Shibata, T. Ikegami, K. Liu, Y. Miura, A. Naito, F. Nanmo, K. Oguri, H. Ohkoshi, K. Otani, M. Shinto, K. Takagi, A. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-TUPO079 English 519-521 TUPO079 rfq MMI linac emittance solenoid Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-TUPO079 http://jacow.org/linac2018/papers/tupo079.pdf Negative hydrogen ion (H⁻) beam dynamics in J-PARC Low Energy Beam Transport (LEBT) has been investigated by numerical modeling which calculates particle transport with effect of space charge and collision processes. Understandings of H⁻ beam transport in LEBT is important for high transmission rate from Ion Source (IS) to Radio Frequency Quadrupole (RFQ) in J-PARC in higher beam current in future. In 2017, 45 mA beam current of H⁻ has been extracted from IS in J-PARC user operation which has been increased from 30 mA in last 2 years. The beam current is planned to be increased to 50 mA in the next upgrade. As the beam current increase, IS/LEBT commissioning becomes more difficult because of the higher space charge (SC). Especially in J-PARC, vacuum pressure is around 10⁻⁵ Pa by 15 mmf orifice located in the center of LEBT. The orifice prevents residual gas injection from IS to LEBT/RFQ and thus produces stronger SC effect. In the presentation, numerical results are compared with actual results from J-PARC Linac beam commissioning. A comparison of the results shows that location of the 15 mmf orifice results in two peaks of RFQ transmission rate against SOL currents.