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Yamamoto, Masanobu; Nomura, Masahiro; Okita, Hidefumi; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*
Proceedings of 13th International Particle Accelerator Conference (IPAC 22) (Internet), p.1336 - 1338, 2022/06
In order to accelerate a high intensity beam in the RCS, a large amplitude of the rf current is provided by a tube amplifier to compensate a heavy beam loading. Tetrode vacuum tubes are used in the RCS, and the control grid voltage enters into a positive region to feed such a large rf current. The positive grid biasing affects the waveform of the control grid voltage; it is deformed due to the induced control grid current under the condition of the multi-harmonic rf driving. Furthermore, the DC bias voltage drop on the control grid is observed because of the exceeding the capability for the control grid power supply. We describe the influence of the positive grid biasing in the RCS.
Yamamoto, Masanobu; Okita, Hidefumi; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Furusawa, Masashi*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; et al.
Proceedings of 12th International Particle Accelerator Conference (IPAC 21) (Internet), p.1884 - 1886, 2021/08
Tetrode vacuum tubes in J-PARC RCS are used under a reduced filament voltage condition compared with the rating value to prolong the tube lifetime. For the first time after 60,000 hour of operation in the RCS, one tube has reached the end of its life in 2020. Therefore, the reduced filament voltage works well because the tube has been running beyond an expected lifetime suggested by the tube manufacturer. However, the reduced filament voltage decreased the electron emission from the filament. Although the large amplitude of the anode current is necessary for the high intensity beam acceleration to compensate a wake voltage, a solid-state amplifier to drive a control grid circuit almost reaches the output power limit owing to the poor electron emission from the filament. We changed the filament voltage reduction rate from 15% to 5%. The required power of the solid-state amplifier was fairly reduced, whereas the accelerated beam power remained the same. We describe the measurement results of the vacuum tube parameters in terms of the filament voltage tuning.
Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Furusawa, Masashi*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*
Proceedings of 10th International Particle Accelerator Conference (IPAC '19) (Internet), p.2017 - 2019, 2019/06
J-PARC RCS has successfully accelerated 1 MW proton beam, and we have considered acceleration with the next target being 1.2 MW. An issue for 1.2 MW beam acceleration is the rf system. The present anode power supply is limited by its output current, and the vacuum tube amplifier suffers from an unbalance of the anode voltage swing, arising from the combination of multi-harmonic rf driving and push-pull operation. We have investigated the mitigation of the maximum anode currents and unbalanced tubes by choosing appropriate circuit parameters of the rf cavity with tube amplifier. We describe the analysis results of the vacuum tube operation for 1.2 MW beam acceleration in the RCS.
Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Furusawa, Masashi*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Sugiyama, Yasuyuki*; Yoshii, Masahito*
Journal of Physics; Conference Series, 1067, p.052014_1 - 052014_6, 2018/10
Times Cited Count：3 Percentile：79.15(Physics, Particles & Fields)The J-PARC RCS employs Magnetic Alloy (MA) loaded cavities. The RF power is fed by vacuum tubes in push-pull operation. We realize multi-harmonic RF driving and beam loading compensation thanks to the broadband characteristics of the MA. However, the push-pull operation has disadvantages in multi-harmonics. An unbalance of the anode voltage swing remarkably appears at very high intensity beam acceleration. We propose a single-ended MA cavity for the RCS beam power upgrade, where no unbalance arises intrinsically.
Ogiwara, Norio; Hikichi, Yusuke*; Kamiya, Junichiro; Kinsho, Michikazu; Yoshida, Hajime*; Arai, Kenta*
Journal of the Vacuum Society of Japan, 60(12), p.475 - 480, 2017/12
Morishita, Takatoshi; Kondo, Yasuhiro; Oguri, Hidetomo; Hasegawa, Kazuo
Journal of Vacuum Science and Technology A, 35(4), p.041602_1 - 041602_5, 2017/07
Times Cited Count：1 Percentile：4.92(Materials Science, Coatings & Films)In the J-PARC, the linac provides 400 MeV hydrogen negative ion beam to the following 3GeV synchrotron. For the beam current upgrade, the new radio-frequency quadrupole (RFQ) linac, in which the design peak beam current was increased from 30 to 50 mA, has been fabricated and installed in the beam line in summer 2014. The beam provision to users started in the beginning of November, 2014. Since then, the RFQ operates without serious problems for more than two years, however, the operation stability of the RFQ with beam acceleration was not enough due to the sparking in the cavity. We consider that the impurities in the vacuum chamber are related to this sparking phenomena. The design and performance of the RFQ vacuum system is described in this paper, then, the relationship among the sparking rates, the residual gas species in the vacuum chamber, and the beam operation parameters are described.
Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*
Nuclear Instruments and Methods in Physics Research A, 835, p.119 - 135, 2016/11
Times Cited Count：6 Percentile：49.29(Instruments & Instrumentation)A magnetic alloy loaded cavity is used to generate multi-harmonic rf voltage in J-PARC RCS. However, a vacuum tube operation analysis under the multi-harmonic driving is very complicated because many variables should be solved with a self consistency. At the conventional operation analysis, a hand work by tracing the constant current curve of the tube was performed, or an appropriate single harmonic wave form was assumed. We have developed a numerical analysis code which calculates the vacuum tube operation automatically and it realizes the multi-harmonic vacuum tube operation analysis. The code is verified at the high power beam acceleration test and we confirm the calculation results are consistent with the measurement ones. We can calculate the vacuum tube operation precisely by using the code, and it will contribute to improving the quality of the beam in the high intensity proton synchrotron.
at the single-atom levelSteinegger, P.*; Asai, Masato; Dressler, R.*; Eichler, R.*; Kaneya, Yusuke*; Mitsukai, Akina*; Nagame, Yuichiro; Piguet, D.*; Sato, Tetsuya; Sch
del, M.; et al.
Journal of Physical Chemistry C, 120(13), p.7122 - 7132, 2016/04
Times Cited Count：23 Percentile：60.73(Chemistry, Physical)A new experimental method "vacuum chromatography" has been developed to measure adsorption enthalpy of superheavy elements, and its feasibility has been examined using short-lived thallium isotopes. The short-lived thallium isotopes were produced at the JAEA tandem accelerator. The thallium ion beam prepared with an on-line isotope separator which ionized and mass-separated the thallium isotopes was injected into an isothermal vacuum chromatography apparatus. A temperature-dependent adsorption property of thallium atom on SiO surface were measured. The adsorption enthalpy of thallium was determined to be 158 kJ/mol. The thallium is a homolog of element 113. Thus, the vacuum chromatography developed in this study enables us to perform chemical experiments for short-lived superheavy elements with half-lives of a order of one second.
Tsuru, Daigo; Sakurai, Shinji; Nakamura, Shigetoshi; Ozaki, Hidetsugu; Seki, Yohji; Yokoyama, Kenji; Suzuki, Satoshi
Fusion Engineering and Design, 98-99, p.1403 - 1406, 2015/10
Times Cited Count：3 Percentile：25.85(Nuclear Science & Technology)Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10
Times Cited Count：1 Percentile：9.74(Nuclear Science & Technology)Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800
C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.
Kamiya, Junichiro; Kinsho, Michikazu; Noshiroya, Shiyoji; Yamamoto, Kazami
Proceedings of 5th International Particle Accelerator Conference (IPAC '14) (Internet), p.2338 - 2340, 2014/07
In high power beam accelerators, pressure of the beam line directly affects the amount of the beam loss. J-PARC RCS is one of the most high power beam accelerators in the world. It aims the 1MW beam power, which corresponds to the average and peak beam current of 333 
A and about 10 A, respectively. In the present stage, the injection line called L3BT line (Linac to 3GeV Beam Transport line), is the section, where the pressure notably produces the beam loss. In this section, H
beam from Linac was converted to H
beam by charge stripping due to the interaction between H beam and the residual gas molecules. Such H beam was not bended by the injection septum magnets and directly hit the vacuum wall. We decided to add the vacuum pumps in this section to reduce the residual gas molecules in the beam line. In this paper, we will present the effectivity of the additional pumps by showing the relation between the beam line pressure and beam loss.
Kamiya, Junichiro; Takayanagi, Tomohiro; Kawakubo, Toshimichi*; Murasugi, Shigeru*; Nakamura, Eiji*
IEEE Transactions on Applied Superconductivity, 16(2), p.168 - 171, 2006/06
Times Cited Count：5 Percentile：29.26(Engineering, Electrical & Electronic)The kicker magnets are installed in the extraction section of the RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) facility. They extract the 3GeV proton beam to a downstream beam transport line. In order to achieve 1MW beam power, kicker is required to have a wide aperture, UHV (ultra-high vacuum) in its chamber, and uniformity of magnetic field. In this paper, we will introduce the specification of the extraction kicker system in the RCS, and report countermeasure against the technical challenge described above.
Inoue, Takashi; Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Watanabe, Kazuhiro; Sakamoto, Keishi
Nuclear Fusion, 46(6), p.S379 - S385, 2006/06
Times Cited Count：35 Percentile：74.54(Physics, Fluids & Plasmas)The JAERI MeV accelerator has been designed extrapolating vacuum insulation design guidelines (the clump theory and Paschen law) to Mega Volt and long vacuum gap. Reduction of electric field concentration at triple junction by a large stress ring was effective to prevent flashover along insulator surface. By the vacuum insulation technology above, the accelerator sustained 1 MV for 8,500 s continuously. Strong enhancement of negative ion surface production has been attained by stopping vacuum leaks due to SF
permeation through Viton O rings and a damage of port by backstream ions, followed by increase of the H ion current density without saturation. Operating the KAMABOKO source with high power arc discharge (
40 kW), H ion beams of 146 A/m
(total ion current: 0.2 A) have been obtained stably at the beam energy of 836 keV (pulse length: 
0.2 s). Bremsstrahlung generation in the accelerator is also estimated from EGS4 analysis, and then discussion on the breakdown possibility follows.
Inoue, Takashi; Hanada, Masaya; Kashiwagi, Mieko; Nishio, Satoshi; Sakamoto, Keishi; Sato, Masayasu; Taniguchi, Masaki; Tobita, Kenji; Watanabe, Kazuhiro; DEMO Plant Design Team
Fusion Engineering and Design, 81(8-14), p.1291 - 1297, 2006/02
Times Cited Count：11 Percentile：60.27(Nuclear Science & Technology)Requirement and technical issues of the neutral beam inejctor (NBI) is discussed for fusion DEMO plant. The NBI for the fusion DEMO plant should be high efficiency, high energy and high reliability with long life. From the view point of high efficiency, use of conventional electrostatic accelerator is realistic. Due to operation under radiation environment, vacuum insulation is essential in the accelerator. According to the insulation design guideline, it was clarified that the beam energy of 1.5
2 MeV is possible in the accelerator. Development of filamentless, and cesium free ion source is required, based on the existing high current/high current density negative ion production technology. The gas neutralization is not applicable due to its low efficiency (60%). R&D on an advanced neutralization scheme such as plasma neutralization (efficiency: 
80%) is required. Recently, development of cw high power semiconductor laser is in progress. The paper shows a conceptual design of a high efficiency laser neutralizer utilizing the new semiconductor laser array.
Mori, Masahiro; ITER Japanese Participant Team
Fusion Engineering and Design, 81(1-7), p.69 - 77, 2006/02
Times Cited Count：1 Percentile：9.98(Nuclear Science & Technology)The ITER Transitional Arrangements (ITA) are conducted by the International Team with supports from participant teams (PTs). The Japanese PT (JA-PT) set up in JAERI has contributed to ITA by sharing a lot of technical tasks to verify feasibilities of fabrication and quality control method in procuring ITER equipments and facilities. For examples, trial fabrications of Nb3Sn strands have been performed by JA-PT with four potential suppliers, and one of the strand which meet the ITER requirements in all key parameters have already been chosen for one of the suppliers. All strands including the other suppliers strands will be fully qualified by the end of 2005. The trial fabrications of CS jackets and material for TF coil structure are also in progress at industrial level. Fabrication of the partial mock-ups of the vacuum vessel is also ongoing. Furthermore, JA-PT has made several technical developments on NB and EC systems to improve reliability of long pulse operations. Completing these technical preparations will make it possible to finalize the specification of ITER procurements.
Nakahira, Masataka; Takeda, Nobukazu
Hozengaku, 4(4), p.47 - 52, 2006/01
The technical structural standard for ITER (International Thermonuclear Experimental Fusion Reactor) should be innovative because of their quite different features of safety and mechanical components from nuclear fission reactors, and the necessity of introducing several new fabrication and examination technologies. Recognizing the international importance of Fusion Standard, Japan and ASME has started the cooperation development of the Fusion Standard. This paper shows the special features of ITER from view points of safety, design and fabrication, and proposes approach for development of the fusion standard.
Nakahira, Masataka
JAERI-Research 2005-030, 182 Pages, 2005/09
JAERI-Research-2005-030.pdf:12.57MB
It is difficult for Vacuum Vessel (VV) of ITER to apply a non-destructive in-service inspection (ISI) and then new safety concept is needed. Present fabrication standards are not applicable to the VV, because the access is limited to the backside of closure weld of double wall. Fabrication tolerance of VV is 
5mm even the structure is huge as high as 10m. This accuracy requires a rational method on the estimation of welding deformation. In this report, an inherent safety feature of the tokamak is proved closing up a special characteristic of termination of fusion reaction due to tiny water leak. A rational concept not to require ISI without sacrificing safety is shown based on this result. A partial penetration T-welded joint is proposed to establish a rational fabrication method of double wall. Strength and susceptibility to crevice corrosion is evaluated for this joint and feasibility is confirmed. A rational method of estimation of welding deformation for large and complex structure is proposed and the efficiency is shown by comparing analysis experimental results of full-scale test.
Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro
Nuclear Fusion, 45(8), p.790 - 795, 2005/08
The R&D of a 1 MeV accelerator and a large negative ion source have been carried out at JAERI. The paper presents following progress as a step toward ITER NB system. (1) Accelerator R&D: According to success in improvement of voltage holding capability, the acceleration test of H ions up to 1 MeV class energy is in progress. H ion beams of 1 MeV, 100 mA class have been generated with a substantial beam current density (100 A/m), and the current density is still increasing by the ion source tuning. (2) Large ion source R&D: One of major causes that limited the NB injection performance was spatial unifomity of negative ion production in existing negative-ion based NB systems. The present study revealed that the negative ions produced in the extraction region of the source were locally destructed by fast electrons leaking through magnetic filter. Some countermeasures and their test results are also described.
Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro
Nuclear Fusion, 45(8), p.790 - 795, 2005/08
Times Cited Count：23 Percentile：59.63(Physics, Fluids & Plasmas)The R&D of a 1 MeV accelerator and a large negative ion source has been carried out at JAERI for the ITER NB system. The R&D is in progress at present toward: (1) 1 MeV acceleration of H ion beams at the ITER relevant current density of 200 A/m, and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H ion beams of 1 MeV, 140 mA level have been generated with a substantial beam current density (100 A/m). In the uniformity study, it has been clarified that electron temperature in the ion extraction region is locally high ( 1 eV), which resulted in destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called "magnetic filter" has been found effective to lower the local electron temperature, followed by an improvement of negative ion beam profile.
negative hydrogen ion beams in a 1 MeV vacuum insulated beam sourceTaniguchi, Masaki; Inoue, Takashi; Kashiwagi, Mieko; Hanada, Masaya; Watanabe, Kazuhiro; Seki, Takayoshi*; Sakamoto, Keishi
AIP Conference Proceedings 763, p.168 - 175, 2005/04
The accelerator for the ITER NB system is required to produce 1 MeV, 40 A D-ion beams for 16.5 MW neutral beam injection per module. In the ITER NB system, conventional gas insulated beam source cannot be adopted because of the radiation-induced conductivity of the insulation gas. Thus a vacuum insulated beam source (VIBS), where the whole beam source is immersed in vacuum, had been developed in JAERI. Recently, voltage holding capability of the VIBS was drastically improved by installing the large stress ring, which reduces the electric field concentration at the negative side triple junction. Having improved the voltage holding capability of the VIBS, the H ion beams were extracted with seeding cesium to enhance the negative ion currents. Up to now, we had been succeeded in accelerating the H beam of 102 A/m (140 mA) at 800 keV. The beam acceleration was quite stable and accomplished for several hundreds shots in several experimental campaigns.
