Observation of direct power deposition of ICRF in EAST plasma boundary

Abstract

Waves in the ion-cyclotron range of frequencies (ICRF) used for plasma heating are known to interact strongly with the scrape-off layer (SOL) plasma, potentially limiting ICRF performance. We present the evidence of direct power deposition of ICRF in the Experimental Advanced Superconducting Tokamak (EAST) plasma boundary, with two ICRF antennas and 12 MW of ICRF source power in support of high-power and long-pulse operation. By applying Retarding Field Analyzer (RFA) diagnostic, a sharp rise in average collected ion parallel energy was obtained during the period of ICRF heating as the RFA probe stayed still at 2 mm behind the main limiter which indicates that a certain amount of power is deposited near the limiter instead of being absorbed by the main plasma. A significant increase of the target floating potential in electron temperature measured by Divertor Langmuir Probes arrays was observed. The wall temperature in the far SOL was also enhanced. As a consequence, an enhancement of the carbon and tungsten impurity concentration was observed both at the plasma boundary and core. Besides, plasma radiation, the impurity concentration of the boundary and core increased, and the temperature rise of the first wall was also observed, which are intuitive and powerful pieces of evidence of ICRF direct power deposition at the boundary.

KEYWORDS:

• Tokamak
• ICRF
• SOL
• power deposition

Acknowledgements

We would like to acknowledge the support and contributions from the rest of the EAST team and collaborators. This work was supported by the National Magnetic Confinement Fusion Energy R&D Program of China under Grant No. 2017YFE0301300, The National Natural Science Foundation of China under Grant No. 11705237. Furthermore, the authors gratefully acknowledge financial support from China Scholarship Council.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [grant number 11705237]; National Magnetic Confinement Fusion Research Program of China under Contract no. [2017YFE0301300].

Notes on contributors

X. L. Li

X. L. Li is currently working toward the Ph.D. degree in Nuclear Energy Science and Technology with Science Island Branch of Graduate School, University of Science and Technology of China, Hefei, China. His research interests include plasma physics, H-mode, Microwave diagnostics.