TY - JOUR
T1 - Influence of collision frequency on neoclassical polarization current
AU - Imada, K.
AU - Wilson, H. R.
PY - 2009
Y1 - 2009
N2 - A kinetic theory for the evolution of magnetic islands is considered in a tokamak plasma, in both the low (νi ≪ εω) and high (νi ≫ εω) collision frequency limits (νi is the ion collision frequency, ε is the inverse aspect ratio and ω is the island propagation frequency in the E × B rest frame). The calculation of the bootstrap current perturbation in the presence of a magnetic island is reviewed, and is confirmed to be independent of ω and the collision frequency regime. The neoclassical polarization current perturbation is calculated in the two collision frequency limits (within the banana regime). The result in the collisional limit is in agreement with a fluid theory. The effect of collisions in the 'dissipation layer' at the trapped/passing boundary is also considered, for νi ≪ εω. It is found that the dissipation layer provides an additional contribution to the neoclassical polarization current perturbation. Consequently, if the polarization current is stabilizing, it provides a critical island width for instability, which is found to scale as [1+r√ νi/εω]1/2 , where r is a weak logarithmic function of √ νi/εω.
AB - A kinetic theory for the evolution of magnetic islands is considered in a tokamak plasma, in both the low (νi ≪ εω) and high (νi ≫ εω) collision frequency limits (νi is the ion collision frequency, ε is the inverse aspect ratio and ω is the island propagation frequency in the E × B rest frame). The calculation of the bootstrap current perturbation in the presence of a magnetic island is reviewed, and is confirmed to be independent of ω and the collision frequency regime. The neoclassical polarization current perturbation is calculated in the two collision frequency limits (within the banana regime). The result in the collisional limit is in agreement with a fluid theory. The effect of collisions in the 'dissipation layer' at the trapped/passing boundary is also considered, for νi ≪ εω. It is found that the dissipation layer provides an additional contribution to the neoclassical polarization current perturbation. Consequently, if the polarization current is stabilizing, it provides a critical island width for instability, which is found to scale as [1+r√ νi/εω]1/2 , where r is a weak logarithmic function of √ νi/εω.
UR - http://www.scopus.com/inward/record.url?scp=70350597579&partnerID=8YFLogxK
U2 - 10.1088/0741-3335/51/10/105010
DO - 10.1088/0741-3335/51/10/105010
M3 - Article
AN - SCOPUS:70350597579
SN - 0741-3335
VL - 51
JO - Plasma Physics and Controlled Fusion
JF - Plasma Physics and Controlled Fusion
IS - 10
M1 - 105010
ER -