The Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven Hˉ ion source has successfully operated with a 57 mA & 50 keV beam for a 50 mA beam at the exit of the J-PARC 400 MeV LINAC for about one year from October 2018. It is also producing a 72 mA beam for the J-PARC LINAC 60 mA operation studies. The world's highest class intensity beam with transverse emittances suitable for RFQs of high energy Hˉ ion LINACs is produced with several unique measures, such as, slight water molecules addition into the hydrogen plasma, the low temperature (about 70 ºC) operation of the 45º-tapered plasma electrode with a 16-mm thickness, a 30-MHz CW plasma igniter, the macro-pulse chopping with a rapid rising time by the Hˉ ion energy modulation being below the RFQ longitudinal acceptance, and so on [1, 2]. Its stable 8 hours 100 mA beam operation was demonstrated in a test stand by increasing the terminal voltage from 50 kV to 62 kV . In this paper, these measures essential for a 100 mA operation are reviewed and explained. The recent transverse emittance improvements with the shortest beam extractor are also presented. The horizontal/vertical 95 % beam normalized rms emittances of a 100 mA & 62 keV beam were improved by about 8 % form 0.262/0.3 ·mm·mrad to 0.242/0.273 ·mm·mrad with the thinnest extraction electrode (1.5 mm thinner) and the ground electrode 1.5 mm extended to upper stream. The emittances of a 66 mA & 50 keV beam and a 80 mA & 56 keV beam ere also improved about 8 % with the shortest beam extractor. About 94 % of each beam with the intensity of 66, 80 or 100 mA is distributed in the transverse phase planes inside of the normalized 1.5 ·mm·mrad ellipse, the water bag distribution in which is commonly used to design RFQs of high energy LINACs.
References and Acknowledgment
 A. Ueno , K. Ohkoshi, K. Ikegami, A. Takagi, K. Shinto, and H. Oguri, AIP Conference Proceedings 2052, 050003
 K. Shinto, K. Ohkoshi, T. Shibata, K. Nanmo, K. Ikegami, A. Takagi, Y. Namekawa, A. Ueno, and H. Oguri, AIP
Conference Proceedings 2052, 050002 (2018).
 A. Ueno, New J. Phys., 19, 015004 (2017).
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