Abstract Details
Abstracts
Author: Ben Zhu
Requested Type: Consider for Invited
Submitted: 2025-02-21 12:37:38
Co-authors: B.Dudson, X.Z.Tang
Contact Info:
Lawrence Livermore National Laboratory
7000 East Avenue, L-440
Livermore, CA 94568
USA
Abstract Text:
We report the discovery of bifurcated solutions in both flux-driven global turbulence simulations and gradient-driven local turbulence simulations. Bifurcation and hysteresis in magnetized plasmas have been observed experimentally on multiple occasions, such as the L-H transition discovered in 1982. However, theoretical and numerical studies have lagged behind due to its inherent multi-scale, multi-physics nature, which requires disentangling turbulence, background profiles, and flows across disparate spatiotemporal scales.
Recent simulations using GDB, a flux-driven global edge turbulence model, confirm bifurcated quasi-stationary solutions. Under the same particle fueling and energy injection, both L-mode-like and H-mode-like edge plasma states can be attained, depending on the initial plasma conditions. These bifurcated states are closely linked to the spontaneously generated ExB flow (or edge transport barriers) near the last closed flux surface. Although difficult to attain, once generated, this flow mediates profile relaxation even when the injected power is reduced. This finding highlights the importance of self-organized structures and the critical role of edge dynamics in shaping global plasma confinement.
In addition to the global system, a new bifurcated solution has been identified in the modified Hasegawa-Wakatani model, an extensively studied local turbulence model. Besides the well-known dynamic zonal flow-turbulence interaction solution, a stable, stationary pure zonal solution is uncovered by initializing the simulation with large amplitude fluctuations that are gradually ramped down. This finding reveals the existence of multiple solution manifolds, which can be accessed via alternative paths even within this minimal turbulence model.
These finding are intellectually intriguing and critical for advancing our understanding of fusion plasma dynamics, providing insights that could inform the design and optimization of future fusion devices.
Characterization: 2.0
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