General Fusion's approach to magnetized target fusion involves compressing a spherical tokamak plasma to achieve fusion conditions. This presentation will detail how COMSOL Multiphysics® software was used in the LM26 fusion demonstration, which has been operating since February 2025. COMSOL® was initially used to simulate magnetomechanical compression of small lithium rings and cylinders. These two-dimensional axisymmetric models integrating nonlinear solid mechanics, magnetic field, and heat transfer moduli were validated using high-speed imaging and laser diagnostics from these experiments. The tested models subsequently played an important role in determining the design of the LM26 compressor and its operating conditions.
The main problem is that the plasma equilibrium characteristics and the lithium liner model parameters need to be adjusted during the compression shot. Although some materials testing was performed on lithium specimens in tension and compression, the range tested was not sufficient to cover all LM26 experimental conditions. To overcome this problem, a Bayesian inference reconstruction process was used to solve the inverse problem. This process began with reconstructing the lithium liner compression sequence using parametric sweeps of COMSOL Multiphysics models that were constrained by experimental structured light reconstruction (SLR) and photon Doppler velocity (PDV) measurements in LM26. This method allowed General Fusion to provide accurate magnetic flux boundary conditions for internal magnetohydrodynamic (MHD) Grad–Shafranov solvers. MHD solvers, in turn, were used to restore plasma equilibrium and determine the plasma density profiles needed to calculate its temperature. This work is critical as General Fusion aims to reach LM26 plasma temperatures of 1 keV, with future plans to reach 10 keV.
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