Speaker
Ryan Sweeney
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1046.pdf
Dependence of the shattered-pellet-mitigated thermal quench radiation
efficiency on the plasma thermal energy in DIII-D with uncertainties
derived from disruption energy flow models
R. Sweeney1, R. Raman2, N. Eidietis3, J. Herfindal4, E. Hollmann5, D. Hu1, M. Lehnen1,
D. Shiraki4, J. A. Snipes1
1
ITER Organization, Rte. de Vinon-sur-Verdon, 13067 St. Paul-Lez-Durance, France
2
University of Washington, Seattle, Washington, USA
3
General Atomics, P.O. Box 85608, San Diego, CA 92186, USA
4
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, USA
5
University of California-San Diego, 9500 Gilman Dr., La Jolla, CA 921093, USA
Experiments were conducted on DIII-D using the shattered pellet injection (SPI) system to
study how the required quantity of neon for full thermal quench (TQ) mitigation changes with
thermal energy. A super H-mode discharge was used and terminated with the SPI as the
thermal energy reached Wth=1.9 MJ. The radiation efficiency (Wrad,th/Wth) as a function of
injected neon quantity for this discharge will be shown and compared with the previously
investigated Wth=0.75 MJ discharge [Shiraki et al., Phys. Plasmas, 2016]. The change in the
required neon quantity for full TQ mitigation will be compared in the high and low energy
cases, and implications for the ITER disruption mitigation strategy will be discussed. To
determine this required neon quantity, the fraction of thermal energy radiated is investigated
using the fast diode arrays and the foil bolometer arrays. The fast diode arrays can temporally
resolve the radiation flash during the TQ, but an estimation of the amount of magnetic energy
dissipated during the TQ is required. The relatively low temporal resolution of the foil
bolometers requires integrating both the radiated thermal and magnetic (Wmag) energies, but
requires modelling the fraction of Wmag dissipated by the vessel and other conductors in close
proximity to the plasma, and requires an estimate of the fraction of Wmag that is not radiated.
For proper energy accounting, a cylindrical 0D model is developed that describes the evolution
of Wmag during the TQ and current spike. The measured current spikes will be compared with
this 0D model, and the implications on the total radiated energy throughout the disruption will
be discussed. Separately, a simple toroidal wire loop model is developed to describe the work
done by the vertical field during the major radial contraction. Implications of the dissipated
vertical field energy on the predicted radiation efficiency will be discussed. This material is
based upon work supported in part by the U.S. Department of Energy under
DE-FC02-04ER54698.
