EPJ Web of Conferences (Jan 2015)

Correlation ECE diagnostic in Alcator C-Mod

  • Sung C.,
  • White A. E.,
  • Howard N. T.,
  • Mikkelsen D.,
  • Irby J.,
  • Leccacorvi R.,
  • Vieira R.,
  • Oi C.,
  • Rice J.,
  • Reinke M.,
  • Gao C.,
  • Ennever P.,
  • Porkolab M.,
  • Churchill R.,
  • Theiler C.,
  • Walk J.,
  • Hughes J.,
  • Hubbard A.,
  • Greenwald M.

DOI
https://doi.org/10.1051/epjconf/20158703007
Journal volume & issue
Vol. 87
p. 03007

Abstract

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Correlation ECE (CECE) is a diagnostic technique that allows measurement of small amplitude electron temperature, Te, fluctuations through standard cross-correlation analysis methods. In Alcator C-Mod, a new CECE diagnostic has been installed[Sung RSI 2012], and interesting phenomena have been observed in various plasma conditions. We find that local Te fluctuations near the edge (ρ ~ 0:8) decrease across the linearto- saturated ohmic confinement transition, with fluctuations decreasing with increasing plasma density[Sung NF 2013], which occurs simultaneously with rotation reversals[Rice NF 2011]. Te fluctuations are also reduced across core rotation reversals with an increase of plasma density in RF heated L-mode plasmas, which implies that the same physics related to the reduction of Te fluctuations may be applied to both ohmic and RF heated L-mode plasmas. In I-mode plasmas, we observe the reduction of core Te fluctuations, which indicates changes of turbulence occur not only in the pedestal region but also in the core across the L/I transition[White NF 2014]. The present CECE diagnostic system in C-Mod and these experimental results are described in this paper.