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Journal Articles

Spin current at a magnetic junction as a probe of the Kondo state

Yamamoto, Tsuyoshi*; Kato, Takeo*; Matsuo, Mamoru

Physical Review B, 104(12), p.L121401_1 - L121401_5, 2021/09

Journal Articles

Spin pumping of two-dimensional electron gas with Rashba and Dresselhaus spin-orbit interactions

Yama, Masaki*; Tatsuno, Masahiro*; Kato, Takeo*; Matsuo, Mamoru

Physical Review B, 104(5), p.054410_1 - 054410_9, 2021/08

Journal Articles

Bound spinon excitations in the spin-$$frac{1}{2}$$ anisotropic triangular antiferromagnet Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$

Nawa, Kazuhiro*; Hirai, Daigoro*; Kofu, Maiko; Nakajima, Kenji; Murasaki, Ryo*; Kogane, Satoshi*; Kimata, Motoi*; Nojiri, Hiroyuki*; Hiroi, Zenji*; Sato, Taku*

Physical Review Research (Internet), 2(4), p.043121_1 - 043121_11, 2020/12

The spin excitations of the $$S$$ = $$frac{1}{2}$$ anisotropic triangular antiferromagnet Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$ were investigated by inelastic neutron-scattering experiments. The spin excitation spectrum exhibits sharp dispersive modes in addition to a spinonlike continuum. The consistency with the simulated spectrum based on the random-phase approximation is better for Ca$$_{3}$$ReO$$_{5}$$Cl$$_{2}$$ than for Cs$$_{2}$$CuCl$$_{4}$$, indicating that the spin system in the former remains closer to a Tomonaga-Luttinger liquidlike disordered state.

Journal Articles

Nanoscale relaxation in "Water-in-Salt" and "Water-in-Bisalt" electrolytes

Gonzal$'e$z, M. A.*; Borodin, O.*; Kofu, Maiko; Shibata, Kaoru; Yamada, Takeshi*; Yamamuro, Osamu*; Xu, K.*; Price, D. L.*; Saboungi, M.-L.*

Journal of Physical Chemistry Letters (Internet), 11(17), p.7279 - 7284, 2020/09

 Times Cited Count:13 Percentile:78.18(Chemistry, Physical)

Journal Articles

Dynamical spin-to-charge conversion on the edge of quantum spin Hall insulator

Araki, Yasufumi; Misawa, Takahiro*; Nomura, Kentaro*

Physical Review Research (Internet), 2(2), p.023195_1 - 023195_11, 2020/05

Journal Articles

Diffusion behavior of methanol molecules confined in cross-linked phenolic resins studied using neutron scattering and molecular dynamics simulations

Shudo, Yasuyuki*; Izumi, Atsushi*; Hagita, Katsumi*; Yamada, Takeshi*; Shibata, Kaoru; Shibayama, Mitsuhiro*

Macromolecules, 51(16), p.6334 - 6343, 2018/08

 Times Cited Count:10 Percentile:37.86(Polymer Science)

Journal Articles

Imaging of ablation dynamics by soft X-ray laser

Tomita, Takuro*; Hasegawa, Noboru; Nishikino, Masaharu; Kawachi, Tetsuya; Suemoto, Toru

Reza Kenkyu, 40(8), p.592 - 597, 2012/08

A single-shot soft X-ray laser pulse was used as a probe to investigate the early stage of the laser ablation process on platinum caused by the femtosecond near-infrared pump pulse. From time-resolved interferometry, we observed the dilation of the ablation front on a scale of 10 nm in the picosecond region. In the reflective imaging, we found three distinct types of dynamical responses, depending on the radial position in the pump beam spot. These characteristic behaviors correspond to different laser fluence and were attributed to different ablation schemes: spallation, homogeneous nucleation, and fragmentation/vaporization, which have been predicted from molecular dynamics simulation.

Journal Articles

Development of the X-ray interferometer and the method of temporal synchronization of X-ray and optical pulse

Hasegawa, Noboru; Yamamoto, Minoru*; Terakawa, Kota*; Nishikino, Masaharu; Ochi, Yoshihiro; Minami, Yasuo*; Tomita, Takuro*; Kawachi, Tetsuya; Suemoto, Toru

AIP Conference Proceedings 1465, p.23 - 27, 2012/07

 Times Cited Count:0 Percentile:0.13

We have developed a soft X-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The depth and lateral resolutions of the interferometer were about 1 nm and 1.8 micron, respectively. We observed the initial stage ($$sim$$50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse. The expansion speed of the Pt surface (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the precision of temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials.

Journal Articles

Picosecond soft-X-ray laser interferometer for probing nanometer surface structure

Ochi, Yoshihiro; Terakawa, Kota*; Hasegawa, Noboru; Yamamoto, Minoru*; Tomita, Takuro*; Kawachi, Tetsuya; Minami, Yasuo*; Nishikino, Masaharu; Imazono, Takashi; Ishino, Masahiko; et al.

Japanese Journal of Applied Physics, 51(1), p.016601_1 - 016601_3, 2012/01

 Times Cited Count:10 Percentile:40.74(Physics, Applied)

We have developed a soft X-ray laser interferometer based on the double Lloyd's mirror and obtained a single shot interferogram by a 7-ps pulse at the wavelength of 13.9 nm. Micrometer grooves with 5-nm depth were successfully reconstructed from the interferogram. The lateral and depth resolutions were estimated to be 1.5 $$mu$$m and better than 1 nm, respectively. This interferometer will be an attractive diagnostic device for observing transiently changing nano-scale deviations on solid surfaces.

Journal Articles

Observation of the laser-induced surface dynamics by the single-shot X-ray laser interferometer

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; Sasaki, Akira; Terakawa, Kota*; Minami, Yasuo*; et al.

Proceedings of SPIE, Vol.8140, p.81400G_1 - 81400G_8, 2011/10

 Times Cited Count:3 Percentile:82.27

We have developed a soft X-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The interferometer consisted of the reflection optics including double Lloyd's mirrors and focusing optics, and the interference fringes are produced on the detector surface. By using this interferometer, the initial stage ($$sim$$50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse was observed. The expansion speed of the surface estimated from the result (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials, to which the pump and probe timing was adjusted by using the X-ray streak camera.

Journal Articles

Development of 20 kW input power coupler for 1.3 GHz ERL main linac; The High power test of the prototype coupler

Shinoe, Kenji*; Sakai, Hiroshi*; Umemori, Kensei*; Cenni, E.*; Sawamura, Masaru; Nakamura, Norio*; Furuya, Takaaki*

Proceedings of 8th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1300 - 1302, 2011/08

We are developing ERL main linac input coupler. Until now, prototypes of ceramic windows were created and performances were tested. Using this ceramic window, we produced a coupler prototype model. The coupler prototype was installed into an insulating vacuum chamber and cooled by liquid nitrogen, and the high power test was performed. This is the condition, where the coupler is actually used in a cryomodule. In this test, we were able to input 25 kW power. It was checked that the magnitude of generation of heat is also satisfactory. It was checked that this coupler fulfills the specification demanded from ERL main linac.

Journal Articles

High power tests of KEK-ERL input coupler for main linac under liquid nitrogen condition

Sakai, Hiroshi*; Furuya, Takaaki*; Nakamura, Norio*; Umemori, Kensei*; Shinoe, Kenji*; Sawamura, Masaru; Cenni, E.*

Proceedings of 15th International Conference on RF Superconductivity (SRF 2011) (Internet), p.356 - 360, 2011/07

We fabricated the prototype of an input coupler with two ceramic windows for ERL main linac and performed the high power test. In high power test, the one cold window was installed into the vacuum insulating chamber and cooled by liquid nitrogen. First, the multipacting limited the power level to 10 kW. The pulse processing method for 8 hours enabled the final power level to 25 kW with standing wave condition. We could also keep 20 kW power feeding into the coupler for 16 hours. The maximum measured temperature rises under feeding the 20 kW power to coupler were 120 K near the bellows parts and these are not so severe values to operate ERL main linac. The thermal cycle test of cold window of coupler was done. After 10-times thermal cycle tests between the room temperature and liquid nitrogen temperature, no leaks or cracks were observed. From these results of high power test, this prototype coupler satisfies our thermal and RF requirements.

Journal Articles

Vertical test results on KEK-ERL 9-cell L-band superconducting cavity

Cenni, E.*; Furuya, Takaaki*; Sakai, Hiroshi*; Umemori, Kensei*; Shinoe, Kenji*; Sawamura, Masaru

Proceedings of 15th International Conference on RF Superconductivity (SRF 2011) (Internet), p.789 - 794, 2011/07

In order to develop the Energy Recovery Linac, we are studying the performance of two prototype L-band superconducting cavities by means of vertical tests. The cavities were inspected through rotating X-ray and temperature mapping system. The performance limiting factor was found to be the field emissions. We observed X-ray emission and temperature raise along the cavity wall. The quench locations were determined with a good agreement between X-ray and temperature sensors. During vertical test we experienced some interesting phenomena such as quality factor degradation and X-ray burst. In the first case the degradation was observed even at low field, however we recovered it with a warming up to room temperature without additional surface treatment. In the latter case new emitters suddenly appeared after some quenches. They remained in the same location also after the warming up.

Journal Articles

Construction of cERL cryomodules for injector and main linac

Umemori, Kensei*; Furuya, Takaaki*; Kako, Eiji*; Noguchi, Shuichi*; Sakai, Hiroshi*; Sato, Masato*; Shishido, Toshio*; Watanabe, Ken*; Yamamoto, Yasuchika*; Shinoe, Kenji*; et al.

Proceedings of 15th International Conference on RF Superconductivity (SRF 2011) (Internet), p.956 - 961, 2011/07

The Compact ERL (cERL) project is advanced in Japan. Its aim is to demonstrate the circulation of 100 mA electron beams with energy of 35-200 MeV. Superconducting cavities are key components for realizing ERL and used for injector part and main linac part. Critical issue for the injector part is the development of input power coupler. Prototype input couplers were fabricated and high power test was performed. Cooling ability of HOM coupler is also important for CW operation of cavity. At main linac part, HOM damped 9-cell cavities are applied to avoid BBU instabilities. Prototypes were fabricated for the cavity, the input coupler and the HOM absorber. Their performance was investigated. For both parts, cryomodules are under construction and will be completed in 2012.

Journal Articles

Generation and applications of ultra-short electron beams in energy-recovery linacs

Hajima, Ryoichi; Shimada, Miho*; Nakamura, Norio*

Nuclear Instruments and Methods in Physics Research A, 637(1, Suppl.), p.S37 - S42, 2011/05

 Times Cited Count:2 Percentile:19.93(Instruments & Instrumentation)

Energy-recovery linacs (ERLs) are in operation and under development in the world for future lightsources, which cover a wide range of photon energy, from THz to $$gamma$$-rays, by using various kinds of photo-emission processes, undulator radiation, free-electron lasers, laser Compton scattering (LCS), and coherent radiation. Availability of ultra-short electron beams is an essential feature of ERLs for future light sources. In this paper, we provide an overview of the generation and applications of ultra-short electron beams in ERLs. Magnetic bunch compression and velocity bunching are the two schemes of ultra-short electron beam generation that are presented with the Compact ERL test facility as an example.

Journal Articles

Journal Articles

Development of a main linac module for compact ERL project

Umemori, Kensei*; Furuya, Takaaki*; Sakai, Hiroshi*; Takahashi, Takeshi*; Shinoe, Kenji*; Sawamura, Masaru

Proceedings of 25th International Linear Accelerator Conference (LINAC 2010) (CD-ROM), p.404 - 406, 2010/09

In order to obtain technology needed for construction of the ERL main linac cryomodule, several developments have been performed. A prototype of 9-cell superconducting cavity was fabricated. Its performance was confirmed through vertical tests. Prototypes of coupler components were also fabricated and tested at the high power test stand. They could successfully pass the specified RF power. A prototype of HOM absorber without ferrite was made. It is under cooling tests. Design work of cryomodule is in progress.

Journal Articles

The Calculation of transverse kick by the input coupler of superconducting cavity for ERL main linac

Muto, Toshiya*; Umemori, Kensei*; Sakai, Hiroshi*; Sawamura, Masaru; Shinoe, Kenji*; Furuya, Takaaki*

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.840 - 842, 2010/08

Energy Recovery Linac (ERL) for future light source has been developed by KEK, JAEA, ISSP and other institutes in Japan. An input coupler must feed high power, which is estimated about 20 kW for 20 MV/m ERL operation, into the main linac superconducting cavities. Because the input coupler induced an asymmetric electromagnetic field in the cavity, accelerating TM010 mode produce a transverse kick similar to higher order modes. Using CST Microwave-Studio (MW-Studio), we calculated the transverse kick of accelerating mode induced by the input coupler. In case of the on crest acceleration, the transverse kick by the transverse electric field and magnetic field are small as compared with the accelerating voltage. We also calculated the dependence with various inserted position of the coupler. In this paper, we will report the calculation of transverse kick and an arrangement of cavities to reduce the transverse kick.

Journal Articles

Development of cavity diagnostics system for ERL superconducting cavity

Sakai, Hiroshi*; Umemori, Kensei*; Takahashi, Takeshi*; Furuya, Takaaki*; Shinoe, Kenji*; Ishii, Atsushi*; Sawamura, Masaru; Muto, Toshiya*

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.173 - 176, 2010/08

We are developing the superconducting (SC) cavity for Energy Recovery Linac (ERL) in Japan. In order to survey the electron emission and the heating spot of the cavity inner surface in detail, cavity diagnostics with the rotating mapping system was applied. Two types of sensors, one of which was the carbon resistor and the other was the Si PIN photo diode, were set to detect the temperature rise and electron emission. By rotating the sensor arrays around the cavity axis, a lot of information was obtained all over the cavity surface in detail. This paper reports the results of vertical tests by using this rotating mapping system with the single-cell and 9-cell Nb ERL cavity.

Journal Articles

Development of 20 kW input power coupler for 1.3 GH ERL main linac; High power test of the renewed ceramic window

Shinoe, Kenji*; Sakai, Hiroshi*; Umemori, Kensei*; Sawamura, Masaru; Nakamura, Norio*; Furuya, Takaaki*

Proceedings of 7th Annual Meeting of Particle Accelerator Society of Japan (DVD-ROM), p.511 - 513, 2010/08

We started to develop an input power coupler for a 1.3 GHz ERL superconducting cavity for main linac. We fabricated power coupler components such as ceramic windows and bellows and carried out the high-power test of the components by using a CW 30 kW IOT power source. During this test, the ceramic window was broken by the sudden heat load. We found that this heat load occurred by the unexpected dipole mode. We renewed the ceramic window and successfully carried out the high power test up to CW 27 kW input power.

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