What the Recent Progress in Laser Fusion Means

On Aug. 8, 2021, Lawrence Livermore National Laboratory’s (LLNL’s) National Ignition Facility (NIF) made a significant step toward ignition, achieving a yield of more than 1.3 megajoules (MJ).

This is still twelve times less than the 20 megajoules that simulations indicate can be achieved. Everything would need to be redesigned to try to get to net power generation for the whole system. 422 megajoules of power are needed to charge the capacitors for each shot. It would probably need to have triple the 422 megajoules to get to replacement breakeven of the energy generation needed to get the power to the outlets to charge the capacitors.

The performance needs further improvement by over 1000 times, the system needs to be recreated with rapid pellet loading and handling in order to create anything approaching a viable energy generation system. This system is not the path to new energy generation. It is a decades-long research project for nuclear weapons.

A one-gigawatt nuclear fission reactor can generate about 8 terawatt-hours of power in a year. This is about 29 billion megajoules in a year. The LLNL nuclear fusion shot produced 22 billion times less energy.

Initial analysis shows an 8X improvement over experiments conducted in spring 2021 and a 25X increase over NIF’s 2018 record yield.

They focused many lasers target the size of a BB that produces a hot-spot the diameter of a human hair, generating more than 10 quadrillion watts of fusion power for 100 trillionths of a second.

The experiment built on several advances gained from insights developed over the last several years by the NIF team including new diagnostics; target fabrication improvements in the hohlraum, capsule shell and fill tube; improved laser precision; and design changes to increase the energy coupled to the implosion and the compression of the implosion.

250 kilo-joules of energy was deposited on the target (roughly 2/3 of the energy from the beams). Lawrence Livermore National Laboratory has its 1.9 MJ laser system running at full power.

Sankey diagram of the laser energy to hohlraum x-ray to target capsule energy coupling efficiency. Note the “laser energy” is after conversion to UV, which loses about 50% of the original IR power. The conversion of x-ray heat to energy in the fuel loses another 90% – of the 1.9 MJ of laser light, only about 10 kJ ends up in the fuel itself.

The name National Ignition Facility refers to the goal of igniting the fusion fuel, a long-sought threshold in fusion research. In existing (non-weapon) fusion experiments the heat produced by the fusion reactions rapidly escapes from the plasma, meaning that external heating must be applied continually in order to keep the reactions going. Ignition refers to the point at which the energy given off in the fusion reactions currently underway is high enough to sustain the temperature of the fuel against those losses. This causes a chain-reaction that allows the majority of the fuel to undergo a nuclear burn. Ignition is considered a key requirement if fusion power is to ever become practical.

NIF is designed primarily to use the indirect drive method of operation, in which the laser heats a small metal cylinder instead of the capsule inside it. The heat causes the cylinder, known as a hohlraum (hollow cavity), to re-emit the energy as intense X-rays, which are more evenly distributed and symmetrical than the original laser beams. Experimental systems, including the OMEGA and Nova lasers, validated this approach through the late 1980s. The baseline NIF pellet design is about 2 mm in diameter, chilled to about 18 kelvins (−255 °C) and lined with a layer of frozen DT fuel. The hollow interior also contains a small amount of DT gas.

In a typical experiment, the laser will generate 3 MJ of infrared laser energy of a possible 4. About 1.5 MJ of this is left after conversion to UV, and about 15 percent of this is lost in the x-ray conversion in the hohlraum. About 15 percent of the resulting x-rays, about 150 kJ, will be absorbed by the outer layers of the target. The coupling between the capsule and the x-rays is lossy, and ultimately only about 10 to 14 kJ of energy is deposited in the fuel itself.

The resulting inward directed compression is expected to compress the fuel in the center of the target to a density of about 1,000 g/cm3 (or 1,000,000 kg/m3);for comparison, lead has a normal density of about 11 g/cm3 (11,340 kg/m3). The pressure is the equivalent of 300 billion atmospheres.

Based on simulations, it was expected this would produce about 20 MJ of fusion energy to be released, resulting in a net fusion energy gain, denoted Q, of about 15 (fusion energy out/UV laser energy in). Improvements in both the laser system and hohlraum design are expected to improve the energy absorbed by the capsule to about 420 kJ (and thus perhaps 40 to 50 in the fuel itself), which, in turn, could generate up to 100-150 MJ of fusion energy. However, the baseline design allows for a maximum of about 45 MJ of fusion energy release, due to the design of the target chamber. This is the equivalent of about 11 kg of TNT exploding.

These output energies are still less than the 422 MJ of input energy required to charge the system’s capacitors that power the laser amplifiers. The net wall-plug efficiency of NIF (UV laser energy out divided by the energy required to pump the lasers from an external source) would be less than one percent, and the total wall-to-fusion efficiency is under 10% at its maximum performance. An economical fusion reactor would require that the fusion output be at least an order of magnitude more than this input. Commercial laser fusion systems would use the much more efficient diode-pumped solid state lasers, where wall-plug efficiencies of 10 percent have been demonstrated, and efficiencies 16-18 percent are expected with advanced concepts under development.

Written By Brian Wang, Nextbigfuture.com

30 thoughts on “What the Recent Progress in Laser Fusion Means”

  1. The issue is that the small MJ output is still much less than the MJ required to run the laser in the first place.
    Doesn't matter how small your spaceship is, this device gives you LESS energy than you started with.

    Plus, the laser is very, very big. Only a particularly huge spaceship could fit it on board anyway.

  2. The best thing about drawing a line through 2 data points is that you get a fit with zero error bars, so you can accurately extrapolate as much as you want.

  3. Curious what you think of magnetized target fusion from General fusion..a reactor that uses steam powered pistons to pressurize..no lasers, no giant tokamak type magnets. Remarkable

  4. Many years back, a fine fellow named Farnsworth (inventor of many of the CRT-based television tube internals) hit upon the idea of a compact neutron fusion source out of big pulsed DC supply and a bunch of deuterium gas.  

    So simple in fact, that 'it' has been done hundreds of times in the last 50+ years by HIGH SCHOOL kids as their Science Fair projects.  

    Farnsworth's idea was to develop a point source to efficiently fuse far more deuterons than necessary to produce power in excess of invested DC.  Like 10s of times more. 

    The many professional physics experiments resulted in something called the 'wiffle ball', a magnetic confinement (not really) thing that showed in few unconvincing terms, that the dream remained that. Dream. 

    Meanwhile, it might surprise everyone to know that teeny-tiny (pinky fingernail) sized Farnsworth devices are presently the triggers of the post-Soviet, American, British, Chinese and Pakistani nuclear weapons warheads.  Just an itty-bitty burst of neutrons is needed, which the FNG can produce to nanosecond timing precision.  

    However, a LARGE fusion-neutron source has the unique ability to cause ²³⁸U to fission in a brief chain reaction. Brief enough that in an emergency, a reactor built upon it could be 'turned off' by just not feeding it fusion neutrons.  

    Kind of nice. 
    And compact!

    Container-sized reactors. 

    To think about.

    ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
    ⋅-=≡ GoatGuy ✓ ≡=-⋅

  5. "The performance needs further improvement by over 1000 times"
    I'd like to see a chart, showing over the years how much more improvement we need. Was it a million times more back in 2010?

    I'd also like to see this shown in terms of efficiency. If we need to go from 5% efficiency to 12% efficiency, that's fairly easy. If we need to go from 99% efficiency to 99.993% efficiency that's much harder.

  6. ~9% in 2018, 2021 ~70%, progress is exponential. We will have ignition in 2022 or 2023. Practical fusion energy in 2024/25

  7. Exactly. They had that more or less designed back in the 60's, and a non-sclerotic society could build one in under 5 years if necessary.

    It's not as cost effective as just building cookie cutter fission reactors, though. But it would derive the majority of the power from fusion!

  8. Fission-fusion hybrid. Just enough U233 to trigger a lithium deuteride pellet, in an underground steel chamber half full of molten salt. Enough thorium to generate more U233. Feasible, but half a dozen different pure fission designs should be cheaper, easier, and less scarey.

  9. But, what about smaller spacecraft? Would weaker MJ output be viable for that even if not for planetary power? I don't have experience in this field, so I probably don't completely understand.

  10. Yep. As soon as it starts working, they'll notice the fusion neutrons and scream horrified at all those machines being irradiated.

    Resulting in a practical ban of fusion as too polluting as well.

    I feel it's like their muted acceptance of public space settlement projects vs vocal opposition to private ones.

    As long as it looks things will never happen, they aren't against.

  11. I tend to agree. Fusion has potential use in space, but if we were to be perfectly practical, we'd drop it like a hot potato. Fission is vastly easier to pull off, the fuel is not going to be in short supply until well after the Sun moves off the main sequence and fries the Earth, and the waste is fairly straightforward to deal with if artificial constraints like the ban on reprocessing can be lifted.

    Fusion is the "best" enemies of nuclear power have set up to be the enemy of the "good enough". Should they get it working, it would immediately be turned on like fission.

  12. Ever since uranium could be extracted from seawater (and is naturally replaced from new bedrock welling up) and used in safe efficient 4th generation fission reactors, Fusion doesn’t really matter. It’s nice to keep up the research but these advances that are still far from a practical power reactor aren’t very significant.

  13. At the size of pellet you'd need for a working reactor, you'd be more likely to set the next town over on fire.

  14. They need larger pellets. The larger the pellet, the more easily you can ignite it.

    Watch out… you might set your hare on fire.

  15. Hard to keep track of fusion news of late.

    There are so many projects and startups, which seem to show a breakthrough here an another there once per quarter.

    Which is good, I guess, assuming the information is true and not just hype and investor baiting. NIF is definitely among the most serious out there, given it's a public lab.

    Under all that mountain of over-excited hype, there ought to be some actual state of the art with energy yields, technologies and published peer reviewed results.

  16. As Brian says, it was really intended as nuclear explosion simulation for the weapons programs. It's not a particularly practical approach to fusion power, but it does help them refine the software they use designing new bombs.

  17. Based on the article, it sounds like NIF isn't designed to produce a viable fusion reactor, but to experimentally refine the ignition technology. Valuable, but it does make me wonder if part of the reason fusion has been 30 years away for the last 50 years, is because of the piecemeal approach.

  18. They need larger pellets. The larger the pellet, the more easily you can ignite it.

    I'm thinking the minimum viable pellet is probably in the kiloton range. (Yield, not mass of pellet, of course!)

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