Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session PO04: Hohlraum and X-ray Cavity PhysicsLive Streamed
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Chair: Dave Strozzi, LLNL; Steve MacLaren, LLNL Room: Ballroom 111 A |
Wednesday, October 19, 2022 2:00PM - 2:12PM |
PO04.00001: Probing the origins of hohlraum wall losses in ICF Michael S Rubery, Alastair S Moore, William A Farmer, Mordy Rosen, Otto L Landen, Marilyn B Schneider, Denise E Hinkel, James S Ross, Jamison Jew, Clay Henning, Martin Havre, Jason Wall, Waltteri Vakki, Fernando Silva, Mark Ratledge, Lorenzo Inandan, Vincent Ho, Eric Gaut Indirect Inertial Confinement Fusion (ICF) experiments at the National Ignition Facility (NIF) convert laser to x-ray energy using gold or depleted uranium hohlraums the dynamics of which strongly impact capsule implosion symmetry and ultimately fusion performance. Laser power multipliers, equivalent to a ~10-20 % in laser energy, are routinely employed in simulations to match experimental observables, such as x-ray flux reported by the Dante calorimeter and fusion bang-time. |
Wednesday, October 19, 2022 2:12PM - 2:24PM |
PO04.00002: Recent experiments to constrain opacity and heat capacity of gold William A Farmer, Mordecai D Rosen, Hui Chen, Alastair S Moore, Michael S Rubery, George F Swadling, Daniel S Clark, Denise E Hinkel, Otto L Landen, Steve A MacLaren, Jose L Milovich, John D Moody, Katya Newman, James S Ross, David J Strozzi, Marilyn B Schneider, Chris R Weber In radiation-hydrodynamic simulations of indirect-drive inertial confinement fusion (ICF) targets, laser power multipliers are routinely employed to tune the simulations to experimental observables like x-ray flux and capsule bang-time. Since the laser power is measured to accuracy well below the needed multipliers, this suggests that the simulated partition of energy in the hohlraum is incorrect. One possible reason for this is that the amount of energy absorbed by the gold wall is larger than predicted. Greater wall loss could occur if the gold opacities or heat capacities used in the simulations are sufficiently incorrect. Here, we report on modeling of a recent gold burn-through experiment which constrains the product of multipliers on both the heat capacity and opacity. We then apply these constrained multipliers to a series of vacuum hohlraum experiments to illustrate the degree to which such an approach can be used to reduce the need for laser power multipliers. |
Wednesday, October 19, 2022 2:24PM - 2:36PM |
PO04.00003: Modeling NIF hohlraum experiments using wall opacity multipliers instead of laser power multipliers Daniel S Clark, Jose L Milovich, William A Farmer, Steve A MacLaren, Mordecai D Rosen, David J Strozzi, Chris R Weber Hohlraum experiments on the National Ignition Facility have shown measured x-ray drives consistently lower than predicted by simulations. This deficit has traditionally been addressed by artificially reducing the laser power incident to the hohlraum in the simulation by 10% or more. This modeling approach can be successful at matching observed implosion shock timing and bang times but invokes a decrement in the delivered laser energy many times the experimental uncertainty and also sacrifices accuracy in modeling the hohlraum plasma conditions. Here the prospects for matching observed hohlraum performance using a decrement in the hohlraum wall emissivity and/or an increment in the hohlraum wall specific heat, but no laser power multipliers, is explored for recent NIF experiments. Combined variations in the wall emissivity and specific heat not far outside of the expected 10% uncertainty are found to be sufficient to approximately match experimental shock timing measurements and bang times. |
Wednesday, October 19, 2022 2:36PM - 2:48PM |
PO04.00004: The measurement of early time laser beam reflection inside a cylindrical hohlraum on the National Ignition Facility Hui Chen, Tod Woods, Nuno Lemos, Marilyn B Schneider, Mordy Rosen, Joe Holder, Nobuhiko Izumi, Michael S Rubery, Steven Ross, Denise E Hinkel, John D Moody, Otto L Landen, Katya Newman, Jared C Delora-Ellefson, Carl M Hardy, Nick Hash, Nathan Masters, Weston Montgomery, Tom Zobrist In a NIF cylindrical hohlraum, any specular reflection off the wall from the outer cone (incident angle of 50° and 45° relative to the wall) laser beams glints onto the capsule. If the glint power is sufficiently large during the picket (early time) of the laser pulse, it may seed high-mode perturbations that can grow during the implosion. To quantify the "glint" power on the capsule during the picket by the outer beams, we performed dedicated experiments on NIF using a witness foil as a surrogate for the capsule in a half-hohlraum target. The glint light intensity is measured via the time-resolved K-shell emission of the irradiated witness plate which is benchmarked to an external reference foil of the same material irradiated with two known laser powers. Measured glint power is lower than predicted by the model using low electron conduction flux limiters (f = 0.03). Detailed results of the measurement and its implications to the ICF experiments will be presented. |
Wednesday, October 19, 2022 2:48PM - 3:00PM |
PO04.00005: High-resolution integrated Eulerian simulations of hohlraum dynamics and capsule implosions Brian M Haines, Carlos A Di Stefano, Ryan S Lester, Joshua P Sauppe, David Stark The xRAGE Eulerian rad-hydro code has undergone improvements to enable credible hohlraum modeling[1]. xRAGE’s adaptive mesh refinement makes it uniquely suited to study small features, such as the 45nm capsule support tent, on hohlraum dynamics. Simulation comparisons to benchmark hohlraum experiments[2] provides confidence in our modeling. Comparisons to plasma interpenetration experiments[3] show improved agreement with plasma transport models[4]. We have also modeled layered capsule implosions[5] to evaluate the impact of the tent, cross-beam energy transfer[6], plasma transport[4], external hardware, and mixed material conductivities. All of these impact the shape of the implosion, though they can’t explain observed bang time discrepancies. The tent traps radiation at early time, producing additional drive on the equator. The agreement with measured X-ray flux data is sensitive to mixed material conductivity methodologies, and different treatments provide better agreement at early and late times. |
Wednesday, October 19, 2022 3:00PM - 3:12PM |
PO04.00006: Developing an Infrastructure for Automated Tuning of Hohlraum Simulations Ryan S Lester, Brian M Haines, Joshua P Sauppe, John Kuczek Indirect-drive implosions at the National Ignition Facility (NIF) have demonstrated laboratory |
Wednesday, October 19, 2022 3:12PM - 3:24PM |
PO04.00007: First indirect drive Inertial Confinement Fusion Campaign on Laser Megajoule Stephane Liberatore, Pascal Gauthier, Jean-Luc Willien, Paul-Edouard Masson-Laborde, Olivier Poujade, Raphael Riquier, Stephane Laffite, Franck Philippe, Xavier Vaisseau, Olivier Landoas, Bruno Villette This study concerns the first ICF experiments on the LMJ facility in the indirect drive scheme. Approximately 150 kJ of laser energy was distributed on 48 beams (12 quads) arranged in two cones. The target consisted of a gold vacuum rugby shaped hohlraum and a plastic capsule located at its center, filled with deuterium gas fuel. With 12 quads, the laser irradiation on the wall generated a three-dimensional (3D) x-radiation flux around the capsule creating 3D deformations on the plastic shell. This constraint forced the design of a robust target (relatively thin ablator, around 40 µm) with a short laser pulse (3 ns). Full-integrated 3D simulations with the radiation-hydrodynamics code TROLL permitted at the same time to build targets and to interpret data (mainly radiation temperature, x-ray images and neutron yield). A good agreement was reached between 3D calculations and experiments, especially for the number of neutrons, which was about 1011. |
Wednesday, October 19, 2022 3:24PM - 3:36PM |
PO04.00008: ICF hohlraum experiments on the LMJ facility Stephane C Laffite, Witold CAYZAC, Sylvie Depierreux, Pascale Fremerye, Marion Lafon, Stephane Liberatore, Paul Edouard Masson Laborde, Franck Philippe, Raphael Riquier, Veronique Tassin, Xavier Vaisseau, Jean Luc Willien We propose here to present a summary of our ICF hohlraum experiments on the LMJ laser facility, from the first one with neutron production to our next milestone, in a few years. The LMJ laser is now capable of producing up to 270 kJ of UV energy on target in 80 beams (20 quads) arranged in four cones, consisting of 5 quads in each cone. We first show how the beam arrangement naturally leads to a rugby shaped hohlraum. Then, we briefly present the first neutron production in a vacuum rugby hohlraum followed by the first gas fill hohraum shots. Finally, we present our future designs for the next years, as more energy and beams will be available. We show how trade-offs must be made between the irradiation symmetry on the capsule and the deleterious effects of laser plasma interaction which could become a main concern with the laser energy increase. |
Wednesday, October 19, 2022 3:36PM - 3:48PM |
PO04.00009: Modeling of nonlocal electron transport in laser-driven double-ablation fronts Kevin H Ma, Mehul V Patel, Eric Johnsen At laser intensities relevant to ICF, steep temperature gradients lead to nonlocal electron thermal transport. This is important for laser-plasmas because energy is transported into the denser plasma via electron and radiation thermal transport. For low- to mid-Z materials, these transport mechanisms are dominant at different locations, producing two distinct fronts in the temperature and density profiles known as double-ablation fronts (DAF)1. This work studies the effect of nonlocal electron transport on the development of DAF features in planar foils. |
Wednesday, October 19, 2022 3:48PM - 4:00PM |
PO04.00010: Design of a long pulse, low adiabat drive in a low gas-fill hohlraum Jose L Milovich, Nobuhiko Izumi, Otto L Landen, Denise E Hinkel, Tilo Doeppner We have revisited an earlier low adiabat design that employs a (non-crystalline) CH ablator1 (allowing higher compression for a given laser energy at the cost of ~2x longer laser pulses) in a low-density gas-filled hohlraum to effect more benign plasma conditions. Recent experiments2 using a subscale CH target suggest that the dynamics of wall plasma ablation using low picket and low long trough pulses differ from typical HDC pulses. Specifically, the ablated wall plasma slows down during the trough delaying its intrusion onto the path of the inner beams. This effect when combined with the use of cross-beam-energy-transfer (CBET) is effective at controlling the low-order drive mode l=2. Additionally, these experiments introduce time-staggering of the two outer cone beams powers of the NIF laser system. Measurements of the inflight capsule symmetry show that this technique is successful at limiting the low-mode l=4 swings. In this paper, we will present simulations of these experiments showing that our model predicts the observed data reasonably well and explore possible directions to scale up to an ignition design. |
Wednesday, October 19, 2022 4:00PM - 4:12PM |
PO04.00011: ICF image restoration using Iterative Regularization methods Naima Naheed, Zhehui Wang, Bradley Wolfe, Shanny Lin Inertial confinement fusion (ICF) is an approach to fusion that relies on the inertia of the fuel mass to provide confinement. A capsule generally is a spherical shell filled with low-density gas (~1.0 mg/cm3). The shell is composed of an outer region, which forms the ablator, and an inner region of frozen or liquid deuterium-tritium (DT), which forms the main fuel. Energy from a driver is delivered rapidly to the ablator, which heats up and expands. As the ablator expands outward, the rest of the shell is forced inward to conserve momentum. X-ray imaging diagnostics revealed correlated signatures of azimuthal implosion asymmetry. This low-mode asymmetry degrades hot-spot conditions at peak convergence that limits implosion performance. One biggest challenge is to retrieve useful information and insight from sparse and noisy ICF images. In this project, a linear inverse problem of the form b=Ax+n is investigated, where b represents the vector of the blurred image and A represents the blurring matrix. Given A and b, the aim is to compute an approximation of the unknown x. Iterative regularization is a good alternative to direct regularization method. In this project two different iterative regularization approaches are explored. The hybrid flsqr and heuristic total variation methods have demonstrated a good mathematical basis for image restoration of ICF images. An efficient regularized solution is produced when the iteration is terminated at minimum error. Out of all the methods mage restoration algorithms, only these two are compared because of their outstanding performance on ICF images. Algorithm validation use synthetic images with noises, and then compared with a synthetic image which do not have any noise. To verify the image quality, SSIM scores are computed. Initial analysis of experimental data using the validated algorithms are also given. |
Wednesday, October 19, 2022 4:12PM - 4:24PM |
PO04.00012: Investigation of Hohlraum Fields with Monoenergetic Proton and Deuteron Radiography Jacob A Pearcy, Graeme D Sutcliffe, Timothy M Johnson, Benjamin L Reichelt, Skylar G Dannhoff, Andrew Birkel, Daniel H Barnak, Richard D Petrasso, Chikang Li A better understanding of laser-driven hohlraum plasmas is critical for the continued development and improvement of ICF experiments. For such plasmas, hydrodynamic calculations are successful in describing the evolution of the plasma at early times. However, at late epochs, kinetic effects become dominant and the hydrodynamic description is insufficient. In these hohlraums, self-generated electric and magnetic fields play an important role in determining plasma dynamics and evolution; however, it has largely been uncertain whether electric fields or magnetic fields dominate these systems. To explore this question, we conducted several experiments at the OMEGA laser facility, using tri-particle (DT3He) monoenergetic proton and deuteron radiography to probe laser-driven vacuum-filled gold and plastic hohlraums. In our analysis, we utilized reconstructive methods to infer information about the structure of electromagnetic fields in the hohlraum, as well as to quantify the relative magnitudes of proton deflections due to electric and magnetic fields, respectively. |
Wednesday, October 19, 2022 4:24PM - 4:36PM |
PO04.00013: Improving hohlraum efficiency at the National Ignition Facility with smaller cylinders Christopher V Young, Joseph E Ralph, Tod Woods, Andrea L Kritcher, Arthur Pak, Thomas D Chapman, Hui Chen, Tilo Doeppner, Shahab F Khan, Katya Newman, Michael S Rubery, Debra A Callahan, Omar A Hurricane, Otto L Landen Recent inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) have set records for fusion energy liberated in a laboratory setting, reaching burning plasma and near ignition conditions. Some of these experiments were conducted with the Hybrid-E cylindrical hohlraum platform, consisting of a 6.4 mm diameter hohlraum with 3.1 mm diameter “laser entrance holes” (LEH’s) driving a CVD diamond capsule of inner radius 1.05 mm. This work represents the next step in improving cylindrical hohlraum efficiency at NIF by placing the same sized capsule in a 6.2 mm diameter cylinder with 2.7 mm diameter LEH’s. This effectively increases the available x-ray drive energy by ~6% by reducing hohlraum losses. Novel beam pointing schemes are required to clear the smaller LEH and implosion symmetry control is accomplished using cross-beam energy transfer (CBET) via laser wavelength detuning (Δλ) between the inner and outer cones. Early tuning experiments and simulations with the radiation-hydrodynamic code HYDRA will be discussed. |
Wednesday, October 19, 2022 4:36PM - 4:48PM |
PO04.00014: Direct measurement of ion-acoustic wave growth rates due to the return current instability Avram Milder, Jeffery Zielinski, Joseph D Katz, Wojciech Rozmus, Dana H Edgell, Aaron M Hansen, Mark Sherlock, Colin J Bruulsema, John P Palastro, David Turnbull, Dustin Froula Return current instability (RCI), the process by which a cold current is driven to compensate for heat flux leading to ion-acoustic turbulence, has been proposed as a mechanism limiting the heat flux in inertial confinement fusion experiments. Here, we present measurements of the ion-acoustic growth rate driven by the return current instability and show it is inherently connected to non-local transport. Thomson scattering was used to measure a maximum growth rate of 5.1× 10 9 Hz, which was three times less than classical Spitzer-Harm theory predicts. The measured plasma conditions suggest that the electrons are non-local and Vlasov-Fokker-Plank (VFP) simulations that account for this non-locality reproduce the measured growth rates. Furthermore, the threshold for the return current instability was measured (δ T =0.017 ±0.002) to be in good agreement with previous theoretical models. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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