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2nd High-Power Laser Workshop and LCLS USER Meeting at SLAC

September 18, 2014

2nd High-Power Laser Workshop and LCLS USER Meeting at SLAC

Graduate students of the High Energy Density Physics (HEDP) research group present posters at the 2nd High-Power Laser Workshop and LCLS USER Meeting at SLAC.
 

 

 

 

Ginevra Cochran 
Criteria for PIC simulations of relativistic electron dynamics in an ultra-intense laser field
We present a study of particle-in-cell simulation error in modeling a free relativistic electron in an ultra-intense laser field, comparing the codes PSC and LSP. We find that an unexpectedly small timestep is required for both codes to resolve the electron motion, decreasing with increasing ao, the normalized vector potential. We consider the particle pusher, grid dispersion, and the field solver as sources of error, and find by comparing the codes with results from a simple particle pusher that the particle pusher error dominates the results, followed by grid dispersion. We derive the constraint imposed by the relativistic Boris particle pusher on the timestep, and we show that this constraint decreases inversely as ao. We find the particle pusher error accumulates on the short trajectory segments where the gamma-factor is approximately unity and the laser fields are strong, and present a sub-cycled version of the simple particle pusher code which reduces error. 

Kevin George 
Diagnosing Temperature and Density of Nanosecond Laser-Shocked Plasmas with a Two-Element Alloy Target
We give a preliminary report on an investigation of the temperature and the density of nanosecond laser-shocked targets through the use of an embedded two-element (Ti/Cr or Sc/V) alloy film. The experiment was conducted at the Matter in Extreme Conditions (MEC) endstation under proposal LD67. The experiment utilized the Linac Coherent Light Source (LCLS) x-ray free electron laser (XFEL) to stimulate x-ray fluorescence (XRF) in the two-alloyed elements which was measured by von Hamos HAPG and single hit CCD spectrometers. Various features of the observed XRF is used to determine the plasma temperature and density. Further experiments look to extend this two-element alloy methodology to embedded nanoparticles as a robust warm dense matter thermometer.
This work was supported by the US Department of Energy, Office of Science, Fusion Energy Sciences, and the National Nuclear Security Administration, through grant DE-SC0008580.

Patrick Poole 
Liquid crystals as variable thickness targets for high repetition rate intense laser applications
As laser facilities improve high repetition rate targets are becoming more critical for ultra-intense laser applications. One such application is ion acceleration, where target thickness determines the relevant physical process. We have developed liquid crystal films that preserve the planar target geometry advantageous to many applications while providing on-demand thickness variation between 50 and 5000 nm. This thickness control is obtained in part by varying the temperature at which films are formed, which governs the phase (and hence molecular ordering) of the liquid crystal material. Liquid crystals typically have vapor pressures well below the 10-6 Torr operating pressures of intense laser target chambers, and these films maintain their thickness indefinitely during alignment and shot preparation. Additionally, the minute volume that comprises a film makes the cost of each target well below one cent, in stark contrast to many standard solid targets, making them ideal for experiments requiring high shot repetition rates. The details of single-shot liquid crystal film formation were recently published in P. L. Poole Phys. Plasmas 21, 063109 (2014). Here we will present recent effort towards producing films in vacuum with repetition rates up to and exceeding 1 Hz, as well as a device based on confocal microscopy to achieve sub-micron precision of these and other targets.
This work was performed with support from DARPA and the US Department of Energy.