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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

A review of five decades of strategic decisions and key results on the path to ignition on the National Ignition Facility

Successful demonstration of an implosion that meets the physics metrics for ignition on the National Ignition Facility (NIF) in August 2021 and demonstration of G > 1 in December 2022 represented the culmination of five decades of research. This review covers the key strategic decisions and physics results from the 20 J Janus laser to the 2 MJ NIF laser. NIF's specifications were set in order to have a margin in performance to account for uncertainty in the physics challenges leading to ignition, particularly for laser–plasma interaction and hydrodynamic instabilities including long-wavelength modes responsible for implosion symmetry. The ignition experiments utilized all that margin. Achieving the laser and target performance utilized in the Hybrid-E experiments that achieved ignition and G > 1 proved to be a challenge that consumed a decade.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Hydrogen-oxygen catalytic ignition and thruster investigation. Volume 1: Catalytic ignition and low pressure thruster evaluations

An experimental and analytical program was conducted to evaluate catalytic igniter operational limits, igniter scaling criteria, and delivered performance of cooled, flightweight gaseous hydrogen-oxygen reaction control thrusters. Specific goals were to: (1) establish operating life and environmental effects for both Shell 405-ABSG and Engelhard MFSA catalysts, (2) provide generalized igniter design guidelines for high response without flashback, and (3) to determine overall performance of thrusters at chamber pressures of 15 and 300 psia (103 and 2068 kN/sq m) and thrust levels of 30 and 1500 lbf, respectively. The experimental results have demonstrated the feasibility of reliable, high response catalytic ignition and the effectiveness of ducted chamber cooling for a high performance flightweight thruster. This volume presents the results of the catalytic igniter and low pressure thruster evaluations are presented.

Johnson, R. J.↗
NASA NTRS1992

Ignition delays, heats of combustion, and reaction rates of aluminum alkyl derivatives used as ignition and combustion enhancers for supersonic combustion

The subject of this paper is the design of supersonic combustors which will be required in order to achieve the needed reaction rates in a reasonable sized combustor. A fuel additive approach, which is the focus of this research, is the use of pyrophorics to shorten the ignition delay time and to increase the energy density of the fuel. Pyrophoric organometallic compounds may also provide an ignition source and flame stabilization mechanism within the combustor, thus permitting use of hydrocarbon fuels in supersonic combustion systems. Triethylaluminum (TEA) and trimethylaluminum (TMA) were suggested for this application due to their high energy density and reactivity. The objective here is to provide comparative data for the ignition quality, the energy content, and the reaction rates of several different adducts of both TEA and TMA. The results of the experiments indicate the aluminum alkyls and their more stable derivatives reduce the ignition delay and total reaction time to JP-10 jet fuel. Furthermore, the temperature dependence of ignition delay and total reaction time of the blends of the adducts are significantly lower than in neat JP-10.

Ryan, Thomas W., III↗
DOE OSTI2021

Direct Numerical Simulation of hydrogen combustion at auto-ignitive conditions: Ignition, stability and turbulent reaction-front velocity

Direct Numerical Simulations (DNS) are performed to investigate the process of spontaneous ignition of hydrogen flames at laminar, turbulent, adiabatic and non-adiabatic conditions. Mixtures of hydrogen and vitiated air at temperatures representing gas-turbine reheat combustion are considered. Adiabatic spontaneous ignition processes are investigated first, providing a quantitative characterization of stable and unstable flames. Results indicate that, in hydrogen reheat combustion, compressibility effects play a key role in flame stability and that unstable ignition and combustion are consistently encountered for reactant temperatures close to the mixture’s characteristic crossover temperature. Furthermore, it is also found that the characterization of the adiabatic processes is also valid in the presence of non-adiabaticity due to wall heat-loss. Finally, a quantitative characterization of the instantaneous fuel consumption rate within the reaction front is obtained and of its ability, at auto-ignitive conditions, to advance against the approaching turbulent flow of the reactants, for a range of different turbulence intensities, temperatures and pressure levels.

42 ENGINEERING↗
DOE OSTI2024

Delivering laser performance conditions to enable fusion ignition, and beyond at the National Ignition Facility

On December 5th, 2022, controlled fusion ignition was demonstrated for the first time at the National Ignition Facility (NIF), a major achievement in the field of Inertial Confinement Fusion (ICF) requiring a multi-decadal effort involving broad national and international collaborations. To drive the fusion ignition reaction with the compressed fuel capsule, that yielded 3.15 MJ of nuclear energy [1], the NIF laser delivered a high-precision pulse shape with 2.05 MJ of ultra-violet (UV) laser energy and a peak power of 440 TW. This laser energy was an increase of ~8 % compared to that delivered on the previous “threshold of ignition” record yield experiment (1.37 MJ of yield for 1.89 MJ of laser energy) on August 8th, 2021. Here we explain how the results of our extensive research in laser technology and UV optics damage mitigation led to major improvements in the NIF laser, enabling this energy increase along with additional accuracy, precision, and power balance enhancements. Furthermore, we will discuss on-going efforts that have enabled operations at 2.2 MJ of UV energy as well as potential new initiatives to push the laser performance –accuracy and delivered energy– to even higher levels in the future as previously demonstrated on a small subset of NIF beams.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Experimental achievement and signatures of ignition at the National Ignition Facility

An inertial fusion implosion on the National Ignition Facility, conducted on August 8, 2021 (N210808), recently produced more than a megajoule of fusion yield and passed Lawson's criterion for ignition [Phys. Rev. Lett. 129, 075001 (2022)]. Here we describe the experimental improvements that enabled N210808 and present the first experimental measurements from an igniting plasma in the laboratory. Ignition metrics like the product of hot-spot energy and pressure squared, in the absence of self-heating, increased by ~ 35%, leading to record values and an enhancement from previous experiments in the hot-spot energy (~ 3×), pressure (~ 2×), and mass (~ 2×). These results are consistent with self-heating dominating other power balance terms. The burn rate increases by an order of magnitude after peak compression, and the hot-spot conditions show clear evidence for burn propagation into the dense fuel surrounding the hot spot. These novel dynamics and thermodynamic properties have never been observed on prior inertial fusion experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Mapping the combustion modes of a dual-fuel compression ignition engine

Compression-ignition (CI) engines can produce higher thermal efficiency (TE) and thus lower carbon dioxide (CO 2 ) emissions than spark-ignition (SI) engines. Unfortunately, the overall fuel economy of CI engine vehicles is limited by their emissions of nitrogen oxides (NO x ) and soot, which must be mitigated with costly, resource- and energy-intensive aftertreatment. NO x and soot could also be mitigated by adding premixed gasoline to complement the conventional, non-premixed direct injection (DI) of diesel fuel in CI engines. Several such “dual-fuel” combustion modes have been introduced in recent years, but these modes are usually studied individually at discrete conditions. This paper introduces a mapping system for dual-fuel CI modes that links together several previously studied modes across a continuous two-dimensional diagram. This system includes the conventional diesel combustion (CDC) and conventional dual-fuel (CDF) modes; the well-explored advanced combustion modes of HCCI, RCCI, PCCI, and PPCI; and a previously discovered but relatively unexplored combustion mode that is herein titled “Piston-split Dual-Fuel Combustion” or PDFC. Tests show that dual-fuel CI engines can simultaneously increase TE and lower NO x and/or soot emissions at high loads through the use of Partial HCCI (PHCCI). At low loads, PHCCI is not possible, but either PDFC or RCCI can be used to further improve NO x and/or soot emissions, albeit at slightly lower TE. These results lead to a “partial dual-fuel” multi-mode strategy of PHCCI at high loads and CDC at low loads, linked together by PDFC. Drive cycle simulations show that this strategy, when tuned to balance NO x and soot reductions, can reduce engine-out CO 2 emissions by about 1% while reducing NO x and soot by about 20% each with respect to CDC. This increases emissions of unburnt hydrocarbons (UHC), still in a treatable range (2.0 g/kWh) but five times as high as CDC, requiring changes in aftertreatment strategy.

Engineering↗
DOE OSTI2021

Impact of low reactivity fuel type on low load combustion, emissions, and cyclic variations of diesel-ignited dual fuel combustion

In this study, cyclic variations in dual fuel combustion with diesel ignition of three different low reactivity fuels (methane, propane, and gasoline) are examined under identical operating conditions. Experiments were performed on a single cylinder research engine (SCRE) at a low load of 3.3 bar brake mean effective pressure (BMEP). The start of injection (SOI) of diesel was varied from 280 to 330 absolute crank angle degrees (CAD). Engine speed, rail pressure, and boost pressure were held constant at 1500 rpm, 500 bar, and 1.5 bar, respectively. The energy substituted by the low reactivity fuel was fixed at 80% of the total energy input. It was found that diesel-methane (DM) and diesel-propane (DP) combustion were affected by diesel mixing to a greater extent than diesel-gasoline (DG) combustion due to the higher reactivity of gasoline. The magnitude of low temperature heat release was greatest for DG combustion followed by DM and DP combustion for all SOIs. The ignition delay for DG combustion was the shortest, followed by DM and DP combustion. DM and DP combustion exhibited more cyclic variations than DG combustion. Cyclic variations decreased for DM and DP combustion when SOI was advanced; however, DG combustion cyclic variations remained essentially constant for all SOIs. Earlier SOIs (280, 290, 300, and 310 CAD) for DM and (280, 290, and 300 CAD) for DP combustion indicated some prior-cycle effects on the combustion and IMEP (i.e. some level of determinism).

Engineering↗
NASA NTRS1932

Influence of several factors on ignition lag in a compression-ignition engine

This investigation was made to determine the influence of fuel quality, injection advance angle, injection valve-opening pressure, inlet-air pressure, compression ratio, and engine speed on the time lag of auto-ignition of a Diesel fuel oil in a single-cylinder compression-ignition engine as obtained from an analysis of indicator diagrams. Three cam-operated fuel-injection pumps, two pumps cams, and an automatic injection valve with two different nozzles were used. Ignition lag was considered to be the interval between the start of injection of the fuel as determined with a Stroborama and the start of effective combustion as determined from the indicator diagram, the latter being the point where 4.0 x 10(exp-6) pound of fuel had been effectively burned. For this particular engine and fuel it was found that: (1) for a constant start and the same rate of fuel injection up the point of cut-off, a variation in fuel quantity from 1.2 x 10(exp-4) to 4.1 x 10(exp-4) pound per cycle has no appreciable effect on the ignition lag; (2) injection advance angle increases or decreases the lag according to whether density, temperature, or turbulence has the controlling influence; (3) increase in valve-opening pressure slightly increases the lag; and (4) increase of inlet-air pressure, compression ratio, and engine speed reduces the lag.

Gerrish, Harold C↗
DOE OSTI2021

Single and Double Shell Ignition Targets for the National Ignition Facility at 527 nm

Converting and using the National Ignition Facility (NIF) to deliver 527 nm light instead of its current 351 nm would allow the laser to deliver more energy and power to ignition targets. We update previous 527 nm target design work to reflect more contemporary target designs using high-density carbon capsules and low density helium gas filled Hohlraums. We extend single shell capsule designs based on current experimental results to higher energy and power and also explore double shell capsules, both driven by green light. These studies were completed using detailed pulse shapes found for targets that converged with acceptable 2D implosion symmetries and then used the Lava Lamp II code to confirm their feasibility at NIF. A 1.2× dimensional scaleup of one tuned NIF target at the limit of its current 351 nm capabilities and shot 170827 uses 3.3 MJ, at the limit of the current NIF's 527 nm capability. With the less-structured pulse of a double shell target, 3.7 MJ could be delivered by the laser. Our LPI calculations do not preclude operation at 527 nm, particularly for low fill Hohlraums, and suggest that the stimulated Raman backscatter may be no worse than the small quantities seen in 170827; stimulated forward Raman scattering may be present. If Stimulated Brillouin Scattering is too great, the much greater laser bandwidth available at 527 nm could be used to decrease backscatter. These larger targets with higher energy and power may offer a better chance of achieving ignition with only modest changes to the NIF laser.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Present understanding of ignition and gain using indirect-drive inertial confinement fusion target designs on the U.S. National Ignition Facility

For many decades, the running joke in fusion research has been that 'fusion' is thirty years away and always will be. Yet, these past few years we find ourselves in a position where we can now talk about the milestones of burning plasmas, fusion ignition, and target energy gain greater than unity (scientific breakeven) in the past tense. Fusion is no longer a joke! Yet getting to fusion ignition, the tipping-point of thermonuclear instability resulting in an explosive increase in ion thermal temperature and fusion reaction-rate, and scientific breakeven (target gain, $G_{target} =$ fusion yield/deposited laser energy >1, in the laser-driven inertial confinement fusion context) has not been easy. Here, in this publication, we discuss our present understanding of the physics and technological challenges surrounding ignition and Gain as well as highlight some outstanding problems that still need resolution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1945

Calculations of the Performance of a Compression-Ignition Engine-Compressor Turbine Combination I : Performance of a Highly Supercharged Compression-Ignition Engine

Small high-speed single-cylinder compression-ignition engines were tested to determine their performance characteristics under high supercharging. Calculations were made on the energy available in the exhaust gas of the compression-ignition engines. The maximum power at any given maximum cylinder pressure was obtained when the compression pressure was equal to the maximum cylinder pressure. Constant-pressure combustion was found possible at an engine speed of 2200 rpm. Exhaust pressures and temperatures were determined from an analysis of indicator cards. The analysis showed that, at rich mixtures with the exhaust back pressure equal to the inlet-air pressure, there is excess energy available for driving a turbine over that required for supercharging. The presence of this excess energy indicates that a highly supercharged compression-ignition engine might be desirable as a compressor and combustion chamber for a turbine.

EXHAUST GASES-TEMPERATURE↗
DOE OSTI2020

Hot-electron generation at direct-drive ignition-relevant plasma conditions at the National Ignition Facility

Laser–plasma interaction instabilities can be detrimental for direct-drive inertial confinement fusion by generating high-energy electrons that preheat the target. Moreover, an experimental platform has been developed and fielded on the National Ignition Facility to investigate hot-electron production from laser–plasma instabilities at direct-drive ignition-relevant conditions. The radiation-hydrodynamic code DRACO has been used to design planar-target experiments that generate plasma and interaction conditions comparable to direct-drive ignition designs: I L ~10 15 W/cm 2 , T e > 3 keV, and density-gradient scale lengths of L n ~ 600 μ m in the quarter-critical density region. The hot-electron properties were inferred by comparing the experimentally observed hard x-ray spectra to Monte Carlo simulations of hard x-ray emission from hot electrons depositing energy in the target. Hot-electron temperatures of ~40 keV to 60 keV and the fraction of laser energy converted to hot electrons of ~0.5% to 5% were inferred in plastic targets for laser intensities at the quarter-critical density surface of (~4 to 14) × 10 14 W/cm 2 . The use of silicon ablators was found to mitigate the hot-electron preheat by increasing the threshold laser intensity for hot-electron generation from ~3.5 × 10 14 W/cm 2 in plastic to ~6 × 10 14 W/cm 2 in silicon. The overall hot-electron production is further reduced in silicon ablators when the intensity threshold is exceeded.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Alpha-heating analysis of burning plasma and ignition experiments on the National Ignition Facility

A recent experiment conducted on the National Ignition Facility (NIF) described in the study by Abu-Shawareb et al. achieved a fusion yield output of 1.3 MJ from ~ 220 kJ of x-ray energy absorbed by the capsule, demonstrating remarkable progress in the field of laser driven inertial confinement fusion. In the study by A. R. Christopherson [“Effects of charged particle heating on the hydrodynamics of inertially confined plasmas,” Ph.D. thesis (2020)], the plasma conditions needed to claim the onset of ignition and burn propagation were outlined and multiple criterion were provided to assess progress in inertial fusion experiments. In this work, we modify the metrics from A. R. Christopherson to accurately calculate performance metrics for indirect-drive experiments on the NIF. We also show that performance metric trends observed in NIF data are consistent with theory and simulations. This analysis indicates that all the identified criterion for ignition and burn propagation have been exceeded by experiment 210 808.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Thermonuclear performance variability near ignition at the National Ignition Facility

We describe our current understanding of the variability and degradation mechanisms observed through a series of five indirectly driven inertial fusion implosions fielded at the National Ignition Facility in the fall of 2021, four of which attempted to reproduce the first experiment to achieve Lawson's criterion for ignition with a thermonuclear yield of 1.35 MJ on August 8, 2021. A large number of absolutely calibrated (imaging, time-resolved, and spectrally resolved) x-ray and neutron diagnostics are fielded on the NIF along multiple lines of sight for each experiment. This allows for a reconstruction of the DT fuel and ablator mix injected into the hotspot around peak burn. We show that nuclear yield variations are well reproduced by numerical modeling when the measured low mode asymmetries and mix mass are included. Furthermore, these observed perturbations during burn are linked to small variations in laser delivery and capsule defects. Stringent specifications are then set to achieve robust ignition with the implosion design studied in this paper.

Divol, L. (ORCID:0000000269699898)↗
DOE OSTI2021

Shock Ignition Laser-Plasma Interactions in Ignition-Scale Plasmas

Here, we use a subignition scale laser, the 30 kJ Omega, and a novel shallow-cone target to study laser-plasma interactions at the ablation-plasma density scale lengths and laser intensities anticipated for direct drive shock-ignition implosions at National Ignition Facility scale. Our results show that, under these conditions, the dominant instability is convective stimulated Raman scatter with experimental evidence of two plasmon decay (TPD) only when the density scale length is reduced. Particle-in-cell simulations indicate this is due to TPD being shifted to lower densities, removing the experimental back-scatter signature and reducing the hot-electron temperature. The experimental laser energy-coupling to hot electrons was found to be 1%–2.5%, with electron temperatures between 35 and 45 keV. Radiation-hydrodynamics simulations employing these hot-electron characteristics indicate that they should not preheat the fuel in MJ-scale shock ignition experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Predicting fusion ignition at the National Ignition Facility with physics-informed deep learning

Here, an inertial confinement fusion experiment, carried out at the National Ignition Facility, has achieved ignition by generating fusion energy exceeding the laser energy that drove the experiment. Prior to the experiment, a generative machine learning model that combines radiation hydrodynamics simulations, deep learning, experimental data, and Bayesian statistics was used to predict, with a probability greater than 70%, that ignition was the most likely outcome for this shot.

Spears, Brian K. [Lawrence Livermore National Labo↗