Plasma and Fusion Research

Volume 14, 2401086 (2019)

Regular Articles

Effect of High Ion Temperature on the Polytropic Coefficient in the End Region of GAMMA 10/PDX
Kunpei NOJIRI, Mizuki SAKAMOTO, Naomichi EZUMI, Satoshi TOGO, Takaaki IIJIMA, Seowon JANG, Akihiro TERAKADO, Yosuke KINOSHITA, Toshiki HARA, Tomonori TAKIZUKA1), Yuichi OGAWA2) and Yousuke NAKASHIMA
Plasma Research Center, University of Tsukuba, Tsukuba 305-8577, Japan
1)
Graduate School of Engineering, Osaka University, Suita 565-0871, Japan
2)
Graduate School of Frontier Sciences, University of Tokyo, Kashiwa 277-8568, Japan
(Received 30 September 2018 / Accepted 9 January 2019 / Published 3 June 2019)

Abstract

The effect of high ion temperature on the ion polytropic coefficient (γ) was experimentally investigated in the end region of the GAMMA 10/PDX tandem mirror. The ion temperature parallel to the magnetic field (Ti∥) was varied using the ion cyclotron range of frequencies (ICRF) waves, which heat the plasma in the central cell, and by applying an additional gas puff in the central cell. Assuming the ion sound speed, γTi∥ was evaluated by a Langmuir probe, and Ti∥ was evaluated in an ion energy analyzer. These parameters were combined to evaluate γ. The time evolutions of γTi∥ obtained from the probe and Ti∥ obtained from the energy analyzer were similar. The plasma in the end region can be regarded as collisionless, but γ was lower with ICRF heating than without the heating. A high Ti∥ component was identified in the heated case. As mentioned in a previous numerical study [B. Lin et al., Phys. Plasmas 23, 083508 (2016)], it is experimentally suggested that γ can be reduced by the high Ti∥ component resulting from the ICRF heating.

Keywords

ion temperature, ion polytropic coefficient, sound speed, Langmuir probe, ion energy analyzer

DOI: 10.1585/pfr.14.2401086

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