The Reversatron II RFP

The Reversatron II RFP is a new version of the Reversatron RFP with new field coils, vacuum chamber, and removable shell. The OH coils generate negligible field (∼ 10G) at the plasma so that the OH coil current does not affect equilibrium. The VF coils are inductively decoupled from both the plasma and the OH circuits to simplify equilibrium control. The OH coils which are near to the plasma have coaxial feeds to minimize field perturbations. The measured nonuniformity of the applied fields is at the 10 Gauss level (peak-to-peak). The vacuum chamber resistance is 40 mΩ to reduce the chamber current and the pumping port (7.5 cm W x 12 cm H) is bridged by two conductors to reduce field errors due to interruption of the chamber current. The 144 turn torroidal coil is uniformly spaced except at the pumping port where four turns are skewred. The shell is of 0.1 mm brass (∼ 0.1 msec penetration time) and has one poloidal and two toroidal gaps. Initial operation with no shell has produced RFP discharges lasting 0.4 msec with 23 kA plasma current in 15 mTorr He. Magnetic probes sensitive to m = 1 modes show fluctuations similar to those seen in Reversatron I with no shell. Preprogramming of the vertical field waveform by varying circuit elements appears to provide adequate equilibrium control. Experiments are planned in which the vertical field index will be varied