The role of current profile broadening in L and H-mode plasmas
Auxiliary heating by neutral beams (NBI) or ion cyclotron resonance heating (ICRH) can broaden or peak the plasma current density profile. A measure of changes to the current density profile J is established by a combination of current moments, which yields a profile broadening parameter. JET experiments are shown to broaden J, when NBI is applied to discharges which exhibit either L or H mode confinement; pellet injection and ICRH are shown to make J peak more sharply. The time evolution of the parameter is shown to correlate with the changes to the D(alpha) emission seen in H-mode discharges with and without ELMs. The broadening of J by NBI, especially for H-mode pulses, starts in the edge region. It is caused by the non-inductive bootstrap current component, as a consequence of steep density profiles. The ohmic current component undergoes only a nominal change. Associated with current profile broadening is an increase in edge pressure and total stored plasma energy W. An analysis of global confinement (variations of W with power P) is made by splitting W into three parts: the fast ion energy, the edge energy which is empirically shown to be proportional to the current profile broadening parameter, and the bulk plasma thermal energy. It is shown that the scaling for the last in the L and H-mode confinement regimes is similar.
Bibliographic Reference: Report: JET-P(89)56 EN (1989)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199010414 / Last updated on: 1994-12-01
Original language: en
Available languages: en