Ion and Electron Acoustic Bursts during Anti-Parallel Magnetic Reconnection Driven by Lasers

Magnetic reconnection converts magnetic energy into thermal and kinetic energy in plasma. Among numerous candidate mechanisms, ion acoustic instabilities driven by the relative drift between ions and electrons, or equivalently electric current, have been suggested to play a critical role in dissipating magnetic energy in collisionless plasmas. However, their existence and effectiveness during reconnection have not been well understood due to ion Landau damping and difficulties in resolving the Debye length scale in the laboratory. Here we report a sudden onset of ion acoustic bursts measured by collective Thomson scattering in the exhaust of anti-parallel magnetically driven reconnection using high-power lasers. The ion acoustic bursts are followed by electron acoustic bursts with electron heating and bulk acceleration. We reproduce these observations with 1D and 2D particle-in-cell simulations in which electron outflow jet drives ion-acoustic instabilities, forming double layers. These layers induce electron two-stream instabilities that generate electron acoustic bursts and energize electrons. Our results demonstrate the importance of ion and electron acoustic dynamics during reconnection when ion Landau damping is ineffective, a condition applicable to a range of astrophysical plasmas including near-Earth space, stellar flares, and black hole accretion engines

A pulsed-laser calibration system for the laser backscatter diagnostics at the Omega laser

A calibration system has been developed that allows a direct determination of the sensitivity of the laser backscatter diagnostics at the Omega laser. A motorized mirror at the target location redirects individual pulses of a mJ-class laser onto the diagnostic to allow the in-situ measurement of the local point response of the backscatter diagnostics. Featuring dual wavelength capability at the 2nd and 3rd harmonic of the Nd:YAG laser, both spectral channels of the backscatter diagnostics can be directly calibrated. In addition, channel cross-talk and polarization sensitivity can be determined. The calibration system has been employed repeatedly over the last two years and has enabled precise backscatter measurements of both stimulated Brillouin scattering and stimulated Raman scattering in gas-filled hohlraum targets that emulate conditions relevant to those in inertial confinement fusion targets

Optimization of plasma amplifiers

Plasma amplifiers offer a route to side-step limitations on chirped pulse amplification and generate laser pulses at the power frontier. They compress long pulses by transferring energy to a shorter pulse via the Raman or Brillouin instabilities. We present an extensive kinetic numerical study of the three-dimensional parameter space for the Raman case. Further particle-in-cell simulations find the optimal seed pulse parameters for experimentally relevant constraints. The high-efficiency self-similar behavior is observed only for seeds shorter than the linear Raman growth time. A test case similar to an upcoming experiment at the Laboratory for Laser Energetics is found to maintain good transverse coherence and high-energy efficiency. Effective compression of a 10 kJ , nanosecond-long driver pulse is also demonstrated in a 15-cm-long amplifier

High-energy-density radiative and material properties studies using picosecond X-ray spectroscopy

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2018.Advanced experimental and theoretical techniques have been applied to outstanding challenges in high energy density science. By careful selection of laser parameters, target geometries, and spectroscopic diagnostics, it is possible to investigate the intense energy flows that are required to create hot dense matter, the plasma conditions that can be achieved, and plasma-dependent effects on atomic energy levels. The measurements presented in this thesis provide new experimental insight to the creation and measurement of unique high energy density systems and demonstrate their use for sensitive atomic properties studies in extreme conditions. Hot and dense plasma conditions were created by high-intensity laser irradiation of solid foils containing thin buried Al or Al/Fe tracer layers. The material response to intense heating was inferred from picosecond time-resolved intensity measurements of the Al Hea thermal line and broadband x-ray emission. The data show two temporally-resolved x-ray flashes when Fe is present in the layer. Fully explicit, kinetic particle-in-cell and collisional-radiative atomic model predictions reproduce these observations, connecting the two flashes with staged radial energy coupling within the target. The measurements contribute novel data for predicting the behavior of energy density inhomogeneities and understanding the response of high-energy-density systems to intense heating. The instantaneous bulk plasma conditions were inferred using picosecond time-resolved measurements of the Heα spectral line emission from the buried tracer layer. The measured Heα-to-satellite intensity ratio and spectral line width was interpreted using a non-local thermodynamic equilibrium (NLTE) atomic kinetics model to provide the plasma temperature and density as a function of time. Statistical and experimental uncertainties in the measured data are propagated to the inferred plasma conditions within a self-consistent model-dependent framework. The measurements show that high thermal temperatures exceeding 500 eV are achieved at densities within 80% of solid and demonstrate a rigorous approach for future spectroscopic temperature and density measurements essential to hot dense matter studies. Picosecond time-resolved dense plasma line shifts of the 1s2p-1s2 transition in He-like Al ions were measured as a function of the instantaneous plasma conditions. The data show spectral line shifts of 5 eV for electron densities of 1–5x10^23 cm-3 and temperatures near 300 eV. Numerical ion-sphere model calculations demonstrate broad agreement with the measured data over the full range of densities and temperatures studied, providing a new test of dense plasma theories for atomic structure and radiation transport in extreme environments. The hot dense matter systems studied in this work exhibit qualities of both the plasma and solid state. Such material resists theoretical description by the established approaches of solid state or plasma physics, emphasizing the need for experimental data to produce a detailed picture for how the atomic, radiative, and thermodynamic properties of matter are modified in extreme conditions. Contributing data toward these aims is the goal of this thesis

The multiple-beam two-plasmon-decay instability

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2016.Recent developments in experimental techniques and simulations have led to an improved understanding of the nonlinear evolution of the two-plasmon-decay (TPD) instability relevant to direct-drive inertial confinement fusion (ICF). Experiments on the OMEGA laser used ultraviolet Thomson scattering to observe TPD electron plasma waves driven by multiple laser beams in a variety of experimental configurations. The experiments were modeled in 3-D using a hybrid code (LPSE) that combines a pseudospectral wave solver with a particle tracker to self-consistently calculate Landau damping. Thomson-scattering measurements of several different plasma wavevectors show a highly anisotropic turbulent TPD driven electron-plasma-wave spectrum and are well reproduced by LPSE simulations. Direct comparison between simulated and measured hot-electron spectra indicate that the hybrid-particle model correctly captures the hot-electron generation mechanism associated with the nonlinear evolution of the TPD instability

Laser ablation and hydrodynamic coupling in direct-drive inertial-confinement-fusion experiments

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2017.In direct-drive inertial confinement fusion, laser beams are used to ablate a capsule and implode it via the rocket effect. Time-gated images of the x-rays emitted by the capsule were used to experimentally study the hydrodynamic coupling of laser energy to the target. The mass ablation rate, the target trajectory, the laser absorption, and the conduction-zone length were simultaneously measured in spherically symmetric (1-D) implosions. These observables completely constrain the coupling models in simulations. They showed that the long-standard Spitzer-Härm thermal transport model with a time-dependent flux-limiter resulted in a significant underestimate of the mass ablation rate and the length of the conduction zone. Simulations that used models for nonlocal electron thermal transport and for cross-beam energy transfer (CBET) recently developed at the Laboratory for Laser Energetics reproduced all measurements. However, the CBET required a gain modification thatwas not explained by theory. Additional experimentswere conducted to isolate the effect of CBET on hydrodynamic coupling and quantify this modification. Laser beams incident on the equator of the target were turned off and the polar beams were repointed to illuminate the target uniformly (in a polar-drive configuration), nearly suppressing CBET at the poles and increasing its effect at the equator. Angularly resolved mass-ablation-rate and target trajectorymeasurementswere used to compare the hydrodynamic couplingwith andwithout CBET. Results on the pole were used to validate the hydrodynamic coupling without CBET in simulations, and a factor on the CBET gain was determined by matching the measured equatorial trajectories. The gain factor was necessary to reproduce the measurements in all configurations and was found to vary with the laser intensity in polar-drive implosions. This suggests that additional physics is needed in the model to fully capture the effect of CBET

Plasma scattering of electromagnetic radiation: theory and measurement techniques

This work presents one of the most powerful methods of plasma diagnosis in exquisite detail to guide researchers in the theory and measurement techniques of light scattering in plasmas. Light scattering in plasmas is essential in the research and development of fusion energy, environmental solutions, and electronics.Referred to as the "Bible" by researchers the work encompasses fusion and industrial applications essential in plasma research. It is the only comprehensive resource specific to the plasma scattering technique. It provides a wide-range of experimental examples and discussion of th