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Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:83 Percentile:0.07(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

Numerical and experimental study of H$$^{-}$$ beam dynamics in J-PARC LEBT

Shibata, Takanori*; Ikegami, Kiyoshi*; Liu, Y.*; Miura, Akihiko; Naito, Fujio*; Nammo, Kesao*; Oguri, Hidetomo; Okoshi, Kiyonori; Otani, Masashi*; Shinto, Katsuhiro; et al.

Proceedings of 29th International Linear Accelerator Conference (LINAC 2018) (Internet), p.519 - 521, 2019/01

Transport process of negative hydrogen ion (H$$^{-}$$) in LEBT (Low Energy Beam Transport) is investigated by comparison of experimental and numerical results. A three dimensional Particle-In-Cell (PIC) particle transport model has been developed in order to take into account (i) axial magnetic field by two solenoids in J-PARC LEBT and (ii) radial electric field by space charge (SC) effect. Ratio of H$$^-$$ beam particles inside the RFQ (Radio Frequency Quadrupole) acceptance to the total particles at the RFQ entrance is calculated for different current conditions in LEBT solenoid 1 and 2. The results are compared with RFQ transmission rate measured in the J-PARC linac commissioning. The double peak of RFQ transmission rate to the solenoid applied current seen in the measurement is explained by the calculation results. The results indicate that presence of the LEBT orifice for differential pumping plays a role as a collimator to reduce emittance at RFQ entrance.

Journal Articles

Solving beam intensity bottlenecks and 100 mA operation of J-PARC cesiated RF-driven H$$^{-}$$ ion source

Ueno, Akira; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Takagi, Akira*; Shinto, Katsuhiro; Oguri, Hidetomo

AIP Conference Proceedings 2052, p.050003_1 - 050003_7, 2018/12

 Times Cited Count:2 Percentile:8.54

In order to specify the beam intensity bottlenecks of the J-PARC cesiated RF-driven H$$^{-}$$ ion source, the extraction and acceleration voltages (V$$_{rm E}$$ and V$$_{rm A}$$) higher than the design values of 10 kV and 40 kV were examined. A 100 mA beam, whose about 93 mA has transverse emittances used for a common RFQ design, was stably operated with a duty factor of 5% (1 ms $$times$$ 50 Hz) by using the V$$_{rm E}$$ and V$$_{rm A}$$ of 12.4 kV and 49.6 kV, respectively. This breakthrough with important information on the space-charge limited bottlenecks in the extraction and acceleration gaps will derive the optimal electrode shapes for the source operated with a beam intensity higher than 100 mA and realize the next generation benchmark H$$^{-}$$ ion source for high intensity and high energy H$$^{-}$$ LINACs.

Journal Articles

Progress of the J-PARC cesiated rf-driven negative hydrogen ion source

Shinto, Katsuhiro; Okoshi, Kiyonori; Shibata, Takanori*; Nammo, Kesao*; Ikegami, Kiyoshi*; Takagi, Akira*; Namekawa, Yuya*; Ueno, Akira; Oguri, Hidetomo

AIP Conference Proceedings 2052, p.050002_1 - 050002_7, 2018/12

 Times Cited Count:2 Percentile:8.54

In the 2017/2018 campaign, the J-PARC cesiated rf-driven negative hydrogen (H$$^-$$) ion source producing H$$^-$$ beam with the beam current of 47 mA accomplished three long-term operations more than 2,000 hours without any serious issues. On the final day of this campaign, the ion source produced an H$$^-$$ beam current of 72 mA so that the linac commissioning group could demonstrate the beam current of 60 mA at the linac exit. We are also conducting an endurance test of a J-PARC-made antenna at a test bench. The antenna achieved the operation time approximately 1,400 hours.

Journal Articles

Status of development on LaB$$_6$$ filament arc-driven multi-cusp ion source for iBNCT

Shibata, Takanori*; Takagi, Akira*; Ikegami, Kiyoshi*; Sugimura, Takashi*; Nammo, Kesao*; Naito, Fujio*; Kobayashi, Hitoshi*; Kurihara, Toshikazu*; Honda, Yosuke*; Sato, Masaharu*; et al.

Proceedings of 15th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.385 - 387, 2018/10

Journal Articles

Present status of the J-PARC cesiated rf-driven H$$^-$$ ion source

Shinto, Katsuhiro; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Takagi, Akira*; Shibata, Takanori*; Nammo, Kesao*; Namekawa, Yuya*; Ueno, Akira; Oguri, Hidetomo

AIP Conference Proceedings 2011, p.050018_1 - 050018_3, 2018/09

 Times Cited Count:3 Percentile:3.74

Journal Articles

Observation of plasma density oscillation with doubled value of RF frequency in J-PARC RF ion source

Shibata, Takanori*; Shinto, Katsuhiro; Takagi, Akira*; Oguri, Hidetomo; Ikegami, Kiyoshi*; Okoshi, Kiyonori; Nammo, Kesao*; Naito, Fujio*

AIP Conference Proceedings 2011, p.020008_1 - 020008_3, 2018/09

 Times Cited Count:4 Percentile:1.18

Journal Articles

How to make extraction electrode current lower than beam and corresponding beam qualities in J-PARC cesiated RF-Driven H$$^{-}$$ ion source 66 mA operation

Ueno, Akira; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Takagi, Akira*; Shinto, Katsuhiro; Oguri, Hidetomo

AIP Conference Proceedings 2011, p.050002_1 - 050002_5, 2018/09

In order to operate the J-PARC cesiated rf-driven H$$^{-}$$ ion source with a beam intensity of 66 mA stably, the conditions to minimize the extraction electrode current (I$$_{EE}$$), whose main component is the electron current co-extracted with the beam, were investigated. The 66 mA H$$^{-}$$ ion beam with a low I$$_{EE}$$ of about 40 mA, which was one-fourth of that in the ordinal operation, were stably extracted by optimizing a rod-filter-field (RFF), a cesium (Cs) density and an axial magnetic field correction (AMFC). Especially, the AMFC of only 40 Gauss had the largest I$$_{EE}$$ reduction of about one-third. The corresponding 95 % beam transverse normalized rms emittances were degraded about 24 % due to the higher RFF and Cs density. The source will be operated in the conditions to compromise the stability and the beam quality by the investigated results.

Journal Articles

Operation status of the J-PARC H$$^{-}$$ ion source

Okoshi, Kiyonori; Shinto, Katsuhiro; Nammo, Kesao*; Shibata, Takanori*; Ikegami, Kiyoshi*; Takagi, Akira*; Ueno, Akira; Namekawa, Yuya*; Oguri, Hidetomo

Proceedings of 15th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.889 - 892, 2018/08

In 2017-2018 campaign, three times of long-time operation more than 2,000 hours of the J-PARC rf-driven negative hydrogen (H$$^{-}$$) ion source producing H$$^{-}$$ beam with the beam current of 47 mA were successfully achieved without any serious problems. At the final day of this campaign, the ion source produced an H$$^{-}$$ beam with the current of 72 mA in order to demonstrate the beam current of 60 mA at the linac exit. We are also conducting an endurance test of a J-PARC-made antenna at a test bench. Approximately 1,400-hour operation with the antenna was successfully performed.

Journal Articles

Operation status of the J-PARC H$$^{-}$$ ion source

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

Proceedings of 14th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.651 - 654, 2017/12

Operation of a cesiated rf-driven negative hydrogen ion source was initiated in September 2014 in response to the requirements of beam current upgrade in J-PARC linac. Delivery of the required beam current from the ion source to the J-PARC accelerators has been successfully performed. In 2016-2017 campaign, continuous operation of the ion source for approximately 1,845 hours (from April to July 2017) was achieved with beam current of 47 mA.

Journal Articles

Operation status of the J-PARC RF-driven H$$^{-}$$ ion source

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

AIP Conference Proceedings 1869, p.030053_1 - 030053_7, 2017/08

 Times Cited Count:5 Percentile:2.99

A cesiated RF-driven negative hydrogen ion source was started to operate in September, 2014 in response to the need for upgrading J-PARC's linac beam current. The ion source mainly comprises a stainless-steel plasma chamber, a beam extractor, and a large vacuum chamber with two turbo molecular pumps of 1500 L/s for differential pumping. The ion source has been successfully providing the required beam current to the accelerator without any significant issues other than a single-incident antenna failure occurred in October, 2014. Continuous operation for approximately 1,000 h was achieved with a beam current and duty factor of 45 mA and 1.25 % (0.5 msec and 25 Hz), respectively. In this paper, we will present the some operation parameters and the beam stability through the long-term user operation.

Journal Articles

High density plasma calculation of J-PARC RF negative ion source

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

AIP Conference Proceedings 1869, p.030017_1 - 030017_11, 2017/08

 Times Cited Count:4 Percentile:4.77

From September 2014, operation of Cs-seeded, multi-cusp, Radio Frequency (RF), hydrogen negative ion source (J-PARC source) has been started. The operation for 1,000 hours of J-PARC source has been achieved with H$$^{-}$$ beam current 45 mA and duty factor of 1.25 % (0.5 msec and 25 Hz). In the present study, mechanisms of hydrogen plasma ramp-up and H$$^{-}$$ production/transport processes in the steady state (which lasts for few 100 us) are investigated by numerical modeling for RF plasma. In the simulation, charged particle (e, H$$^{+}$$, H$$_2^{+}$$, and Cs$$^{+}$$) transport, time variations of inductive and capacitive electromagnetic field, collision processes between charged and neutral (H, H$$_{2}$$) particles are solved simultaneously. The model is applied to KEK parallel computation System-A with 32 nodes and 256 GB memory in order to solve high density RF plasma up to around 10$$^{18}$$ m$$^{-3}$$ with adequate statisticity. In the presentation, time variations of plasma density distributions and average energy are shown with electromagnetic field variations.

Journal Articles

Emittance improvements of cesiated RF-driven H$$^{-}$$ ion source to enable 60 mA operation of high-energy and high-intensity LINACs by plasma impurity controls

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

AIP Conference Proceedings 1869, p.030011_1 - 030011_10, 2017/08

 Times Cited Count:5 Percentile:2.99

At the Japan Proton Accelerator Research Complex (J-PARC), the operation of a 400-MeV linear accelerator (LINAC) with an extraction H$$^{-}$$ ion beam intensity of 60 mA is under investigation. This intensity is 20% higher than the 50 mA achieved by the J-PARC LINAC and about 50% higher than those of operating similar LINACs in the world. Recently, the J-PARC cesiated RF-driven H$$^{-}$$ ion source successfully produces a beam enabling the 60 mA operation. A 66-mA beam with 95%-beam transverse normalized rms emittance of 0.23 $$pi$$mm$$cdot$$mrad is produced by controlling the impurities of argon, nitrogen and water molecules in the hydrogen plasma and tuning rod-filter-field.

Journal Articles

Transverse RMS emittance evaluation based upon explicit and reasonable definitions of 100% and 95% beams

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

AIP Conference Proceedings 1869, p.030052_1 - 030052_7, 2017/08

 Times Cited Count:3 Percentile:8.08

In order to compare brightnesses of beams produced by different ion sources, a transverse emittance evaluation procedure with consistency and small ambiguity for different background noises is required. The procedure to evaluate emittances of beams produced by the Japan Proton Accelerator Research Complex (J-PARC) cesiated RF-driven H$$^{-}$$ ion source is presented in this paper. The ambiguity in emittance evaluations is eliminated by defining uniquely 100% and 95% beams with a reasonably corrected beam-signal base-level. Two 95%-beam transverse normalized root mean square emittances of beams, which are produced with almost the same 2-MHz RF power and cesiation condition but with different background noise, are estimated as almost the same values by this procedure.

Journal Articles

LEBT commissioning of the J-PARC LINAC

Shibata, Takanori*; Ikegami, Kiyoshi*; Liu, Y.*; Maruta, Tomofumi*; Naito, Fujio*; Takagi, Akira*; Asano, Hiroyuki; Kondo, Yasuhiro; Miura, Akihiko; Oguri, Hidetomo; et al.

Proceedings of 28th International Linear Accelerator Conference (LINAC 2016) (Internet), p.251 - 253, 2017/05

After upgrade of J-PARC Linac in 2014, Low Energy Beam Transport (LEBT) beam commissioning of the J-PARC LINAC has been made for improving H$$^{-}$$ beam intensity extracted from Linac. Currents of two solenoid coils and steering magnets in LEBT are optimized with extraction and acceleration voltages for static acceleration in ion source (IS) which decides on an initial emittance diagram of H$$^{-}$$ beam. As a result of LEBT and IS parameter optimization, beam transmission rate of RFQ has been reached up to 96% in 50 mA H$$^{-}$$ current operation. Moreover, PIC-MC (Particle-In-Cell Monte-Carlo) simulation models developed for H$$^{-}$$ transport in LEBT. Comparison between experimental and numerical results are presented to clarify beam physics from IS exit to RFQ entrance.

Journal Articles

Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates

Yamasaki, Atsushi*; Fujiwara, Hidenori*; Tachibana, Shoichi*; Iwasaki, Daisuke*; Higashino, Yuji*; Yoshimi, Chiaki*; Nakagawa, Koya*; Nakatani, Yasuhiro*; Yamagami, Kohei*; Aratani, Hidekazu*; et al.

Physical Review B, 94(11), p.115103_1 - 115103_10, 2016/11

AA2016-0587.pdf:2.55MB

 Times Cited Count:12 Percentile:32.92(Materials Science, Multidisciplinary)

In this study, we systematically investigate three-dimensional(3D) momentum-resolved electronic structures of Ruddlesden-Popper-type iridium oxides Sr$$_{n+1}$$Ir$$_{n}$$O$$_{3n+1}$$ using soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO$$_{2}$$-plane structure. This transition occurs when the spin-orbit-coupled $$j_{eff}$$ = 1/2 band changes its behavior in the dispersion relation and moves across the Fermi energy. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO$$_{3}$$ and $$k_{z}$$-dependent oscillations of photoelectron intensity in Sr$$_{3}$$Ir$$_{2}$$O$$_{7}$$. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole Brillouin zone and provides a panoramic view of electronic structures.

Journal Articles

Status of the J-PARC RF ion source

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

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.940 - 943, 2016/11

In 2014 October, operation of cesium-seeded Radio Frequency (RF)-driven negative hydrogen ion (H$$^{-}$$) source was started in J-PARC LINAC. Due to the skillful RF antenna screening and the proper pre-conditioning process, long term unscheduled beam stop due to the antenna failure did not occur for more than 1 year. The continuous operation of 1,350 hours with a peak beam current of 45 mA was achieved in the recent beam run. Moreover, the fluctuation of beam current in a low energy beam transport (LEBT) is kept within $$pm$$2% of target value by application of three feedback systems. An ion source test-stand was assembled to investigate the ion source beam characteristic, for example, the emittance at the position of the RFQ entrance. In the presentation, we will report the recent status of the ion source operation and some experimental results obtained at the ion source test-stand.

Journal Articles

Development of beam scrapers using a 3-Mev linac at J-PARC

Hirano, Koichiro; Asano, Hiroyuki; Ishiyama, Tatsuya; Ito, Takashi; Okoshi, Kiyonori; Oguri, Hidetomo; Kondo, Yasuhiro; Kawane, Yusuke; Kikuzawa, Nobuhiro; Sato, Yoshikatsu; et al.

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.310 - 313, 2016/11

We have used a beam scraper with the incident angle of 65deg to reduce the beam power deposition density in the MEBT between a 324 MHz RFQ and a 50-MeV DTL of the J-PARC linac. The 65$$^{circ}$$ scraper was irradiated by the H$$^{-}$$ beam up to particle number of 1.47E22. We observed a lot of surface projections with several hundred micrometers high in the beam irradiation damage on the scraper by using the laser microscope. In order to study the limits of scrapers, we constructed a new 3 MeV linac at J-PARC. We will conduct the scraper irradiation test at the end of this year.

Journal Articles

Beam commissioning of the linac for iBNCT

Naito, Fujio*; Anami, Shozo*; Ikegami, Kiyoshi*; Uota, Masahiko*; Ouchi, Toshikatsu*; Onishi, Takahiro*; Oba, Toshiyuki*; Obina, Takashi*; Kawamura, Masato*; Kumada, Hiroaki*; et al.

Proceedings of 13th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1244 - 1246, 2016/11

The proton linac installed in the Ibaraki Neutron Medical Research Center is used for production of the intense neutron flux for the Boron Neutron Capture Therapy (BNCT). The linac consists of the 3-MeV RFQ and the 8-MeV DTL. Design average beam current is 10mA. Target is made of Beryllium. First neutron production from the Beryllium target was observed at the end of 2015 with the low intensity beam as a demonstration. After the observation of neutron production, a lot of improvement s was carried out in order to increase the proton beam intensity for the real beam commissioning. The beam commissioning has been started on May 2016. The status of the commissioning is summarized in this report.

Journal Articles

Space charge neutralization studies with H$$^{-}$$ beam in low energy beam transport test stand

Artikova, S.; Takagi, Akira*; Shibata, Takanori*; Ikegami, Kiyoshi*

Proceedings of 7th International Particle Accelerator Conference (IPAC '16) (Internet), p.677 - 679, 2016/06

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