INTERNAL TOROIDAL FIELD-MEASUREMENTS ON THE HELICITY INJECTED TOKAMAKUSING THE TRANSIENT INTERNAL PROBE

Measurements of the local toroidal magnetic field have been achieved o n the helicity injected tokamak (HIT) using the transient internal pro be (TIP). HIT is a low aspect (a = 1.5, R = 0.35 m) ratio tokamak desi gned to study steady state current drive. The TIP diagnostic involves accelerating a small diamond clad magneto-optic probe through the plas ma at high velocities (similar to 2 km/s) using a light gas gun. The l ocal field is obtained by illuminating the probe with a laser and meas uring the amount of Faraday rotation in the reflected beam. Measuremen ts were conducted using unclad magneto-optic probes directed along a c hord tangent to the toroidal field. Plasma conditions were typically n (e) similar to 7 x 10(19) m(-3) and T-e similar to 40-80 eV. Measureme nt uncertainty is less than 2%. No changes in plasma parameters were o bserved during the first 200 ms (similar to 40 cm) of probe travel in the plasma. A temporary dip in plasma current, probably due to ablatio n of the retroreflecting material on the probe, is observed as the pro be exits the plasma. Density is unaffected by the presence of the prob e in the plasma. No long term deleterious effects to tokamak performan ce were observed as the TIP diagnostic was found to be quite compatibl e with the tokamak. (C) 1997 American Institute of Physics.