1 - Nuclear Sciences and Applications - IAEA

'Z 1
IAEA-CN-50/A-V-2-2 285
o
o°
o .
••I*
SHOT IO5IO7
• DENSITY
OSOFT X-RAY
200 400 600
minor radius (cm )
FIG. 4. The time-to-peak, p tp, dependence on minor radius squared for heat and density pulses;
p p
13
BT = 2 T, Ip = 200 kA and ne0 = 3 x 10 13 -3
,
A comparison of the time-to-peak, tp(r), characteristics of the heat and particle
pulses is made in Fig. 4. The data are quite similar, suggesting that the heat and particle
transport occur at essentially the same rate. Employing a previously described
diffusive mode [1] to the density perturbation provides an estimate of the average
1.5 m 2 -s"' (= r 2 /^^,) in the confinement zone. The standard diffusive
model for heat transport [3] indicates x" p — 2 m 2 -s"' (= i 2 /^). The validity of this
model is, however, suspect since it assumes the density perturbation to be negligible,
thereby contradicting experimental results on TEXT. These estimated values for the
transport coefficients are both larger, by a factor of two to three, than D^ GF
deduced from modulated gas feed experiments [4] and x PB deduced from steady
state power balance calculations [5]. The modulated gas feed results are thought to
be more indicative of the steady state because of their slow time scale
(fmod > rE) and edge fuelling characteristics. The inverse slopes r 2 /^ for density and
temperature perturbations are generally comparable for all discharges except those
at the high density or low-q limit for TEXT. In these extreme cases, heat and density
pulse propagation are no longer thought to be accurately described by a diffusive-type
model.
To further investigate the relationship between heat and particle transport after
the sawtooth crash, the scaling behaviour of rVtp for density and temperature
perturbations is examined. The effects of qa and iieo scaling are most clearly
obtained by performing a regression analysis yielding (r 2 /tp) DP