Millimeter-wave beam scattering by plasma turbulence in TORPEX and TCV

Edge Physics Forum

  • Date: Dec 11, 2019
  • Time: 03:30 PM - 05:00 PM (Local Time Germany)
  • Speaker: Oulfa Chellai
  • EPFL Lausanne, Switzerland
  • Location: Garching
  • Room: Seminarraum D3

In magnetically confined fusion devices, the use of electromagnetic radiations ranges from plasma diagnostics to plasma heating and current drive. On the one hand, the electromagnetic emission from the plasma is studied to understand the turbulence from the plasma core and measure plasma parameters. On the other hand, externally injected mm-waves (mmw) in the electron cyclotron (EC) range of frequencies are used for plasma heating, current profile control and, surgically, for neoclassical tearing modes stabilization. Recently, interest in the study of the influence of the plasma turbulence on EC-beam propagation has grown, particularly when concerns were raised for ITER where it has been estimated that plasma turblence could be repsonsible for an EC-beam broadening of up to a factor of two; potentially leading to a loss of efficiency in their surgical use and possibly preventing tearing modes stabilization at the expected power levels.


Millimeter-wave beam scattering by plasma turbulence is investigated in the basic plasma physics device TORPEX and the Tokamak à Configuration Variable (TCV), both located at the Swiss Plasma Center. The two devices are equipped with an extensive set of diagnostics which provides an ideal environment to diagnose plasma turbulence and associated structures, such as blobs. A mmw-beam is in injected from the top of the device and the power is measured at the bottom. We show both experimentally and numerically, in the two devices, that blobs are responsible for local fluctuations of the mmw-power by defocusing the mmw-beam. In TCV, using the WKBeam code, we show that plasma turbulence is responsible for a 50% broadening of the EC-beam.

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