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| MOP005 | Beam Dynamics for Intense L-band Electron Linac | electron, linac, bunching, focusing | 37 | ||
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We are now developing an intense L-band electron linac with a traveling-wave accelerating structure for irradiation applications. It is capable to produce 10 MeV electron beams of 30 kW by a pulsed klystron of 25 MW with a 60 kW average power. Bunching and accelerating cavities operated with 2π/3 mode at 1.3 GHz are designed by the SUPERFISH code. Focusing solenoids are designed by the POISSON code. Using electromagnetic field configurations obtained by these codes, a simulational study on the beam dynamics is conducted by the PARMELA code. As results, the beam envelope supports a transmission efficiency over 91% with the E-gun current of 1.6 A.
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| MOP007 | Turn Around Loop and Chicane for Bunch Compression and Path Length Tuning in the CLIC Drive Beam | emittance, electron, kicker, dipole | 43 | ||
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The phase feedback of the CLIC drive beam consists of phase and energy measurement stations in front of the turn around loops and chicanes for bunch compression and path length correction behind the loops. The chicanes are foreseen to compress the bunches from 4 mm to 0.4 mm and should allow a path length tuning of at least 0.1 mm. Suitable layouts for the turn around loops and the chicanes and results of beam dynamics simulations including incoherent and coherent synchrotron radiation are presented.
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| MOP010 | Massively Parallel Wake Field Computations in Long Accelerator Structures | vacuum, shielding, diagnostics, electron | 52 | ||
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The X-FEL project and the ILC require a high quality beam with ultra short bunches. The knowledge of the short-range wakefields in the TESLA cavities and the collimators is needed to predict the beam quality in terms of the single bunch energy spread and emittance. Especially for the high energy collimators these calculations are limited by numerical dispersion. Earlier we presented wake field calculations for short bunches in long structures for rotationally symmetric components with the code ECHO. Now we present first results from our new wake field code in fully 3D. To calculate the effect of the longitudinal and transverse wakefields we have used the time domain numerical approach. For sufficient resolution of the geometric boundaries and the short bunches (down to the nm-range), huge computational resources are needed. Thus in 3D massive parallelisation of the code is necessary. In addition we used the technique of a moving grid, which gives access also to very long structures, i.e. a complete module of eight TESLA cells or a high energy collimator.
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| MOP017 | 4GLS Beam-Break-Up Investigations | focusing, linac, recirculation, quadrupole | 67 | ||
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Beam Break Up (BBU) thresholds have been studied as part of the Linac focusing scheme for the proposed 4GLS accelerator. A graded gradient focusing scheme, with a triplet of quadrupoles between each of the modules within the Linac has been chosen. These quadrupoles are set-up in a defocusing – focusing – defocusing format with strengths of -1/2k, k, -1/2k. This value of k was altered and the BBU thresholds for the machine calculated using various BBU codes. Alternate cavity designs have also been investigated using CST’s Microwave Studio to see how the effects of higher order modes (HOMs) can be minimised whilst maintaining fundamental field flatness across theaccelerating cells. The number of cells/unit length and cell-to-cell geometries have also been parameterised and the corresponding BBU thresholds presented as a function of cavity geometry, with the intention of providing an optimum solution for 4GLS.
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| MOP022 | Simulation and Design of a Small LIA Stand | electron, linac, induction, gun | 82 | ||
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A small LIA experiment stand is designed and manufactured at Accelerator Lab, Tsinghua University. It consists of a thermal cathode DC gun, two induction acceleration cells, pulse power supply system, beam transportation and diagnostics. The electron gun can produce an electron beam of 80 ns, 1.2A and 80keV. Two induction cells accelerate beam energy up to 240keV. The time interval of each two pulses is 300 ns, and the beam pulse flat-top is 80ns. Simulations of the beam transportation by PARMELA code and the optimized results of the beam line will be presented in this paper.
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| MOP024 | Electromagnetic Green's-Function-Based Simulations of Photocathode Sources | space-charge, cathode, electromagnetic-fields, gun | 88 | ||
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We show the results of beam simulations for photocathode sources using a newly developed Green's function based code called IRPSS (Indiana Rf Photocathode Source Simulator). In general, a fully electromagnetic treatment of space-charge fields within simulations of photocathode sources is typically difficult since the beam is most often tightly bunched. The problem is further complicated by the inclusion of nearby conducting structures, i.e. cathode and cavity walls, from which the fields are reflected. The entire problem can be solved self-consistently using an electromagnetic Green's function method. Since Green's functions are generated by a Delta function source while simultaneously satisfying the boundary conditions of the system, they are an effective tool when solving for fields within photocathode source simulations. Using IRPSS we show the results of multiparticle simulations for a variety of photocathode source experiments.
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| MOP025 | Study on High-Current Multi-Bunch Beam Acceleration for KEKB Injector Linac | klystron, linac, beam-loading, acceleration | 91 | ||
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The KEKB injector linac is usually operated to accelerate only two 10 nC electron bunches to generate positron, since more bunch cannot be equalized the beam energy using the conventional pulse compressor (SLED) and the simple phase modulation. The aim of this study is to find how to accelerate more bunches without any modification of high power RF distribution. One way is that a part of the acceleration units is used to compensate the beam energy difference. On the other hand, the recent electron linac is designed for the multi-bunch operation by compensating the beam loading. And this beam loading compensation method is usually realized by combining the output power of two or more klystrons. However our linac system consists of one 50 MW klystron in one acceleration unit, and eight klystrons are driven by a 100kW klystron. Another way to realize the multi-bunch acceleration in our linac is using the amplitude modulation of the klystron. This is realized using the I-Q modulation of the low level RF considering the non-linear characteristics of the total amplification system including klystrons. Further we developed a FPGA board with 100 MHz DACs and ADCs to realize this.
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| MOP031 | Beam Distribution System for the MSU-RIA Driver Linac | kicker, emittance, linac, target | 106 | ||
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The proposed Rare Isotope Accelerator (RIA) facility will deliver up to 400 kW of any stable isotope to multi-target areas to create radioactive ion beams using either Isotope Separation On Line or Particle Fragmentation methods. Operational and programmatic efficiency will be best served by a system that can simultaneously distribute the beam current over a large dynamic range to several targets. The proposed RIA beam switchyard uses an rf kicker-magnetic septum system to distribute the beam to multi-target areas on a micro-bunch by micro-bunch basis. The micro-bunches can be differentially loaded in the RIA driver linac front end utilizing a scheme similar to that successfully used at Mainz and JLAB CEBAF facility. In these cases, consecutive electron micro-bunches are deflected by an rf kicker and their intensity separately adjusted through variable apertures with an identical second rf kicker returning the micro-bunches on-axis. The feasibility of using a similar system in RIA driver linac front end was explored. The overall concept of the RIA beam distribution system including the differential bunch loading system and the results of the beam dynamics studies will be presented.
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| MOP039 | The SPL (II) at CERN, a Superconducting 3.5-GeV H- Linac | linac, proton, injection, target | 127 | ||
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A revision of the physics needs and recent progress in the technology of superconducting (SC) RF cavities have triggered major changes in the design of a SC H- linac at CERN. With 4 - 5 MW beam power, the SPL can be the proton driver for a next generation ISOL-type radio-active beam facility ("EURISOL") and/or supply protons to a neutrino facility (conventional superbeam + beta-beam or neutrino factory). Furthermore the SPL can replace Linac2 and the PS booster, improving significantly the beam performance in terms of brightness, intensity, and reliability for the benefit of all proton users at CERN, including LHC and its luminosity upgrade. Compared with the first conceptual design, the beam energy is almost doubled (3.5 GeV instead of 2.2 GeV) while the length is reduced by 40%. At a repetition rate of 50 Hz, the linac re-uses decommissioned 352.2 MHz RF equipment from LEP in the low-energy part. Beyond 90 MeV the RF frequency is doubled, and from 180 MeV onwards high-gradient SC bulk-niobium cavities accelerate the beam to its final energy of 3.5 GeV. This paper presents the overall design approach, together with the technical progress since the first conceptual design in 2000.
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| MOP043 | Upgrade of 1-MeV Heavy Ion ISR RFQ Accelerator | ion, rfq, ion-source, acceleration | 139 | ||
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The upgrade of 1 MeV ISR RFQ accelerator has been launched for exploring the possibilities of a few mA heavy ion beam acceleration and its applications on the material science, biological irradiation and RFQ-AMS carbon chronology. A new ECR ion source with extracting voltage of 22kV, and the LEBT matching section have been redesigned and tested to increase the injection beam current and to realize the beam matching. The experimental tests for the different operating parameters have been compared to the simulations by self developed code RFQDYN. The preliminary results will be presented in this paper.
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| MOP052 | First Performance Test of an Integrated RFQ-Drifttube-Combination | rfq, ion, bunching, proton | 162 | ||
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In the frame of a collaboration with the GSI in Darmstadt an RFQ-Drifttube-Combination for the Heidelberg cancer therapy center HICAT has been designed, built and successfully beam tested at the IAP Frankfurt. The integration and combination of both an RFQ and a rebunching drifttube unit inside a common cavity forming one single resonant RF-structure has been realized for the first time with this machine. The results of the beam measurements and questions about the beam dynamics simulations have been investigated in detail with the code RFQSIM.
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| MOP058 | Heavy-Ion-Beam Emittance Measurements at the GSI UNILAC | emittance, ion, linac, heavy-ion | 177 | ||
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The GSI UNILAC, a linac for high current heavy ion beams, serves as an injector for the synchrotron SIS 18 and hence being a part of the future FAIR (Facility for Antiproton and Ion Research) project. The UNILAC post stripper section consists of an Alvarez accelerator with a final energy of 11.4 MeV/u. In order to meet the requirements of the FAIR project (15emA U28+, transversal normalised emittances of ex = 0.8 and ey = 2.5 mm mrad) a part of the UNILAC upgrade program is the increase of the beam brilliance. A detailed understanding of the correlation between space charge forces and focusing during acceleration of high intensity ion beams is necessary. A suited quantity to study is the beam brilliance dependency on the phase advances in the Alvarez section. Measurements are planned in 2006 and coincide with the beam dynamics work package of the European network for High Intensity Pulsed Proton Injector (HIPPI). Results of the measurements are presented as well as corresponding beam dynamics simulations.
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| MOP061 | The 70-MeV Proton Linac for the Facility for Antiproton and Ion Research FAIR | proton, linac, rfq, emittance | 186 | ||
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A significant part of the experimental program at FAIR is dedicated to antiproton (pbar) physics requiring up to 7·1010 cooled pbars per hour. Taking into account the pbar production and cooling rate, this is equivalent to a primary proton beam of 2·1016 protons per hour to be provided by a 70 MeV proton linac preceding two synchrotrons. It has to deliver a pulsed proton beam of 70 mA of 36 μs duration at a repetition rate of 4 Hz. The normalized transverse emittances must not exceed 2.8 mm mrad and the total relative momentum spread must be less than 0.1%. The normal conducting DTL comprises 12 Crossed-bar H-cavities (CH) fed by six rf-power sources in total. The basic layout of the linac as well as the overall cost estimate has been completed including several reviews by external committees. A technical report has been completed in May 2006. This paper gives a general overview on the status of the project.
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| MOP066 | Wake Fields and Beam Dynamics Simulations for the 3.9-GHz Cavities of the ILC | emittance, luminosity, dipole, damping | 196 | ||
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Crab cavities are used for the ILC in order to increase the luminosity of the colliding beams. These cavities operate at the 3rd harmonic of the accelerating frequency (1.3GHz). We study the LOM (Lower Order Modes) and HOM (Higher Order Modes) excited by the beam. The corresponding wake field is calculated and simulations are conducted on the beam dynamics of the interaction of the wake field with the multi-bunch beam train.
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| MOP067 | Higher Order Mode Wakefield Simulations and Beam Dynamics Simulations in the ILC Main Linacs | emittance, linac, electron, superconductivity | 199 | ||
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The progress of approximately 3000 electron (and positron) bunches down the main linacs of the ILC (International Linear Collider) can readily give rise to dipole modes which distrupt the progress of the beam. We investigate the transverse modes which are excited and monitor the resulting emittance dilution which occurs down the linac. At present there are two design configurations for the ILC: the BCD (Baseline Configuration Design) and the ACD (Alternate Configuration Design). We investigate the wake fields and beam dynamics for both configurations. In particular, the influence of trapped modes on the emittance of the beam is studied.
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| MOP068 | Beam-Loss Measurement and Simulation of Low-Energy SNS Linac | linac, SNS, radiation, beam-losses | 202 | ||
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We have installed a number of Neutron detectors from the MEBT to the end of CCL [186 MeV]. These detectors are made in collaboration with INR. In this paper we present our implementation and simulation of the losses by inserting Faraday Cups at different energies. We also calibrated neutron detectors and their high voltage dependence. The measured losses are simulated by 3-D transport codes during SCL commissioning. We also discuss future improvements such as interpreting the loss signal in terms of beam current lost in warm part of SNS linac with accurate longitudinal loss distribution as well as plan to automate voltage dependence of the neutron detectors. We compare two different sets of Beam Loss Monitors: Ionization Chambers (detecting X-ray and gamma radiation) and Photo-Multiplier Tubes with a neutron converter (detecting neutrons). We outline such combination is better way to deal with the beam losses than relying on detectors of one type.
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| TU2004 | Results on the Beam Commissioning of the Superconducting-RFQ of the New LNL Injector | rfq, emittance, ion, beam-losses | 227 | ||
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A new injector for the heavy ion superconducting linac ALPI has been built at LNL. This new accelerator, named PIAVE, is designed to accelerate ions with A/Q=<8.5 up to 1.2 MeV/u. The main components are an ECRIS source operating on a high voltage platform, a three harmonic buncher, a superconducting RFQ cryomodule containing two bulk niobium structures and two QWR cryomodules housing 4 cavities each. In the last year the injector has been commissioned, with O, Ar, Ne and Xe beams, and put into operation. The beam performances, and the results of longitudinal and transverse emittance measurements will be shown and compared with simulations. Neon and argon beams have been delivered to the experiments (after acceleration with PIAVE and ALPI) for a total of about 400 hours. It should be noted that this is the first superconducting RFQ in operation; the design opportunities offered by this technology for a wider field of applications will be briefly discussed. The heart of these opportunity is given by the high intervane voltage in a cw RFQ (PIAVE can operate cw with an intervane voltage higher than 250 kV).
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| TUP014 | Electron Signal Detection for the Beam-Finder Wire of the Linac Coherent Light Source Undulator | electron, undulator, scattering, photon | 274 | ||
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The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) based on the final kilometer of the Stanford Linear Accelerator. The tight tolerances for positioning the electron beam close to the undulator axis calls for the introduction of Beam Finder Wire (BFW) device. A BFW device close to the upstream end of the undulator segment and a quadrupole close to the down stream end of the undulator segment will allow a beam-based undulator segment alignment. Based on the scattering of the electrons on the BFW, we can detect the electron signal in the main dump bends after the undulator to find the beam position. We propose to use a threshold Cherenkov counter for this purpose. According to the signal strength at such a Cherenkov counter, we then suggest choice of material and size for such a BFW device in the undulator.
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| TUP021 | Wire Profile Monitors in J-PARC Linac | electron, linac, proton, rfq | 293 | ||
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We plan to install wire scanners for J-PARC linac in order to measure beam profile and emittance. They have been designed to capture electrons in H-, 7um-diameter carbon wires are used in 3MeV point and 30um-diameter tungsten wires are used for 50-181MeV point. We plan to set 36 wire scanners in linac and beam dumps. In this paper, we report the result of beam test with 3MeV beam at KEK and the calculation about signal and wire temperature.
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| TUP042 | A Proposal for Post Acceleration, Matching and Measuring the H- Ion Beam at CERN's Linac 4 Test Stand | emittance, linac, ion, rfq | 343 | ||
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CERN's proposed future Linac 4 is a 160 MeV H- Linac injecting into the Proton Sychrotron Booster. We propose that the ion source parameters (80mA, 500us pulse length, 2Hz repetition rate, 0.25 mm.mrad normalised emittance at 1 σ) may be achieved by improving an existing 2MHz RF multicusp source. In this report, we explain the proposal to post-accelerate the beam from 35keV to 95keV, and to focus the beam into the RFQ with solenoids, with the aimof avoiding substantial emittance growth. Finally, details of the diagnostics required to test the source are given.
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| TUP059 | Photoinjector Production of a Flat Beam with Transverse Emittance Ratio of 100 | emittance, quadrupole, laser, electron | 382 | ||
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The generation of a flat electron beam directly from a photoinjector is an attractive alternative to the electron damping ring as envisioned for linear colliders. It also has potential applications to light sources such as the generation of ultrashort x-ray pulses or Smith-Purcell free electron lasers. In this paper, we report on the experimental generation of a flat beam with a measured transverse emittance ratio of 100±20 for a bunch charge of ≅0.5~nC*. The experimental data, obtained at the Fermilab/NICADD Photoinjector Laboratory, are compared with numerical simulations and the expected scaling laws. Possible improvement of the experiment along with application for such a flat beams are discussed
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* P. Piot, Y.-E. Sun and K.-J. Kim, Phys. Rev. ST Accel. Beams 9, 031001 (2006) |
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| TUP064 | Adaptive Three-Dimensional RMS Envelope Simulation in the SAD Accelerator Modeling Environment | space-charge, optics, controls, background | 397 | ||
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The capability for three-dimensional RMS envelope simulation, including space charge, has been implemented in the SAD accelerator modeling environment used at KEK. The SAD (for Strategic Accelerator Design) modeling system consists of a compiled simulation engine, an in-house scripting language SADScript, and user interface support both in Tcl/tk script and SADScript. The RMS envelope simulator is implemented primarily in the SADScript language, which much resembles the Mathematica language. The dynamics within the model are similar to that used by TRACE3D, TRANSPORT, and XAL. Specifically, the symmetric matrix of all second-order beam moments is propagated using a linear beam optics model for the beamline. However, the current simulation engine employs an adaptive space-charge algorithm which actively adjusts the solution integration to maintain a specified accuracy, as well as imposing the symplectic condition. It is designed to keep the integration step size as large as possible while enforcing that the residual solution error remain below a given tolerance. The paper concentrates primarily on the adaptive nature of the RMS simulation, since this is the novel feature.
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| TUP065 | Longitudinal Beam Dynamic Simulation of S-DALINAC Polarized Injector | electron, gun, emittance, polarization | 400 | ||
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In future, a polarized gun will extend the experiment possibilities of the superconducting recirculating linear electron accelerator S-DALINAC. Therefore a new injector has to be designed where a new 100 keV polarized source SPIN will be added to the present unpolarized thermionic source. A polarization degree of 80%, a mean current of 60 uA and a 3 GHz cw structure are required. All features of the new source will be tested and measured at an offset beam line. The longitudinal beam dynamics of the injector are studied. The electron bunch length behind the gun is about 50 ps. The electrons has to be bunched to 5 ps for capturing the electrons to the main linac. Therefore a chopper/prebuncher system based on the devices used at MAMI is designed. The system consists of a harmonic chopper cavity, a slit, a first and a second harmonic prebuncher. The recent simulation results will be presented here.
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| TUP066 | Particle Dynamics Calculations and Emittance Measurements at the FETS | rfq, emittance, ion, ion-source | 403 | ||
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High power proton accelerators in the MW range have many applications including drivers for spallation neutron sources, neutrino factories, transmuters (for transmuting long-lived nuclear waste products) and energy amplifiers. In order to contribute to the development of HPPAs, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the front end test stand is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. An overview on the status of the project together with the results of numerical simulations of the particle dynamics from the ion source to the RFQ exit will be presented. The particle distributions gained from the particle dynamics simulations will be compared with recent measurements of the transversal beam emittance behind the ion source and the results discussed.
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| TUP067 | Tune-up Scenario for Debuncher System in J-PARC L3BT | injection, monitoring, linac, target | 406 | ||
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We plan to start beam commissioning of J-PARC linac and the succeeding beam transport line in December 2006. The beam transport line, to which we refer as L3BT, has two key functionalities to satisfy the requirements for the succeeding ring injection. One is to reduce the momentum jitter and momentum spread, and the other is to scrape off the transverse tail. To realize the former functionality, a debuncher system is installed in L3BT which enables longitudinal gymnastics of the beam to reduce the momentum spread at the ring injection. In this presentation, the tune-up scenario for the debuncher system is presented together with simulation results on the effects of debuncher system.
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| TUP069 | Design of 132MeV DTL for CSNS | SNS, focusing, linac, vacuum | 412 | ||
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A description is given to the drift-tube-linac (DTL) of the Beijing Spallation Neutron Source (BSNS). The DTL accelerate a 3MeV, 30mA H- beam from the RFQ to the LRBT. Tank body and drift tube configuration design using the SUPERFISH code has enabled efficient optimization of the effective shunt impedance and avoided high surface field. Accelerating cells design and particle tracking were made by using PARMILA code. Special emphasis is given to the transverse focusing system design, which was compared with two usual schemes, constant phase focusing and equipartitioning focusing. Details of beam dynamics analysis will be presented in this paper.
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| TUP070 | Comparison of Phase Scan vs Acceptance Scan for the SNS DTL | linac, SNS, Spallation-Neutron-Source, target | 415 | ||
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There are two widely used techniques for setting the rf set-point of the Drift Tube Linac (DTL). The Phase Scan and the Acceptance Scan techniques were applied to the SNS DTL and were benchmarked against each other. Commissioning data indicate that both techniques produce quite consistent results and the model used is quite accurate. Both of the models are based on multiparticle tracking with space charge effects.
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| TUP071 | Beam-Loading Effects on Phase Scan for the Superconducting Cavities | linac, beam-loading, SNS, impedance | 418 | ||
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When the beam is passing through superconducting cavities, it excites beam induced field in cavities. A systematic study was performed to study the beam loading effects by the nonrelativistic beam for β = 0.81 superconducting cavities of the SNS linac. The analysis indicates that the induced field level is quite close to the estimation and its effect on the phase scan is consistent with the model.
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| TUP072 | Beam Dynamics Studies of the 8-GeV Superconducting H- Linac | linac, beam-losses, focusing, rfq | 420 | ||
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A 8-GeV H-minus linac has been proposed to enhance the accelerator complex at Fermilab as a high-intensity neutrino source.* The linac is based on 430 independently phased superconducting cavities. The front-end of the linac (up to 420 MeV) operating at 325 MHz is based on RIA-type multi-spoke cavities. The rest of the linac (from 420 MeV to 8 GeV) uses ILC-type elliptical cavities. We have performed large scale end-to-end beam dynamics simulations of the driver linac using the code TRACK** including all sources of machine errors and detailed beam loss analysis. The results of these simulations will be presented and discussed.
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* G. W. Foster and J. A. MacLachlan, Proceedings of LINAC-2002, p.826. |
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| TUP073 | Simulations of RF Errors in the SNS Superconducting Linac | linac, emittance, SNS, beam-losses | 423 | ||
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Minimizing beam emittance growth in the SNS superconducting linac due to RF errors, either correlated or uncorrelated, is essential since it can lead to beam loss in the linac and in the downstream ring. From multi-particle simulation studies of both matched and mismatched linac lattices, for the design peak beam current of 38 mA, as well as a typical commissioning beam current of 20 mA, we conclude that the linac may tolerate much higher non-correlated RF errors, especially in the second half of the superconducting linac, where errors in synchronous phase up to 10 degrees and that of cavity field amplitude up to 10% is acceptable. However, tolerance to correlated RF errors in the linac is within only 0.5 degree and 0.5 %, from simulations using a simple longitudinal linac model. Beam parameter measurement results acquired during linac beam commissioning confirmed the simulations.
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| TUP074 | Beam Dynamics Simulations of SARAF Accelerator including Error Propagation and Implications for the EURISOL Driver | linac, proton, lattice, rfq | 426 | ||
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Beam dynamics simulations of the SARAF (Soreq Applied Research Accelerator) superconducting RF linear accelerator have bean performed in order to establish the linear accelerator design. The multi-particle simulation includes 3D realistic electromagnetic field distributions, space charge forces and fabrication, misalignment and operation errors. A 4 mA deuteron beam is accelerated up to 40 MeV with a moderated rms emittance growth and a high real-estate acceleration gradient of 2 MeV/m. An envelope of 40,000 macro-particles is kept under a radius of 11 mm, well below the beam pipe bore radius. The accelerator design for SARAF is proposed as an injector for the EURISOL driver accelerator. The basic Accel 176 MHz β0=0.09 and β0=0.15 HWR lattice was extended to 90 MeV based on the LNL 352 MHz β0=0.31 HWR. The matching between both lattices ensures smooth transition and the possibility to extend the accelerator to the required EURISOL ion energy.
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| TUP075 | Automatic Transverse and Longitudinal Tuning of Single and Multiple Charge State Ion Beams | linac, beam-losses, focusing, emittance | 429 | ||
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Extensive end-to-end beam dynamics simulations of the RIA driver linac using the code TRACK and including all sources of machine errors and detailed beam loss analysis* showed that the losses could be significantly reduced for a fine-tuned linac. For this purpose we have developed an automatic longitudinal tuning proceedure for multiple charge state heavy-ion beams.** For a complete tuning tool, we have recently developed an automatic transverse tuning proceedure to produce smooth transverse beam dynamics by minimizing the RMS beam sizes after each focusing period. We have also extended the automatic longitudinal proceedure to produce smooth longitudinal beam dynamics for single and multiple charge state ion beams. In addition to improving an existing tune, this powerful automatic beam tuning tool can be used to retune the linac and restore the beam after one or more elements failures and to develop new tunes for ion beams with different Q/A ratios. After presenting the method, the results from some applications will be presented and discussed.
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* P. Ostroumov, V. Assev and B. Mustapha, Phys. Rev. ST-AB 7 (2004) 090101 |
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| TUP076 | First TRACK Simulations of the SNS Linac | linac, SNS, lattice, focusing | 432 | ||
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In an effort to benchmark the code TRACK* against the recent commissionnig data from the SNS linac, we started updating the code TRACK to support SNS-type elements like DTL's and CCL's. 2D electric field tables were computed using SUPERFISH and 3D magnetic fields from PMQ's were calculated using EMS-Studio. A special DTL routine was implemented and successfully tested. The first results of TRACK simulations using a realistic beam will be presented. A comparison with the code PARMILA will also be presented and discussed.
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* "TRACK: The New Beam Dynamics code", V. N. Aseev et al, in Proceedings |
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| TUP077 | Transverse Beam Matching and Correction Procedures in INR Linac | linac, quadrupole, controls, focusing | 435 | ||
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An interactive procedure for the transverse beam matching and correction has been developed and implemented in several areas of INR Linac. The profile measurements are used for determination of the main transverse beam parameters. These data are applied for calculation the dipole correction currents and quadrupole gradients to transport the beam with minimum sizes and off axis displacements. The user friendly interface and graphics support has been developed for data treatment and beam behavior presentation. The proposed algorithm of beam matching, beam steering and data treatment is discussed. Some experimental and simulation results for different INR Linac operation modes are presented.
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| TUP078 | Status of the End-to-End Beam Dynamics Simulations for the GSI UNILAC | rfq, emittance, ion, synchrotron | 438 | ||
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The heavy ion high current GSI linac UNILAC serves as an injector for the synchrotron SIS18. The UNILAC mainly consists of a High Current Injector (HSI), the stripper section at 1.4 MeV/u, and the Alvarez postaccelerator (11.4 MeV/u). During the last years the systematic experimental and numerical studies resulted in an increase of the U73+ beam intensity of up to a factor of seven. The needs of the FAIR project (Facility for Antiproton and Ion Research at Darmstadt) require further improvement of the beam brilliance coming from UNILAC up to a factor of five. End-to-end beam dynamics simulations with the DYNAMION code have already been started. The general goal is to establish a simulation tool which can calculate the impact of the planned upgrade measures on the performance of the whole UNILAC. The results of the HSI calculations including influence of the beam intensity on the beam parameters (current, emittance, Twiss-parameters) at the stripper section are presented. Recent calculations and measurements of the beam matching to the Alvarez section under space charge conditions are discussed in the paper.
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| TUP079 | RIAPMTQ/IMPACT: Beam-Dynamics Simulation Tool for RIA | linac, emittance, beam-losses, rfq | 441 | ||
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We describe a multiple-charge-state simulation-code package for end-to-end computer simulations of the RIA heavy-ion driver linac, extending from the low-energy beam transport after the ECR source to the end of the linac. The work is being performed by a collaboration including LANL, LBNL, ANL, and MSU. The package consists of two codes, the code RIAPMTQ for the linac front end including the LEBT, RFQ, and MEBT, and the code IMPACT for the superconducting linac. This code package has been benchmarked for rms beam properties against previously existing codes at ANL and MSU. The simulation tool will allow high-statistics runs on parallel supercomputing platforms, such as NERSC, as well as runs on desktop PC computers for low-statistics design work. It will address an important near-term need for the RIA project, allowing evaluations of candidate designs with respect to beam-dynamics performance including beam losses, which can be compared with predictions of other existing simulation codes.
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| TUP080 | Tuning the Magnetic Transport of an Induction Linac Using Emittance | emittance, background, diagnostics, optics | 444 | ||
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The Lawrence Livermore National Laboratory Flash X-Ray (FXR) machine is a linear induction accelerator used to produce a nominal 20-MeV, 3-kA, 60-ns pulse width electron beam for hydrodynamic radiographs. A common figure of merit for this type of radiographic machine is the x-ray dose divided by the spot area on the bremsstrahlung converter. Several characteristics of the beam affect the minimum attainable x-ray spot size. The most significant are emittance, chromatic aberration, and beam motion. FXR is in the midst of a multi-year optimization project to reduce the spot size. This paper describes the effort to reduce beam emittance by adjusting the fields of the transport solenoids. If the magnetic transport is not correct, the beam will be mismatched and undergo envelop oscillations increasing the emittance. We measure the divergence and radius of the beam in a drift section after the accelerator by imaging the optical transition radiation (OTR) and beam envelope on a foil. These measurements are combined with transport simulations to calculate an emittance. Relative changes in the emittance can be quickly estimated allowing for an efficient, real-time study.
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| TUP085 | Beam Simulations for the MSU-RIA Driver Linac Using IMPACT Code | linac, beam-losses, emittance, ion | 457 | ||
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Previous end-to-end three-dimensional (3D) beam dynamics simulation studies at Michigan State University (MSU) utilizing the LANA code and including experimentally-based ion source beam parameters, alignment and rf errors, and the effect of charge-stripping foils have indicated that the MSU Rare Isotope Accelerator (RIA) driver linac has adequate transverse and longitudinal acceptances to accelerate light and heavy ions to final energies of ≥ 400 MeV/u with beam powers of 100 to 400 kW. Recently, to evaluate beam dynamics performance under various error scenarios with high statistics, the end-to-end 3D beam dynamics simulation studies for the driver linac were performed on the high performance parallel computers at MSU using the parallel code IMPACT that is an element of the advanced beam dynamics simulation tool: RIAPMTQ/IMPACT. The results of these beam dynamics studies will be presented.
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| TUP086 | Linac Code Benchmarking for the UNILAC Experiment | emittance, space-charge, linac, lattice | 460 | ||
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In the framework of the European network HIPPI (High Intensity Pulsed Proton Injectors) a linac code comparison and benchmarking program have been promoted. An intermediate goal is to compare different space charge solvers and lattice modelling implemented in each code in preparation of experimental validations from future measurements to be carried out at the UNILAC of GSI. In the last two years a series of different tests and comparisons among several codes (DYNAMION, HALODYN, IMPACT, LORASAR, PARMILA, PATRAN, PATH and TOUTATIS) have been undertaken. The quality of Poisson solvers has been evaluated and a number of code adjustments has been carried out to obtain the best agreement in terms of RMS moments. In this paper we report on the status of this program.
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| TUP087 | Ion Charge Stripping Foil Model for Beam Dynamics Simulation | ion, linac, scattering, heavy-ion | 463 | ||
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An efficient computer model for the stripping foil simulation was proposed at NSCL/MSU as part of the Rare Isotope Accelerator (RIA) development. The model was successfully implemented in the LANA beam dynamics simulation code. Later this model was also included in the IMPACT code as well as in some other beam dynamics simulation tools. The derivation of the algorithm is presented and the application of the model for the uranium beam stripping simulation in context of the RIA driver linac studies at NSCL/MSU is analysed in the paper.
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| TUP088 | Benchmarking of Simulation Codes TRACK and ASTRA for the FNAL High-Intensity Proton Source | space-charge, emittance, rfq, proton | 466 | ||
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The FNAL High Intensity Proton Source is an 8-GeV superconducting H-minus Linac conceived with the primary mission of enabling 2 MW beam power from the Main Injector at 120 GeV for the Fermilab neutrino program. The main tool used for the design of this accelerator is the beam dynamics code TRACK developed by Argonne National Laboratory to fulfill the requirements of proton and heavy-ion linacs. ASTRA, developed by DESY (Hamburg, Germany) and mainly used for the design of electron photo-injectors, also offers the possibility to simulate acceleration of hydrogen ions. Benchmarking of TRACK and ASTRA is presented in this paper for a zero current and a 30 mA beam from the exit of the RFQ (2.5 MeV) to the end of the accelerating section (8 GeV).
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| TUP089 | Computer Simulations of a High-Current Proton Beam at the SILHI-LEBT | ion, emittance, proton, space-charge | 469 | ||
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For the injection of a proton beam into the future proton LINAC for FAIR the ion source and the low energy beam transport system have to deliver a 100 mA proton beam with an energy of 95 keV at the entrance of the RFQ within an acceptance of 0.3 π mm mrad (normalized, rms). A 2-solenoid focusing system is foreseen as an injection scheme. The beam parameters of the SILHI ion source and the 2-solenoid LEBT setup at CEA/Saclay fulfill these requirements. Therefore joint emittance measurements on various beam parameters have been performed at the end of 2005. This article presents the computer simulations of the ion source extraction and LEBT, which supplemented these measurements using the KOBRA3-INP computer code in order to study the influence of space charge effects. These simulations have been performed for various solenoid settings and for different space charge compensation degrees clearly revealing that the ion beam transport within the LEBT is influenced by space charge forces.
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| WE1002 | The 4GLS at Daresbury | linac, electron, radiation, undulator | 481 | ||
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4GLS is a next generation proposal for an advanced light source to be built at Daresbury Laboratory. The facility will consist of three integrated accelerator systems: a 25-60 MeV linear accelerator driving an Infra-Red Free-Electron Laser (FEL) at 13 MHz; a 750-950 MeV branch driving a 10-100 eV XUV-FEL at 1 kHz; a 600 MeV energy recovery linac carrying 100 mA current driving a suite of spontaneous sources at 1.3 GHz or a VUV-FEL (up to 10 eV) at 4 MHz. The latter two accelerator systems share a common superconducting linac based on 1.3 GHz TESLA technology, which will simultaneously accelerate the two bunch types (1 nC and 77 pC) whilst decelerating the returning 77 pC bunches. This paper will outline the project and its key features, including the 35 MeV ERL Prototype accelerator presently being commissioned, and will discuss the accelerator physics and technology challenges to be explored in the present Design Study.
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| WE2001 | Neutralized Drift Compression Experiments (NDCX) | plasma, ion, vacuum, acceleration | 492 | ||
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Intense ion beams offer an attractive approach to heating dense matter uniformly to extreme conditions, because their energy deposition is nearly classical and volumetric. Simultaneous transverse and longitudinal beam compression, in a neutralizing plasma medium, along with rapid beam acceleration, are being studied as a means of generating such beams, which will be used for warm dense matter (WDM), high energy density physics (HEDP), and fusion studies. Recently completed experiments on radial and longitudinal compression demonstrated significant enhancements in beam intensity. In parallel with beam compression studies, a new accelerator concept, the Pulse Line Ion Accelerator (PLIA), potentially offers cost-effective high-gradient ion beam acceleration at high line charge density. We report experimental results on beam neutralization, neutralized focusing, neutralized drift compression from a series of experiments. We also report energy gain and beam bunching in the first beam dynamics validation experiments exploring the PLIA.
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| TH2001 | High-Power Couplers for Linear Accelerators | linac, vacuum, emittance, impedance | 531 | ||
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High power input couplers are a fundamental component of the linear accelerating structures and in particular of the superconducting structures. In fact, in this case, the power couplers function is not only the power transfer and the vacuum separation but includes also the thermal transition and the integrity of the cavity cleanliness. A lot of activity has been recently worked out in the framework of different project on both CW (KEK and Cornell) and pulsed (SNS and TTF) power couplers. Particular attention has been devoted to the design phase to take care about the thermo mechanical and electromagnetic performances, the multipacting thresholds, the preparation procedures and, last but not least, the cost that in the case of high energy linacs is a fundamental parameter. In this framework not only the design phase but also the conditioning of the couplers has stimulated different studies. Partial reviews of the existing designs and of the couplers characteristics will be presented taking into account the different challenges.
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| THP008 | Detailed Modeling of the SNS RFQ Structure with CST Microwave Studio | rfq, SNS, dipole, quadrupole | 580 | ||
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We report detailed RF modeling on the SNS RFQ structure using CST Microwave Studio code. Due to the complexity of the RFQ structure, a three-dimensional model with large mesh ratio is required to adequately model the necessary details of the structure. Old 3-D codes are not capable of giving accurate predictions of resonant frequency and fields, or for including mode stabilizers and terminations. A physical prototype is needed to verify resonant frequency and field profile, including mode stabilizers and end terminations, which is expensive and time consuming. Taking advantage of CST Microwave Studio’s new Perfect Boundary Approximation (PBA) technique, we constructed a 3-dimensional computational model based on the as-built SNS RFQ dimensions with pi-mode stabilizers, end cutbacks and tuners and simulated it in the frequency domain using the CST Eigenvalue Solver. Simulation results accurately predicted the resonant frequency and field distributions. We are applying the simulation technique to the design of another RFQ.
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| THP016 | Active Compensation of Lorentz Force Detuning of a TTF 9-Cell Cavity in CRYHOLAB | klystron, controls, feedback, radiation | 598 | ||
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Linear colliders and free-electron lasers projects based on the superconducting RF technology require high gradient pulsed operation of superconducting elliptical multicells. The cavities are subject to Lorentz force detuning which reflects on an increased RF power consumption when trying to stabilize the accelerating field during the beam passage. This pulsed detuning can be mechanically compensated using a fast piezoelectric tuner. A new tuner with integrated piezoelectric actuators has been developed in the framework of CARE/SRF european program. The tuning system has been tested on a fully equipped 9-cell TTF cavity in the CRYHOLAB horizontal cryostat using the pulsed 1.3 GHz 1 MW RF source. In virtue of the high pulse to pulse repeatability of the detuning, the compensation of Lorentz detuning was achieved successfully using a simple feed forward scheme.
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| THP018 | Design Progress of the Re-bunching RF Cavities and Hybrid Quadrupoles for the RAL Front-End Test Stand (FETS) | quadrupole, linac, impedance, proton | 604 | ||
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The proposed FETS project at RAL will test a fast beam chopper in a 3.0 MeV H- Medium Energy Beam Transport (MEBT) line. Space restrictions in the MEBT line place constraints on component length and drive the requirement to identify compact component configurations. Two candidate re-bunching RF cavity designs are considered: the space efficient Drift Tube Linac type (DTL) with integrated quadrupoles, and the high shunt impedance Coupled Cavity Linac type (CCL) with external quadrupoles. Preliminary RF simulations in 2D and 3D are presented, and a comparison, emphasising the advantages and disadvantages of each design is made. The compact hybrid quadrupole configurations considered are the 'tandem' combination of permanent magnet (PMQ) and electro-magnetic (EMQ) types, and the concentric combination of PMQ and laminar conductor (Lambertson) EMQ types. The suitability of the compact hybrid quadrupole for implementation in the low energy Drift Tube Linac (DTL) is suggested and discussed.
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| THP024 | Development of Ultra-fast Silicon Switches and their Applications on Active X-Band, High-Power RF Compression Systems | coupling, plasma, laser, resonance | 619 | ||
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In this paper, we present the recent results of our research on the ultra-high power fast silicon RF switch and its application on active X-Band RF pulse compression systems. This switch is composed of a group of PIN diodes on a high purity silicon wafer inserted into a cylindrical waveguide operating in the TE 01 mode. Switching is performed by injecting carriers into the bulk silicon through a high current pulse. A switch module is composed of the silicon switch, a circular waveguide T with the silicon switch at the center port and a movable short at the other end of silicon switch. The module can tune the S-matrix of on and off states to desired value. Our current design uses a CMOS compatible process and the fabrication is accomplished at SNF (Stanford Nanofabrication Facility). The switch has achieved <300ns on time with ~3% loss on the wafer. The RF energy is stored in a room-temperature, high-Q 400 ns delay line; it is then extracted out of the line in a short time using the switch. The pulse compression system has a achieved a gain of 7, which is the ratio between output and input power. Power handling capability of the switch is estimated at the level of 10MW.
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| THP027 | Study of PPM-Focused X-band Pulse Klystron | klystron, cathode, linear-collider, collider | 628 | ||
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The R&D of PPM (Periodic Permanent Magnet)-focused X-band pulse klystrons has been conducted since 1999, originally for Global Linear Collider (GLC) project. So far six prototype tubes have been tested. Some of them successfully produce the power required in GLC (75MW, 1.6μsec pulse width). However their performance was not perfect as a GLC tube. The problems are the stability of RF output and the gun performance. Since GLC programs were terminated in 2004, some limited work on the improvement of the PPM tubes continues at X-Band Test Facility (XTF) in KEK. The work includes the test to evaluate the performance of revised (rebuilt) tubes as well as disassembling these tubes after the test for further inspection. Recent results are reported.
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| THP028 | Master Oscillator for Fermilab ILC Test Accelerator | controls, power-supply, resonance, linear-collider | 631 | ||
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The low phase-noise master oscillator generates and distributes the various frequencies required for the LLRF system controlling ILCTA cavities. Two chassis have been developed for this design, generating the programmable frequencies and performing the distribution and amplification, respectively. It has been successfully used with the SNS and the DESY-SIMCON LLRF systems, driving two different superconducting cavities. The design approach and a full characterization of the master oscillator are presented in this paper. The measurement results include the frequency stability and the phase and amplitude noise spectrums of the multiple frequency outputs.
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| THP029 | Development of an RFQ Input Power Coupling System | rfq, vacuum, coupling, SNS | 634 | ||
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An RF input coupler system is designed, manufactured, and tested for future upgrade of the coupling system of the RFQ in the SNS linac. The design employs two coaxial loops in vacuum side of two coaxial ceramic windows through coaxial transmission lines that are connected to a magic-T waveguide power splitter for 402.5 MHz operation. The couplers will be used with up to total 800 kW peak power at 8% duty cycle. RF properties of the system and fabricated structure along with vacuum and thermal properties are discussed. Two couplers are joined together through an evacuated bridge waveguide for high power RF processing. Result of the high power conditioning that is performed in the RF test facility of the SNS is presented.
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| THP030 | Investigation of Ferroelectrics for High-Power RF Phase Shifters in Accelerator Systems | impedance, vacuum, SNS, klystron | 637 | ||
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High power vector modulators enable independent control of RF power to each accelerating cavity, allowing a fan-out configuration to be used to power many cavities from a single high-power klystron. Previously, ferrite materials have been used in high-power phase shifters and vector modulators. It is shown that ferroelectric materials such as barium-strontium titanate (BST) can also be used in such tunable structures. Since ferroelectrics are controlled by an electric, rather than magnetic field, tuning can be faster than tuning a ferrite-loaded device. A BST-loaded coaxial structure is investigated theoretically and experimentally. Good high voltage performance is critical since DC biasing voltages of up to 80 kV can be impressed on the BST sections for tuning. It can also be seen that matching structures around the BST can improve performance over a wider range of amplitudes and phases.
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| THP031 | Pulse Cables For XFEL Modulators | klystron, impedance, pulsed-power, radiation | 640 | ||
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For the XFEL, housed in a single tunnel, most of the modulators will be placed in a central modulator building outside of the tunnel. The pulse transformers and the klystrons will be positioned inside the tunnel near the superconducting linac. Therefore the energy has to be transported via pulse cables. These cables have lengths between 350m and 1.7 km. The power is up to 16.8 MW per pulse with a repetition rate of 10 Hz. In order to keep the rise time short and match the klystron impedance four 25Ohm cables will be put in parallel. A tri-axial design was chosen to prevent magnetic field outside of the cables in order not to disturb electronics or electron beam. A prototype of the cable was produced in industry and delivered to DESY. A set of four 1.5km long parallel cables is in test at present at one of the modulators of the TTF/VUV-FEL at DESY. The cable design criteria and test results are presented in this paper.
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| THP034 | Effective Standing-Wave RF Structure for Charged-Particle Beam Deflector | RF-structure, linac, coupling, impedance | 649 | ||
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In this report we describe new standing wave pi-mode rf structure for charged particles deflection. For L-band frequency range parameters of the proposed structure are compared with classical TM110 mode deflecting cavity ones. With originating TE11n mode, our proposal has several times higher rf efficiency, one order wider pass-band and smaller (in times) transverse dimensions. The cavity design idea and typical are parameters are presented. Some particularities of the beam dynamics in the proposed structure are pointed out. Preferable field of structure application is discussed.
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| THP035 | Design on Accelerating Tube of High-Power Electron Linac for Irradiation Processing | electron, linac, beam-losses, bunching | 652 | ||
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There is an unstable phenomenon for high-power electron linacs for irradiation processing. The main source of the instability of this type of linac comes from the thermal effect of the accelerator tube under an intense heat load. If a lot of injected electrons are lost in the tube, they can cause an intense and uneven heat load on the tube that may deform the cavities of the accelerator tube and deviate the correct acceleration phase relationship. In this paper, a constant gradient accelerating structure is chosen to accelerate the electron beam, and the designed phase velocity is gradually increased along the tube. By adjusting the size of the accelerating cavities and the phase velocity function, a high capture-efficiency is reached. After a series of simulations studies, we obtained a 90% capture-efficiency, which minimizes the probability of the unstable phenomenon in the high power electron linac.
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| THP040 | New Concept of Small Delay Line Type RF Pulse Compressor Using Coupled Cavities | beam-loading, klystron, linac, coupling | 667 | ||
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I propose a new concept for the RF pulse compressor using the coupled cavities to make a small delay line. This new concept is a hybrid scheme of a cavity type and a delay line type of the RF pulse compressor. The delay line produces the pulse compression outputs through resultant RF beat between two inputs connected both ports of the coupled cavities. The time constant of the beat is matched to the time constant of the power flow of the coupled cavities. Further the special test stand for the coupled cavities was developed to easily adjust the resonant frequency of such high-Q coupled cavities.
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| THP042 | Development of High-Current 201.5-MHz Deuteron RFQ Accelerator | rfq, linac, ion-source, ion | 673 | ||
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The beam dynamics for a 201.5MHz 50mA 2.0MeV Deuteron RFQ accelerator with duty cycle of 10% has been further improved by using equipartitioning method. The RFQ structure, mechanical design, thermal analysis and its cooling method have been investigated. The tuning of RF cavity for the field and other parameters has been simulated. A new developed ECR ion source and its setup have been completed and tested. The LEBT for the injection of RFQ is under the construction, and the HEBT at RFQ exit for the further applications has been designed and to be constructed in the near future. All the development results will be presented in this paper.
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| THP046 | Status of 3.9-GHz Deflecting-Mode (CRAB) Cavity R&D | dipole, luminosity, beam-loading, positron | 682 | ||
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The superconducting 3.9GHz deflecting mode cavity design which has been under development as a beam slice diagnostic is planned for use as the ILC crab cavity. We describe the applications and review the status of the R & D, giving both prototype test results and computational studies of beam interaction.
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| THP047 | Prototyping of a Single-Cell Half-Reentrant Superconducting Cavity | superconductivity, vacuum, resonance, coupling | 685 | ||
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As superconducting niobium cavities achieve higher gradients, it is anticipated they will reach a performance limit as the peak surface magnetic field approaches the critical magnetic field. "Low loss" and "reentrant" cavity designs are being studied at CEBAF, Cornell, DESY, and KEK, with the goal of reaching higher gradients via lower surface magnetic field, at the expense of higher surface electric field. At present, cavities must undergo chemical etching and high-pressure water rinsing to achieve good performance. It is not clear whether this can be done effectively and reliably for multi-cell low loss or reentrant cavities using traditional techniques. A "half-reentrant" cavity shape has been developed with RF parameters similar to the low loss and reentrant cavities, but with the advantage that the surface preparation can be done easily with existing methods. Two prototype single-cell half-reentrant cavities are being fabricated at 1.3 GHz; the non-reentrant wall angle is 8 degrees, the beam tube radius is 29 mm, and the cell-to-cell coupling is 1.47%. The half-reentrant cavity design and the results and status of the prototyping effort will be presented.
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| THP053 | Simulations and Optimizations of a New Power Coupler for 3.9-GHz Superconducting Cavities at Fermilab | electron, coupling, impedance, cryogenics | 701 | ||
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3.9 GHz third harmonic superconducting cavities have been used to increase the peak bunch current and to compensate for non-linear distortions in the longitudinal phase space due to sinusoidal 1.3 GHz accelerating cavity voltage. The power coupler is one of the important and complicated components of the third harmonic system for the TTF3 project. From electromagnetic, multipacting, and thermal simulations of the power coupler, optimized designs have been achieved, enabling one to minimize or eliminate potential problems in advance. This paper presents our recent work on simulation and optimization of the power coupler.
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| THP059 | Coaxial HOM Coupler Designs Tested on a Single-Cell Niobium Cavity | coupling, pick-up, vacuum, damping | 716 | ||
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Coaxial higher order mode (HOM) couplers have been developed for HERA cavities and are used in TESLA, SNS and Jlab upgrade cavities. The principle of operation is the rejection of the fundamental mode by the tunable filter of the coupler and the transmission of the HOMs. It has been recognized recently that inappropriate thermal designs of the feed through for the pick-up probe of the HOM coupler will not sufficiently carry away the heat generated in the probe tip by the fundamental mode fields, causing a built-up of the heating of the niobium probe tip and subsequently, a deterioration of the cavity quality factor has been observed in cw operation. An improvement of the situation has been realized by a better thermal design of the feed through incorporating a sapphire rf window [1]. An alternative is a modification of the coupler loop (“F” – part) with an extension towards the pick-up probe. This design has been tested on a single cell niobium cavity in comparison to a “standard TESLA” configuration. by measuring the Eacc behavior at 2 K. The measurements clearly indicate that the modified version of the coupler loop is thermally much more stable than the standard version.
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[1] C. Reece et al; http://accelconf.web.cern.ch/accelconf/, paper TPPT082 |
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| THP061 | High Field Test Results of Superconducting 3.9-GHz Accelerating Cavities at FNAL | resonance, pick-up, linac, pulsed-power | 722 | ||
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The XFEL facilities are planning to use section with a few third harmonic cavities (3.9GHz) to improve beam performance [1]. Fermilab is developing superconducting third harmonic section for the FLASH(TTF/DESY) upgrade. This section will include four cavities equiped with couplers and blade tuners installed in cryostat. Up to now, two cavities are completed and one of them is under vertical test. The gradient of the cavity was limited by multipactor in HOM coupler. The visual inspection of the HOM couplers after cold tests showed that both couplers were damaged. In paper we discuss the results of vertical tests, multipactoring analysis in HOM coupler and a new design for HOM coupler.
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| THP065 | High-Gradient Generation in Dielectric-Loaded Wakefield Structures | electron, laser, gun, klystron | 731 | ||
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Dielectric loaded wakefield structures have potential to be used as high gradient accelerator components. Using the high current drive beam at the Argonne Wakefield Accelerator Facility, we employed cylindrical dielectric loaded wakefield structures to generate accelerating fields of up to 43 MV/m at 14 GHz. Short electron bunches (13 ps FWHM) of up to 86 nC are used to drive these fields, either as single bunches or as bunch trains. One of these structures consists of a 23 mm long cylindrical ceramic tube (cordierite) with a dielectric constant of 4.76, and inner diameter of 10 mm, inserted into a cylindrical copper waveguide. This standing-wave structure has a field probe near the outer edge of the dielectric to sample the RF fields generated by the electron bunches. The signal is sent to a mixer circuit, where the 14 GHz signal is down converted to 5 GHz and then sent to an oscilloscope. A similar structure, with smaller inner diameter and an operating frequency of 9 GHz, is ready for initial tests. Its accelerating fields will be twice as high as the fields in the 14 GHz structure, for the same bunch charge.
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| THP066 | Lorentz-Force Detuning Analysis for Low-Loss, Re-entrant and Half-Reentrant Superconducting RF Cavities | coupling, linear-collider, collider, superconducting-RF | 734 | ||
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The RF design of a superconducting elliptical cavity requires a trade-off in the optimization of the cell shape between the region of high electric field and the region of high magnetic field. In practice, the cavity performance may be limited not by the RF characteristics, but by detuning due to the Lorentz force, bath pressure fluctuations, or microphonics; Lorentz force detuning is of concern primarily for pulsed accelerators such as the proposed International Linear Collider. Hence the structural properties must also be taken into account in the cavity design. Several new cavity shapes are being developed in which the surface magnetic field is decreased relative to the TeSLA cavity shape, with the goal of reaching a higher accelerating gradient. This study will compare the Lorentz force detuning characteristics of the TeSLA, "low-loss", "reentrant", and "half-reentrant" cavity middle cells, and explore possible methods for stiffening the structures.
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| THP067 | Status of the Tuner for the 19-Cell Superconducting CH Prototype Cavity | cryogenics, radio-frequency, vacuum, linac | 737 | ||
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The radio frequency tuning of the multi-cell superconducting CH structure for beta equal to 0.1 is investigated for a 19-cell niobium cavity operated at liquid helium temperature. By applying external mechanical forces the deformation of the structure is studied and the resulting change in frequency is analysed. The ruling equations of elasticity and the electromagnetic eigenvalue problem are solved by using commercial finite element tools. The quantitative results form the basis of an optimized tuning device. In order to guarantee a long lifetime of the cavity, fracture criteria are defined to avoid mechanical damage. Wherever possible the results are compared with experimental data obtained from measurements performed on the first CH prototype developed at the Institute of Applied Physics at Frankfurt. In addition a fast piezo device will be integrated into the slowly acting mechanical tuner. The whole system will operate in an existing horizontal cryostat for testing purposes.
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| THP070 | Study of BSNS RFQ Design | rfq, coupling, dipole, quadrupole | 746 | ||
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A new 324MHz RFQ used for the project of Beijing Spallation Neutron Source (BSNS) is being designed. The designed injection and output energy are 50keV, 3.0MeV, respectively. The designed pulsed current is 40mA though the required current of BSNS at its first stage is only 20mA. The pulsed width is 420 s with a 50% chopping ratio and repetition rate is 25Hz. The transverse structure of BSNS RFQ will be basically the same as the former RFQ used for ADS, but the length of 3.62m is shorter comparing to the length of 4.75m of the former. The beam dynamics design and the RF structure design of the RFQ will be presented in this paper.
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| THP073 | High-Current Elliptical Cavity Design and Prototyping | pick-up, vacuum, linac, injection | 752 | ||
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Beam instabilities due to undamped higher-order modes (HOMs) in the cavities can limit the performance of high-current superconducting accelerators, such as energy recovery linacs. If the accelerator is designed such that the bunch frequency is equal to the accelerating mode frequency and the beam pipe radius is chosen such that the cutoff frequency is less than twice that of the accelerating mode, all of the monopole and dipole HOMs that can be driven by the beam can be well-damped. A 6-cell elliptical cavity for speed-of-light particles and a 2-cell elliptical injection cavity have been designed for high-current accelerator applications. Both cavities have an aperture 29% larger than the TeSLA cavity, at the expense of peak surface fields about 10% higher for the same gradient. The injection cavity has a geometric β of 0.81 and was designed to accelerate electrons from 50 keV to 1 MeV, and the 6-cell cavity has a geometric β of 1 for further acceleration. Both cavities are designed for the purpose of accelerating hundreds of milliamps without HOM-induced beam breakup and to operate at 2.45 GHz. The cavity designs and prototype injection cavity results will be presented.
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| THP083 | Generation of Ellipsoidal Beam Through 3-D Pulse Shaping of a Photoinjector Drive Laser | laser, emittance, electron, gun | 776 | ||
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Due to the linear space-charge force, an ellipsoidal beam is expected to have much smaller emittance in comparison with beams of other geometries, which is critical for many accelerator applications. Up to now, no practical way of generating such beams is available. In this paper we present a few schemes for 3-D laser pulse shaping that can be used to generate ellipsoidal laser pulses that in turn can be applied for generating ellipsoidal electron bunches from a photoinjector. Our simulations show that 3D laser pulse shaping can be realized through laser phase tailoring in combination with properly designed refractive and diffractive optics. Performance of an electron beam generated from such shaped laser pulses is compared with that of the ideal flat-topped and Gaussian electron bunches by numerical simulation, showing improvement in both beam dynamics and performance.
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| THP094 | GeV Laser Wakefield Acceleration and Injection Control at LOASIS | laser, electron, plasma, injection | 806 | ||
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Experiments at the LOASIS laboratory of LBNL have demonstrated production of GeV electron beams with low energy spread and divergence from laser wakefield acceleration. The pondermotive force of a 40 TW laser pulse guided by a 3 cm capillary discharge plasma density channel drove an intense plasma wave (wakefield), producing acceleration gradients on the order of 50 GV/m. Electrons were trapped from the background plasma and accelerated. Beam energy was increased from 100 to 1000 MeV*, compared to earlier experiments**, by using a longer guiding channel at low density, demonstrating the anticipated scaling to higher beam energies. Particle simulations are used to understand the trapping and acceleration mechanisms. Other experiments and simulations are also underway to control injection of particles into the wake, and hence improve beam quality and stability further. Recent experimental and simulation results from channel guided laser acceleration, and initial injection results, will be presented.
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*W. P. Leemans et al, submitted. |
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