(TH/P3-17) Current Drive with Oscillating Magnetic Fields and Helicity Injection and Neutral Beam Injection in a D-He³ FRC Reactor

Abstract.  The use of oscillating helical magnetic fields to produce and sustain the toroidal and poloidal currents in a Reversed Field Pinch (RFP) is investigated. A simple physical model that assumes fixed ions, massless electrons and uniform density and resistivity is employed. Thermal effects are neglected in Ohm’s law and helical coordinates are introduced to reduce the number of coupled nonlinear equations that must be advanced in time. The results show that it is possible to produce RFP like magnetic field profiles with pinch parameters close to the experimental values. The efficiencies obtained for moderate resistivity, and the observed scaling, indicate that this could be a very attractive method for high temperature plasmas. The effect of finite electron mass on the formation and sustainment of a FRC by rotating magnetic fields (RMF) is studied. The importance of inertial effects is measured by the ratio between the RMF frequency and the electron-ion collision frequency. When this ratio is very small previous results corresponding to massless electrons are recovered. When this ratio increases there are significant changes in the value of the minimum external rotating field needed to sustain the FRC and the time needed to reach a steady state. Since the collision frequency decreases with increasing temperature and decreasing density these effects are expected to become more important as fusion relevant temperatures are approached. The injection of high energy (1 MeV) neutral beams in a D-He³ FRC reactor (L=17 m, B=6.7 T, T=87.5 keV) is studied with a Monte Carlo code already used to study NBI in moderate size FRCs and Spheromaks. A 3D, finite volume, resistive MHD code is employed to study the formation and sustainment of a flux core spheromak by helicity injection through magnetized electrodes. The energy content of the different modes, the decay rates of the ideal invariants and their cascades are studied.

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