Progress in Frustraum Research on the NIF

The delivery of x-ray capsule absorbed energy E_cap greater than 300 kJ can improve ignition performance margins and tolerance to high fuel adiabats. The Frustraum hohlraum geometry consists of a pair of joined cones at the equator to promote high E_cap while delivering adequate drive symmetry [1]. The inclined angle of the hohlraum wall (~23°) reduces the outer-beam spot intensity and hence high-Z wall “bubble” blow-in speed, and potentially increases outer-cone specular glint and CBET to the inner beams for improved inner-cone laser propagation to the equator at late time. The large diameter of the Frustraum (>9 mm) accommodates a large capsule of 2.4 mm inner diameter for high E_cap while providing reduced hohlraum filling. A recent campaign on the NIF has established the Frustraum as a robust hohlraum platform that delivers symmetric implosions, high capsule implosion speeds, and low laser backscatter. The first DT-layered implosion in a Frustraum (N210117) met all performance goals while delivering >10¹⁶ neutrons and yield amplification ~2. A survey of the Frustraum validation effort, resulting spinoff ignition campaigns, and updates on the latest data are presented. [1] P. Amendt et al., Phys. Plasmas 26, 082707 (2019). Prepared by LLNL under Contract DE-AC52-07NA27344.