A short history of heavy ion beam probing

The author describes some aspects of research on controlled thermonuclear fusion as an energy source, starting in the late 1950s. There was a need for new diagnostic techniques for studying high temperature plasmas. The author proposed a diagnostic for measuring plasma density by probing a deuterium plasma with a deuterium beam and measuring the proton production from the D-D nuclear reaction. By the mid 1960s, it was possible to do so. After carrying out a D-D measurement, the author suggested switching over to an H₂⁺ beam and looking for an H⁺ signal. The H+ was loud and clear and that was the last of the nuclear measurements. One of the first things done using the molecular break-up of the H₂⁺ to measure the density of the hollow cathode arc plasma was a study of a coherent instability. The frequency response wasn´t sufficient to measure the instability directly, so a Langmuir probe was used to detect the instability. The Langmuir probe gave a signal from a fixed spatial location but the beam probe signal was swept across the plasma giving 2D spatial resolution. This was the first detailed mapping of a plasma instability. Attempts to apply the ion beam probe to measuring the plasma current density in the ST Tokamak are described. Heavy ion beam probing measurements using hollow cathode arcs as target plasmas made it possible to measure T_e at low temperatures and to identify space potential fluctuations. Installation of a beam probe on the Laser Initiated Target Experiment are described, along with work on the ELMO Bumpy Torus, the VERSATOR Tokamak, TMX, TEXT, ISX-B, the Ergodic Magnetic Limiter and ATF