Power and particle balance during neutral beam injection in TFTR

Abstract

Detailed boundary plasma measurements on TFTR have been made during a NBI power scan in the range P tot = 1–20 MW in the L-mode regime. The behaviour of the plasma density 〈 n e〉, radiated power P red, carbon and deuterium fluxes Γ c, Γ D, and Z eff can be summarized as: (1) 〈 n e〉 ∝ P 1/2 tot, (2) P rad, Γ c, Γ D ∝ P tot, (3) Z eff ≈ constant. These results obtained during NBI heating in TFTR are very similar to recent JET observations during ICRF heating and suggest that the form of heating plays little role in the behaviour of the discharge parameters. In the case of NBI in L-mode discharges it is shown that central fuelling plays a minor role in the particle balance of the discharge. More important is the NBI role in the power balance. Both the TFTR data during NBI and the JET data during ICRH are consistent with a simple model of particle and power balance in which the particle sources originate primarily at the graphite limiter.