Pre-conditioning procedure suitable for internal-RF-antenna of J-PARC RF-driven H− ion source

Abstract

The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H(-) ion source has been successfully operated for about 1 yr. By the world brightest level beam, the J-PARC design beam power of 1 MW was successfully demonstrated. Although no internal-RF-antenna failure, except for the once caused by an excess cesium due to a misoperation, occurred in the operation, many antennas failed in pre-conditionings for the first hundred days. The antenna failure rate was drastically decreased by using an antenna with coating thicker than a standard value and the pre-conditioning procedure repeating 15 min 25 kW RF-power operation and impurity-gas evacuation a few times, before the full power (50 kW) operation.

Record performance of and extraction studies with the Spallation Neutron Source H− injector

“…However, when scaled with the 12 min cesiation time, <0.6 mg/A·h of H -ions is a more likely amount. This is several orders of magnitude less than reported for similar [20,25] or other [31,32] sources. This means that the SNS ion source delivers at least 1200 H -ions per injected Cs atom, or more likely ~10 4 H -ions per injected Cs atom, and that usually without noticeable decay.…”

“…J-PARC's lower RF power and its high consumption of Cs explain their slightly different findings, including their preference of thicker coatings [25].…”

Cesiated surface H− ion source: optimization studies

“…High-power and high-duty conditioning with cesium-abundant plasma for smaller emittances During the commissioning of a brand-new PCH, several RF-antennas are inevitably broken, probably due to the impurity elements sputtered from the PCH inner surface. The preconditioning procedure [13] has been applied to each RF-antenna. After failure of three RF-antennas, #7′ PCH with ventilation pathways for O-ring grooves successfully produces the 66 mA beam with the superior emittance shown in figure 13.…”

“…Similar emittances were measured two times for 66 mA beams produced using #2 PCH without ventilation pathways. All three degraded beams were produced after the preconditioning procedure [13], in which T PE was kept at the high value of 300°C for eight hours in the initial stage of the procedure, and a 24 h usual beam operation. The elimination of impurity elements with the high T PE is essential to reproduce the beams with similar emittances.…”

“…The latter requirements have been satisfied using the superior internal RF-antenna developed at the Spallation Neutron Source (SNS) [3]. Several measures have been implemented to increase the beam brightness [4][5][6][7][8][9][10][11][12][13][14][15][16]. Almost all effective measures were found, in persistent experiments, to reproduce the accidentally produced H − ion beam with the record-breaking smallest emittances.…”