Modeling of Trapped Electron Effects on Electron Cyclotron Current Drive for Recent DIII-D Experiments
Owing to its potential capability of generating localized non-inductive current, especially off-axis, Electron Cyclotron Current Drive (ECCD) is considered a leading candidate for current profile control in achieving Advanced Tokamak (AT) operation. In recent DIII-D proof-of-principle experiments [1], localized off-axis ECCD has been clearly demonstrated for first time. The measured current drive efficiency near the magnetic axis agrees well with predictions of the bounce-averaged Fokker-Planck theory [2,3]. However, the off-axis current drive efficiency was observed to exceed the theoretical results, which predict significant degradation of the current drive efficiency due to trapped electron effects. The theoretical calculations have been based on an assumption that the effective collision frequency is much smaller than the bounce frequency such that the trapped electrons are allowed to complete the banana orbit at all energies. The assumption might be justified in reactor-grade tokamak plasmas, in which the electron temperature is sufficiently high or the velocity of resonant electrons is much larger than the thermal velocity, so that the influence of collisionality on current drive efficiency can be neglected. For off-axis deposition in the present-day experiments, the effect of high density and low temperature is to reduce the current drive efficiency, but the increasing collisionality reduces the trapping of current-carrying electrons, leading to compensating increases in the current drive efficiency. In this work, we use the adjoint function formulation [4] to examine collisionality effects on the current drive efficiency.
- Research Organization:
- General Atomics, San Diego, CA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC03-99ER54463
- OSTI ID:
- 766825
- Report Number(s):
- GA-A23161; TRN: US0110510
- Resource Relation:
- Conference: 26th European Conference on Controlled Fusion and Plasma Physics, Maastricht (NL), 06/14/1999--06/16/1999; Other Information: PBD: 1 Aug 1999
- Country of Publication:
- United States
- Language:
- English
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