Speaker
Kurt Flesch
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1030.pdf
RMP reduces effective particle confinement time during RMP application
at MAST
K. Flesch1, H. Frerichs1, J. Harrison2, A. Kirk2, O. Schmitz1, I. Waters1
1
Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI, USA
2
Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxfordshire, UK
The application of resonant magnetic perturbations (RMPs) on plasma discharges at
MAST leads, in many cases, to reduced particle confinement of the core plasma, known as
density pump-out. This can be described by the characteristic particle confinement time p
obtained from a global, single reservoir particle balance analysis. During all discharges with
pump-out, the ionization source increased as the RMPs are turned on, but the confinement
time decreased substantially enough to cause an overall density decrease. In L-mode plasma,
up to a 15% reduction in p is measured, and in H-mode plasma, a similar level of p reduction
is seen, however, the exact value depends on the RMP mode number and phasing.
The results presented in this paper relate this pump out for the first time for MAST to
the neutral fueling and exhaust fluxes using a single reservoir, global particle balance. This
particle balance was assembled using the plasma density and Dα emission measured by
filter-scopes and a calibrated 1-D camera, as well as local values of S/XB coefficients
determined by edge plasma parameter measurements, to infer the particle flux loss from the
plasma and the incoming neutral recycling flux maintaining the plasma density.
In order to resolve the underlying effects in the neutral fueling and exhaust household
inside the recycling and ionization layer, a multi-reservoir particle balance model [1] was
revived, which includes both molecular and atomic species as well as the plasma and wall
inventory. This model allows for experimental inputs such as fueling from gas puffing and
neutral beam injection and estimates of parameters like the probability of particles adsorbing
on the wall and the efficiency with which ionized particles are confined. Using the previously
determined confinement time p, the model is able to accurately reproduce the time evolution
of the plasma density, vacuum vessel neutral pressure, and Dα emission that would be
measured by the filterscope. The results from this experimental analysis with both particle
balance models are compared to results from numerical analysis with the EMC3-EIRENE
code. Initial results from this comparison supports increased fueling efficiencies and reduced
particle confinement times as a reason for the observed particle pump out.
[1] G.P. Maddison, et al., Plas. Phys. & Contr. Fus. 48 (2006) 71-107
Acknowledgement: This work was funded in part by the U.S. DoE under grant DE-SC0012315.
