Speaker
John Christopher Wright
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.115.pdf
Waveguide to Core: A New Approach to RF Modelling*.
J. C. Wright1, S. Shiraiwa1, J. Myra2
1
Plasma Science and Fusion, Massachusetts Institute of Technology, Cambridge, MA, USA
2
Lodestar Research Corporation, Boulder, CO, USA
Modelling of coupling, propagation and absorption of RF
waves in plasmas is known to be a complex task and is
typically modelled in separate stages. We present a novel
technique for the calculation of RF waves in toroidal
geometry that enables, for the first time, the simultaneous
incorporation of antenna geometry, plasma facing
components (PFCs), the scrape off-layer (SOL), and core
Figure 1: Rotated C-Mod Antenna
propagation [Shiraiwa, Wright et al, Nucl. Fusion 57
086048 (2017)]. Calculations with this technique naturally capture wave propagation in the
SOL, reflection from the core plasma or walls, and wave interactions with non-conforming
PFCs as shown in Fig. 1. The technique combines the finite element approach for the SOL
and antenna structure and the spectral method for the hot core using a domain decomposition
technique with impedance matching to construct the full solution. Using open source
software on leadership class computer permits solutions in excess of 30 Million degrees of
freedom enabling the resolution of the slow and fast waves together in 3D geometries.
Applications of this model to ICRF minority heating in strong and weak absorption regimes
in Alcator C-Mod predict heating loss of 10% and 50% respectively, in the SOL due to
collisional processes, in-line with experimental measurements of heating efficiency. Sheaths
are an additional loss mechanism in the SOL that can cause localized sputtering. To address
the effect of RF rectified sheaths on PFCs we use a post-processing technique that uses the
finite element method SOL solution [Myra and Kohno, EPJ Web of Conferences 157 03037
(2017)] to model sheath rectification. To resolve short wavelength structures at the lower
hybrid resonance in front of ICRF antennas, the edge SOL plasma model keeps finite Larmor
radius effects to resolve the slow wave to ion Bernstein wave mode conversion that occurs at
this layer. Simulations applying these models to the LAPD long cylindrical device, JET, and
the Alcator C-Mod field aligned antenna in three dimensions will be presented.
*Work supported by US DoE Contracts DE-FC02-01ER54648 and DE-FC02-99ER54512.
