Plasmas and Controlled Nuclear Fusion

Contains research objectives and reports on six research projects.U. S. Atomic Energy Commission (Contract AT(30-1)-3980

Kinetic Theory of Plasmas: Translational Energy

In the present contribution, we derive from kinetic theory a unified fluid model for multicomponent plasmas by accounting for the electromagnetic field influence. We deal with a possible thermal nonequilibrium of the translational energy of the particles, neglecting their internal energy and the reactive collisions. Given the strong disparity of mass between the electrons and heavy particles, such as molecules, atoms, and ions, we conduct a dimensional analysis of the Boltzmann equation. We then generalize the Chapman-Enskog method, emphasizing the role of a multiscale perturbation parameter on the collisional operator, the streaming operator, and the collisional invariants of the Boltzmann equation. The system is examined at successive orders of approximation, each of which corresponding to a physical time scale. The multicomponent Navier-Stokes regime is reached for the heavy particles, which follow a hyperbolic scaling, and is coupled to first order drift-diffusion equations for the electrons, which follow a parabolic scaling. The transport coefficients exhibit an anisotropic behavior when the magnetic field is strong enough. We also give a complete description of the Kolesnikov effect, i.e., the crossed contributions to the mass and energy transport fluxes coupling the electrons and heavy particles. Finally, the first and second principles of thermodynamics are proved to be satisfied by deriving a total energy equation and an entropy equation. Moreover, the system of equations is shown to be conservative and the purely convective system hyperbolic, thus leading to a well-defined structure

Modelling of edge plasma rotation accounting for a poloidal divertor and helical perturbation coils in TEXTOR

The impact of helical perturbations on the rotation velocity and thus on the energy confinement is calculated on the basis of the ambipolarity constraint, the parallel momentum equation of the revisited neoclassical theory and a simplified temperature equation. The helical perturbations can act as means for ergodizing the magnetic field and/or as momentum source or sinks, whereas at the separatrix (effective radius r(s)) of the poloidal divertor a temperature pedestal may arise due to the strong shear flow reducing the transport to a neoclassical level. The neoclassical theory allows the prediction of the parallel and poloidal flow speeds and thus of the 'subneoclassical' heat conductivity chi(sub) used in the heat conduction equation. This heat conductivity allows us to compute the temperature pedestal and to reproduce the power balance in ALCATOR if one assumes that chi = chi(sub) in the radial sheath with the thickness of Delta approximate to 0.7 cm, centred around the inflection radius r(in), and chi = chi(L) for r < r(in) - Delta/2. chi(L) is the normal L-mode heat conductivity. Source terms account for momentum deposition by neutral beam injection (NBI), by pressure anisotropization and the j x B force density, the latter two due to Fourier components of (rotating) helical fields.Source terms for the power deposition by NBI, Ohmic heating and radiation are also included.The main results can be summarized as follows:At a dynamic ergodic divertor in TEXTOR frequency of 10 kHz, a toroidal velocity gradient of 1.2 x 10(6) s(-1) may be achieved which is enough to suppress the ion temperature gradient and thus to generate an ITB.The poloidal divertor suppresses the neutral gas influx and thus effects a (sub)neoclassical sheath with a temperature pedestal of T-ped approximate to 400 eV and an increase of the central value by roughly the same amount. In the case of edge localized mode-control with an ergodic layer of Delta approximate to 2.5 cm, generated by the helical coils, the height of the pedestal stays unaffected if in the pedestal region a transition from L-mode confinement to subneoclassical confinement is assumed