Coupling of ICRF waves and axial transport of high-energy ions owing to spontaneously excited waves in the GAMMA 10 tandem mirror

Abstract

Plasmas with high ion-temperature of several keV and strong temperature anisotropy of more than 10 have been produced by using ion-cyclotron range of frequency (ICRF) heating in the GAMMA 10 tandem mirror. In such high performance plasmas with strong anisotropy, high-frequency fluctuations, so-called Alfvén-Ion-Cyclotron (AIC) waves, are spontaneously excited. The AIC waves have several discrete peaks in the frequency spectrum. Couplings between ICRF waves for heating and excited AIC waves are clearly observed in the central cell of GAMMA 10. Low frequency waves which have differential frequencies between discrete peaks of the AIC waves are also observed. Parametric decay of ICRF waves are discussed and pitch angle scattering of high-energy ions owing to those low-frequency waves are clearly detected. Energy transport along the magnetic field line is one of the important subjects when the ICRF power is injected in the perpendicular direction to magnetic field line.

Development of internal ICRF wave detection using microwave reflectometry on GAMMA 10

“…The reflectometer has already shown its usefulness especially on nonlinear phenomena occurring inside the hot plasma; a magnetic probe installed at periphery has less sensitivity for such phenomena compared with the reflectometer. Enhanced wave-wave couplings between ICRF waves including the AIC waves have been observed along with the saturation of confined energy [4]. Bispectral analysis applied to fluctuation data obtained by the reflectometer showed that the difference frequencies between the discrete AIC frequencies were produced by wave-wave coupling between the AIC waves with radial dependence; stronger coupling occurred near the core region [5].…”

Direct Observation of Electron Heating by Electron Landau Damping of Alfvén Ion Cyclotron Waves Using Thomson Scattering System in the Tandem Mirror GAMMA 10/PDX

“…Detailed description of GAMMA 10/PDX has been provided elsewhere [1][2][3][4][5][6][7][8][9][10][11][12]. The magnetic field strength at the midplane of the central cell is 0.405 T, and the mirror ratio of the central cell is 5.…”

“…A microwave reflectometer (RM) was constructed for studying high-frequency fluctuations in the plasma core region [9]. This system consists of two simple heterodyne reflectometers.…”

“…In such a strong temperature anisotropy condition, slow Alfvén ion cyclotron (AIC) waves were spontaneously excited in the central cell of GAMMA 10/PDX [3][4][5][6]. The AIC mode is normally observed using magnetic probes [7] and reflectometers [8,9]. Diamagnetism increases with increased power of heating, and the anisotropy becomes strong.…”

Multi-point measurement using two-channel reflectometer with antenna switching for study of high-frequency fluctuations in GAMMA 10

“…An understanding of the wave-particle interactions that cause the axial transport of the high-energy ions and an assessment of a) Electronic mail: ikezoe@prc.tsukuba.ac.jp the nonlinear phenomena that may be related to the observed heating efficiency degradation would also be helpful. 11,12 For all the research described above, a multi-point measurement system that can obtain the amplitude and phase profiles of these high-frequency small-amplitude fluctuations is required.…”