Abstract
Neoclassical tearing mode (NTM) can degrade plasma confinement or even cause disruptions in existing tokamaks. Stabilization of the NTMs by radio frequency (rf) current is investigated by the modified Rutherford equation (MRE) in this paper. In a range of parameters, the required rf current for mode stabilization is obtained, which is linearly proportional to the bootstrap current density for both modulated current drive (MCD) and non-modulated current drive (NMCD), linearly (quadratically) to the radial width of the rf current for MCD (NMCD), and quadratically to the radial deviation of the rf current from the rational surface for both MCD and NMCD.
Highlights
The neoclassical tearing mode (NTM) is expected to form a magnetic island structure which locally flattens the plasma pressure, losing the bootstrap current [1] [2] [3] [4]
Stabilization of the m / n = 3 / 2 Neoclassical tearing mode (NTM) by radio frequency current is investigated by the modified Rutherford equation (MRE) in this paper
In a range of parameters, the required rf current for mode stabilization is obtained, which is linearly proportional to the bootstrap current density for both modulated current drive (MCD) and non-modulated current drive (NMCD), linearly to the radial width of the rf current for MCD (NMCD), and quadratically to the radial deviation of the rf current from the rational surface for both MCD and NMCD
Summary
The neoclassical tearing mode (NTM) is expected to form a magnetic island structure which locally flattens the plasma pressure, losing the bootstrap current [1] [2] [3] [4]. Low mode number NTMs, especially the m / n = 3 / 2 (m and n are the poloidal and toroidal mode numbers)and 2/1 modes, are observed to cause the confinement degradation and/or disruptions, limiting the achievable plasma β value well below the predictions of ideal magnetohydrodynamic (MHD) calculations for positive magnetic shear [4]-[12]. The driven current should be in the direction along the equilibrium plasma current, to compensate the missing bootstrap current inside the island [8] [9] [10] [13] [14] [15] [16]. The predictions of the required rf current for mode stabilization are still in question and this is the purpose of this paper
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