Electric field and plasma potential measurements on TEXT-U using the 2 MeV heavy ion beam probe (HIBP)

Summary form only given, as follows. The 2 MeV HIBP on TEXT-Upgrade has been used to measure the plasma potential for a variety of discharge conditions. Small scale, multiple point measurements throughout a cross section of the plasma give variations in electric field with a resolution of better than 10 V/cm. Scan lines through the plasma produce a potential profile along a radial path from plasma center to edge. Changes in electric field and potential are monitored during impurity injection and with 500 kW of ECH heating. Fluctuations in plasma potential have been observed deep within the plasma with 40 V rms sensitivity.