title: Laser propagation measurements in long-scale-length underdense plasmas relevant to magnetized liner inertial fusion.
abstract: We report experimental results and simulations showing efficient laser energy coupling into plasmas at conditions relevant to the magnetized liner inertial fusion (MagLIF) concept. In MagLIF, to limit convergence and increase the hydrodynamic stability of the implosion, the fuel must be efficiently preheated. To determine the efficiency and physics of preheating by a laser, an Ar plasma with n_{e}/n_{crit}∼0.04 is irradiated by a multi-ns, multi-kJ, 0.35-μm, phase-plate-smoothed laser at spot-averaged intensities ranging from 1.0×10^{14} to 2.5×10^{14}W/cm^{2} and pulse widths from 2 to 10 ns. Time-resolved x-ray images of the laser-heated plasma are compared to two-dimensional radiation-hydrodynamic simulations that show agreement with the propagating emission front, a comparison that constrains laser energy deposition to the plasma. The experiments show that long-pulse, modest-intensity (I=1.5×10^{14}W/cm^{2}) beams can efficiently couple energy (∼82% of the incident energy) to MagLIF-relevant long-length (9.5 mm) underdense plasmas. The demonstrated heating efficiency is significantly higher than is thought to have been achieved in early integrated MagLIF experiments [A. B. Sefkow et al., Phys. Plasmas 21, 072711 (2014)10.1063/1.4890298].
authors.affiliation: Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Harvey-Thompson
authors.affiliation: Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
authors.forename: A B
authors.initials: AB
authors.lastname: Sefkow
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Wei
authors.affiliation: Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
authors.forename: T
authors.initials: T
authors.lastname: Nagayama
authors.affiliation: Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623-1299, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Campbell
authors.affiliation: General Atomics, P.O. Box 85608, San Diego, California 92186, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Blue
authors.affiliation: Lawrence Livermore National Laboratories, P.O. Box 808, L-472, Livermore, California 94551, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Heeter
authors.affiliation: Lawrence Livermore National Laboratories, P.O. Box 808, L-472, Livermore, California 94551, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Koning
authors.affiliation: Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Peterson
authors.affiliation: Naval Research Laboratory, Washington, DC 20375, USA.
authors.forename: A
authors.initials: A
authors.lastname: Schmitt