Effect Of Toroidal Field Research Articles

The effect of toroidal field on the rotating magnetic field current drive in rotamak plasmas

A rotamak is one kind of compact spherically shaped magnetic-confinement device. In a rotamak the plasma current is driven by means of rotating magnetic field (RMF). The driven current can reverse the original equilibrium field and generate a field-reversed-configuration. In a conventional rotamak, a toroidal field (TF) is not necessary for the RMF to drive plasma current, but it was found that the present of an additional TF can influence the RMF current drive. In this paper the effect of TF on the RMF current drive in a rotamak are investigated in some detail. The experimental results show that addition of TF increases the RMF driven current greatly and enhances the RMF penetration dramatically. Without TF, the RMF can only penetrate into plasma in the edge region. When a TF is added, the RMF can reach almost the whole plasma region. This is an optimal strength of toroidal magnetic field for getting maximum plasma current when Bv and radio frequency generator power are fixed. Besides driving current, the RMF generates high harmonic fields in rotamak plasma. The effect of TF on the harmonic field spectra are also reported.

Toroidal field effects on dipole equilibrium and stability at finite plasma pressure

The influence of a toroidal magnetic field on the equilibrium and stability of a plasma confined by the magnetic field of a point dipole is considered, since it may be necessary to introduce a toroidal magnetic field to smooth electron heating or other asymmetries in the toroidal direction that can lead to toroidal electric fields and a loss of confinement due to radial E×B drift. To begin, a toriodal magnetic field is shown to restore confinement by reducing electron heating departures from axisymmetry. Then the Grad–Shafranov equation for a point dipole in the presence of a toroidal field is solved to explicitly demonstrate that an equilibrium exists. Finally, it is shown that a toroidal magnetic field destabilizes the otherwise stable point dipole ballooning modes at high plasma pressure. Consequently, if a toroidal magnetic field is necessary to remove toroidal heating asymmetries in a dipole equilibrium, the heating may have to be performed transiently or at lower plasma pressures.

Consideration of the Magnetic Field Ripple in the Design of Plasma Edge Components for Tore Supra

Design of edge components for a plasma device requires a description of heat and particle flows at the edge of the device. In a tokamak, the ripple of the toroidal field effects the direction of such flows by affecting the direction of the field. In Tore Supra, in particular, the ripple is large (less than or equal to8% at the outboard edge). This causes a substantial (less than or equal to factor of 2) increase in heat flux deposited onto the limiter and antenna face. It also reduced the particle removal efficiency of the pump limiters by increasing the distance between the throat opening and the plasma edge. It is therefore important to include the ripple when designing plasma edge components such as pump limiters and rf antennas. A simple, but accurate, scheme for field line tracing is found and used to study this effect. Modeling of the ripple is discussed. 18 refs., 10 figs.

Toroidal field effects on the stability of a Heliotron configuration

The addition of a small toroidal field to the Heliotron E configuration [Plasma Phys. 13, 243 (1981)] improves the stability of the n=1 mode and increases the value of the stability beta critical. Total stabilization of this mode can be achieved with added toroidal fields between 5% and 15% of the total field. In this situation, the plasma can have direct access to the second stability regime. For the Heliotron E configuration, the self-stabilization effect is due to the shear, not to the magnetic well. The toroidal field threshold value for stability depends strongly on the pressure profile and the aspect ratio of the plasma.