KEK, Ibaraki
A 6-m cryomodule, which includes four Tesla-like 9-cell cavities, was assembled and installed in the STF tunnel in April, 2008. After cooldown of the cryomodule, high power tests of four cavities had been carried out at 2 K from September to December, 2008. A cavity package consists of a 9-cell niobium cavity with two HOM couplers, an input coupler with a cold and a warm rf window, and a frequency tuning system with a mechancal and a piezo tuner. The performance as a total sc cavity system was checked in the cryomodule test with high rf power. One of the cavities was achieved a stable pulsed operation at 32 MV/m higher than the specific operating gradient (31.5 MV/m) in ILC. The maximum accelerating gradients (Eacc,max) obtained in the vertical cw tests was maintained or slightly improved in the cryomodule tests with a pulsed operation of 1.5 msec and 5 Hz. Compensation of Lorentz force detuning at 31 MV/m was successfully demonstrated by using piezo tuner and pre-detuning.
KEK, Ibaraki
A cryomodule including three 2-cell sc cavities was designed for the ERL injector Linac, which is operated at the beam energy of 10 MeV and the beam current of 100 mA. A prototype 2-cell cavity with two input coupler ports and four HOM couplers was fabricated. The double input couplers is to reduce the power per coupler and to keep a symmetric filed configuration around the coupler port. Required rf power in the input couplers is about 200 kW in the cw operation. First vertical test of the 2-cell cavity will be carried out in March.
KEK, Ibaraki
Kyoto ICR, Uji, Kyoto
The inspections of the superconducting RF cavities seem essential in achieving high accelerating gradient. The Kyoto camera system is a good tool to survey a defect location and to be analysis a defect shape in the inner surface of the superconducting rf cavities. The cavity inspections of the AES, ACCEL, ZANON and STF Baseline cavities were inspected to study relations between a defect shape and a heating gradient of the superconducting rf cavities. The STF Baseline #5 and #6 cavities with each surface treatment (as received, after Pre-EP, after EP-1, and after vertical test with EP-2) were inspected to trace a changing spots shape. The full inspection of the EBW seam, the HAZ (heat affected zone) and hot spots region were carried out before EP-2 process and a vertical test then the shape analysis of a discovered spots was done. The vertical tests of these cavities with T-map of fixed 9-cell type were measured at STF from September 2008. The inspection and shape analysis of these cavities were made after vertical tests for based on T-map data. The result of vertical tests and changing a shape of a discovered spots with EP-2 process will be presented.
KEK, Ibaraki
ISSP/SRL, Chiba
TIPC, BeiJing
A new vertical test facility for L-band multi-cell cavities has been completed in support of development efforts of ILC (International Linear Collider) and ERL (Energy Recovery Linac) projects at STF (Superconducting rf Test Facility) of KEK. The facility possesses a clean booth for pre-tuning the cavities, four cavity stands to prepare the cavities prior to vertical testing, a half-underground pit which accommodates up to two vertical cryostats which can be pumped and operated separately under a movable iron shield. Vertical testing of the cavities, with a 400 W high-power amplifier and with a temperature-mapping (T-mapping) and additional monitoring systems, is supervised from a control room which overlooks the entire facility. This paper describes the specific details of the facility and results from its initial pilot operation that was conducted in Summer-Fall of 2008.
KEK, Ibaraki
TIPC, BeiJing
A pulsed RF operation of four units of 9-cell L-band (1.3 GHz) cavities in a horizontal cryostat (cryo-module) was conducted in 2008 as part of R&D efforts at STF at KEK for ILC. A series of compensation experiments were conducted for Lorentz-detuning effects, which are critically important for pulsed RF operation of high-gradient linacs based on superconducting cavity technologies. The experiments were done at a repetition rate of 5 Hz with RF pulses of a width of 1.5 msec, and the typical accelerating gradient within the cavities was 20 32 MV/m. Two types of compensation techniques have been tested. In a “feed-forward” method, piezo actuators on individual cavity tuners are activated to mechanically control the tuning of the cavity in synchronization with the RF pulses. In a “feed-back” method, the low-level RF system is driven so as to maintain the average of “I” and “Q” components of the cavities as constant. This paper reports the experimental results using the various parameters of the piezo control to compensate the effect of Lorentz-detuning. These results are consistent with the numerical calculation postulating that two mechanical modes mainly contribute to the effect.
KEK, Ibaraki
ISSP/SRL, Chiba
TIPC, BeiJing
A new cavity diagnostic system has been introduced for vertical testing of nine-cell L-band superconducting cavities at KEK-STF. The present system is based on approximately 300 carbon resistors for temperature-mapping (T-mapping), and approximately 40 PIN photo diodes for detecting emission of X-rays. The system can accommodate up to total 600 sensors in needed in the future. While most of the sensors are attached to the cavity exterior in a pre-determined regular pattern, some sensors can be strategically placed at non-regular positions so as to watch the areas which are considered “suspicious” as per the surface inspection done prior to vertical testing. Data from the sensors can be collected every 100 msec. The data can be graphically displayed online and are stored for offline analysis. This paper describes the details of this system, together with results from its initial pilot operation which was done with a nine-cell cavity on loan from FNAL (AES#001). Effectiveness of the combined use of T-mapping and PIN photo diodes in operation of the pi-mode and other pass-band modes in conjunction with surface inspection is discussed.
KEK, Ibaraki
JAEA/ERL, Ibaraki
JASRI/SPring-8, Hyogo-ken
ISSP/SRL, Chiba
UVSOR, Okazaki
HU/AdSM, Higashi-Hiroshima
Hiroshima University, Graduate School of Science, Higashi-Hiroshima
AIST, Tsukuba
Future synchrotron light source project using an energy recovery linac (ERL) is under proposal at the High Energy Accelerator Research Organization (KEK) in collaboration with several Japanese institutes such as the JAEA and the ISSP. We are on the way to develop such key technologies as the super-brilliant DC photo-injector and superconducting cavities that are suitable for both CW and high-current operations. We are also promoting the construction of the Compact ERL for demonstrating such key technologies. We report the latest status of our project, including update results from our photo-injector and from both superconducting cavities for the injector and the main linac, as well as the progress in the design and preparations for constructing the Compact ERL.