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 UO04: ICF: Compression and Burn IVLive Streamed
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Chair: Maria Gatu-Johnson, MIT Room: Ballroom 111 A |
Thursday, October 20, 2022 2:00PM - 2:12PM |
UO04.00001: Gamma-ray images show where the carbon is, during DT burn in NIF capsules Nelson M Hoffman, Verena Geppert-Kleinrath, Carl H Wilde, Noah W Birge, Matthew Freeman, Kevin D Meaney, Hermann Geppert-Kleinrath, Yongho Kim For carbon-ablator capsules imploded at NIF, inelastic scattering of DT neutrons on 12C nuclei produces intense gamma radiation, via the process 12C(n,n') -> γ(4.4 MeV). Images of the escaping gamma rays allow us to infer the spatial distribution of carbon near the core of the implosion, since the volume emissivity of 4.4-MeV gamma rays depends only on the product of DT neutron flux and carbon density. Often the images are fairly symmetric, and can be explained as resulting from a 1D spherical distribution of carbon. For such cases, we have developed a 5-parameter static 1D model of the “carbon cloud”, computed the resulting model gamma-ray image (including DT gamma rays) with MCNP6® transport simulations, and used Markov-chain Monte Carlo with Bayesian inference to determine probable values of the model parameters, along with their uncertainties. Some useful outputs of this procedure include the maximum density of compressed carbon during burn, and the mass and density of carbon mixed into the burning core. |
Thursday, October 20, 2022 2:12PM - 2:24PM |
UO04.00002: Progress on magnetized ignition experiments at the National Ignition Facility John D Moody, Brad B Pollock, Hong Sio, David J Strozzi, Darwin D Ho, Chris A Walsh, Elijah Kemp, Yuan Shi, Sergei O Kucheyev, Jeremy Kroll, Bernard Kozioziemski, Vincent Tang, Jay Javedani, William Stygar, Chris Provencher, Suhas D Bhandarkar, James Sater, Lisle Hagler, Burl G Logan, Brandon J Lahmann, Scott E Winters, Ed P Hartouni, Laurent Divol, Jeremy P Chittenden, Sam O'Neill, Brian D Appelbe, Aidan Boxall, Aidan C Crilly, Jonathan R Davies, Jonathan L Peebles, Arijit Bose, Shinsuke Fujioka Magnetized indirect-drive implosions of D2-gas-filled capsules on NIF show a 40% ion-temperature increase and 3.2x neutron-yield increase due to reduced electron thermal conduction [Moody, 2022 submitted]. Similar increases in hot-spot temperature and yield are expected for magnetized DT cryo-layered implosions currently being planned for NIF. This talk will summarize current NIF and Omega experiments that are investigating high-energy-density-physics issues relevant to magnetized ignition. We will also outline the status of implementing magnetized DT-layered implosions on NIF. |
Thursday, October 20, 2022 2:24PM - 2:36PM |
UO04.00003: Modeling the First Magnetized NIF Hohlraum Implosions David J Strozzi, George B Zimmerman, John D Moody, H. Sio, Chris A Walsh, Darwin D Ho, Bradley B Pollock, Chris R Weber, Gregory E Kemp We have performed 7 room-temperature hohlraum-driven implosions on NIF, with imposed magnetic fields in the capsule of 0 - 26 Tesla (J. D. Moody et al., submitted to Phys. Rev. Lett.). We have modeled these shots with the radiation-magneto-hydrodynamic code Lasnex, and developed multipliers on the laser power and cone fraction (inner / total beam power) to match observed time of peak capsule emission and hotspot x-ray shape. The values are similar to those needed for comparable BigFoot shots (C. A. Thomas et al., Phys. Plasmas 2020), and do not clearly vary with imposed field. Cross-beam energy transfer (CBET) removes the need for cone fraction multipliers, though with a lower δne/ne saturation clamp (5*10-4 – 2*10-3) than typical for current NIF platforms (~0.01). Fusion yield and ion temperature agree well with BigFoot data but less well for our platform - with or without imposed field - in an absolute sense (yields 2-6x data). The modeling is close to the measured relative effect of a 26 T field: 1 keV Tion increase, 2.7x yield increase. We are using capsule-only modeling to quantify different sources of discrepancy, such as capsule quality, longer coast time, lower capsule gas fill density, and capsule fill tube perturbation. |
Thursday, October 20, 2022 2:36PM - 2:48PM |
UO04.00004: Non-Linear Ablative Rayleigh-Taylor Instability: Increased Growth due to Self-Generated Magnetic Fields Chris Walsh, Daniel S Clark Simulations of inertial confinement fusion (ICF) capsules suggest hot-spot perturbation growth is enhanced by self-generated magnetic fields [1]. This work studies the Rayleigh-Taylor instability (RTI) with Biermann battery magnetic field generation to show how the enhanced growth depends on perturbation size and wavelength. This theory is broken into 3 key stages. First, the magnetic flux generation around a single spike is found to be proportional to the spike height (this agrees with more detailed scalings [2]). Second, the peak electron magnetization is strongly enhanced by Nernst advection to the tip of the spike, with a strong wavelength dependence. Lastly, the change in spike velocity depends on both the suppressed thermal conduction and enhanced Righi-Leduc heat-flow. The overall non-linear ablative RTI theory can then be used to estimate the impact of self-generated magnetic fields in ICF implosions, as these fields are not typically incorporated into modelling. A discussion of the potential impact of magnetic fields on high-yield experiment N210808 will also be included. |
Thursday, October 20, 2022 2:48PM - 3:00PM |
UO04.00005: Modeling high-yield magnetized implosions on the National Ignition Facility Sam T O'Neill, Jeremy P Chittenden, Aidan C Crilly, Chris A Walsh, Chris A Walsh, John D Moody, John D Moody, David J Strozzi Current experiments taking place at the National Ignition Facility are using magnetic fields of ~26 T to pre-magnetize indirectly driven gas filled capsules (symcaps) [1]. Reduction of thermal conduction due to these fields has been observed to enhance ion temperature (Ti) and neutron yield. Simulations of these experiments show that Ti is likely to be enhanced by ~1 keV and yields by a factor of ~2. Application of magnetic fields to high-yield cryogenic capsules, such as the recent NIF record yield shot, could lead to significant enhancements to fusion energy output. Simulations have been carried out using ‘Chimera’ a 3D radiation-magnetohydrodynamics code to investigate key physics questions relating to these experiments. These include changes to shock propagation and implosion shape; the impact of fields on hotspot ignition, including alpha particle magnetization; and the possible impact of magnetic fields on burn propagation in ICF capsules. |
Thursday, October 20, 2022 3:00PM - 3:12PM |
UO04.00006: Magnetized ICF for high yield, reduction of laser energy, and the generalization of the GLP with B field George B Zimmerman, Darwin D Ho, Alexander L Velikovich, John D Moody Magnetized ICF boosts the yield around ignition threshold1 and can reduce the required laser energy, without changing the capsule configuration, for high-yield implosions.2 We show that by increasing the fuel thickness and dopant level, magnetization can boost yield by 40%, in the high-yield regime, while preserving robustness. For robust implosions, yield can be boosted by 70x around ignition. To maximize the reduction of laser energy by magnetization, the dopant level is lowered, and the laser energy can be reduced by 15% while the robustness and yield are preserved. To quantify the magnetized robustness, we modify the Generalized Lawson Parameter (GLP) with the inclusion of B field. Universal ignition conditions with and w/o B field are derived and the amount of velocity reduction from magnetization can then be obtained. New physics findings, e.g., magnetized ignition condition for Ti is higher than the conventional condition of 12 keV, and the design options opened up by magnetization are presented. |
Thursday, October 20, 2022 3:12PM - 3:24PM |
UO04.00007: Hydroscaling implosions for high yield using HDC ablator Darwin D Ho, Peter A Amendt, Kevin L Baker, John L Lindl, Otto L Landen The goal of the Hydroscaling upwards1 is to increase fusion yield well past the ignition threshold by increasing the scale of the capsule from outer radius of 1128.4 mm for the current highest yield implosion N210808 to about 1200 mm. The larger capsule is driven by a lower-loss Frustraum hohlraum configuration2 with peak Tr > 300 eV and the capsule absorbed energy increases to above 300 kJ from 230 kJ of N210808. The foot of the Tr pulse is similar to that of N210808 and gives similar fuel adiabat of 3.2. Increased scale and absorbed energy increase the robustness (i.e. the Generalized Lawson Parameter GLP) of the implosion that delivers 1D yield of 17 MJ. 2D simulations including expected residual low-mode radiation asymmetries (modes 1, 2, and 4), surface and interface roughness, fill tube, and tent features give a yield > 5 MJ. Imposing a 40T seed magnetic field improves the performance noticeably by increasing the robustness, boosting the yield or reduce the required laser energy. |
Thursday, October 20, 2022 3:24PM - 3:36PM |
UO04.00008: Anomalous X-Ray Emission at Early Stages of Hot-Spot Formation in Deuterium-Tritium Cryogenic Implosions Rahul C Shah, Duc Cao, Valeri N Goncharov, Suxing Hu, Igor Igumenshchev We recently reported data from deuterium–tritium cryogenic implosions that show an onset of hot-spot x-ray self-emission at a larger shell radius than is predicted by a 1-D radiation-hydrodynamic implosion model.[1] A candidate explanation is the presence of unmodeled sources of hydrodynamic perturbations, leading to an increase of hot-spot mass at the start of deceleration. Alternatively, mistimed shock formation may relax the dense shell profile, leading to the accelerated development of the hot spot. We will review the previous results and discuss new experiments designed to arbitrate these candidate hypotheses by characterizing the emission onset for implosions with stability increased by use of a thicker initial cryogenic layer (i.e., reduced in-flight aspect ratio). [1] R. C. Shah et al., Phys. Rev. E 103, 023201 (2021).
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Thursday, October 20, 2022 3:36PM - 3:48PM |
UO04.00009: Experiments to Study the Impact of the Beam-to-Target Ratio in Direct-Drive DT Cryogenic Implosions on OMEGA Christian Stoeckl, Cliff A Thomas, Joshua Baltazar, K. A Bauer, Riccardo Betti, Duc Cao, Kristen Churnetski, Timothy J Collins, Chad J Forrest, Vladimir Y Glebov, Varchas Gopalaswamy, James P Knauer, Aarne Lees, Sean P Regan, Michael J Rosenberg, K. M Woo, Wolfgang R Theobald Experimental data and theoretical modeling indicate that the performance of laser-direct-drive cryogenic DT inertial confinement fusion implosions depends strongly on the ratio between the radius of the beams that illuminate the shell and its radius (Rb/Rt). To quantitatively study this effect, a series of shots was performed with targets of varying radii. Both the laser intensity and the stability properties of the imploding target were kept constant in these experiments. Targets of 780-μm, 870-μm, and 1020-μm diameter were irradiated with 60 overlapped beams from the OMEGA laser, each having an intensity profile with a super-Gaussian shape of the order of ~5 and a 95% encircled energy diameter of ~850 μm, scanning Rb/Rt from ~1.09 to ~0.83. A comprehensive summary of the experimental observables from both neutron and x-ray detectors and a comparison with the theoretical modeling will be presented. |
Thursday, October 20, 2022 3:48PM - 4:00PM |
UO04.00010: Progress in the Understanding of Primary Neutron Spectra Moments Brian Appelbe, Aidan C Crilly, Jeremy P Chittenden, Chad J Forrest, Sean P Regan, Maria Gatu Johnson, Alastair S Moore, David J Schlossberg Recent experiments on NIF and OMEGA have identified the presence of non-Maxwellian ion distributions in the stagnation phase of ICF experiments. The physical mechanisms generating these distributions remain poorly understood. Identification was achieved by measuring the ratio of first and second moments of the time-integrated primary neutron spectra. Theoretical models show that the measured ratio values cannot be produced by plasmas composed of Maxwellian distributions. |
Thursday, October 20, 2022 4:00PM - 4:12PM |
UO04.00011: Computational Studies of the Mounting Stalk Diameter in Direct-Drive Implosions Kenneth Anderson, Edward C Hansen, John A Marozas, Timothy J Collins, Valeri N Goncharov, Michael M Marinak, Scott M Sepke The target mounting stalk is a notable source of asymmetry in direct-drive implosions that is rarely modeled, and when modeled is generally either in 2-D or a limited 3-D geometry and/or with a simplified treatment of laser-energy propagation. A 3-D simulation platform has been developed in HYDRA to model the effect of the target mounting stalk in a full-sphere, 4p geometry with no grid symmetry assumptions and with a fully 3-D treatment of laser propagation. The effect of beam shadowing using this platform was previously discussed for a 17-mm-diam stalk.[1] A new study showing the effect of varying stalk diameter on symmetry and yield will be presented. The effect of the glue spot attaching the stalk to the capsule will also be discussed. [1] K. S. Anderson et al., Bull. Am. Phys. Soc., JO04.00003 (2021).
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Thursday, October 20, 2022 4:12PM - 4:24PM |
UO04.00012: Reconstruction of experimental core conditions of OMEGA high performance implosions Dhrumir P Patel, Riccardo Betti, Ka Ming Woo, Varchas Gopalaswamy, Rahul C Shah, Duc Cao OMEGA cryogenic shot 96806 produced a yield of 1.55 10^14 and areal density of about 160 mg/cm^2. To better understand the implosion performance, 2 dimensional simulations are used to reproduce experimental observables for this shot such as yield, areal density, hot-spot size, neutron-averaged ion temperature, emission averaged electron temperature, burn-width and bang-time. This was done by extracting hydrodynamic profiles at peak velocity from a 1-D LILAC simulation and by simulating the deceleration phase in DEC2D with imposed low mode and mid-mode of selected amplitude to match the aforementioned observables. The initial profiles are modified to mimic small yield degradation arising from laser imprinting and Helium build up in gas. Then the extrapolation to 2.0 MJ of symmetric illumination is carried out by assuming hydrodynamic scaling. In addition, the performance of scaled implosions is projected with corrected (removed) individual modes. |
Thursday, October 20, 2022 4:24PM - 4:36PM |
UO04.00013: Inertial Fusion Energy Target Designs to Capitalize on Next-Generation Laser Technologies William T Trickey, Valeri N Goncharov, Igor V Igumenschev, Timothy J Collins, Christophe Dorrer, Russell K Follett, Michael J Rosenberg, Nathaniel R Shaffer, Rahul C Shah, Alexander Shvydky, Wolfgang R Theobald, Stefano Atzeni, Francesco Barbato, Lorenzo Savino, Mike Campbell The recent demonstration of 1.3 MJ of fusion yield with laser indirect drive (LID) at the National Ignition Facility, along with progress in target performance of laser-direct-drive (LDD) inertial confinement fusion (ICF) implosions, has sparked interest in using ICF for energy production. Recent performance improvements in both LID and LDD implosions have pushed toward designs with high adiabats and high implosion velocities with a focus on effectively coupling of energy into the hot spot. This is largely because of high levels of hydrodynamic instability and the presence of laser–plasma interactions (LPI’s) that can limit laser coupling and significantly reduce the ablative drive pressure. By contrast, in the case of high-gain designs (G > 100), lower-adiabat designs with higher mass assemblies and low implosion velocities are required. Such designs are not compatible with the LPI limitations imposed by current laser technology. Development of next-generation, broadband UV laser technologies should significantly reduce the effects of deleterious LPI, significantly increasing the drive pressure while also reducing hydrodynamic instability seeding generated by imprint. It is therefore an opportune time to explore a design space relevant to IFE that will be opened up by these technologies. We present a number of target designs with wetted foam that explore this space. Additionally, a route to widening the ignition design space is investigated using “dynamic-shell” targets. |
Thursday, October 20, 2022 4:36PM - 4:48PM |
UO04.00014: Measurements of dense fuel hydrodynamic conditions in burning plasma NIF experiments using backscattered neutron spectroscopy Aidan C Crilly, Dave Schlossberg, Brian D Appelbe, Chad J Forrest, Alastair S Moore, Edward P Hartouni, Justin Jeet, Jeremy P Chittenden Measurement of the dense fuel hydrodynamic conditions, such as areal density, temperature, and velocity, during fusion burn is key in understanding the performance on inertial confinement fusion (ICF) experiments. Previous theoretical studies and experiments on the OMEGA 60 laser have shown that backscattered neutron spectroscopy can be used to directly measure dense fuel conditions during stagnation. In particular, the nT backscatter edge was measured and analysed, this spectral feature is produced by the 180 degree scattering of 14 MeV DT neutrons from tritons in the fuel. As recent ICF experiments on NIF enter the burning plasma regime, evidence for changing dense fuel conditions is looked for in the nT backscatter edge. In simulation, hotspot self-heating leads to the dense fuel being heated by thermal conduction and alpha deposition. In addition, burn will continue into the expansion phase such that the dense fuel will be exploding outwards at the time of peak neutron production. The NIF neutron time-of-flight spectroscopic measurements of the nT edge show evidence of these phenomena. A simple model is used to extract velocities and apparent temperatures of the dense fuel. |
Thursday, October 20, 2022 4:48PM - 5:00PM |
UO04.00015: Takeaways from shot N210808 Baolian Cheng, Paul A Bradley The National Ignition Facility (NIF) has made significant progress recently in creating a burning plasma. Shot N210808 on the NIF is the first time that Lawson's ignition criterion was achieved in the laboratory. While researchers continue making design changes in an effort to further increase target gain or implosion robustness so as to achieve ignition in the near future, the authors performed a careful study of shot N210808. Our study indicates that the remarkable success of shot N210808 has just revealed the immense challenge of the present N210808 capsule design to achieve ignition and propagating burn. The experimental data from N210808 show that it is nearly impossible to have burn propagation without terminating the thermonuclear burn in the initial burning hot spot. The mass swept up by the explosion shock wave adjacent to the hot spot is multiple times that of the hot spot, and thus is too large to be heated to the point of having self-sustained thermonuclear burn. As a result, heating via nuclear energy released from the burning hot spot is far less than the energy required to burn the fuel mass swept up by the expanding shock wave. Therefore, innovative revisions of the N210808 capsule design are required for achieving ignition and significant gain. Quantitative analysis and suggestions for improved capsule designs are presented in this work (LA-UR-22-25882). |
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