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Wada, Motoi*; Shibata, Takanori*; Shinto, Katsuhiro
Journal of Instrumentation (Internet), 19(2), p.C02019_1 - C02019_7, 2024/02
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)A negative hydrogen (H
) ion source with the plasma excited by 2 MHz radio frequency (RF) power serves as the beam source for the Japan Proton Accelerator Research Complex (J-PARC). We have been studying the H ion beam intensity modulation at the frequency of plasma excitation RF power since we have found the beam carried the fluctuation at 2 MHz after the RFQ linac. Higher frequency components were found present in the peripheral region of the plasma, and the highspeed emittance measurement system developed to clarify the change of the beam in phase space revealed the existence of diverging halo component oscillating at 2 MHz. The fluctuation amplitude at the beam center was less than about 20%, while there was observed the component oscillating at 4 MHz. The 4 MHz component seems related to the production of high energy electrons by the RF antenna as the intensity of the RF induction electric field takes the maximum twice in each cycle. On the other hand, the direction of RF magnetic field and the direction of electron flow change at 2 MHz frequency. Thus, H ion formation mechanisms in the ion source can be estimated through precisely characterizing the extracted H ion beam. The H ion beam fluctuation can be observed in the H ion current measured with a Faraday cup. Before introducing Cs, the measured beam current showed the fluctuation at 4 MHz frequency when the axial magnetic field correction (AMFC) coil was turned off. The main fluctuation frequency changed to 2 MHz as the voltage to excite the coil to induce AMFC was increased. Injection of Cs into the ion source increased the H ion current, while the 4 MHz component nearly disappeared for both cases of AMFC on and AMFC off. Possible mechanisms responsible for diminishing 4 MHz fluctuation component by Cs injections are discussed.
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
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)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.
ion sourceUeno, Akira; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Oguri, Hidetomo
Journal of Instrumentation (Internet), 18(8), p.C08002_1 - C08002_8, 2023/08
Times Cited Count：2 Percentile：15.22(Instruments & Instrumentation)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.
