LLE Review 153

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Highlights

This volume of the LLE Review, covering October–December 2017, features “Nuclear Science Experiments with a Bright Neutron Source from Fusion Reactions on the OMEGA Laser System,”” which uses yields and energy spectra of neutrons from D(n,2n)p to study the breakup reaction measured at a forward angle of θ_lab = 3.5°±3.5° using a sensitive, high-dynamic-range neutron time-of-flight spectrometer.

Additional highlights of research presented in this issue include the following:

• Fifth-harmonic generation using a pulsed Nd:YLF laser in a cascade of nonlinear crystals with a record efficiency of 30% is demonstrated. Cesium lithium borate is used in a Type I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes to optimize efficiency. Energies up to 335 mJ in 2.4-ns pulses were demonstrated.
• A design of an ultrafast x-ray streak camera for time-resolved studies of high-energy-density experiments is presented. The streak camera’s electro-optical imaging system features a polarity-reversible quadrupole doublet, allowing two imaging modes depending on the scientific mission need. The streak camera’s temporal impulse, detector efficiency, and linear dynamic range were qualified using a synchronized sub-picosecond, 263-nm probe laser incident on a gold photocathode.
• Results of a CBET study are presented, where wavelength tuning to vary the amount of energy transfer between two beams in a quasi-stationary plasma with carefully controlled conditions. The amount of transfer agreed well with calculations assuming linear ion-acoustic waves with amplitudes up to δn/n ≈ 0.015. Increasing the initial probe intensity to access larger ion-acoustic wave amplitudes for otherwise fixed conditions yields evidence of saturation beyond this level.
• Laser frequency detuning was shown to potentially be used to suppress the two-plasmon–decay (TPD) instability using three-dimensional laser–plasma interaction simulations. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion (ICF) implosion on the OMEGA laser, the simulations show that ~0.5% laser frequency detuning is sufficient to eliminate TPD driven hot-electron generation in current experiments.
• The distribution of tritium was studied between the near surface and the bulk in 316 stainless steel using two independent techniques: pulsed-plasma exposures and a zinc-chloride wash.
• Experiment data and simulation results of a study of direct laser acceleration (DLA) of electrons in a laser-wakefield accelerator (LWFA) operating in the forced or quasi-blowout regimes is presented.