Effects of midplane density gradient in the propagation of high-harmonic fast waves considering high temperature anisotropy in the scrape-off layer of NSTX-U

Journal Article · Wed Oct 01 00:00:00 EDT 2025 · Physica Scripta

DOI:https://doi.org/10.1088/1402-4896/ae08fc· OSTI ID:2998619

Rodriguez, Ricardo De Levante ^[1]; Baek, Seung-Gyou ^[1]; Shiraiwa, Syun’ichi ^[2]; Bertelli, Nicola ^[2]; Bonoli, Paul ^[1]

---

1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
2. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

High-Harmonic Fast Wave (HHFW) heating experiments in NSTX have shown that up to 60% of the injected power can be lost in the Scrape-Off Layer (SOL) when the density is above the fast wave cutoff density in front of the antenna, for which the fast wave is able to propagate into the plasma. This work models HHFW propagation in the SOL plasmas of NSTX-U using a 2D divertor SOL profile derived from the pressure assumption and the finite element temperature solution, which accounts for the high anisotropy of heat conduction in a 2D axisymmetric geometry. In this work, the two-dimensional axisymmetric SOL temperature profile is first evaluated by solving the steady-state non-linear heat conduction equation, in which thermal conductivity depends on temperature, using a finite element approach in the Petra-M workbench. A 2D density profile is then obtained from a prescribed density profile at the outer midplane assuming pressure is uniform along a flux tube in the SOL. This approach results in density and temperature profiles in which the strong asymmetric nature of heat conduction between the parallel and perpendicular background magnetic field is successfully captured. Furthermore, this work focuses on investigating the effect of the SOL plasma density profile on parasitic HHFW propagation in the SOL. The simulation results show that the radial gradient of the density profile affects the wavefield propagation in the SOL. As the density profile broadens, the wavefield intensity and its poloidal extent are reduced in the SOL, and the core coupling increases. Similarly, as shown by collisional power deposition, a proxy for power absorption, the fraction of power deposited in the SOL decreases with a broadening profile.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: National Energy Research Scientific Computing Center (NERSC); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC02-05CH11231; AC02-09CH11466; SC0021120
• OSTI ID: 2998619
• Journal Information: Physica Scripta, Journal Name: Physica Scripta Journal Issue: 10 Vol. 100; ISSN 1402-4896; ISSN 0031-8949
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

HHFW
ICRF
MFEM Simulation
NSTX-U
Petra-M
Plasma Waves