Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session GO04: ICF: Hohlraum PhysicsOn Demand
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Chair: Hui Chen, Lawrence Livermore National Laboratory Room: Rooms 304-305 |
Tuesday, November 9, 2021 9:30AM - 9:42AM |
GO04.00001: Observation of hydrodynamic processes of radiation-ablated plasma in a small-scale hole Hang Li, Jiamin Yang, Tianming Song In the hohlraum used in laser indirect-drive inertial confinement fusion experiments, hydrodynamic processes of radiation-ablated high-Z plasma have a great effect on laser injection efficiency, radiation uniformity and diagnosis of hohlraum radiation field from diagnostic windows (DW). To study plasma filling in the DWs, a laser-irradiated Ti disk was used to generate 2-5 keV narrow energy band X-ray as the intense backlighter source, and laser-produced X-ray in a hohlraum with low-Z foam tamper was used to heat a small-scale hole surrounded by gold wall with 150 μm in diameter and 100 μm deep. The gold plasma hydrodynamic movement in the small-scale hole was measured by an X-ray framing camera and the results are analyzed. Quantitative measurement of the plasma areal density distribution and evolution in the small-scale hole can be used to assess the effect of plasma filling on the diagnosis from the DWs. |
Tuesday, November 9, 2021 9:42AM - 9:54AM |
GO04.00002: Design of burning plasma in HYBRID-E and future experiments Andrea L Kritcher, Alex B Zylstra, Debra A Callahan, Omar A Hurricane, Joseph E Ralph, Arthur E Pak, Chris Weber, Daniel S Clark, Christopher V Young, Daniel T Casey, Kevin L Baker, Pravesh K Patel, Steven Ross, Harry F Robey, Matthias Hohenberger, Tilo Doeppner, Denise E Hinkel, Laurent Divol, Otto L Landen, Richard P Town, Mark C Herrmann, John C Edwards One of the last remaining milestones in fusion research before reaching ignition is creating a burning plasma state, where alpha particles from deuterium-tritium (DT) fusion reactions redeposit their energy as the dominant source of heating in the plasma. Recently we have delivered more energy to the hot spot than ever before, while maintaining the extreme pressures required for inertial confinement, which resulted in a burning plasma state and a record ICF fusion energy of 170kJ. This was achieved by developing more efficient hohlraums to symmetrically implode larger fusion targets (1050um inner radius High density Carbon ablators containing 65um thick DT) with long laser pulses designed for lower adiabat, compared to previous experiments. Symmetry was controlled by moving energy between laser beams by wavelength detuning in cylindrical hohlraums, allowing for these larger implosions to be driven at NIF's present laser energy and power capability. In this talk we present the design of these implosions, radiation hydrodynamics simulations of the hot spot burning plasma conditions, and future improvements. Examples of future improvements leverage further development of hohlraum efficiency by reducing the size of laser entrance holes. |
Tuesday, November 9, 2021 9:54AM - 10:06AM |
GO04.00003: Measurements of Improved Hohlraum Efficiency for Near Term Burning Plasma Designs Joseph E Ralph, Andrea L Kritcher, Tod Woods, Debra A Callahan, Tilo Doeppner, Matthias Hohenberger, Alex B Zylstra, Hui Chen, Shahab Khan, Michael S Rubery, Omar A Hurricane, Otto L Landen Experiments conducted on the NIF using a 420 TW, 1.7 MJ Hybrid E design (see A. Zylstra invited) 3-rise laser pulse and a pure gold hohlraum have demonstrated an increase in radiation temperature by 20 eV from 292 to 312 eV. The experimental results show the systematic increase in radiation temperature with decreasing diameter of the laser entrance hole from 3.64 mm to 3.1 mm. A 1.1 mm inner radius high density carbon ablator filled with deuterium and Helium-3 was used to assess the performance gains and impact on implosion symmetry. Results show the higher radiation temperatures led to increases in velocity measured through in-flight radiography and peak x-ray core emission time, a doubling of the DD fusion yield and a 15% increase in hot spot temperature. These increases in hohlraum efficiency were obtained while maintaining P2 symmetry within 7 microns of round. Results from hydrodynamic simulations will be shown and compared to experimental results. Simulations, closely matching the experimental results indicate these improvements could increase energy to the capsule in a hybrid E like design from 214 presently to as high as 330±20 kJ. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. |
Tuesday, November 9, 2021 10:06AM - 10:18AM |
GO04.00004: Progress in Frustraum Research on the NIF Peter A Amendt, Kevin Baker, Darwin Ho, Shahab F Khan, Nino Landen, John Lindl, Yuan Ping, Steven Ross, Vladimir Smalyuk The delivery of x-ray capsule absorbed energy Ecap greater than 300 kJ can improve ignition performance margins and tolerance to high fuel adiabats. The Frustraum hohlraum geometry consists of a pair of joined cones at the equator to promote high Ecap while delivering adequate drive symmetry [1]. The inclined angle of the hohlraum wall (~23°) reduces the outer-beam spot intensity and hence high-Z wall “bubble” blow-in speed, and potentially increases outer-cone specular glint and CBET to the inner beams for improved inner-cone laser propagation to the equator at late time. The large diameter of the Frustraum (>9 mm) accommodates a large capsule of 2.4 mm inner diameter for high Ecap while providing reduced hohlraum filling. A recent campaign on the NIF has established the Frustraum as a robust hohlraum platform that delivers symmetric implosions, high capsule implosion speeds, and low laser backscatter. The first DT-layered implosion in a Frustraum (N210117) met all performance goals while delivering >1016 neutrons and yield amplification ~2. A survey of the Frustraum validation effort, resulting spinoff ignition campaigns, and updates on the latest data are presented. [1] P. Amendt et al., Phys. Plasmas 26, 082707 (2019). Prepared by LLNL under Contract DE-AC52-07NA27344. |
Tuesday, November 9, 2021 10:18AM - 10:30AM |
GO04.00005: High-Volume and -Adiabat Capsule (HVAC) experiments using advanced hohlraums Yuan Ping, Peter A Amendt, Kevin L Baker, Darwin Ho, Vladimir Smalyuk, Otto L Landen, John D Lindl, David J Strozzi, David N Fittinghoff, Shahab Khan, Annie L Kritcher, John D Moody, Arthur E Pak, James S Ross, Michael Stadermann, Robert E Tipton, Brandon Woodworth, Kevin Meaney Recent experiments using advanced hohlraums have demonstrated 20-30% energy coupling, or 300-500kJ, to capsules with diameters 2.5-3.4mm on the NIF (Ping et al. Nature Phys. 15, 138, 2019; Phys. Plasmas, 27, 100702, 2020; Nuclear Fusion, 2021). Such a high energy coupling efficiency makes it possible to explore a single-shell volume ignition scheme named HVAC, where the entire DT fuel forms a large hot spot and the confinement is provided by the remaining ablator shell (P. Amendt et al., Phys. Plasmas 27, 122708, 2020). The advantages over the conventional central hot spot ignition include lower convergence requirement, higher adiabat to suppress instabilities, less conduction loss, longer confinement time, and more tolerance to defects. 2D simulations have shown promising performance in yield, symmetry and instability mitigation. A set of NIF shots has been planned and the initial experimental results will be presented. The prospect of HVAC as a complementary path toward ignition will also be discussed. This work was performed under the auspices of the US DOE by LLNL under contract number DEAC52- 07NA27344. |
Tuesday, November 9, 2021 10:30AM - 10:42AM |
GO04.00006: Achieving a symmetric, low adiabat CH implosion in a low-gas fill hohlraum* Jose L Milovich, Otto L Landen, Denise E Hinkel, Nobuhiko Izumi, Tilo Doeppner To reach ignition in inertial confinement fusion (ICF), the burning central fuel must be surrounded by a symmetric shell of high areal mass, to maximally capture the energy of the produced fusion products. In indirect drive, this needs a symmetric hohlraum x-ray drive during the entire laser pulse, a requirement that is challenging in low-gas fill hohlraums (proven to reduce Raman and Brillouin backscatter losses) driven by long laser pulses, typically used in high-compression low-adiabat CH targets. Specifically, the control of the low-order mode 2 is difficult due to hohlraum wall expansion limiting the inner beam transport, and outer beams may be stopped by the endcap blow-off. Additionally, larger excursions of the outer beam spots lead to significant swings in mode 4 which may cause severe shell areal density variations at stagnation. In this talk, we contend, using simulations, that these problems can be efficiently overcome by larger laser-entrance-holes and outer beam time staggering. Furthermore, we show that the dynamics of laser-induced wall ablation is different for pulses with long troughs, permitting an effective control of inner beam propagation. As a result, we show that a symmetric high-compression CH design driven by a 1 MJ-class laser is possible. |
Tuesday, November 9, 2021 10:42AM - 10:54AM |
GO04.00007: Improving inner-cone beam transport in hohlraums by azimuthally staggered in time outer-cone beams at the National Ignition Facility Nobuhiko Izumi, Tilo Doeppner, Jose L Milovich, Otto L Landen, John D Moody, Thomas R Dittrich, Denise E Hinkel, Brian J MacGowan, Debra A Callahan, Cohl Vardon Houldin Hatala, Scott Vonhoff, Jeremy J Kroll, Katya Newman, James S Ross Hohlraums with low density gas fill (< 0.6 mg/cc) have been used frequently because of their high energy coupling. However, because of reduced tamping, the ablated wall material (bubble) penetrates further into the interior of the hohlraum and interferes with the inner cone beam transport at the end of the pulse. Thus, a low adiabat designs (requiring longer pulses) in a low gas-fill density hohlraum (having faster bubble growth) are not, in principle, compatible. |
Tuesday, November 9, 2021 10:54AM - 11:06AM |
GO04.00008: Impact of external LEH hardware on implosion shape and laser-to-hohlraum coupling in indirect drive implosions at the National Ignition Facility* Tilo Doeppner, Steve A MacLaren, Otto L Landen, Denise E Hinkel, Peter A Amendt, Joseph E Ralph, Alex B Zylstra, Annie L Kritcher, Jared C Delora-Ellefson In order to simplify and speed up integrated hydrodynamic simulations of indirect drive implosion experiments, such simulations historically have not included target components outside of the hohlraum near the laser entrance hole (LEH). More sophisticated simulations have shown evidence that aluminum ablated from the LEH washer enters into the laser beam paths, in particular in the presence of a large (4.0 mm diameter) LEH where the inner diameter (ID) of the washer is exposed to hohlraum wall emission. In order to quantify the impact of this effect on implosion velocity and shape, we are fielding an experiment where the washer ID was increased from 4.04 to 4.88 mm compared to its predecessor experiment [1]. Results and conclusions will be discussed. |
Tuesday, November 9, 2021 11:06AM - 11:18AM |
GO04.00009: Planned experiments to determine the cause of the drive deficit William A Farmer, Hui Chen, Denise E Hinkel, Nobuhiko Izumi, Otto L Landen, Duane A Liedahl, Steve A MacLaren, John D Moody, Alastair S Moore, Katya Newman, James S Ross, Mordecai D Rosen, Michael S Rubery, Marilyn B Schneider, George F Swadling The drive-deficit is a long-standing problem present in laser-driven hohlraums used in inertial confinement fusion (ICF) and high-energy density (HED) experiments. These platforms routinely have simulated x-ray fluxes that exceed measurements and simulated capsule bang-times that occur earlier than observed. Determining the source of the drive-deficit is difficult due to the highly integrated nature of these experiments and the complexity of the physics involved. Here, we report on focused experiments that have been proposed to help better determine the source of the drive-deficit. The first is an x-ray burn-through experiment that seeks to constrain the opacity and heat capacity of gold and quantify the discrepancy with existing models. The second is a series of experiments that will begin with a simple vacuum hohlraum, adding incremental complexity to quantify the drive-deficit at each step. The goal of these efforts is to provide measurements that will focus attention on possible hypotheses that can solve this long-standing problem. |
Tuesday, November 9, 2021 11:18AM - 11:30AM |
GO04.00010: Impact of multi-species physics and cross-beam-energy-transfer in near vacuum hohlraum simulations Drew P Higginson, Dave Bailey, Nathan Meezan, David J Strozzi, Scott Wilks, George Zimmerman Inertial confinement fusion (ICF) experiments performed on the National Ignition Facility have found that low density hohlraum fill improves laser coupling, reduces hot electron generation, and increases laser propagation to the hohlraum wall. However, the ability of rad-hydro codes to model the P2/P0 capsule symmetry at these lowest densities (He fill = 0.03 mg/cc) has historically been poor. This makes the design process at these densities problematic and motivates the use of He fill >0.15 mg/cc. The disagreement was previously attributed to multi-species (MS) physics; but it was not possible to simulate this until recently. This work utilizes rad-hydro simulations with a novel MS fluid physics package to investigate the source of the P2 asymmetry. Surprisingly, we find that MS physics alone makes only slight modifications to P2 symmetry. However, the use of an inline cross-beam-energy-transfer (CBET) package dramatically increases P2 of the capsule to a more prolate implosion; an effect that is amplified by the MS physics package. Understanding the details of MS and CBET physics in hohlraums is thus shown to be important in the development of predictive ICF modeling, especially in realizing the potential of low-fill hohlraums. |
Tuesday, November 9, 2021 11:30AM - 11:42AM Not Participating |
GO04.00011: Exploration of the physics between colliding expanding gold and carbon plasmas in the context of hohlraum dynamics Robert VanDervort, Matthew Trantham, Joshua S Davis, Sallee Klein, Paul A Keiter, R P Drake, Carolyn C Kuranz Indirect-drive uses a laser-irradiated hohlraum to uniformly irradiate a fusion capsule with soft-x-rays. Deviations in irradiation symmetry promote asymmetrical capsule collapse which reduces the fusion yield. Capsule performance is tied to understanding the complex, underlying hohlraum physics. Absorption of laser and x-ray radiation creates plasma flows, which refract and absorb incident laser beams and alter the implosion symmetry. Plasma flows can also create conditions for laser plasma instabilities. We present results from quasi-one dimensional experiments probing the interaction of expanding carbon and gold plasmas. |
Tuesday, November 9, 2021 11:42AM - 11:54AM |
GO04.00012: Observed Suppression of Self-Generated Magnetic Fields in a Laser-Driven Cylindrical Implosion Peter V Heuer, Luis S Leal, Jonathan R Davies, Edward C Hansen, Daniel H Barnak, Jonathan L Peebles, Andrew Birkel A cylindrical implosion using the mini-MagLIF platform at the Omega Laser Facility used oblique proton radiography to measure self-generated magnetic fields produced by the Biermann battery mechanism in the coronal plasma. Proton radiography oblique to the axis of the cylindrical target allows axially resolved measurements of self-generated azimuthal magnetic fields, which are not possible at normal incidence. These experimental measurements are compared to synthetic proton radiographs generated by the PlasmaPy proton radiography module [1] using fields from three-dimensional HYDRA simulations. This comparison shows that magnetohydrodynamics (MHD) overpredicts the self-generated field by a factor of ~2 to 3. Simulations also show that collisionality is low in the region where the fields are generated, suggesting that nonlocal effects may be responsible for the discrepancy. This result provides experimental evidence for previous theoretical predictions that nonlocal effects can result in suppressed self-generated magnetic fields relative to MHD. [1] PlasmaPy Community et al., PlasmaPy (Version 0.6.0), Zenodo, Accessed 14 March 2021, http://doi.org/10.5281/zenodo.4602818. |
Tuesday, November 9, 2021 11:54AM - 12:06PM |
GO04.00013: Measurements of the Return-Current Instability with Ion-Acoustic Thomson Scattering Avram Milder, Wojciech Rozmus, John P Palastro, Aaron M Hansen, Mark Sherlock, Dustin H 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 to limit the heat flux in inertial confinement fusion experiments. Here, the threshold for the instability was studied experimentally as a function of temperature gradient scale length. Temporally resolved ion-acoustic wave Thomson-scattering measurements showed the red-shifted wave grew consistently with electron Landau damping feeding the instability. Measurements of the ion-acoustic wave growth at multiple spatial locations and heating levels showed the level of growth was associated with the temperature gradient scale length in the plasma. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
Tuesday, November 9, 2021 12:06PM - 12:18PM |
GO04.00014: Modelling Laser Plasma Instabilities for Hydro-codes Arun Nutter, Alessandro Ruocco, Robbie H Scott, Nigel C Woolsey Laser driven inertial fusion is an exciting approach to fusion power that uses lasers to compress millimetre scale capsules of deuterium-tritium fuel. Direct drive inertial fusion uses high intensity lasers over pulse durations of order 10 ns, creating conditions that are favourable for laser plasma instabilities. The instabilities remove energy from the drive, reducing implosion efficiency and symmetry, while accelerating electrons which can preheat the fuel. Predicting the behaviour of these instabilities with accuracy and computational efficiency is difficult with current simulation capabilities. We are creating a fast computational model combining linear theory, pump depletion and saturation mechanisms which will run in-line with hydro-code laser ray-tracing routines, simulating the growth of these instabilities along the paths of the rays. Combining computational efficiency with accurate, but reduced, physics models, our goal is to enable more accurate design of future inertial fusion experiments. |
Tuesday, November 9, 2021 12:18PM - 12:30PM |
GO04.00015: Identifying low gas-fill hohlraum designs for high performance implosions on the Laser Mega Joule facility Marion Lafon, Mathieu Marciante, Paul-Edouard Masson-Laborde, Raphael Riquier, Stephane Laffite The final commissioning of the LMJ facility will use 40 laser quads to deliver 1.2 MJ of laser energy and 400 TW of laser power. Because of specific technical constraints, such as lower available energy and power, different laser beam balance and smaller focal spots than on the National Ignition Facility (NIF), a dedicated configuration has to be determined to guide high-performance designs. Integrated 2D simulations of low gas-fill rugby-shaped hohlraum implosions are performed using the TROLL radiation hydrodynamics code. This work presents an overview of these designs described by different case-to-capsule ratios, ablator materials and beam pointings. Key features such as hohlraum shape, inner beam propagation and energy coupled to the implosion are compared to recent NIF campaigns. A trade-off between hohlraum size, late-time inner beam propagation and achievable implosion velocity is defined to maintain implosion symmetry control. The effects of cross-beam energy transfer on low-mode implosion symmetry are also investigated for the first time on LMJ designs. |
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