Measurements of shear Alfvén waves are used to test the predictions of a variety of different electron collision operators, including several Krook collision operators as well as a Lorentz collision operator. New expressions for the collisional warm-plasma dielectric tensor resulting from the use of the fully magnetized collisional Boltzmann equation are presented here. Theoretical predictions for the parallel phase velocity and damping as a function of perpendicular wave number k⊥ are derived from the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfvén waves were made to test these theoretical predictions in both the kinetic (vte⪢vA) and inertial (vte⪡vA) parameter regimes and at several wave frequencies (ω<ωci). Results show that, in the inertial regime, the best match between measurements and theory occur when any of the Krook operators are used to describe electron collisions. In contrast, the best agreement in the kinetic regime is found when collisions are completely ignored.

Measurements of the dispersion relation for shear Alfvén waves as a function of perpendicular wave number are reported for the inertial regime for which V{A}>V{Te}. The parallel phase velocity and damping are determined as k{ perpendicular} varies and the measurements are compared to theoretical predictions. The comparison shows that the best agreement between theory and experiment is achieved for a fully complex plasma dispersion relation which includes the effects of electron collisions.

We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense (ω(pe) > ω(ce)). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency ω(ce). As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation ω - k([parallel])v([parallel]) = ω(ce). The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.

Electron plasmas are trapped in a novel “partially” toroidal (or “C”-shaped) trap designed to study issues of equilibrium, stability, and confinement of toroidal nonneutral plasmas. Plasmas with densities as high as 3.3×106 cm−3 are trapped and decay on a 100 μs timescale in a 196 G magnetic field. Successful trapping of dense electron plasmas requires the application of a strong horizontal electric field (5–10 V/cm). The confinement time scales as the 32 power of the magnetic field. Oscillations in the image charge current to a grounded probe have a frequency that is proportional to 1/B and roughly proportional to the vacuum horizontal electric field. However, the frequency is independent of the amount of charge in the trap. Some evidence points toward the ion resonance instability as the driving mechanism for this new toroidal electron mode.

A detailed characterization of the high-frequency range of the fluctuation spectrum in reversed field pinch plasmas is presented, revealing a variety of new features distinct from global tearing modes and the cascade that they are thought to drive. The anisotropic broadband spectrum of the fluctuating electric field is measured. The power in the fluctuating kinetic energy ð1=2Þm i n iṼ 2 EÂB 0 , previously measured to be smaller than the magnetic energy in the tearing-mode-unstable frequency range, becomes greater than and diverges from the magnetic energy above 60-80 kHz. The lack of equipartition at high frequencies coincides with the measured signatures of the independent fluctuation activity broadly consistent with the drift-wave fluctuations. Statistical coherence measurements reveal the mode activity that is compressive with a large amplitude in the vicinity of strong density gradients and with a phase speed comparable to the electron drift speed. There is a distinct highfrequency correlation between the fluctuations of density and the parallel magnetic field. Elevated coherences associated with this fluctuation feature return more quickly after a sawtooth event than the corresponding coherences associated with tearing activity. Published by AIP Publishing.