Heavy ion beam probe development

Summary form only given, as follows. Heavy ion beam probe diagnostic (HIBP) systems are in operation on the Madison Symmetric Torus (MST) at Wisconsin and on a helicon plasma experiment at Rensselaer. Determination of the plasma potential in the core of the MST Reversed Field Pinch (RFP) is one of the primary purposes of the HIBP. In particular, the relationship between the equilibrium electric field and plasma rotation and transport is being investigated. Preliminary measurements inside the core indicate that the plasma potential is positive and in the range of 0.5 kV to 2.5 kV for standard discharges. This is the first such measurement in the core of a RFP with moderate temperature and density. As with other HIBP systems, the other key experimental goal is to obtain measurements of density and potential fluctuations. On MST, magnetic fluctuation measurements should also be possible. Initial signals observed are closely correlated with low frequency MHD activity. Measurements have been obtained over a broad range of plasma conditions. The intriguing results point to a significant role for HIBP measurements in an RFP. At RPI we are conducting experiments with the goal of developing a non-perturbing diagnostic technique for measuring the RF field and density fluctuations in fusion plasmas. A helicon plasma with an HIBP diagnostic has been constructed. The helicon plasma has a magnetic field of up to 1.5 kG produced by a set of circular coils. A 1 kW, 13.56 MHz RF generator is used to drive helicon waves in the plasma. The diagnostic apparatus utilizes a 60 keV HIBP diagnostic beam and an electrostatic energy analyzer. The detection electronics has been modified to operate at higher frequencies. The present status of the experiment as well as key issues in extending HIBP measurements to higher frequencies are discussed.