KEK, Ibaraki
New vertical test system was constructed at KEK-STF in 2008. Pilot test for system check including surface treatment process (Electro-Polishing) was successful using AES#001 cavity, which was on loan from FNAL, because the gradient was increased from 15.7 MV/m to 21.8 MV/m. After that, vertical test for MHI cavities is routinely done, which goal is to achieve above 35 MV/m. New cavity diagnostic system was recently completed for vertical testing of 9-cell L-band superconducting cavities, which is composed of T-mapping and X-ray-mapping. The present system is based on 352 carbon resistors for T-mapping, and 82 PIN photo diodes for detecting emission of X-rays. 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 (pinpoint attachment). Although the T-mapping system identified perfectly the heating location in every vertical test, there was no correlation between the heating location and the suspicious spot.
KEK, Ibaraki
JAEA/ERL, Ibaraki
ISSP/SRL, Chiba
The 9-cell superconducting cavities have been developed for realizing the high current ERLs. Along with high accelerating gradient of 15-20 MV/m, strong HOM damping is also important issue for ERL main linacs, to avoid the Beam Breakup instabilities. For this aim, cavity cell shapes were optimized with large iris diameter, and large diameter beampipe HOM dampers were applied for effective HOM damping. Eccentric fluted beampipe structure was also proposed for damping of quadrupole HOMs. A prototype of niobium 9-cell cavity was fabricated. After a series of surface treatments, vertical tests were performed for the cavity. At present, the accelerating gradient is limited to 16-17MV/m due to field emissions. A developed rotating X-ray mapping system was used at the measurements and observed some X-ray traces. It is a powerful tool to locate a place of an emitter. We report on these activities with focus on the results of vertical testing.
KEK, Ibaraki
A new vertical test (VT) facility was built in KEK-STF (Superconducting rf Test Facility) and in operation since July/2008. Vertical test for S1-Global project is regularly done using MHI#5-#9 cavities, which were newly fabricated in Japan in 2008-2009. In this paper, we report the recent results of vertical test and discuss on cause of field limitation in these tests. For identifying the cause of the filed limitation, it is crucial to check the correlation between pass-band mode measurement and T-mapping. In the pass-band mode measurement, the achievable gradient for each cell is obtained by using seven pass-band modes from π to 3π/9. MHI#5 cavity achieved 27.1 MV/m at third VT and was limited by the thermal quenching due to defect or contamination. Although MHI#6 cavity had almost same results as MHI#5 in first and second VT, third VT was not completed due to cable breakdown. On May/2009, Electro-Polishing acid was exchanged for new one. After that, many brown stains were observed in the interior surface of MHI#6, #7 and #8 cavities. Such a phenomenon appeared for the first time at STF and the investigation for it is thoroughly being done at present.
KEK, Ibaraki
ISSP/SRL, Chiba
JAEA/ERL, Ibaraki
We started to develop an input coupler for a 1.3GHz ERL superconducting cavity. Required input power is about 20kW for the cavity acceleration field of 20MV/m and the beam current of 100 mA in energy recovery operation. The input coupler is designed based on the STF-BL input coupler and some modifications are applied to the design for the CW 20kW power operation. We fabricated input coupler components such as ceramic windows and bellows and carried out the high-power test of the components by using a 30kW IOT power source and a test stand constructed for the high-power test. In this report, we mainly describe the design strategy of the input coupler for the 1.3GHz CW superconducting cavity and results of the high-power test of ceramic window and bellows.
JAEA/ERL, Ibaraki
KEK, Ibaraki
ISSP/SRL, Chiba
HOM absorbers are one of the key components to determine the ERL cavity performance to reduce the HOM problem for the high current operation. When a beam line HOM damper is installed inside the cryomodule, the HOM damper is cooled down to liquid nitrogen temperature. The RF absorber used for the HOM damper is required to have good frequency and temperature properties. Some ferrites and ceramics are tested for permittivity and permeability of frequency-dependence and temperature-dependence measured with a GM refrigerator from room temperature to 40 K. The HOM damper is designed by optimizing the parameters such as length, thickness and position with microwave simulation codes. Test models of the HOM damper are being designed and fabricated to test the RF, mechanical, cooling and temperature properties.
KEK, Ibaraki
JAEA/ERL, Ibaraki
ISSP/SRL, Chiba
A construction of the Compact ERL is planned in KEK, in order to test the key technology to realize the future ERL based X-ray light sources. The operation of 60-200 MeV beam energy and 100 mA beam current are proposed. The superconducting cavity is one of the key components and applied for the injector part and the main acceleration part. At the injector part, three 2-cell cavities accelerate the electron beams up to 5-10 MeV. Each cavity has two input couplers and fire HOM couplers. Large beam loading, however, requires the handling of more than 100 kW for each input coupler. The main linac part consists of 9-cell cavities, whose main issue is a suppression of the Beam Breakup instability. Strong HOM damping is realized by optimized cell shapes and large diameter of beampipes. Tests of these cavities and components have been actively performed. The design of cryomodules has been also under way. These statuses are reported.
