Researchers Have Once Again Kicked Fusion’s Ass With Bitchin’ Lasers
3:45 PM EDT on August 7, 2023
The scientists tinkering with inertial confinement fusion at the Lawrence Livermore National Laboratory warmed up and fired their spread of big honkin' lasers again, once again triggering a brief and explosive plasma fusion reaction inside a thimble-sized gold cartridge of nuclear fuel. This latest shot, which took place on July 30 and was first reported by Financial Times, reproduced the energy breakeven of the breakthrough shot from December, but this time with an even higher energy yield. Researchers have so far declined to specify the net energy gain of this latest experiment—they told the Washington Post Sunday that they will soon "share the results at scientific conferences and peer-reviewed publications"—but rest assured that it would wreak fabulously gruesome destruction on the skull and tender brain meat of anyone who put their smiling face at the reactor's point of ignition in order to encounter God. But these researchers are not after doomsday weapons, they are after clean and infinitely abundant energy. Any improvement in surplus energy from a controlled plasma fusion reaction moves mankind closer to a future where fusion energy has practical applications, up to and possibly including commercial energy production.
Clean fusion energy as a replacement for fossil fuels and a solution to mankind's voracious energy consumption is, unfortunately, still not exactly around the corner. What the researchers at the Lawrence Livermore Laboratory's National Ignition Facility (NIF) have done now is prove and then verify that it is possible, with lasers and diamonds and heavy hydrogen isotopes, to trigger a reaction that produces more energy via the fusing of atoms than it consumes in direct input energy. That's no small thing! That surplus energy, if harvested in sufficiently, uhh, big, uhh, units, could in theory one day be used to power things like, you know, civilization. Scientists have been hunting energy-positive fusion reactions for decades, using a whole variety of wacky reactors. The the NIF has now done it twice, and continues to successfully increase the yield by tinkering with the same reactor, is a huge scientific breakthrough.
The method pursued by the NIF—called inertial confinement fusion—would need an incredible amount of refining and creative upscaling in order to produce what you or I would consider a commercially significant amount of surplus energy. The reaction happens inside a little gold-plated cylinder called a hohlraum, about the size of the tip of your pinky finger. The interior of the hohlraum is lined with diamond; inside that diamond is a miniscule sphere of foam soaked in deuterium, which is a heavy and stable hydrogen isotope abundant in seawater. The hohlraum is held by a robotic arm in a very futuristic-looking chamber. A switch is flipped by a scientist with quite possibly the coolest job on Earth, and 192 lasers immediately send the hohlraum to hell. For the December shot, the 192 lasers bombarded the hohlraum with 2.05 megajoules of energy. That energy superheats the hohlraum and causes a chain reaction, the climax of which is an explosion which condenses the deuterium with such force that its atoms fuse together into heavier elements, releasing lots of very bright and hot energy. Energy from nuclear fusion, in a self-sustaining reaction, would be sufficient to trigger further fusion reactions, for the most part obviating the need for additional laser input, but that part—longer, self-powered reactions and bitchin' yields—is, for now, still largely theoretical. Here the reaction is over in a hot flash of light; the hohlraum is spectacularly eradicated; spectrometers and assorted other gadgets take measurements of the energy output. When the big show-stopping December shot was completed, it had produced approximately enough fusion energy to power a single incandescent lightbulb for three days. Sources told Financial Times that the July shot at least topped 3.50 megajoules, which still isn't doing much more than lighting your hallway closet for part of one week.
However much NIF researchers might've increased the yield during this July shot, we are likely still talking about very little energy in absolute terms. Then there's this: Dr. Johan Frenje, Head of the High-Energy-Density-Plasmas Division at the MIT Plasma Science and Fusion Center, told Defector back in December that it takes something like 300 megajoules of electricity for the NIF to warm up and fire their 192 lasers such that 2.05 megajoules of energy are blasted into the hohlraum. "It's a very inefficient process with the laser technology used at NIF today," explained Dr. Frenje, whose team collaborates with NIF researchers and provides diagnostics for their fusion experiments. This is partly because the NIF was upgraded to more-or-less its current form way back in the 1990s. These experiments with inertial confinement fusion are being done with lasers that were designed and built 30 and 40 years ago, according to Dr. Frenje. This is not a facility or a reactor that could or even should be used as a prototype for commercial reactors. This is pure experimentation. No one is prepared to even guess what a fully operational inertial confinement fusion reactor could look like. When your unfathomably hot plasma is "contained" only by implosion forces, it can be a challenge to work out a model for anything sustaining, let alone self-sustaining. Implosions, it seems, are spectacularly violent reactions.
But! That NIF is reaching breakeven and beyond with obsolete old lasers is, if anything, a sign of just how much progress is there for the making. For example: That ground-breaking December shot yielded 3.15 megajoules of fusion energy from 2.05 megajoules of thermal input while using a slightly crummy hohlraum. "The 3.15-megajoule fusion energy shot actually had a capsule that was a little bit worse than the one used in 2021," explained Dr. Frenje, who says that the implosion process at the reaction's climax can suffer significantly from even microscopic imperfections in the surface of the capsule, due to something called the Rayleigh-Taylor Instability. In the fusion reaction, the more uniform the pressure pushing inward on the deuterium fuel, the more powerful the eventual implosion forces. But "nanometer-sized dust things" on the surface of the capsule cause turbulence that inevitably depresses yield. The December capsule was far from perfect, but NIF researchers were working on "precision capsules" and further laser efficiency improvements for subsequent shots. Those may be the source of the improved yield from the July shot. "If we can build capsules like the one we shot in 2021, I don't know where we would be today," said a euphoric Dr. Frenje, high on the success of the December shot. "It would be certainly more than 3.15 megajoules."
So the findings are encouraging and important, and not just for the few facilities with updated, cutting edge lasers aimed at nanometer-perfect hohlraums. For scientists developing magnetic confinement fusion reactors, or tokamaks—where self-sustaining Breath Of God plasma clouds are contained by astonishingly powerful supercooled electromagnets, a reactor model that is considered tantalizingly close to viable for energy production—the NIF's breakthroughs will be important for refining their methods of igniting and burning plasmas, and will aid in the development of neutron diagnostics, which is something that I definitely understand super well. Much as I want to interpret the state of fusion science as a take-no-prisoners competition between inertial confinement fusion researchers and magnetic confinement fusion researchers, it is probably for the best that technological advances and scientific breakthroughs at NIF are treated as a triumph for the entire field. Eventually someone is gonna need to be able to flip a switch on a fusion reactor that does more than make scientifically significant pops of brilliant light, so that you and I can continue to play Zelda without destroying the planet.