Akio Sanpei

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The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition(More)
Tangential soft-x ray (SXR) imaging diagnostic has been developed and three-dimensional (3D) structure of the internal magnetic surface has been deduced by comparing the experimental and calculated two-dimensional SXR images in a reversed field pinch. The SXR imaging system, consisting of a MCP, a fluorescent plate, and an intensified charge coupled device(More)
Makoto MIYAGISHI, Akihiko IRIE, Haruhiko HIMURA, Sadao MASAMUNE, Akio SANPEI, Noriyuki HASUIKE, Nobuyuki ICHINOSE, and Takashi WAKASUGI Department of Electronics, Kyoto Institute of Technology, Kyoto 606-8585, Japan Department of Comprehensive Sciences, Kyoto Institute of Technology, Kyoto 606-8585, Japan Department of Chemistry and Materials Technology,(More)
A vortex crystal is a quasistationary, symmetric array of intense vortices (clumps). A low level of background vorticity is experimentally observed to assist three clumps in forming an equilateral triangle starting from initial positions on a linear array. The triangle constitutes a unit cell of a crystal in a many-vortex system. The background vortex curbs(More)
In nonneutral plasma, depleted regions (holes) in the vorticity often play a controlling role in the evolution of two-dimensional turbulence. We report experimental investigations of the generation process of ring holes (three-dimensionally annular depletion) surrounding a strongly-peaked clump of vorticity (point vortex) immersed in the background of a(More)
This paper experimentally investigates the applicability of a micro-channel plate (MCP) followed by a phosphor screen to charged particles along with a calibration method for estimating the acceptable limit of input particle flux and appropriate operation parameters of a particular MCP. For the first time, plasmas consisting of only lithium ions are(More)
©2009 by The Japan Society of Plasma Science and Nuclear Fusion Research (Received: 3 September 2008 / Accepted: 5 January 2009) Numeri al Investigation of Velo ity Map of Outward Ele trons Penetrating in Heli al Magneti Surfa es Kazutaka NAKAMURA1), Haruhiko HIMURA1), Mitsutaka ISOBE2), Akio SANPEI1), and Sadao MASAMUNE1) 1)Kyoto Institute of Te hnology,(More)
The reversed-field pinch (RFP) is a compact, high-beta magnetic confinement concept with a great advantage of weak external toroidal magnetic field. Lowering the aspect ratio (A) of RFP has the possibilities of enhanced neoclassical bootstrap current and simpler magnetic mode dynamics. Initial results from a low-A RFP machine RELAX is reported. The low-A(More)
Dynamics of a point vortex in interaction with a broad profile of background vorticity is studied experimentally by using an electron plasma. The observed motion of the vortex compares favorably with a recently proposed theoretical model [D. A. Schecter and D. H. E. Dubin, Phys. Rev. Lett. 83, 2191 (1999)]. Perturbations in the background distribution in(More)