Developing solid cryogenic fuel configurations for magnetic direct drive inertial confinement fusion targets

Solid deuterium and deuterium-tritium (DT) fuels are used in a range of thermonuclear fusion platforms. Within inertial confinement fusion (ICF) targets, solid DT surrounds gaseous fuel. Upon stagnation, thermonuclear reaction products from the central plasma initiate a radially propagating burn wave, increasing fusion yield. The ICF program and Sandia National Laboratories (SNL) studies magnetically imploded cylindrical liners on the 20-MA, 100-ns Z Facility (Z). For example, Magnetized Liner Inertial Fusion (MagLIF) implosions produce greater than 10¹³ DD neutrons [1]. Solid fuel layers can benefit MagLIF both on Z and on a future driver. On Z, a solid fuel layer placed on the inner surface of the liner can reduce mix-enhanced radiation losses by buffering the plasma from the metal wall. On a higher-current driver, millimeters-thick DT ice placed on the liner's inner wall provides layered fuel for high gain “ice burner” MagLIF target designs [2]. Controlled growth of thin and thick deuterium ice shells has been demonstrated using a desublimation process, where a slow flow of gas enters the target and freezes to the walls. Such layers may also be grown with uniformly distributed spectroscopic dopants (e.g., Kr), but the gas-fill tube must be held warm to avoid inadvertently cryopumping the dopant before reaching the target. Solid-fuel fibers are also of interest. For example, a current-carrying fiber can be used to generate the central plasma target to be compressed by a metallic liner in a magnetized target fusion system. A screw-driven deuterium-ice-rod extruder [3] has been commissioned on the Z Facility in two recent experiments, demonstrating the technology needed for such fuel configurations.