Research Interests: Magnetized HEDP

Chris’ research is conducted in the areas of High-Energy-Density-Plasmas (HEDP) and Inertial Confinement Fusion (ICF), focusing on the effect of magnetic fields on plasma dynamics and transport. During his PhD at Imperial College London, Chris played a major role in the development of the 3-D extended-MHD code Gorgon. Specific contributions to the code include anisotropic thermal transport (including Righi-Leduc and numerical super-stepping), extended magnetic transport (by Nernst, cross-gradient-Nernst, etc.), Biermann Battery generation of magnetic fields, and laser ray-tracing. The implementation and testing of these modules enabled research into both the effect of self-generated magnetic fields on ICF implosions, as well as how the application of an external magnetic field can improve fusion performance. Experience has been gained simulating capsules driven directly and indirectly, with research relevant to experiments performed on both the OMEGA and NIF laser facilities.

At Lawrence Livermore National Laboratory, Chris provides expertise in the effect of magnetic fields on transport. In the Capsule Working Group, he has developed theoretical models that demonstrate how magnetic flux generation in an ICF hot-spot depends on wavelength and amplitude of perturbations, as well as bulk hot-spot quantities. These theoretical models compare favorably with simulations, enabling their use as a post-process tool on radiation-hydrodynamics calculations without MHD capabilities. The effect of Biermann Battery magnetic fields on non-linear ablative stabilization in hot-spots is an ongoing research topic, with strong indications that magnetized heat-flow enhances perturbation growth in ICF hot-spots. Recently, Chris has also moved to modelling hohlraum-relevant experiments. Planar experiments allow for a simple configuration diagnosable with proton probing. Quantification of magnetic flux generation in laser ablation regions is sought, with favorable agreement once non-local corrections are included into the Gorgon code. Features of the proton radiographs enable the investigation of the so-called ‘hohlraum drive deficit’. Experiments are currently being undertaken to further constrain the models at higher laser intensity.

Within the magnetized hohlraum LDRD SI, Chris conducts pre-magnetized capsule simulations of NIF experiments currently underway. Predictions of enhanced ion temperature and yield from a 30T magnetic field originate from anisotropic changes to hot-spot ablation. Changes of ablation velocities to perturbation growth is also under investigation. Extending the outlook to high convergence capsules, where magnetic tension reduces perturbation growth perpendicular to the magnetic field, is also underway.

Chris also engages in theoretical and fundamental research relevant to extended-MHD plasmas. A recent PRL in 2021 proposes improved transport coefficients that correctly capture the transport of magnetic field at low electron magnetizations. Experiments currently supported by Chris’ modeling include: magnetized shock propagation; quantification of Nernst transport; enhancement of laser imprint by magnetization; magnetization of exploding pushers; imploding cylinders with substantial magnetic pressure.

Ph.D., Physics, Imperial College London, 2018

MEng, Engineering, University of Cambridge, 2014

Select publications below. For full list, see ‪Christopher A. Walsh - ‪Google Scholar

C. A. Walsh, et. al,  Magnetized ICF Implosions: Scaling of Temperature and Yield Enhancement, Physics of Plasmas (under review)

C. A. Walsh, Magnetized ablative Rayleigh-Taylor instability in three dimensions, Physical Review E 105, 025206 (2022)

C. A. Walsh, et. al, Exploring extreme magnetization phenomena in directly driven imploding cylindrical targets, Plasma Physics and Controlled Fusion 64, 025007 (2022)

P. T. Campbell, C. A. Walsh, et. al, Measuring magnetic flux suppression in high-power laser–plasma interactions, Physics of Plasmas 29, 012701 (2022)

C. A. Walsh, J. D. Sadler & J. R. Davies, Updated magnetized transport coefficients: impact on laser-plasmas with self-generated or applied magnetic fields, Nuclear Fusion 61, 116025 (2021)

C. A. Walsh & D. S. Clark, Biermann battery magnetic fields in ICF capsules: Total magnetic flux generation, Physics of Plasmas 28, 092705 (2021)

J. D. Sadler, C. A. Walsh & H. Li, Symmetric Set of Transport Coefficients for Collisional Magnetized Plasma, Physical Review Letters 126, 075001 (2021)

P. T. Campbell, C. A. Walsh, et. al, Magnetic Signatures of Radiation-Driven Double Ablation Fronts, Physical Review Letters 125, 145001 (2020)

C. A. Walsh, A. J. Crilly & J. P. Chittenden, Magnetized directly-driven ICF capsules: increased instability growth from non-uniform laser drive, Nuclear Fusion 60, 106006 (2020)

C. A. Walsh, et. al,  Extended-magnetohydrodynamics in under-dense plasmas, Physics of Plasmas 27, 022103 (2020)

C. A. Walsh, et. al, Perturbation modifications by pre-magnetisation of inertial confinement fusion implosions, Physics of Plasmas 26, 022701 (2019)

C. A. Walsh,  Extended magneto-hydrodynamic effects in indirect-drive inertial confinement fusion experiments, PhD Thesis, Imperial College London (2018)

C. A. Walsh, et. al, Self-Generated Magnetic Fields in the Stagnation Phase of Indirect-Drive Implosions on the National Ignition Facility, Physical Review Letters 118, 155001 (2017)