1 - Nuclear Sciences and Applications - IAEA

640 ALLADIO et al.
4
T (keV)
3
2 -
1 -
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a
I
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D
n
1
B
D
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1
a
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OH
RF
-4 0 8 12 16 20
r(cm)
FIG. 2. Electron temperature profile before and during RF phase. ne = 3.5 X 10 13 cm 3 .
(ii) The loop voltage decreases from 1.7 to 1.3 V, as a consequence of the
application of RF power. This, together with a small increase in the
plasma current, causes a reduction in the Ohmic power input of about
80 kW. So, during the RF phase, the total power input exceeds the input
during the Ohmic phase by only 120 kW.
(iii) In spite of the experimental uncertainties (mainly on the electron thermal
content), the plasma energy increase seems to be consistent with the
increase in the total power input if the energy confinement time does not
change. This suggests that the RF power is transferred to the plasma bulk,
a result which is in agreement with the main conclusion of the 2.45 GHz
experiment performed with higher RF power.
More interesting for the purposes of the present experiment is the high density
case.
In Fig. 3, we report the electron temperature profiles before and during the
application of RF power to a plasma with n,. = 10 l4 cm" 3 .
In this case, the electron temperature increases over the whole profile.
The plasma current was 365 kA and the Ohmic power input, in the Ohmic
phase, was 460 kW. The effective ion charge, obtained from the plasma conductance,
is close to unity (Zeff = 1.3). The total energy content of 16.3 kJ gives a confinement
time of 35 ms.
During the RF phase, the Ohmic input remains practically constant because a
slight decrease in the loop voltage is compensated for by an increase in the plasma
current; thus, the total power injected into the plasma is 650 kW while the total thermal
energy is about 20 kJ. From these figures, taking into account that in this case
the experimental uncertainties are lower than in the low density case, we may conclude
that most of RF power is transferred to the plasma.
Indeed, the energy confinement time is now 30 ms, on the assumption that the
entire RF power is absorbed by the plasma.
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