Abstract
The generalized Spitzer function, which determines the current drive efficiency in toka- maks and stellarators is modelled for finite plasma collisionality with help of the drift kinetic equation solver NEO-2 [1]. The effect of finite collisionality on the global ECCD efficiency in a tokamak is studied using results of the code NEO-2 as input to the ray tracing code TRAVIS [2]. As it is known [3], specific features of the generalized Spitzer function, which are absent in asymptotic (collisionless or highly collisional) regimes result in current drive from a symmetric microwave spectrum with respect to parallel wave numbers. Due to this effect the direction of the current may become independent of the microwave beam launch angle in advanced ECCD scenarii (O2 and X3) where due to relatively low optical depth a significant amount of power is absorbed by trapped particles.
Highlights
The generalized Spitzer function is an important part of current drive calculations within the adjoint approach [4] where it plays the role of current drive efciency in phase space
The dimension of the kinetic equation does not exceed two because the generalized Spitzer function has a parametric dependence on spatial coordinates
Specic features of the global ECCD eciency resulting from nite plasma collisionality are studied here with help of the ray tracing code TRAVIS [2] using the Spitzer function pre-computed by the code NEO-2
Summary
[4]), the ux surface averaged parallel current density is expressed through the adgjoint generalized Spitzer function (current drive efciency) as follows, j b = eb d3p v f = e lc d3p g QRF , (3). The adjoint function in (3) is expressed g through the generalized Spitzer function as follows, g(v ) = −g(−v ), where g(v ) is the solution to the conductivity problem, v h · ∇fM g − LCLfM g b v lc fM. Within geometrical optics used for calculation of ECRH/ECCD, the quasilinear ux density is described in a local approximation. As follows from (5), gthe behavior of the derivative of over perpendicular momentum at the resonance curve is of main importance for ECCD
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