Yamamoto Y.

Paper	Title	Page
MO405	Construction and Commissioning of KEKB Superconducting Crab Cavities	63
	K. Hosoyama, K. Hara, A. Honma, A. Kabe, Y. Kojima, Y. Morita, H. Nakai, K. Nakanishi, K. Akai, K. Ebihara, T. Furuya, S. Mitsunobu, M. Ono, Y. Yamamoto KEK K. Okubo, K. Sennyu, H. Hara, T. Yanagisawa MHI Kobe
	The superconducting crab cavities for KEKB were constructed and installed into KEKB electron-positron collider in January 2007. After cool-down of the crab cavities, the commissioning of the crab cavities started in February 2007 and continued until end of June. Effective head on collision of electron and positron has been achieved successfully for the first time during this spring operation of the KEKB. A luminosity of above 10^34/cm2/sec could be obtained at high beam currents operation (1.3A in the low energy positron and 0.7A in high energy electron).
	Slides(PDF)
TUP23	Status of KEKB Superconducting Cavities	170
	S. Mitsunobu, T. Furuya, S. Takano, Y. Yamamoto KEK
	KEKB HER(high Energy ring) operating stably by using 8 superconducting cavities. The Maximum current is more than 1.4 A, so the HOM(higher order mode) power of each cavity is as high as 16 kW, and the beam power of 400kW is handled by each cavity. To increase beam current more than 2 A and future Super KEKB project, HOM dampers of 3 mm thick ferrite have been constructed to test higher absorbing power of more than 40 kW. The construction of input coupler for 500 kW operation power is also starting with new industry TiNOx coating.
TUP60	High Power Input Couplers for the STF Baseline Cavity System at KEK	270
	E. Kako, H. Hayano, S. Noguchi, T. Shishido, K. Watanabe, Y. Yamamoto KEK
	An input coupler, which consists of a cold coupler and a warm coupler, has two Tristan-type coaxial disk rf windows. There is no tuning mechanism for varying coupling for simplicity and cost reduction. Fabrication of four input couplers was completed, and the rf measurements with low rf power were carried out. The input couplers were assembled with coupling waveguides and doorknob-type transitions, and they were installed in a high power rf system. High power tests of four input couplers were carried out in the test stand with a 5 MW pulsed klystron. Rf processing up to 1.0 MW in a 1.5 msec and 5 Hz operation (1.9 MW in a short pulse) was successfully performed without any troubles. One cavity for the STF Phase-0.5 was assembled with an input coupler and a tuning system, and the cavity was installed in one of the 6m-cryomodules. Rf processing of the input coupler in the cryomodule was carried out at room temperature up to 250 kW in a 1.5 msec step pulse and 5 Hz operation. First cool-down and high power test of the cryomodule had been started in October, 2007.
WEP10	Vertical test results on the STF baseline 9-cell cavities at KEK	453
	E. Kako, H. Hayano, S. Noguchi, T. Shishido, K. Umemori, K. Watanabe, Y. Yamamoto KEK H. Sakai, K. Shinoe ISSP, Univ.  of Tokyo S. I. Moon POSTECH Q. J. Xu IHEP, CAS
	The STF-Baseline superconducting cavity system, which includes four TESLA-type 9-cell cavities, input couplers and frequency tuners, has been developed for the future ILC project. A main improvement in the cavity system is a very stiff design in a He vessel and a cavity tuning system, which can relax a cavity deformation due to Lorentz force. Making clear the performance level of four 9-cell cavities, which were fabricated by a Japanese company and were prepared by existent infrastructures at KEK, is the most important purpose in the whole vertical test. Total 14 vertical tests on four 9-cell cavities were carried out repeatedly. The obtained Eacc,max in the final performance was 29.4 MV/m in the #2 cavity, and the others are 20.8, 20.5 and 20.2 MV/m, where the Qo values higher than 1x1010 was achieved in all cavities. Peculiar phenomena, like increasing of Qo values with higher Eacc or very slow degradation of Qo values, were observed in the vertical tests. Summary of the vertical test results on four 9-cell cavities is described in this paper.
WEP13	Cavity diagnostic system for the vertical test of the baseline SC cavity in KEK-STF	464
	Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Umemori, K. Watanabe KEK H. Sakai, K. Shinoe ISSP, Univ.  of Tokyo S. I. Moon POSTECH Q. J. Xu IHEP, CAS
	Four STF-Baseline superconducting cavities were fabricated from 2005 to 2006. They were named BL1, 2, 3 and 4. The feature is that these cavities have the stiffer structure than TESLA cavity. From Feb/2006 to Feb/2007, the vertical tests were done totally 14 times at KEK. These cavities were re-processed and measured repeatedly. The surface treatment processes are composed of Centrifugal Barrel Polish (CBP), Electro-Polish (EP) and High Pressure Rinsing (HPR). And, HF or H2O2 rinsing were added as the additional process later. In the vertical tests, a monitoring system was introduced to search the heating spot on the equator and to check the radiation level around the cavity. It is composed of the carbon resistors and the PIN photo diodes. They were attached on the equator of each cell every 90 degree, a few resistors around the HOM couplers and a few diodes on the top and bottom flanges of the cavity. MX-100 (YOKOGAWA) for the carbon resistors and NR-1000 (KEYENCE) for the PIN photo diodes are used as the data logger. The sampling time is 100 or 200msec. The heating spot was successfully observed during the test. The appearance of that on the equator was coincident with the quench of the cavity. On the other hand, the diodes were useful for checking the presence or absence of the field emission and they also were useful for monitoring the radiation level during the RF processing. The mapping display was introduced to identify the location. Consequently, it is conceivable that the quality of the electron beam welding was somewhat poor, when the dumbbells were connected.
WEP23	Fabrication and test of the 500 MHz SC modules for the BEPCII	503
	Z. Q. Li, G. W. Wang, W. M. Pan, Y. Sun, S. P. Li, Q. Ma IHEP, CAS T. Furuya, S. Mitsunobu, K. Akai, Y. Yamamoto KEK Y. Kijima, M. Arakawa, Y. Okada MELCO, Mitsubishi Electric Co.
	Two KEKB type HOM damped SC cavities were constructed during past three years. These SC modules were re-designed to meet the RF frequency of 500 MHz of the BEPCII, the upgrade project of the Beijing Electron and Positron Collider, and have already been operated smoothly. It is a product of the successful collaboration among Mitsubishi Electric Co. (MELCO), KEK and IHEP of China. The cavity modules were fabricated and surface-treated by MELCO with the help and support of KEK. The vertical test of niobium cell, and the high power test of couplers and dampers were carried out in KEK, and the final acceptance tests were done in IHEP.
WEP27	Horizontal tests for crab cavities in KEKB	520
	Y. Yamamoto, K. Akai, K. Ebihara, T. Furuya, K. Hara, T. Honma, K. Hosoyama, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Ono KEK H. Hara, K. Sennyu, T. Yanagisawa MHI Kobe T. Kanekiyo HITACHI T. Nakazato JASRI
	Two Crab cavities were fabricated at KEK in 2006. After the completion of the assembly, a horizontal test is normally carried out for a superconducting cavity in KEK. The horizontal test is an overall test for the cavity without a beam. Both cavities achieved above an operational kick voltage of 1.4MV. Although the HER (High Energy Ring for electron) Crab cavity had no trouble, the LER (Low Energy Ring for positron) had a trouble of tuner operation. Due to the limited time, both cavities were installed into the tunnel at the beginning of Jan. in 2007. After the beam commissioning, it was found that this problem was not so much significant for the operation. The LER Crab cavity is being operated above 1A at present.
WEP50	Input Couplers for KEKB Crab Cavities	606
	K. Nakanishi, K. Hara, K. Hosoyama, Y. Kojima, S. Mitsunobu, Y. Yamamoto KEK K. Okihira, K. Sennyu MHI Kobe T. Tanaka Broad Wireless Corporation
	The RF input couplers for KEKB crab cavities were designed, fabricated and installed. The input coupler is shown in figure 1. The RF input coupler has a ceramic RF window and a T-stub structure. The shape of T-stub structure and length of the probe were decided using RF simulation program. The RF window and the doorknob translator may cause some reflection. The RF windows for superconducting accelerator cavities for KEKB (KEKB-SCC) and the doorknob translators for TRISTAN were used. According to the procedure of assembling the RF input coupler for KEKB-SCC, they were rinsed and assembled. Aging was done individually. After that, they were installed into cryostats for crab cavities. These cryostats were installed to KEKB and have been working. Three input couplers, which are included for prototype cryostat, were prepared.
WEP55	Beam-induced RF modes and RF power in the crab cavity for KEKB	623
	Y. Morita, K. Akai, T. Furuya, T. Honma, K. Hosoyama, S. Mitsunobu, Y. Yamamoto KEK
	Two superconducting crab cavities were installed in the KEKB rings and the crab crossing operation started early in 2007. Each crab cavity has two ferrite RF absorbers (HOM dampers), which were developed for the superconducting accelerating cavities of KEKB. One is attached in a beam pipe and the other is attached in a coaxial coupler. The dampers have to damp not only the higher order modes but the lower order modes, since the crabbing mode is not the lowest mode. These parasitic modes should be sufficiently damped for the high current operation. Several antennas were set on the beam pipe to monitor beam-induced RF modes. The most dangerous mode, TM010-like mode, was detected in the RF spectrum. However, its Q-factor was below the instability criterion and consistent with the measured value at the horizontal test before installation. No dangerous modes with high Q-factor were observed in the beam-induced RF spectrum. KEKB stored the beam currents of 1.7A and 1.35 A in the low energy positron ring and the high energy electron ring, respectively. No serious beam instabilities caused by the parasitic modes were observed and the HOM dampers successfully absorbed the beam-induced RF power up to 12 kW. We will present HOM dampers used for the KEKB crab cavities, and measurement results of the beam-induced RF modes and RF power. Simulation results for the beam-induced RF power will be also discussed.
WEP57	Commissioning and Beam Operation of KEKB Crab RF System	632
	K. Akai, K. Ebihara, T. Furuya, K. Hara, T. Honma, K. Hosoyama, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Ono, Y. Yamamoto KEK
	Two heavily damped superconducting crab cavities were installed in KEKB, one for the low-energy positron ring (LER) and the other for the high-energy electron ring (HER). After adjusting the RF system and conditioning the cavities, beam operation started in February 2007. During the four-and-a-half-month operation until summer shut down, the crab cavities have been operating very stably to conduct crab crossing experiment. They have shown excellent performance with high stored beam currents up to 1.7 A in the LER and 1.35 A in the HER. It was also demonstrated that the crab crossing works at a high luminosity over 10^34/cm2s that exceeds the KEKB design luminosity. Machine tuning with crab crossing will continue for achieving a big boost in luminosity, as expected from beam-beam simulations. In this paper, we present an RF system for the crab cavities, commissioning process, performance of the crab cavities with high-current beams, and beam-loading-related issues on the crabbing mode.