Potato, banana, local, and nonlocal transport

The relationship between potato and banana transport theories is addressed using the solution of the drift kinetic equation. It is shown that they are two limits of a complete theory. The potato theory is the psi-->0 limit an d the banana theory is the psi-->infinity limit. Here, psi is the poloidal Bur function. These local transport theories are valid even in the steep gr adient situations because the real orbit width is usually smaller than the gradient scale length when the appropriate orbit squeezing effects are take n into account. The characteristic feature of a nonlocal theory is also dis cussed. It is shown that the equilibrium distribution in such a theory must be non-Maxwellian and nonexpandable. (C) 2000 American Institute of Physic s. [S1070-664X(00)05112-0].