A new delta f method for neoclassical transport studies

A new delta f method is presented in detail to solve the drift kinetic equa tion for the simulation study of neoclassical transport. It is demonstrated that valid results essentially rely on the correct evaluation of the marke r density g in the weight calculation. A new weighting scheme is developed without assuming g in the weight equation for advancing particle weights, u nlike previous schemes. This scheme employs an additional weight function t o directly solve g from its kinetic equation based on the delta f method it self. Therefore, the severe constraint that the real marker distribution mu st be consistent with the initially assumed g is relaxed. An improved like- particle collision scheme is also presented. By compensating for momentum, energy and particle losses, the conservations of all three quantities are g reatly improved during collisions. With the improvement in both the like-pa rticle collision scheme and the weighting scheme, the delta f simulation sh ows a significantly improved performance. The new delta f method is applied to the study of ion neoclassical transports due to self-collisions, taking the effect of finite orbit width into account. The ion thermal transport n ear the magnetic axis is shown to be greatly reduced from its conventional neoclassical level, like that of previous delta f simulations. On the other hand, the direct particle loss from the confinement region may strongly in crease the ion thermal transport near the edge. It is found that the ion pa rallel how near the axis is also largely reduced due to non-standard orbit topology.