Abstract
This paper reports on a new investigation of the long-standing, unresolved discrepancy between Thomson Scattering (TS) and Electron Cyclotron Emission (ECE) measurements of electron temperature in high temperature tokamak plasmas. At the Alcator C-Mod tokamak, ion cyclotron range of frequency (ICRF) heating is used to produce high temperature conditions where the TS- ECE discrepancy, as observed in the past at JET and TFTR, should appear. Plasmas with Te(0) up to 8 keV are obtained using three different heating scenarios: Ion Cyclotron Resonance Heating (ICRH), ICRF mode conversion heating and a combination of the two heating methods. This is done in order to explore the hypothesis that ICRH-generated fast ions may be related to the discrepancy. In all high temperature cases at C-Mod, we find no evidence for the type of discrepancy reported at JET and TFTR. Here we present the C-Mod results along with a summary of past work on the TS-ECE discrepancy.
Highlights
In some tokamak experiments featuring strong neutral beam and ion cyclotron range of frequency (ICRF) auxiliary heating have shown the existence of a clear discrepancy between Te measured by Thomson Scattering (TS) and Electron Cyclotron Emission (ECE) when Te >7keVinTFTR [1,2] and when Te >5keV in JET[3,4]
This paper reports on a new investigation of the long-standing, unresolved discrepancy between Thomson Scattering (TS) and Electron Cyclotron Emission (ECE) measurements of electron temperature in high temperature tokamak plasmas
The discrepancy that was observed at TFTR and JET is characterized by ECE measurements of electron temperature that are systematically higher than the TS measurements at high temperatures
Summary
In some tokamak experiments featuring strong neutral beam and ion cyclotron range of frequency (ICRF) auxiliary heating have shown the existence of a clear discrepancy between Te measured by TS and ECE when Te >7keVinTFTR [1,2] and when Te >5keV in JET[3,4]. The existence of a temperaturedependent TS-ECE discrepancy presents a significant challenge for ITER where core electron temperatures above 20 keV are expected. We mention some possible paths for future work on this topic.
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