This work is concerned with the investigation of non-ideal
(resistive) MHD effects on
the excitation of Alfvén waves by externally launched
fast-mode waves, in simulated
tokamak plasmas; both continuum range, CR
({ωAlf(r)}min <ω<
{ωAlf(r)}max) and
discrete range, DR, where global Alfvén eigenmodes, GAEs
(ω<{ωAlf(r)}min) exist,
are considered. (Here,
ωAlf(r)≡ωAlf[n(r),
B0(r)] is an eigenfrequency of the shear
Alfvén wave.) For this, a cylindrical current carrying plasma surrounded
by a helical sheet-current antenna and situated inside a perfectly
conducting shell is used.
Toroidicity effects are simulated by adopting for the axial equilibrium
magnetic
field component a suitable radial profile; shear and finite relative
poloidal magnetic
field are properly accounted for. A dielectric tensor appropriate to
the
physical conditions considered in this paper is derived and presented.
When
the resistive wave equation is solved and the current drive by helicity
injection,
IHICD, is calculated,
the following illustrative results are found to hold. For CR, (i) the maximum
power
absorption as well the maximum helicity injection current drive increase
significantly with decreasing resistivity (i.e. with
increasing temperature); (ii) unlike the
power absorption, which is a maximum at a frequency between the lower and
the
upper edge of the CR, the total current drive is a maximum at the lower
edge, and
decreases strongly with increasing frequency; (iii) the behaviour of the
efficiency
closely follows that of the current drive; (iv) the smaller the
resistivity, the smaller
is the radial distance from the axis (x=0) of
the maximum current-drive density.
For DR, (i) the maximum power absorption in the discrete GAE case increases
with decreasing resistivity even more strongly than in the CR case; (ii)
unlike the
CR case, the total helicity-injection current has, for almost all GAEs,
a symmetric
frequency dependence about the line centre; its maximum value as well as
the
efficiency increase strongly with decreasing resistivity; (iii) unlike
the
continuum case,
the efficiency is almost constant over the entire width of the discrete-mode
range;
its value increases strongly with the GAE rank.