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Alpha Channeling and Current Drive with Lower Hybrid Waves

Author: Nathaniel J. Fisch
Requested Type: Consider for Invited
Submitted: 2015-01-19 11:30:22

Co-authors: I. E. Ochs, N. Bertelli

Contact Info:
Princeton Plasma Physics Lab
Box 451, Forrestal Campus
Princeton, NJ   08543
USA

Abstract Text:
Lower hybrid current drive [1] may be inhibited by damping on alpha particles [2]. However, in the presence of a strong alpha particle birth gradient, this interaction can produce wave amplification rather than wave damping, a process known as alpha channeling [3]. Other waves, such as the ion Bernstein wave, produce more effective channeling effects, mainly because very large poloidal wavenumbers can be produced [4].

Recently, however, advantages have been found for the LH wave, particularly using high field launch [5]. It turns out that lower hybrid current drive, alpha channeling, and k_parallel upshift are all fundamentally coupled, but in such a way that it could be advantageous to the joint optimization of current drive efficiency and alpha channeling. Moreover, the poloidal wavenumber of the lower hybrid wave can be made large precisely at maximum penetration of the tokamak core, where maximum channeling and current drive can take place. These results are timely in view of the recent proposals to use inside launch of the lower hybrid wave for steady state reactor operation [6], and in fact were stimulated by those interesting proposals.

1. Confining a Tokamak Plasma with RF-Driven Currents, N. J. Fisch, PRL 41, 873 (1978).

2. Interaction of alpha Particles with Intense Lower Hybrid Waves, N. J. Fisch and J-M. Rax, PRL 69, 612 (1992).

3. Effects of Ion-Cyclotron Harmonic Damping on Current Drive in The Lower Hybrid Frequency-Range, K. L. Wong and M. Ono, Nuclear Fusion 24, 615 (1984).

4. Excitation of Large k_theta Ion-Bernstein Waves in Tokamaks, E. J. Valeo and N. J. Fisch, PRL 73, 3536 (1994).

5. Coupling of alpha channeling to k-parallel upshift in lower hybrid current drive, I. E. Ochs, N. Bertelli and N. J. Fisch, arXiv:1409.0053 (2014).

6. ARC: A compact, high-field, fusion nuclear science facility and demonstration power plant with demountable magnets, B.N. Sorbom et al., arXiv:1409.3540v1 (2014).

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