Both external and internal magnetic probes have been used in low-current discharges and external probes in high-current discharges to study the magnetic field configuration and its fluctuations in the OHTE toroidal pinch with toroidal field reversal. The equilibrium magnetic field configuration is close to that of the Taylor state in the central half of the plasma (μ≡μ0bJ/B is constant) but differs in the outer half (μ gradually goes to zero at the plasma edge). Measurements of the magnetic fluctuations indicate that the dominant fluctuation mode observed is the resistive internal kink with m=1, n≂18. The measured relative level of magnetic field fluctuations scales as B̃/B∼S−1/2, where S is the magnetic Reynolds number.
A simple model of three-body recombination in a freely expanding plasma which is initially isothermal but whose initial density decreases with radius leads to a variation of ion charge state within the ion flow, in qualitative agreement with that observed in laser-produced plasma experiments.
Reversed-field pinch configurations produced in the OHTE device using a resistive shell were maintained for up to 7.5 times the shell resistive time. The plasma density, resistance, and magnetic fluctuations do not evolve significantly while the plasma current is sustained, and the plasma behaviour is similar to that previously observed in conducting shell OHTE/RFP experiments. The experimental observations suggest that a highly conducting shell may not be required for the stability of a reversed-field pinch.
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