1 - Nuclear Sciences and Applications - IAEA

696 WILSON et al.
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Time (s)
FIG. 4. Neutron emission rate for 7.5 MW of neutral beam injection from 3.5 to 4.5 s (bottom curve)
and with the addition of 2 MW ICRF from 4.0 to 4.5 s flop curve).
4. ICRF plus Neutral Beam Heating
ICRF heating has been combined with deuterium neutral beam heating
in a deuterium target plasma at Bt= 3.3 T. 2.0 MW of rf power (out-of-phase
excitation) has been combined with up to 7.5 MW of neutral beams. For the
case of co- only neutral beams (Fig. 4), an increase in neutron emission of -25%
is observed . The central electron temperature is seen to rise by 1.5 keV. For a
case of 5 MW balanced injection the increase in neutron emission is only
-10-15% even though the central electron temperature increase is similar. In
both cases there is a density rise of -20%. SNAP analyses of these discharges
indicate that the production of neutrons via beam-target reactions should rise
(because of both an increase in Te and nA) and the beam-beam contribution
should fall (due to the increased density). In the co- only case SNAP predicts a
net increase in neutron emission, while in the balanced case SNAP predicts no
increase, in good agreement with the experiment. Adding rf to cases where
counter beams predominate is found to increase the sawtooth oscillation period.
Incremental amounts of rf or beam power have identical effects on the radiated
power from the plasma. Plasma energy confinement for incremental amounts of
ICRF or neutral beam power is found to be similar. The power levels of these
experiments do not extend into the so-called "supershot 1 " regime where,
because of higher plasma density, beam-target neutrons predominate and
incremental electron heating is predicted to have a stronger effect. Stabilization
of MHD modes in high 6 supershots by central rf electron heating is yet to be
investigated.
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