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arXiv · 2607.29229

Space-charge compensation of a low-energy He2+ beam with fluorine-containing gases

Takashi Nagatomo·Yasuyuki Morita·Osamu Kamigaito
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Abstract

This study investigates the space-charge compensation (SCC) of a low-energy He2+ beam by introducing fluorine-containing gases into the low-energy beam transport line (LEBT) of the RIKEN Heavy-Ion Linear Accelerator. The introduction of SF6, C3F8, and CHF3 improved beam transmission through the LEBT, and the largest improvement was obtained using SF6. In contrast, the increase in the beam current with Kr was relatively small, and its effect was less pronounced than that of the fluorine-containing gases. The introduction of fluorine-containing gases increased the rise time of the chopped beam to approximately 10 ms. Experiments performed without the prebuncher confirmed that the prebuncher was largely responsible for this slow rise. Furthermore, the substantial difference in the rise time between Kr and the fluorine-containing gases suggests that different charge carriers may contribute to the SCC in these two cases. Based on the results, a new grid-type beam chopper was installed immediately upstream of the radio-frequency quadrupole linac (RFQ). This configuration allows short beam pulses to be generated immediately before the RFQ while maintaining a direct-current beam in the LEBT, thereby achieving both an effective SCC and a fast beam-current rise. In an acceleration test using the new chopper, a 19.3 micro A He2+ beam was successfully and stably accelerated to the radioisotope-production beamline at a duty factor of 10%. This corresponds to approximately 193 micro A in continuous-wave mode operation, demonstrating that the proposed method is effective for realizing the acceleration of a 200 micro A-class He2+ beam.

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Takashi Nagatomo, Yasuyuki Morita, Osamu Kamigaito. 2026-07-31. Space-charge compensation of a low-energy He2+ beam with fluorine-containing gases. https://arxiv.org/abs/2607.29229

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