Table of contents

A universal Ohm's law is derived for the ion bootstrap current relative to the impurity ions. The contribution driven by q_ir, the neoclassical plus electrostatic part of the ion heat flux, is found to be J_iz = n_ie (_i||−_z||) = 1.5 e²q_irB_θ/m_iT_i(ν_iz + 2ν_ii) and the frictional heating of the ions is J_izE_ϕ[1−(1/Z_eff)], which typically can be 10% to 15% of the total Ohmic heating when n_zZ²⩾n_i.

Expressions are derived for the rates of energy transfer between electrons and ions associated with the neoclassical, electrostatic and Pfirsch-Schlüter contributions to the diffusion and also the anomalous contribution caused by electrostatic drift-wave turbulence. The rates vary in sign as well as magnitude. As a result, even when the resultant diffusion is small, there can be a substantial energy transfer between electrons and ions comparable with the collisional transfer rate.

The eigenmode equation governing both the toroidicity-induced and the ion-temperature-gradient-driven modes of arbitrary wavelengths in tokamaks is derived by employing the ballooning-mode formalism. For the toroidicity-induced mode (electron driftwave), the ion magnetic drift resonances are de-stabilizing and can have a significant effect when the temperature ratio, T_e/T_i, is of order unity. The ion-temperature-gradient-driven mode (ion drift wave), which is unstable in a sheared slab geometry, is found to be further de-stabilized by the ion magnetic drifts, resulting in a lower critical ion temperature gradient (η_i).

The effect of finite-ion-Larmor-radius averaging and of ion Landau damping on ballooning modes is investigated for a large-aspect-ratio circular-cross-section tokamak equilibrium. – Finite-Larmorradius (FLR) effects are found to be weakly de-stabilizing for small values of the FLR parameter ka_i, but become strongly stabilizing for ka_i ∼ 0.5. A residual instability driven by inverse ion Landau damping persists, however, at shorter wavelengths (ka_i > 0.5).

The parametric excitation of ion-cyclotron waves by a lower-hybrid pump field is studied on the assumption that the magnitude of the pump is constant. The spatial amplification factor is given as a function of the wavenumber mismatch as produced by the plasma density gradient, and of the linear damping rates of the excited ion-cyclotron and sideband waves. The analysis is applied to plasma edge parameters relevant to the JFT2 heating experiment. It is found that ion-cyclotron harmonic modes are excited depending on pump frequency and plasma density. These modes are shown to have finite damping rates. The parallel refractive indices n_1z of the excited sideband fields are found to be always larger than that of the driven pump field. Transition to quasi-mode decay occurs either by decreasing the pump frequency or by increasing the applied RF-power.

In a tokamak configuration, superposition of the magnetic field of resonant helical windings which surround the toroidal plasma current outside the first wall destroys the magnetic surfaces in the boundary layer (ergodization). A transport model is analysed, where convective flow of the plasma from the boundary layer to the first wall permits elevated particle densities in the boundary layer and leads to very high particle and energy transport. The convective flow is driven by the pressure gradient along the field lines which intersect the toroidal wall at an oblique small angle . The required thickness Δ of the boundary layer is around 10¹⁵ n⁻¹·cm⁻². As a result, the plasma temperature there can be reduced towards the threshold of critical plasma-wall-interaction processes, the plasma core can be shielded against impurities from the wall and, at the same time, a very short life-time of all particles in the boundary layer can be achieved (use of pumpholes and/or scrape-off-limiters for removing ash). Thus, this model also improves the concepts of edge radiation cooling. An estimate is given of the parameters of INTOR using only a weak helical perturbation field which conserves the magnetic surfaces in the plasma core: one can reach wall temperatures T_w between 20 and 30 eV in the presence of wall densities n_w approaching 10¹⁴cm⁻³.

Soft X-ray spectroscopic diagnostics of laboratory plasmas are considered. To start with, the state of the art in the knowledge of rate coefficients, cross-sections, transition probabilities, and ionization equilibrium calculations is reviewed. Next, the plasma spectral emission, i.e. continuum and line emission (including satellites), line broadening (including opacity), and total emitted radiation as an energy loss process, is considered. To conclude, a short discussion of X-ray plasma sources and instrumental problems is presented.

The non-linear development of the m = 0 resistive 'g' mode has been studied in the reverse-field pinch. A saturation process is shown to exist in which the perturbations cause a quasi-linear flattening of the equilibrium pressure near the m = 0 resonant surface. The mechanism for this flattening is discussed.

By making use of a general formulation of the MHD energy theorem the power deposited by ideal-MHD waves in a stable plasma is calculated in a straightforward way. When applied to very-low-frequency waves with is the wave vector and the Alfvén velocity vector), the principle shows that heating at the shear Alfvén wave resonance is inefficient. Then, a low-frequency heating scheme which, unlike the different kinds of TTMP studied so far in the literature can have substantial overall efficiency in thermonuclear toroidal devices is considered. It makes use of purely poloidal m ≠ 0, n = 0 RF-coils, which can be located so close to the vacuum wall that the plasma cross-section is not appreciably reduced.