Speaker
Description
See the full abstract here:
http://ocs.ciemat.es/EPS2019ABS/pdf/P1.1080.pdf
High field side lower hybrid current drive (HFS LHCD) has potential to provide efficient off-axis current drive consistent with advanced tokamak (AT) scenarios via improved wave accessibility and penetration.[1] Due to the quiescent HFS scrape off layer, HFS LHCD has potentially dramatically reduced plasma material interaction (PMI) issues and improved coupling.[1] DIII-D AT discharges provide an opportunity to validate HFS RF wave physics and LHCD physics models and to demonstrate PMI and coupling challenges are mitigated.
In DIII-D AT discharges, HFS launch below mid-plane allows LH waves to penetrate and single pass damp in region rho~0.6-0.8 with driven current up to 140 kA/MW coupled sufficient for current profile control. In addition, an optimized discharge based on QH-mode has been identified where up to 250 kA/MW coupled is predicted.
To accommodate a HFS coupler in DIII-D, the center post tile thickness is planned to be increased by 2.5 cm while keeping the divertor floor height unmodified. Within this physical envelope, a compact coupler where the expected power density is ~32 MW/m^2 has been designed using a cold plasma model load in COMSOL. The coupler distributes power poloidally utilizing a traveling wave, 4-way splitter and a six way multi-junction to split and set the wave spectrum.[2] For the coupler and in-vessel waveguide, copper cannot be utilized as structural material due to the 380°C machine bake (anneals copper) and disruption loads. The primary material options include copper plated Inconel, copper plated stainless and GRCop-84(Cu-8%Cr-4%Nb)[3]. To facilitate assembly, an RF/vacuum flange has been have designed and tested. The latest simulations, design and system status will be presented.
Work supported by the U.S. DoE, Office of Science, Office of Fusion Energy Sciences, using User Facility DIII-D, DE-FC02-04ER54698, and by Scientific Discovery through Advanced Computing Initiative, DE-FC02-01ER54648.
[1] P.T. Bonoli, et al, "High Field Side Lower Hybrid Wave Launch for Steady State Plasma Sustainment," Nucl. Fusion 58, 126032, (2018)
[2] A. Seltzman et al., "A High Field Side Multijunction Launcher with Aperture Impedance Matching for Lower Hybrid Current Drive in DIII-D Advanced Tokamak Plasmas," Nucl. Fusion (submitted 2018).
[3] D. L. Ellis, "GRCop-84: A High-Temperature Copper Alloy for High-Heat-Flux Applications," Vols. NASA/TM - 2005-213566, 2005.
