Laser-produced pair plasma in a magnetic mirror

Confinement of laser-produced positron-electron pair plasma in a magnetic mirror was studied on the Omega EP facility of the Laboratory for Laser Energetics (LLE) of the University of Rochester, NY. The plasma was produced by interaction of a high-intensity, 800~J, 10~ps laser beam with a 1mm-thick Au target. Two MIFEDS current generators discharged a 30~kA, 0.5~ms current pulse through two 4-loop magnetic coils. The coils, each with an inner diameter of 10~mm, were separated by 15~mm creating a magnetic mirror configuration with a mirror field of 15~T and a mirror ratio of 2.5. The particle losses and their energy spectra were measured by several magnetic particle energy analyzers situated around the target. To optimize the positron confinement, a parallel campaign on increasing the yield of low-energy positrons was conducted. The positron energy spectra were varied by manipulating the sheath electric field at the back of positron target using a secondary plasma produced by a 1~ns laser beam. The experimental results and their comparison to simulations will be presented. This work is supported the U.S. Department of Energy by LLNS, LLC, under Contract No. DE-AC52-07NA27344 under LDRD 20-LW-021. LLNL-ABS-811921.