Jumpei Nakamura

Ultra Slow Muon Microscope at MUSE / J-PARC

We report current constructing states of the Ultra Slow Muon Beam at U-line / MUSE / J-PARC, which are supported by thermal muonium (Mu, μ+e−) production with the most intense pulsed slow muon beam, laser resonant ionization, and transportation of Ultra Slow Muon Beam. A thermal Mu is produced by a hot tungsten foil in a Mu-production chamber. At the laser resonant ionization process, a thermal Mu is ionized by coherent vacuum ultraviolet radiation and coherent 355-nm radiation. The coherent radiation sources are developed at RIKEN, installed in a laser cabin, and connected via a VUV steering chamber with the Mu-production chamber.

Current status of the J-PARC muon facility, MUSE

The muon science facility (MUSE), along with the neutron, hadron, and neutrino facilities, is one of the experimental areas of the J-PARC project. The MUSE facility is located in the Materials and Life Science Facility (MLF), which is a building integrated to include both neutron and muon science programs. Since the autumn of 2008, users operation is effective and making use of the pulsed muon beam particularly at the D-Line. Unfortunately, MUSE suffered severe damages from the earthquake on March 11, 2011, the so-called Higashi-Nippon Dai-Shinsai. We managed to have a stable operation of the superconducting solenoid magnet with use of the on-line refrigerator on December, 2012, although we had to overcome a lot of difficulties against components not working properly. But we had to stop again the whole operations on May 2013, because of the radioactive materials leakage accident at the Hadron Hall Experimental Facility. Finally we restarted the users runs on February 2014.

Construction of Ultra Slow Muon Beam Line at J-PARC

T. Nagatomo1, Y. Ikedo1, P. Strasser1, S. Makimura1, J. Nakamura1, K. Nishiyama1, K. Shimomura1, N. Kawamura1, A. Koda1, H. Fujimori1, Y. Kobayashi1, T.U. Ito2, W. Higemoto2, A.D. Pant3, R. Kadono1, E. Torikai3 and Y. Miyake1 1Muon Science Laboratory, High Energy Accelerator Research Organization (KEK), Ibaraki 319-1106, Japan 2Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Ibaraki 319-1184, Japan 3Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi 400-0016, Japan

Development of High-Rate Positron Tracker for the Muonium Production Experiment at J-PARC

1 Department of Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan 2 Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba, Ibaraki, Japan 3 Institute of Particle and Nuclear Studies, KEK, 1-1 Oho, Tsukuba, Ibaraki, Japan 4 Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama, Japan 5 Department of Physics, Korea University, 145, Aman-ro, Seongbuk-gu, Seoul, 137-713, Korea 6 Department of Physics, Tokyo University of Science, 1-3, Kagurazaka, Sinjuku-ku, Tokyo, Japan

Optimal crossed overlap of coherent vacuum ultraviolet radiation and thermal muonium emission for μSR with the Ultra Slow Muon

For μSR with ultra slow muon, we are constructing U line in materials and life science facility (MLF), J-PARC at present. Generation of ultra slow muon requires thermal muonium generation and laser resonant ionization process with vacuum ultraviolet radiation (1S→2P) and 355-nm radiation (2P→unbound). For laser resonant ionization, the coherent radiations and the thermal muonium emission must be coincident in time and space. The radiations can be steered in a chamber for reasonable overlap in space, and they can be easily overlapped in time because they are generated from one laser source. The trigger signal of the accelerator is useful for stable overlap in time.

Design and construction of the ultra-slow muon beamline at J-PARC/MUSE

At the J-PARC Muon Science Facility (MUSE), a new Ultra-Slow Muon beamline is being constructed to extend the μSR technique from bulk material to thin films, thus empowering a wide variety of surface and nano-science studies, and also a novel 3D imaging with the ultra-slow muon microscope. Ultra-slow muons will be produced by the re-acceleration of thermal muons regenerated by the laser resonant ionization of muonium atoms evaporated from a hot tungsten foil, a method that originated from the Meson Science Laboratory at KEK. The design parameters, construction status and initial beam commissioning are reported.

Present Status of Muon Production Target at J-PARC/MUSE

Shunsuke MAKIMURA*1, 2, Naritoshi KAWAMURA1, 2, Satoshi ONIZAWA3, Yukihiro MATSUZAWA3, Masato TABE4, Yasuo KOBAYASHI1, 2, Ryo SHIMIZU3, Hiroshi FUJIMORI1, 2, Yutaka IKEDO1, 2, Ryosuke KADONO1, 2, Akihiro KODA1, 2, Kenji M. KOJIMA1, 2, Kusuo NISHIYAMA1, 2, Jumpei NAKAMURA1, 2, Koichiro SHIMOMURA1, 2, Patrick STRASSER1, 2, Masaharu AOKI5, Yohei NAKATSUGAWA2, and Yasuhiro MIYAKE1, 2 . 1Muon Section, Materials and Life Science Division, J-PARC center, Tokai, Ibaraki 319-1195, Japan 2Muon Science Laboratory, High Energy Accelerator Research Organization (KEK-IMSS), Tokai, Ibaraki 319-1195, Japan 3The NIPPON ADVANCED TECHNOLOGY CO., LTD (NAT), Tokai, Ibaraki 319-1112, Japan 4Seekel Co., Ltd., Mito, Ibaraki 310-0851, Japan 5Osaka University, Toyonaka, Osaka 560-0043, Japan

Development of muon rotating target at J-PARC/MUSE

A pulsed muon beam with unprecedented intensity will be generated by a 3-GeV 333-micro A proton beam on a muon target made of 20-mm thick isotropic graphite at J-PARC. The current muon target with a fixed target method has been utilized without replacements since the first muon beam generation on September of 2008 till June of 2014. However, the proton irradiation damage to graphite is significant for our case. To extend the lifetime, the developments of the muon rotating target, in which the radiation damage is distributed to a wider area, have been performed.

U-line at MLF/J-PARC for Ultra Slow Muon Microscopy

Yutaka Ikedo1,2, Yasuhiro Miyake1,2, Koichiro Shimomura1,2, Patrick Strasser1,2, Naritoshi Kawamura1,2, Kusuo Nishiyama1,2, Shunsuke Makimura1,2, Hiroshi Fujimori1,2, Akihiro Koda1,2, Jumpei Nakamura1,2, Takashi Nagatomo1,2, Yasuo Kobayashi1,2, Taihei Adachi3, Amba Datt Pant4, Toru Ogitsu5,2, Tatsushi Nakamoto5,2, Kenichi Sasaki5,2, Hirokatsu Ohhata5,2, Ryutaro Okada5,2, Akira Yamamoto5, Yasuhiro Makida6,2, Makoto Yoshida6,2, Takahiro Okamura6,2, Ryuji Ohkubo7, Wataru Higemoto8,2, Takashi U. Ito8,2, Kazutaka Nakahara9, Kazuhiko Ishida10 1Muon Science Laboratory, Institute of Material and Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 2J-PARC Center, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan 3Faculty of Science, University of Tokyo, 7-3-1 hongo, Bunkyo, Tokyo 113-0501, Japan 4Interdiscplinary Graduate School of Medicine and Engineering, Yamanashi University, 4-3-11 Takeda, Kofu, Yamanashi 400–8511, Japan 5Cryogenics Science Center, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 6Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 7Mechanical Engineering center, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan 8Advance Science Research Center, Japan Atomic Energy Agency, 2-4 shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan 9Department of Physics, University of Maryland, College Park, MD 20742 4111, USA 10Advanced Meson Science Laboratory, Nishina Center, RIKEN, 2-1 hirosawa, Wako, Saitama 351-0198, Japan

Photoionization pathways and thresholds in generation of Lyman-α radiation by resonant four-wave mixing in Kr-Ar mixture

We develop a set of analytical approximations for the estimation of the combined effect of various photoionization processes involved in the resonant four-wave mixing generation of ns pulsed Lyman-α (L-α) radiation by using 212.556 nm and 820-845 nm laser radiation pulses in Kr-Ar mixture: (i) multi-photon ionization, (ii) step-wise (2+1)-photon ionization via the resonant 2-photon excitation of Kr followed by 1-photon ionization and (iii) laser-induced avalanche ionization produced by generated free electrons. Developed expressions validated by order of magnitude estimations and available experimental data allow us to identify the area for the operation under high input laser intensities avoiding the onset of full-scale discharge, loss of efficiency and inhibition of generated L-α radiation. Calculations made reveal an opportunity for scaling up the output energy of the experimentally generated pulsed L-α radiation without significant enhancement of photoionization.