| Paper | Title | Page |
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| MOPAN039 | Development of Hybrid Type Carbon Stripper Foils with High Durability at >1800K for RCS of J-PARC | 242 |
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| The Japan Proton Accelerator Research Complex (J-PARC) requires thick carbon stripper foils (250-500 ug/cm2) to strip electrons from the H- beam supplied by the linac before injection into the RCS of J-PARC. For this high-intensity H- beam and circulating bunch beam, which gives much damage to conventional carbon stripper foils. Thus carbon stripper foils with high durability at 1800K produced by energy deposition in the foil are indispensable for this accelerator. Recently, we have successfully developed hybrid type thick boron mixed carbon stripper foils (HBC-foil). Namely, the lifetime measurement of the foils was tested by using a 3.2 MeV, Ne+ DC beams of 2.5 uA, in which a significant amount of energy was deposited in the foils. The maximum lifetime was found to be extremely long, 30-and 250-times longer than those of Diamond and commercially available best carbon foils, respectively. The foils were also found to be free from any shrinkage, and to show an extremely low thickness reduction rate even at a high temperature of 1800K during long beam irradiation. In this conference the foil preparation procedures and lifetime measurements with a 3.2 MeV, Ne+ is presented. | ||
| MOPAN040 | Comparative Study on Lifetime of Stripper Foil using 650keV H- Ion Beam | 245 |
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Funding: This work is supported by the Japan Society for the Promotion of Science, under contract No. 18540303. Thick carbon stripper foils of >300 μg/cm2 will be used as a stripping of H-ion beam for 3GeV Rapid Cycling Synchrotron (3GeV-RCS) of the J-PARC. The carbon foils with long lifetime even at >1800 K are required. For this purpose, we have developed a new irradiation system for the lifetime measurement using high current pulsed and dc H- beams of the KEK Cockcroft-Walton accelerator. These high power 650keV H- Ion beams can simulate the high energy deposition in carbon stripper foils at the J-PARC RCS. An automatic data acquisition system is also developed for recording the data of foil temperature and irradiated beam current. The Hybrid Boron mixed Carbon (HBC) stripper foils, which are developed at KEK are irradiated by high current H- ion beam up to 2000 K. A few SNS-diamond and commercially available carbon (CM) foils are also tested for comparing with HBC-foils. The results of the lifetime measurement of HBC and SNS-diamond including CM stripper foils are reported. |
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| MOPAN045 | Longitudinal Particle Tracking of J-PARC RCS for Synchronization | 260 |
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| We have performed particle tracking simulation of J-PARC RCS to study the synchronization process. A frequency offset is added to the nominal RF frequency pattern to shift the center of the bunch, under the condition of the offset value should be 'adiabatic' with respect to the synchrotron motion. Since the synchrotron frequency of the J-PARC RCS is substantially changed during acceleration, the particle tracking simulation helps to decide upper limit of the frequency offset which can be employed. | ||
| MOPAS081 | Spallation Neutron Source (SNS) Diamond Stripper Foil Development | 620 |
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Funding: SNS is managed by UT-Battelle, LLC, for the U. S. DOE under contract DE-AC05-00OR22725. DOE contract W-7405-ENG-36 (LANL) and Japan SPS contract 18540303 (KEK) supported work at those institutions. Diamond stripping foils are under development for the SNS. Free-standing, flat 350 microgram/cm2 foils as large as 17 x 25 mm have been prepared. These nano-textured polycrystalline foils are grown by microwave plasma-assisted chemical vapor deposition in a corrugated format to maintain their flatness. They are mechanically supported on a single edge by a residual portion of their silicon growth substrate; typical fine foil supporting wires are not required for diamond foils. Six foils were mounted on the SNS foil changer in early 2006 and have performed well in commissioning experiments at reduced operating power. A diamond foil was used during a recent experiment where 12 microCoulombs of protons, approximately 40% of the design value, were stored in the ring. A few diamond foils have been tested at LANSCE/PSR, where one foil was in service for a period of five months (820 Coulombs of integrated injected charge) before it was replaced. Diamond foils have also been tested in Japan at KEK (650 keV H-) where their lifetimes slightly surpassed those of evaporated carbon foils, but fell short of those for Sugai's new hybrid boron carbon (HBC) foils. |
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| TUPAN063 | High Power Test of MA Cavity for J-PARC RCS | 1532 |
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| We have been testing the RF cavities for the J-PARC RCS, we can operate the cavities without sever problems. Before some MA cores were damaged, then we found such cores have low ribbon resistance. After that we have tested the cavities loaded with improved ribbon resistance. | ||
| WEPMN038 | Development of the Beam Chopper Timing System for Multi-Turn Injection to the J-PARC RCS | 2125 |
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| Multi-turn injection using charge exchange is employed for the J-PARC Rapid Cycling Synchrotron (RCS). To improve the bunching factor of the beam in the ring, the momentum offset injection scheme is used. In each turn, the bunch trains from the linac are injected into the RF buckets with a momentum offset. The bunch train is called the "intermediate pulse". The intermediate pulses are generated in the low energy section of the linac by the RF chopper and pre-chopper. Since the pulse must be synchronized to the RF voltage in the ring, the timing signals for the choppers are generated by the low-level RF (LLRF) system of the RCS and the signals are sent to the chopper control. The RF chopper and the pre-choppers require different pulse widths. Thanks to the direct digital synthesis (DDS) in the LLRF system, precise zero-cross signals for the reference of the chopper pulses are generated without difficulties. The cable route from the RCS LLRF system to the linac chopper control system is more than one kilometer. Thus, the chopper pulses are sent via optical cables. We developed the chopper timing module. We describe the details of the hardware and the preliminary test results. | ||
| WEPMN040 | MA Cavities for J-PARC with Controlled Q-value by External Inductor | 2131 |
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The original J-PARC RCS cavity design* used cut-cores to control the Q-value. Adjusting the distance between the C-shaped core parts the optimum Q=2 is reached. Because of problems related to the cut-core surfaces, the "hybrid cavity" was introduced, using tanks with uncut cores (Q=0.6) in parallel to tanks with cut cores with a wider gap (Q=4), resulting in total Q=2. This was successfully tested. The manufacturing procedure for cut-cores involves more steps than for uncut cores. To reduce risks for long-term operation, the RCS cavities will be loaded with uncut cores for day-1 operation. With uncut cores (Q=0.6) the maximum beam power is limited. Therefore we introduce a parallel inductor, placed in the push-pull tube amplifier driving the cavity, to adjust the Q-value to 2. Parallel vacuum capacitors shift the resonance near to 1.7 MHz. Each of the 10 cavity systems for RCS, necessary for day-1 operation, is tested for at least 300 hours to detect initial problems before installation into the RCS tunnel. We report the results of cavity performance tests with external inductor, which simulate 25Hz operation and the optimization of the combined system of cavity and amplifier.
* C. Ohmori at. al, "High Field-Gradient Cavity for J-PARC 3 GeV RCS", PAC 2004 |
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| TUPAN055 | Present Status of J-PARC Ring RF Ring RF Systems | 1511 |
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The RCS high frequency accelerating systems are prepared for beam commissioning in September 2007. Installations of cavities, power supplies and amplifiers have been carried out. The systems have been checked for operation and interoperability. For the MR high frequency accelerating system, the examination of the whole system and its final adjustment are done aiming at installation in October 2007. Here, we report on various issues which had been found and solved during the examination and installation period.
masahito.yoshii@kek.jp |