Speaker
Matthias Knolker
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.108.pdf
Test of the Eich model for ELM energy densities in DIII-D
M. Knolker1, A. Bortolon2, T. Evans1, A.W. Leonard1, R. Nazikian2, H. Zohm3
1
General Atomics, San Diego, USA
2
PPPL, Princeton, USA
3
IPP, Munich, Germany
A non-dimensional collisionality scan conducted on DIII-D confirms the model for ELM
energy densities recently put forward by Eich [1], but also reveals key effects that may
explain the large scatter typically observed about the scaling. The values of the peak parallel
ELM energy density 𝜀∥ are found to be within 0.5 - 2 x the prediction of the Eich model,
where 𝜀∥ is the maximum of the time-integrated heat flux during ELMs mapped onto the
divertor. The experiment did not reveal an explicit pedestal-pressure dependence of 𝜀∥ as
proposed in the model. The ratio of heating power to the power required to overcome the L-
H-threshold is identified as a parameter determining the accuracy of the model, with
discharges marginally above the threshold
exceeding the prediction by up to a factor of
two and showing the largest scatter in the
database. Operation close to the L-H-
threshold comes with low ELM frequency
and large ELM heat loads. In general, the
divertor peak heat flux is found to be slightly
higher on the inner than on the outer divertor
target. Using linear stability calculations,
ELM energy densities are shown to be Figure 1 Inverse proportionality between linear mode
number with the highest growth rate and peak parallel
inversely proportional to the most unstable
ELM energy density for type-I ELMy plasmas
linear mode number 𝑛𝑚𝑎𝑥 before the ELM
crash (figure 1). Low n peeling-ballooning modes come with large ELM sizes, especially if
close to the L-H-threshold, the ITER operational space. Hence, our studies encourage further
machine comparisons regarding low heating scenarios and influence of mode numbers on
ELM energy densities.
1
This material is based upon work supported by the U.S. Department of Energy under Award Number(s) DE-
AC05-00OR22725, DE-AC02-09CH11466, and DE-FC02-04ER54698.
[1] T. Eich et al., Nuclear Materials and Energy 12 (2017) 84–90
