Two modes of low-frequency oscillations have been observed in the central cell of the tandem mirror experiment (TMX). A mode at about 7 kHz has m=1 and probably drives radial transport at large radii. The mode identification is uncertain. A mode at about 13 kHz has m=0. The two end plugs oscillate 180° out of phase with each other and in phase with the amplitude (envelope) of the ion cyclotron frequency oscillations in each plug. This mode is identified as a sound wave; the frequency is apparently locked to the E×B rotation frequency, probably through an associated m=1 component. Neither mode severely limits confinement in the central cell, and both may be controllable. The lower-frequency mode is sensitive to the density profile and to the fueling and is not always present. The higher-frequency mode may be less important (or absent) in devices in which the plugs are stable at the plug’s ion cyclotron frequencies.

No abstract

A three-mirror laser interferometer for measuring electron densities in repetitively pulsed plasmas is described and analyzed. The instrument has a sensitivity equivalent to a density of 1013/d cm−3, where d is the length of the plasma in centimeters. It has a time resolution of a few microseconds. The response of the laser intensity to a changing dielectric (e.g., plasma) is calculated in the quasistatic approximation, and the factors contributing to the finite time response are considered. The analysis applies to laser interferometers in general, as well as to the present instrument.

No abstract

No abstract