Broadening of mm-wave beam by plasma turbulence in the basic plasma physics device TORPEX and TCV tokamak

Concerns have recently been raised about loss of efficiency in Neoclassical Tearing Modes (NTM) stabilization by Electron Cyclotron (EC) due to broadening of mm-wave beams interacting with plasma turbulence at the edge and the scrape-off layer (SOL) of tokamak plasmas. This has stimulated a number of experimental and theoretical studies on well diagnosed basic plasma physics devices and tokamaks. The SOL, characterized by open field lines, is populated by field-aligned structures, dubbed “blobs”, driven by the underlying turbulence. An externally injected mm-wave beam interacting with blobs is scattered, leading to a broader time-averaged beam profile at the targeted absorption location. On next-generation fusion devices, such as ITER, this would lead to a reduced efficiency of NTM stabilization that may require modulation of the beam to recover the required performance.