JASRI/SPring-8, Hyogo-ken
KEK, Ibaraki
MHI, Tokyo
Mitsubishi Heavy Industries Ltd. (MHI), Takasago
We have been developing a system to generate a short pulse X-ray using crab cavities at SPring-8 Storage Ring. The ring holds 30-m long straight sections and the vertical beam size at the center of the straight sections is 6.5 micrometers in standard deviation. If we install four superconducting crab cavities and a mini-pole undulator in one of the straight sections, we can convert the time distribution of the electron bunch into the spatial distribution. After slicing the emitted photons with vertical slits, we can obtain a sub-picosecond X-ray pulse. In this scheme, the maximum repetition rate of the short pulse X-ray is the same as the acceleration frequency of the ring (508MHz) and user experiments at other beam-lines are not disturbed by this short pulse generation. We are planning to install KEKB type crab cavities as vertical deflectors. Phase fluctuation among crab cavities must be reduced less than 14 mdeg in order to avoid residual deflection in the vertical direction. In this paper, we report an overview of the short pulse generation scheme and topics of hardware development for stabilization of the RF phase fluctuation.
KEK, Ibaraki
Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura
Two superconducting crab cavities have been operated stably without any significant trouble for three years in KEKB since Feb/2007. At present (Dec/2009), maximum beam current with 'Crab ON' achieves 1200mA for HER (High Energy Ring, electron) and 1640mA for LER (Low Energy Ring, positron), respectively. RF trip rate per day due to crab cavity during 'physics run' was 2.8/day for HER and 0.4/day for LER at the beginning, and is 0.8/day for HER and 0.1/day for LER at present, respectively. Although Piezo actuator was frequently broken down at the beam abort with RF trip of the crab cavity, it was controlled stably by only LLRF (Low Level RF) feed-back system without Piezo actuator. Maximum HOM (Higher Order Mode) power, which is measured at HOM dampers made from ferrite, is 9.1kW for HER and 14.6kW for LER at the maximum beam current, respectively. LER crab voltage, which had suddenly dropped from 1.50MV to 1.10MV on March/2007, was gradually recovered from 1.14MV to 1.33MV in 2008.
KEK, Ibaraki
JAEA/ERL, Ibaraki
ISSP/SRL, Chiba
A prototype module including a couple of 1.3 GHz superconducting 9-cell cavities has been designed as the main linac of cERL which is the test facility to establish the basic ERL technology at KEK. The shape of 9-cell Nb structure has been optimized to accelerate a CW beam of 100 mA with sufficiently damped higher order modes (HOM) which is achieved by adopting an eccentric fluted beam pipe and a cylindrical beam pipe of a large diameter of 123 mm. Extracted HOMs are absorbed by the ferrite cylinders bonded on the copper beam pipes by HIP process. A power coupler with double disk-ceramics has been developed to transfer an RF of 20 kW CW to the cavity in full reflection. The test results of fabrication, cooling and RF performance for these components are integrated as the prototype module of the main linac for cERL facility.
KEK, Ibaraki
Hydrogen absorbed in niobium was measured using effect of hydrogen Q-degradation. A niobium cavity was designed and manufactured for this experiment. Hydrogen was introduced from outside of the cavity by electrolysis of diluted sulfuric acid on the outer surface of the cavity with an anode made by stainless steel. The Q-factor is one of the most unstable property of superconducting cavities. Especially, the reproducibility of Q-factor cannot be so expected after disassembled and reassembled it. In this experiment, the Q-factor was measured without disassembling, because hydrogen was introduced from outside of the cavity. The Q-degradation was observed successfully. And the Q-factor becomes worse and worse, when hydrogen was introduced more and more. To estimate the amount of hydrogen which is absorbed in niobium, small and thin niobium samples were prepared. They were warmed by the energizing heating in vacuum after having introduced hydrogen. The out-gas was analyzed by QMS, and the amount of hydrogen was estimated. This method can be applied to measure the absorbed hydrogen during electro or chemical polishing of cavities without some influence of changing the surface morphology.
KEK, Ibaraki
UVSOR, Okazaki
JAEA/ERL, Ibaraki
JASRI/SPring-8, Hyogo-ken
HU/AdSM, Higashi-Hiroshima
ISSP/SRL, Chiba
Yamaguchi University, Ube-Shi
Nagoya University, Nagoya
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
Tohoku University, School of Scinece, Sendai
AIST, Tsukuba
Future synchrotron light source using a 5-GeV-class energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting active R&D efforts for that. We are developing super-brilliant DC photocathode guns, two types of cryomodules for both injector and main superconducting linacs, 1.3 GHz high CW-power rf sources, and other important components. We are also constructing a compact ERL for demonstrating the recirculation of low-emittance, high-current beams using those key components. We present our recent progress in this project.
KEK, Ibaraki
Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura
Two superconducting crab cavities were successfully installed into the KEKB accelerator in January 2007. Since then the crab cavities have been in stable operation for 3 years up to now, thanks to reliable operation of the cryogenic system of the KEKB including a large-scale helium refrigerator. This means that the cryostat for the crab cavities was well designed and constructed properly, although there are some technical complexities in the cryostat, such as two helium vessels in a cryostat, a movable coaxial coupler which is cooled with liquid helium and so on. The KEKB cryogenic system was also appropriately modified to operate the two crab cavity cryostats stably. This cryogenic system is described in this presentation. A calorimetric method to measure the Q-factors of the crab cavities is suggested, which employs an electric compensation heater in the cryostat, instead of the conventional method, which measures the descending rate of liquid helium level. Measurement results of the Q-factors of crab cavities after being assembled in the cryostat and after being installed into the KEKB accelerator are compared with the vertical test results.