Assessment of the 60-Beam OMEGA Geometry for Applications to Future Laser Systems

The success of the 60-beam OMEGA laser makes the OMEGA geometry and its variations interesting candidates for future direct-drive laser systems. This work examines two variations that retain geometrically identical beams: (1) each pentagon can be stretched to shift the five beams at its corners away from its center and (2) the five beams can be rotated around the pentagon. The optimum stretching factor (pent edge/hex–hex edge), 1.2 for OMEGA, is found to be the same for an ignition-scale target. Rotation through 18° generates a system that avoids opposing beam ports and can have even better uniformity than OMEGA. This can also be achieved by repointing the OMEGA beams to rotated aim points. For a future design where each of the 60 locations supports a cluster of N beams with distinct properties (e.g., phase plate, wavelength, pulse shape), the selection of N combinations of stretching factor and rotation angle maintains geometrically identical 60-beam sets. The 60 beams can also be partitioned into 24- and 36-beam subsets based on a cubic geometry,[1] each of which can provide reasonable uniformity with appropriate beam repointing. Finally, the cubic geometry allows for 48 of the 60 beams to be used to drive a spherical hohlraum with six laser entrance holes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.

[1] M. Temporal et al., Sci. Rep. 13, 10010 (2023).