Calibration and initial operation of the HIBP on the MST

For the first time, a heavy ion beam probe (HIBP) has been installed on a r eversed field pinch, i.e., Madison symmetric torus (MST), to measure the pl asma potential profile, potential, and electron density fluctuations, etc. The application of a HIBP on MST has presented new challenges for this diag nostic. The primary sources of difficulty are small access ports, high plas ma, and, ultraviolet (UV) flux and a confining magnetic field produced larg ely by plasma currents. The requirement to keep ports small so as to avoid magnetic field perturbations led to the development of the cross-over sweep system. The effectiveness and calibration of this sweep system will be rep orted. In addition, this diagnostic is now operating with greater plasma/UV loading effects than most previous Rensselaer HIBPs. The plasma flux is re duced by using a magnetic suppression structure. The UV flux appears to be the dominant cause of the remaining loading, which is substantial. The magn etic field being largely produced by the plasma makes determination of meas urement locations exclusively from trajectory calculations difficult. Initi al operation results have shown that the magnetic field model we are using to calculate our ion trajectories has an inaccuracy of about 10%, and thus subsequent development of improved confining field models is important. Sec ondary signals have been detected, and the levels are smaller than that fro m the UV induced noises. Methods to increase the signal levels are discusse d. A very rough estimation of the potential at a typical MST core location is 0.8-2 kV. Fluctuations in the frequency range 100-20 kHz have also been observed. (C) 2001 American Institute of Physics.