KEK, Ibaraki
The superconducting RF test facility (STF) in KEK is aiming to promote R&D of superconducting linear accelerator to be used in the International Linear Collider (ILC). The phass-1 STF construction was completed in 2008. They included high power RF operation of four 1.3GHz SC cavities in the short-cryostat and infrastructure construction to support the superconducting accelerator module fabrication. The new phase, STF phase-2 plan is aiming to realize ILC RF unit construction and demonstration its performance together with preparation and study of industrial production. We will construct 12m-long ILC-RDR cryomodules including total 26 superconducting cavities and 1 SC quadrupole magnet. It has also ILC structure electron beam generated by a photo-cathode RF gun and conditioned by following two SC capture cavities. Phase-2 also includes the compact bright X-ray source development referred as ‘quantum beam project’ which is founded by the MEXT as an intermediate milestone. The industrialization of cavity fabrication and cost reduction is also one of the targets of this phase-2 construction. This paper summarized the STF phass-1 results and conclusion, and plans of phase-2.
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
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.
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.