EPJ Web of Conferences (Jan 2019)

Side emissions during EC injection for PDI studies in FTU tokamak

  • Bruschi Alessandro,
  • Alessi Edoardo,
  • Baiocchi Benedetta,
  • Bin William,
  • D’Arcangelo Ocleto,
  • Fanale Francesco,
  • Figini Lorenzo,
  • Galperti Cristian,
  • Garavaglia Saul,
  • Gittini Giuseppe,
  • Granucci Gustavo,
  • Grosso Giovanni,
  • Lubyako Lev,
  • Mazzotta Cristina,
  • Mellera Vittoria,
  • Moro Alessandro,
  • Orsitto Francesco,
  • Pallotta Fabrizio,
  • Rocchi Giuliano,
  • Simonetto Alessandro,
  • Tartari Umberto,
  • Tudisco Onofrio

DOI
https://doi.org/10.1051/epjconf/201920302005
Journal volume & issue
Vol. 203
p. 02005

Abstract

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The evidence of Parametric Decay Instabilities (PDI) excited by the ECH power injected in O-Mode has been explored in FTU Tokamak, using the Collective Thomson Scattering (CTS) diagnostic. The experiments show evidences to support the hypothesis of low-threshold excitation of waves generated by PDI mechanisms, formerly proposed in the case of 2nd harmonic X-mode injection in TEXTOR and ASDEX-U. Theoretical analysis predicts low-threshold parametric decay also for O-mode pump-wave injection, which can be injected in FTU at frequencies close to the first Harmonic EC resonance. Experiments were made at different magnetic fields, injecting the 140 GHz probe and observing the emission from the second antenna of the EC launcher in poloidally symmetric and asymmetric configurations, in presence of MHD islands. The signal is detected by the CTS radiometers, with a fast digitizer allowing the spectral reconstruction at very fine time and frequency scales. Different types of emissions are studied in detail, comparing them with the magnetic island rotation frequency in different plasma conditions. In order to locate the plasma volume originating the emissions, a new antenna and receiving line has been installed.