AORSA full wave calculations of helicon waves in DIII-D and ITER

Abstract

Helicon waves have been recently proposed as an off-axis current drive actuator for DIII-D, FNSF, and DEMO tokamaks. Previous ray tracing modeling using GENRAY predicts strong single pass absorption and current drive in the mid-radius region on DIII-D in high beta tokamak discharges. The full wave code AORSA, which is valid to all order of Larmor radius and can resolve arbitrary ion cyclotron harmonics, has been used to validate the ray tracing technique. If the scrape-off-layer (SOL) is ignored in the modeling, AORSA agrees with GENRAY in both the amplitude and location of driven current for DIII-D and ITER cases. These models also show that helicon current drive can possibly be an efficient current drive actuator for ITER. Previous GENRAY analysis did not include the SOL. AORSA has also been used to extend the simulations to include the SOL and to estimate possible power losses of helicon waves in the SOL. AORSA calculations show that another mode can propagate in the SOL and lead to significant (~10%–20%) SOL losses at high SOL densities. Optimizing the SOL density profile can reduce these SOL losses to a few percent.

DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy

“…Vertical top launch of EC power increased the ECCD efficiency by a factor of 2 for offaxis deposition. Calculations indicate that planned high harmonic fast wave (HHFW) injection [70][71][72][73] with a recently installed helicon antenna, and planned unique high field side (HFS) lower hybrid (LH) slow wave injection [70,74] will contribute substantially to the ability to control the current profile in the high-density core plasmas [75] needed to couple to effective radiative divertor solutions in DIII-D.…”

Tests of advanced RF off-axis current drive techniques on DIII-D

“…The goals of these experiments are to verify helicon current drive efficiency that is predicted by ray- tracing [12] and full-wave [17] models, (2) attempt to evaluate the importance of nonlinear effects such as parametric decay instability [18], and scattering of helicon waves from turbulent density fluctuations ('stimulated mode conversion' [19]), in addition to the non-linear effects on coupling discussed earlier. If possible deleterious nonlinear effects are ignored, the expected dimensionless current drive efficiency defined in Eq.…”

Helicon and lower hybrid current drive comparisons in tokamak geometry

“…Investigating helicon (or whistler) waves as a means to drive a parallel current in a tokamak is a less studied area of current drive (Pinsker 2015) than the more common mechanism of lower hybrid waves (Fisch 1978;Karney & Fisch 1979, 1985Fisch & Boozer 1980;Fisch & Karney 1981;Cordey, Edlington & Start 1982;Taguchi 1983;Cohen 1987;Giruzzi 1987;Chiu et al 1989;Ehst & Karney 1991) which is extensively reviewed by Bonoli (2014). Nonetheless, helicon current drive (HCD) remains of considerable interest (Vdovin 2013;Prater et al 2014;Pinsker 2015;Wang et al 2017;Lau et al 2018Lau et al , 2019Pinsker et al 2018) because of its many similarities to lower hybrid current drive (LHCD) and its ability to efficiently access higher density regions (Li et al 2020a,b;Lau et al 2021;Li, Li & Liu 2021;Yin et al 2022). Both HCD and LHCD rely on a Landau resonance and the preferential heating of electrons, although HCD uses a perpendicular component of the applied electric field rather than the parallel component used for LHCD.…”