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| TUPMS002 | Successful Completion of the Femtosecond Slicing Upgrade at the ALS | 1194 |
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Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, U. S. Department of Energy under Contract No. DE-AC02-05CH11231. An upgraded femtosecond slicing facility has been commissioned successfully at the Advanced Light Source. In contrast to the original facility at the ALS which pioneered the concept, the new beamline uses an undulator (the first in-vacuum undulator at the ALS) as the radiator producing the user photon beam. To spatially separate the femtosecond slices in the radiator, a local vertical dispersion bump produced with 12 skew quadrupoles is used. The facility was successfully commissioned during the last 1.5 years and is now used in routine operation. |
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| TUPMS003 | Status of the Top-off Upgrade of the ALS | 1197 |
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Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, U. S. Department of Energy under Contract No. DE-AC02-05CH11231. The Advanced Light Source is currently being upgraded for top-off operation. This major facility upgrade will provide an improvement in brightness from soft x-ray undulators of about one order of magnitude and keep the ALS competitive with the newest intermediate energy light sources. Major components of the upgrade include making the booster synchrotron capable of full energy operation, radiation safety studies, improvements to interlocks and collimation systems, diagnostics upgrades as well as emittance improvements in the main storage ring. The project status will be discussed as well as results of major parts of the commissioning. |
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| TUPMS005 | Quiet Start Method in HGHG Simulation | 1200 |
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Funding: Work supported by U. S. DOE under contract No DE-FG02-92ER40747 and U. S NSF under contract No PHY-0552389 Quiet start scheme is broadly utilized in Self Amplified Spontaneous Radiation (SASE) FEL simulations, which is proven to be correct and efficient. Nevertheless, due to the existing of energy modulation effect and the dispersion section, the High Gain Harmonic Generation (HGHG) FEL simulation will not be improved by the traditional quiet start method. A new approach is presented to largely decrease the macro-particles per slice that can be implemented in both time-independent and time-dependent simulation, accordingly expedites the HGHG FEL simulation especially high order harmonic cascade case and makes the multi-parameter scanning be possible. |
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| TUPMS007 | NSLS VUV Ring Lifetime Study | 1203 |
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| Beam lifetime at VUV ring of National Synchrotron Light Source(NSLS) at BNL is limited by Touschek effect. This effect is affected by momentum acceptance and beam density. The geometry near injection septum, dynamic aperture and the RF acceptance all can limit the over all momentum acceptance. Extensive experiments including coupling, gas scattering, RF acceptance, have been done for understanding the lifetime, and the result is confirmed with theoretical predictions. | ||
| TUPMS010 | Fabrication and Measurement of Efficient, Robust Cesiated Dispenser Photocathodes | 1206 |
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Funding: This work is funded by the Office of Naval Research and the Joint Technology Office. Photocathodes for high power free electron lasers face significant engineering and physics challenges in the quest for efficient, robust, long-lived, prompt laser-switched operation. The most efficient semiconductor photocathodes, notably those responsive to visible wavelengths, suffer from poor lifetime due to surface layer degradation, contamination, and desorption. Using a novel dispenser photocathode design, rejuvenation of cesiated surface layers in situ is investigated for semiconductor coatings building on previous results for cesiated metals. Cesium from a sub-surface reservoir diffuses to the surface through a microscopically porous, sintered tungsten matrix to repair the degraded surface layer. The goal of this research is to engineer and demonstrate efficient, robust, long-lived regenerable photocathodes in support of predictive photocathode modeling efforts and suitable for photoinjection applications. |
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| TUPMS014 | Commissioning of the Booster Injector Synchrotron for the HIGS Facility at Duke University | 1209 |
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Funding: This work is supported by the US DoE grant #DE-FG02-01ER41175 A booster synchrotron has been built and recently commissioned at Duke University Free Electron Laser Laboratory (DFELL) as part of the High Intensity Gamma-ray Source (HIGS) facility upgrade. HIGS is developed collaboratively by the DFELL and Triangular Universities Nuclear Laboratory (TUNL). The booster will provide top-off injection into the Duke FEL storage ring in the energy range of 0.27 - 1.2 GeV. When operating the Duke storage ring to produce high energy Compton gamma ray beams above 20 MeV, continuous electron beam loss occurs. The lost electrons will be replenished by the booster injector operating in the top-off mode. The compactness of the booster posed a challenge for its development and commissioning. The booster has been successfully commissioned in 2006. This paper reports experience of commissioning and initial operation of the booster. |
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| TUPMS015 | Challenges for the Energy Ramping in a Compact Booster Synchrotron | 1212 |
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Funding: This work is supported by the US DoE grant #DE-FG02-01ER41175 A booster synchrotron has been recently commissioned at Duke University FEL Laboratory as a part of the High Intensity Gamma-ray Source (HIGS) facility. The booster will provide top-off injection into the storage ring in the energy range of 0.27 - 1.2 GeV. In order to minimize the cost of the project, the booster is designed with a very compact footprint. As a result, unconventionally high field bending magnets at 1.76 T are required. A main ramping power supply drives all dipoles and quadrupoles. Quadrupole trims are used to compensate for tune changes caused by the change of relative focusing strength during ramping. Sextupoles compensate for chromatic effects caused by dipole magnet pole saturation. All these compensations have to be performed as a function of beam energy. Above 1.1 GeV, where the magnets are heavily saturated, the reduction of dynamic aperture is compensated by redistribution of strength among the sextupole families. With these compensations, effects of the magnet saturation do not cause any considerable beam loss during energy ramping. |
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| TUPMS017 | Accelerator Physics Research and Light Source Development Programs at Duke University | 1215 |
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Funding: This work is supported by the US AFOSR MFEL grant #FA9550-04-01-0086 and by U. S. DoE grant DE-FG05-91ER40665. The Duke Free-Electron Laser Laboratory (DFELL) has recently completed two major accelerator/light source development projects - we successfully commissioned the world's first distributed optical klystron FEL (DOK-1 FEL) and a new 0.27-1.2 GeV booster synchrotron. The DOK-1 FEL has a much improved FEL gain compared with traditional optical klystrons. This allows the DOK-1 FEL to become a versatile light source for UV-VUV operation and as a driver for a high-intensity Compton gamma-source. The top-off booster injector for the Duke storage ring is part of the upgrade project of High Intensity Gamma-ray Source (HIGS), a facility jointly developed by the DFELL and Triangle Universities Nuclear Laboratory (TUNL). The accelerator and light source development has created new opportunities for the accelerator physics research. In this paper, we will report our recent progress in accelerator and light source development as well as the ongoing accelerator physics research programs to meet the new challenges in the areas of beam dynamics and beam instability. |
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| TUPMS019 | Ion Effects and Ion Elimination in the Cornell ERL | 1218 |
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Funding: Supported by Cornell University and NSF grant PHY 0131508 In an energy recovery linac (ERL) where beam-loss has to be minimal, and where beam positions and emittances have to be very stable in time, optic errors and beam instabilities due to ion effects have to be avoided. Here we explain why ion clearing electrodes are the least unattractive way of eliminating ions in an ERL and we present calculations of the remnant ion density and its effect on the beam. We also show a design of the clearing electrodes that should be distributed around the accelerator and illustrate their wake-field properties. |
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| TUPMS020 | Thermal Emittance Measurements from Negative Electron Affinity Photocathodes | 1221 |
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Funding: Work supported by the National Science Foundation under contract PHY 0131508 Recent computational optimizations have demonstrated that it should be possible to construct electron injectors based on photoemission cathodes in very high voltage DC electron guns in which the beam emittance is dominated by the thermal emittance from the cathode. Negative electron affinity photocathodes have been shown to have a naturally low thermal emittance. However, the thermal emittance depends on the illuminating wavelength; the degree of negative affinity; and the band structure of the photocathode material. As part of the development of a high brightness, high average current photoemission electron gun for the injector of an ERL light source, we have measured the thermal emittance from negative affinity GaAs and GaAsP photocathodes. The measurements were made by measuring the electron beam spot size downstream of a counter-wound solenoid lens as a function of the lens strength. Electron beam spot sizes were measured by two techniques - a 20 micron wire scanner, and a CVD diamond screen. Both Gaussian and 'tophat' spatial profiles were used, and measurements were made at several wavelengths. Results will be presented for both cathode types. |
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| TUPMS021 | Performance of a Very High Voltage Photoemission Electron Gun for a High Brightness, High Average Current ERL Injector | 1224 |
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Funding: Work supported by the National Science Foundation under contract PHY 0131508 We have constructed a very high voltage photoemission electron gun as the electron source of a high brightness, high average current injector for an energy recovery linac (ERL) synchrotron radiation light source. The source is designed to deliver 100 mA average current in a CW 1300 MHz pulse train (77 pC/bunch). The cathode voltage may be as high as 750 kV. Negative electron affinity photocathodes are employed to obtain small thermal emittances. The electrode structure is assembled without touching any electrode surface. A load-lock system allows cleaning and activation of cathode samples prior to installation in the electron gun. Cathodes are cleaned by heating and exposure to atomic hydrogen, and activated with cesium and nitrogen trifluoride. Two cathode electrode sets, of 316LN stainless steel and Ti4V6Al alloy, have been used. The anode is beryllium. The internal surface of the ceramic insulator of the gun has a high resistivity fired coating, providing a path to drain away charge from field emission. Non-evaporable getters provide a very high pumping speed for hydrogen. Operating experience with this gun will be presented. |
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| TUPMS022 | Beam Breakup Simulations for the Cornell X-ray ERL | 1227 |
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Funding: Supported by Cornell University and NSF grant PHY 0131508 Multi-pass, multi-bunch beam-breakup (BBU) can limit the current in linac-based recirculating accelerators. We have therefore made the computation of the transverse and longitudinal BBU-threshold current available in Cornell's main optics design and beam simulation library BMAD. The coupling of horizontal and vertical motion as well as time of flight effects are automatically contained. Subsequently we present a detailed simulation study of transverse and longitudinal BBU in the proposed 5GeV Energy Recovery Linac light source at Cornell University, including the use of frequency randomization, polarized cavities and optical manipulations to improve the threshold current. |
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| TUPMS023 | Measurement of Permanent Magnet Material Demagnetization Due to Irradiation by High Energy Electrons | 1230 |
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Funding: Work supported by the National Science Foundation under contract PHY 0202078 The design of insertion device depends on the properties of the permanent magnet material used. While magnetic material properties such as coercive force, residual induction and magnetization variation with temperature are provided by manufacturer, demagnetization caused by radiation can be only roughly estimated based on very few published data. To obtain data which can be reliably used in ERL insertion device design, we irradiated two materials of very different coercive forces and measured their demagnetization as function of radiation dose. For irradiation we used 5GeV electron beam from Cornell 12GeV Synchrotron. Radiation dose was measured using the calorimetric technique. One of the materials was similar to what we plan to use in construction of ERL undulators. Detailed information on experimental setup, radiation dose measurement techniques, results and analysis will be presented. |
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| TUPMS024 | Development of a 100 mm Period Hybrid Wiggler for the Australian Synchrotron Project | 1233 |
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Funding: Australian Synchrotron Project This paper summarizes the final magnetic measurement for a hybrid wiggler installed at the Australian Synchrotron Project (ASP). This device uses an anti-symmetric, hybrid design with a period of 100 mm and 40 full-strength Vanadium-Permendur poles surrounded by Neodynium-Iron-Boron magnets. It is designed to operate at two gaps with critical energies of 11.4 (14mm) and 9.6 keV (18.16mm) and to have a maximum gap with the field strength By ≤ 50 G. The wiggler's drive mechanism is capable of moving from minimum to maximum gap in 96 seconds. End terminations are designed to maintain the electron trajectory on-axis. The straightness of the electron orbit is controlled by moving the poles vertically and horizontally. The integrated multipoles are controlled over the interval |x| < 25 mm and all gap sizes by moving the side magnets, installing correction magnets at the wiggler entrance and exit and using correction coils. All adjustments have been made using threaded fasteners. No shims have been used. |
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| TUPMS026 | Design of Control Instrumentation of two In-Vacuum Undulators IVU25s | 1236 |
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Funding: Shanghai Institute of Applied Physics This paper summarizes the primary controller that is based on Schneider Premium PLC for two in-vacuum undulators to be installed at SSRF. The PLC controls a single gap stepper motor and driver, both made by Parker-Hannifin. Position feedback is derived from a TR Electronics linear absolute LTS-240 encoder mounted across the gap. The encoder resolution is programmable down to .1 um per count. Since the encoder is absolute there will be no need to home the gap axis. The advantage of linear encoders is the measurement is more direct and is not subject to wind-up and deflection that a rotary encoder would see on the end of a ball screw. Two encoders are planned, one on each end of the magnet array. One encoder will be the primary feedback for the axis and the other will detect deflection errors and girder taper. Four limits are provided as well as 4 kill switches. The 4 switches (2 limits and 2 kills) at min gap are optical and the 4 outer switches (2 limits and 2 kills) are mechanical. The limits prevent further motion in the direction they protect but allow the axis to be driven in the other direction (off the switch). |
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| TUPMS027 | Development of Software to Control 8-Motor Elliptically Polarizing Undulators | 1239 |
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Funding: Swedish Natural Research Council (Vetenskapsrdet) Advanced Design Consulting developed control software entitled IDcontrol for its state-of-the-art Apple II insertion devices (ID). These IDs feature 8 controllable axes: four servo motors control the gap and taper of two main girders, and four servo motors control the photon polarization-state by manipulating four sub-girders. IDcontrol simultaneously positions all 8 axes with high precision in real-time using 0.1 micron linear encoders attached directly to the girders and sub-girders. Helical and Inclined Plane phase modes are supported with automated mode switching. Magnetic-field-correction-coil current and girder taper are adjustable as functions of gap, phase, and phase mode. IDcontrol continuously monitors redundant encoder velocity and position data for maximal reliability, encoder failure detection, and damage prevention. Combined with ADCs Graphical User Interface (GUI) entitled IDgui, IDcontrol manipulates the ID, provides user notification and automated recovery from errors, management of correction data, and isometric visualization of the ID's girders. The functionality of both IDcontrol and IDgui has been demonstrated at MAX lab and the results will be discussed. |
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| TUPMS028 | Commissioning of a High-Brightness Photoinjector for Compton Scattering X-Ray Sources | 1242 |
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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. Compton scattering of intense laser pulses with ultra-relativistic electron beams has proven to be an attractive source of high-brightness x-rays with keV to MeV energies. This type of x-ray source requires the electron beam brightness to be comparable with that used in x-ray free-electron lasers and laser and plasma based advanced accelerators. We describe the development and commissioning of a 1.6 cell RF photoinjector for use in Compton scattering experiments at LLNL. Injector development issues such as RF cavity design, beam dynamics simulations, emittance diagnostic development, results of sputtered magnesium photo-cathode experiments, and UV laser pulse shaping are discussed. Initial operation of the photoinjector is described and transverse phase space measurements are presented. |
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| TUPMS029 | Gamma-Ray Compton Light Source Development at LLNL | 1245 |
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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 W-7405-Eng-48. A new class of tunable, monochromatic gamma-ray sources capable of operating at high peak and average brightness is currently being developed at LLNL for nuclear photo-science and applications. These novel systems are based on Compton scattering of laser photons by a high brightness relativistic electron beam produced by an rf photoinjector. Key technologies, basic scaling laws, and recent experimental results will be presented, along with an overview of future research and development directions. |
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| TUPMS030 | Optimal Design of a Tunable Thomson-Scattering Based Gamma-Ray Source | 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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| TUPMS031 | High-energy Picosecond Laser Pulse Recirculation for Compton Scattering | 1251 |
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Funding: This work was performed under the auspices of the U. S Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
Frequency upconversion of laser-generated photons by inverse Compton scattering for applications such as nuclear spectroscopy and gamma-gamma collider concepts on the future ILC would benefit from an increase of average source brightness. The primary obstacle to higher average brightness is the relatively small Thomson scattering cross section. It has been proposed that this limitation can be partially overcome by use of laser pulse recirculation. The traditional approach to laser recirculation entails resonant coupling of low-energy pulse train to a cavity through a partially reflective mirror.* Here we present an alternative, passive approach that is akin to "burst-mode" operation and does not require interferometeric alignment accuracy. Injection of a short and energetic laser pulse is achieved by placing a thin frequency converter, such as a nonlinear optical crystal, into the cavity in the path of the incident laser pulse. This method leads to the increase of x-ray/gamma-ray energy proportional to the increase in photon energy in frequency conversion. Furthermore, frequency tunability can be achieved by utilizing parametric amplifier in place of the frequency converter.
* G. Klemz, K. Monig, and I. Will, "Design study of an optical cavity for a future photon-collider at ILC", Nucl. Instrum. Meth. A 564, 212-224 (2006). |
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| TUPMS033 | Chicane Radiation Measurements with a Compressed Electron Beam at the BNL ATF | 1254 |
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| The radiation emitted from a chicane compressor has been studied at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). Coherent edge radiation (CER)is emitted from a compressed electron beam as it traverses sharp edge regions of a magnet. The compression is accompanied by strong self-fields, which are manifested as distortions in the momentum space called beam bifurcation. Recent measurements indicate that the bunch length is approximately 100 fs rms. The emitted THz chicane radiation displays strong signatures of CER. This paper reports on the experimental characterization and subsequent analysis of the chicane radiation measurements at the BNL ATF with a discussion of diagnostics development and implementation. The characterization includes spectral analysis, far-field intensity distribution, and polarization effects. Experimental data is benchmarked to a custom developed start-to-end simulation suite. | ||
| TUPMS034 | Seeded VISA: A 1064 nm Laser-Seeded FEL Amplifier at the BNL ATF | 1257 |
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| An experimental study of a seeded free electron laser (FEL) using the VISA undulator and a Nd:YAG seed laser will be performed at the Accelerator Test Facility at Brookhaven National Laboratory. The study is motivated by the demand for a short Rayleigh length FEL amplifier at 1 micron for high power transmission with minimal damage of transport optics. Planned measurements include transverse and longitudinal coherence, angular distribution, and wavelength spectrum of the FEL radiation. The effects of detuning the electron beam energy will be studied, with an emphasis on control of the radiation emission angles and increase of the amplifier efficiency. Results of start-to-end simulations will be presented with preliminary experimental results. | ||
| TUPMS035 | The FINDER Photoinjector | 1260 |
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| The FINDER project at LLNL is an inverse-Compton scattering demonstration, aimed at creating MeV-class, narrow band photons for interrogation of nuclear materials. The requirements experiment requires a state-of-the-art photoinjector. Such a device is under development by a UCLA/LLNL collaboration. We report on a number of design innovations, such as photocathode gun RF symmetrization and large mode separation, which sets this device apart from previous generations of the BNL/SLAC/UCLA 1.6 cell gun. Measurements characterizing the RF photocathode gun and emittance compensation solenoid are presented. | ||
| TUPMS036 | Characterization of Orbital Angular Momentum Modes in FEL Radiation | 1263 |
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| Optical guiding of the radiation pulse through the source electron bunch in a free-electron laser is a well known phenomena that suppresses diffraction of the output radiation, and thus enhances the gain. The resulting radiation can be described by an expansion of orthogonal modes that are also composed of eigenstates of orbital angular momentum (OAM). In the VISA-FEL experiment at the ATF-BNL, gain guiding has been observed under self-amplified spontaneous emission conditions at 840 nm with a strongly chirped input electron beam. The resulting far-field transverse radiation profiles are observed to contain multiple modes in the angular intensity spectrum, and exhibit both hollow and spiral structures characteristic of single or multiply interfering OAM modes. Current efforts to characterize the transverse radiation profile both experimentally and through start-to-end simulations are presented. | ||
| TUPMS037 | Simulation of an Iris-guided Inverse Free-electron Laser Micro-bunching Experiment | 1266 |
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| The Free-Electron Laser code Genesis 1.3 has been modified to include waveguides within the undulator, reducing the diffraction effects for long wavelength FELs. Several types of waveguides are considered, which are rectangular and circular waveguides as well as iris-loaded open waveguides. Studies are presented here on the enhancement of FEL and IFEL with these wave-guiding structures in comparison to free-space propagation of the radiation wave. | ||
| TUPMS038 | Recent Upgrade to the Free-electron Laser Code Genesis 1.3 | 1269 |
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| The time-dependent code GENESIS 1.3 has be modified to address new problems in modeling Free-electron Lasers. The functionality has been extended to include higher harmonics and to allow for a smoother modeling of cascading FELs. The code has been also exported to a parallel computer architecture for faster execution using the MPI protocol. | ||
| TUPMS039 | Coherence Properties of the LCLS X-ray Beam | 1272 |
| Self-amplifying spontaneous radiation free-electron lasers, such as the LCLS or the European X-FEL, rely on the incoherent, spontaneous radiation as the seed for the amplifying process. Though this method overcomes the need for an external seed source one drawback is the incoherence of the effective seed signal. The FEL process allows for a natural growth of the coherence because the radiation phase information is spread out within the bunch due to slippage and diffraction of the radiation field. However, at short wavelengths this spreading is not sufficient to achieve complete coherence. In this presentation we report on the results of numerical simulations of the LCLS X-ray FEL. From the obtained radiation field distribution the coherence properties are extracted to help to characterize the FEL as a light source. | ||
| TUPMS040 | Development of a THz Seed Source for FEL Microbunching Experiment at the Neptune Laboratory | 1275 |
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Funding: This work is supported by US Department of Energy Grant No. DE-FG03-92ER40727
Seeded FEL/IFEL techniques can be used for modulation of a relativistic electron beam longitudinally on the radiation wavelength. However, in the 1-10 THz range, which is of particular importance for matched injection of prebunched electrons into a laser-driven plasma accelerating structure, a suitable radiation source is not available. At the UCLA Neptune Laboratory we have built and fully characterized a radiation source tunable in the range of 1-3 THz. The THz pulse is produced by mixing two CO2 laser lines in a noncollinear phase-matched GaAs crystal at room temperature. The crystal is pumped by 200 ns pulses of a dual beam TEA CO2 laser running at 1 Hz. A grating placed in each lasing section allowed to cover the spectral range for the difference frequency from 0.5-4.5 THz with a step of 30-40 GHz. The achieved narrow bandwidth of ~10-5 and the output power of 2kW are sufficient for seeding a single-pass, waveguide FEL amplifier-prebuncher*. These pulses were used to measure the coupling efficiency and the attenuation for different types of THz waveguides and the results will be reported.
* C. Sung et al. "Seeded FEL/IFEL techniques for radiation amplification and electron microbunching in the terahertz range" Phys. Rev. STAB, 2006 (to be published) |
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| TUPMS041 | The Wisconsin VUV/Soft X-ray Free Electron Laser Project | 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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| TUPMS042 | A Superconducting Linac Driver for the Wisconsin Free Electron Laser | 1281 |
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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. We present an initial design of the driver for the Wisconsin VUV/Soft Xray FEL facility, which will provide high intensity coherent photons from 5 eV to 1.2 keV. It uses a 2.5 GeV, L-band CW superconducting linac with a 1.7 GeV tap-off to feed the lower energy FELs. In order to support multiple high rep-rate FELs, the average design current is 1 mA. Sub-nanocoulomb bunches with normalized transverse emittances of order 1 micron are generated in a photoinjector for beamlines operating at repetition rates from kHz to MHz. Multi-stage bunch compression provides 1 kA peak current to the FELs, with low energy spread and a suitable current profile. Compressed bunch lengths of several hundred femtoseconds will allow generation of photon pulses in the range 10 to 100 fs using cascaded FELs. Consideration has been given to removing the residual energy chirp from the beam, and minimizing the effects of space charge, coherent synchrotron radiation, and microbunching instabilities. A beam switchyard using RF separators and fast kickers delivers the desired electron bunches to each of the FELs. Details of the design will be presented, including those areas requiring the most development work. |
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| TUPMS043 | Design of a 2.1 GeV Electron Storage Ring | 1284 |
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Funding: This research was supported by National Science Foundation Grant no. DMR-0537588. A 2.1 GeV electron storage ring can serve as a third-generation light source for photon energies of 1-2000 eV. We design a ring with emittance of 1.5 nm-rad, circumference of 215 m, and twelve 5.5 m long straight sections. With a 100 MHz radiofrequency (rf) system, the computed Touschek current-lifetime product is 2800 mA-hr. Two passive fifth-harmonic cavities may be used to suppress parasitic coupled-bunch instabilities while increasing the bunchlength and lifetime by a factor of four. For stable operation with ring currents up to 600 mA, microwave-instability simulations indicate that the reduced longitudinal impedance should not exceed 1.5Ω. |
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| TUPMS044 | Design of a 980 MeV Energy Recovery Linac | 1287 |
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Funding: This research was supported by National Science Foundation grant no. DMR-0537588. A 980-MeV energy recovery linac with radiofrequency (rf) of 1.5 GHz is designed. Electrons are accelerated by two passages through a 480-MeV superconducting linac, and decelerated by two subsequent passages. Recirculation is accomplished with six 60-degree bending magnets. The threshold current for beam breakup instability exceeds 100 mA. Gaussian bunches with normalized transverse emittances of 0.1 mm-mrad and rms length of 1.85 ps may be compressed by a factor of 180 (to a bunch length of 10 fs) with only a slight increase in transverse normalized emittance. Bunch charges up to 8 pC may be compressed at 980 MeV without excessive degradation from coherent synchrotron radiation, allowing operation with beam currents up to 12 mA. |
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| TUPMS045 | Improvements to the Aladdin Synchrotron Light Source | 1290 |
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Funding: Work supported by the U. S. National Science Foundation under Award No. DMR-0537588. Aladdin is an IR to soft x-ray synchrotron light source operated by the University of Wisconsin at Madison. As part of the ongoing program of upgrades and improvements, several changes have recently been made to the ring. It had previously been determined that physical apertures (BPMs) at the QF quadrupoles were limiting beam lifetime when the ring was operated in its low emittance configuration. Increasing the size of these apertures has resulted in a significant increase in lifetime. Also as part of the aperture opening process, a number of ring components were redesigned and replaced, lowering the ring impedance. This has led to an increase in the threshold beam current for microwave instability. Another modification was the design and installation of discrete trim coils on the quadrupole pole-tips to facilitate using the quads as steering correctors. Details of these and other improvements will be presented. |
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| TUPMS046 | Integration of the Optical Replica Ultrashort Electron Bunch Diagnostics with the Current-Enhanced SASE in the LCLS | 1293 |
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In this paper, we present a feasibility study of integrating the optical replica (OR) ultrashort electron bunch diagnostics * with the current-enhanced SASE (ESASE) scheme ** in the LCLS. Both techniques involve using an external laser to energy-modulate the electron beam in a short wiggler and converting the energy modulation to a density modulation in a dispersive section. While ESASE proposes to use the high-current spikes to enhance the FEL signal, the OR method extracts the optical coherent radiation produced by a density modulated electron beam for frequency resolved optical gating (FROG) diagnostics. We discuss the optimization studies of combining the OR method with the ESASE after the second bunch compressor in the LCLS. Simulation results show that the OR method is capable of reproducing the expected double-horn current profile of a 200-fs bunch. The possibilities and limitations of reconstructing the longitudinal phase space profile are also explored.
* E. Saldin et al, Nucl. Instr. and Meth. A 539, 499 (2005).** A. Zholents, Phys. Rev. ST Accel. Beams 8, 040701 (2005); A. Zholents et al., in Proceedings of FEL2004, 582 (2004). |
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| TUPMS047 | Results of the SLAC LCLS Gun High-Power RF Tests | 1296 |
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Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC03-76SF00515. The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented. |
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| TUPMS048 | Measurement and Analysis of Field Emission Electrons in the LCLS Gun | 1299 |
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Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC03-76SF00515. The field emission was measured during the high-power testing of the LCLS photocathode RF gun. A careful study and analysis of the field emission electrons, or dark current is important in assessing the gun's internal surface quality in actual operation, especially those surfaces with high fields. The charge per 2 microsecond long RF pulse (the dark charge) was measured as a function of the peak cathode field for the 1.6 cell, 2.856GHz LCLS RF gun. Faraday cup data was taken for cathode peak RF fields up to 120MV/m producing a maximum of 0.6nC/RF pulse for a diamond-turned polycrystalline copper cathode installed in the gun. The field dependence of the dark charge is analyzed using a temperature-dependent Fowler-Nordheim (FN) theory to obtain the field enhancement factor and other emitter parameters. Digitized images of the dark charge were taken using a 100 micron thick YAG crystal for a range of solenoid fields to determine the location and angular distribution of the field emitters. The FN plots and emitter image analysis will be described in this paper. |
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| TUPMS049 | Initial Commissioning Experience with the LCLS Injector | 1302 |
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Funding: U. S. Department of Energy contract #DE-AC02-76SF00515. The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was installed during the Fall of 2006. Initial system commissioning with an electron beam takes place in the Spring and Summer of 2007. The second phase of construction, including the second bunch compressor and the FEL undulator, will begin later, in the Fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, energy spectrometers, S-band and X-band RF systems, the first bunch compressor stage, and the various beam diagnostics. |
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| TUPMS050 | Simulation of Ultra-Short Pulses in a Storage Ring | 1305 |
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Simulation study was performed with the tracking code Elegant [M. Borland, APS Report LS-287] to show beam quality evolution for a short, intense electron bunch after being injected to the SPEAR3 storage ring. The electron bunch with an intensity of 1mA (0.78nC) and a length of nearly 1ps (FWHM) is found to degrade rapidly due to coherent synchrotron radiation (CSR) which causes large uneven longitudinal phase space distortion. The bunch length remains short and the longitudinal line density remains smooth for about 10 turns. For such a beam to circulate in the ring, a total of 10MV rf power is needed to compensate for the energy loss.
* M. Borland, APS Report LS-287 |
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| TUPMS051 | Low Alpha Mode for SPEAR3 | 1308 |
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| In the interest of obtaining shorter bunch length for shorter X-ray pulses, we have developed a low-alpha operational mode for SPEAR3. In this mode the momentum compaction factor is reduced by a factor of 21 or more from the usual achromat mode by introducing negative dispersion at the straight sections. We successfully stored 100~mA with the normal fill pattern at a lifetime of 30hrs. The bunch length was measured to be 6.9ps, compared to 17ps in the normal mode. In this paper we report our studies on the lattice design and calibration, orbit stability, higher order alpha measurement, lifetime measurement and its dependence on the sextupoles, injection efficiency and bunch lengths. | ||
| TUPMS055 | SPEAR3 Accelerator Physics Update | 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. | ||
| TUPMS057 | An Efficient 95-GHz, RF-Coupled Antenna | 1314 |
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Funding: Work supported by U. S. Dept. of Energy contract DE-AC02-76SF00515. This paper presents an efficient, RF-coupled, 95-GHz undulatory (snake-like) antenna that can be fabricated using IC technology. While there are many uses for directed power at this frequency our interest is in understanding the propagation of the input power through the circuit and its radiative characteristics for comparison to earlier work in the THz range (see PAC05). 95 GHz was chosen because test equipment was available (WR-10 waveguide and HP network analyzer). Different materials, heights and widths of the circuit were considered on a low-loss, 0.10-mm thick quartz substrate e.g. 0.75 microns of elevated gold corresponding to three skin depths. The design is compared to more conventional RF technology using a low energy, high power electron beam and to higher energy, lower power Smith Purcell gratings and free-electron-lasers (FELs). The FDTD results show narrow-band, 80% radiation efficiency with a dipole-like radiation pattern that is enhanced by adding periods. The radiated power was calculated using two different techniques that agreed quite well i.e. by integrating the far-field Poynting vector as well as subtracting the output power from input power. |
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| TUPMS058 | The LCLS Injector Drive Laser | 1317 |
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| Requirements for the LCLS injector drive laser present significant challenges to the design of the system. While progress has been demonstrated in spatial shape, temporal shape, UV generation and rep-rate, a laser that meets all of the LCLS specifications simultaneously has yet to be demonstrated. These challenges are compounded by the stability and reliability requirements. The drive laser and transport system has been installed and tested. We will report on the current operational state of the laser and plans for future improvements. | ||
| TUPMS059 | LCLS Undulator Tuning And Fiducialization | 1320 |
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Funding: Work supported in part by the DOE Contract DE-AC02-76SF00515. The LCLS x-ray free electron laser project at SLAC requires 40 undulators: 33 in the beamline, 6 spares, and one reference undulator. A new facility was constructed at SLAC for tuning and fiducializing the undulators. The throughput of the facility must be approximately one undulator per week. Much effort has gone into automating the undulator tuning. Because of tight alignment tolerances, accurate techniques were developed to fiducialize the undulators. The new facility, the tuning techniques, and the fiducialization techniques will be discussed. |
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| TUPMS062 | National High Magnetic Field Laboratory FEL Injector Design Consideration | 1323 |
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| A Numerical study of beam dynamics was performed for two injector systems for the proposed National High Magnetic Field Laboratory at the Florida State University (FSU) Free Electron Laser (FEL) facility. The first considered a system consisting of a thermionic DC gun, two buncher cavities operated at 260 MHz and 1.3 GHz and two TESLA type cavities, and is very similar to the injector of the ELBE Radiation Source. The second system we studied uses a DC photogun (a copy of JLab FEL electron gun), one buncher cavity operated at 1.3 GHz and two TESLA type cavities. The study is based on PARMELA simulations and takes into account operational experience of both the JLab FEL and the Radiation Source ELBE. The simulations predict the second system will have a much smaller longitudinal emittance. For this reason the DC photo gun based injector is preferred for the proposed FSU FEL facility. | ||
| TUPMS064 | RF Gun Optimization Study | 1326 |
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Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.
Injector gun design is an iterative process where the designer optimizes a few nonlinearly interdependent beam parameters to achieve the required beam quality for a particle accelerator. Few tools exist to automate the optimization process and thoroughly explore the parameter space. The challenging beam requirements of new accelerator applications such as light sources and electron cooling devices drive the development of RF and SRF photo injectors. RF and SRF gun design is further complicated because the bunches are space charge dominated and require additional emittance compensation. A genetic algorithm has been successfully used to optimize DC photo injector designs for Cornell* and Jefferson Lab**, and we propose studying how the genetic algorithm techniques can be applied to the design of RF and SRF gun injectors. In this paper, we report on the initial phase of the study where we model and optimize gun designs that have been benchmarked with beam measurements and simulation.
* I. Bazarov, et al., "Multivariate Optimization of a High Brightness DC Gun Photoinjector", PRST-AB 2005.** F. Hannon, et al., "Simulation and Optimisation of a 100 mA DC Photoinjector", EPAC 2006. |
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| TUPMS065 | JLAMP: An Amplifier Based FEL in the JLab SRF ERL Driver | 1329 |
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Funding: This work supported by the Off. of Naval Research, the Joint Technology Off., the Commonwealth of Virginia, the Air Force Research Lab, Army Night Vision Lab, and by DOE Contract DE-AC05-060R23177. Notional designs for ERL-driven high average power free electron lasers often invoke amplifier-based architectures. To date, however, amplifier FELs have been limited in average power output to values several orders of magnitude lower than those demonstrated in optical-resonator based systems; this is due at least in part to the limited electron beam powers available from their driver accelerators. In order to directly contrast the performance available from amplifiers to that provided by high-power cavity-based resonators, we have developed a scheme to test an amplifier FEL in the JLab SRF ERL driver. We describe an accelerator system design that can seamlessly and non-invasively integrate a 10 m wiggler into the existing system and which provides, at least in principle, performance that would support high-efficiency lasing in an amplifier configuration. Details of the design and an accelerator performance analysis will be presented. |
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| TUPMS069 | Proposed Tabletop Laser-driven Coherent X-Ray Source | 1332 |
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| Laser-driven particle acceleration shows promise for compact ultra-low emittance, GeV/m electron sources. The first proof-of-principle demonstration for this particle acceleration technique has been carried out and a comprehensive experimental program to develop dielectric based micro-accelerator structures is under way. Therefore it is natural to explore the possibility for applying these future accelerators for SASE-FEL based X-ray generation. We employ well-established numerical models based on the standard SASE-FEL theory to find a plausible set of undulator and electron beam parameters to accomplish the desired X-ray pulse structure. | ||
| TUPMS071 | Upgrade Alternatives for the NSLS Superconducting Wiggler | 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. | ||
| TUPMS072 | Longitudinal Beam Parameter Tolerances of NSLS II | 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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| TUPMS073 | Dispersion Tolerance Calculation for NSLS-II | 1341 |
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| The approach for the proposed National Synchrotron Light Source II to reach small transverse emittances is to deploy damping wigglers. In the ideal lattice the dispersion is zero in the straight sections, therefore the damping wigglers supply only damping effect. In reality the residual dispersion can be generated by the lattice errors, trim dipoles, and the insertion devices. We will discuss dispersion introduced by different sources and calculate the tolerances. Possible correction schemes will also be presented. | ||
| TUPMS074 | Collective Effects in the NSLS-II Storage Ring | 1344 |
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Funding: This work was supported by Department of Energy contract DE-AC02-98CH10886. A new high-brightness synchrotron light source (NSLS-II) is under design at BNL. The 3-GeV NSLS-II storage ring has a double-bend achromatic lattice with damping wigglers installed in zero-dispersion straights to reduce the emittance below 1nm. In this note, we present an overview of the impact of collective effects upon the performance of the storage ring. Subjects discussed include Touschek lifetime, intra-beam scattering, instability thresholds due to ring impedance, and use of a third-harmonic Landau cavity. |
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| TUPMS076 | Status of R&D Energy Recovery Linac at Brookhaven National Laboratory | 1347 |
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Funding: Work performed under the auspices of the U. S. Department of Energy and partially funded by the US Department of Defence. In this paper we present status and plans for the 20-MeV R&D energy recovery linac, which is under construction at Collider Accelerator Department at BNL. The facility is based on high current (up to 0.5 A of average current) super-conducting 2.5 MeV RF gun, single-mode super-conducting 5-cell RF linac and about 20-m long return loop with very flexible lattice. The R&D ERL, which is planned for commissioning in 2008, aims to address many outstanding questions relevant for high current, high brightness energy-recovery linacs. |
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| TUPMS077 | Injection Simulations for NSLS-II Storage Ring | 1350 |
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| Operation of the NSLS-II storage ring in the top-up mode requires highly reliable injection with low losses. In this paper we provide results of the injection simulations for the storage ring. The alignment tolerances as well as requirements for the injected beam parameters are also discussed. | ||
| TUPMS078 | IBS Effects in a Wiggler Dominated Light Source | 1353 |
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| Intra-beam scattering (IBS) is often thought of as a fundamental limitation to achieving lower emittance and hence higher brightness in modern storage ring light sources. However, as we show in this paper analytically and by simulations using SAD code, this limitation may no longer be relevant in a wiggler dominated 3rd generation light source. Instead, lowering the emittance by increasing the amount of wiggler radiation does not result in significant IBS induced emittance blow-up, as higher beam density (and IBS rates) is compensated by faster radiation damping. We show that under some practical assumptions the relative ratio of the emittance including the IBS effect to the emittance at zero current is emittance independent. | ||
| TUPMS079 | Ion Trapping and Cathode Bombardment by Trapped Ions in DC Photoguns | 1356 |
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Funding: Work supported by U. S. DOE under contract No DE-AC02-98CH1-886, Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177. DC photoguns are used to produce high-quality, high-intensity electron beams for accelerator driven applications. Ion bombardment is credited as the major cause of degradation of the photocathode efficiency. Additionally to ions produced in the accelerating cathode-anode gap, the electron beam can ionize the residual gas in the transport line. These ions are trapped transversely within the beam and can drift back to the accelerating gap and contribute to the bombardment rate of the cathode. This paper proposes a method to reduce the flow of ions produced in the beam transport line and drifting back to the cathode-anode gap by introducing a positive potential barrier that repels the trapped ions. The reduced ion bombardment rate and increased life time of photocathodes will reduce the downtime required to service photoinjectors and associated costs. |
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| TUPMS081 | Design considerations of the NSLS-II Injection Linac | 1359 |
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| The NSLS-II injector consists of a 3 GeV booster injected by a 200MeV linac. Specifications of the linac are derived from Booster and Storage ring beam requirements. Linac design considerations are presented to meet these specifications. | ||
| TUPMS083 | Conceptual Design of the NSLS-II Injection System | 1362 |
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Funding: This work was supported by Department of Energy contract DE-AC02-98CH10886. We present conceptual design of the NSLS-II injection system. The injection system consists of low-energy linac, booster and transport lines. We review the requirements on the injection system imposed by the storage ring design and means of meeting these requirements. We discuss main parameters and layout of the injection system components. |
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| TUPMS085 | Photoemission Tests of a Pb/Nb Superconducting Photoinjector | 1365 |
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Funding: This work has been partially supported by the EU Commission, contract no. 011935 EUROFEL-DS5, US DOE under contract number DE-AC02-98CH10886. We report recent progress in the development of a hybrid lead/niobium superconducting (SC) injector. The goal of this effort is to produce an all-SC injector with the SCRF properties of a niobium cavity along with the superior quantum efficiency (QE) of a lead photocathode. Two prototype hybrid injectors have been constructed, one utilizing a cavity with a removable cathode plug, and a second consisting of an all-niobium cavity arc-deposited with lead in the cathode region. We present the results of QE measurements on these cavities, along with tests of the effect of the laser on the cavity RF performance. |
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| TUPMS086 | Insertion Device R&D for NSLS-II | 1368 |
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| NSLS-II is a medium energy storage ring of 3GeV electron beam energy with sub-nm.rad horizontal emittance and top-off capability at 500mA. Damping wigglers will be used not only to reduce the beam emittance but also for broadband sources for users. Cryo-Permanent Magnet Undulators (CPMUs) are considered for hard X-ray linear device, and permanent magnet based Elliptically Polarized Undulators(EPUs) are for polarization control. Rigorous R&D plans have been established to pursue the performance enhancement of the above devices as well as building new types of insertion devices such as high temperature superconducting wiggler/undulators. This paper describes the details of these activities and discuss technical issues. | ||
| TUPMS088 | Efficiency Enhancement Experiment with a Tapered Undulator in a Single-pass Seeded FEL at the NSLS SDL | 1371 |
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Funding: This work is supported by the Office of Naval Research under contract No. N0002405MP70325 and U. S. Department of Energy under contract No. DE-AC02-98CH1-886. We report the experimental characterization of the FEL efficiency enhancement using a tapered undulator in a single-pass seeded FEL amplifier at the NSLS SDL. The last 3 m of the 10 m NISUS undulator was linearly tapered so that the magnetic field strength at the end of the undulator was reduced by 5 %. The FEL energy gain along the undulator was measured for both the tapered and un-tapered undulator. The FEL energy with the taper was measured to be about 3.2 times higher than that without the taper. We also experimentally characterized the spectrum and the transverse distribution of the FEL light for both the tapered and un-tapered undulator. The experimental results are compared with the numerical simulation code, GENESIS 1.3. |
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| TUPMS089 | Thermal Emittance Measurement Design for Diamond Secondary Emission | 1374 |
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| Thermal emittance is a very important characteristic of cathodes. A lower thermal emittance cathode has a better performance in limiting emittance for transport down the beam line. A diamond amplified photocathode, being a negative electron affinity (NEA) cathode, promises to deliver a very small thermal emittance. A carefully designed method of measuring the emittance of secondary emission from diamond is presented for the first time. Comparison of possible schemes is carried out by simulation, and the most accessible and accurate method and values are chosen. Systematic errors can be controlled within a very small range, and are carefully evaluated. Aberration and limitations of all equipment are taken into account. | ||
| TUPMS091 | A Theoretical Photocathode Emittance Model Including Temperature and Field Effects | 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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| TUPMS092 | GdfidL Simulations of Non-Linear Tapers for ILC Collimators | 1380 |
| This paper summarises the GdfidL simulations relating to non-linear collimators, which offer the potential for improved wakefield performance at the ILC. Such collimators provide a further method for understanding the performance of simulation software in this challenging regime. Our results are compared with data from ESA at SLAC. | ||
| TUPMS093 | Computations of Wakefields in the ILC Collimators | 1383 |
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The collimators in the ILC serve the dual purpose of reducing the beam halo and as of a form of machine protection from potentially miss-steered beams. However, there is a significant wakefield in the immediate vicinity of the beam caused by their presence. It is important to be able to predict this short-range wakefield and the extent which it dilutes the emittance of the beam. We extend the previous analysis*, ** of wake-fields in collimators to realistic short bunches applicable to the ILC. We achieve these results using the finite difference code GdfidL. The angular wake is decomposed into its constituent components for rectangular collimators and compared with their circular collimator counterparts. Comparisons are made between these simulations, existing analytical models, and experimental results.
* C. Beard and R. M. Jones, EUROTeV-Report-2006-103** C. Beard and J. Smith, EPAC06 Proc. MOPLS070 |