[en] One of the remaining problems in the control of thermonuclear fusion is the development of a suitable method of bringing the plasma to ignition temperature. Relativistic electron beams provide a possible technique. They are a well developed and readily available technology with power levels sufficient to meet the demanding requirements of plasma heating. An advantageous configuration utilizes a beam rotating about a guide magnetic field. A theory was developed for the interaction in two stages. The first stage treats the plasma response induced by the propagating beam. Plasma return currents neutralize both the axial and azimuthal beam current. Induced fields slow the beam, trapping it in the plasma. Stopping length for the rotating beam is reduced by the factor (v/sub parallel//v/sub perpendicular/)³ as compared to non-rotating beams (v/sub parallel/ is the beam's axial velocity, v/sub perpendicular/ its rotational velocity). After dissipating a small fraction of its energy during trapping, the second stage of plasma heating begins. The beam rotating within the plasma emits a magnetosonic shock type wave. Wave energy is half magnetic and half ion particle energy with other components being negligible. The process thus heats ions directly. Numerical estimates for a small scale experiment indicate ion energies in the kilovolt range. Beam energy is dissipated in a fraction of a microsecond. Some aspects of beam stability, which can potentially interfere with this process, are also considered

[en] It is shown that turbulent diffusion of electrons across the rational surface, due to a combination of shear (delta k/sub parallel//delta r identical with k'/sub parallel/ not equal to 0) and random E Vector x B Vector fluctuations and/or stochastic magnetic perturbations, results in a finite amplitude-induced version of the absolute universal instability. Physically, the turbulent scattering of electrons across the rational layer leads to an effective finite value for k/sub parallel/ which destroys the stabilizing influence of the nonresonant electrons. At larger amplitudes, the electron growth is reduced and the ion shear damping is enhanced by spatial broadening of the mode, yielding nonlinear stabilization

[en] An advantageous configuration for plasma heating with a relativistic beam utilizes an annular beam rotating about a guide magnetic field. In this first paper (of two), the return current process for such a configuration is considered. For the parameters expected to prevail in an experiment, the plasma response can be described as magnetic diffusion or critically damped magnetosonic waves - these being equivalent. Equations for the axial and angular return currents are derived and take the form of decoupled diffusion equations. The effects of pulse shape, boundary conditions, etc. are then treated. The drag force on the beam resulting from the interaction is greatly enhanced and leads to a stopping length reduction by the factor ¹/₂(V/sub parallel bars//c)³ as compared to non-rotating beams. The implications of these effects for a plasma heating application are discussed

[en] It is shown that the radial variation of the electron-to-ion temperature ratio induced by neutral beam injection in PLT could account for the observed spatial dependence of the electron thermal conductivity coefficient. Quantitative evaluations using the experimental temperature and electron thermal conductivity (chi/sub e/) profiles show consistency of the measured data with a finite beta drift wave turbulence model and also demonstrate the failure of a simple electron temperature power law scaling for chi/sub e/

[en] Ambipolar flow in a turbulent plasma is investigated by combining a WKB treatment of the waves with a turbulent collision operator resulting from either quasi-linear theory or certain renormalized turbulence theories. If the wave momentum has a flow from outgoing waves, then particle diffusion is not intrinsically ambipolar, and the time variation of the electric-potential profile is determined by the turbulent spectrum. However, in most cases of practical interest, as in the drift-wave problem, this effect is small; and, in steady state, equal rates of stochastic diffusion are predicted for electrons and ions

[en] The electromagnetic instability of a relativistic electron beam in a plasma that is current and charge neutralized in the beam channel. In addition to the usual filamentary instability one finds an instability that is localized to the surface of the beam. The large azimuthal mode number growth rate in cylindrical geometry is ω/sub i/ = ω/sub b// radical 2γ. The effects of collisions, a conducting wall, magnetic field, hollow beam geometry and different plasma densities, inside and outside the beam, are calculated

[en] A derivation and approximate solution of renormalized mode coupling equations describing the turbulent drift wave spectrum is presented. Arguments are given which indicate that a weak turbulence formulation of the spectrum equations fails for a system with negative dissipation. The inadequacy of the weak turbulence theory is circumvented by utilizing a renormalized formation. An analytic moment method is developed to approximate the solution of the nonlinear spectrum integral equations. The solution method employs trial functions to reduce the integral equations to algebraic equations in basic parameters describing the spectrum. An approximate solution of the spectrum equations is first obtained for a mode dissipation with known solution, and second for an electron dissipation in the NSA

[en] Previously studied processes by means of which energy is transferred from an intense relativistic electron beam to a plasma involve instabilities associated with the primary energetic electrons and indirect coupling of the plasma return current. For return current coupling, a simple treatment was developed based on diffusion equations so that boundary conditions, pulse shape, etc., can be accounted for. This treatment has been applied to a rotating beam produced, for example, by passing an annular beam through a magnetic cusp. The result is that an electric field is set up within the plasma by the Hall effect. The magnitude of this electric field is E/sub r/ = 300 (n/sub b//n/sub p/)B/sub z/ where n/sub b/ is beam density, n/sub p/ is plasma density; E/sub r/(k-volts/cm) and B/sub z/(k-gauss) are the electric and magnetic fields. The guiding center drift of electrons at velocity v₀ = cE/sub r//B/sub z/ accounts for the plasma return current. Ions for which the magnetic field can be neglected would be accelerated in the E/sub r/-field to multi-kilovolt energy. The stopping power of the beam is greatly enhanced compared to a non-rotating beam, and the energy is transferred almost entirely to ions. The coupling does not involve instabilities. (U.S.)

[en] The effect of spatial electron diffusion on the stability properties of the universal drift mode in a sheared magnetic field are studied using an initial value code, TEDIT. Previous studies of this problem by Hirshman and Molvig relied on an approximation to the electron resonance function equivalent to making a Krook approximation for the spatial diffusion operator, D par. delta²/par. delta x². The present work treats the diffusion operator precisely and also allows the treatment of a realistic parallel velocity dependence of the diffusion coefficient, D = D(v/sub parallel/). For the case of a velocity independent diffusion coefficient, the qualitative features found by Hirshman and Molvig are observed. The modes with k/sub y/rho/sub i/ > 1 destabilize at small values of the diffusion coefficient and saturate at higher values, corresponding to several orders of magnitude in D. There are quantitative discrepancies with the previous work that, near the saturation point, can be accounted for reasonably well by a simple asymptotic theory

[en] Previously studied processes by means of which energy is transferred from an intense relativistic electron beam to a plasma involve instabilities associated with the primary energetic electrons and indirect coupling of the plasma return current. For return current coupling, a simple treatment based on diffusion equations has been developed so that boundary conditions, pulse shape, etc., can be accounted for. This treatment has been applied to a rotating beam produced, for example, by passing an annular beam through a magnetic cusp. The result is that an electric field is set up within the plasma by the Hall effect. The magnitude of this electric field is Esub(r)=300(nsub(b)/nsup(p))Bsub(z) where nsub(b) is the beam density, and nsub(p) is the plasma density; Esub(r)(kV.cm^-1) and Bsub(z)(kG) are the electric and magnetic fields. The guiding-centre drift of electrons at velocity v theta=cEsub(r)/Bsub(z) accounts for the plasma return current. Ions for which the magnetic field can be neglected would be accelerated in the Esub(r)-field to multi-kilovolt energy. The stopping power of the beam is greatly enhanced compared to a non-rotating beam, and the energy is almost entirely transferred to the ions. The coupling does not involve instabilities. (author)