Electron Density Measurement by Using a Multi-Channel Interferometer System in the Tandem Mirror GAMMA 10

Abstract

Fluctuation in the plasma is important to be measured for studying the improvement of the plasma confinement by the formation of the plasma confinement potential. Density fluctuation is observed using microwaves, such as interferometer, reflectometry and Fraunhofer diffraction method. We have constructed a new multichannel microwave interferometer for measuring the plasma density and fluctuation radial profiles in a single plasma shot. In order to study higher density plasma operation, we have started sub-millimeter hydrogen ice pellet injection experiments into the potential confined plasma. We successfully measured the time dependent density and line-integrated density fluctuation radial profiles in the pellet injection experiments using the multi-channel microwave interferometer.

Study of Fluctuation Suppression during Potential Formation in the Tandem Mirror GAMMA 10

“…The radial electric field E arising from the potential causes an E × B plasma rotation in the direction of the ion diamagnetic drift velocity, which may enhance instabilities, such as rotational flute and drift-wave modes, and degrade radial confinement. However, present studies show the suppression of low-frequency fluctuations of the density and the potential during axial confining potential formation during plug-ECH (P-ECH) [1][2][3][4][5][6]. Earlier works by Sanuki [7] and Chaudhry et al [8] discussed the effects of the ambipolar potential on the stability of drift waves.…”

“…1). The details on GAMMA 10 are provided elsewhere [1][2][3][4][5][6]. The x-axis and y-axis are perpendicular to the magnetic field in the vertical and horizontal directions, respectively.…”

“…In the tandem mirror GAMMA 10, an electrostatic potential for improving axial confinement is created by applying electron cyclotron resonance heating (ECH) in the end mirrors (plug/barrier cells) [1][2][3][4][5][6]. Two types of instability, a rotationally driven mode with the lowest azimuthal mode number and a drift-wave mode with high azimuthal mode numbers, are observed during the existence of confining potentials.…”

“…The density fluctuation is observed using microwaves, for example, by interferometry, reflectometry, and the Fraunhofer diffraction method, and electrostatic probes [1-3, 5, 6]. GAMMA 10 has a good potential measurement system consisting of a gold neutral beam probe (GNBP) system [4,6,9]. We can observe density and potential fluctuations during axial confinement potential formation when P-ECH is applied in a single plasma shot.…”

Two dimensional density and its fluctuation measurements by using phase imaging method in GAMMA 10

“…[1][2][3][4][5][6] The radial electric field due to this potential causes an E ϫ B rotation shear and suppression of instabilities such as a drift-wave mode. [1][2][3][4][5][6] The radial electric field due to this potential causes an E ϫ B rotation shear and suppression of instabilities such as a drift-wave mode.…”