The role of power and magnetic connection to the active antenna in the suppression of intermittent structures by ion cyclotron resonance heating

摘要

The effect of the ion cyclotron resonance heating (ICRH) on the scrape-off layer (SOL) is still an open issue, where, lately it was shown on the ASDEX-Upgrade tokamak that turbulence large-scale structures, known as blobs or avaloids, are suppressed by ICRH (Antar et al 2010 Phys. Rev. Lett. 105 165001). Furthermore, it was shown that the edge localized mode-induced turbulent transport is also reduced significantly. However, the reasons behind this interaction remain unknown. On the Tore Supra tokamak, we confirm that the ICRH suppresses large-scale structures while small-scale structures are enhanced; overall, the turbulence level of fluctuations is reported to drop from about 40% to 25%. This confirms that the effects on turbulence are independent of the type of plasma confinement, L-mode on Tore Supra versus H-mode on ASDEX-Upgrade. The dependence on the ICRH power showed that if a threshold existed it would be below 500 kW and that above this power, no additional effects on the SOL turbulence are reported. The other study reported in this paper deals with the importance of the magnetic field line connections or, in other words, whether the interaction between ICRH and turbulence is global, affecting the whole plasma, or local, affecting regions that are magnetically connected to the active antenna. We found that the toroidal connection to the active antenna is not critical in the sense that turbulence in regions close to the antenna but not necessarily connected are affected. For regions that are not connected and far from the active antenna, turbulence does not change much when applying ICRH.