Key results of long pulse ICRH operation in Tore Supra

Abstract

Long pulse operation on the Tore Supra tokamak has entered a new phase, characterized by the use of heating power level in excess of 10 MW, during pulses lasting several tens of resistive times. This has been made possible by the use of ion cyclotron range of frequency (ICRF) heating (9 MW coupled to the plasma at 57 MHz), combined with lower hybrid current drive (LHCD: 3 MW at 3.7 GHz) and efficient fuelling techniques (supersonic gas injection, pellets). This paper addresses key technological, operational and physics issues related to the long pulse operation of the Tore Supra ICRF system and required for a reactor: R&D on the ICRF plant, real-time control and safety procedures, integration with other tokamak subsystems, experimental investigation and theoretical modelling of the edge ICRF physics (wave coupling, heat loads on antenna front faces). As far as possible lessons are drawn from the experience gained on Tore Supra for the design and operation of a next-step device.

Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the “wide sheath” asymptotic regime

“…This parametric dependence is valuable for design and experimental studies. In particular, the RFinduced heat loads in the RF antenna vicinity were inferred experimentally to scale as E //ap 1 , 29,30 consistent with the first order theory. The particular simulation showed in Ref.…”

“…6,16,29,[31][32][33] A. RF part of the model: Full-wave propagation in bounded 3-dimensional (3D) SOL plasma…”

“…From a practical point of view, this is also a critical regime since experimentally the deleterious plasma-wall interaction related to the sheaths gets exacerbated at high RF power. 18,[28][29][30] Sections III and IV detail the asymptotic resolution for several configurations of the excitation and of the target plasma. The way to refine iteratively the solution from its asymptotic value is also outlined.…”

Spectral effects on fast wave core heating and current drive

“…Parametric decay instabilities may account for some of the losses, but as discussed above, are not large enough to account for the observed degradation of the core heating efficiency on NSTX, so that a number of processes may be contributing to the net loss. Sheath rectification losses in particular are associated with hot spots on antennas and nearby limiters and in general are exacerbated when the current straps are not aligned with the equilibrium magnetic field [16,17,18]. Visible light pictures, taken with a fast camera at the end of the 2008 experimental campaign, of a few NSTX H-mode discharges with and without HHFW Figure 5 Visible light camera picture showing toroidally localized HHFW interaction with the divertor in an NSTX H-mode plasma (I p = 1 MA, P NB = 2 MW, B T = 0.55 T, P rf ~ 1.8 MW, -90˚ phasing).…”

A radio-frequency sheath boundary condition and its effect on slow wave propagation

“…by restricting operation to high-k || phasing 7 or lower power levels. In longer-pulse experiments 15 and future burning plasma experiments, the requirements will be even more severe: even a small level of antenna-plasma interaction may result damaging localized heat deposition during the shot.…”