J-PARC MR horizontal exciter test for transversal noise application

Transversal noise用のJ-PARC MR horizontal exciter試験

Schnase, A.; 佐藤 健一郎*; 冨澤 正人*; 外山 毅*; 魚田 雅彦*; 吉井 正人*

Schnase, A.; Sato, Kenichiro*; Tomizawa, Masahito*; Toyama, Takeshi*; Uota, Masahiko*; Yoshii, Masahito*

To improve the duty factor of the proton beam, extracted by slow extraction to the Hadron hall, we applied transversal noise using the existing horizontal exciter in J-PARC Main-Ring (MR). For noise center frequencies of 5 and 7.5 MHz, operation was possible; however in a band above 6 MHz, we noticed that the pressure in the vacuum chamber increased near the exciter structure. Higher noise center frequencies seem to improve the duty factor seen by the Hadron experiment, therefore we tried frequencies near 30, 25, and 20 MHz. Problems with vacuum pressure rise prevented longer time operation. Therefore, we mapped safe and unsafe operation points as function of frequency and amplifier output power. We found a safe operation area for the extraction beam time planned for the April 2011 run, however due to the big Tohoku earthquake the beam time was postponed. Improved noise signals, where the amplitude distribution is independent of noise bandwidth have been created and we drove the exciter with them to confirm the feasibility. We confirmed that a solenoid around the exciter improves the multi-pactor issues. With a solenoid current of 2 A, the frequency range from 1 to 35 MHz is free from vacuum problem for the whole output power range of the used 1 kW RF transistor-amplifiers.