First observation of electron fishbones associated to the double-kink mode

We report here the observation of MHD modes identified as electron fishbones in Tore Supra discharges using Lower Hybrid (LH) waves for generating most of the plasma current. Fish-bone modes are marginally stable ideal modes, which are destabilised by trapped suprathermal particle, via wave-particle resonance at the toroidal precession frequency. Ion fishbone modes are driven by deeply trapped ions, and they destabilise the internal kink [1], as well as the double-kink modes [2]. This latter form of ion fishbone has been observed in JET Optimised Shear scenario [3]. The mechanism for electron fishbone is similar, except that the ideal mode is destabilized by barely trapped electrons. Up to now, electron fishbone modes have only been observed associated to the internal (q = 1) mode, in discharges heated at the Electron Cyclotron frequency [4] [5] [6], or with LH waves [7]. But it is natural that, in reversed magnetic shear plasmas with a suprathermal electron population, electron fishbone can exist in association with the double-kink mode. This is what we observe in Tore Supra for the first time, where the elec-tron fishbone mode is observed in association with the double-kink mode on q = 2 and q = 3/2. The Tore Supra tokamak [8] is equipped with two LH antennas capable of delivering about 3 MW for long duration (best present result is 3 MW for 370 s). Electron fishbone modes ar