Interesting experimental results in Japan Proton Accelerator Research Complex H− ion-source development (invited)

Abstract

The following interesting experimental results observed in Japan Proton Accelerator Research Complex (J-PARC) H(-) ion-source developments are reviewed. It was proven that almost all of H(-) ions were produced with surface reactions in cesium (Cs)-free J-PARC H(-) ion-sources. The world's most intense class H(-) ion current of 38 mA in Cs-free ion sources for a high-energy linac was attained by an optimal shape and high temperature of the plasma electrode (PE), usage of a lanthanum hexaboride (LaB(6)) filament, and a newly devised high-power constant-current pulsed-arc power supply indispensable for it. It was also proven that the H(-) ion current could be increased to more than 40 mA by optimizing LaB(6)-filament shape. The surface elemental analysis of the PE after operation with a LaB(6)-filament showed that it was coated by boron (B) 95.5%, lanthanum (La) 2.5%, and oxygen (O) 1.9%. The H(-) ion current decreased by about 20% when a tungsten (W) filament was used instead of a LaB(6)-filament. The H(-) ion current could not be increased by seeding cesium (Cs) if the LaB(6)-filament was used. On the other hand, it was increased to more than 70 mA with much lower arc current of 150 A if Cs was seeded when a W-filament was used.

Operation Status of the J-PARC Ion Source

“…Although the ion source almost satisfies the J-PARC first-stage requirements for an H -ion current, it was proven that the current was not increased by using cesium [4]. In order to satisfy the J-PARC second-stage requirements for an H -ion beam current of 60 mA, a cesiated RF-driven source using an internal antenna is being developed by modifying the J-PARC prototype source [5].…”

Rod-filter-field optimization of the J-PARC RF-driven H− ion source

“…This phenomenon is understandable as the unstableness of the Cs condition of the PE surface due to the insufficient RFF. The CG around 0.3~0.4mm, which should be the optimum to produce the I H -more than 70mA with the P RFN lower than 40kW with sufficient RFF for the stable operation, was not investigated, since the  rmsnx and  rmsny with T PE =200C were rather larger than those for an PCH made of oxygenfree-copper (OFC) with T PE =120C [4] and the sparking rate on the high-voltage gaps was not negligible (several times for 8h operation) as described in reference [3]. The operation with T PE lower than 120C was investigated in detail at first by using #2 PCH, in which the RFMs with the same cross-section (5mm10mm) used in the OFC PCH could be installed, since there was some possibility of that the OFC PCH's lower emittances were produced not only by the low T PE but also by the RFF shape.…”

“…The J-PARC new source was developed by using an internal-antenna developed at the spallation neutron source (SNS) [2], based upon J-PARC prototype sources driven with a LaB 6 or two tungsten (W) filaments [3], in order to satisfy the requirements of an H¯ ion beam of 60mA within normalized emittances of 1.5mm•mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500s25Hz) and a life-time of longer than 1month [4,5,6,7,8]. By using the experimental set-up of an ionsource test-stand (IS-TS) described in reference [9], the H¯ ion beam performances were measured with various rodfilter-magnets (RFMs) to find out the optimum rod-filter-field (RFF) maximizing the H¯ ion beam intensity (I H -) with a net 2MHz-RF power (P RFN ) lower than 50kW, minimizing the horizontal and vertical rms normalized emittances ( rmsnx and  rmsny ) and making the operation easy.…”

Maintenance and operation procedure, and feedback controls of the J-PARC RF-driven H− ion source

“…(1) The 45-tapered PE with the thickness of 16mm, which increases the I H -by about 1.5 times [3]. (2) The AMFC around the beam hole of the PE, which increases the I H -by about 1.1 times [8].…”

“…The J-PARC new source was developed by using an internal-antenna developed at the spallation neutron source (SNS) [2], based upon J-PARC prototype sources driven with a LaB 6 or two tungsten (W) filaments [3], in order to satisfy the requirements of an H¯ ion beam of 60mA within normalized emittances of 1.5mm•mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500s25Hz) and a life-time of longer than 1month [4,5,6,7,8]. The 1.5mm•mrad is the 100% value of a water-bag distribution emittance with the root-mean-square (rms) normalized value of 0.25mm•mrad, which is used in the benchmark beam simulation of many of RFQs for high-energy H¯ linacs.…”