Impurity and Particle Transport and Control in TFTR

摘要

Degassing of the TFTR graphite limiter by low density deuterium or helium discharges enables the limiter to pump deuterium, thereby reducing recycling and improving energy confinement in neutral-beam-heated discharges. During a helium degassing sequence the hydrogen influx decreased by a factor of 20. As a consequence of degassing sequences the low density limit in 0.8 mA deuterium discharges decreased from 1 x 10 sup 19 m sup -3 to 0.5 x 10 sup 19 m sup -3 , the density-decay time dropped from greater than 10 s to 0.15 s, and the recycling coefficient dropped from nearly 1 to less than 0.4. Z/sub eff/ values in 2.2 MA L-mode discharges on the toroidal limiter with neutral-beam-heating power up to 15 MW are between 2 and 3 if the pre-beam plasma has low Z/sub eff/ (high density), but can be as high as 4.5 if the pre-beam target has high Z/sub eff/ (low density). Z/sub eff/ values in enhanced confinement shots drop from 7 during the ohmic phase to 3 with neutral beam heating. The radiated power drops from 60 to 70% of total heating power to 30 to 35% for beam powers from 10 to 20 MW. (ERA citation 12:038382)