Estimate of pre-thermal quench non-thermal electron density profile during Ar pellet shutdowns of low-density target plasmas in DIII-D

The radial density profile of pre-thermal quench (pre-TQ) early-time non-thermal (hot) electrons is estimated by combining electron cyclotron emission and soft x-ray data during the rapid shutdown low-density ( n e ? 10 19 m ? 3 ) DIII-D target plasmas with cryogenic argon pellet injection. This technique mostly limited in these experiments to pre-TQ phase quickly loses validity TQ. Two different cases are studied: a high (10 keV) temperature low (4 target. results indicate that early-time, low-energy (?10 hot form ahead as it enters plasma, affecting ablation rate; hypothesized this may be caused cross field transport ions or electrons. Fokker–Planck modeling two shots suggests current quite significant (up 50% total current). Comparison between modeled post-TQ inferred from avalanche theory increases high-temperature TQ but decreases low-temperature uncertainties estimate large; however, if true, loss could larger than previously DIII-D.