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Effective critical electric field for runaway electron generation

Author: Adam Stahl
Requested Type: Consider for Invited
Submitted: 2015-01-19 03:31:48

Co-authors: E. Hirvijoki, J. Decker, O. Embreus & T. Fulop

Contact Info:
Chalmers University of Technology
Nuclear Engineering
Gothenburg, Vastra Got   41296
Sweden

Abstract Text:
In this work we investigate factors that influence the effective critical electric field for runaway electron generation in tokamaks. We present numerical solutions of the kinetic equation, and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature, and (2) synchrotron radiation losses. We also address the effective critical field in the context of a transition from runaway growth to decay. We find agreement with recent experiments in DIII-D, but show that the observation of an elevated effective critical field can mainly be attributed to changes in the momentum-space distribution of runaways, and only to a lesser extent to a de facto change in the critical field.

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