Recent Publications

Superpermeation and Compression Through Vanadium Foil

Joshua Ruby, Zachary Robinson, W. Udo. Schröder, Matthew Sharpe

University of Rochester

Multi-petawatt physics at new and future laser user facilities

Jonathan D. Zuegel, Antonino Di Piazza, Karl M. Krushelnick, Daniele Margarone

University of Rochester, University of Michigan, The Extreme Light Infrastructure ERIC

The mini-conference on Multi-Petawatt Physics at New and Future Laser User Facilities, held at the 2024 Annual Meeting of the American Physical Society Division of Plasma Physics, updated worldwide progress at the frontier of multi-petawatt physics, including theoretical, computational, experimental, and technical advances.

Size scaling of acceleration phase energetics and its effects on direct-drive DT-layered implosions

D. Patel, R. Betti, V. Gopalaswamy, A. Lees, D. Cao, R. C. Shah

University of Rochester

A fundamental question in inertial confinement fusion is how implosion performance, and therefore ignition thresholds and fusion gain, evolve with target size. In laser-driven direct drive fusion, the scaling of laser-drive performance with size is critical to this evolution and to extrapolating results from the 30-kJ OMEGA laser-fusion experiments to ignition-class facilities such as the National Ignition Facility. Beyond the well-known adverse effects of cross-beam energy transfer (CBET) on drive performance, here we demonstrate that effects related to the non-scaling physics of thermal conduction and electron–ion energy equilibration exert an influence on drive behavior with scale that equals or surpasses that of CBET. We find that a significant portion of the lost implosion performance with increasing scale is due to the loss of shell implosion velocity. Furthermore, we show that while modest modifications to hydro-scaled designs can recover most of the lost implosion velocity, a full hydro-equivalent performance extrapolation is difficult to achieve without CBET mitigation or subcooling below the triple point of DT.

Transforming Water Detritiation: Process Design and AI-Driven Material Selection

Rashad Ahmadov, Joshua Ruby, Mark Wittman, Zachary Robinson, Matthew Sharpe

University of Rochester

Updating the Gas Chromatography Methodology for Measuring Hydrogen Isotopologues at the Laboratory for Laser Energetics

Matthew Sharpe

University of Rochester

Precision mapping of laser-driven magnetic fields and their evolution in high-energy-density plasmas

Lan Gao, PM Nilson, IV Igumenshchev, MG Haines, DH Froula, R Betti, DD Meyerhofer

University of Rochester, Imperial College

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations.

Magnetic field generation by the Rayleigh-Taylor instability in laser-driven planar plastic targets

L Gao, PM Nilson, IV Igumenschev, SX Hu, JR Davies, C Stoeckl, MG Haines, DH Froula, R Betti, DD Meyerhofer

University of Rochester, Imperial College

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\sim$4-kJ, 2.5-ns laser pulses focused to an intensity of $\sim$10$^{14}$ W$/$cm$^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations.

Observation of Self-Similarity in the Magnetic Fields Generated by the Ablative Nonlinear Rayleigh-Taylor Instability

L. Gao, P. M. Nilson, I. V. Igumenschev, G. Fiksel, R. Yan, J. R. Davies, D. Martinez, V. Smalyuk, M. G. Haines, E. G. Blackman, et al.

University of Rochester, Lawrence Livermore National Laboratory, Imperial College

Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth.

Hot Spot Evolution Measured by High-Resolution X-Ray Spectroscopy at the National Ignition Facility

Lan Gao, B. F. Kraus, K. W. Hill, M. B. Schneider, A. Christopherson, B. Bachmann, M. Bitter, P. Efthimion, N. Pablant, R. Betti, et al.

Lawrence Livermore National Laboratory, Princeton Plasma Physics Laboratory, Princeton University, Laboratory for Laser Energetics, University of Rochester

Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility (NIF). The capsules were filled with DD gas with trace levels of Kr, and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr He$β$ spectra, absolutely calibrated by a simultaneous time-integrated measurement, allows inference of the electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. By matching the calculated hot spot emission using a collisional-radiative code to experimental observations, the hot spot size and areal density are determined. These advanced spectroscopy techniques further reveal the effect of W dopant in the ablator on the hot spot parameters for their improved implosion performance.

Absolute Calibration of a Time-Resolved High Resolution X-ray Spectrometer for the National Ignition Facility (invited)

Lan Gao, B. F. Kraus, K. W. Hill, M. Bitter, P. Efthimion, M. B. Schneider, A. G. MacPhee, D. B. Thorn, J. Kilkenny, J. Ayers, et al.

Lawrence Livermore National Laboratory, Princeton Plasma Physics Laboratory, Princeton University, Laboratory for Laser Energetics, University of Rochester

A high resolution, Diagnostic Instrument Manipulator (DIM)-based x-ray Bragg crystal spectrometer has been calibrated for and deployed at the National Ignition Facility (NIF) to diagnose plasma conditions in ignition capsules near stagnation times. The spectrometer has two conical crystals in the Hall geometry focusing rays from the Kr He$α$, Ly$α$, and He$β$ complexes onto a streak camera, with the physics objectives of measuring time-resolved electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. A third von Hámos crystal that time-integrates the Kr He$α$, He$β$ and intervening energy range provides in-situ calibration for the streak camera signals. The spectrometer has been absolutely calibrated using a microfocus x-ray source, an array of CCD and single-photon-counting detectors, and multiple K- and L-absorption edge filters at the Princeton Plasma Physics Laboratory (PPPL) x-ray laboratory. Measurements of the integrated reflectivity, energy range, and energy resolution for each crystal are discussed. These calibration data provide absolute x-ray signal levels for NIF measurements, enabling precise filter selection and comparisons to simulations.

Study of shock wave dynamics in strong magnetic fields

Z. J. Minaker, V. V. Ivanov, R. C. Mancini, L. S. Leal, A. V. Maximov

University of Nevada, Livermore Lawrence National Laboratory, University of Rochester

Shock waves in magnetized plasmas are central in many astrophysical systems, yet laboratory measurements have remained limited by 10–20 T. This work studies the dynamics of shock waves without and with magnetic fields as strong as 100–150 T generated by the 1 MA pulsed power machine. A shock wave in hydrogen was produced by a 0.8 ns laser pulse with intensity of 5 × 1014 W/cm2. Laser imaging diagnostics including multi-frame and two-color interferometry, shadowgraphy, and schlieren imaging providing sub-nanosecond temporal and 10 μm spatial resolution of shock wave evolution. The density of hydrogen gas was in the range of (2–10) × 1018 cm−3. Results show that without an applied magnetic field, shock waves expand symmetrically with velocities up to 1600 km/s. For shock waves in a magnetic field there is suppressed radial expansion perpendicular to the B-field and enhanced azimuthal expansion parallel to the B-field. In hydrogen, a laser-initiated ionization wave formed ahead of the shock waves. Plasma instability was observed on the front of the shock wave in the magnetic field. MHD simulations confirm that magnetic fields modify the shock wave conditions, with velocity anisotropy scaling with field strength, establishing a laboratory platform to study magnetically mediated and collisionless shock wave physics.

Inferring performance metrics for laser direct drive experiments on OMEGA

V. Gopalaswamy, L. Ceurvorst, A. Lees, D. Patel, J. P. Knauer, R. C. Shah, R. Betti

Laboratory for Laser Energetics, University of Rochester

Quantifying performance improvements on the OMEGA laser facility requires robust inference of established no-alpha performance metrics, which requires, at minimum, a model to infer the shocked fuel mass and pressure of the confined fusion plasma. In this work, we describe the methodology used to infer performance metrics on OMEGA and present the current state-of-the art model used to infer these metrics from OMEGA experiments. In particular, since neutron images of cryogenic implosions are not available on OMEGA at present, we present how x-ray sizes are determined on OMEGA using a Gaussian Process regression model and how the neutron production region's size is inferred from them. We end by benchmarking the model using synthetic data and 1-D LILAC simulations and test its experimental self-consistency across available x-ray diagnostic channels.