Density rise experiment on PLT

The evolution of the density profile in PLT during intense gas puffing is documented and analyzed. Measurements of the spectrum of low energy edge neutrals and of the change in central neutral density indicate that charge-exchange processes alone cannot account for the central density rise. The transient density profile changes can be reproduced numerically by a diffusivity of approx. 104 cm2/s, and a spatially averaged inward flow of 103 cm/s. These transport coefficients are 10 → 102 times larger than neoclassical. The ion energy confinement is reduced, the small scale density fluctuations are increased, and runaway electrons losses are increased during the density rise