A study of the coupling and propagation of electron plasma waves excited by waveguide arrays is presented. The waves are generated in a low-temperature, linear plasma column in a homogeneous magnetic field. As predicted from a theoretical model, under appropriate conditions efficient coupling to plasma waves can be obtained. These studies are of relevance to plasma heating in that the modes are identical with those that must be generated in any lower hybrid heating experiment. We discuss the implications of these results with respect to future heating experiments on large devices.

Plasma electron heating was accomplished by exciting plasma oscillations with a pulsed, 10-kV, 1-A electron beam drifting in a longitudinal magnetic field of 100 to 1000 Oe. The oscillatory energy gained by plasma electrons leads to an increase in their density and mean kinetic energy. The resulting plasma, which is called the ``beam-plasma discharge,'' is an rf discharge in which a beam-plasma interaction generates the rf fields. At the beginning of a beam pulse, beam electrons generate a plasma by ionization of the background gas. Within a few microseconds excited plasma electrons become the dominant ionization source. This paper describes the transient rf oscillations that appear in the first few microseconds of the beam pulse. From a detailed study of this transient it was concluded that a nonconvective instability initiates the oscillations, which first appear at the electron cyclotron frequency, and that a convective instability at the plasma frequency generates the oscillations that sustain the discharge.

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A novel experiment to investigate single-surface multipactor on a dielectric surface was developed and tested. The compact apparatus consists of a small brass microwave cavity in a high vacuum system. The cavity is ϳ15 cm in length with an outer diameter of ϳ10 cm. A pulsed variable frequency microwave source at ϳ2.4 GHz, 2 kW peak excites the TE 111 mode with a strong electric field parallel to a dielectric plate ͑ϳ0.2 cm thickness͒ that is inserted at midlength of the cavity. The microwave pulses are monitored by calibrated microwave diodes. An electron probe measures electron current and provides temporal measurements of the multipactor electron current with respect to the microwave pulses. Phosphor on the dielectric surface is used to detect multipactor electrons by photoemission. The motivation of this experiment is to test recent theoretical calculations of single-surface multipactor on a dielectric.