Development of a correlation ECE radiometer for electron temperature fluctuation measurements in Heliotron J

G Weir ,Satoshi Yamamoto,Takashi Minami,Jinxiang Zhu,Yuji Nakamura,H Okada ,S Kado ,X X Lu ,S Ohshima ,S Kobayashi ,M Luo ,A Ishizawa ,Y Yoshimura ,N B Marushchenko ,L Zang ,S Konoshima ,K Nagasaki ,T Mizuuchi

doi:10.1051/epjconf/201920303013

Abstract

A radial correlation ECE radiometer diagnostic has been developed for electron temperature fluctuation measurements in the helical-axis heliotron device, Heliotron J. The radiometer consists of two heterodyne detection systems. One system scans the frequency of a local oscillator from 52 to 64 GHz with a single intermediate frequency filter, and the second system has a fixed frequency, 56 GHz local oscillator with four intermediate frequency filters. This frequency range covers measurement positions spanning from the plasma core to the half radius. Laboratory tests indicate that each system has narrow intermediate frequency bandwidth and high-sensitivity over a large dynamic range. During plasma experiments with NBI heating, radiation temperature fluctuation measured by the CECE radiometer decrease with increasing ECCD commensurate with previous measurements of energetic particle driven modes on Heliotron J.

Highlights

Turbulence in density and temperature is believed to govern energy and particle confinement in magnetically confined fusion plasmas
While plasma density fluctuations may be directly measured in the confinement region with microwave or optical diagnostics, electron temperature fluctuations are measured indirectly through decorrelation of Electron Cyclotron Emission (ECE) [4]
The first proof-ofprinciple measurements of core electron temperature fluctuations were reported from the W7-AS stellarator [5] and the TEXT-U tokamak [6,7,8,9], and electron temperature fluctuations might contribute significantly to the anomalous electron heat flux when they are correlated with potential fluctuations [10]

Summary

Introduction

Turbulence in density and temperature is believed to govern energy and particle confinement in magnetically confined fusion plasmas. While plasma density fluctuations may be directly measured in the confinement region with microwave or optical diagnostics, electron temperature fluctuations are measured indirectly through decorrelation of Electron Cyclotron Emission (ECE) [4]. This is necessary because thermal noise dominates electron temperature fluctuations in the ECE spectrum and standard ECE radiometry techniques are not suitable for measuring high-frequency, small amplitude temperature fluctuations. We have designed and installed a new correlation ECE radiometer system to measure core electron temperature fluctuations on the medium-sized stellarator/heliotron (S/H) device, Heliotron J. We will concentrate on the spectral decorrelation method and report on the development of a correlation ECE (CECE) radiometer for temperature fluctuations and recent plasma experimental results in the helical-heliotron device, Heliotron J.

The Heliotron J device

Correlation ECE radiometer

Laboratory tests

Plasma experiments

Findings

Summary