Tuesday, December 13, 2022

The fusion story of the day

There is a press conference going on right now announcing a breakthrough at the National Ignition Facility at Livermore.   The NIF is an inertial confinement fusion facility that uses 192 laser beams to compress a fuel pellet containing deuterium and tritium.  The pellet is inside a gold hohlraum, and it's really the x-rays from the gold that do a lot of the heavy lifting in this experiment.  The claim is that the energy output from the D-T fusion (which comes in the form of energetic helium nuclei, 14 MeV neutrons, and x-rays) has now exceeded the energy input from the lasers.  That's clearly necessary if there is ever to be any hope of using this approach to generate actual electricity, but it is far from sufficient. 

There is some very interesting materials science at work throughout the project that bears on this.  Right now, the lasers used in the NIF are based on doped glass amplifiers, and those get very hot under use, so that there needs to be hours between shots.  Also, they basically rebuild the sample mounting for the hohlraum after each shot.  This is fine for proof-of-concept physics experiments, but it's very far from a workable power plant.  

This is an exciting time for fusion research, in that there is a fair bit of activity, including startups.  (Note also that some of these approaches are aiming for scales closer to US Navy sized, like 20 MWe, rather than city power which is more like 2 GWe.)   To give a sense of my age and the timescale for these projects, when I was an undergrad, I spent a summer doing heat transfer calculations for the cable-in-conduit conductors for the D magnets for ITER.  That was in 1992.  The cliché is that fusion is always 20 yrs away, but we should know considerably sooner than that whether the startup approaches are likely to get there.  


Anonymous said...

This was a bit of a bs press conference. They got about 1 percent of energy out of the fusion from what was needed for the lasers.

Methinks they needed a splash after the Brits had their 5 seconds continuous (!) energy production milestone last year.

Anonymous said...

422 MJ IR in, made 200 MJ of UV, made 170 MJ of x-rays, made 20 MJ of laser input, which made 25 MJ output.

And it's a batch process.

Anonymous said...


No guarantee the writing is correct (have not read there before), but the intro is good.

Anonymous said...

i wrote up some notes on the commercial and engineering problems of fusion devices that tries to cut through the hype. Your readers might find interesting: https://lvenneri.com/blog/ConFusion

Douglas Natelson said...

Thanks, everyone. Insightful comments.