Complete Stabilization of Neoclassical Tearing Modes with Lower Hybrid Current Drive on COMPASS-D

Abstract

Lower hybrid current drive (LHCD) with modest powers ( approximately 10% of the total power input) has been used for the first time to completely stabilize performance limiting neoclassical tearing modes in many COMPASS-D tokamak discharges. The stabilizing effect in these experiments is consistent with a reduction in the free energy available in the current profile to drive tearing modes (i.e., the stability index, delta(')) resulting from favorable current gradients (from the LHCD driven current) around the rational surface.

Control of neoclassical tearing modes

“…At COMPASS-D successful stabilization of NTMs with Lower Hybrid Current Drive (LHCD) could be achieved [47,48]. In these experiments it is reported, that the main effect for the stabilization of a (2/1)-NTM comes from the variation of the current gradient at the resonant surface, i.e.…”

“…In COMPASS-D a complete stabilization of a (2/1)-NTM with LHCD has been shown [47,48]. As mentioned above, the main effect for the stabilization of the (2/1)-NTM was done via the current gradient at the resonant surface, i.e.…”

Maximization of the lower hybrid power coupling in the Frascati Tokamak Upgrade via extremum seeking

“…This coupling, similar to the core idea behind a microwave oven, allows to perform plasma heating and to drive current within the plasma at very specific locations. This type of non-inductive current drive allows to achieve several tasks, in particular proper shaping of the spatial distribution of current for the advanced or steady state scenarios and stabilization of magneto-hydrodynamic (MHD) activity-see, e.g., Crisanti et al (2002), Fujita et al (2001), Litaudon and Tope Supra Equipe (1996) and Warrick et al (2000).…”

Physics basis and simulation of burning plasma physics for the fusion ignition research experiment (FIRE)

“…The precise condition for these modes to become unstable in the burning plasma regime is uncertain, and so the FIRE design has chosen to operate at low βN. Initial simulations of stabilization of the (3,2) island with lower hybrid current drive (LHCD) for FIRE appear promising, and both experimental [12] and theoretical [13] evidence indicate this should be possible by locally altering the current profile to make ∆' more negative. LHCD is considered an upgrade for FIRE, and is why a low operating βN is used.…”