Mj. Alava et al., ON THE ORIGIN OF PARASITIC MODES IN NUMERICAL MODELING OF WAVE-PROPAGATION IN PLASMAS, Journal of computational physics, 114(1), 1994, pp. 85-99
The mode mixing encountered in solving the boundary value problem aris
ing in studies of Wave propagation in hot one-dimensional plasmas is i
nvestigated. The wave differential equations, second order in ion Larm
or radius, are shown to contain close to the ion cyclotron resonance a
n unwanted coupling mechanism, closely related to mode conversion driv
en by the equilibrium gradients. Consequently, the solution mixes with
parasitic modes which carry power out of the resonance zone. In the c
ase of strong coupling, this may lead to a generation of excess energy
flux for complex valued coefficients of the wave equations. The impor
tance and effects of this phenomenon are demonstrated in the special c
ass of simulations of minority ion cyclotron heating in tokamaks. It i
s shown that the mode mixing can be avoided by adjusting the elements
of the coefficient matrix of the wave equations, which makes the secon
d-order system amenable to the problems with high minority concentrati
on which is important for studies of fusion physiCS. (C) 1994 Academic
Press, Inc.