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| MOOPMA05 | R&D on Vacuum Components for High-Current Accelerators | electron, vacuum, impedance, radiation | 41 | ||||
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In anticipation of coming high current accelerators era, R&D on various vacuum components has been carried out at KEK. Copper beam ducts with ante-chambers were designed to deal with the intense synchrotron radiation (SR) power density emitted from the high current beam. The ante-chamber structure is also effective to reduce photoelectrons around positron beam, which is helpful to suppress the electron cloud instability (ECI). A comb-type RF-shield was developed to reduce the beam impedance and improve the thermal strength compared to the conventional finger-type one, and applied to bellows chambers and gate valves. The connection flange with the same cross section to the beam duct was also developed in parallel. Novel structure of a movable mask (collimator) was recently proposed, which had lower impedance compared to the conventional one, and now the test model was under fabrication. The beam ducts, the bellows chambers, and the gate valves have been installed in the KEK B-factory (KEKB) positron ring for several years. The performance of these components has been studied during beam operation, and the promising results have been obtained.
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| TUC3MA03 | Ultimate Abilities of Conventional Positron Sources | target, electron, linac, acceleration | 97 | ||||
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Significant increasing of desired luminosity for future e+e- colliders leads to corresponding enlargement of positron production rate. Conventional technology of positron production have not reached yet its technical limits. Experimental study in order to find out these limits for basic subsystems of positron source is presented in this paper.
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| TUPMA066 | Energy Equalization by using S-band and X-band Accelerator Modules | linac, simulation, klystron, acceleration | 205 | ||||
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To reduce the beam loss and to restrict the expanse of the bunch length of the positron beam from the KEKB injector, the energy spread of ±0.25% or less is required for the beam transport line of the KEKB ring. Generally, the positron beam has a large energy spread because the original bunch length is large and all positrons do not see the same accelerating filed. Thus, an energy compression system which consists of six rectangular magnets and two 2-m S-band accelerating structures is implemented at the end of the linac but it has a demerit that the beam bunch is lengthened. We propose a new method to suppress the energy spread without enlarging the bunch length. This method utilizes the superimposed acceleration of the S-band modules and X-band modules.
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| WEXMA01 | Status of KEKB and Upgrade Plan to SuperKEKB | luminosity, electron, linac, klystron | 280 | ||||
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The KEKB is an electron-positron two-ring collider for the leading B meson factory. It consists of an 8 GeV electron ring (HER) and a 3.5 GeV positron ring (LER) and their injector linac. It has been operated since December 1998, and has recently marked the peak luminosity of 16.52 /nb/s. This peak luminosity is obtained under the crab-ready beam optics having the robust operating condition by some efforts to solve the optics problems. The integrated luminosity has also recently exceeded 1.2 /fb /day under the continuous injection mode. We are aiming more luminosity improvement after the crab cavity installation. Further the major upgrade plan for SuperKEKB is expected to achieve 400 /nb/s keeping the baseline of the original proposal and another upgrade plans are also considered towards over 1000 /nb/s based on the recent beam-beam simulation. This paper describes the recent status of KEKB and upgrade plans for SuperKEKB.
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| WEXMA02 | The BEPCII: Construction and Initial Commissioning | linac, cryogenics, luminosity, vacuum | 285 | ||||
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As a natural extension of the Beijing Electron-Positron Collider (BEPC), the BEPCII project has started its construction since the beginning of 2004. The BEPCII will operate in beam energy of 1-2.1 GeV, its design luminosity is 1*1033cm-2s-1 at 1.89 GeV with double-ring structure. The upgraded collider will also serve as a synchrotron radiation source with higher beam energy and intensity than the BEPC. Some key technologies, such as superconducting RF system, low impedance vacuum devices, superconducting micro-beta quadrupoles, etc. are developed. The injector linac reached its design specification by the summer of 2006. Most storage ring components have been manufactured, installed and tested. The final checkout of the storage ring subsystems is underway. For the delay of the cryogenic and high current test of the superconducting quadrupoles, the commissioning of the storage rings will be started with normal magnets in the interaction region in autumn of 2006. The project is scheduled to complete in 2008. This paper will present the updated status and preliminary commissioning results of the BEPCII.
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* For the BEPCII team |
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| WEPMA030 | The Bunch Lengthening due to Electron Cloud in Positron Storage Ring | electron, simulation, storage-ring, damping | 366 | ||||
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The electron cloud generates not only the transverse wake field but also the longitudinal wake field. The mechanism of the bunch lengthening due to longitudinal wake produced by the electron cloud in the positron storage ring is analyzed. The longitudinal field, which depends on the density of the electron cloud in the storage ring, arises from the accumulation of the electrons near to the center of the bunch during the bunch passage. Based on the longitudinal wake field, tracking method is used to simulate variation of the bunch longitudinal profile in different electron cloud density. According to simulation, the longitudinal action on the bunch from electron cloud is the similar as the potential-well distortion to shift the bunch distribution and give a rise to the bunch deformation. The result has been used to the simulation for BEPCII.
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| WEPMA109 | Positron Injector Accelerator and RF System for the ILC | target, electron, photon, linac | 473 | ||||
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Due to the extremely high energy deposition from positrons, electrons, photons and neutrons behind the positron target, and because a solenoid is required to focus the large emittance positron beam, the 1.3 GHz pre-accelerator has to use normal conducting structures up to energy of 400 MeV. There are many challenges in the design of the normal-conducting portion of the ILC positron injector system such as obtaining high positron yield with required emittance, achieving adequate cooling with the high RF and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. Considering issues of feasibility, reliability and cost savings for the ILC, the proposed design for the positron injector contains both standing-wave (SW) and traveling-wave (TW) L-band accelerator structures. A short version of the new type of the SW section is under fabrication and testing, an updated status report is given. This paper also covers the acceleration vs. deceleration for pre accelerator sections, SW vs. TW structures, as well as the longitudinal matching from target to linac and linac to damping ring.
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* Work supported by U. S. Department of Energy, contract DE-AC02-76SF00515. |
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