ECCD Power Required for NTM Stabilization
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Philadelphia, Pennsylvania, October 30-November 3, 2006
| Abstract |
|
High values of plasma β can cause ideally nested magnetic flux
surfaces to tear and reconnect, leading to the formation of magnetic
islands. The Neoclassical Tearing Mode (NTM) instability drives the
islands to grow to their saturated widths, at which they can persist
stably in the plasma. The bootstrap current density is nearly absent
within each island because of the local flattening of the pressure
profile. One common method of stabilizing NTMs and therefore shrinking
the island widths involves replacing this lost current via Electron
Cyclotron Current Drive (ECCD). The level of ECCD power required for
the stabilization of the NTM is studied using the ISLAND module [1],
implemented in the BALDUR code, for noncircular axisymmetric plasmas
with multiple islands. In the absence of feedback stabilization, NTM
driven islands are predicted to cover more than 25% of the plasma
minor radius, which severely degrades plasma confinement and fusion
power production in ITER simulations [2]. The current density within
each island is governed by the current peaking factor, which is varied
in simulated ITER tokamak discharges. The dependence of the
stabilizing power level on the misalignment between the ECCD and the
island, as well as on other uncertainties of the system, is part of
the numerical study.
[1] C.N. Nguyen, et al., Phys. Plasmas, 11, 3460 (2004).
[2] F.D. Halpern, et al., Phys. Plasmas, 13, 062511 (2006).