Table of contents

The Hamiltonian structure of the E*B drift equations is exploited to describe the onset of stochasticity for test particles in drift waves. In contrast to a longitudinal plasma wave, a drift wave acts over the entire single particle phase space. This feature precludes a simple use of the techniques presently available for predicting the onset of chaos in Hamiltonian systems. For two drift waves a generalized Chirikov (1979) overlap criterion is derived. The present work gives conditions on the drift wave spectrum for global stochasticity and the validity of the diffusion approximation.

The ponderomotive force exerted by a circularly polarized electromagnetic wavefield in a uniform, magnetized plasma column is calculated. The effect of the self-consistent nature of the wavefields in the plasma is illustrated for the case of long wavelength excitation. The contribution to the total ponderomotive force of the interaction between the induced magnetization and the magnetic field is determined. It is shown that self-consistency plays a dominant role in determining the ponderomotive potential and induced magnetization of each plasma species if the wave frequency is in the vicinity of either the cyclotron frequency or an eigenfrequency of the plasma column.

By the method of multiple scales a nonlinear Schrodinger equation is derived, which describes the nonlinear evolution of a plasma wave packet propagating in a cylindrical waveguide filled with hot plasma immersed in an infinite axial magnetic field. From this equation, instability criteria for all modes of propagation are determined. It is found that the lowest order mode becomes modulationally unstable if the wavenumber exceeds a critical value and this critical value decreases with the increase of temperature. Maximum growth rate of instability and the corresponding wavenumber of perturbation are calculated for the lowest order mode for four different values of temperature. Both these quantities are found to increase with the increase in temperature.

The acceleration of a thin foil using a laser pulse is studied. It is shown that the acceleration efficiency eta _H is heavily dependent on the behaviour of the corona ejected by the foil: there is no universal relation eta _H( Delta M/M₀),M₀ and Delta M being initial foil mass and ablated mass, respectively. Known results on the coronal flow are used to check the theory against experimental data available in the literature; effects due to both a non-planar corona, and the time-dependence of the laser irradiance, are considered. The agreement with experiments is substantially better than that for previous analyses. Acceleration of thin spherical shells is also discussed.

Equilibrium of an electron beam moving in external magnetic and self electric and magnetic fields is determined self consistently. This approach is shown to be equivalent to the model that treats the electron beam as a ring current. The result is applied to two external magnetic field configurations: a betatron field and a uniform magnetic field. The equilibrium is shown to be independent of the toroidal magnetic field present in most high current betatrons.

A zero-dimensional code is described for modelling the plasma formation and preheating in a Tokamak, by means of extraordinary waves in the electron-cyclotron frequency range. Numerical results are presented, which give the increase in time of the electron density and temperature, together with the power balance in the steady-state plasma Extrapolation of these results, shows that the RF plasma in larger size Tokamaks may reach temperatures larger than the impurity radiation barriers.

Using self-consistent initial conditions obtained from the full-wave solution of the field radiated by an ion-cyclotron resonance heating (ICRH) antenna, the ray-tracing technique is applied to generate r.f. power-deposition profiles in non-circular large Tokamaks such as JET and NET/INTOR. An analytic expression has been used to simulate the shape of the flux surfaces, which fit reasonably well to the numerical solutions of the Grad-Shafranov equation describing the Tokamak equilibrium, by adjusting three free parameters: the flux-surface shift Delta , the elongation ratio kappa and the triangularity parameter delta . For an elliptic INTOR plasma, it is found that the focussing of rays is much reduced and when the absorption layer is located in the center, the r.f. power density figures are lower approximately by a factor of 1.9 compared to that obtained in an equivalent circular case. This reduction in power density is not so significant when the power is deposited off-center, as demonstrated by an example treated for the JET D-shaped plasma.

A new model is developed for the collisional Weibel instability based upon a Cartesian tensor expansion of the electron Fokker-Planck equation. Its results are substantially different from those predicted by an equivalent 2 electron fluid model (Mochizuki et al. 1980). Growth rates ( approximately 10¹¹ s^-1) and optimum wavelengths ( approximately 10 mu m) correlate well with experimental observations of filamentary structures in laser-plasmas. The model suggests that the instability may disrupt implosion symmetry, particularly for high-Z targets irradiated by short wavelength lasers.

A novel electron distribution function is used in deriving analytic expressions for the synchrotron emissivity and absorption coefficient of relativistic loss cone and anti-loss cone distributions. Under most circumstances these expressions can be written in the form of the product of the corresponding expression for an isotropic plasma and a factor due to the anisotropy. Good agreement with numerical results is found under a wide variety of conditions. The new expressions give considerable insight into the variation of the emission and absorption with various physical parameters and enable the approximate forms of actual electron distributions to be inferred from the properties of the emitted radiation. It is shown that amplification of the synchrotron continuum is impossible for loss cones with Maxwellian distributions in energy, no matter how strong their anisotropy.

An experimental relation between diameter integrated density fluctuations and electron energy confinement is shown for conversion mode RF heating in TFR.

An experimental investigation shows that the electrostatic ion-cyclotron instability, driven by an electron current to a positively biased collector, is accompanied by strong coherent two-dimensional fluctuations of the plasma potential in front of the collector. These results suggest that this instability evolves like a two-dimensional potential relaxation instability.