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| MOP012 | Upgrade Status and Commissioning of BEPCII Linac | linac, gun, klystron, electron | 55 | ||
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BEPCII- an upgrade project of the BEPC is a factory type of e+e- collider. It requires its injector linac to have a higher beam energy (1.89 GeV) for on-energy injection and a higher beam current (40 mA e+ beam) for a higher injection rate (≥50 mA/min.). In five months from May 1st of 2005, we’ve installed and upgraded major parts of the machine, and then it ran for busy BSRF operation. We took a limited time to commission the machine and got a preliminary but satisfied result, the positron beam at the linac end was about 60mA. Now the linac is running smoothly, almost all design goals were reached. In this paper, we’ll present the upgrades for better beam quality, such as phasing system, beam feedback system, and report the present status of the BEPCII linac.
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| MOP026 | Positron Source from X-rays Emitted by Plasma Betatron Motion | electron, plasma, photon, ion | 94 | ||
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A new method for generating positrons has been proposed that uses betatron X-rays emitted by an electron beam in a high-K plasma wiggler. The plasma wiggler is an ion column produced by the head of the beam when the peak beam density exceeds the plasma density. The radial electric field of the beam blows out the plasma electrons transversely, creating an ion column. The focusing electric field of the ion column causes the beam electrons to execute betatron oscillations about the ion column axis. At the proper plasma density, this leads to synchrotron radiation in the 1-50 MeV range. These photons strike a thin (.5Xo), high-Z target and create electron-positron pairs. A computational model was written and matched with experimental results taken at the Stanford Linear Accelerator Center. This model was then used to design a more efficient positron source, giving positron yields of 0.44 positrons/electron, a number that is close to the target goal of 1-2 positrons/electron for future positron sources.
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| TUP007 | Low-Energy Linacs and Their Applications in Tsinghua University | linac, electron, klystron, scattering | 256 | ||
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During these years, several kinds of low energy linacs were developed for cargo inspection, non-destructive-test and irradiation in Tsinghua University cooperated with NUCTECH company. The newly finished interlaced pulse dual energy 9/6MeV linac for material distinguishing cargo inspection and several others will be described here. The beam dynamics simulation and the experiment results together with some applications of these linacs will be given in this paper.
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| TUP048 | Beam-Loading Effect in the Normal-Conducting ILC Positron Source Pre-Accelerator | beam-loading, focusing, linac, linear-collider | 355 | ||
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Significant positron bunch charge (several nC) in the ILC Positron Source results in high pulse beam loading for normal-conducting accelerating structures in Positron Pre-Accelerator (PPA). Time interval between bunches (~ 300 ns) is not negligibly small in comparison with accelerating structure time constant (rise time for Standing Wave (SW) or filling time for Traveling Wave (TW) options). As the result, beam loading effect has particularities both from stored energy acceleration regime and continuous beam loading one. Taking into account particular PPA beam structure, beam loading effect is estimated for the present ILC base line parameters, both for SW and TW PPA options. Possible solutions for beam loading compensation are discussed.
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| TUP050 | Microwave Helical Undulator-Based Production of Polarized Photons and Positrons | undulator, radiation, polarization, linear-collider | 361 | ||
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Linac-driven undulator technology and capabilities are considered for production of polarized positrons and polarized high-brightness X-rays. Challenging requirements for polarized positron production reveal a number of benefits of a microwave undulator compared with a conventional magnetic undulator: larger gap, simpler construction, shorter length, reduced requirements on tolerances and alignment. Two novel approaches are introduced for open and closed structures: cross-polarized excitation of a circular waveguide and a twisted structure. For the CLIC project the microwave undulator becomes an integral part of the TBA, and as it is naturally powered by the same decelerator. Other applications include emittance dampers, synchrotron radiation sources, and FELs. Additionally the twisted undulator provides unique opportunity for studies of circular dichroism and multi-photon anomalous diffraction (MAD) in protein crystallography.
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| THP033 | Pulsed RF Heating Particularities in Normal-Conducting L-band Cavities | gun, booster, cathode, linac | 646 | ||
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For present projects, such as X-FEL and ILC, the SC technology is chosen for the main linacs. However, in some special parts, NC cavities are applied, operating with high electric and magnetic fields. RF gun cavities with an electric field up to 60 MV/m at the photo cathode are now under development. Capture cavities in the ILC positron source should operate with an accelerating gradient of up to 15 MV/m, practically the same value (14 MV/m), as for the CDS booster cavity in the Photo Injector Test Facility at DESY in Zeuthen (PITZ). High field strength leads to high specific RF heat loading. In combination with long RF pulses (~ 1ms) it results in substantial surface temperature rise, small cavity shape deformations and measurable frequency shifts. In this report we discuss both particularities and some general regularities related to long pulse operation of L-band cavities. Results of 3D numerical simulations for cavity surface temperature, displacements distributions and corresponding frequency shifts for different cavities are presented and compared with existing experimental data. The presented results will give the input for cavities optimization and sub-systems improvements.
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| THP046 | Status of 3.9-GHz Deflecting-Mode (CRAB) Cavity R&D | dipole, luminosity, simulation, beam-loading | 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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| THP087 | Status of C-band Accelerating Section Development at the KEKB Injector Linac | linac, klystron, impedance, acceleration | 788 | ||
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This paper reports on C-band accelerating section development for future energy upgrade of the KEKB injector linac. Target field gradient is 42 MV/m, that is twice of the present S-band sections in the linac. Until now, we have developed four 1m-long sections based on a half-scale design of the S-band section with improvements in coupler cavity shape and in fabrication method. And the fifth accelerating section is in fabrication now. The four sections have already installed in the beam line of the linac. Together with a unit of C-band rf source (50 MW klystron, pulse modulator, rf-pulse compressor) installed in the linac, we will perform an operation test of a model C-band accelerator module that has almost same configuration as a design module in the upgrade. Results of the long-term operation test and beam acceleration study will be described. And present status of development of the fifth accelerating section will also be given.
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| THP091 | Experimental Study of Positron Production from Monocrystalline Targets at the KEKB Injector Linac | target, electron, radiation, linac | 797 | ||
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Intense positron sources are widely investigated for the next-generation of linear colliders and B-factories. A new method utilizing an axially-oriented crystal as a positron-production target is one of the bright schemes since it provides a powerful photon source through channeling and coherent bremsstrahlung processes when high-energy electrons penetrate the target. A series of positron-production experiments with tungsten crystal alone and diamond target combined with an amorphous tungsten plate have been carried out at the KEKB injector linac. The tungsten crystals with different thicknesses (2.2, 5.3, 8.9, 12.0 and 14.2 mm) and the diamonds with different thicknesses (4.57 and 7.25 mm) were tested on a goniometer by using 4 and 8-GeV electron beams, respectively. The positron-production yields were measured with a magnetic spectrometer at the positron momentum of 10 and 20 MeV/c. In this report the experimental results are summarized on the enhancements of the positron yield from these crystal targets compared to amorphous targets of the same thickness.
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*Email address: tsuyoshi.suwada@kek.jp |
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| THP092 | Control System for a Limitation of an Integrated Amount of Beam Charges Delivered from the KEKB Injector Linac | injection, controls, linac, electron | 800 | ||
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A new control system is under construction for radiation safety at the KEKB injector linac. The control system restricts the integrated amount of the beam charges delivered from an electron gun in order to keep the radiation safety with high reliability in a daily operation of the linac. The old control system of the radiation safety has been working based on a software control implemented on a UNIX-based workstation. However, this control system is not possible to be implemented for the long-term linac operation with high reliability. The new control system comprises a charge-integration-type analog circuit mounted along with a CPU chip and a data acquisition system based on programmable logic controllers. The fast analog circuit can detect the beam-charge signals delivered from a wall-current monitor, and control the beam-abort trigger pulses pulse-by-pulse. The new hardware-based control system may stabilize the radiation safety control for the long-term linac operation. In this report the design of the new control system is described along with preliminary test results.
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