Speaker
Description
We tackle a critical challenge in simulating $MeV$-range fusion products, such as $\alpha$-particles and auxiliary heating beam ions: accurately modeling their relatively long slowing down in the presence of Alfvén eigenmode (AE) instabilities, including toroidicity-induced Alfvén eigenmodes (TAEs) and reversed shear Alfvén eigenmodes (RSAEs). Fusion reactors like ITER are expected to rely on the confinement of high-energy fusion products to compensate for thermal plasma energy losses. The long simulation challenge arises primarily from the radial transport of fast ion due to low-frequency AE instabilities [1].
We are utilizing the recently developed resonance-broadened quasi-linear code RBQ [2], based on a revised quasi-linear theory [3]. Our results show that AE instabilities can affect both neutral beam ions and alpha particles, though the resulting fast ion transport is expected to be small under the assumption of classical particle slowing down [1].
Our investigation explores the long-term dynamics of energetic particle (EP) relaxation using a variety of tools: a comprehensive linear stability study of the sub-cyclotron Alfvénic spectrum, computed with ideal MHD code NOVA; drift-kinetic NOVA-C code to assess wave-particle interactions and AE growth/damping rates; and predictive RBQ quasi-linear modeling, coupled with the global particle code NUBEAM [4]. As a part of TRANSP tokamak plasma simulations, NUBEAM is capable of selfconsistent long-time simulations and reveals significant depletion of EP population near the plasma center, with the timescale comparable to EP energy slowing down time [1]. The long-term simulations incorporate the temporal evolution of EP beta, $\beta_{f}\left(t\right)$, which is used for the renormalization of AE-driven EP diffusion coefficients obtained by RBQ at time $t_{0}$: \begin{equation} D_{xyf}\left(\Gamma:t\right)=D_{xyf0}\left(\Gamma:t_{0}\right)\left(\beta_{f}/\beta_{f0}\right)^{4/3},\end{equation}where the exponential dependence is inferred from theoretical predictions [5] assuming that the AE growth rate is proportional fast particle pressure, $\gamma_{LAE}\sim\beta_{f}$. One potential challenge for ITER operations is the effect of Alfvénic modes on the current drive, which could undermine the self-sustained steady-state plasma scenario.
$^{\flat}$This work is supported by US DOE contract no. DE-AC02-09CH11466.
References
[1] N. N. Gorelenkov, V. N. Duarte, M. V. Gorelenkova, Z. Lin, and S. D. Pinches, Nucl. Fusion 64, 076061 (2024).
[2] N. N. Gorelenkov and V. N. Duarte, Phys. Lett. A 386, 126944 (2021).
[3] V. N. Duarte, J. B. Lestz, N. N. Gorelenkov, and R. B. White, Phys. Rev. Lett. 130, 105101 (2023).
[4] A. Pankin, D. McCune, R. Andre, G. Bateman, and A. Kritz, Comp. Phys. Communications 159, 157 (2004).
[5] H. L. Berk and B. N. Breizman, Physics of Fluids B: Plasma Physics 2, 2246 (1990).
| Presentation type | Oral |
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