1 - Nuclear Sciences and Applications - IAEA

204 BURRELL et al.
> CO
t
Q
<
DC
X =
H TARGET •
0.0 0.2 0.4 0.6 0.8 1.0
p/a
FIG. 8. Thermal diffusivity versus flux coordinate for H-mode, L-mode and Ohmic (target) plasmas.
shown. Error bands are determined by propagating random and possible
systematic errors through the analysis in the manner described by Groebner
[32]. Within these errors, the thermal diffusivity in H-mode is about
a factor of three lower than that in L—mode over the outer half of the
plasma; however, the diffusivities are quite similar in the central region of
the discharge. The H-mode diffusivity is quite comparable to the Ohmic
plasma diffusivities over most of the plasma. Accordingly, it is clear that
the confinement improvement in H-mode occurs over a significant portion
of the plasma, not just at the plasma edge.
The power balance from this analysis shows the overwhelmingly
dominant energy loss process in these plasmas is heat conduction. Integrated
out to the plasma edge, the radiative losses are only 20% of the
input power and the convection losses are only a few percent.
REFERENCES
[1] WAGNER, F.W., et al., Phys. Rev. Lett. 49 (1982) 1408.
[2] BURRELL, K.H., et al., Phys. Rev. Lett. 59 (1987) 1432.
[3] SUZUKI, N., et al., in Controlled Fusion and Plasma Physics (Proc. 14th Eur. Conf. Madrid,
1987), Vol. 11D, European Physical Society (1987) 217.
[4] OHYABU, N., JAHNS, G.L., STAMBAUGH, R.D., STRAIT, E.J., Phys. Rev. Lett. 58
(1987) 120.
[5] LOHR, J.M., et al., Phys. Rev. Lett. 60 (1988) 2630.
[6] HINTON, F.L., STAEBLER, G.M., Paper IAEA-CN-50/D-IV-15, these Proceedings, Vol. 2.