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Time‐integrated emission spectra from the pulsed discharge of a 3.5‐MeV electron beam, with 90‐kA peak current of about 30‐nsec duration, and guided by a glass rod protruding from the cathode in a field‐emitting diode, have been studied with a quartz‐prism spectrograph. With anodes of graphite or polyethylene, the spectrum in the near‐uv to visible range is found to consist mainly of emission lines from C, C+, C++, and C+3, and similar ones from silicon. The spatial dependence of emission intensity indicates that a hot spot is present during the discharge near the anode surface. The temperature and the electron density in the plasma are estimated through a theoretical analysis of the composition of carbon in the gas phase.

Normal mode representation of HF properties of inhomogeneous plasma, analyzing Vlasov equation for free oscillations under external driving field

Ion acoustic wave propagation, near the sheath developed at a plasma‐wall boundary, has been investigated in a low‐pressure (∼ 5 × 10−4 Torr) argon plasma by an electron beam probing technique. Waves propagating into the plasma are found to have velocities ∼ 2 × 105 cm/sec, increasing with distance from the wall. The results are consistent with an analysis in terms of an ion free‐fall model of the sheath. The model also makes plausible the observed zero reflection coefficient for small ion acoustic disturbances at the plasma boundary.

The spectrum of undriven electron plasma oscillations of a realistic, nonuniform, collisionless plasma with a sheath is determined. The spectrum is found to be discrete.

The stability of realistic, inhomogeneous, plasmas with sheaths is studied by examining the interaction between an electron beam and the discrete, longitudinal, normal modes of a stable, Maxwellian plasma. A weak beam just displaces the discrete plasma eigenfrequencies in a way depending on beam current and energy. For first four eigenfrequencies we calculate ω‐plane maps. Instability is confined to a few intermediate modes, and growth rates are not large.

Numerical solutions of the Vlasov equation for plasma wave propagation through a sheath into a nonuniform plasma have been obtained. A strong wave is excited for frequencies slightly above the plasma frequency at the sheath edge.