[en] It has often been assumed that the anomalous transport from saturated plasma instabilities is ''diffusive'' in the sense that the particle flux, Γ, the electron energy flux, q_e, and the ion energy flux, q_i, can be written in forms that are linear in the density gradient, dn/dr, the electron temperature gradient, dT_e/dr, and the ion temperature gradient dT_i/dr. In the simplest form, Γ = - D_nⁿ(dn/dr), q_e = - D_e^en(dT_e/dr), and q_i = -D_iⁱn(dT_i/dr). A possible generalization of this is to include so-called ''off-diagonal'' terms, with Γ = nV_n - D_nⁿ(dn/dr) - D_n^e(n/T_e)(dT_e/dr) - D_nⁱ(n/T_i)(dT_i/dr), with corresponding forms for the energy fluxes. Here, general results for the quasilinear particle and energy fluxes, resulting from tokamak linear microinstabilities, are evaluated to assess the relative importance of the diagonal and the off-diagonal terms. A further possible generatlization is to include also contributions to the fluxes from higher powers of the gradients, specifically ''quadratic'' contributions proportional to (dn/dr)², (dn/dr)(dT_e/dr), and so on. A procedure is described for evaluating the corresponding coefficients, and results are presented for illustrative realistic tokamak cases. Qualitatively, it is found that the off-diagonal diffusion coefficients can be as big as the diagonal ones, and that the quadratic terms can be larger than the linear ones. The results thus strongly suggest that the commonly used ''diffusive'' approximation with only diagonal terms, Γ = -D_nⁿ(dn/dr), and correspondingly for the energy fluxes, is not adequate in practice. 9 refs., 1 tabs

[en] The effect of varying ''input realism'' or varying completeness of the input data for linear microinstability calculations, in particular on the critical value of the ion temperature gradient for the ion temperature gradient mode, is investigated using gyrokinetic and gyrofluid approaches. The calculations show that varying input realism can have a substantial quantitative effect on the results

[en] Three distinct types of high toroidal mode number instabilities are obtained from a comprehensive kinetic calculation, using as input transport code results from the analysis of a recent design for the Burning Plasma Experiment (BPX). These instabilities are: the collisionless trapped-electron ion-temperature-gradient mode, the magnetohydrodynamic ballooning mode, and a high toroidal mode number version of the toroidicity-induced Alfven eigenmode or ''gap'' mode. The dependence of the instability linear eigenfrequencies on minor radius, beta, and toroidal mode number are investigated, along with the effects of hot alpha particles. Relative quasilinear fluxes of particles and energy for each species are also obtained. In addition, the beta dependence of the magnetohydrodynamic ballooning mode is investigated for a case using as input the results of a transport code calculation for the Tokamak Fusion Test Reactor (TFTR) in an extrapolation to a deuterium-tritium mixture. The effects of alpha particles and the relative quasilinear fluxes are also investigated for this case. 13 refs., 13 figs., 4 tabs

[en] Hot α-particles and thermalized helium ash particles in tokamaks can have significant effects on high toroidal mode number instabilities such as the trapped-electron drift mode and the kinetically calculated magnetohydrodynamic ballooning mode. In particular, the effects can be stabilizing, destabilizing, or negligible, depending on the parameters involved. In high-temperature tokamaks capable of producing significant numbers of hot α-particles, the predominant interaction of the mode with the α-particles is through resonances of various sorts. In turn, the modes can cause significant anomalous transport of the α-particles and the helium ash. Here, results of comprehensive linear eigenfrequency-eigenfunction calculations are presented for relevant realistic cases to show these effects. 24 refs., 12 figs., 6 tabs

[en] The analysis of electromagnetic kinetic toroidal eigenmodes for general magnetohydrodynamic (MHD) equilibria has been extended to include the effects of non-Maxwellian equilibrium distribution functions. This is necessary to properly represent the response of the hot beam-ion species produced during neutral beam injection heating and the response of the alpha-particle species in a thermonuclear plasma. The influence of these components on low-frequency tokamak microinstabilities is investigated for realistic cases typical of the PLT and PDX experiments

[en] An improved Krook model collision operator is presented for use in calculations of low-frequency microinstabilities in toroidal geometry. A comparison is made with results from calculations which use a Lorentz collision operator and with a previously employed Krook operator. The results with the new Krook operator agree with the results obtained using the Lorentz operator in the small collision frequency limit, whereas those with the old Krook operator do not

[en] It has recently been proposed that the presence of high energy ions from neutral beam injection can have a strong stabilizing effect on kinetically-modified ideal MHD ballooning modes in tokamaks. In order to assess realistically the importance of such effects, a comprehensive kinetic stability analysis, which takes into account the integral equation nature of the basic problem, has been applied to this investigation. In the collisionless limit, the effect of adding small fractions of hot beam ions is indeed found to be strongly stabilizing. On the other hand, for somewhat larger fractions of hot ions, a new beam-driven mode is found to occur with a growth rate comparable in magnitude to the growth rate of the MHD ballooning mode in the absence of hot ions. This implies that there should be an optimal density of hot particles which minimizes the strength of the relevant instabilities. Employing non-Maxwellian equilibrium distribution functions to model the beam species makes a quantitative, but not qualitative, difference in the results. Adding collisions to the calculation tends to reduce considerably the stabilizing effect of the hot ions

[en] A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfven eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables one to look at many familiar modes simultaneously and thus to study the modifications of and the interactions between them in a systematic way. Especially, the authors are able to investigate self-consistently the kinetic MHD phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a 2D finite element code has been developed and tested. In this paper, they present the basic theoretical formalism and some of the preliminary results

[en] Previous calculations of the linear growth rate and two-dimensional spatial structure of trapped-electron modes are made more general and more accurate in several ways. First, an integral equation formulation of the eigenmode problem allows arbitrary values of k/sub r/rho/sub i/ (where k/sub r/ is the radial wavenumber and rho/sub i/ is the ion gyroradius) to be treated. Second, the ion response is generalized so that arbitrary ratios of the ion magnetic drift frequency to the mode frequency are allowed. Finally, the electron and ion collision operators have been improved to allow consideration of the plateau and Pfirsch-Schluter regimes in addition to the usual banana regime. It is therefore possible to follow the transition in toroidal geometry from the trapped-electron mode to the collisionless and collisional drift modes. The method used involves expansion of the perturbed electrostatic potential in complete sets of radial and poloidal basis functions to convert the quasineutrality integral equation into a matrix equation

[en] A prominent characteristic of auxiliary-heated tokamak discharges which exhibit improved (''H-mode type'') confinement properties is that their density profiles tend to be much flatter over most of the plasma radius. Depsite this favorable trend, it is emphasized here that, even in the limit of zero density gradient, low-frequency microinstabilities can persist due to the nonzero temperature gradient