Density fluctuations in the tendem mirror Gamma 10

Abstract

The tandem mirror GAMMA 10 utilizes an electron cyclotron resonance heating (ECRH) for forming a confinement potential. Density fluctuation is observed using microwaves, such as interferometer, reflectometry and Fraunhofer diffraction (FD) method. An ultrashort-pulse reflectometry has an advantage of detecting fluctuation locally. The wave number can be obtained by the FD method. In the edge plasma region electrostatic probes are used. Fluctuation with coherent mode in several kHz is excited in the hot-ion mode plasma. When the ECRH is applied, electron density in the central cell increases gradually. On the contrary, intensity of the density fluctuation decreases and coherent mode is suppressed. Its frequency also varies with the density increase. In that time, radial potential distribution, i.e., electric field, changes along with the formation of plug potential. From this behaviour it is deduced that the fluctuation deeply relates to the potential formation and improvement of the confinement.