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Ono, Ayato; Takayanagi, Tomohiro; Fuwa, Yasuhiro; Shinozaki, Shinichi; Ueno, Tomoaki*; Horino, Koki*; Sugita, Moe; Yamamoto, Kazami; Kinsho, Michikazu; Ikoma, Naoya*; et al.
Proceedings of 20th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.871 - 876, 2023/11
In J-PARC, an ignitron is used for the crowbar device of the klystron power supply to excite the RF acceleration voltage in a Linac cavity. Mercury, that is used in the ignitron, would be prohibition of use in the future due to environmental protection. Therefore, we designed a semiconductor crowbar switch for short-circuit protection of klystron using a MOS gate thyristor. We have manufactured an oval-type board module that realizes an operating output of 3kV, 40kA, and 50us per board. Because a high voltage of 120 kV is applied on each board, we adopted a self-power supply method to supply a electricity for the control system. This method can create the electricity from a high-voltage DCDC converter. We confirmed the operating performance on a 1/2 scale (60 kV, 40 kA) of the voltage in the existing ignitron system (120 kV, 40 kA). We also studied a test circuit in a higher voltage range of more than 90 kV. Our latest result is well promising for an alternative system of ignitron.
Ono, Ayato; Takayanagi, Tomohiro; Fuwa, Yasuhiro; Shinozaki, Shinichi; Ueno, Tomoaki*; Horino, Koki*; Sugita, Moe; Yamamoto, Kazami; Kinsho, Michikazu; Ikoma, Naoya*; et al.
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.395 - 399, 2023/01
At J-PARC, an ignitron is used for the crowbar device of the klystron power supply for high-frequency acceleration of a linear accelerator. Ignitron uses mercury, which is of limited use worldwide, and is expected to be discontinued in the future. Therefore, we designed a semiconductor crowbar switch for short-circuit protection of klystron using a MOS gate thyristor. We have manufactured an oval-type board module that realizes an operating output of 3 kV, 40 kA, and 50 
s per board. For the control power supply to each board module assuming a high voltage of 120 kV, we adopted a self-power supply method that creates a control power supply with a high-voltage DCDC converter from the voltage shared and charged by each board module. It was possible to confirm the operating performance on a 1/2 scale (60 kV, 40 kA) against the voltage of the existing equipment (120 kV, 40 kA) by connecting twenty oval board modules in series. The output test result will be reported.
Takayanagi, Tomohiro; Ono, Ayato; Fuwa, Yasuhiro; Shinozaki, Shinichi; Horino, Koki*; Ueno, Tomoaki*; Sugita, Moe; Yamamoto, Kazami; Oguri, Hidetomo; Kinsho, Michikazu; et al.
Proceedings of 19th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.242 - 246, 2023/01
At J-PARC, semiconductor short pulse power supplies to replace kicker power supplies and semiconductor long pulse power supplies to replace klystron power supply systems are under construction. We have fabricated a 40kV/2kA/1.2s unit power supply that employs a linear transformer drivers (LTD) system for kickers. Currently, we are working on a high voltage insulating cylinder insulator that suppresses corona discharges using only the insulator structure, without using insulating oil. In addition, the MARX system was adopted for klystron power supply system. A main circuit unit for 8kV/60A/830s rectangular pulse output and an 800V/60A correction circuit unit that improves the flat top droop from 10% to 1% were manufactured. Furthermore, a 2.2kV/2.4kW high voltage SiC inverter charger has been fabricated for this MARX power supply. The presentation will report the evaluation results of each test and prospects for semiconductor pulse power supplies.
Fuwa, Yasuhiro; Takayanagi, Tomohiro; Iwashita, Yoshihisa*
IEEE Transactions on Applied Superconductivity, 32(6), p.4006705_1 - 4006705_5, 2022/09
Times Cited Count：0 Percentile：0(Engineering, Electrical & Electronic)Space charge compensation technique using multipole magnetic field components has been proposed to transport high intensity beam in the J-PARC linac. In order to realize this compensation technique, a compact size permanent hybrid multi-pole magnet would be suitable. A magnet system for the simultaneous production of quadrupole and adjustable octupole components using permanent magnet materials and have manufactured a first model of the magnet systems.
Fuwa, Yasuhiro; Moriya, Katsuhiro; Takayanagi, Tomohiro
Proceedings of 31st International Linear Accelerator Conference (LINAC 2022) (Internet), p.364 - 367, 2022/09
MEBT1 (Medium Energy Beam Transport 1) of the J-PARC LINAC is a 3 MeV beam transport system located between the RFQ (Radio Frequency Quadrupole) and DTL (Drift Tube Linac). In the MEBT1, the beam-optical matching for injection into DLT and chopping for injection into acceleration phase of 3 GeV synchrotron, located downstream to the LINAC, are performed. The characteristics of MEBT1 are an important factor in determining the beam quality in the J-PARC accelerator facility. To achieve beam power of 1 MW and beyond, improving the stability and reliability of MEBT1 is an important development issue. The application of permanent magnets to the beam focusing system to the MEBT1 is under consideration to achieve improved stability and reliability. In this presentation, we report the design of focusing magnets using permanent magnet material and the results of the lattice study of MEBT1 with permanent magnets.
Fuwa, Yasuhiro; Iwashita, Yoshihisa*; Kondo, Akihiro*
IEEE Transactions on Applied Superconductivity, 32(6), p.4007304_1 - 4007304_4, 2022/06
Times Cited Count：0 Percentile：0(Engineering, Electrical & Electronic)High-field magnets are often demanded advanced scientific studies. Although a hybrid coil design comprising Nb-Ti, Nb
Sn, and HTS (High-Temperature Superconductors) are potential candidates for such application, the costs of NbSn and HTS are expensive compared with Nb-Ti. By generating an additional field of about 1 T by permanent magnets, the required amounts of superconducting material may be reduced. Magnetic properties of some magnetic materials have been studied by other works at temperatures as low as 100 K. The remanent field of conventional NdFeB magnets decreases at 100 K due to spin reorientation. PrFeB magnets consisting of praseodymium (Pr) instead of neodymium (Nd) do not show such degradation and the coercivity of PrFeB at 100 K is 7 T. In this study, the B-H curve, as a primary magnetic property, of a PrFeB magnet sample was measured in the temperature range down to 4 K. As a result, no decrease in magnetization of the praseodymium magnets, and the coercivity was 10 T.
Fuwa, Yasuhiro; Iwashita, Yoshihisa*; Kuriyama, Yasutoshi*; Tongu, Hiromu*; Hayano, Hitoshi*; Geng, R. L.*
Proceedings of 20th International Conference on RF Superconductivity (SRF 2021) (Internet), p.323 - 325, 2022/05
In order to evaluate the performance of a superconducting cavity, we are developing a mapping system to measure the distribution of cavity temperature, field emission X-rays, and trapped magnetic flux with high positional resolution. In order to construct a system with high positional resolution, a large number of sensors are required. However, as the number of sensors increases, so does the amount of wiring, which increases the complexity of the wiring in the cryogenic apparatus, and also increases the heat transfer through the wiring, which disturb efficient operation of cavity tests. We are developing an efficient mapping system with a multiplexer that scans the readout signal on the same circuit as the sensor in the cryogenic dewar where the cavity test is conducted. In this presentation, we report the outline and test results of the mapping system under development
Fuwa, Yasuhiro; Ono, Ayato; Takayanagi, Tomohiro; Shinozaki, Shinichi; Mizobata, Satoshi*; Fang, Z.*
Proceedings of 17th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.780 - 782, 2020/09
In the J-PARC linac, High Voltage DC power supplies (HVDC) to drive klystrons. These HVDCs are modulating-anode power supplies with a rated voltage of 110 kV and are operated by connecting up to four klystrons to a single HVDC. Since multiple klystrons are driven by a single HVDC, a voltage droop in the capacitor bank of the HVDC occurs in the beam pulse. This effect causes a decrease in the output power of the klystron. Half of the existing HVDC in J-PARC were installed at the J-PARC construction, and the other half were installed at the LINAC 400 MeV upgrade, and the capacitors show signs of age-related degradation. In the near future, the capacitors will be necessary to be replaced partially or completely. On the replacement of the capacitors, it will be necessary to re-evaluate the operating behavior of the HVDC when the capacitor bank configuration is changed. In this presentation, we evaluated the effect of the voltage droop on the klystron with the present configuration and the effect of changing the capacitor bank configuration with numerical and experimental results, and we discussed the countermeasure for the stable beam operation.
Fuwa, Yasuhiro; Shinozaki, Shinichi; Chishiro, Etsuji; Hirane, Tatsuya; Fang, Z.*; Fukui, Yuji*; Futatsukawa, Kenta*; Mizobata, Satoshi*; Iwama, Yuhei*; Sato, Yoshikatsu*; et al.
Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.611 - 613, 2019/10
In the J-PARC linac, a proton accelerator is operated using 45 units of 324 MHz and 972 MHz klystrons. In the future stabilization and advancement of the accelerator, it is important to acquire the klystron output characteristics near the maximum output accurately. In order to understand this characteristics, measurement of the characteristics of the replaced klystron for some reason such as discharge, as well as the new klystron. However, such measurements have not been performed because of the risk of damage including peripheral equipment due to discharge and the temporal interference with the operation of the accelerator. Therefore, we set up a klystron test stand in the linac building and measured the high-voltage characteristics and input/output characteristics of the klystron under various operating parameters. By using this measurement result, the characteristics of klystron can be obtained before installation, and it becomes possible to determine the optimum operation parameters and make effective plan of klystron replacements. In addition, basic data for predicting the degradation tendency of klystron was acquired by comparing the characteristics of the used and used klystron.
Kuriyama, Yasutoshi*; Iwashita, Yoshihisa*; Hirota, Katsuya*; Hayano, Hitoshi*; Fuwa, Yasuhiro
Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.32 - 35, 2019/10
Research and development of gradient enhancement of superconducting RF accelerating cavity is carried out by accelerator research institute in the world, but defects on the cavity surface limit accelerating electric field. Therefore, development of "Inside inspection system for superconducting accelerated cavity" that optically visualizes the state of the inner surface of the superconducting cavity has been carried out, and results have been achieved. In this research, we apply image processing technology that has developed remarkably in recent years to the internal inspection system, and advanced the defect recognition method. Extraction of depth information and image synthesis were performed from images obtained with different focal positions with the camera for internal surface inspection. Also, by performing pattern recognition processing on the images, automatic detection of defects has become possible. By integrating these techniques into the cavity inner surface inspection system, it becomes possible to shorten the scan time for defect search and acquire the defect shape.
Abe, Masashi*; Iwashita, Yoshihisa*; Terunuma, Nobuhiro*; Fuwa, Yasuhiro; Yako, Tomoki*
Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.700 - 702, 2019/10
Application of permanent magnets to the damping ring of International Linear Collider (ILC) is investigated. Replacing electromagnets with permanent magnets can reduce not only electricity for exciting the coils and maintenance cost of power supplies but also leakage accidents of cooling water. Bending magnets and correction magnets are used in damping ring, but we tried to calculate magnetic field distributions in a correction magnets using permanent magnets with 3D magnetic field code CST studio. The orbit correction magnet requires that the polarity and the intensity of the generated magnetic field be variable in order to correct the beam orbit error. In this research, adjustment of the generated magnetic field was made possible by mounting the rotation mechanism on the permanent magnet in the magnetic circuit in the correction magnet. In addition, in order to suppress deterioration of beam quality due to an incorrect multipole magnetic field, optimization of the shape of the magnetic circuit was performed, and a magnet design that could be installed on a accelerator was established.
Yako, Tomoki*; Iwashita, Yoshihisa*; Abe, Masashi*; Kurihara, Toshikazu*; Fukuda, Masafumi*; Sato, Masaharu*; Sugimura, Takashi*; Fuwa, Yasuhiro; Takamiya, Koichi*; Iinuma, Yuto*
Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1003 - 1005, 2019/10
Permanent magnets are used as materials for beam optics elements, but it is known that radiation demagnetization occurs in neodymium magnets and samarium cobalt magnets. However, there is not enough information on the radiation demagnetization of ferrite magnets which is weak in strength but inexpensive. In order to verify the suitability of the ferrite magnet as a beam optics element, radiation demagnetization experiments by neutron irradiation of the ferrite magnet were carried out at the Kyoto University Research Reactor (KUR). In the experiment, neutron fluence up to 
cm
was irradiated, and no significant demagnetization was detected on the fluence.
Fuwa, Yasuhiro*; Iwamoto, Hiroki; Nishihara, Kenji
no journal, ,
no abstracts in English
Fuwa, Yasuhiro; Iwashita, Yoshihisa*
no journal, ,
In the development of quantum beam applications, increasing the beam intensity is an important issue to achieve efficient beam utilization. One of the most important problem to be solved in realizing intense beam is the suppression of the emittance growth of the beam caused by the space charge effect. In this study, we report the basic design of a magnet that realizes the application of a multipole magnet component to a beam transport line, which was proposed as a means to suppress the new space charge effect. In this magnet, a permanent magnet is used to efficiently generate the multipole component, and by giving the permanent magnet a movable mechanism, the strength of the multipole component can be adjusted and utilized for transporting various beams.
Fuwa, Yasuhiro; Kuriyama, Yasutoshi*; Iwashita, Yoshihisa*
no journal, ,
Radiation demagnetization by neutron irradiation has been measured using the Kyoto University research reactor to evaluate the radiation resistance of permanent magnet materials used for beam optics of accelerators. In the demagnetization evaluation, it is essential to measure the magnetization before and after neutron irradiation accurately, but in the case of measuring the magnetic field using a Hall probe, the displacement of the measured value due to the probe position is relatively large and causes errors in the demagnetization evaluation. In order to realize magnetization measurement with less systematic error, we have developed a method to measure the magnitude of magnetization from the induced electromotive force on coils by rotating the magnet near the coil. By adopting this rotating-magnet method for magnetization measurements, the error of the measured value can be reduced to 0.1%, and the measurement accuracy of radiation demagnetization has been improved.
Fuwa, Yasuhiro; Moriya, Katsuhiro; Takayanagi, Tomohiro
no journal, ,
In the high-intensity operation of the J-PARC Linac, it is necessary to suppress the beam loss caused by the emittance growth and the beam halo formation due to the space charge in the low-energy region. As a method to suppress the space charge effect, it has been proposed to cancel the effect of higher-order components of the space charge effect by using higher-order multipole fields such as octupole fields. In this presentation, we will report the characteristics of the multipole magnets fabricated for the MEBT1 of the J-PARC Linac and simulation results on the suppression of the space charge effect based on the magnetic field distribution generated by the fabricated magnet.
Moriya, Katsuhiro; Harada, Hiroyuki; Kondo, Yasuhiro; Tamura, Jun; Kamiya, Junichiro; Fuwa, Yasuhiro; Matsuda, Makoto; Kabumoto, Hiroshi; Kinsho, Michikazu; Oguri, Hidetomo
no journal, ,
no abstracts in English
Fuwa, Yasuhiro; Kuriyama, Yasutoshi*; Iwashita, Yoshihisa*; Hirota, Katsuya*; Yamada, Masako*; Kitaguchi, Masaaki*; Shimizu, Hirohiko*
no journal, ,
A neutron mirror with a magnetic repulsive wall is under development. Since neutrons have a magnetic dipole moment, they are subject to forces in a magnetic field gradient. Using this phenomenon, a potential wall for neutrons can be formed by arranging permanent magnets in a planar configuration of a Halbach array. This potential wall acts as a mirror for a polarized neutron beam. A prototype mirror 20 mm high and 30 mm wide was fabricated, and preliminary neutron reflection experiments were conducted at the MINE2 port of JRR-3. As the next step, we plan to fabricate a mirror with a larger size and conduct experiments at the J-PARC MLF. In this presentation, the principle of the mirror, the results of preliminary experiments at JRR-3, and the status of the mirror fabrication for the experiment at J-PARC will be reported.
Fuwa, Yasuhiro; Iwashita, Yoshihisa*; Kuriyama, Yasutoshi*; Yamada, Masako*; Hirota, Katsuya*; Kitaguchi, Masaaki*; Shimizu, Hirohiko*
no journal, ,
Since neutrons have a spin magnetic moment, they are subject to a force due to their interaction with the magnetic field gradient. The direction of this force coincides with the direction of the magnetic field gradient vector, and the force acts in the opposite direction depending on the direction of the spin. By utilizing this force, the neutron beam can be manipulated. If the magnetic field gradient is transverse to the beam axis, the beam is deflected. Therefore, if a sextupole magnet is used to generate a magnetic field, the magnetic field gradient changes in proportion to the distance from the center of the beam axis, which causes the same effect as a lens, and the neutron beam can be focused. In addition, by arranging permanent magnets in a Halbach array on a plane and generating a uniform magnetic field gradient in the direction normal to the plane, a neutron beam reflecting wall can be formed, which can be combined in a duct-like configuration to form a guide tube. The magnetic field gradient in the longitudinal direction relative to the beam axis can change the energy of the neutrons. The integral value of this energy change is zero if the neutrons just pass through, but if the spins are flipped in the magnetic field gradient, the neutron beam can be accelerated or decelerated with the energy corresponding to the magnetic flux density at the flipped location. By applying this technique, spatial focusing and energy modulation of neutron beams are possible. In this presentation, the principle and configuration of the instruments we are developing for neutron beam manipulation and the planned experiments are described, and their potential applications are discussed.
Fuwa, Yasuhiro; Iwashita, Yoshihisa*
no journal, ,
The magnetic moment of the neutrons is forced due to its interaction with the gradient of the magnetic field, which bends the flight path of the neutrons. This effect makes a sextupole magnet, whose magnetic field gradient is proportional to its distance from the lens axis, acts as a lens for the neutron beam. When the magnitude of the sextupole magnetic field is fixed, the focal length of the lens changes with the wavelength of the neutrons. However, by modulating the magnetic field strength synchronously with the TOF of pulsed neutrons, the focal length of the neutron beam can be controlled to be constant over a wide wavelength range. In this study, we have developed a neutron lens with a magnetic field modulation function and aim to realize imaging using magnification optics. A preliminary experiment performed at HUNS (Hokkaido University Neutron Source) has demonstrated imaging with a magnification factor of 4x for neutrons in the 9 to 13 angstrom wavelength range. The magnification factor and the covered wavelength range can be adjusted by changing the modulation intensity of the magnet and the number of lens units. This optical system can be extended to enable wavelength-dependent imaging that functions as a microscope.
