Study of Pellet-Plasma Interaction in the GAMMA 10 Tandem Mirror

In the GAMMA10 tandem mirror, the first pellet injection experiments in open systems have started.¹ The tandem mirror machine is suitable for measuring propagation of pellet-fueled particles along the magnetic field lines. We observed a very low frequency oscillation in various diagnostic signals from the plasmas with a pellet injection. The frequency of the oscillation is a few hundred Hz. It is found that the phase of those signals changes to anti-phase at a certain place. The oscillation continued during plug-ECH for the formation of confining potential and its amplitude decays within a several ms after the end of ECH pulse. Measurements at several locations along the field lines indicates that this oscillation is a standing wave along field lines of plasma density perturbation due to the pellet injection. The wavelength of the oscillation is estimated to be about 6m. The oscillation has mode number n = 3.