Every fusion story you read is about the laser. How much energy it fires, how often it fires, how big a building it needs to sit in. The fuel gets a sentence, maybe two. But if you want a power plant instead of a physics experiment, somebody has to feed that laser a fresh pellet ten times a second, and the people who make the best fuel pellets in the world these days turn out a handful a year.
Inertia Enterprises says it’s knocked one piece of that off. Working with Lawrence Livermore National Laboratory, the startup says it can now grow the frozen fuel layer inside a target in two to three hours. At the National Ignition Facility next door, the machine that first pulled more energy out of a fusion reaction than its lasers put in, the same step runs for days and sometimes more than a week, with technicians stepping in by hand when a crystal comes out wrong.
It’s the same outfit that opened a fuel-target factory in Livermore in July.
That target is smaller than you’re probably picturing. It’s a hollow carbon sphere roughly 0.16 to 0.20 inches across (4 to 5 mm), with a thin shell of frozen deuterium and tritium coating the inside of it and a bubble of the same stuff, as gas, sitting in the middle. Deuterium and tritium are both hydrogen carrying extra neutrons, and they’re the pair that fuses at the lowest temperature.
So why does the ice have to be smooth?
Because the laser never touches the fuel. It hits a gold can wrapped around the capsule, the can turns that light into X-rays, and the X-rays crush the carbon shell inward from every side. Everything has to arrive together, and you don’t get a second attempt.
A groove in the ice doesn’t stay a groove. It grows while the shell collapses, stirring cold fuel into the hot spot forming at the center, and the reaction quits before it burns through. That’s why the NIF crew grows its crystals slowly and throws out the lumpy ones.
Inertia published a chart of the roughness it measured on the fast-grown layers, broken out by how fine or coarse the wobble is. Those measurements land inside NIF’s own ignition specification, which the company points out is tighter than the one its own design needs. LLNL then ran those layers through the same simulation codes it uses to design ignition shots. Next it dialed the defects up several times past anything that had actually been measured, just to see what broke. Fusion energy output stayed within 10 percent of maximum.
The plan is to overbuild the laser
Here’s where Inertia’s design can do something the lab can’t. NIF puts about 2 megajoules into a target. Inertia is designing for 10, and a bigger hammer means the fuel doesn’t have to be flawless.
“A groove that would be problematic on NIF is acceptable at Inertia’s scale,” said Chris Weber, an inertial confinement physicist and capsule modeling team lead at LLNL, in the company’s announcement. His reasoning is that Inertia’s ice layer is thicker than NIF’s, and a thicker layer damps out a defect of the same size.
Jeff Lawson, Inertia’s co-founder and CEO, put it to TechCrunch more plainly: “That’s our strategy, to oversize our driver, our laser.” Spending your money on the single most expensive component so you can be sloppier everywhere else is a fairly unusual way to run an engineering program, and as far as I can tell it’s the plan for the entire plant.
Inertia thinks that same margin gets layering under an hour eventually. I’d file that one under ambition. Nobody’s fired a shot at a commercially made Inertia capsule, the company hasn’t said how many layers it grew to get these numbers, and two to three hours is the one number here that’s got measurements behind it.
Tritium is the awkward half of the fuel
Deuterium you can pull out of seawater. Tritium’s radioactive, it decays at about 5.5 percent a year, and TechCrunch puts the going rate near $30,000 a gram with roughly 25 kilograms stockpiled worldwide, citing the journal Science. We went through that arithmetic when Britain hired an American startup to breed the stuff inside a reactor.
So the faster you build a fuel layer, the less tritium sits around in your factory waiting. That cuts what you’ve got to buy up front, what you’ve got to store, and what a regulator’s going to come and inspect. It’s a boring-sounding benefit and probably the most useful one on this list.
One box down, nine to go
Inertia published a list of ten things it has to show before it can talk seriously about a plant, and fast fueling is the first one checked off. The other nine are bigger jobs. It’ll need high-power laser diodes around 50 times cheaper than today’s, an amplifier that fires ten times a second rather than roughly once a day, and a target that gives back more than 25 times the energy going in. By Inertia’s own accounting, NIF’s current target puts out over 8 megajoules for the 2 megajoules of laser light going in, a gain of about four, so the company is asking for roughly six times that.
Inertia’s own write-up doesn’t carry a date on it, which is a slightly annoying habit for a company publishing technical results. TechCrunch got the story on August 20, the American Nuclear Society wrote it up on August 25, and the Livermore factory where all of this eventually has to happen by the million opened on July 10.
