Engineering topics

Ting, Antonio C.

Publications and source records attributed to Ting, Antonio C..

2 records

DOE OSTI2023

Proton acceleration in an overdense hydrogen plasma by intense CO 2 laser pulses with nonlinear propagation effects in the underdense pre-plasma

We report on proton acceleration from intense CO 2 laser-irradiated hydrogen plasmas at near-critical densities, with the density gradient steepened by Nd:YAG laser ablation-driven hydrodynamic shocks. While the experimental results, such as the quasi-monoenergetic proton spectra and their scaling with respect to the laser energy, are generally in agreement with the simulations, certain laser shots produced significantly higher proton energies than anticipated during the experiment. The increased proton energy may be linked to nonlinear propagation effects in the steepened plasma density ramp before the critical surface, including relativistic self-focusing and, for the case of temporally-structured laser pulses observed in the experiment, focusing of the trailing pulse through the plasma channel formed by the leading pulse 25 ps ahead. The occurrence of channel focusing in the underdense hydrogen plasma is supported by a subsequent pump-probe experiment with a dark-field imaging technique, where the formation of ion channels was observed after the passage of an intense CO 2 laser pulse

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1986

Turbulent relaxation processes in magnetohydrodynamics

Competing processes previously called 'selective decay' and 'dynamic alignment' are studied numerically for two-dimensional magnetohydrodynamic turbulence. In selective decay, the energy decays relatively to mean-square vector potential, and in dynamic alignment, the energy decays relatively to cross helicity. In the former case, the kinetic (fluid) energy decays to zero and the magnetic energy occupies the largest scales allowed by the boundary conditions. In the latter case, the velocity field and magnetic field become aligned and energetically equipartitioned. An extensive study of the initial value problem, with viscous and resistive dissipation, indicates that four distinct regimes of behavior are possible: a magnetically dominated regime, a velocity dominated regime, a dynamic alignment dominated regime, and a transition regime separating the others in parameter space. An analytical variational problem predicts several features seen in the computations, including geometrical alignment of velocity and magnetic fields, constraints on global quantities in the long-time limit, and in some cases, condensation to long wavelength modes.

Ting, Antonio C.↗