Operation status of the J-PARC ion source

A cesium-free H^- ion source driven with a LaB₆-filament is being operated at the Japan Proton Accelerator Research Complex (J-PARC) without any serious trouble since the restoration from the halt due to the March 2011 earthquake. The H^- ion current extracted from the ion source has been restrained to approximately 19 mA for the 50-days continuous operation without any lifetime problem on the filament. During the operation period from Jan. 5 to Feb. 22 2013 (scheduled operation time was 1200h), the extracted beam current from the ion source was increased to 22 mA in order to increase the beam power delivered to the J-PARC experimental halls. The filament current necessary for the constant arc-power, after it reached the maximum value at around 200h from the start of the operation, usually almost linearly decreases as time. The decreasing speed of the filament current changed from about 0.02A/h to about 0.6A/h at 1108h from the start of the operation. After 10h from the observation of the high decreasing speed, the filament was broken. By the unusual quick maintenance, in which only the end-plate with a Lab₆-filament instead of the whole ion source chamber form the end plate to the plasma electrode was changed, the beam operation was restarted with beam stop time of about 8h. The parameters measured during the LaB₆-filament braking process and the prediction method of the LaB₆-filament life-time are presented in this paper. Also, the ion source operation more than 30 mA for 8 days and the status of the front-end test stand consisting of the ion source and the 50 mA-RFQ for the J-PARC upgrade to 1 MW are presented. (author)