RF heating and current drive experiments in the Madison Symmetric Torus reversed field pinch

Auxiliary heating and current drive using rf waves promise to advance the performance of the reversed field pinch (RFP). Edge-localized current drive has been shown to suppress tearing mode activity that is responsible for much of the energy transport in the RFP. There are two rf experiments on the Madison Symmetric Torus with aspirations to non-inductively drive parallel current in the plasma edge. The electron Bernstein wave (EBW) is an attractive heating and current drive scheme, similar to standard ECCD as there is strong absorption at the electron cyclotron resonance, but the EBW propagates with no upper bound on density. Thus it can deposit energy into the overdense RFP plasma where electromagnetic waves are cutoff well outside the cyclotron resonance. Studies performed at low power (< 10 watts) have shown that a significant fraction of launched electromagnetic power at 3.6 GHz successfully couples to the electron Bernstein mode and there is an optimized launch angle with finite perpendicular wavenumber. A 130kW experiment (roughly 25% of the Ohmic input power of target discharges) shows a slight increase in soft x-ray emission during EBW injection. A new antenna capable of delivering 250kW is installed and initial experiments underway. The lower hybrid (LH) wave is being studied as a current drive technique in the RFP. An antenna with 300kW capacity is installed and operates at 800 MHz. The power flowing through the antenna has been measured with pickup loops installed in the antenna backplane. The measured power damping length of 2-4 parallel wavelengths is sufficiently long to prevent diffraction of the launched nll spectrum. Hard x-ray emission is observed from the plasma with up to 80 kW of LH power injection. Advancement toward full power (250-300kW) operation of the antenna is underway. This work is supported by the USDOE.