The magnetic fields associated with plasmas frequently exhibit small-amplitude MHD fluctuations. It is useful to have equations for the magnetic field averaged over these fluctuations, the so-called mean field equations. Under very general assumptions, it is shown that the effect of MHD fluctuations on a force-free plasma can be represented by one parameter in Ohm's law, which is effectively the coefficient of electric current viscosity.

The beat-wave scheme for current drive is studied in the frame of plasma weakturbulence theory. The value of the driven current is limited by a quasi-linear diffusion mechanism. The one-dimensional problem, corresponding to the resonant excitation of electron plasma oscillations by two beating electromagnetic beams is discussed in detail. The results may be relevant to the continuous operation of tokamak discharges.

Lie group transformations are found which allow the removal of background inhomogeneity and non-steadiness from the nonlinear Schrödinger equation for the envelopes of HF waves. Background profiles are determined for which this removal can be realized.

The dynamo mechanism in an RFP is explained on the basis of new terms in the MHD equations which are proportional to the electron mass and are traditionally neglected. A new azimuthal dynamo current is obtained which is shown to be positive definite. Sustained, spontaneous self-reversal of the toroidal field naturally follows from this. The (F, Θ) curve calculated from this theory under certain assumptions agrees well with experimental data. The theory predicts the presence of large-Larmor-radius particles in the RFP. It also predicts a spontaneous axial magnetic field in linear Z-pinches. Preliminary experiments on low-energy Z-pinches corroborate this prediction.

A simple argument based on energetics is presented to bring out the similarities between diverse plasmas which undergo current filamentation. The predictions of this argument are found to be in agreement with more detailed theoretical results and experimental data.

Evolutional drift-theory representations are used to consider suprathermal drift of a switched-on electron through a warm collisional plasma. The general suprathermal solution for an arbitrarily time-varying electron is made up of two nontrivial constituents. One of these exists in the interior R2 of an expanding thermal front Г. The other exists in a drifting-extending region R1 enclosed by part of Г, together with a sheet that diverges downstream from the suprathermal electron (outside Г) and terminates tangentially at Г. The solution vanishes identically beyond R1, R2 and their boundaries. Two- and three-dimensional closed forms of an exact solution are next extracted in R1 for the pulsating electron with complex frequency. Furthermore, two-dimensional near-ultimate state results are asymptotically derived deep within R2 for a real electron frequency and a collisionless plasma. Hyperbolic/hyperboloidal attenuation normally affects space-time dissipation.

The linear stability of steady flow of an inhomogeneous, incompressible hydromagnetic fluid is considered. Circle theorems which provide bounds on the complex eigenfrequencies of the unstable normal modes are obtained. Sufficient conditions for stability follow in a number of special cases.

With an infinite system of balance equations, derived from the Boltzmann equation, conductivity expressions are obtained in the form of three-term recurrence relations leading to continued fractions. Without collisions, only Landau damping causes attenuation. Its modification by collisions is illustrated for some simple collision models.

Each of the dielectric tensor elements in a Maxwellian magnetoplasma is expressed in terms of various derivatives of a single functional expression. The relationships for all the elements are given, first for the general case of a relativistic plasma, then for the slightly relativistic case, and finally for the non-relativistic case, when the perpendicular wavenumber is either large or small. We also derive new relations useful for the computation of the slightly relativistic plasma dispersion function.

Using the KBM perturbation technique, the stability of oblique modulation on ion-acoustic waves in a plasma with two species of warm ions is studied. The effect of the temperatures of two ion species on the modulational instability is discussed in detail. The nonlinear frequency shift and the change in zeroth-order density are also calculated for different values of ion temperatures. Predictions of the theory are in fairly good agreement with the experimental observation of modulational instability.

Relativistic electron beams propagating in plasma broaden as electric and magnetic fields scatter them. We calculate the beam spreading expected from errors in the ambient magnetic field, and from both electrostatic and magnetic waves generated by the beam itself. All these effects can be important in contemplated experimental regimes. Beam expansion can serve to set limits on the strength, size and phase velocity of caviton waves. Beam-driven magnetic waves can scatter beams effectively even if applied field errors are small. This can affect schemes for transport of beams in inertial fusion, and plasma heating schemes.

Some recent numerical simulations of driven magnetic field-line reconnection by Biskamp show no evidence of the Petschek mechanism when the reconnection rate or magnetic Reynolds number are large. Instead, an electric current sheet forms on the symmetry axis, across which a magnetic field is annihilated. The sheet terminates at a Y-point. Fluid driven into the current sheet escapes as jets along the separatrices emanating from the Y-point. This paper shows how many of the features such as the jets can be explained by a simple analytical model. Since the numerical simulations are necessarily on a bounded domain, the importance of the external boundary conditions in setting up a steady-state solution is stressed by illustrative examples.

The neutral density and particle confinement time in the ELMO Bumpy Torus-Scale Experiment (EBT-S) have been determined by two different techniques. These involve a spectroscopic measurement of molecular and atomic hydrogen emissions and a time-decay measurement of a fast-ion population using a diagnostic neutral beam. The results from both diagnostics exhibit identical trends for either estimate, although the absolute values differ by a factor of 2 to 3. The observed variations with fill gas pressure and microwave power from either technique are consistent with measurements of electron density and temperature. In this paper, the measurement techniques are discussed, and the results are compared in the context of consistency with independently observed plasma behaviour.

Results are presented of the stability analysis against small parallel perturbations of two classes of nonlinear waves in cold unmagnetized electron plasmas emphasizing similarities and differences. The first class is a stationary longitudinal wave set up by two counter-streaming cold electron beams; the second class is a mixed transverse-longitudinal standing wave in a relativistic plasma with a circularly polarized transverse electric field whose amplitude is periodically modulated in the longitudinal direction. The perturbation dispersion relations are discussed for all perturbation wavenumbers and all nonlinear wave amplitudes. Particular attention is given to the appearance of gaps in those dispersion relations.

The theory of resonant electron diffusion as an effective saturation process of the auroral kilometric radiation has been formulated. The auroral kilometric radiation is assumed to be amplified by the synchrotron maser instability that is driven by an electron distribution of the loss-cone type. The calculated intensity of the saturated radiation is found to have a significantly lower value in comparison with that caused by the quasi-linear diffusion process as an alternative saturation process. This indicates that resonant electron diffusion dominates over quasi-linear diffusion in saturating the synchrotron maser instability.

The boundary term in the energy integral (105) is superfluous and should be dropped. If we use the Jacobian relation (86) to transform the dummy variables of integration from ψ, θ, to x, y (recalling that B = Bmax = const. at the ends), we see that this term reduces to the integral of a fixed function of x and y over a fixed region of the (x, y) plane. In other words, it reduces to a pure constant.