Does this announcement mean fusion as a power source is near? I love NIF and think they do great science, but fusion has long suffered from being too promising so we need to make sure we have a appropriate context for these results.

I mentioned in the main post that NIF takes about 400 MJ per shot to power the bulbs that pump the laser material, this produces a 4 MJ IR laser pulse which is frequency converted to a 2 MJ UV laser pulse. This obviously means that the 3.15 MJ is obviously not greater than the total energy expended on the system. Huge gains in energy efficiency can certainly be achieved in the laser, as efficiency was not the goal, but this will absolutely be necessary along with a huge gain in experiment throughput, likely comparable to the 2500% breakthrough achieved last year. past. . They may have it in them, we'll have to wait.

Obviously, the energy is not recovered. A working Fusion plant needs some sort of energy recovery system, normally thought of as a lithium shell that absorbs neutrons, heats water into steam to drive the turbines, and as a bonus produces tritium fuel for its reactor.

NIF can do about 1 shot a day, at 3MJ per shot, which works out to something like 30 watts. A power plant using inertial confinement fusion (ICF) will probably need to fire several shots per second. In reality, this is an extremely complicated task that requires a complete rethink of the entire machine.

Related, shots are extraordinarily expensive. Last I heard it was $60k a shot, but I suspect that's out of date. Ice pellets need to be perfect, just like gold holraum, and being tiny, they are extremely expensive to craft. The level of quality control must also be extremely high, the non-linearity of the compression wave traveling through the pickup presents a ridiculous physical challenge. As such, I expect there to be a lot of variation between experiments due to small imperfections or differences between the pickup and the pulse shape.

Those are the main caveats about this experiment, though there are definitely others.

How ​​about the tokamaks?

I want to compare this to similar results from tokamaks that are compared in the relevant news articles, usually the fusion experiments people are most familiar with. I've worked on tokamaks for years and as such probably has an inherent bias. I have a bias in the degree to which I am informed about the various machines.

The Joint European Torus (JET) holds the record in terms of energy going out to energy going into tokamaks. In tokamaks, this ratio is called the Q value.

Aside from the value of q – Many news articles calculate the q of NIF and compare it to tokamaks, which is inappropriate in my opinion. In tokamaks, the q value is defined as the ratio between the heating power alpha (energy produced by fusion reactions that is trapped in the machine) and the heating power input. The reason this is used is due to a simple idea: if I'm needing 25 MW of external heat to keep a reactor at a given temperature, I could replace it with 25 MW of internal heat and keep it the same temperature. In practice the whole thing is much more complicated and probably means that you always need at least some of the external heat. We call the situation, where there are 25MW internal and 25MW external, Q=1.

There are two ways energy is emitted in DT fusion where D+T -> He + n, the alpha power (or the energy of the helium nucleus) remains trapped in the tokamaks but the energy imparted to the neutron escapes the magnetic field towards the environment. In DT fusion, about 80% of the energy goes to the neutrons and escapes the reactor, so if you had 25 MW of alpha power, you would have 100 MW of neutron power. You use alpha power to keep your plasma hot, and you use the neutrons in your steam turbines for power.

In NIF, they don't need the alpha power because the reaction is not self-sustaining, and in fact there is no magnetic field, so everything just as easily escapes to be used anyway (although the alpha radiation is obviously collected by the machine walls rather than requiring an external blanket). This means that when NIF cites an energy output, it means alpha + neutron combined.

Ok, with that out of the way, I have no problem with NIF using full energy instead of alpha power because it makes a lot of sense, but when this is compared to MCF experiments that only quote alpha power, it makes hairs. in my neck rises.

back on topic. So JET got a q value of about 0.7 in 1996 when they did DT campaigns, they got about 17 MW of alpha power from 25 MW of external heating. JET are currently running DT campaigns again but they are focused on sustained power production and with massive upgrades in the intervening years to the neutral beam heating system now producing around 30 MW alpha for 45-50 MW external heating . for an aq of about 0.6 (but held for about 6-8 seconds).

ITER, the next-generation tokamak experiment, is tentatively expected to produce around 500 MW from 50-60 MW of heating, but with those experiments 10 years from now, it remains to be seen how close they get to that goal.

I mentioned the 400 MJ power budget to pump the laser and it's true that JET has additional power costs as well. The magnets only use 800MW to power themselves! However, there is a much clearer path (in my opinion) to reduce this cost, since the superconducting magnets in ITER and other experiments bring the power needed for the magnets to almost 0 and the other energy sinks are trivial in comparison. There is no comparable reduction available for lasers on ICF machines which must always pump inefficiently.

In a broader sense, the steady-state nature (well, we can hope that one day they will be) of tokamaks makes the path to power generation clearer. In my opinion, ICF just has a few more bumps in the road (and they're really big bumps, too).

I have rambled too long and my fingers are cold so I definitely have to end this comment here and I definitely have to end this on the positive note that I love NIF and have seen some amazing results but the title hogs it. "positive energy fusion reaction" doesn't do it for me. With no clear path to the next step (a demonstration power plant), it seems almost irrelevant to me how much backlash produces, though I grudgingly admit that it helps the pooling of funds to have these stories.

We've been able to create fusion reactions for a long time, but only now can we create one that produces more energy than it takes to start it.

This is huge because if we're going to use fusion as an energy source, obviously that's only possible if the reaction creates more energy than it consumes.

The reason this matters is that commercially available fusion reactors would solve many of our problems at once. As fuel, it uses hydrogen, the most abundant element in the universe and which we can easily and cheaply get from air or water, and produces helium, which is safe for humans (plus, we're running out of it and need it for various applications industrial), and tritium, which is MUCH, MUCH less dangerous than fission reactor byproducts, and has a very short half-life (12 years compared to 24,000 years for plutonium-239), so it decays quickly and doesn't really need to be stored forever.

Edit to add: Also, fusion reactors can't have runaway reactions like Chernobyl, Fukushima, or Three Mile Island. The reaction simply stops when you stop the process, which is another big safety advantage.

We are not yet at the point of producing net power from fusion. That is made up of 3 separate milestones: On (when the reaction produces more energy than it uses, i.e. it self-heats), Scientific Breakeven (when it produces more energy than the systems direct input, i.e. the lasers ) and engineering break-even point (when it produces more power than is used by all the necessary systems, i.e. things that power the lasers and keep everything running). This is the second, the first was cleared in February. The third is unfortunately a long way off, because lasers are terribly inefficient. And then it would take to the point of commercialization it would take decades and decades of development and advancement that would gradually decrease its efficiency until it was better than everything else

It is a great achievement, but there is still a lot of work to be done;

☑️ The Fusion Energy Output must be greater than the Fusion Energy Input.

☐ The output of the melt, reduced by the efficiency of the steam turbine, must be greater than the input.

☐ The process must be cheap enough to be economically viable.

☐ To scale, we need a cheap and energy efficient way to create fuels, deuterium and tritium.

Pretty sure we're still a few decades away from generating net power to the grid. So in the short term it means spending a lot more money on research while nobody does much about climate change.

…I'm not saying we don't spend money on fusion research, I'm just saying it would be nice if we did more to prevent a climate apocalypse. Fusion probably won't scale over time.

They've figured out a way to make fusion happen with net energy, so logically positively the next step is to figure out how to harness it. It's still going to take a long time for that breakthrough to arrive.

I think it's similar to when the Wright brothers determined the basic conditions needed to generate flight, they narrowed the scope of variables for everyone else. In 70 years, humanity went from being unable to fly to putting a man on the moon. I'm still young enough to get to experience a significant part of how the merger will affect humanity, and I'm fucking excited!