Yes, the title contains the phrase "fusion milestone passed", plz refrain from moistening your collective nuclear panties.
The BBC story gives almost zero useful detail here, as is to be expected from them on big science stories when the byline
isn't my boy Pallab Ghosh <3. However, it appears an internal email of NIF relevant to this "milestone" was leaked to
the local Livermore rag, The Independent, in which the following interesting information is conveyed and from which we can infer quite a lot:
"According to the email from program leader Ed Moses, in Saturday’s experiment, NIF fired 1.8 million joules of energy along its 192 arms, generating a record 15 quadrillion neutrons from a frozen heavy hydrogen (deuterium-tritium) target with an energy output nearly 75 percent higher than the previous record."
This, while interesting, is NOT something to flip out over, as I will explain in detail why below. Also notice that while the BBC doesn't the word "breakeven" (the specific fusion parameter of Q≥1) outright, that is indeed what they are claiming has occurred here when they say:
"The BBC understands that during an experiment in late September, the amount of energy released through the fusion reaction exceeded the amount of energy being absorbed by the fuel."
This is a highly dubious claim and I strongly suspect some very creative numberfucking is going on behind the scenes if this is indeed the claim being made by NIF. Since we can easily deduce the total energy released by fusion reactions in a shot with a credible yield of 1.5x1016 (15 quadrillion) neutrons each possessing a kinetic energy of 14.1 MeV as must be the case in deuterium tritium fusion reactions of the kind this laser is attempting - the answer is ≈40 Kilojoules - there is obviously some accounting to be done between that number and the number of Kj the target likely absorbed.
Now, the laser itself consumes about a hundred metric FUCKTONS of energy to fire a single shot: the capacitor bank that fires the thousands of
enormous xenon flashlamps to pump the neodymium doped laser glass of the system together consume nearly HALF A GIGAJOULE of electricity when charging up. Clearly that is NOT the comparison they're making to that 40Kj of fusion energy out that would meet breakeven. What about the energy of the laser itself, maybe that's the comparison? No. NIF produces 4 megajoules in 192 beams of near-infrared radiation which is then frequency converted to the ultraviolet for a total of ~2 Mj of 351 nanometer UV laser light. Clearly that is not the comparison either. What about the thermal x-rays inside the gold hohlraum in which the fuel is contained and on which the lasers impinge that's depicted in that inset picture in the article? Nope, there's about a megajoule of x-rays inside that little pencil eraser sized oven at the bangtime. Ok, well then what about the total energy of x-rays
actually delivered to the BB sized hydrogen fuel capsule surface itself during the actual microballoon ablation and implosion drive of the fuel? NO. After all that, about 200 Kj of x-rays are being delivered to the capsule during the 10 nanoseconds of fuel assembly and adiabatic compression.
So HOW did this notion of breakeven start to get bandied about somewhere behind the scenes here? Well the only way I can see, is that they're using the energy actually deposited
inside the compressed hundred micron diameter ultrahot core of the imploded fuel pellet at the time of maximum compression and density which, considering the inefficiencies of core compression and ablative blowoff of the rest of the outer layers of the core during assembly, MAY approach the low end of the ~50-100 kilojoule range. That's pretty damn deceptive if you ask me. 40Kj out with 400+ MJ in = hilariously abysmal wall plug efficiency.
Why am I being so critical? Because this device was sold to the public as AN IGNITION MACHINE. The scientists working on the project over the past 2 decades were so confident that it would achieve ignition and burn with very high gain factors of Q>100 in some simulations that they put the word ignition in the goddamn title of the project. It is now clear, in spite of "hopeful" stories like this one that they seem to be pumping out with strange regularity, that NIF will NEVER achieve ignition, and that is because the gap between the current fusion yields, even the latest one they're singing hosannas about here that's nearly 2X the last highest yield achieved last year,
are still well over an order of magnitude away from achieving the goal of ignition. And nobody has the slightest fucking clue why. There are practically innumerable energy sapping mechanisms that suck energy away from an imploding capsule during a shot: stimulated Brillouin scattering, x-ray heating of the hohlraum, stimulated Raman scattering, two-plasmon decay, Rayleigh-Taylor hydrodynamic instabilities in the imploding fuel layers, inverse electron-cyclotron resonance heating of the electrons in the capsule blowoff plasma, etc., etc., etc., etc. and just like all the previous huge laser fusion experiments done since the 70s, nobody knows where the excess energy leakage is going on these new experiments. Everyone thought that this was going to be it, that 2 MJ of UV radiation was going to be enough to get this shit done.
Well it wasn't, and this is now the sad, ignominious, devastating 4 billion dollar end of the road for laser fusion.
