Decadal operation of the cesiated RF-driven ion source for negative hydrogen ions at J-PARC

Shinto, Katsuhiro; Okoshi, Kiyonori; Shibata, Takanori*; Nammo, Kesao*; Kawai, Isao*; Ikegami, Kiyoshi*; Takagi, Akira*; Asano, Hiroyuki*; Ueno, Akira; Oguri, Hidetomo

JPS Conference Proceedings (Internet), 45, p.011137_1 - 011137_10, 2026/06

https://doi.org/10.7566/JPSCP.45.011137

In the autumn of 2014, we initiated the operation of a cesiated radio frequency (RF)-driven negative hydrogen (H) ion source at J-PARC in response to the necessity for increased beam intensities in the experimental facilities. The RF-driven ion source has extracted H beams with a beam energy of 50 keV and a beam current of 33 mA at the outset, 47 mA since January 2016, and 60 mA since October 2018. The last value fulfills the requirement that the linac injects the H beams with a beam current of 50 mA as specified in the initial design value into the 3-GeV rapid-cycling synchrotron (RCS). Prior to the 2021/2022 campaign, the ion source had been exchanged on one to three occasions during a campaign. Because it was challenging to ascertain the operational longevity that the RF-driven ion source could deliver beams without any significant issues necessitating the suspension of operations. However, from the 2022/2023 campaign onwards, a single RF-driven H ion source has functioned to deliver the H beams, with the continuous operation time exceeding 4,400 hours. Over the course of this decade, three instances of antenna failure and several other issues have been encountered. This presentation provides the statistical data pertaining to the RF-driven H ion source in terms of user operations, along with an overview of the R&D status in relation to the future J-PARC upgrades.

A 3D Particle-In-Cell calculation of J-PARC RF ion source; Effects due to near antenna electric field

Shibata, Takanori*; Nakano, Haruhisa*; Wada, Motoi*; Shinto, Katsuhiro; Okoshi, Kiyonori; Nammo, Kesao*; Kawai, Isao*; Oguri, Hidetomo

JPS Conference Proceedings (Internet), 45, p.011154_1 - 011154_8, 2026/06

https://doi.org/10.7566/JPSCP.45.011154

In the high-power proton accelerator facilities, Radio Frequency (RF) driven negative hydrogen ion (H) sources are adopted as particle sources for the maintenance-free duration over several months and for the stability of the H beam characteristics in the long-term operation. Techniques of RF plasma excitation are also introduced in the fusion field as ion sources of the neutral beam injection (NBI). On the other hand, the RF ion sources have a feature that the extracted beam current and phase space show slight oscillation with input RF frequency. The oscillation of the phase space may lead to mismatches of Twiss parameters or beam loss at the accelerator cavities in the higher-power beam operation. A 3D Particle-In-Cell (PIC) modeling based on Monte-Carlo collision was developed to elucidate the beam oscillation mechanisms. The presentation reports the effects upon the beam formation due to the electric potential fluctuation caused by a capacitive coupling to the internal antenna coil.

J-PARC LINAC 50 Hz operation verification study

Kondo, Yasuhiro; Chimura, Motoki; Cicek, E.*; Fukui, Yuji*; Futatsukawa, Kenta*; Fuwa, Yasuhiro; Goto, Rikuto*; Hirano, Koichiro; Ishikawa, Masaki*; Ito, Takashi; et al.

Proceedings of 22nd Annual Meeting of Particle Accelerator Society of Japan (Internet), p.124 - 129, 2026/03

https://www.pasj.jp/web_publish/pasj2025/proceedings/PDF/FRO6/FRO601.pdf

Various upgrade plans of the J-PARC linac are underway, and repetition-rate doubling project is one of the most important part. Currently, the linac supplies a 400~MeV H ion beam to the 3~GeV synchrotron (RCS) at a repetition rate of 25~Hz. However, to deliver the beam to both RCS and proton-beam irradiation facility under planning, it is necessary to raise the repetition rate from 25~Hz to 50~Hz. Prior to construction of the beamline to the irradiation facility, we conducted a verification of the 50~Hz operation of all the linac apparatus simultaneously within the current operational limits in May 2025. And also, the verification of the 50~Hz operation of the particle counter system, which is one of the most important safety device of the J-PARC accelerator, was conducted. As a result, any significant problems were not found out, and it is now ready for the upcoming 50~Hz-beam acceleration demonstration. This paper describes this details of the demonstration of the 50~Hz operation, without beam acceleration, of the J-PARC linac.

Progress in linac beam commissioning for high-intensity operations for J-PARC power upgrades

Liu, Y.*; Otani, Masashi*; Miyao, Tomoaki*; Nakazawa, Yuga*; Shibata, Takanori*; Nammo, Kesao*; Fang, Z.*; Futatsukawa, Kenta*; Fukui, Yuji*; Mizobata, Satoshi*; et al.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.855 - 857, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-TUAD1

Operation status of the J-PARC high-intensity RF-driven negative hydrogen ion source in 2023/2024

Shinto, Katsuhiro; Okoshi, Kiyonori; Shibata, Takanori*; Nammo, Kesao*; Kawai, Isao*; Ikegami, Kiyoshi*; Ueno, Akira

Proceedings of 21st Annual Meeting of Particle Accelerator Society of Japan (Internet), p.525 - 528, 2024/10

https://www.pasj.jp/web_publish/pasj2024/proceedings/PDF/WEP0/WEP096.pdf

A decade has elapsed since the radio frequency (RF)-driven negative hydrogen (H) ion source initiated operation at J-PARC. In the 2023/2024 campaign, a single RF-driven H ion source has generated H beams with a beam current of 60 mA, which enabled the J-PARC linac to inject them into the 3 GeV rapid cycling synchrotron (RCS) with a beam current of 50 mA. The continuous operation time of the ion source reached exceeding 4,900 hours in this campaign, which signifies a notable enhancement in operational longevity in comparison to the preceding longest campaign in 2022/2023, which spanned 4,412 hours. This paper provides the operational status of the RF-driven H ion source during this campaign and the current status of the J-PARC-made antenna, which is currently under development.

Development of a new J-PARC-made internal antenna for the J-PARC RF-driven H ion source

Shinto, Katsuhiro; Shibata, Takanori*; Okoshi, Kiyonori; Nammo, Kesao*; Kawai, Isao*; Ikegami, Kiyoshi*

Journal of Physics; Conference Series, 2743, p.012023_1 - 012023_5, 2024/05

https://doi.org/10.1088/1742-6596/2743/1/012023

We have been conducting the test of a new J-PARC-made internal antenna for the J-PARC RF-driven cesiated H ion source. After the development of the first J-PARC-made antenna, the composition of the porcelain enamel coating of the antenna was changed because we were afraid of the outgassing of the impurities from the previous antenna coating. During the test of high-density plasma production by the new antenna, we monitored the outgassing characteristics of the new antenna by measuring mass spectrometry and optical spectrum analysis. It is confirmed that no remarkable impurities were emitted from the new antenna. We also carried out the H beam extraction and measured the H beam characteristics by using the new antenna. It is found that the emittances of the H beam extracted from the J-PARC RF-driven cesiated H ion source by using the new antenna were similar to those in the case by using the SNS-made antenna. To accelerate the endurance test of the new antenna, we applied the antenna for the high-density plasma production to the 5% duty factor (1 ms pulse width with 50 Hz repetition rate) with the 2 MHz RF input power of approximately 60 kW, whose values were much higher than those in the J-PARC nominal operation; 0.8 ms pulse width with 25 Hz repetition rate (the duty factor of 2%) with the RF input power of approximately 30 kW. This presentation shows the results of the characteristics of the new J-PARC-made antenna and discusses the feasibility of the new antenna for use in the J-PARC accelerator operation.

Discoloration of RF antenna coil surface after long-term operation of J-PARC ion source

Shibata, Takanori*; Shinto, Katsuhiro; Nammo, Kesao*; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Oguri, Hidetomo; Ishida, Masaki*; Wada, Motoi*

Journal of Instrumentation (Internet), 19(1), p.C01009_1 - C01009_8, 2024/01

https://doi.org/10.1088/1748-0221/19/01/C01009

From Nov. 2020 to Apr. 2021, the continuous ion source operation for 3,651 hours (5 months) was achieved. As the lifetime of the RF ion source is mainly limited by failure on the enamel coating of the RF antenna, detailed evaluation of the antenna surface is required to ensure feasibility of the further extension of the operation time. In the present study, surface discoloration on the RF antenna coil observed after the 5 months operation is investigated by application of digital microscope and SEM/EDS analyses. The material mapping and the line spectrum obtained by the EDS analysis show that depositions of the sputtered source chamber wall materials and the injected cesium on to the enamel coating are the most possible candidate for the discoloration. The dimension measurements of the RF antenna thickness before and after the long-term operation support the idea that the discoloration is due to the deposited materials and hence insulation of the RF antenna coil by enamel coating is maintained. The emittance measurement after the operation also shows that the RF plasma and the beam formations are not affected by the deposition on the antenna.

120 mA operation of J-PARC cesiated RF-driven H ion source

Ueno, Akira; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Oguri, Hidetomo

Journal of Instrumentation (Internet), 18(8), p.C08002_1 - C08002_8, 2023/08

https://doi.org/10.1088/1748-0221/18/08/C08002

On 2020, the stable operation of the J-PARC cesiated RF-driven H ion source (IS) with a 65 keV 110 mA beam, whose emittances were suitable for the radio-frequency quadrupole LINAC, was reported. In the J-PARC IS operation, the stable plasma production with a 50 kW 2 MHz RF power for more than 3 months, an RF power efficiency higher than 2.6 mA/kW and the possibility of the space charge limited beam intensity pulling up by increasing the extraction and acceleration voltages (V and V) were proven. The stable operation results with a 69.9 keV 120 mA beam realized by increasing the withstand voltage around the 2 MHz RF matching circuit are presented. The 107.8 mA of the beam was measured inside the emittances used for the RFQ design.

Outgassing characteristics from the J-PARC-made internal antenna for a high-intensity radio-frequency H ion source

Shinto, Katsuhiro; Shibata, Takanori*; Okoshi, Kiyonori; Nammo, Kesao*; Ikegami, Kiyoshi*; Oguri, Hidetomo

Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.675 - 679, 2023/01

In J-PARC, we have been conducting the test of a J-PARC-made internal antenna in order to establish the production method and understand the beam characteristics of the antenna. At this time, we investigated the outgas characteristics during the production of a high-density plasma by using the J-PARC-made antenna. It is confirmed that no remarkable impurities are emitted from the antenna by a residual gas analysis using a quadrupole mass analyzer installed downstream the ion source and a spectroscopic analysis of the plasma in the ion source. It is found that the emittances of the H beam extracted from the J-PARC radio-frequency H ion source by using the antenna was similar as those in case by using SNS antenna.

Soundness evaluation of J-PARC RF ion source after 5-month continuous operation

Shibata, Takanori*; Okoshi, Kiyonori; Shinto, Katsuhiro; Nammo, Kesao*; Ikegami, Kiyoshi*; Oguri, Hidetomo

Journal of Physics; Conference Series, 2244, p.012041_1 - 012041_5, 2022/04

https://doi.org/10.1088/1742-6596/2244/1/012041

In the J-PARC user operation from Nov. 2020 - Apr. 2021, continuous operation of J-PARC Radio Frequency (RF) negative hydrogen ion (H) source up to 3,651 hours (5 months) has been achieved. The ion source was operated with the output H current of 60 mA, the duty factor (for plasma generation) 2% and the input RF power up to 30 kW. After the operation, phase space diagrams at the Radio Frequency Quadrupole (RFQ) entrance were measured by the emittance monitor at the ion source test stand (IS-TS) under the same operation condition as in the J-PARC Linac. Comparison of the phase spaces and the beam emittances between the ion sources in the present and the previous operations shows slight difference. From the direct observation of the antenna coil, no exhaustion or the decrease in the thickness of the enamel coating of the coil have been confirmed. The results indicate the possibility of the next goal of the long-run up to 7 months, which is the same as the full duration of the J-PARC user operation in 1 year.