Biblio

The pre-magnetization of inertial confinement fusion capsules is a promising avenue for reaching hotspot ignition, as the magnetic field reduces electron thermal conduction losses during hotspot formation. However, in order to reach high yields, efficient burn-up of the cold fuel is vital. Suppression of heat flows out of the hotspot due to magnetization can restrict the propagation of burn and has been observed to reduce yields in previous studies [1] . This work investigates the potential suppression of burn in a magnetized plasma utilizing the radiation-MHD code ‘Chimera’ in a planar geometry.. This code includes extended-MHD effects, such as the Nernst term, and a Monte-Carlo model for magnetized alpha particle transport and heating. We observe 3 distinct regimes of magnetized burn in 1D as initial magnetization is increased: thermal conduction driven; alpha driven; and suppressed burn. Field transport due to extended-MHD is also observed to be important, enhancing magnetization near the burn front. In higher dimensions, burn front instabilities have the potential to degrade burn even more severely. Magneto-thermal type instabilities (previously observed in laser-heated plasmas [2] ) are of particular interest in this problem.

The MagNIF team at LLNL is developing a pulsed power platform to enable magnetized inertial confinement fusion and high energy density experiments at the National Ignition Facility. A pulsed solenoidal driver capable of premagnetizing fusion fuel to 40T is predicted to increase performance of indirect drive implosions. We have written a specialized Python code suite to support the delivery of a practical design optimized for target magnetization and risk mitigation. The code simulates pulsed power in parameterized system designs and converges to high-performance candidates compliant with evolving engineering constraints, such as scale, mass, diagnostic access, mechanical displacement, thermal energy deposition, facility standards, and component-specific failure modes. The physics resolution and associated computational costs of our code are intermediate between those of 0D circuit codes and 3D magnetohydrodynamic codes, to be predictive and support fast, parallel simulations in parameter space. Development of a reduced-order, physics-based target model is driven by high-resolution simulations in ALE3D (an institutional multiphysics code) and multi-diagnostic data from a commissioned pulser platform. Results indicate system performance is sensitive to transient target response, which should include magnetohydrodynamic expansion, resistive heating, nonlinear magnetic diffusion, and phase change. Design optimization results for a conceptual NIF platform are reported.

A new pulse power system is being developed with the goal of generating up to 40T seed magnetic fields for increasing the fusion yield of indirect drive inertial confinement fusion (ICF) experiments on the National Ignition Facility. This pulser is located outside of the target chamber and delivers a current pulse to the target through a coaxial cable bundle and custom flex-circuit strip-lines integrated into a cryogenic target positioner. At the target, the current passes through a multi-turn solenoid wrapped around the outside of a hohlraum and is insulated with Kapton coating. A 11.33 uF capacitor, charged up to 40 kV and switched by spark-gap, drives up to 40 kA of current before the coil disassembles. A custom Python design optimization code was written to maximize peak magnetic field strength while balancing competing pulser, load and facility constraints. Additionally, using an institutional multi-physics code, ALE3D, simulations that include coil dynamics such as temperature dependent resistance, coil forces and motion, and magnetic diffusion were conducted for detailed analysis of target coils. First experiments are reported as well as comparisons with current modelling efforts.

The single most important scientific question in fusion research may be confinement in a fusion plasma [1] . A recently-developed theoretical model [2] is reviewed for the confinement time of ion kinetic energy in a material where fusion reactions occur. In the theoretical model where ion stopping was considered as a key mechanism for ion kinetic energy loss, an estimate was obtained for the confinement time of ion kinetic energy in a D-T plasma - and found to be orders of magnitude lower than required in the Lawson criterion. As ions transfer their kinetic energies to electrons via ion stopping and thermalization between the ions and the electrons takes place, spontaneous electron cyclotron radiation is identified as a key mechanism for electron kinetic energy loss in a magnetically confined plasma. The energy confinement time is obtained and found in agreement with measurements from TFTR [1] and Wendelstein 7-X [3] . An advanced Lawson criterion is obtained for a magnetically confined thermonuclear fusion reactor.

Traditional magnetic mirrors are appealing because of their comparably simple geometry which lends itself to cost-effective construction. However, magnetic mirrors suffer from several inherent problems that make them poor choices for confining and heating plasmas. The chief concerns are the loss-cone instability which continuously saps hot particles from the trap and the interchange instability which effectively transports hot plasma from the core of the trap to the edges where it is lost to the walls. Centrifugal confinement schemes address these concerns with the addition of supersonic poloidal rotation which can effectively shut off the loss-cone. In addition, velocity shear in the flow may mitigate or even turn off the interchange instability if high enough rotation speeds can be achieved. Previous experiments have verified the efficacy of centrifugal confinement but have been unable to achieve sufficient rotation velocities to entirely shut down the interchange modes. [1] The rotation velocity in these experiments was limited by the Critical-Ionization-Velocity (CIV) instability. [3] We plan an experiment to verify that the CIV is the limiting factor in supersonic plasma centrifuges and to explore strategies for avoiding the CIV limit and achieving sufficient rotation speeds to enable stable plasma confinement.

X-ray radiography has been used to diagnose a wide variety of experiments at the Z facility including inertial confinement fusion capsule implosions, the growth of the magneto-Rayleigh-Taylor instability in solid liners, and the development of helical structures in axially magnetized liner implosions. In these experiments, the Z Beamlet laser (1 kJ, 1 ns) was used to generate the x-ray source. An alternate x-ray source is desirable in experiments where the Z Beamlet laser is used for another purpose (e.g., preheating the fuel in magnetized liner inertial fusion experiments) or when multiple radiographic lines of sight are necessary.

Magnetized Liner Inertial Fusion (MagLIF) is a magneto-inertial fusion (MIF) concept being studied on the Z-machine at Sandia National Laboratories. MagLIF relies on quasi-adiabatic heating of a gaseous deuterium (DD) fuel and flux compression of a background axially oriented magnetic field to achieve fusion relevant plasma conditions. The magnetic flux per fuel radial extent determines the confinement of charged fusion products and is thus of fundamental interest in understanding MagLIF performance. It was recently shown that secondary DT neutron spectra and yields are sensitive to the magnetic field conditions within the fuel, and thus provide a means by which to characterize the magnetic confinement properties of the fuel. 1 , 2 , 3 We utilize an artificial neural network to surrogate the physics model of Refs. [1] , [2] , enabling Bayesian inference of the magnetic confinement parameter for a series of MagLIF experiments that systematically vary the laser preheat energy deposited in the target. This constitutes the first ever systematic experimental study of the magnetic confinement properties as a function of fundamental inputs on any neutron-producing MIF platform. We demonstrate that the fuel magnetization decreases with deposited preheat energy in a fashion consistent with Nernst advection of the magnetic field out of the hot fuel and diffusion into the target liner.

Here, we propose a simple design approach based on metal-masked titanium dioxide nanopillars, which can realize strong Mie resonance in metasurfaces and enables light confinement within itself over the range of visible wavelengths. By selecting the appropriate period and diameter of individual titanium dioxide nanopillars, the coincidence of resonance peak positions derived from excited electric and magnetic dipoles can be achived. And the optical properties in this design have been investigated with the Finite-Difference Time-Domain(FDTD) solutions.