Reduction of the ion drive and rho*(theta) scaling of the neoclassical tearing mode.

In the theoretical description of the neoclassical tearing mode it is usually assumed that the ion banana width w(b) is much smaller than the island width W. This assumption is questionable at least for the island size at the mode onset. We show that a significant fraction of the (ion) bootstrap current survives inside the island when w(b) is comparable to W. This effect also leads to a linear scaling of beta(onset)theta with the normalized ion poloidal gyroradius rho*(theta), in agreement with the experimental results of ASDEX Upgrade.