Plasma and Fusion Research

Volume 14, 3403103 (2019)

Regular Articles


Mode Purity of Electron Cyclotron Waves after Their Passage through the Peripheral Plasma in the Large Helical Device
Kota YANAGIHARA1), Shin KUBO1,2), Toru I. TSUJIMURA2) and Ilya Y. DODIN3)
1)
Nagoya University, Nagoya 464-8601, Japan
2)
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
3)
Princeton Plasma Physics Laboratory, Princeton 08543, USA
(Received 9 January 2019 / Accepted 19 April 2019 / Published 19 June 2019)

Abstract

Plasma heating and current drive with Electron Cyclotron Waves (ECWs) require precise control over the polarization state of ECWs to ensure that the entire input power is deposited where intended. However, due to the magnetic shear in the peripheral plasma, the polarization state can change. This effect is particularly pronounced in the Large Helical Device (LHD), where the magnetic field is sheared strongly. Here, we present a new code PARADE (PAraxial RAy DEscription) that can simulate the evolution of the polarization state along the beam propagation without resorting to full-wave modeling. We apply PARADE to the LHD plasma and simulate the evolution of the beam transverse structure, including the local amplitudes of the two electromagnetic eigenmodes. The results surpass those yielded by the code LHDGauss used in the past. Based on these new results, we discuss how to improve the mode purity of ECWs by controlling the initial polarization state. A remarkable improvement is predicted numerically.


Keywords

electron cyclotron resonance heating, Large Helical Device, ray tracing, extended geometrical optics, polarization, mode conversion, peripheral plasma

DOI: 10.1585/pfr.14.3403103


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