arXiv subjects

S. Ohshima

Publications and source records attributed to S. Ohshima.

2 recordsLinked to original sources

arXiv2018

Development of the poloidal Charge eXchange Recombination Spectroscopy system in Heliotron J

A Charge eXchange Recombination Spectroscopy (CXRS) system designed to measure the poloidal rotation velocity is developed in Heliotron J. The poloidal CXRS system measures the carbon emission line (C VI, n=8-7, 529.05nm) and the Doppler shift of the emission line provides the information of plasma rotation velocity. A high throughput photographic-lens monochromator (F/2.8) with 0.73nm/mm dispersion is adopted to achieve high rotation velocity and temporal resolution. Since two heating neutral beams from two tangential injectors (NBI) are used as the diagnostic beams, a wide observation range (0.26 < 0.06) at peripheral region (r/a>0.6). The system design and the calibration method are presented. The initial results of poloidal rotation measurement show an electron diamagnetic rotation in an NBI heated plasma, while an ion diamagnetic rotation is observed when ECH is additionally applied. The evaluated radial electric field profile shows a positive Er at plasma core region in the ECH+NBI plasma, and a negative Er in the NBI heated plasma.

physics.plasm-ph↗

arXiv2003

Simple test for high Jc and low Rs superconducting thin films

A simple method, fishing high-Tc superconductor thin films out of liquid nitrogen bath by a permanent magnet (field > Hc1) due to the effect of high flux pinning, has been suggested to identify films having high critical current density (Jc > 106 A/cm2 at 77 K) and thus a low microwave surface resistance (Rs). We have demonstrated that a Nd-Fe-B magnet, having a maximum field of ~ 0.5 T, could fish out Tl-1223 superconducting thin films on LSAT substrate with a thickness of ~ 5000 Angstrong having Jc > 1 MA/cm2 (at 77 K) whereas it could not fish out other films with Jc < 0.1 MA/cm2 at 77 K. The fished out films exhibit Rs values 237 - 245 ((at 77 K and 10 GHz, which is lower than that (Rs = 317 (() of the best YBCO film at the same temperature and frequency. On the other hand, the non-fishable films show very high Rs values. This method is a very simple tool to test for high Jc and good microwave properties of superconducting films of large area which otherwise require a special and expensive tool.

cond-mat.supr-con↗