Density Fluctuation Measurements in the MST Reversed Field Pinch Using a Heavy Ion Beam Probe

Localized measurements of density fluctuations in the hot core of the Madison Symmetric Torus (MST) reversed field pinch have been made with a Heavy Ion Beam Probe (HIBP). The density fluctuations are 10 - 20% in the region 0.25<r/a<0.75. Results are presented for both standard and improved confinement discharges. To have confidence in the results it is necessary to account for possible signal corruption, such as ion path effects and electronic noise. The HIBP on MST has 2 additional factors that are not common to most HIBPs. The small machine ports (2" injection port and 4.5" detection port) can result in vignetting of the beam and the constantly changing magnetic fields causes the beam's sample location to move. It is shown that such instrument effects can be accounted for and are small in selected data sets.