Refine your search:     
Report No.
 - 
Search Results: Records 1-20 displayed on this page of 87

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Investigation of the electronic structure of the Mg$$_{99.2}$$Zn$$_{0.2}$$Y$$_{0.6}$$ alloy using X-ray photoelectron spectroscopy

Miyazaki, Hidetoshi*; Akatsuka, Tatsuyoshi*; Kimura, Koji*; Egusa, Daisuke*; Sato, Yohei*; Itakura, Mitsuhiro; Takagi, Yasumasa*; Yasui, Akira*; Ozawa, Kenichi*; Mase, Kazuhiko*; et al.

Materials Transactions, 64(6), p.1194 - 1198, 2023/06

We investigated the electronic structure of the Mg$$_{99.2}$$Zn$$_{0.2}$$Y$$_{0.6}$$ alloy using hard and soft X-ray photoemission spectroscopy and electronic band structure calculations to understand the mechanism of the phase stability of this material. Electronic structure of the Mg$$_{99.2}$$Zn$$_{0.2}$$Y$$_{0.6}$$ alloy showed a semi-metallic electronic structure with a pseudo-gap at the Fermi level. The observed electronic structure of the Mg$$_{99.2}$$Zn$$_{0.2}$$Y$$_{0.6}$$ alloy suggests that the presence of a pseudogap structure is responsible for phase stability.

Journal Articles

110 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 2373, p.040002_1 - 040002_8, 2021/07

On 2018, the stable operation of the J-PARC cesiated RF-driven H$$^{-}$$ ion source (IS) with a 62 keV 100 mA beam, whose emittances were suitable for the radio-frequency quadrupole LINAC (RFQ), 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 2.4 mA/kW and the possibility of the space charge limited beam intensity pulling up by increasing the extraction and acceleration voltages were proven. On the other hand, the withstand voltage for the stable operation with an RF plasma production of the present 2 MHz matching circuit and the high voltage power supply was measured as about 66 kV. In the operation with the presently highest beam energy of 65 keV, a 110 mA beam with emittances suitable for the RFQ was stably produced. Since 102.5 mA of the beam was measured inside the emittances used for the RFQ design, the next generation 100 mA LINAC will be possible with the IS.

Journal Articles

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

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

JPS Conference Proceedings (Internet), 33, p.011008_1 - 011008_7, 2021/03

A cesiated RF-driven negative hydrogen ion source was initiated 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 equipped with two turbo molecular pumps, each having the pumping speed of 1500 L/s, for differential pumping. The user operation was started with the beam current of 33 mA from the ion source. We gradually increased both beam current and continuous operation time of the ion source. In July, 2018 (Run#79), approximately 2,200 hours operation was achieved with the typical beam current, pulse length and repetition rate of 47 mA, 300 $$mu$$s and 25 Hz, respectively. Since October, 2018 (Run#80), the ion source has been delivering a nominal beam current of approximately 60 mA.

Journal Articles

Development of long pulse arc driven ion source for iBNCT

Shibata, Takanori*; Sugimura, Takashi*; Ikegami, Kiyoshi*; Takagi, Akira*; Sato, Masaharu*; Naito, Fujio*; Okoshi, Kiyonori; Hasegawa, Kazuo

JPS Conference Proceedings (Internet), 33, p.011009_1 - 011009_6, 2021/03

Upgrade of beam current in the Linac of Ibaraki Boron Neutron Capture Therapy (iBNCT) is one of the most important requirements to realize clinical trial. By 2018, the measurement of the produced neutrons characteristics and the neutron irradiation experiment for living cells have been done by producing 8-MeV proton beam current at the beryllium target with average current up to 2 mA. In order to satisfy the original clinical trial conditions, 5 mA average beam current is required at the target. For this goal, peak beam current extracted from the ion source should be increased to 60 mA from the present 30 mA with duty factor up to more than 10% (pulse width up to 1 ms and repetition rate up to more than 100 Hz). Stability of the peak current in the macro pulse is also important for the clinical application.

Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

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; Oguri, Hidetomo

Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.554 - 557, 2019/07

In September 2014, a cesiated RF-driven negative hydrogen ion (H$$^{-}$$) source was initiated to operate at the Japan Proton Accelerator Research Complex (J-PARC). The extracted H$$^{-}$$ beam current and the continuous operation time of the ion source have been improved upon their own records. In the RUN#79 (from April to July 2018), the ion source delivered the H$$^{-}$$ beam current of 47 mA to the post-accelerators for 2,201 hours continuously. In October 2018, the beam current from the ion source was increased to 60 mA in order to inject the beam current of 50 mA into the 3 GeV synchrotron. In the RUN#80 (from October to December 2018), the continuous operation time of 1,791 hours was achieved. For the past year, we had the antenna failures twice during the operation, and needed to replace to a spare ion source. We have been developed the J-PARC-made antenna by using a test-stand. Recent experiment result showed the continuous operation time of 2,083 hours was achieved with the J-PARC-made antenna.

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:233 Percentile:99.74(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:72.2

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:6 Percentile:93.99

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:82.43

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:5 Percentile:91.9

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:89.25

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:85.26

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:6 Percentile:91.88

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:78.89

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.

87 (Records 1-20 displayed on this page)