The paper presents laboratory measurements of the beam-plasma discharge (BPD) produced when an energetic electron beam traverses an initially neutral gas. The results show that the critical beam current is related to energy, magnetic field, and the system length by an empirical relationship at pressures below 2 times 10 to the -5th power torr. This relationship describes the accumulation of ambient plasma density collisionally produced by the beam to a critical value at which ignition occurs. Additional measurements of the narrow-band cyclotron-related waves observed at beam currents below BPD threshold do not clearly establish whether this instability is a precursor to the BPD.

Further laboratory measurements of the beam-plasma discharge.

Further laboratory measurements of the beam-plasma discharge (BPD) produced when an energetic electron beam traverses an initially neutral gas are presented. The experimental data indicate that the critical beam current Ic at energy V, magnetic field B, and system length L required for ignition obeys the empirical relationship Ic ∝ V3/2/B0.7 PL at pressures P < 2 × 10−5 torr. This relationship appears to primarily describe the accumulation of ambient plasma density, collisionally produced by the beam itself, to a critical value where ωpe² ≈ ωce² at which ignition occurs. Additional measurements of the narrow-band cyclotron-related waves (fce < f < 1.4fce) observed at beam currents below BPD threshold do not clearly establish whether this instability is a necessary precursor to the BPD. The relevance of these experiments to past and planned electron beam experiments in space is briefly discussed.

Further laboratory measurements of the beam-plasma discharge. [for aerospace technology application]

The paper describes electron beam injection experiments which clarify observational results obtained in rocket flights. A column of enhanced density plasma, exceeding the density expected from ionization by primary beam electrons, was observed in a large vacuum system at low magnetic fields (1 to 1.5 G) and low ambient pressures (10 to the minus 6 to 10 to the minus 5 torr). The peak luminosity of the discharge was about 10 times that of the beam alone, and the radius increased by a factor of three. In the absence of the discharge, RF emission is observed at 1.1 to 1.2 times the cyclotron frequency, and a strong band of RF noise with upper frequency cutoff at about the cyclotron frequency is observed in the discharge mode, along with higher frequency noise at or near the plasma frequency. The onset of the plasma discharge is critically dependent on beam current. The described results agree with observations obtained at much higher densities and magnetic fields in fusion research studies.

Electron beam injection experiments: The beam‐plasma discharge at low pressures and magnetic field strengths

A comprehensive review of electron pitch angle scattering in the magnetosphere and the plasma waves responsible for it is presented, emphasizing the strong diffusion of diffuse auroral electrons by electrostatic electron cyclotron harmonic waves. The weak diffusion of energetic radiation belt electrons within the plasmasphere is reviewed briefly. Several new suggestions concerning the quasilinear diffusion from and saturation of electrostatic waves are included.

Electrostatic waves and the strong diffusion of magnetospheric electrons

The first active beam-plasma experiments utilizing the space shuttle were carried out in March 1982 as part of the NASA Office of Space Science mission on the third space shuttle flight. A fast pulse electron generator emitted a 1-keV, 100-mA electron beam in either a continuous (dc) mode or an on/off modulated mode in the ELF to HF frequency range. Stimulated electrostatic and electromagnetic waves and associated plasma effects were measured with the plasma diagnostics package as it was maneuvered through and near the beam by the remote manipulator system. For the dc beam the wave spectrum was electrostatic, was peaked in the 300- to 500-Hz range with a spectral density of 4 × 10−3 V2 m−2 Hz−1, and was unpolarized. Above the nominal lower hybrid resonance frequency the intensity decreased but was polarized. Strong emissions near the electron gyrofrequency and the plasma frequency were occasionally detected. The background spectrum was similar to the dc case for VLF and ELF modulations, but the emissions at the modulation frequency were more electromagnetic and more intense with field strengths of up to 1 Vm−1.

Wave emissions from dc and modulated electron beams on STS 3

Electric field emissions at frequencies of (n + ½)fce have been generated in a large-scale electron beam experiment in the giant NASA vacuum facility in Ohio These emissions arise when a contrastreaming beam configuration exists, the primary beam consisting of monoenergetic electrons (50 eV to 5 keV) and the other beam of lower-energy ‘backscattered’ secondary electrons It is suggested that the same mechanism could also be the source of the observed emissions at auroral latitudes In the absence of the beam-beam instability, weak oscillations were observed at the plasma frequency In the latter case no significant modifications of the primary beam velocity distribution occurred, and the beam configuration is adequately described by single-particle motion in the ambient magnetic field

Laboratory observations of RF emissions at ω pe and (n + ½)ω ce in Electron beam‐plasma and beam‐beam interactions

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Laboratory observations of RF emissions at ω pe and (n + ½)ω ce in Electron beam‐plasma and beam‐beam interactions