Central helium density measurements in PLT

The central helium density in PLT has been deduced from measurements of the ratio of d- 3 He to d-d fusion reactions during deuterium neutral-beam injection. The inward transport time for 3 He puffed at the edge plasma was 10 to 30 ms. The decay time of the central 3 He density increased with electron density, varying from 0.3 s to greater than 1.0 s over the density range of (1–5) × 10 13 cm −3