The estimated X-ray flux density was 1 x 1011 photons/sec/mrad2/A for 3.4 keV X-rays.
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TUPMN049 | Improvement of Soft X-ray Generation System Based on Laser Compton Scattering | laser, electron, scattering, cathode | 1031 | |||||
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Funding: This work is supported by MECSST High Tech Research Center Project No. 707 and JSPS (B) (2) 18340079. |
At Waseda University, we have succeeded in generating soft X-rays based on laser Compton scattering. The energies are within "Water Window" part (250~500eV) where the X-ray absorption coefficient of water is much less than that of constituent elements of living body such as carbon, hydrogen and nitrogen. For this reason, it is expected to apply to a bio-microscope with which we can observe living cells without dehydration. To improve the generation system, we remodeled our collision chamber and adopted 3-pass flash lamp amplifier system. With these modifications, we achieved high S/N ratio. The photon number detected by MCP was 278/pulse, tenfold increase of that in last year. Moreover, we succeeded in generating soft X-rays stably for more than 10 hours. Now we are planning to measure two-dimensional distribution of the X-rays by CCD. In this conference, experimental results and future plans will be reported. |
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TUPMN050 | Development of Pulsed-Laser Super-Cavity for Compact X-Ray Source Based on Laser-Compton Scattering | laser, electron, feedback, storage-ring | 1034 | |||||
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A compact and high quality x-ray source is required from various field, such as medical diagnosis, drug manifacturing and biological sciences. Laser-Compton based x-ray source that consist of a compact electron storage ring and a pulsed-laser super-cavity is one of the solutions of compact x-ray source. Pulsed-laser super-cavity has been developed for a compact high brightness x-ray sources at KEK-ATF. The pulsed-laser super-cavity increases the laser power and stably makes small laser beam size at the collision point with the electron beam. Recently, 357MHz mode-locked Nd:VAN laser pulses can be stacked stably in a 420mm long Fabry-Perot cavity with 1'000 enhancement in our R&D. Therefore, we have planned a compact hard x-ray sources using 50MeV multi-bunch electrons and a pulse stacking technology with 42cm Fabry-Perot cavity. (LUCX Project at KEK) The photon flux is multiplied with the number of bunches by using multi-bunch beam and super-cavity. Development of the super-cavity and present result of LUCX will be presented at the conference.
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TUPMN051 | Development of Photocathode RF Gun and Laser System for Multi-collision Laser Compton Scattering | laser, electron, scattering, gun | 1037 | |||||
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A compact soft and hard X-ray source via laser Compton scattering is required for biological, medical and industrial science because it has many benefits about generated X-rays such as short pulse, quasi-monochromatic, energy tunability and good directivity. Our X-ray source is conventionally the single collision system between an electron pulse and a laser pulse. To increase X-ray yield, we have developed a multi-collision system with a multi-bunch electron beam and a laser optical cavity. The multi-bunch beam will be generated from a Cs-Te photocathode rf gun sytem using a multi-pulse UV laser. The laser optical cavity will be built like the regenerative amplification including a collision point between the electron pulse and the laser pulse to enhance the laser peak power per 1 collision on laser Compton scattering. In this conference, we will describe the results of preliminary experiments for the multi-collision system and future plans.
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TUPMN070 | Magnet Block Arrangements for the Apple-II Elliptically Polarized Undulator | polarization, undulator, multipole, storage-ring | 1079 | |||||
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The good field region (magnetic field roll-off) of the horizontal and vertical field distribution in the elliptically polarized undulator (EPU) of the APPLE II structure is too short. Meanwhile, the strong force variation will be created between the magnet arrays on different phase. Hence, a magnet block was magnetized with an tilt angle has been studied to enlarge the good field region and a different arrangement of magnet block module is used to reduce the force variation. In addition, the pure and hybrid structure of the EPU with different end pole design has been studied. This study will obtain a small variation of the first and second field integral on different gap and phase. This work will report the scheme of the magnet block arrangement and the end pole design for the APPLE II elliptically polarized undulator.
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TUPMN071 | Planning of Insertion Devices for 3 GeV Taiwan Photon Source | undulator, insertion, insertion-device, wiggler | 1082 | |||||
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The Taiwan Photon Source (TPS) has 24 straight sections (10.9 m x6,5.7 m x18). It has at least three long straight and 18 medium straight for installing insertion devices. Most of the insertion devices are the in-vacuum undulator and produce intense X-rays with a brilliance of up to 1x1020 photons/s/mr2/mm2/0.1%bw. However, the cryogenic permanent magnet undulator with a periodic length of 1.8 cm (CU1.8) will be developed to provide an energy over 20 keV. One or two types of undulators can be installed in the long straight section to provide low photon energy or enable experiments to be conducted in situ in a single beam line. Meanwhile, some elliptically polarized undulators (APPLE II structure) are planned to provide circular and any linear polarization light. One or two superconducting wigglers with a field strength of 3.5 T will be used to yield the photons with energies of over 25 keV. A study project of superconducting undulator is for the energies of 2.5 - 25 keV. This work will report the design philosophy for the insertion devices and what kinds of insertion devices will be operated at TPS.
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TUPMN089 | Configuration, Optics, and Performance of a 7-GeV Energy Recovery Linac Upgrade for the Advanced Photon Source | emittance, linac, undulator, storage-ring | 1121 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The Advanced Photon Source (APS) is a 7-GeV storage ring light source that has been in operation for over a decade. In order to make revolutionary improvements in the performance of the existing APS ring, we are exploring the addition of a 7-GeV energy recovery linac (ERL) to the APS complex. In this paper, we show the possible configuration of such a system, taking into account details of the APS site and the requirement that stored beam capability be preserved. We exhibit a possible configuration for the single-pass, 7-GeV linac. We discuss optical solutions for transport from 10 MeV to 7 GeV and back, including a large turn-around arc that would support 48 additional user beamlines. Tracking results are shown that include incoherent and coherent synchrotron radiation, resulting in predictions of the beamline performance. |
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TUPMN091 | Planned Use of Pulsed Crab Cavities for Short X-ray Pulse Generation at the Advanced Photon Source | impedance, storage-ring, single-bunch, damping | 1127 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
In recent years, we have explored application to the Advanced Photon Source (APS) of Zholents'* crab-cavity-based scheme for production of short x-ray pulses. Work concentrated on using superconducting (SC) cavities in order to have a continuous stream of crabbed bunches and flexibility of operating modes. The challenges of the SC approach are related to the size, cost, and development time of the cavities and associated systems. A good case can be made for a pulsed system** using room-temperature cavities. APS has elected to pursue such a system in the near term, with the SC-based system planned for a later date. This paper describes the motivation for the pulsed system and gives an overview of the planned implementation and issues. Among these are overall configuration options and constraints, cavity design options, frequency choice, cavity design challenges, tolerances, instability issues, and diagnostics plans.
*A. Zholents et al., NIM A 425, 385 (1999).**P. Anfinrud, private communication. |
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TUPMN092 | Phasing of Two Undulators with Different K Values at the Advanced Photon Source | undulator, brilliance, coupling, emittance | 1130 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
Two full-length 2.4-m-long undulators, with period lengths 2.3 cm and 2.7 cm, were recently installed in tandem in the 5.6-m-long straight on the storage ring in sector 14. One part of the user research program requires that both undulators be tuned to 12.0 keV and the x-ray intensity maximized. The total intensity is sensitive to the phasing between the undulators, so the distance between the devices must be optimized and the ends tuned appropriately. Because of the different period lengths, the gaps and K values of the undulators will be different: 10.6-mm gap and a K value of 1.17 for the shorter-period device and 15.7-mm gap and a K value of 0.93 for the longer-period device. A special shield was designed and installed between the devices to eliminate interference. Results of magnetic measurements, tuning, and computer simulations of the spectral performance are presented. |
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TUPMN093 | A Kilohertz Picosecond X-Ray Pulse Generation Scheme | synchrotron, kicker, storage-ring, damping | 1133 | |||||
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The duration of the x-ray pulse generated at a synchrotron light source is typically tens of picoseconds. Shorter pulses are highly desired by the users. In electron storage rings, the vertical beam size is usually orders of magnitude less than the bunch length due to radiation damping; therefore, a shorter pulse can be obtained by slitting the vertically tilted bunch. Zholents proposed tilting the bunch using rf deflection. We found that tilted bunches can also be generated by a dipole magnet kick. A vertical tilt is developed after the kick in the presence of non-zero chromaticity. The tilt was successfully observed and a 4.2-ps pulse was obtained fom a 27-ps electron bunch at the Advanced Photon Source. Based on this principle we propose a short-pulse generation scheme that produces picosecond x-ray pulses at a repetition rate of 1~2 kHz, which can be used for pump-probe experiments. The tilt phenomenon can also be utilized for machine parameter measurement.
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TUPMN100 | LCLS Undulator Production | undulator, factory, linac, extraction | 1148 | |||||
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Funding: Work supported by the U. S. Dept. of Energy, under contract numbers DE-AC02-06CH11357 and DE AC03-76SF00515. |
Design and construction of the undulators for the Linac Coherent Light Source (LCLS) is the responsibility of Argonne National Laboratory. A prototype undulator* was constructed in-house and was extensively tested. The device was tunable to well within the LCLS requirements and was stable over a period of several years. Experience constructing the prototype undulator led us to conclude that with appropriate engineering design and detailed assembly procedures, precision undulators can be constructed by qualified vendors without previous undulator-construction experience. Our detailed technological knowledge and experience were transferred to the successful bidders who have produced outstanding undulators. Our production concept for the 40 3.4 m long, fixed-gap, planar-hybrid undulators with a 30 mm period is presented. Manufacturing, quality assurance, and acceptance testing details are also presented.
*LCLS Prototype Undulator Report, Argonne National Laboratory Report ANL/APS/TB-48, January 2004, R. Dejus, Editor. |
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TUPMN104 | A Design Study for Photon Diagnostics for the APS Storage Ring Short-Pulse X-ray Source | electron, diagnostics, undulator, laser | 1156 | |||||
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
A short x-ray pulse source based on the crab cavity scheme proposed by Zholents* is being developed at the Advanced Photon Source (APS). Photon diagnostics that visualizes the electron bunches with transverse momentum chirp and verifies the performance of the short x-ray pulse is required. We present a design study for the imaging diagnostics inside and outside of the crab cavity zone, utilizing both x-ray and visible synchrotron radiation. Several design options of monochromatic and polychromatic x-ray optics will be explored for their compatibility with the short-pulse source. The diagnostics outside of the crab cavity zone will be used to map out stable operation parameters of the storage ring with crab cavities, and to perform single-bunch single-pass imaging of the chirped bunch, which facilitates the tuning of the crab cavity rf phase and amplitude so the performance of the short pulse source can be optimized while other users around the ring will not be disturbed.
* A. Zholents et al., NIM A 425, 385 (1999). |
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TUPMN109 | A High Repetition Rate VUV-Soft X-Ray FEL Concept | electron, emittance, gun, laser | 1167 | |||||
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Funding: This work was supported by the Director, Office of Science, High Energy Physics, U. S. Department of Energy under Contract No. DE-AC02-05CH11231. |
The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, and wavelength; utilization of harmonics to attain shorter wavelengths; and precise synchronization of the x-ray pulse with laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FELs, each producing high average brightness, tunable over the soft x-ray-VUV range, and each with individual performance characteristics determined by the configuration of the FEL SASE, enhanced-SASE (ESASE), seeded, self-seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands. FELs would be tailored to specific experimental needs, including production of ultrafast pulses even into the attosecond domain, and high temporal coherence (i.e. high resolving power) beams. |
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TUPMN112 | ALS Top-off Simulation Studies for Radiation Safety | simulation, injection, radiation, vacuum | 1173 | |||||
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Funding: Work supported by the U. S. Department of Energy under Contract No. DE-AC03-76SF00098 |
We plan to commission top-off injection at the Advanced Light Source in the near future. In order to guarantee radiation safety, we have been simulating the injection process to exclude the possibility of injected electrons traveling down the user's photon beam lines. As the final stage of our simulation study, we use photon beam line CAD drawings to define the beam line's aperture in the phase space which electrons must not enter. Then we virtually inject electrons from within these phase spaces backwards into the storage ring to prove that such electrons can never get back to the real injection point under any possible scenario. This paper summarizes such inverse tracking studies. |
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TUPMS030 | Optimal Design of a Tunable Thomson-Scattering Based Gamma-Ray Source | electron, laser, emittance, scattering | 1248 | |||||
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Funding: This work was performed under the auspices of the U. S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. |
Thomson-Scattering based systems offer a path to high-brightness high-energy (> 1 MeV) x-ray & gamma-ray sources due to their favorable scaling with electron energy. LLNL is currently engaged in an effort to optimize such a device, dubbed the "Thomson-Radiated Extreme X-Ray" (T-REX) source, targeting up to 680 keV photon energy. Such a system requires precise design of the interaction between a high-intensity laser pulse and a high-brightness electron beam. Presented here are the optimal design parameters for such an interaction, including factors such as the collision angle, focal spot size, optimal bunch charge and laser intensity, pulse duration, and laser beam path. These parameters were chosen based on extensive modelling using PARMELA and in-house, well-benchmarked scattering simulation codes. Also discussed are early experimental results from the newly commissioned system. |
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TUPMS041 | The Wisconsin VUV/Soft X-ray Free Electron Laser Project | laser, electron, linac, scattering | 1278 | |||||
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Funding: Work supported by the University of Wisconsin - Madison. SRC is supported by the U. S. National Science Foundation under Award No. DMR-0537588. |
The University of Wisconsin-Madison and its partners are developing a design for an FEL operating in the UV to soft x-ray range that will be proposed as a new multidisciplinary user facility. Key features of this facility include seeded, fully coherent output with tunable photon energy and polarization over the range 5 eV to 1240 eV, and simultaneous, independent operation of multiple beamlines. The different beamlines will support a wide range of science from femto-chemistry requiring ultrashort pulses with kHz repetition rates to photoemission and spectroscopy requiring high average flux and narrow bandwidth at MHz rates. The facility will take advantage of the flexibility, stability, and high average pulse rates available from a CW superconducting linac driven by a photoinjector. This unique facility is expected to enable new science through ultra-high resolution in the time and frequency domains, as well as coherent imaging and nano-fabrication. This project is being developed through collaboration between the UW Synchrotron Radiation Center and MIT. We present an overview of the facility, including the motivating science, and its laser, accelerator, and experimental systems. |
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TUPMS055 | SPEAR3 Accelerator Physics Update | optics, feedback, injection, electron | 1311 | |||||
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The SPEAR3 storage ring at Stanford Synchrotron Radiation Laboratory has been delivering photon beams for three years. We will give an overview of recent and ongoing accelerator physics activities, including 500 mA fills, work toward top-off injection, long-term orbit stability characterization & improvement, fast orbit feedback, new chicane optics, low alpha optics & short bunches, low emittance optics, and new insertion devices. The accelerator physics group has a strong program to characterize and improve SPEAR3 performance.
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TUPMS071 | Upgrade Alternatives for the NSLS Superconducting Wiggler | wiggler, radiation, insertion, insertion-device | 1335 | |||||
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The superconducting wiggler (SCW) with 4.2 Tesla field in 5 main poles has been in operation on the NSLS X-ray storage ring for more than 20 years. The inefficient cryogenic system of this wiggler uses a closed-cycle refrigerator requiring constant maintenance. It is possible to replace this insertion device with a 13-pole SCW originally built by Oxford Instruments. The cryostat of this device could be upgraded to reduce the liquid He consumption using cryocoolers, thereby greatly reducing the refrigerator operating expense. A second option is a new design of a SCW with a magnetic period and number of poles appropriate to the current users needs. All these upgrade possibilities will be described in the paper.
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TUPMS072 | Longitudinal Beam Parameter Tolerances of NSLS II | emittance, controls, synchrotron, radiation | 1338 | |||||
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Funding: National Synchrotron Light Source II |
A notable feature of the proposed National Synchrotron Light Source II is that the vertical emittance is close to the diffraction limit of 1 Angstrom. With such a small emittance, the brightness is strongly affected by the longitudinal parameters, such as the momentum spread. Various effects are discussed and tolerances on the longitudinal parameters will be given. The lower level RF feedback system will be designed based on these tolerances. |
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TUPMS091 | A Theoretical Photocathode Emittance Model Including Temperature and Field Effects | emittance, electron, brightness, laser | 1377 | |||||
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Funding: We gratefully acknowledge funding by the Joint Technology Office and the Office of Naval Research. |
A recently developed model* of the emittance and brightness of a photocathode based on the evaluation of the moments of the electron emission distribution function admits an analytical solution for the zero-field and zero-temperature asymptotic model. Here, the model has been extended to account for the critical modifications of temperature and field dependence, which are tied to material issues with the cathode. Temperature impacts the nature of scattering within the photoemitter material and therefore affects quantum efficiency significantly. Field changes the emission probability at the surface barrier, and is particularly important for low work function coatings, as occur for the cesiated surfaces characteristic of our controlled porosity dispenser photocathodes. Extensions of the theoretical models shall be given, followed by an analysis of their comparison with numerical simulations of the intrinsic emittance and brightness of a photocathode. The methodology is designed to facilitate the development of photoemission models into comprehensive particle-in-cell (PIC) codes to address issues otherwise not readily treated, e.g., variation in surface coverage and topology.
* K. L. Jensen, P. G. O'Shea, D. W. Feldman, and N. A. Moody, Applied Physics Letters 89, 224103 (2006). |
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WEXC02 | The Impedance Database Computation and Prediction of Single Bunch Instabilities | impedance, single-bunch | 1996 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The Impedance Database is a standardized 3D computation of the wake potential generated by a high-intensity beam. The database concept is described and compared to analytical and model-based approaches. The talk will address the computational challenges introduced by tapers, collimators, and very short bunches. Finally, single-bunch instabilities are predicted through tracking and compared to measurements at the Advanced Photon Source and other accelerators. |
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WEOCC03 | Halo Estimates and Simulations for Linear Colliders | scattering, simulation, linac, electron | 2041 | |||||
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Funding: This work is supported by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899. |
Halo simulations and estimates are important for the design of future linear accelerators. We present simulations performed for the ILC and CLIC and compare these with semi-analytical estimates and other simulations. |
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WEPMN085 | The Advanced Photon Source Pulsed Deflecting Cavity RF System | klystron, storage-ring, controls, electron | 2224 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The Phase I Advanced Photon Source Deflecting Cavity System for producing short X-ray pulses uses one multi-cell, S-band cavity to apply a deflecting voltage to the stored electron beam ahead of an undulator that supports a beamline utilizing short picosecond X-rays. Two additional multi-cell cavities are then used to cancel out the perturbation and redirect the electron beam along the path of its nominal orbit. The pulsed rf system driving the deflecting cavities is described. Design tradeoffs are discussed with emphasis on topology considerations and digital control loops making use of sampling technology in a manner consistent with the present state of the art. |
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WEPMS038 | RF Design of Normal Conducting Deflecting Structures for the Advanced Photon Source | damping, impedance, electron, gun | 2427 | |||||
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Use of normal conducting deflecting structures for production of short x-ray pulses is now being implemented at the Advanced Photon Source (APS). The structures have to produce up to 6 MV maximum deflection per structure at a 1kHz repetition rate. At the same time, the nominal beam quality must be maintained throughout the APS ring. Following these requirements, we proposed 2815 MHz standing wave deflecting structure with heavy wakefield damping. In this paper, we discuss the design considerations and present our current results.
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THOAC01 | ATF Extraction Line Laser-Wire System | laser, electron, extraction, background | 2636 | |||||
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Funding: PPARC LC-ABD Collaboration Royal Society Daiwa Foundation Commission of European Communities under the 6th Framework Programme Structuring the European Research Area, contract number RIDS-011899 |
The ATF extraction line laser-wire (LW) aims to achieve a micron-scale laser spot size and to verify that micron-scale beam profile measurements can be performed at the International Linear Collider beam delivery system. Recent upgrades to the LW system are presented together with recent results including the first use of the LW as a beam diagnostic tool. |
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THYC01 | RHIC Hydrogen Jet Luminesence Monitor | optics, proton, polarization, scattering | 2648 | |||||
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Funding: US Department of Energy |
A hydrogen jet polarimeter was developed for the RHIC accelerator to improve the process of measuring polarization. Particle beams intersecting with gas molecules can produce light by the process known as luminescence. This light can then be focused, collected, and processed giving important information such as size, position, emittance, motion, and other parameters. The RHIC hydrogen jet polarimeter was modified in 2005 with specialized optics, vacuum windows, light transport, and camera system making it possible to monitor the luminescence produced by polarized protons intersecting the hydrogen beam. This paper will describe the configuration and preliminary measurements taken using the RHIC hydrogen jet polarimeter as a luminescence monitor. |
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THOBC02 | Absolute Bunch Length Measurements at the ALS by Incoherent Synchrotron Radiation Fluctuation Analysis | radiation, synchrotron, synchrotron-radiation, electron | 2661 | |||||
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Funding: This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121 |
By analysing the pulse to pulse intensity fluctuations of the radiation emitted by a charge particle in the incoherent part of the spectrum, it is possible to extract information about the spatial distribution of the beam. At the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory, we have developed and tested a simple scheme based on this principle that allows for the absolute measurement of the bunch length. A description of the method and the experimental results are presented. |
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THPMN009 | Backscattering of Secondary Particles into the ILC Detectors from Beam Losses Along the Extraction Lines | extraction, electron, simulation, collider | 2725 | |||||
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At the International Linear Collider (ILC) the beams will be focused to extremely small spot sizes in order to achieve the desired luminosity. After the collision the beams must be brought to the dump with minimal losses. In spite of all the attention put into the design of the extraction line, the loss of some disrupted beam particles, beamstrahlung or synchrotron radiation photons is unavoidable. These losses will generate low-energy secondary particles, such as photons, electrons and neutron, a fraction of which can be back-scattered towards the interaction point and generate backgrounds into the detector. In this paper we present an evaluation of such backgrounds, using the BDSIM and Mokka simulations, for several presently considered ILC extraction lines and detectors.
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THPMN017 | Polarized Positron Production and Tracking at the ILC Positron Source | positron, target, polarization, simulation | 2742 | |||||
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Funding: This work is supported by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899. |
A positron source based on a helical undulator system is planned to be used for the future International Linear Collider (ILC). Depending on the accelerator design it will be possible to get polarized positrons at the interaction point. A source performance with high positron yield and high polarization is the aim of our design studies. We focus on the optimization of target and capture section using several simulation codes. FLUKA is a suitable tool to calculate the positron yield, heat deposition, neutron generation and induced activity of source parts. The ASTRA code is used to calculate positron capture efficiency into the optical matching device. The new release of Geant4 includes the spin dependence of all QED processes and allows to perform a helicity-dependent tracking of particles through target and capture section. Starting with a cross-check, the synergy of these three codes allowed to specify the the parameters of a polarized positron source. |
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THPMN023 | Study of an Electron Linac Driven X-Ray Radio-Tomographic System Response as a Function of the Electron Beam Current | electron, linac, target, simulation | 2757 | |||||
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At the Dipartimento di Fisica, Universita di Messina, a high energy x-ray radio-tomography system driven by a 5 MeV electron linac, has been recently assembled. It has been tested and has already provided good results in inspecting heavy materials. In order to achieve good radiographic results, especially when inspecting heavy or thick materials, an enhancement of the x-ray dose at the sample position can be required and most of times this is associated to an enhancement of the grey level in the acquired image according to a linear function. Nevertheless, in the hypothesis to work at the maximum magnetron power, a variation of the x-ray dose, obtained changing the electron beam current, is associated to a variation of the electron beam energy. As a consequence, the x-ray energy spectrum varies thus influencing the response of the radio-tomographic system. This does not allow a linear correspondence between the x-ray fluence (or the electron beam current) and the image grey level. By means of MCNP-4C2 simulations, the influence of electron beam energy variations on the produced bremsstrahlung spectrum has been studied and the theoretical results have been experimentally confirmed.
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THPMN024 | A Study for the Characterization of High QE Photocathodes | cathode, electron, emittance, gun | 2760 | |||||
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Funding: Work supported by the European Community, contract number RII3-CT-2004-506008 |
Based on our experience on photocathode production, we present in this paper the results of the application of different optical diagnostic techniques on fresh and used photocathodes. These techniques allow to study effects like non uniformity, cathode aging, etc. In particular, photocathode optical parameters and QE characterization, both done at different wavelengths, give fundamentals information for the construction of a model of the photoemission process to be applied to Cs2Te photocathodes. These studies are useful for further improving key cathode features, such as its robustness and lifetime as well as to study and control the photocathodes thermal emittance. |
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THPMN057 | New Concept for a CLIC Post-Collision Extraction Line | extraction, quadrupole, vacuum, dipole | 2835 | |||||
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Funding: This work is supported by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", with contract number RIDS-011899. |
Strong beam-beam effects at the interaction point of a high-energy e+e- linear collider such as CLIC lead to an emittance growth for the outgoing beams, as well as to the production of beamstrahlung photons and e+e- coherent pairs. We present a conceptual design of the post-collision line for CLIC at 3 TeV, which separates the various components of the outgoing beam in a vertical magnetic chicane and then transports them to their respective dump. |
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THPMN064 | Luminosity Upgrade of CLIC-LHC ep/gp Collider | collider, luminosity, electron, proton | 2853 | |||||
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An energy-frontier or QCD-exploring ep and gp collider can be realized by colliding high-energy photons generated by Compton back-scattered off a CLIC electron beam, at either 75 GeV or 1.5 TeV, with protons or ions stored in the LHC. In this study we discuss a performance optimization of this type of collider by tailoring the parameters of both CLIC and LHC. An estimate of the ultimately achievable luminosity is given.
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THPMN080 | Incoherent pair background processes with full polarizations at the ILC | polarization, background, luminosity, collider | 2892 | |||||
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Funding: This work is supported in part by the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area", contract number RIDS-011899. |
Incoherent background pair production processes are studied with respect to full polarizations of all states. Real initial photon polarizations are obtained via a QED calculation of the beamstrahlung process. Virtual photon polarizations are related to the electric field of the colliding bunches at the point of pair production. An explicit expression for the virtual photon polarization vector is developed and found to have no circular polarization component. Pair polarization states are highly dependent on initial state circular polarization and are consequently produced almost unpolarized. The Breit-Wheeler cross-section with full polarizations is calculated and coded into the CAIN pair generator program. Numerical evaluations of the ILC operating in the seven proposed collider parameter sets shows that there are 10-20% less low energy pairs than previously thought. Collider luminosity as calculated by CAIN remains the same. |
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THPMN089 | Enhancement of Heat Removal using Concave Liquid Metal Targets for High-Power Accelerators | target, proton, linear-collider, collider | 2915 | |||||
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The need is increasing for development of high power targets and beam dump areas for the production of intense beams of secondary particles (IFMIF, SNS, RIA, LHC). The severe constraints arising from a MW beam power deposited on targets and absorbers, call for non-trivial procedures to dilute the beam. This study describes the development of targets and absorbers and the advantages of using flowing liquid metal in concave channels first proposed by IFMIF to raise the liquid metal boiling point by increasing the pressure in liquid supported by a centrifugal force. Such flow with a back-wall is subject to the Taylor-Couette instability. The instability can play a positive role of increasing the heat transfer from the hottest region in the target/absorber to the back-wall cooled by water. At the laminar stage of the instability with a certain wave number of vortexes, the heat transfer from a chain of vortexes to the wall increases heat removal by enhancing the convective transport inside the liquid bulk and from the bulk to the wall. Results of theoretical analysis and numerical modeling of both targets and dump areas for the IFMIF, ILC, and RIA facilities are presented.
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THPMN090 | Systematic Study of Undulator Based ILC Positron Source: Production and Capture | undulator, positron, target, polarization | 2918 | |||||
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A systematic study of the positron production and capture systems for the undulator-based ILC positron source has been performed. Various undulator parameters, such as k and λ, were considered. Our model starts from the electron beam production of the polarized photons in the undulator section, photon transport and collimation in the drift section, and photon interaction on the target (titanium or tungsten). Next, our model transports the produced polarized positrons from the target, through the tapered capturing magnet, and through the normal conducting linac to several hundred MeV. Finally, the captured positrons meeting the damping ring emittance and energy spread requirements are accelerated up to 5 GeV using the standard ILC superconducting cavities. We will present parametric studies for the different scenarios (e.g. 60% polarization vs. unpolarized; target immersed in magnetic field vs. non-immersed) currently under consideration and report on the capturing yield and polarizations achieved for each.
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THPMS059 | Correlating Pulses from Two Spitfire, 800nm Lasers | laser, acceleration, electron, background | 3121 | |||||
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Funding: Department of Energy contracts DE-AC02-76SF00515, DE-FG03-97ER41043-III |
The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800nm, Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:Sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.
Yoshihiro Takagi et al, 'Multiple- and Single-shot autocorrelator based on two-photon conductivity in semiconductors.' Optics Letters, Vol. 17, No. 9, May 1, 1992. |
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THPMS095 | Experimental Demonstration of Feasibility of a Polarized Gamma-source for ILC Based on Compton Backscattering Inside a CO2 Laser Cavity | laser, electron, positron, scattering | 3208 | |||||
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Funding: Work supported by US Department of Energy contract DE-AC02-98CH10886 |
Compton interaction point incorporated into a high-average-power laser cavity is the key element of the Polarized Positron Source (PPS) concept proposed for ILC [1]. According to this proposal, circularly polarized gamma rays are produced in Compton backscattering from a 6 GeV linac e-beam inside a CO2 laser amplifier cavity. Intra-cavity positioning of the interaction point allows multiple laser recycling to match the electron bunch train format. We conducted experimental tests of multi-pulse operation of such active Compton cavity upon injection of a picosecond CO2 laser beam. Together with earlier demonstration of a high x-ray yield via the e-beam/CO2-laser backscattering, these new results show a viability of the entire PPS concept and closely prototype the laser source requirements for ILC.
[1] V. Yakimenko and I. V. Pogorelsky, Phys. Rev. ST Accel. Beams 9, 091001 (2006) |
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THPAN031 | Optimization of the Beam Line Characteristics by Means of a Genetic Algorithm | electron, laser, scattering, emittance | 3295 | |||||
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The optimization of the optics in a LINAC requires a very demanding tuning of the involved parameters, particularly in the case of high brightness electron beams applied to the production of X-ray in a Thomson back-scattering source. The relationship between the parameters is non-linear and it is not possible to treat them as independent variables, causing the impossibility of setting them handily. A genetic algorithm is a powerful tool able to circumvent this difficulty. We have applied the genetic algorithm to the case of the SPARC beam line.
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THPAN089 | Beam Dynamics, Performance, and Tolerances for Pulsed Crab Cavities at the Advanced Photon Source for Short X-ray Pulse Generation | emittance, sextupole, undulator, radiation | 3429 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The Advanced Photon Source (APS) has decided to implement a system using pulsed* crab cavities to produce short x-ray pulses using Zholents'** scheme. This paper describes beam dynamics issues related to implementation of this scheme in a single APS straight section. Modeling of the cavity is used to demonstrate that the deflection will be independent of transverse position in the cavity. Parameters and performance for a standard and lengthened APS straight section are shown. Finally, tolerances are discussed and obtained from tracking simulations.
* M. Borland et al., these proceedings.** A. Zholents et al., NIM A 425, 385 (1999). |
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FRZKI03 | Next Generation Advanced Light Source Science | laser, radiation, controls, proton | 3840 | |||||
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Recent advances in accelerator science make feasible the provision of XUV and harder X-ray FELs that will generate short (fs regime) pulses of light that is broadly tuneable and >106 times more intense than spontaneous undulator radiation*. Energy recovery technology** offers the promise of short pulse, high peak flux spontaneous radiation, with particular advantages in the IR and THz parts of the spectrum. The new science enabled by these 4th generation sources is reviewed. A key feature is dynamic measurements. Pump-probe experiments will allow real-time measurements of reaction pathways and short-lived intermediates. The high intensity of FEL radiation will allow very high resolution in imaging applications. The very high field intensity of the XUV radiation will lead to the creation of new states of matter, while at the highest X-ray energies, the goal is to achieve single molecule diffraction. The talk will be illustrated by experiments proposed in the Science Cases for the major world 4th generation projects. Some of the science already undertaken using IR and UV FELs, and results obtained from new XUV sources (such as FLASH at DESY***) will be discussed.
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* e.g. J Andruszkow et al., Phys. Rev. Lett., 85, 3825, (2000).**e.g. G. R. Neil et al., Phys. Rev. Lett. 84, 662, (2000).*** e.g. H Wabnitz et al., Nature, 420, 467, (2002), T Laarmann et al., Phys. Rev. Lett., 95, 063402 (2005) |
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FRPMN039 | Measurement of Quadrupolar Tune Shifts After the Reconstruction of the Photon Factory Storage Ring | quadrupole, storage-ring, betatron, factory | 4039 | |||||
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The tune shift of transverse quadrupolar oscillations is a measure of a quadrupolar component of wakefields in the storage ring*. By measuring both dipolar and quadrupolar tune shifts, one can estimate the dipolar and the quadrupolar components of wakefields (exactly, kick factors) independently. We carried out such measurements before and after the upgrade of the Photon Factory storage ring. The results showed the change in the tune shifts which were caused by the replacement of many (about two-thirds of the ring) vacuum chambers.
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* S. Sakanaka, T. Mitsuhashi, and T. Obina, Phys. Rev. ST Accel. Beams 8, 042801 (2005). |
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FRPMN042 | Continued Study on Photoelectron and Secondary Electron Yield of TiN Coating and NEG (Ti-Zr-V) Coatings at the KEKB Positron Ring | electron, simulation, positron, synchrotron | 4054 | |||||
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In order to investigate a way to mitigate the electron-cloud instability (ECI), the secondary electron and photoelectron yields (SEY and PEY) of a TiN coating and a NEG (Ti-Zr-V) coating have been studied at the KEK B-Factory (KEKB) positron ring. Following the previous study at an arc section*, the test chambers were installed a straight section, where the line density was less than 1/10 of that at the arc section. The number of electrons around the beam orbit was measured up to a stored beam current of about 1.7 A (1389 bunches). The electron current of the NEG-coated and TiN-coated chambers were about 60% and 30% of that for a copper chamber, respectively. The difference between the copper and the NEG coating was clearer than the measurement at the arc section, where the intense SR obscured the effect of SEY. The evaluated max values for the TiN coating, the NEG coating and the copper were 0.9 - 1.0, 1.0 - 1.1 and 1.3 - 1.4, respectively, which were almost consistent with the previous results. The experiments using a beam duct with ante-chambers are also briefly touched upon.
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* Y. Suetsugu et al., NIM-PR-A, Vol.556 (2006) 399. |
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FRPMN050 | Multiple parameter characterizations for electron beam with diffraction radiation | electron, radiation, target, emittance | 4096 | |||||
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There are growing interests in developing non-intercepting method for real-time monitoring electron beam parameters for International linear collider and X-ray free electron lasers. In this paper we present both theorectical considerations and experimental demonstration of the ability of diffraction radiation for measuring electron beam profile, divergence, emittance and bunch length*. The possibility of using optical diffraction radiation to direct image electron beam profile is studied**.A new method for bunch length measurement with diffraction radiation deflector is also proposed and analysed***.
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* Dao Xiang and Wen-Hui Huang, Nucl. Instr. and Meth. in Phys. Res. B, 254 (2007) 165.** Dao Xiang and Wen-Hui Huang, Nucl. Instr. and Meth. in Phys. Res. A, 570 (2007) 357.*** Dao Xiang and Wen-Hui Huang, Phys. Rev. ST-AB, 10 (2007) 012801. |
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FRPMN094 | Beam Profile Measurements with the 2-D Laser-Wire at PETRA | laser, electron, positron, simulation | 4303 | |||||
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Funding: Work supported by the PPARC LC-ABD collaboration and the Commission of the European Communities under the 6th Framework Programme Structuring the European Research Area, contract number RIDS-011899. |
The current PETRA II Laser-Wire system, being developed for the ILC and PETRA III, uses a piezo-driven mirror to scan laser light across an electron bunch. This paper reports on the recently installed electron-beam finding system, presenting recent horizontal and vertical profile scans with corresponding studies. |
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FRPMN104 | Impedance Database II for the Advanced Photon Source Storage Ring | impedance, simulation, storage-ring, single-bunch | 4336 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The first Impedance Database* constructed at the Advanced Photon Source was successfully used in reproducing the main characteristics of single-bunch instabilities observed in the storage ring. However, the finite bandwidth of the corresponding impedance model was limited to 25 GHz, which happens to be the resolution limit of the density modulation observed in the microwave instability simulation. In order to resolve simulation results never verified in the experiments, we decided to extend the calculated bandwidth of impedance to 50 GHz by recalculating the wake potentials excited by a shorter bunch. Since low-order electromagnetic code requires 20-40 grid points per wavelength, reducing the bunch length required a large number of grids for the 3D structure. We used bunch lengths of 1- and 2-mm in the Gaussian distribution in the Impedance Database II project. For the large-scale computation we used the 3D electromagnetic code GdfidL ** for wake potential calculation at the cluster equipped with 240 GB of memory. The resultant wake potential excited by the short bunch together with application to the storage ring for collective effects is presented in the paper.
* Y.-C. Chae, "The Impedance Database and Its Application to the APS Storage Ring" Proc. 2003 PAC, p. 3017.** http://www.gdfidl.de |
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FRPMN105 | The Wakefield Effects of Pulsed Crab Cavities at the Advanced Photon Source for Short-X-ray Pulse Generation | single-bunch, impedance, storage-ring, simulation | 4339 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
In recent years we have explored the application to the Advanced Photon Source (APS) of Zholents' crab-cavity-based scheme for production of short x-ray pulses. As a near-term project, the APS has elected to pursue a pulsed system using room-temperature cavities*. The cavity design has been optimized to heavily damp parasitic modes while maintaining large shunt impedance for the deflecting dipole mode**. We evaluated a system consisting of three crab cavities as an impedance source and determined their effect on the single- and multi-bunch instabilities. In the single-bunch instability we used the APS impedance model as the reference system in order to predict the overall performance of the ring when the crab cavities are installed in the future. For multi-bunch instabilities we used a realistic fill pattern, including hybrid-fill, and tracked multiple bunches where each bunch was treated as soft in distribution. To verify the electrical design, the realistic wake potential of the 3D structure was calculated using GdfidL and this wake potential was used in the multi-bunch simulations.
* M. Borland et al., "Planned Use of Pulsed Crab Cavities at the APS for Short X-ray Pulse Generation," these proceedings.** V. Dolgashev et al., "RF Design of Normal Conducting Deflecting Structures for the APS," these proceedings. |
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FRPMN106 | Progress toward a Hard X-ray Insertion Device Beam Position Monitor at the Advanced Photon Source | target, insertion, insertion-device, undulator | 4342 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
Long-term pointing stability at synchrotron light sources using conventional rf-based particle beam position monitoring is limited by the mechanical stability of the pickup electrode assembly. Photoemission-based photon beam position monitors for insertion device beams suffer from stray radiation backgrounds and other gap-dependent systematic errors. To achieve the goal of 500-nanoradian peak-to-peak pointing stability over a one-week period, the development of a photon beam position detector sensitive only to hard x-rays (> several keV) using copper x-ray fluorescence has been initiated. Initial results and future plans are presented. |
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FRPMN108 | Coupled-Bunch Instability Study of Multi-cell Deflecting Mode Cavities for the Advanced Photon Source | damping, dipole, impedance, feedback | 4348 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The short-pulse X-ray project at the Advanced Photon Source (APS) uses three room-temperature nine-cell 2.815 GHz deflecting-mode cavities in a straight section. Undamped, these cavities' higher-order and lower-order resonator modes will cause multi-bunch instabilities in longitudinal and transverse planes for any bunch pattern of a 1'000mA store. Damping of these modes must be part of the design of the cavities. We report calculations of instability growth rates and tracking simulations that were essential in specifying the rf design of the damping structures. We used various operating bunch patterns and scanned levels of damping of the cavities. Because one of the operating bunch patterns is not symmetric, we used a normal mode analysis * implemented in the APS code clinchor. Our calculation included random sampling of resonator frequencies in a reasonable range. We found that staggering of frequencies is only effective for modes that could not be heavily damped.
* K. Thompson and R. Ruth, PAC 1989 |
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FRPMN115 | A Novel FPGA-Based Bunch Purity Monitor System at the APS Storage Ring | storage-ring, electron, controls, injection | 4384 | |||||
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 |
Bunch purity is an important source quality factor for the magnetic resonance experiments at the Advanced Photon Source. Conventional bunch-purity monitors utilizing time-to-amplitude converters are subject to dead time. We present a novel design based on a single field-programmable gate array (FPGA) that continuously processes pulses at the full speed of the detector and front-end electronics. The FPGA provides 7778 single-channel analyzers (six per RF bucket). The starting time and width of each single-channel analyzer window can be set to a resolution of 178 ps. A detector pulse arriving inside the window of a single-channel analyzer is recorded in an associated 32-bit counter. The analyzer makes no contribution to the system dead time. Two channels for each RF bucket count pulses originating from the electrons in the bucket. The other four channels on the early and late side of the bucket provide estimates of the background. A single-chip microcontroller attached to the FPGA acts as an EPICS IOC to make the information in the FPGA available to the EPICS clients. |
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FRPMN119 | Vector Processing Enhancements for Real-Time Image Analysis | background, controls, diagnostics | 4399 | |||||
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Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
A real-time image analysis system was developed for beam imaging diagnostics. An Apple Power Mac G5 with an Active Silicon LFG frame grabber were used to capture video images that were processed and analyzed. Software routines were created to utilize vector processing hardware to reduce the time to process images as compared to conventional methods. These improvements allow for more advanced image processing diagnostics to be performed in real time. |
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FRPMN120 | Tuning the Narrow-band Beam Position Monitor Sampling Clock to Remove the Aliasing Errors in APS Storage Ring Orbit Measurements | feedback, storage-ring, controls | 4402 | |||||
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. |
The Advanced Photon Source storage ring employs a real-time orbit correction system to reduce orbit motion up to 50 Hz. This system uses up to 142 narrow-band rf beam position monitors (Nbbpms) in a correction algorithm by sampling at a frequency of 1.53 kHz. Several Nbbpms exhibit aliasing errors in orbit measurements, rendering these Nbbpms unusable in real-time orbit feedback. The aliasing errors are caused by beating effects of the internal sampling clocks with various other processing clocks residing within the BPM electronics. A programmable external clock has been employed to move the aliasing errors out of the active frequency band of the real-time feedback system (RTFB) and rms beam motion calculation. This paper discusses the process of tuning and provides test results. |
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FRPMS001 | Numerical Simulation of Optical Diffraction Radiation from a 7-GeV Beam | radiation, simulation, polarization, electron | 3850 | |||||
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Funding: Work supported by U. S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. |
Interest in nonintercepting (NI) beam size monitoring for top-up operations at the Advanced Photon Source (APS) motivated our investigations of optical diffraction radiation (ODR) techniques. We have reported our experiment results earlier. In particular, we wanted to monitor the beam size in the booster-to-storage ring (BTS) transport line using near-field ODR. An analytical model was numerically evaluated for the APS BTS beam size cases. In addition, the simulations show that near-field ODR profiles have sensitivity to beam size in the 20- to 50-μm region, which are relevant to X-ray FELs and the international linear collider (ILC). The simulation indicates that the orthogonal polarization component is close to a Gaussian distribution and more sensitive to beam size variations, and therefore is more suitable for beam size measurement. Under some circumstances the parallel polarization component shows a non-Gaussian distribution that is also beam size dependent. This report describes the simulation method, the results, and the comparison with experiment results. |
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FRPMS035 | Vector Diffraction Theory and Coherent Transition Radiation Interferometry in Electron Linacs | radiation, electron, simulation, laser | 4015 | |||||
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Funding: Work supported by US. Department of Energy, under Contract No. DE-FG02-06ER41435 with Northern Illinois University |
Electrons impinging on a thin metallic foil are seen to deliver small bursts of transition radiation (TR) as they cross the boundary from one medium to the next. A popular diagnostic application is found for compact electron bunches. In this case they will emit radiation more or less coherently with an N-squared enhancement of the intensity on wavelengths comparable to the bunch size, generating coherent transition radiation (CTR). Several detailed analytical descriptions have been proposed for describing the resulting spectral distribution, often making different simplifying assumptions. Given that bunches tenths of millimeters long can generate measurable spectra into the millimeter range, concern may arise as to weak diffraction effects produced by optical interference devices containing elements with dimensions in the centimeter range. The work presented here is a report on an upcoming graduate thesis exploring these effects as they apply to the Fermilab/NICADD photoinjector laboratory using a minimal C++ code that implements the methods of virtual quanta and vector diffraction theory. |
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FRPMS043 | The Feasibility Study of Measuring the Polarization of a Relativistic Electron Beam using a Compton Scattering Gamma-Ray Source | electron, polarization, scattering, laser | 4057 | |||||
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The Compton scattering of a circularly polarized photon beam and a polarized electron beam leads to an asymmetric distribution of the gamma rays. This asymmetry has been calculated for the High Intensity Gamma-ray Source (HIGS) beam at Duke University. Owing to the high intensity of the HIGS beam, this asymmetry is determined to be measurable with a small statistic error using a simple gamma-ray beam imaging system. We propose to set up this system to measure the polarization of the electron beam in the Duke storage ring.
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