Electron temperature profile behaviour in TFTR during neutral beam injection and multiple pellet fuelling

Abstract

The electron temperature profiles on the Tokamak Fusion Test Reactor (TFTR) are determined by several diagnostics, including multi-point Thomson scattering and electron cyclotron emission measured with heterodyne radiometers and a Michelson interferometer. The electron temperature profiles are characterized by very high central temperatures (>8 keV) and large Shafranov shifts (>35 cm). The large Shafranov shifts suggest the necessity of mapping to magnetic flux surfaces when investigating the profile behaviour. During 1986 ,TFTR was operated with up to 20 MW of deuterium neutral beam injection (NBI) and a deuterium pellet injector. The electron temperature profile measurements were made on plasmas with 2.7 < BT < 5.1 T, βpdia up to 2.2, 1 × 1019<n̄e<1.5 × 1020 m−3 and 2.5 < qcyl < 10. In many of the NBI plasmas the core was broadened by either sawteeth or convection. In multiple pellet fuelled discharges, where pellets penetrate to the plasma core, the radiation profile became significantly peaked on axis, resulting in hollow temperature profiles. In the light of work on ‘profile consistency’, various methods of mapping Te(R) to flux surfaces are investigated as well as the extent to which the electron temperature profile away from the core remains invariant to these perturbations.