First neutral-beam heating experiments in JET

Abstract

Hydrogen beams at particle energies of up to 65 keV, total beam powers of up to 5.5 MW , and beam-pulse durations of up to 7 s have been injected into deuterium plasmas. Experiments were performed over a wide range of plasma parameters with limiter plasmas and inner-wall plasmas. The operational regime was extended by 70% over the current ohmic density limit. In medium density experiments, ion temperatures of ca . 6.5 keV were reached with electron temperatures of 4.8 keV. The expected degradation of energy confinement with additional heating was observed. At 4 MA plasma current and 8 MW total input power, the global energy confinement time is ca. 0.4 s. The metallic impurity concentration and Zeff drop with the rise of plasm a density during beam pulses. The rise of radiated power closely follows that of the density. In most cases, the highest value of the radiated power stays below 50 % of the power input, with very low radiation from the centre of the plasma.