1 - Nuclear Sciences and Applications - IAEA

184 ZARNSTORFT et al.
Abstract
TRANSPORT IN TFTR SUPERSHOTS.
Thermal transport is analyzed for TFTR supershot plasmas using measured ion and electron
temperature profiles. Outside the convection-dominated core, the ion thermal diffusivity is found to be
much larger than neoclassical predictions. The ion and electron thermal diffusivities do not vary significantly
with IP and Pinj. The calculated Xj is found to depend strongly (and xe weakly) on the peaking
of the density profile. Xi is significantly larger in plasmas having L-mode confinement than in
supershots.
1. Introduction
Local transport has been analyzed in auxiliary-heated TFTR plasmas
with emphasis on understanding the enhanced confinement observed in the
"supershot" regime [1]. This regime is interesting because of its strongly
peaked density profiles, iwhich result from the primary particle source being
in the plasma core, rather than at the plasma edge, as in the L- or
H-mode. During the past year the supershot regime has been extended to
lp = 1.6 MA, and up to 30.5 MW [2] of near-balanced co- and countertangential
deuterium neutral beam injection into deuterium plasmas with
carefully conditioned pumping carbon limiters [3]. Typical plasma parameters
are Te(0) = 7-8 keV, ne(0) = 5-9x 10 19 m" 3 , T;(0) = 25-32 keV,
and very high fusion reactivity, reaching QDD up to 1.55 x 10~ 3 . The density
profiles are very peaked, with ne(0)/ < ne > up to 3, where < ne > is
the volume average density. The global confinement time T^f, as determined
by magnetic measurements, is up to three times greater than that predicted
by Goldston L-mode scaling [4]. The global confinement time is found to be
roughly independent of Ip and Pmj [2].
This paper will describe the transport processes in supershot plasmas
and the scaling of the inferred transport coefficients, followed by a comparison
between the transport in supershots and plasmas having approximately
L-mode confinement. All plasmas discussed here have balanced coand
counter-tangential injection. Transport in plasmas with unbalanced injection
is discussed by Scott et al. [5].
2. Supershot Transport Analysis
Figure 1 shows the density and temperature profiles for a high-confinement
supershot. This Ip = 1.4 MA plasma was heated by 22 MW of neutral beam
power, and had ne = 3.9 X 10 19 m~ 3 and Zeg = 2.4. The global energy confinement
time was 0.18 sec determined from magnetic measurements while
L-mode scaling [4] would predict 0.056 sec.