Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGA

Goncharov, V. N.; Sangster, T. C.; Betti, R.; Boehly, T. R.; Bonino, M. J.; Collins, T. J. B.; Craxton, R. S.; Delettrez, J. A.; Edgell, D. H.; Epstein, R.; Follett, R. K.; Forrest, C.; Froula, D. H.; Glebov, V. Yu.; Harding, D. R.; Henchen, R.J.; Hu, S. X.; Igumenshchev, I. V.; Janezic, R.; Kelly, John; Kessler, T. J.; Kosc, T. Z.; Loucks, S. J.; Marozas, J.A.; Marshall, F. J.; Maximov, A. V.; McCrory, R. L.; McKenty, P. W.; Meyerhofer, D. D.; Michel, D. T.; Myatt, J. F.; Nora, R.; Radha, P. B.; Regan, S. P.; Seka, W.; Shmayda, W.T.; Short, R. W.; Shvydky, A.; Skupsky, S.; Stoeckl, C.; Yaakobi, B.; Frenje, J. A.; Johnson, M. Gatu; Petrasso, R. D.; Casey, D. T.

doi:10.1063/1.4876618

Cited by 149 publications

(40 citation statements)

References 53 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The goal of achieving laboratory fusion and progress made with direct-drive ICF over the last decade motivate direct-drive implosions on NIF [8,9]. Hot-spot formation for spherically symmetric, direct-drive, DT-layered implosions is studied on the 60-beam, 30-kJ, 351-nm OMEGA Laser System [10] using hydrodynamically scaled ignition targets [11]. The radius of the target and the laser pulse duration scale with the laser energy as E 1=3 laser , and the laser power scales as E…”

mentioning

confidence: 99%

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

Regan¹,

Goncharov²,

Igumenshchev³

et al. 2016

Phys. Rev. Lett.

Self Cite

View full text Add to dashboard Cite

A record fuel hot-spot pressure P hs ¼ 56 AE 7 Gbar was inferred from x-ray and nuclear diagnostics for direct-drive inertial confinement fusion cryogenic, layered deuterium-tritium implosions on the 60-beam, 30-kJ, 351-nm OMEGA Laser System. When hydrodynamically scaled to the energy of the National Ignition Facility, these implosions achieved a Lawson parameter ∼60% of the value required for ignition [A. Bose et al., Phys. Rev. E 93, LM15119ER (2016)], similar to indirect-drive implosions [R. Betti et al., Phys. Rev. Lett. 114, 255003 (2015)], and nearly half of the direct-drive ignition-threshold pressure. Relative to symmetric, one-dimensional simulations, the inferred hot-spot pressure is approximately 40% lower. Three-dimensional simulations suggest that low-mode distortion of the hot spot seeded by laserdrive nonuniformity and target-positioning error reduces target performance. DOI: 10.1103/PhysRevLett.117.025001 The spherical concentric layers of a direct-drive inertial confinement fusion (ICF) target nominally consist of a central region of a near-equimolar deuterium and tritium (DT) vapor surrounded by a cryogenic DT-fuel layer and a thin, nominally plastic (CH) ablator. The outer surface of the ablator is uniformly irradiated with multiple laser beams having a peak overlapped intensity of <10 15 watts=cm 2 . The resulting laser-ablation process causes the target to accelerate and implode. As the DT-fuel layer decelerates, the initial DT vapor and the fuel mass thermally ablated from the inner surface of the ice layer are compressed and form a central hot spot, in which fusion reactions occur. ICF relies on the 3.5-MeV DT-fusion alpha particles depositing their energy in the hot spot, causing the hotspot temperature to rise sharply and a thermonuclear burn wave to propagate out through the surrounding nearly degenerate, cold, dense DT fuel, producing significantly more energy than was used to heat and compress the fuel. Ignition is predicted to occur when the product of the temperature and areal density of the hot spot reach a minimum of 5 keV × 0.3 g=cm 2 [1-3]. Currently, the 192-beam, 351-nm, 1.8-MJ National Ignition Facility (NIF) [4] is configured for indirectdrive-ignition experiments using laser-driven hohlraums to accelerate targets via x-ray ablation. Approximately 26 kJ of thermonuclear fusion energy has been recorded on the NIF using indirect-drive ICF targets [5], where alpha heating has boosted the fusion yield by a factor of ∼2.5 from that caused by the implosion system alone [6,7]. The indirect-drive NIF implosions have achieved over 60% of the Lawson parameter Pτ required for ignition, where P is the pressure and τ is the confinement time [6]. Here P and τ are estimated without accounting for alpha heating to assess the pure hydrodynamic performance. The goal of achieving laboratory fusion and progress made with direct-drive ICF over the last decade motivate direct-drive implosions on NIF [8,9]. Hot-spot formation for spherically symmetric, direct-drive, DT-layered implosions is st...

show abstract

mentioning

confidence: 99%

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

Regan¹,

Goncharov²,

Igumenshchev³

et al. 2016

Phys. Rev. Lett.

Self Cite

View full text Add to dashboard Cite

show abstract

“…comparison of 1D simulation results using LILAC with the data shows good agreement between the two for a variety of target designs and drive conditions [18]. One-dimensional simulations include nonlocal thermal transport model [27], a ray-based cross beam energy transfer (CBET) model [28] (see discussion on CBET in section 2.5), and first-principle EOS (FPEOS) models [29] for both the DT ice and CD ablator.…”

Section: D Physicsmentioning

confidence: 80%

“…To emphasize the importance of drive conditions in ignition target designing, the 1D scaling laws (which exclude multidimensional effects) for peak pressure and hot-spot energy are written in terms of implosion parameters: implosion velocity v imp (the peak mass-averaged shell velocity), the peak drive (ablation) pressure p a , adiabat of the unablated fuel mass α (ratio of the shell pressure to Fermi pressure at shell density), and peak in shell kinetic energy E kin [18]:…”

Section: D Physicsmentioning

confidence: 99%

“…Equation (7) shows that the hot-spot pressure and the ignition pressure parameter P can be increased in 1D mainly by raising the shell IFAR (by reducing the shell mass, for example) and by making the laser drive more efficient (by increasing the ablation pressure and shell kinetic energy). The maximum value of IFAR in a design is set by the target stability properties and the level of nonunifomity seeds: the short-scale modes (which satisfy k 1 ∆ < , where k is the perturbation wave number and ∆ is the inflight shell thickness) disrupt the shell during the implosion if IFAR is too large {current cryogenic implosions on OMEGA are unstable if IFAR 20 3 1.1 ( / ) α > [18]}. The longwavelength perturbations (k 1 ∆ > ) seeded by the laser power imbalance, laser mispointing, and target misalignment can prevent the hot spot from reaching the 1D stagnation pressures if RT and Bell-Plesset (BP) [1] nonuniformity growth is excessively large during deceleration.…”

Section: Multidimensional Effectsmentioning

confidence: 99%

See 1 more Smart Citation

National direct-drive program on OMEGA and the National Ignition Facility

Goncharov

Regan

Campbell

et al. 2016

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

A major advantage of the laser direct-drive (DD) approach to ignition is the increased fraction of laser drive energy coupled to the hot spot and relaxed hot-spot requirements for the peak pressure and convergence ratios relative to the indirect-drive approach at equivalent laser energy. With the goal of a successful ignition demonstration using DD, the recently established national strategy has several elements and involves multiple national and international institutions. These elements include the experimental demonstration on OMEGA cryogenic implosions of hot-spot conditions relevant for ignition at MJ-scale energies available at the National Ignition Facility (NIF) and developing an understanding of laser-plasma interactions and laser coupling using DD experiments on the NIF. DD designs require reaching central stagnation pressures in excess of 100 Gbar. The current experiments on OMEGA have achieved inferred peak pressures of 56 Gbar (Regan et al 2016 Phys. Rev. Lett. 117 025001). Extensive analysis of the cryogenic target experiments and two-and three-dimensional simulations suggest that power balance, target offset, and target quality are the main limiting factors in target performance. In addition, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling. Reaching the goal of demonstrating hydrodynamic equivalence on OMEGA includes improving laser power balance, target position, and target quality at shot time. CBET must also be significantly reduced and several strategies have been identified to address this issue.

show abstract

“…Conditions during the shock phase result in large mean-free-path lengths of the ions relative to the size of the fusing-plasma region (see Table I). These conditions are also typical of ignition-scalable direct-drive cryogenic implosions [7] during the shock phase; however, cryogenic targets differ from exploding pusher targets in two respects. First, most of the neutron yield in a cryogenic implosion occurs later in the implosion, during the compression phase, when the kinetic energy is converted to the internal energy of the hot spot.…”

mentioning

confidence: 99%

First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions

et al. 2017

Self Cite

View full text Add to dashboard Cite

The deuterium-tritium (D-T) and deuterium-deuterium neutron yield ratio in cryogenic inertial confinement fusion (ICF) experiments is used to examine multifluid effects, traditionally not included in ICF modeling. This ratio has been measured for ignition-scalable direct-drive cryogenic DT implosions at the Omega Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] using a high-dynamic-range neutron time-of-flight spectrometer. The experimentally inferred yield ratio is consistent with both the calculated values of the nuclear reaction rates and the measured preshot target-fuel composition. These observations indicate that the physical mechanisms that have been proposed to alter the fuel composition, such as species separation of the hydrogen isotopes [D. T. Casey et al., Phys. Rev. Lett. 108, 075002 (2012)], are not significant during the period of peak neutron production in ignition-scalable cryogenic direct-drive DT implosions. DOI: 10.1103/PhysRevLett.118.095002 In direct-drive inertial confinement fusion (ICF) ignition designs, a cryogenic deuterium-tritium (DT) shell surrounding a vapor and encased in a thin-CH or thin-CD ablator (<10 μm) is symmetrically heated with nominally identical laser beams. In most designs, laser ablation launches one or multiple shocks through the converging shell and into the vapor region. The shock-transit stage of the implosion is followed by a deceleration phase, where the kinetic energy of the converging shell is converted to the internal energy of the hot spot. Thermonuclear fusion reactions are initiated in both the shock phase and the compression phase once sufficiently high temperatures and densities are reached [1]. To achieve conditions relevant for ignition implosion designs, the hot-spot size must exceed the mean free path of fusing ions. This requirement is essential to maximize the energy deposition of the alpha particle in the hot spot.Previous experiments on OMEGA [2] have reported anomalous Y DT =Y DD values (different by as much as a factor of 4) with the measured preshot fuel composition and experimentally inferred ion temperatures in roomtemperature implosions [3]. Several studies suggest that species separation of the hydrogen isotope resulting from multifluid effects [4,5] is likely responsible for the observed discrepancies in the yield ratios. This class of implosions, for example, exploding pushers that use thin-glass (∼3-μm SiO 2 ) or thin-CH (<16 μm) shells are, however, characterized by fusion reactions that occur predominantly during the shock phase at very high temperatures (≥10 keV) and relatively low densities (≤10 mg=cm 3 ). The mean free path for 90°deflection is given by λ ii ∼ T 2 i =Z 2 i Z 2 ρ [6] for ions of charge Z i , average ion temperature T i , ion charge Z, and density ρ. Conditions during the shock phase result in large mean-free-path lengths of the ions relative to the size of the fusing-plasma region (see Table I). These conditions are also typical of ignition-scalable direct-drive cryogenic implosions [7] during ...

show abstract

Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGA

Cited by 149 publications

References 53 publications

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

National direct-drive program on OMEGA and the National Ignition Facility

First Measurements of Deuterium-Tritium and Deuterium-Deuterium Fusion Reaction Yields in Ignition-Scalable Direct-Drive Implosions

Contact Info

Product

Resources

About