A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the ...National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled (0.3 mg/cc of helium) bare depleted uranium hohlraums, resulting in a peak hohlraum radiative temperature ∼290 eV. The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of 380 km/s resulting in a peak kinetic energy of ∼21 kJ, which once stagnated produced a total DT neutron yield of 1.9×10^{16} (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. It resulted in hot spot areal density (ρr∼0.3 g/cm^{2}) and stagnation pressure (∼360 Gbar) never before achieved in a laboratory experiment.
Inertial confinement fusion seeks to create burning plasma conditions in a spherical capsule implosion, which requires efficiently absorbing the driver energy in the capsule, transferring that energy ...into kinetic energy of the imploding DT fuel and then into internal energy of the fuel at stagnation. We report new implosions conducted on the National Ignition Facility (NIF) with several improvements on recent work Phys. Rev. Lett. 120, 245003 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.245003; Phys. Rev. E 102, 023210 (2020)PRESCM2470-004510.1103/PhysRevE.102.023210: larger capsules, thicker fuel layers to mitigate fuel-ablator mix, and new symmetry control via cross-beam energy transfer; at modest velocities, these experiments achieve record values for the implosion energetics figures of merit as well as fusion yield for a NIF experiment.
Obtaining a burning plasma is a critical step towards self-sustaining fusion energy
. A burning plasma is one in which the fusion reactions themselves are the primary source of heating in the plasma, ...which is necessary to sustain and propagate the burn, enabling high energy gain. After decades of fusion research, here we achieve a burning-plasma state in the laboratory. These experiments were conducted at the US National Ignition Facility, a laser facility delivering up to 1.9 megajoules of energy in pulses with peak powers up to 500 terawatts. We use the lasers to generate X-rays in a radiation cavity to indirectly drive a fuel-containing capsule via the X-ray ablation pressure, which results in the implosion process compressing and heating the fuel via mechanical work. The burning-plasma state was created using a strategy to increase the spatial scale of the capsule
through two different implosion concepts
. These experiments show fusion self-heating in excess of the mechanical work injected into the implosions, satisfying several burning-plasma metrics
. Additionally, we describe a subset of experiments that appear to have crossed the static self-heating boundary, where fusion heating surpasses the energy losses from radiation and conduction. These results provide an opportunity to study α-particle-dominated plasmas and burning-plasma physics in the laboratory.
Abstract
In a burning plasma state
1–7
, alpha particles from deuterium–tritium fusion reactions redeposit their energy and are the dominant source of heating. This state has recently been achieved ...at the US National Ignition Facility
8
using indirect-drive inertial-confinement fusion. Our experiments use a laser-generated radiation-filled cavity (a hohlraum) to spherically implode capsules containing deuterium and tritium fuel in a central hot spot where the fusion reactions occur. We have developed more efficient hohlraums to implode larger fusion targets compared with previous experiments
9,10
. This delivered more energy to the hot spot, whereas other parameters were optimized to maintain the high pressures required for inertial-confinement fusion. We also report improvements in implosion symmetry control by moving energy between the laser beams
11–16
and designing advanced hohlraum geometry
17
that allows for these larger implosions to be driven at the present laser energy and power capability of the National Ignition Facility. These design changes resulted in fusion powers of 1.5 petawatts, greater than the input power of the laser, and 170 kJ of fusion energy
18,19
. Radiation hydrodynamics simulations
20,21
show energy deposition by alpha particles as the dominant term in the hot-spot energy balance, indicative of a burning plasma state.
Producing a burning plasma in the laboratory has been a long-standing milestone for the plasma physics community. A burning plasma is a state where alpha particle deposition from deuterium-tritium ...(DT) fusion reactions is the leading source of energy input to the DT plasma. Achieving these high thermonuclear yields in an inertial confinement fusion (ICF) implosion requires an efficient transfer of energy from the driving source, e.g., lasers, to the DT fuel. In indirect-drive ICF, the fuel is loaded into a spherical capsule which is placed at the center of a cylindrical radiation enclosure, the hohlraum. Lasers enter through each end of the hohlraum, depositing their energy in the walls where it is converted to x-rays that drive the capsule implosion. Maintaining a spherically symmetric, stable, and efficient drive is a critical challenge and focus of ICF research effort. Our program at the National Ignition Facility has steadily resolved challenges that began with controlling ablative Rayleigh-Taylor instability in implosions, followed by improving hohlraum-capsule x-ray coupling using low gas-fill hohlraums, improving control of time-dependent implosion symmetry, and reducing target engineering feature-generated perturbations. As a result of this program of work, our team is now poised to enter the burning plasma regime.
Hydrodynamic instabilities are a major factor in degradation of inertial confinement fusion (ICF) implosions. In the highest performing implosions on National Ignition Facility, yield amplification ...(YA) due to alpha particle heating approached ∼3, while YA of ∼15-30 is needed for ignition. Understanding and mitigation of the instabilities are critical to achieving ignition. This article reviews several experimental platforms that have been developed to directly measure these instabilities in all phases of ICF implosions. Measurements of ripple-shock propagation at OMEGA laser has provided results on initial seeds for the instabilities in three ablators-plastic (CH), beryllium, and high-density carbon. At the ablation front, instability growth of pre-imposed modulations was measured in the linear regime using the hydrodynamic growth radiography platform. This platform was extended for modulation growth of 'native roughness' modulations and engineering features (fill tubes and capsule support membranes or 'tents'). Several new experimental platforms have or are being developed to measure instability growth at the ablator-ice interface. In the deceleration phase of implosions, complementary 'self-emission' and 'self-backlighting' platforms were developed to measure low-mode asymmetries and high-mode perturbations near peak compression.
Understanding and leveraging physicochemical processes at the pore scale are believed to be essential to future performance improvements of supercapacitors and capacitive desalination (CD) cells. ...Here, we report on a combination of electrochemical experiments and fully atomistic simulations to study the effect of pore size and surface charge density on the capacitance of graphitic nanoporous carbon electrodes. Specifically, we used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to study the effect of potential and pore size on the capacitance of nanoporous carbon foams. Molecular dynamics simulations were performed to study the pore-size dependent accumulation of aqueous electrolytes in slit-shaped graphitic carbon pores of different widths (0.65 to 1.6 nm). Experimentally, we observe a pronounced increase of the capacitance of sub-nm pores as the applied potential window gets wider, from a few F g
−1
for narrow potential ranges (−0.3 to 0.3 V
vs.
Ag/AgCl) to ∼40 F g
−1
for wider potential windows (−0.9 V to 0.9 V
vs.
Ag/AgCl). By contrast, the capacitance of wider pores does not depend significantly on the applied potential window. Molecular dynamics simulations confirm that the penetration of ions into pores becomes more difficult with decreasing pore width and increasing strength of the hydration shell. Consistent with our experimental results, we observe a pore- and ion-size dependent threshold-like charging behavior when the pore width becomes comparable to the size of the hydrated ion (0.65 nm pores for Na
+
and 0.79 nm pores for Cl
−
ions). The observed pore-size and potential dependent accumulation of ions in slit-shaped carbon pores can be explained by the hydration structure of the ions entering the charged pores. The results are discussed in view of their effect on energy-storage and desalination efficiency.
Electrochemical experiments and atomistic simulations reveal the effects of pore size and pore surface charge density on the capacitance of graphitic nanocarbon electrodes.
Porosity generally embrittles ceramics. In contrast to such expectations, this report demonstrates that an effective fracture strain of nanoporous silica aerogels increases with increasing porosity. ...At ultralow relative densities of <0.5%, nanoporous monoliths start exhibiting super‐compressible deformation with effective fracture strains of >50%. This is attributed to consequences of an increase in the aspect ratio of ligaments with decreasing density.
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