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An experimental program is currently underway at the National Ignition Facility (NIF) to compress deuterium and tritium (DT) fuel to densities and temperatures sufficient to achieve fusion and energy gain. The primary approach being investigated is indirect drive inertial confinement fusion (ICF), where a high-Z radiation cavity (a hohlraum) is heated by lasers, converting the incident energy into x-ray radiation which in turn drives the DT fuel filled capsule causing it to implode. Previous experiments reported DT fuel gain exceeding unity [O.A. Hurricane et al., Nature 506, 343 (2014)] and then exceeding the kinetic energy of the imploding fuel [S. Le Pape et al., Phys. Rev. Lett. 120, 245003 (2018)]. We report on recent experiments that have achieved record fusion neutron yields on NIF, greater than 100 kJ with momentary fusion powers exceeding 1PW, and have for the first time entered the burning plasma regime where fusion alpha-heating of the fuel exceeds the energy delivered to the fuel via compression. This was accomplished by increasing the size of the high-density carbon (HDC) capsule, increasing energy coupling, while controlling symmetry and implosion design parameters. Two tactics were successful in controlling the radiation flux symmetry and therefore the implosion symmetry: transferring energy between laser cones via plasma waves, and changing the shape of the hohlraum. In conducting these experiments, we controlled for known sources of degradation. Herein we show how these experiments were performed to produce record performance, and demonstrate the data fidelity leading us to conclude that these shots have entered the burning plasma regime.

Low-mode asymmetries prevent effective compression, confinement, and heating of the fuel in inertial confinement fusion (ICF) implosions, and their control is essential to achieving ignition. Ion temperatures (T[subscript ion]) in ICF experiments are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn also impacts broadening and will lead to artificially inflated “T[subscript ion]” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured T[subscript ion]. We report on intentionally asymmetrically driven experiments at the OMEGA laser facility designed to test the ability to accurately predict and measure line-of-sight differences in apparent T[subscript ion] due to low-mode asymmetry-seeded flows. Contrasted to chimera and xrage simulations, the measurements demonstrate how all asymmetry seeds have to be considered to fully capture the flow field in an implosion. In particular, flow induced by the stalk that holds the target is found to interfere with the seeded asymmetry. A substantial stalk-seeded asymmetry in the areal density of the implosion is also observed., United States. Department of Energy (Award DE-NA0002949)

Few-body nuclear physics often relies upon phenomenological models, with new efforts at the ab initio theory reported recently; both need high-quality benchmark data, particularly at low center-of-mass energies. We use high-energy-density plasmas to measure the proton spectra from [superscript 3]He+T and [superscript 3]He + [superscript 3]He fusion. The data disagree with R-matrix predictions constrained by neutron spectra from T+T fusion. We present a new analysis of the [superscript 3]He + [superscript 3]He proton spectrum; these benchmarked spectral shapes should be used for interpreting low-resolution data, such as solar fusion cross-section measurements., United States. Department of Energy (Grant DE-NA0001857), United States. Department of Energy (Grant DE-FC52-08NA28752), United States. Department of Energy (Grant DE-FG02-88ER40387), United States. Department of Energy (Grant DE-NA0001837), United States. Department of Energy (Grant DE-AC52-06NA25396)), Lawrence Livermore National Laboratory (B597367), University of Rochester. Laboratory for Laser Energetics (415935-G), University of Rochester. Fusion Science Center (524431), National Laser User’s Facility (DE-NA0002035)

A study of the transition from collisional to collisionless plasma flows has been carried out at the National Ignition Facility using high Mach number (M>4) counterstreaming plasmas. In these experiments, CD-CD and CD-CH planar foils separated by 6–10 mm are irradiated with laser energies of 250 kJ per foil, generating ∼1000 km/s plasma flows. Varying the foil separation distance scales the ion density and average bulk velocity and, therefore, the ion-ion Coulomb mean free path, at the interaction region at the midplane. The characteristics of the flow interaction have been inferred from the neutrons and protons generated by deuteron-deuteron interactions and by x-ray emission from the hot, interpenetrating, and interacting plasmas. A localized burst of neutrons and bright x-ray emission near the midpoint of the counterstreaming flows was observed, suggesting strong heating and the initial stages of shock formation. As the separation of the CD-CH foils increases we observe enhanced neutron production compared to particle-in-cell simulations that include Coulomb collisions, but do not include collective collisionless plasma instabilities. The observed plasma heating and enhanced neutron production is consistent with the initial stages of collisionless shock formation, mediated by the Weibel filamentation instability.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from student-submitted PDF version of thesis., Includes bibliographical references., By measuring energetic charged-particle products from fusion reactions occurring in plasmas, nuclear diagnostics can be used to study the properties of the burning plasma, as a probe of the plasma, or of the fundamental fusion reaction physics. In this thesis, fusion product spectroscopy is used to study ignition-scale inertial fusion implosions, measure charged-particle stopping in dense plasmas to high accuracy, and study reactions relevant to nuclear astrophysics. 'Surrogate' plastic-shell implosions at the National Ignition Facility with D³He fuel produce 14.7-MeV protons. Spectrometry capability developed for the NIF has been used to study these protons produced at the 'shock' burn in these implosions, which proceeds the main 'compression' burn by several hundred picoseconds (ps). A 1-D implosion model was developed to interpret the spectra of the emitted shock-produced protons. Higher areal densities ([rho]R) are observed for implosions where the laser is kept on for a longer duration ('no-coast'); combining these data with x-ray radiography reveals that the shock-bang time occurs anomalously late in these implosions relative to hydrodynamic simulations. By using multiple detectors, low-mode (~2) implosion asymmetries are measured. When compared to stagnation x-ray self-emission an anomalously-low growth factor is observed relative to models, indicating potential time-dependent asymmetries or that the x-ray shape underestimates the asymmetry amplitude of the surrounding shell. Charged-particle spectroscopy relies upon untested theory for the stopping power as the particle traverses the dense imploding plasma. These theories are also critical for modeling [alpha]-particle self-heating and burn. By using D³He protons to probe a x-ray isochorically-heated subject plasma in the warm dense matter (WDM) regime, the stopping power has been measured to high accuracy for the first time in a dense plasma. This measurement is also a strong constraint on WDM electron stru, by Alex B. Zylstra., Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from student-submitted PDF version of thesis., Includes bibliographical references., By measuring energetic charged-particle products from fusion reactions occurring in plasmas, nuclear diagnostics can be used to study the properties of the burning plasma, as a probe of the plasma, or of the fundamental fusion reaction physics. In this thesis, fusion product spectroscopy is used to study ignition-scale inertial fusion implosions, measure charged-particle stopping in dense plasmas to high accuracy, and study reactions relevant to nuclear astrophysics. 'Surrogate' plastic-shell implosions at the National Ignition Facility with D³He fuel produce 14.7-MeV protons. Spectrometry capability developed for the NIF has been used to study these protons produced at the 'shock' burn in these implosions, which proceeds the main 'compression' burn by several hundred picoseconds (ps). A 1-D implosion model was developed to interpret the spectra of the emitted shock-produced protons. Higher areal densities ([rho]R) are observed for implosions where the laser is kept on for a longer duration ('no-coast'); combining these data with x-ray radiography reveals that the shock-bang time occurs anomalously late in these implosions relative to hydrodynamic simulations. By using multiple detectors, low-mode (~2) implosion asymmetries are measured. When compared to stagnation x-ray self-emission an anomalously-low growth factor is observed relative to models, indicating potential time-dependent asymmetries or that the x-ray shape underestimates the asymmetry amplitude of the surrounding shell. Charged-particle spectroscopy relies upon untested theory for the stopping power as the particle traverses the dense imploding plasma. These theories are also critical for modeling [alpha]-particle self-heating and burn. By using D³He protons to probe a x-ray isochorically-heated subject plasma in the warm dense matter (WDM) regime, the stopping power has been measured to high accuracy for the first time in a dense plasma. This measurement is also a strong constraint on WDM electron stru, by Alex B. Zylstra., Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from student-submitted PDF version of thesis., Includes bibliographical references., By measuring energetic charged-particle products from fusion reactions occurring in plasmas, nuclear diagnostics can be used to study the properties of the burning plasma, as a probe of the plasma, or of the fundamental fusion reaction physics. In this thesis, fusion product spectroscopy is used to study ignition-scale inertial fusion implosions, measure charged-particle stopping in dense plasmas to high accuracy, and study reactions relevant to nuclear astrophysics. 'Surrogate' plastic-shell implosions at the National Ignition Facility with D³He fuel produce 14.7-MeV protons. Spectrometry capability developed for the NIF has been used to study these protons produced at the 'shock' burn in these implosions, which proceeds the main 'compression' burn by several hundred picoseconds (ps). A 1-D implosion model was developed to interpret the spectra of the emitted shock-produced protons. Higher areal densities ([rho]R) are observed for implosions where the laser is kept on for a longer duration ('no-coast'); combining these data with x-ray radiography reveals that the shock-bang time occurs anomalously late in these implosions relative to hydrodynamic simulations. By using multiple detectors, low-mode (~2) implosion asymmetries are measured. When compared to stagnation x-ray self-emission an anomalously-low growth factor is observed relative to models, indicating potential time-dependent asymmetries or that the x-ray shape underestimates the asymmetry amplitude of the surrounding shell. Charged-particle spectroscopy relies upon untested theory for the stopping power as the particle traverses the dense imploding plasma. These theories are also critical for modeling [alpha]-particle self-heating and burn. By using D³He protons to probe a x-ray isochorically-heated subject plasma in the warm dense matter (WDM) regime, the stopping power has been measured to high accuracy for the first time in a dense plasma. This measurement is also a strong constraint on WDM electron stru, by Alex B. Zylstra., Ph. D.

Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability efficiently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. This result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts.

Collisionless shocks can be produced as a result of strong magnetic fields in a plasma flow, and therefore are common in many astrophysical systems. The Weibel instability is one candidate mechanism for the generation of sufficiently strong fields to create a collisionless shock. Despite their crucial role in astrophysical systems, observation of the magnetic fields produced by Weibel instabilities in experiments has been challenging. Using a proton probe to directly image electromagnetic fields, we present evidence of Weibel-generated magnetic fields that grow in opposing, initially unmagnetized plasma flows from laser-driven laboratory experiments. Three-dimensional particle-in-cell simulations reveal that the instability efficiently extracts energy from the plasma flows, and that the self-generated magnetic energy reaches a few percent of the total energy in the system. This result demonstrates an experimental platform suitable for the investigation of a wide range of astrophysical phenomena, including collisionless shock formation in supernova remnants, large-scale magnetic field amplification, and the radiation signature from gamma-ray bursts.