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I'm not sure if it's theoretically impossible. But it's certainly an incredible challenge to build a high efficiency laser system that can consistently generate

I'm not sure if it's theoretically impossible. But it's certainly an incredible challenge to build a high efficiency laser system that can consistently generate many pulses per second without degrading either the laser head itself or any associated micro-focussing optics. Can we stop pretending this isn't about nuclear weapons research and - basically - continued funding? LLNL is at least a decade behind its initial predictions of ignition. The current lasers may be inefficient but they've been fine-tuned very precisely for optical quality. There's no guarantee more efficient lasers would have the same characteristics and could be focussed in the same way. I'm sure LLNL know the maximum theoretical fusion gain for a realistic pellet design, and it's worth nothing that that number hasn't been mentioned anywhere. Clearly there's only so much energy available for each cycle. If that energy is on the wrong side of what's needed to release it even after efficiency improvements, the entire system isn't workable, no matter how it's re-engineered.

danbruc 4y ago
My point was purely about the claimed impossibility of a hundredfold efficiency increase which is only true if you are already about 1 % efficient. I have no real opinion on what the NIF is doing or not, at best my layman judgment would be that laser fusion is way further from becoming practical than tokamaks or stellerators.
- tmikaeld 4y ago
  You're right that we don't have enough information here, I've been reading a lot about it's theory and practicality throughout the years. There's also theories about ignition in parallell, by using multiple pellets. Since the first step has been taken, there's a lot of avenues for improvement. However, one also has to take into account the "chaos" created by the ignition in the first place, re-introducing an additional pellet or chain reaction has it's own challenges.
scythe 4y ago
>Can we stop pretending this isn't about nuclear weapons research The laser practicality issue that prevents this from directly becoming a power source would also be a major barrier to its application as a weapon. The laser fires in the UV-B (351 nm), which is scattered and attenuated by air, to say nothing of smoke or dust; it also requires incredibly high targeting precision (<2 mm target diameter) and consequently precise placement of a target weighing only milligrams. Additionally, the various optical components of the laser must be very well aligned, which is difficult to achieve in any battlefield conditions. And the whole thing is a very obvious and vulnerable target. I ascribe a small possibility to its utility as a weapon in space, but practically zero on Earth without other major developments. >I'm sure LLNL know the maximum theoretical fusion gain for a realistic pellet design, and it's worth nothing that that number hasn't been mentioned anywhere. I wouldn't be so sure. Fusion is in general quantum chromodynamics, which is not so well characterized (being the subject of the famous YM mass gap conjecture). Even in this case it was stated that the yield exceeded expectations and damaged the sensors, which was probably not desired.
- scythe 4y ago
  Past the edit time limit, but Kawata and Kurawaki predicted the practicality of pellet sizes up to 1 gram (maximum theoretical yield 377 GJ) in 1996: https://aip.scitation.org/doi/abs/10.1063/1.50451 https://aip.scitation.org/doi/abs/10.1063/1.50451
- p_j_w 4y ago
  NIF isn't used for research into a new kind of weapon, in the context of nuclear weapons, it's used to generate similar conditions to an actual nuclear explosion, as the US government has signed treaties that agree to not test nuclear weapons anymore.

danbruc 4y ago

My point was purely about the claimed impossibility of a hundredfold efficiency increase which is only true if you are already about 1 % efficient. I have no real opinion on what the NIF is doing or not, at best my layman judgment would be that laser fusion is way further from becoming practical than tokamaks or stellerators.

tmikaeld 4y ago
You're right that we don't have enough information here, I've been reading a lot about it's theory and practicality throughout the years. There's also theories about ignition in parallell, by using multiple pellets. Since the first step has been taken, there's a lot of avenues for improvement. However, one also has to take into account the "chaos" created by the ignition in the first place, re-introducing an additional pellet or chain reaction has it's own challenges.

scythe 4y ago

>Can we stop pretending this isn't about nuclear weapons research The laser practicality issue that prevents this from directly becoming a power source would also be a major barrier to its application as a weapon. The laser fires in the UV-B (351 nm), which is scattered and attenuated by air, to say nothing of smoke or dust; it also requires incredibly high targeting precision (<2 mm target diameter) and consequently precise placement of a target weighing only milligrams. Additionally, the various optical components of the laser must be very well aligned, which is difficult to achieve in any battlefield conditions. And the whole thing is a very obvious and vulnerable target. I ascribe a small possibility to its utility as a weapon in space, but practically zero on Earth without other major developments. >I'm sure LLNL know the maximum theoretical fusion gain for a realistic pellet design, and it's worth nothing that that number hasn't been mentioned anywhere. I wouldn't be so sure. Fusion is in general quantum chromodynamics, which is not so well characterized (being the subject of the famous YM mass gap conjecture). Even in this case it was stated that the yield exceeded expectations and damaged the sensors, which was probably not desired.

scythe 4y ago
Past the edit time limit, but Kawata and Kurawaki predicted the practicality of pellet sizes up to 1 gram (maximum theoretical yield 377 GJ) in 1996: https://aip.scitation.org/doi/abs/10.1063/1.50451 https://aip.scitation.org/doi/abs/10.1063/1.50451
p_j_w 4y ago
NIF isn't used for research into a new kind of weapon, in the context of nuclear weapons, it's used to generate similar conditions to an actual nuclear explosion, as the US government has signed treaties that agree to not test nuclear weapons anymore.