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Title: CFD Modeling of Droplets Heated by an X-ray Free Electron Laser
Material in HED regimes are at very high pressures and temperatures but can often still be modeled in the plasma-fluid approximation. Historically HED regimes were created using large laser/ion- beam drivers heating solid targets. Exciting data was obtained from these single shot experiments. In recent years there has been a shift to obtain HED related data from a large number of shots by using high-repetition-rate drivers. For high-repetition-rate experiments a series of droplet targets are often used to have a fresh target/droplet for each shot. However, one must make sure that target debris from the previous shot does not degrade the target for subsequent shots. This is a challenging CFD problem as one needs to model the initial dynamics of the heated droplet and the subsequent interaction with the following droplets. We use the CFD modeling code PISALE to study this complex problem. We discuss results for liquid hydrogen droplets heated by an x-ray free electron laser (XFEL). We first show 2D results for single heated droplet then 3D results for a heated droplet interacting with two unheated droplets. more »« less
Treffert, F.; Glenn, G. D.; Chou, H. -G. J.; Crissman, C.; Curry, C. B.; DePonte, D. P.; Fiuza, F.; Hartley, N. J.; Ofori-Okai, B.; Roth, M.; et al(
, Physics of Plasmas)
High-power lasers can generate energetic particle beams and astrophysically relevant pressure and temperature states in the high-energy-density (HED) regime. Recently-commissioned high-repetition-rate (HRR) laser drivers are capable of producing these conditions at rates exceeding 1 Hz. However, experimental output from these systems is often limited by the difficulty of designing targets that match these repetition rates. To overcome this challenge, we have developed tungsten microfluidic nozzles, which produce a continuously replenishing jet that operates at flow speeds of approximately 10 m/s and can sustain shot frequencies up to 1 kHz. The ambient-temperature planar liquid jets produced by these nozzles can have thicknesses ranging from hundreds of nanometers to tens of micrometers. In this work, we illustrate the operational principle of the microfluidic nozzle and describe its implementation in a vacuum environment. We provide evidence of successful laser-driven ion acceleration using this target and discuss the prospect of optimizing the ion acceleration performance through an in situ jet thickness scan. Future applications for the jet throughout HED science include shock compression and studies of strongly heated nonequilibrium plasmas. When fielded in concert with HRR-compatible laser, diagnostic, and active feedback technology, this target will facilitate advanced automated studies in HRR HED science, including machine learning-based optimization and high-dimensional statistical analysis.
We have experimentally demonstrated a simplified method for performing single-shot supercontinuum spectral interferometry (SSSI) that does not require pre-characterization of the probe pulse. The method, originally proposed by D. T. Vu, D. Jang, and K. Y. Kim, uses a genetic algorithm (GA) and as few as two time-delayed pump-probe shots to retrieve the pump-induced phase shift on the probe [Opt. Express26,20572(2018)]. We show that the GA is able to successfully retrieve the transient modulations on the probe, and that the error in the retrieved modulation decreases dramatically with the number of shots used. In addition, we propose and demonstrate a practical method that allows SSSI to be done with a single pump-probe shot (again, without the need for pre-characterization of the probe). This simplified method can prove to be immensely useful when performing SSSI with a low-repetition-rate laser source.
A comprehensive understanding of heat transfer mechanisms and hydrodynamics during droplet impingement on a heated surface and subsequent evaporation is crucial for improving heat transfer models, optimizing surface engineering, and maximizing overall effectiveness. This work showcases findings related to heat transfer mechanisms and simultaneous tracking of the moving contact line (MCL) for subcooled impinging droplets across a range of surface temperatures, utilizing a custom MEMS device, at multiple impact velocities. Experimental results show that heat flux caused by droplet impingement has a weaker dependence on surface temperature than receding MCL heat transfer due to evaporation, which is significantly surface temperature dependent. The measurements also demonstrate that when a droplet impacts a heated surface and evaporates, the process can be divided into two segments based on the effective heat transfer rate: an initial conduction-dominated segment followed by another segment dominated by surface evaporation. For subcooled impinging droplets, the effect of oscillatory motion is found to be negligible, unlike in a superheated regime; hence, heat conduction into the droplet entirely governs the first segment. Results also show that heat flux at the solid-liquid interface of an impinging droplet increases with the rise of either impact velocity or surface temperature. In the subcooled regime, droplets impacting a heated surface have approximately 1.6 times higher vertical heat flux values than gently deposited droplets. Furthermore, this study quantifies the contributions of buoyancy and thermocapillary convection within the droplet to the overall heat transfer.
High-intensity, short-pulse lasers are crucial for generating energetic electrons that produce high-energy-density (HED) states in matter, offering potential applications in igniting dense fusion fuels for fast ignition laser fusion. High-density targets heated by these electrons exhibit spatially non-uniform and highly transient conditions, which have been challenging to characterize due to limitations in diagnostics that provide simultaneous high spatial and temporal resolution. Here, we employ an X-ray Free Electron Laser (XFEL) to achieve spatiotemporally resolved measurements at sub-micron and femtosecond scales on a solid-density copper foil heated by laser-driven fast electrons. Our X-ray transmission imaging reveals the formation of a solid-density hot plasma localized to the laser spot size, surrounded by Fermi degenerate, warm dense matter within a picosecond, and the energy relaxation occurring within the hot plasma over tens of picoseconds. These results validate 2D particle-in-cell simulations incorporating atomic processes and provide insights into the energy transfer mechanisms beyond current simulation capabilities. This work significantly advances our understanding of rapid fast electron heating and energy relaxation in solid-density matter, serving as a key stepping stone towards efficient high-density plasma heating and furthering the fields of HED science and inertial fusion energy research using intense, short-pulse lasers.
Grace, E. S.; Djordjevic, B. Z.; Guang, Z.; Mariscal, D.; Scott, G. G.; Simpson, R. A.; Swanson, K. K.; Zeraouli, G.; Stuart, B.; Trebino, R.; et al(
, Review of Scientific Instruments)
We report recent single-shot spatiotemporal measurements of laser pulses, including pulse-front tilt (PFT) and spatial chirp, taken at the Compact Multipulse Terawatt laser at the Jupiter Laser Facility in Livermore, CA. STRIPED FISH, a device that measures the complete 3D electric field of fs to ps laser pulses on a single shot, was adapted to near infrared for these measurements. We present the design of the instrument used for these experiments, the on-shot measurements of systematic high-order PFT, and shot-to-shot variations in the measurements of spatiotemporal couplings. Finally, we simulate the effect of PFT in target normal sheath acceleration experiments. These simulations showed that pulse front tilt can steer hot electrons, shape the distribution of the accelerating sheath field, and increase the variability of cutoff energy in the resulting proton spectra. While these effects may be detrimental to experimental accuracy if the pulse front tilt is left unmeasured, hot electron steering shows promise for precision manipulation of the particle source for a range of applications, including irradiation of secondary targets for opacity measurements, radiography, or neutron generation.
Parisuaña, C., Eder, D. C., Gauthier, M., Schoenwaelder, C., Stan, C. A., and Glenzer, S. H. CFD Modeling of Droplets Heated by an X-ray Free Electron Laser. Retrieved from https://par.nsf.gov/biblio/10420558. Proceedings of the International Conference on Computational Fluid Dynamics .
Parisuaña, C., Eder, D. C., Gauthier, M., Schoenwaelder, C., Stan, C. A., & Glenzer, S. H. CFD Modeling of Droplets Heated by an X-ray Free Electron Laser. Proceedings of the International Conference on Computational Fluid Dynamics, (). Retrieved from https://par.nsf.gov/biblio/10420558.
Parisuaña, C., Eder, D. C., Gauthier, M., Schoenwaelder, C., Stan, C. A., and Glenzer, S. H.
"CFD Modeling of Droplets Heated by an X-ray Free Electron Laser". Proceedings of the International Conference on Computational Fluid Dynamics (). Country unknown/Code not available. https://par.nsf.gov/biblio/10420558.
@article{osti_10420558,
place = {Country unknown/Code not available},
title = {CFD Modeling of Droplets Heated by an X-ray Free Electron Laser},
url = {https://par.nsf.gov/biblio/10420558},
abstractNote = {Material in HED regimes are at very high pressures and temperatures but can often still be modeled in the plasma-fluid approximation. Historically HED regimes were created using large laser/ion- beam drivers heating solid targets. Exciting data was obtained from these single shot experiments. In recent years there has been a shift to obtain HED related data from a large number of shots by using high-repetition-rate drivers. For high-repetition-rate experiments a series of droplet targets are often used to have a fresh target/droplet for each shot. However, one must make sure that target debris from the previous shot does not degrade the target for subsequent shots. This is a challenging CFD problem as one needs to model the initial dynamics of the heated droplet and the subsequent interaction with the following droplets. We use the CFD modeling code PISALE to study this complex problem. We discuss results for liquid hydrogen droplets heated by an x-ray free electron laser (XFEL). We first show 2D results for single heated droplet then 3D results for a heated droplet interacting with two unheated droplets.},
journal = {Proceedings of the International Conference on Computational Fluid Dynamics},
author = {Parisuaña, C. and Eder, D. C. and Gauthier, M. and Schoenwaelder, C. and Stan, C. A. and Glenzer, S. H.},
}
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