Grant-in-Aid for Scientific Research (B)
|Allocation Type||Single-year Grants |
|Research Institution||KEK, High Energy Accelerator Research Organization |
FURUYA Takaaki KEK, High Energy Accelerator Research Organization Accelerator Lab., Associate Professor, 加速器研究施設, 助教授 (70156975)
MITSUNOBU Shinii KEK, High Energy Accelerator Lab., Professor, 加速器研究施設, 教授 (50100821)
EZURA Eizi KEK, High Energy Accelerator Lab., Professor, 加速器研究施設, 教授 (60044749)
KUROKAWA Shin-ichi KEK, High Energy Accelerator Lab., Professor, 加速器研究施設, 教授 (90044776)
AKAI Kazunori KEK, High Energy Accelerator Lab., Associate Professor, 加速器研究施設, 助教授 (10184061)
FUKUMA Hitoshi KEK, High Energy Accelerator Lab., Associate Professor, 加速器研究施設, 助教授 (40150007)
|Project Period (FY)
2000 – 2002
Completed (Fiscal Year 2002)
|Budget Amount *help
¥15,000,000 (Direct Cost: ¥15,000,000)
Fiscal Year 2002: ¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2001: ¥6,000,000 (Direct Cost: ¥6,000,000)
Fiscal Year 2000: ¥6,100,000 (Direct Cost: ¥6,100,000)
|Keywords||superconducting / cavities / KEKB / collider / HOM / ferrite / coupler / synchrotron / 蓄積電流 / 電流値 / 高周波高電力試験装置 / Bファクトリー加速器 / 超伝導破壊 / ビーム不安定性|
Superconducting (SC) RF cavities provide a high accelerating field gradientin constant wave operation, which is several times higher than that achieved by conventional normal conducting (NC) cavities. This superior performance has a clear advantage in the application to high intensity electron (positron) storage rings, where the less number of cavities is desired so as to reduce the total higher order mode (HOM) impedance and to avoid beam instabilities.
KEKB is an electron and positron collider for B meson physics, in which extreme high intensity beams of 1.1 A and 2.6 A are accumulated and collided each other to achieve a luminosity of 10^<34> cm^<-2>S^<-1>. To keep such a high intensity beam, new SC cavities based on a HOM damping scheme using ferrite absorbers have been developed and commissioned in the electron ring (HER). The mission of this research projefct is to make clear the performance of the SC cavities and also to establish the operation technology of SC cavities in high c
The important results will be summarized as follows.
1) During this research project, the beam intensity has gradually been improved and finally reached the full current of 1.1 A. This result demonstrates that the new SC cavity with ferrite absorbers is quite useful as an RF cavity for high intensity storage accelerators in various fields.
2) The cavity has a strong interaction with the beam in such a high intensity operation. As a result, just a small movement of the beam disturbs the cavity voltage and causes a trip of the cavities. Tfte analysis study of all the trips showed clearly that 90 % of die trips were caused by the instabilities and the loss of the beam. On the other hand, the SC cavity itself was quite stable, and tripped once or twice per month that was caused by discharging.
3) The study of an input coupler demonstrated that multipacting discharging happened on the wall of outer conductor, which was in agreement with a simulation result under a DC bias voltage between the conductors.
4) RF power absorbed by ferrite dampers has been measured and analyzed under various beam intensity and bunch configurations. The results show that the power caused by wide-range HOMs is dominant, and that the ferrite dampers sufficiently damps the Q of all the HOMs in th cavity so as not to introduce the beam instabilities. Because of an operation mode of higher bunch current, absorbed power has already reached two times higher than the design level.
Besides these results, the study of a cavity shape of 500MHz gave a solution of the SC cavity in synchrotron light source rings. As a result this research project has made clear the feasibility of SC cavities in high current use. Less