Plasma and Fusion Research

Volume 3, 013 (2008)

Rapid Communications

Direct Measurement of a Mode-Converted Electron Bernstein Wave in the Internal Coil Device Mini-RT
Eiichi YATSUKA, Daisuke SAKATA, Kiyotake KINJO, Junji MORIKAWA1) and Yuichi OGAWA1)
Graduate School of Frontier Sciences, University of Tokyo, Kashiwa 277-8561, Japan
1)
High Temperature Plasma Center, University of Tokyo, Kashiwa 277-8568, Japan
(Received 21 December 2007 / Accepted 30 January 2008 / Published 6 March 2008)

Abstract

An electric field measurement system in the Electron Cyclotron Range of Frequency (ECRF) has been developed for the direct detection of mode-converted Electron Bernstein Waves (EBWs), where a low-power ECRF wave (1-2.1 GHz, 10 W) is injected into overdense plasmas (typical peak density is 7 × 1016 m-3 ), and the ECRF electric field is directly measured using a small monopole antenna (an element size of 5 mm) inserted into the confined plasma. A density gradient is an important parameter for mode conversion to EBW. In the internal coil device, Mini-RT, a steep density gradient (e.g., Ln ∼ 5 cm) is available at the plasma surface. We have detected short-wavelength waves with refractive indices of ∼10 or more around the electron cyclotron harmonic resonance layers, and confirmed a phase reversal of an ECRF electric field at the same locations. Since the EBW is a backward wave with a short wavelength, experimental results suggest the direct measurement of the mode-converted EBW in plasma.

Keywords

electron Bernstein wave (EBW), mode conversion, backward wave, interferometry, RF wave field measurement, overdense plasma

DOI: 10.1585/pfr.3.013

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This paper may be cited as follows:

Eiichi YATSUKA, Daisuke SAKATA, Kiyotake KINJO, Junji MORIKAWA and Yuichi OGAWA, Plasma Fusion Res. 3, 013 (2008).