The first year of operation of the heavy ion beam probe (HIBP) on the advanced torooidal facility (ATF)

Installation of the HIBP on the A TF torsatron was completed in Spring 1990. During the past year this diagnostic has been used to make measurements of the plasma radial potential profile and electron density fluctuations. Initial potential profile measurements in ECH-heated plasmas at 0.95 T indicate a positive plasma potential of several hundred Volts. This value of potential is approximately half of the electron temperature. A strong 20-50 kHz oscillation has been observed in the plasma edge region. The interior of the plasma has a low fluctuation level. The diagnostic has four major subsystems: a 160 kV ion accelerator, a beamline, a 35 kV parallel plate electrostatic energy analyzer, and primary beam detectors. The beamline provides a magnetically shielded vacuum connection between the accelerator and the A TF vacuum vessel. Four sets of high voltage sweep plates for directing the ion beam and two beam profile monitors for characterizing the beam shape and relative intensity are housed within the beamline. The parallel plate electrostatic analyzer has three sets of entrance slits/detector plates for making fluctuation correlation measurements. Three gridded wire detectors, located on or near to the inside surface of the A TF vacuum vessel, are used to verify primary beam trajectories. A coordinate axis measuring machine was used during the assembly and alignment of the beamline and analyzer. The complexity of the A TF magnetic field presented several implementation problems primarily due to fields that exist outside of the main plasma volume. The field in the beamline region exerts a one ton sideways force on the beamline during 1.95 Tesla operation and has demagnetized permanent magnets in the beam profile monitors. The magnetic field in the analyzer region causes it to behave quite differently from what was expected as a result of calibrations done on a laboratory test stand. The trajectories of the Cs
⁺⁺
ions are changed and secondary electrons leaving detector plates can now be detected at other plates, thus disturbing plasma potential measurements. Recalibration with in-situ measurements has become essential along with developing an accurate computer model for the analyzer.