Session PI02: Invited: DEIA II and Inertial Confinement Fusion III

Introducing fusion awareness to K-12 students and their communities through culturally relevant STEM education enrichment

Fusion energy is poised to be a leading clean energy sector. Several advancements have occurred in recent years, including the first demonstration of fusion ignition at Lawrence Livermore National Laboratory's National Ignition Facility and the White House Summit on Developing a Bold Decadal Vision for Commercial Fusion Energy. These milestones signal substantial progress toward fusion energy's commercialization. The mission of Energy for the Common Good is to foster the acceptance of fusion energy by diverse stakeholders prior to its commercialization, with timely impact on mitigating the climate crisis. The greater the degree of fusion energy's acceptance among stakeholders, the more rapidly it can be integrated into the electrical grid, ensuring widespread access to its advantages. Fusion awareness is a fundamental prerequisite for acceptance. One of the primary ways we've sparked fusion awareness is through our Generation Fusion education program, an informal K-12 STEM enrichment after school program. We prioritize students residing in communities on the front lines of the climate crisis. The fusion sector presents a unique opportunity to actively engage and integrate vulnerable communities in its development. We began disseminating fusion awareness to fifth grade elementary school students, the majority of whom had no prior exposure to fusion or other physics concepts. Taking this into consideration, our students obtained understanding about the climate crisis, clean energy, and fusion energy through culturally relevant experiential learning methods including interactive activities, direct engagement with subject matter experts, and project-based learning. Learning about fusion and other clean energy sources has given our students hope for their futures and inspired them to participate in creating solutions. We've found that our students naturally spread their newfound fusion awareness to family, friends, community members, and school district personnel. This prompts communities to learn more about fusion and explore opportunities in this nascent clean energy sector. This session will define cultural relevance and outline optimal approaches to center students and communities. It will address both enhancing fusion awareness and fostering partnerships in informal physics education.   

A robust reconstruction of three-dimensional asymmetries in ICF implosions at the NIF, using a physics model and neural networks applied to multiple heterogeneous data sources

Three-dimensional (3D) asymmetries represent major performance-degradation mechanisms in inertial-confinement fusion (ICF) implosions at the National Ignition Facility (NIF).  These asymmetries can be diagnosed with the three neutron imaging systems (NIS) fielded with orthogonal views to the implosion.  Conventional tomographic reconstructions are typically used to reconstruct the 3D morphology of the hot-spot and surrounding high-density fuel-shell in an implosion using NIS data, but the reconstruction problem is ill-posed with only three imaging lines of sight.  Under certain assumptions, relative low-mode asymmetries of the surrounding high-density fuel-shell can also be diagnosed with the suite of real-time neutron activation diagnostics (RTNADs) and the neutron time-of-flight (nTOF) detectors.  In this work, a machine-learning based 3D reconstruction technique has been developed and used to overcome these limitations by combining information from NIS, RTNAD and nTOF data.  In this reconstruction technique, a physics model combined with a group of neural networks is used to analyze the NIS, RTNAD and nTOF data to robustly reconstruct the 3D morphology of the hot-spot and surrounding high-density fuel-shell in a NIF implosion.  This technique provides new insights about the origins of the 3D asymmetries in an implosion, information that cannot be obtained from the different data sources individually.  In this presentation, development and use of this technique will be discussed, and how it will be used to guide the program toward minimizing asymmetries in ICF implosions and achieving higher performance.   

Three-Dimensional Reconstruction of Inertial Confinement Fusion Hot-Spot Plasma from X-Ray and Nuclear Diagnostics on OMEGA

Multidimensional effects limit the neutron yield and the compressed areal density of laser-direct drive-inertial confinement fusion implosions on the OMEGA Laser System with layered deuterium–tritium cryogenic targets. Low-mode asymmetry studies have concentrated on the reduced performance caused by an increasing mode-1 amplitude perturbation, [1,2] but the effect from the mode-2 perturbations requires a closer examination. A comprehensive 3D reconstruction technique to infer hot-spot and shell conditions at stagnation from four x-ray and nine neutron detectors distributed around the target chamber will be presented. Neutron diagnostics, providing measurements of the neutron yield, hot-spot flow velocity, and ion-temperature distribution, are used to infer the mode-1 perturbation at stagnation. The x-ray imagers record the shape of the hot-spot plasma to diagnose mode-1 and mode-2 perturbations. [3] A deep-learning convolutional neural network [4] trained on an extensive set of 3D radiation-hydrodynamic simulations [5] is used to interpret the x-ray and nuclear measurements to infer the 3D plasma profiles of the hot spot. Three-dimensional reconstructions of implosions are used to infer the amount of laser energy coupled to the hot-spot plasma and the perturbations to the plasma profiles caused by low-mode asymmetries. The dependence of the hot-spot flow velocity, ion temperature asymmetry, and neutron yield on low-mode asymmetries is derived from a parametric study of the 3D simulation database. This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number(s) DE-NA0004144.

 

Collaborators: K.M. Woo, W. Theobald, R. Betti, L. Ceurvorst, C.J. Forrest, V. Gopalaswamy, P.V. Heuer, S.T. Ivancic, J.P. Knauer, A. Lees, M. Michalko, M.J. Rosenberg, R.C. Shah, C. Stoeckl, C.A. Thomas, and S.P. Regan

Applying dielectric coatings and enhanced input parameters to generate a stable, high performing MagLIF configuration

.The Magnetized Liner Inertial Fusion (MagLIF) platform [1,2] requires three critical inputs to achieve robust fusion conditions: an applied axial magnetic field that provides thermal insulation, laser preheat that reduces convergence requirements, and a z-pinch implosion of a solid metal liner, that provides the PdV work and confinement of the fuel. In recent years, improving these capabilities has been a focus of the MagLIF efforts [2,3,4] on the Z machine, enabling enhanced performance and scaling studies. Although fusion yields achieved in experiments increased, they did not achieve the possibilities predicted by ideal 2D simulations with these improved capabilities.

 

State-of-the-art 3D HYDRA MHD modeling of experiments performed on Z show the magneto-Rayleigh-Taylor instability significantly degrades implosion quality compared to 2D simulations and disrupts expected scaling to higher currents. To improve stability, we have introduced dielectric coatings aimed at reducing instability seeds [5]. To simulate this dielectric, we have developed a simple model to transition the coating from insulator to conductor guided by comparisons to experimental radiographs of imploding coated liners. Guided by insights from 3D modeling, recently two aspect ratio 9 (AR=r_out/\delta_liner) dielectric coated integrated experiments were performed combining improved preheat (~ 2.3 kJ), improved current coupling (18 MA), and increased applied field (15 T), producing record D-D neutron yields roughly a factor of two greater than the previous record. Initial analysis of the morphology also shows improved stability compared to uncoated liners driven with 20 MA. Beyond this successful demonstration, we believe the platform can be further improved with higher quality targets, optimization of the dimensions and reduced convergence ratio.   

Voltage pre-pulse as a tool for lowering anode electron losses in magnetically insulated transmission line

The development of magnetically-insulated transmission lines (MITL) was a singular achievement in pulsed power. On Z today at Sandia National Laboratories, MITLs routinely deliver tens of terawatts of electric power to a small volume for inertial-confinement fusion, radiation physics, astrophysics, and other HEDP experiments. MITL designs have largely relied on demonstrated experimental performance and, most recently, on validated circuit simulations to keep the power flow losses within acceptable levels. 

 

One of the desired parameters for Z and for all future pulsed-power installations is to keep the anode heating in MITLs below 400°C. When a high-voltage pulse enters the MITL and the cathode starts to spontaneously emit electrons at about 200 kV/cm, these electrons are not initially magnetically insulated and deposit their energy to the anode. With present MITL designs on Z, these onset electron losses last for several tens of nanoseconds and do not deposit a significant amount of heat into the anode. However, when scaled to larger high-current drivers, these initial electron losses can lead to significant anode heating that may degrade MITL performance and limit the total power delivered to the load.

 

We have demonstrated in simulations, for the first time, that the introduction of a voltage pre-pulse into the MITL significantly reduces or even eliminates these initial electron losses. The voltage pre-pulse, when properly designed, keeps the MITL voltage below the emission threshold while enabling the gradual buildup of MITL current and magnetic field. By the time the main voltage pulse enters the MITL, the emitted electrons experience more cathode current and become magnetically insulated in a shorter amount of time. This effectively results in less current being deposited into the anode, allowing for more robust MITL operation. The proposed method may increase the total current delivered to the load on Z today by safely redesigning the existing 4-level MITL and could have a significant impact on the design of future high-current drivers.   

Assessing explanations for unexpected fuel-ablator mixing measurements in HDC implosions at the NIF

Inertial confinement fusion (ICF) implosions using high-density-carbon (HDC) ablators have achieved ignition and delivered record fusion yields. At the same time, there are signs that these implosions have significant mixing of the HDC ablator into the dense fuel. Such mixing can reduce compression and might also end up limiting the fuel burn-up fraction as designs push to higher performance. Mixing of fuel and ablator is a complex process that depends on the integrated impact of many factors, including the radiation drive history, ablator and fuel material properties, and instability seeds. Using simulations that vary these factors within expected uncertainties, here we show how in-flight mixing data from high-resolution radiography of HDC implosions at the National Ignition Facility (NIF) challenge current modeling of instability. While high-resolution mixing simulations reasonably match experiments for implosions with undoped ablators or ablators with a buried tungsten dopant layer, this is not the case for so-called W-inner capsules where the dopant extends all the way to the fuel-ablator interface. High dopant W-inner implosions are predicted by simulations to be much more stable than observations suggest, resulting in significant optical depth discrepancies between simulation and experiment. These results suggest more pernicious instability seeds than expected, or unexpected deviations in modeling inputs such as ablator opacity or drive history. We introduce a new planned series of in-flight radiography measurements, designed to help disambiguate potential mechanisms for these surprising results, in part by constraining in-flight shell opacities.