Ueno Akira
J-PARC Center, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195, Japan.
Rev Sci Instrum. 2020 Mar 1;91(3):033312. doi: 10.1063/1.5126365.
In July 2019, a design beam of 8.3 × 10 protons/pulse, whose 25 Hz operation produced the design beam power of 1 MW, was accelerated for 10.5 h by using the J-PARC 3 GeV rapid cycling synchrotron. During the operation, a J-PARC H ion source and a 400 MeV linear accelerator (LINAC) were operated with the design beam duty factor (BDF) of 1.25% (0.5 ms × 25 Hz) and ejected beam intensities of 58 mA and 50 mA, respectively. Furthermore, as expected from the transverse emittances measured in an H ion source test-stand, they were successfully operated with the BDF of 1.5% (0.6 ms × 25 Hz) and ejected beam intensities of 72 mA and 60 mA, respectively. In the operation, the beam pulse accelerated by the J-PARC radio-frequency quadrupole LINAC (RFQ) had a rapid rise-time of about 10 µs and an excellent flatness with a slow variation of ±0.2%. A flat beam pulse was produced by the predicted 100% space-charge neutralization (SCN) in the upstream half of the J-PARC low-energy beam transport (LEBT) with a vacuum pressure of 3.6 × 10 Pa and the unpredicted high and almost constant SCN of about 69% in the downstream half of the LEBT with a vacuum pressure of 2.8 × 10 Pa. The rapid rise-time was produced by the preformed 100% SCN with a preceding 100 µs 40 keV beam, which was not accelerated by the RFQ due to the low energy outside the RFQ acceptance. In the test-stand operated with the terminal voltage of 62 kV and BDF of 5% (1 ms × 50 Hz), the transverse emittances of a 100-mA beam were also measured to be suitable for the RFQs of high energy LINACs. A 100-mA high energy and high duty factor LINAC could be realized with this source since the transverse emittances were further improved by about 8% with the shortest beam extractor in the test-stand.
2019年7月，利用日本质子加速器研究中心（J-PARC）的3 GeV快速循环同步加速器，加速了一束设计束流为每脉冲8.3×10个质子，其25 Hz的运行产生了1 MW的设计束流功率，加速时间为10.5小时。在运行期间，J-PARC H离子源和一台400 MeV直线加速器（LINAC）以1.25%（0.5 ms×25 Hz）的设计束流占空比（BDF）运行，引出束流强度分别为58 mA和50 mA。此外，正如在H离子源试验台上测量的横向发射度所预期的那样，它们成功地以1.5%（0.6 ms×25 Hz）的BDF运行，引出束流强度分别为72 mA和60 mA。在运行中，由J-PARC射频四极直线加速器（RFQ）加速的束脉冲上升时间约为10 µs，平坦度极佳，缓慢变化±0.2%。在J-PARC低能束传输（LEBT）上游半部，真空压力为3.6×10 Pa时，通过预测的100%空间电荷中和（SCN）产生了平坦的束脉冲；在LEBT下游半部，真空压力为2.8×10 Pa时，出现了约69%的意外高且几乎恒定的SCN。快速上升时间是由预先形成的100% SCN和一个100 µs的40 keV前置束产生的，由于该束能量低于RFQ接受范围，未被RFQ加速。在终端电压为62 kV、BDF为5%（1 ms×50 Hz）运行的试验台上，还测量了100 mA束流的横向发射度，结果表明其适用于高能LINAC的RFQ。由于试验台上最短的束流引出器使横向发射度进一步提高了约8%，因此利用该离子源可以实现100 mA的高能高占空比LINAC。
