KEK, Ibaraki
The inspection of inner surface of the superconducting rf cavities is essential in achieving high accelerating gradient. The high resolution camera system developed by Kyoto-KEK collaboration is a good tool to survey defect locations and to analyze a defect shapes in the inner surface of the cavities for boost accelerating gradient yield of 1.3 GHz superconducting 9-cell cavities. The heights or depths of observed surface defects can be estimated by examining the patterns of shades which are created by the lighting system which allows to illuminate the cavity surfaces with varying light angles by selecting a series of strip-line illuminators in steps. A good correlation has been so far observed between the hot spots localized by thermometry measurements in the vertical test and the positions of surface defects found by this system. The cavity surface study with this camera system started in FY2008, and so far, the ACCEL, ZANON, AES and MHI cavities have been examined in KEK, DESY and FNAL. Other camera systems for cavity inspection are developed in J-Lab, LosAlamos and Cornell etc. The optical inspection methods and result will be presented.
KEK, Ibaraki
The Cryomodule test was finished at KEK-STF (Superconducting rf Test Facility) on December/2008. The four 9-cell cavities (MHI#1-#4) were installed into it and measured around 2K for totally a few months. MHI#2 cavity achieved around 32 MV/m (29 MV/m at vertical test) with the feed-back and the others around 20 MV/m. During the high power test with a klystron, the Lorenz detuning was observed and measured for these cavities. Generally, the Lorentz detuning is almost compensated by setting the offset of the cavity frequency in advance (pre-detuning) and driving the Piezo actuator with an optimum condition. The optimum driving condition for Piezo actuator was obtained, which controlled the detuning frequency of the cavity within ±30Hz. MHI#2 cavity was stably operated around 30 MV/m with Piezo compensation for several hours. During this operation, the r.m.s. of the detuning frequency was about 5Hz and the peak-to-peak of the gradient at the flat-top was below 0.1%. The “Two Modes Model” was devised to offer the physics explanation for the observational results of the Lorentz detuning. It was found that this model is valid, since it reproduces the real data.
KEK, Ibaraki
A 6-m cryomodule, which includes for Tesla-like 9-cell cavities, was assembled and tested at 2 K in 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 mechanical and a piezo tuner. One of the cavities achieved a stable pulsed operation at 32 MV/m higher than the target operating gradient for ILC. Compensation of Lorentz force detuning at 31 MV/m was successfully demonstrated by using piezo tuner and pre-detuning.
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.
Kyoto ICR, Uji, Kyoto
KEK, Ibaraki
Some nondestructive inspection systems are investigated for SRF cavities. It includes improvements of optical inspection, development of temperature mapping, eddy current testing, etc. All these are heading for high resolution feature. These efforts will be presented.
KEK, Ibaraki
Development of a SC Cavity Injector Cryomodule for the compact ERL (Energy-Recovery Linac) is being continued at KEK since 2006. An injector for cERL is required to accelerate a CW electron beam of 100mA to 10MeV. In this application, critical hardware components are not cavities but RF input couplers and HOM dampers. Several combinations of number of cavity and cells per cavity were examined, and a three 2-cell cavity system was chosen for cERL. Each cavity is drove by two input couplers to reduce required power handling capacity and also to compensate coupler kick. HOM coupler scheme was chosen for HOM damping, and 4 or 5 HOM couplers are put on beam pipes of each cavity. Because of simplicity cavities are cooled by jacket scheme. Two proto-type 2-cell cavities (#01 and #02) and two input couplers for compact ERL were fabricated in 2007 and 2008. The vertical test of #01 cavity with HOM pickup probe was carried out at April 2009. The result of vertical test and schedule will be reported.
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
LAL, Orsay
IHEP Beiing, Beijing
High power tests of the STF cryomodule including four MHI cavities and STF-1 input couplers were carried out at KEK. The maximum input rf power of 360 kW was successfully transfered to the cavity operated at high gradients at 2 K. After the cryomodule tests, the conditioning test of the coupler at room temperature was carried out, and rf processing up to 650 kW (1.5 ms and 5 Hz) was achieved. TTF-V couplers were shipped from LAL to KEK, and the high power test was carried out at KEK-STF. Rf processing up to 2 MW in the short pulse of 400 us (5 Hz) and 1 MW in the long pulse of 1.5 ms (5Hz) was demonstrated. The results of the coupler processing at KEK will be reproted in this talk.
JLAB, Newport News, Virginia
KEK, Ibaraki
GUAS/AS, Ibaraki
We report the results of surface characterization of niobium samples electropolished together with single-cell niobium cavities. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe respectively. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive x-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.
KEK, Ibaraki
CEA, Gif-sur-Yvette
JLAB, Newport News, Virginia
GUAS/AS, Ibaraki
The Electro-Polishing (EP) process is the best candidate of final surface treatment for the production of ILC cavities. Nevertheless, the broad distribution of the gradient caused by field emitters in cavities is sitll a serious problem for the EP process. A candidate source of field emitter is the sulfur component which is produced in the EP process and remains the inner-surface of cavities. We studied the effect of Ethanole- and degreaser-rinse processes after the EP process by a unique method. Moreover, we tried to test the sponge cleaning as the post-EP process to remove the field emitter inside the cavcity. This article describe the results of series tests of the post-EP process at KEK.
KEK, Ibaraki
JLAB, Newport News, Virginia
GUAS/AS, Ibaraki
In this article, two subjects would be described. the first subject is on the production of stains on the surface of Nb sample plates in Electro-polishing (EP) process and the second subject is on the development of defects/pits in the EP process on the surface of a Nb sample plate. Recently, some 9-cell cavities were treated with new EP acid at KEK and the performance of these cavities were limited by heavy field emissions. On the inside surface of these cavities, brown stains were observed. We made an effort to reproduce the brown stains on Nb sample plates with an EP setup in laboratory with varying the concentration of Nibium in the EP acid. We found that the brown stains would appear only when processed with new EP acid. In the second subject, we made artificial pits on the surface of a Nb-sample plate and observed the development of the pits after each step of 30um-EP process where 120um was removed in total by the EP process. This article describes these series EP-tests with Nb sample plates at KEK.
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.