Observation of parametric decay instability on TST-2 lower hybrid wave driven plasma

Yongtae Ko; Yuichi Takase; Akira Ejiri; Naoto Tsujii; Osamu Watanabe; Hibiki Yamazaki; Charles P. Moeller; Yasuo Yoshimura; Kotaro Iwasaki; Yuki Aoi; Kyohei Matsuzaki; James H.P. Rice; Yi Peng; Yuki Osawa

doi:10.1585/PFR.15.2402007

Observation of parametric decay instability on TST-2 lower hybrid wave driven plasma

Yongtae Ko^*, Yuichi Takase, Akira Ejiri, Naoto Tsujii, Osamu Watanabe, Hibiki Yamazaki, Charles P. Moeller, Yasuo Yoshimura, Kotaro Iwasaki, Yuki Aoi, Kyohei Matsuzaki, James H.P. Rice, Yi Peng, Yuki Osawa

^*Corresponding author for this work

Biochemistry and Molecular Genetics

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Abstract

Parametric decay instabilities (PDIs) in lower hybrid (LH) frequency range were observed in TST-2 in a various parameter range. LH wave measurement has been performed using four RF magnetic probes. We have been studied experiments aiming at efficient non-inductive current drive with the outboard and the top antennas installed on the outboard side and the top side of the vacuum vessel, respectively. Since PDIs are believed to deteriorate the current drive efficiency, we investigated conditions to avoid them. Operations with various combination of antennas (outboard, top), toroidal magnetic field strength and direction (CW, CCW B_T), working gas (hydrogen, deuterium) and density (normal, high) were investigated. In the outboard launch case, PDI sideband frequency δf associated with ion cyclotron quasi-modes was observed with large degree in any B_T strength in both hydrogen and deuterium plasma. On the other hand, no clear such sideband δf peak was observed only in deuterium plasma with the top launch case. Among various scenarios, the top launch with CW and CCW toroidal field in deuterium plasma seems to be desirable in terms of avoiding PDIs.

Original language	English (US)
Article number	2007
Journal	Plasma and Fusion Research
Volume	15
DOIs	https://doi.org/10.1585/PFR.15.2402007
State	Published - 2020

Funding

This work is supported by Grant-in-Aid for Scientific Research (S) (21226021), by National Institute for Fusion Science Collaboration Research Programs NIFS14KOCR001, NIFS18KOAR022 and NIFS12KUTR078. This work is also supported in part by Japan/US Cooperation in Fusion Research and Development and US DoE Cooperative Agreement DE-FC02-04ER54698.

Keywords

Lower hybrid wave
Magnetic probe
Parametric decay instability
Spherical tokamak

ASJC Scopus subject areas

Condensed Matter Physics

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1585/PFR.15.2402007

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title = "Observation of parametric decay instability on TST-2 lower hybrid wave driven plasma",

abstract = "Parametric decay instabilities (PDIs) in lower hybrid (LH) frequency range were observed in TST-2 in a various parameter range. LH wave measurement has been performed using four RF magnetic probes. We have been studied experiments aiming at efficient non-inductive current drive with the outboard and the top antennas installed on the outboard side and the top side of the vacuum vessel, respectively. Since PDIs are believed to deteriorate the current drive efficiency, we investigated conditions to avoid them. Operations with various combination of antennas (outboard, top), toroidal magnetic field strength and direction (CW, CCW BT), working gas (hydrogen, deuterium) and density (normal, high) were investigated. In the outboard launch case, PDI sideband frequency δf associated with ion cyclotron quasi-modes was observed with large degree in any BT strength in both hydrogen and deuterium plasma. On the other hand, no clear such sideband δf peak was observed only in deuterium plasma with the top launch case. Among various scenarios, the top launch with CW and CCW toroidal field in deuterium plasma seems to be desirable in terms of avoiding PDIs.",

keywords = "Lower hybrid wave, Magnetic probe, Parametric decay instability, Spherical tokamak",

author = "Yongtae Ko and Yuichi Takase and Akira Ejiri and Naoto Tsujii and Osamu Watanabe and Hibiki Yamazaki and Moeller, {Charles P.} and Yasuo Yoshimura and Kotaro Iwasaki and Yuki Aoi and Kyohei Matsuzaki and Rice, {James H.P.} and Yi Peng and Yuki Osawa",

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year = "2020",

doi = "10.1585/PFR.15.2402007",

language = "English (US)",

volume = "15",

journal = "Plasma and Fusion Research",

issn = "1880-6821",

publisher = "The Japan Society of Plasma Science and Nuclear Fusion Research (JSPF)",

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TY - JOUR

T1 - Observation of parametric decay instability on TST-2 lower hybrid wave driven plasma

AU - Ko, Yongtae

AU - Takase, Yuichi

AU - Ejiri, Akira

AU - Tsujii, Naoto

AU - Watanabe, Osamu

AU - Yamazaki, Hibiki

AU - Moeller, Charles P.

AU - Yoshimura, Yasuo

AU - Iwasaki, Kotaro

AU - Aoi, Yuki

AU - Matsuzaki, Kyohei

AU - Rice, James H.P.

AU - Peng, Yi

AU - Osawa, Yuki

PY - 2020

Y1 - 2020

N2 - Parametric decay instabilities (PDIs) in lower hybrid (LH) frequency range were observed in TST-2 in a various parameter range. LH wave measurement has been performed using four RF magnetic probes. We have been studied experiments aiming at efficient non-inductive current drive with the outboard and the top antennas installed on the outboard side and the top side of the vacuum vessel, respectively. Since PDIs are believed to deteriorate the current drive efficiency, we investigated conditions to avoid them. Operations with various combination of antennas (outboard, top), toroidal magnetic field strength and direction (CW, CCW BT), working gas (hydrogen, deuterium) and density (normal, high) were investigated. In the outboard launch case, PDI sideband frequency δf associated with ion cyclotron quasi-modes was observed with large degree in any BT strength in both hydrogen and deuterium plasma. On the other hand, no clear such sideband δf peak was observed only in deuterium plasma with the top launch case. Among various scenarios, the top launch with CW and CCW toroidal field in deuterium plasma seems to be desirable in terms of avoiding PDIs.

AB - Parametric decay instabilities (PDIs) in lower hybrid (LH) frequency range were observed in TST-2 in a various parameter range. LH wave measurement has been performed using four RF magnetic probes. We have been studied experiments aiming at efficient non-inductive current drive with the outboard and the top antennas installed on the outboard side and the top side of the vacuum vessel, respectively. Since PDIs are believed to deteriorate the current drive efficiency, we investigated conditions to avoid them. Operations with various combination of antennas (outboard, top), toroidal magnetic field strength and direction (CW, CCW BT), working gas (hydrogen, deuterium) and density (normal, high) were investigated. In the outboard launch case, PDI sideband frequency δf associated with ion cyclotron quasi-modes was observed with large degree in any BT strength in both hydrogen and deuterium plasma. On the other hand, no clear such sideband δf peak was observed only in deuterium plasma with the top launch case. Among various scenarios, the top launch with CW and CCW toroidal field in deuterium plasma seems to be desirable in terms of avoiding PDIs.

KW - Lower hybrid wave

KW - Magnetic probe

KW - Parametric decay instability

KW - Spherical tokamak

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Observation of parametric decay instability on TST-2 lower hybrid wave driven plasma

Abstract

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