120mA operation of J-PARC cesiated RF-driven H~- ion source

摘要

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H~- ion source (IS) has been stably operated for about eight years by using an internal-RF-antenna developed at the Spallation Neutron Source (SNS). From Sep. 2018, the J-PARC 400MeV LINAC has been steadily operated with the design H~- ion beam intensity (I_H~- ) of 50 mA, when an about 60mA beam is injected from the IS. At each end of about 3 months J-PARC operation, the IS supplies a 52.5 keV 72mA beam for the LINAC 60mA acceleration. The IS superior emittances predicted in a test-stand were proven by the high RFQ acceleration efficiency of 94.3 (I_(H~-RFQ) = 67.9 mA). The high intensity beam with transverse emittances suitable for the RFQ is produced with several unique measures, such as, slight water molecules addition into hydrogen plasma, the low temperature (about 70°C) operation of 45°-tapered 16-mm thick plasma electrode with the precise cesium (Cs) density control, the impurity elimination in the hydrogen plasma along with the filter-field optimization, the continuous-wave igniter plasma driven with a 42-W 30-MHz RF, and so on. The 120mA operation results of the IS in the test-stand are presented in this paper. A 69.9 keV 120mA H~- ion beam, about 107.8mA of which was inside the transverse emittances used for a common RFQ design, was stably operated with a duty factor of 4 (1 ms × 40 Hz). The IS is the benchmark one for the next generation high energy H~- LINACs aiming for 100mA class intensity.