ABOUND

Advancing plasma boundary dynamics through simulations and experiments, with a focus on fluctuations (especially small edge-localized modes), edge-scrape-off layer coupling, and divertor exhaust control.

The Advanced Boundary Plasma Dynamics (ABOUND) project seeks to advance the understanding of boundary plasma physics by developing advanced multi-scale, multi-physics simulation capabilities. Through the integration of advanced computation, theory, modeling, and experimentation, our goal is to optimize the management of tokamak plasma exhaust while maintaining high confinement in H-mode. We focus on critical areas including small edge-localized modes (ELMs), pedestal turbulence, pedestal scrape-off layer (SOL) coupling, edge relaxation dynamics, and divertor heat load control, all of which are vital for the operation of ITER and the Fusion Pilot Plant (FPP).

Addressing these challenges involves a comprehensive suite of numerical simulations—spanning fluid models to full gyrokinetics—and necessitates collaborative efforts to achieve breakthroughs in complex boundary plasma dynamics. Success in these pursuits promises significant contributions to fusion science, including enhanced confinement characterization, the SOL width broadening, more accurate heat load predictions, prevention of H-L back transitions, and improved control of detachment while avoiding ELM burn-through in future fusion reactors.

Research

(top) Geometry of a tokamak with a single-null divertor, in this case DIII-D. (bottom) Particles and energy flow across separatrix and down the scrape-off layer (SOL) onto the divertor plate. Alt: A tokamak with a single-null divertor above a diagram showing how particles and energy flow across separatrix and down the scrape-off layer onto the divertor plate.

Our research aims to address critical challenges in achieving magnetic fusion energy (MFE) by focusing on boundary plasma dynamics. To realize practical MFE, researchers must connect a high-temperature core plasma to a cooler boundary plasma region while ensuring efficient fusion in the core and protecting plasma-facing components (PFCs). Maintaining high confinement plasmas and managing exhaust plasma flows to divertor plates are crucial. The project leverages advanced computational tools and simulations to gain a deep understanding of these complex plasma regions, contributing to the development of ITER experiments and FPP designs.

Boundary plasma studies pose unique challenges due to small equilibrium scales, complex geometry, and varying collisionality. To address these complexities, we will employ a suite of numerical simulations, ranging from fluid models to gyrokinetics. Our research focuses on ELM dynamics, stability and turbulence transport, control of divertor-plasma detachment, and management of heat and particle exhaust. Key objectives include:

• Achieving steady-state high-performance operation
• Mitigating large ELMs
• Exploring small ELM regimes

Our ultimate goal is to provide predictive tools for future fusion reactor designs while maintaining stability against plasma variations.

Proposed project and tasks

Our proposed physics research project represents a multifaceted initiative aimed at pushing the boundaries of our comprehension regarding the critical physics challenges encountered in magnetically confined fusion experiments. Comprising intricately interlinked tasks, this project squarely addresses a spectrum of issues encompassing ELMs, pedestal turbulence, divertor-plasma detachment, and the critical aspect of simulation validation.

Overview of the project’s tasks.

Fusion Energy Science (FES) physics

• Task 1: Simulate ELM dynamics, focusing on access conditions and the physics of small ELMs.
• Task 2: Explore pedestal gyrokinetic turbulence and transport in small/no ELM regimes.
• Task 3: Investigate detached divertor-plasma and ELM-detachment interactions.
• Task 4: Verify and validate on DIII-D and other tokamaks.

Advanced Scientific Computing Research (ASCR)

• Task 5: Develop advanced time integration and model coupling algorithms.
• Task 6: Accelerate BOUT++ using GPU technology.
• Task 7: Enhance data analysis, visualization, and code-coupling technology.

LLNL’s project role

LLNL’s expertise in high-performance computing and computational science contributes to pioneering work in devising innovative computational methodologies, addressing the imperative of computational efficiency, and developing robust code-coupling strategies.

LLNL is providing a central role in this endeavor while collaborating with other national laboratories, universities, and industry. LLNL’s involvement extends to harnessing advanced time-integration algorithms, notably those drawn from the SUNDIALS software library, and leveraging multigrid solvers from the HYPRE library, all aimed at augmenting the performance of simulation codes. Central to the project’s objectives is the mitigation of risks associated with code coupling and GPU acceleration, while diligently safeguarding code stability and flexibility in adapting to the evolving landscape of GPU architectures.

This collaboration seamlessly aligns with LLNL’s broader mission to not only advance scientific knowledge but also to bolster national security and contribute to the broader realm of scientific progress.