1. LSP Modeling of Ultra-Intense Lasers on Cone-Coupled Wire Targets:
Effect of Cone Thickness
Chris Orban1, Vladimir Ovchinnikov1, Kramer Akli1, Douglass Schumacher1, and Anthony Link1,2 1The Ohio State University, Department of Physics 2Lawrence Livermore National Laboratory
Results
PIC Simulations
Motivation
The Fast Ignition (FI) route to high-gain fusion requires detailed knowledge of laser-to-hot-electron coupling and transport physics
Cone-coupled wire targets (see image below) offer a simple geometry where theoretical understanding of these phenomena can be tested
1.2mm
LSP is an implicit PIC code capable of modeling laser-plasma interactions in solid density targets; stable even for ωp Δ t > 2, Δx / λD > 10
Significant speedup from variable resolution grid which allows small cell sizes (Δx = λ / 8 = 0.12 μm) near the laser-plasma interactions and large cells away from the cone (Δx = 1 μm)
Physics includes dE/dx drag on fast electrons, fully self-consistent E & B fields, and Kα production using ITS
2-D Cartesian Geometry Assumed
Comparison to simulations currently hindered by long
≥ 15 ps timescales for Kα signal
Preliminary 0.5mm & 1mm wire simulations with short (50fs) laser pulses show that the growth of the Ka signal simply tracks the number of hot (E > 8 keV) electrons in the wire
However, the hot electron behavior is complicated and the Kα photon generation only slows after the hot electrons reflux off the end of the wire
Both the observed experimental trend with cone thickness and the preliminary simulation results suggest a non-trivial coupling between the hot electrons and the cone
Experimental Data
Copper Kα Signal
Experiment
Simulation Results
References
Three different Al cone thicknesses (12um, 20um and buried-cone ~160um) were irradiated by the Titan laser (LLNL)
(Akli et al. 2010)
Acknowledgements
In simulations the Kα signal grows until ≥ 15 ps
Experimenting with transition to courant-limited time steps some time after the laser pulse turns off (factor of 2.5 speedup in execution time)
Experiments see clear trend of decreasing Kα yield with increasing cone thickness
This work was supported by the U.S. Department of Energy under contract DE-FG02-05ER54834 (ACE), and allocations of computer time at the Ohio Supercomputer Center.
FSC