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The nonlinear evolution and spectral properties of ion temperature gradient-driven modes in a three-dimensional sheared magnetic field with multiple rational surfaces have been investigated using gyrokinetic plasma simulation techniques. A detailed study of the electrostatic potential fluctuation spectra shows that it is dominated by the modes with moderate poloidal wavelength (0.1{le}{ital k}{sub {ital y}}{rho}{sub {ital s}}{le}0.5). The measured thermal flux in the steady state, which is lower than the quasilinear value at saturation, is found to decrease weakly with an increase in the magnetic shear strength.

The VLF wave spectra detected by a separable payload during the continuous electron beam emissions of the BERT-1 rocket, are presented here. The observations include broadband turbulence attributed to a plasma cloud formed through beam ionization of ambient neutrals; electrostatic waves that vary with plasma density with frequency separations of approximately twice the hydrogen gyrofrequency; and electromagnetic modes near even harmonics of the hydrogen cyclotron frequency.

On 16 March 1980 a rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The purpose of the experiment, named “King Crab,” was to advance knowledge of the instabilities, waves, and optical and magnetic effects produced. The TV images of the injection are spectacular, revealing three major regimes of expanding material which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km “black hole” surrounding the injection point. Preliminary computer simulations show a similar rayed structure development due to an electrostatic instability.

A rocket launched from Poker Flat, Alaska, carried a new type of high-explosive barium shaped charge to 571 km, where detonation injected a thin disk of barium vapor with high velocity nearly perpendicular to the magnetic field. The TV images of the injection are spectacular, revealing three major regimes of expanding plasma which showed early instabilities in the neutral gas. The most unusual effect of the injection is a peculiar rayed barium-ion structure lying in the injection plane and centered on a 5 km 'black hole' surrounding the injection point. Preliminary electrostatic computer simulations show a similar rayed development.

Electromagnetic particle simulations are performed in order to investigate the coupling between an energetic electron beam and a thermal, multi-ion component magnetized plasma. For intermediate beam strengths (vb ≲ 6 vTe) a substantial fraction of the beam energy is converted into magnetic fluctuations, propagating oblique to the magnetic field. The dominant emissions occur near even cyclotron harmonics of the lightest ion constituents, for the oblique modes. The VLF electromagnetic modes are stimulated through a Cerenkov process, which couples perpendicular beam energy with the component of the wave electric field perpendicular to the magnetic field.

In order to achieve the stated objectives of key future experiments such as CIT, it will be necessary to maintain plasmas with confinement properties significantly improved over those observed in auxiliary-heated L-mode-type tokamak discharges. This underscores the importance of understanding the physics responsible for the favorable trends exhibited, for example, by ''supershot'' discharges in TFTR and by H-mode-type divertor plasmas. In addressing this general issue, the present paper reports results of theoretical investigations dealing with: the onset conditions of the microinstabilities most likely to influence enhanced confinement behavior; gyrokinetic particle simulations and analytic studies of the saturation and transport properties of the most persistent forms of these instabilities; and detailed comparisons of experimental results with predictions from transport codes using appropriate microinstability-based diffusivities and with local diffusivities from various theoretical models. 19 refs., 2 tabs.