A systematic study of non-inductive current drive via helicity
injection by global
Alfvén eigenmode (GAE) waves is carried out. For illustration, the
first
radial mode
of the discrete resonant GAE spectrum is considered. The following aspects
are
given special attention: spectral analysis, radial dependence and efficiency
–
all of these as functions of the characteristics of the waves launched
by an external,
concentric antenna (i.e. wave frequency and poloidal and toroidal wavenumbers).
The tokamak plasma is simulated by a current-carrying cylindrical plasma
column
surrounded by a helical sheet current and situated inside a perfectly conducting
shell, with incorporation of equilibrium (simulated) toroidal field, magnetic
shear
and a relatively large poloidal magnetic field component. Within the framework
of low-β MHD model equations and for typical tokamak physical parameters,
the
following basic results are obtained: (1) in the range of poloidal wavenumbers
−3[les ]m[les ]3 and toroidal wavenumbers
−20[les ]n[les ]20, resonant GAE peaks below the Alfvén
continuum are found; (2) the power absorption (P), current drive
(I) and corresponding frequency of the GAE modes depend strongly
on
the sets of (m, n) values considered; (3) the ‘net’
current drive is positive (i.e. flows in the direction of the equilibrium
current
j0z) for m=−1, −2, −3
and −20[les ]n[les ]−1 as well as for
m=+1, +2, +3 and n>10; (4) in the cases
m=−1, −2, −3, the efficiency of current drive,
I/P, increases with [mid ]m[mid ] and
1/[mid ]n[mid ]; (5) the radial localization of the current
drive in each of the cases considered is determined and tabulated.