Anisotropy and tail formation in ICRF-heated tokamak plasmas

Abstract

A local, two-dimensional (in velocity space), time-dependent, quasi-linear Ion Cyclotron Range of Frequencies (ICRF) Fokker-Planck model is used to study heating in PLT and NUWMAK reactor plasmas. It is found that PLT ICRF experimental results, including tail formation, are well modelled when charge-exchange, radial and radiation losses and Ohmic heating are incorporated. For the NUWMAK reactor parameters, the lower-radiofrequency power per resonant particle and high density provide an isotropic Maxwellian plasma describable by fluid models.

Analytical treatment of the distortion of velocity distributions in the presence of ICRH

“…The parallel phase velocity of the RF wave can be inferred from Ref. [7] (k,,^ 0.1 cm, i m(co/k ll ) 2 ^ 3.6 MeV > thermal ion energies) which justifies our neglect of RF-induced parallel velocity diffusion. Furthermore, with these parameters the influence of the tail on <P> may be neglected.…”

“…In the case of second-harmonic heating (n = 2) and approximating J 2 (x) = x 2 /4, we obtain F 2 0 (v) = Ts v 2 and the following asymptotic expressions for A(v) and B(v) can be derived: An explicit expression for A(v), as given by Eq. (7) in the case of fundamental heating, has been obtained in Ref. [6], using elegant approximations for the collision coefficients oc and j3 and assuming JQ (x) = 1.…”

“…For second-harmonic ICRH the only investigations so far are numerical (see, for instance, Ref. [7]). Thus, ana-lytical information about the distortion of the distribution function in the presence of ICRH is incomplete in the case of fundamental heating and lacking in the case of second-harmonic heating.…”

Fokker-Planck calculations for JET ICRF heating scenarios

“…We add the quasi-linear ICRF heating terms as well as energy lifetimes to obtain time-dependent solutions which simulate tokamak devices. The RF quasi-linear diffusion terms have been derived [9,12,13] and can be expressed in our current co-ordinate system as…”

“…Blackfield and Scharer [13] have presented a formulation of the ICRF Fokker-Planck equation and applied it for the cases of PLT experimental results and a full-scale high-density (n e = 2 X 10 14 cm" 3 ) reactor scenario. To model radial conduction and convection losses, finite energy (rg) confinement times can be introduced for different species.…”