[scythe]

In this case, it's not clear how the analogy could apply, because you can't realistically deliver more fuel to the "reactor" while it's "running". An ultrafast laser pulse hits a target and it undergoes fusion for a few nanoseconds, maybe less, generating a huge explosion. You can't operate a fuel injector on that timeframe. So you need a big gain in terms of efficiency.

You can hopefully make a bigger fuel pellet, but that kind of scaling hasn't been demonstrated and isn't guaranteed, because it begins to disperse as soon as fusion initiates in this inertial confinement scheme. So "just" a matter of runtime is harder than it might seem at first.

I'm curious if you could power boats like this, though. It might not be economical for electricity. But the power-to-weight ratio is probably pretty good.

[noobermin]

You do not need a continuous stream injecting at every nano second...you can operate much slower than that. If you watched the stream, they said a few hertz is enough. A milisecond is an eternity compared to a nanosecond, you remove the neutrons away from the interaction site well before the next start of the rep-rate when you inject the next pellet / holhraum. You just need to have something to capture the neutrons and convert that into heat to boil water, which will accumulate over various repetitions of course (water boils much slower than a GHz), and that thing need not be where the pellets are blasted.

That said, I'd need to think about it the design, I just don't think it's impossible.

[scythe]

From the PDF (page 15):

https://suli.pppl.gov/2018/course/Ma.pdf

typical confinement time for ICF is on the order of a tenth of a nanosecond. I don't expect they have made a factor-of-millions improvement on this. I generally avoid watching videos whenever possible, but I think you are referring to the frequency at which the fuel pellets can be repeatedly ignited by a laser — there are no plans to use the output of one fuel pellet to directly ignite the next. In fact not even the "magneto-inertial" techniques with putative confinement times in the microseconds have a roadmap to achieve this.

[noobermin]

You don't use the ignition of one pellet for the next...each pellet ignites itself.

It isn't a nuclear fission reaction where it is a chain reaction between pellets. Each pellet interaction produces energy, and you capture that energy. It is ignition for the pellet, not other pellets in the machine. The boiling of water thankfully happens on a much longer timescale, being accumulationf of energy of many pellets over a few cycles.

[scythe]

The pellets produce a net energy release larger than the energy used by the laser. This energy gain is called "ignition" in fusion parlance. A fuel pellet does not ignite itself — otherwise, they would be destroyed as soon as they are produced, like the critical ball in a nuclear warhead. That's what I was saying from the beginning: the laser does not function like the spark plug on a car engine; it is required for every ignition. It's pretty clear if you go back and read the analogy I initially responded to.