New high-performance indirect drive target designs taking full advantage of a seed magnetic field

Magnetization of inertial confinement fusion (ICF) targets has been tested on the National Ignition Facility (NIF), showing a 3x yield increase due to a 26T axial seed field. These experiments utilized a design derived from the Big Foot ICF campaign. The following questions naturally arise: is 3x the best possible yield improvement from magnetization? Is the optimum magnetized design the same as the (much-explored) optimum unmagnetized design?

This presentation shows the first attempt to redesign a spherical ICF implosion to best utilize the benefits of applying an external magnetic field. The sub-ignition experiment N170601 is taken as the baseline design, which used 1.57MJ of laser energy. The optimum magnetized design benefits from increasing the shell thickness by 14μm and decreasing the ice thickness by 18μm, resulting in a neutron yield of 8.9x10¹⁷. This is 34x greater than the unmagnetized simulation of the same design, and 18.5x the greatest unmagnetized simulation across all designs simulated. The resultant implosion velocity for the magnetized design is lower, which would also reduce ablation front instability growth. This design was found by using a simplified 1D magnetization model, then validated against full 2D extended-MHD capsule simulations with radiation asymmetries applied to correct the shape.

Extensions of this work to incorporate changes to the laser pulse will also be presented, with delivered laser energies increased to the full capacity of NIF. A full redesign of a magnetized implosion will utilize Bayesian optimization efforts to explore the large number of free variables in design.