1 - Nuclear Sciences and Applications - IAEA

704 ASKINASI et al.
TABLE I. LOCATION OF RESONANCE ABSORPTION REGIONS
m
Z
Bres(T)
rres(m)
N +6
14
6
0.608
0.08
O +7
16
7
0.594
0.067
N +5
14
5
0.729
0.157
o+a
16
6
0.692
0.136
N-"
14
4
0.911
0.235
O +5
16
5
0.83
0.205
became flat in the central region of the plasma column (up to r « 10 cm). The location
of the maximal increase in electron temperature was close to the mode conversion
zone.
It should be noted that in earlier experiments on the TUMAN-3 tokamak [2]
electron heating was recorded (ATe = 250 eV, PRF = 150 kW) at 77 « 10%, when
the conversion mode zone was located near to the plasma axis (Bo = 0.6 T, n = 1.8
x 10 19 m" 3 ). Ion and electron heating in the wave conversion regime should be
assumed to be due to propagation and absorption of Bernstein waves.
It is well known that the FMS wave excited from the low field side of the torus
is coupled to the Bernstein wave which penetrates into the high field region. In a
hydrogen-deuterium plasma, the Bernstein wave is absorbed by the electrons. The
location of the conversion zone depends on the ratio of hydrogen to deuterium in the
plasma and shifts towards higher magnetic fields with increasing amount of hydrogen.
In some conditions, the presence of heavier ions with m/Z 5: 2 could play an
important role in Bernstein wave absorption. This effect was predicted in Refs [3, 4]
and checked in some special experiments, where a small addition of vanadium [5] or
neon [6] was studied. For these ions, the second cyclotron harmonic zone was close
to the mode conversion zone, but coming from the high magnetic field side. The
injection of a small amount of heavy ions led to an increase in the ion heating efficiency.
In plasmas of moderate electron temperatures (