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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.

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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.

A cesium-free H À ion source driven by a LaB 6 filament is being operated for the beam commissioning of the accelerators at Japan Proton Accelerator Research Complex (J-PARC). The beam commissioning started in November 2006. As of June 2008, there have been 17 beam commissioning runs. The duration of each run was approximately 4-5 weeks. In these runs, the ion source has succeeded in providing beam to the J-PARC accelerators for 2720 hours. The interruption time due to the failure of the ion source is only approximately 50 hours. The availability of the ion source is calculated to be 98%. Since the fluctuation of the beam current is small, tuning the beam current once a day is sufficient to maintain the beam current within the error of a few percent. Recently, the ion source succeeded in producing the beam current of 36 mA with a flattop pulse width of 500 s and a repetition rate of 25 Hz as required for the first stage of J-PARC.