Speaker
Edward Thomas Hinson
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1029.pdf
Enhancement of Helium Exhaust During Application of
Resonant Magnetic Perturbation Fields at DIII-D*
E. Hinson1, H. Frerichs1, O. Schmitz1, G. McKee1, Z. Yan1, C. Collins2, C. Paz-Soldan2,
M. Wade2, T.E. Evans2, T. Abrams2, D. Thomas2, B. C. Lyons2, B. Grierson3, I. Bykov4,
R.A. Moyer4, E.A. Unterberg5
1 University of Wisconsin-Madison, Madison, United States
2 General Atomics, San Diego, United States
3 Princeton Plasma Physics Laboratory, Princeton, United States
4 University of California at San Diego, San Diego, United States
5 Oak Ridge National Laboratory, Oak Ridge, United States
Resonant magnetic perturbation (RMP) fields used to suppress Edge Localized Modes
(ELMs) in high confinement (H-mode) tokamak plasmas are found to lead to strong
enhancement of global helium exhaust, as measured by the effective He particle
confinement time τp*He, in recent experiments at DIII-D. In ELM-suppressed H-modes,
τp*He was reduced by 40% compared to unsuppressed discharges, and τp*He/τE where τE is
energy confinement time, was reduced by between 10-20%. These first-time findings are
important for ITER, where application of RMP fields is planned for ELM control, as they
suggest RMP fields can replace the impurity exhaust produced by the ELM events.
Improved helium exhaust was obtained for ITER-shaped plasmas at DIII-D using argon
frosted divertor cryo-panels for active pumping of He injected in short test pulses into a
deuterium plasma. A multiple-reservoir particle balance model was used for analysis of the
experimental data. In both the plasma edge and core reservoirs, midplane He density
measurements from charge-exchange spectroscopy show reduced magnitudes and faster
decay times during ELM suppression, suggesting faster outward transport and/or reduced
He back-fueling after recycling. Increased He-I and He-II emission in the Scrape-off Layer
(SOL) and increased neutral He pressure in the pumping plenum show that more He is
retained in the SOL and neutral reservoirs, which is important for effective removal of He
from the entire plasma. EMC3-EIRENE fluid plasma edge and kinetic neutral transport
modeling of comparable scenarios, in addition to the experimental measurements, suggests
two mechanisms behind the beneficial enhancement of helium exhaust. First, reduced
parallel temperature gradients due to magnetic field stochastization in the vicinity of the
separatrix can increase the friction force acting on impurities relative to the thermal force,
which enhances outward transport in the region of the perturbed magnetic field. Second, the
evolution of helical lobes, which connect the separatrix region to the divertor via a helical
magnetic footprint, yields increased He neutral pressure due to increased divertor plasma
plugging. Both effects are being analyzed with dedicated EMC3-EIRENE modeling
including plasma response from M3D-C1 extended MHD code, which defines the level of
magnetic field stochastization at the separatrix.
*Work supported by US DOE DE-FC02-04ER54698, DE-SC0013911, DE-FG02-07ER54917, DE-
AC52-07NA27344, DE-AC05-06OR23100, DE-AC05-00OR22725, DE-AC04-94AL85000, DE-
AC02-09CH11466
