Submitted by Robo-Connery t3_zl56h9 in science
Robo-Connery OP t1_j06psgk wrote
Reply to comment by zbobet2012 in National Ignition Facility (NIF) announces net positive energy fusion experiment by Robo-Connery
I can try to answer these follow ups:
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For sure there is efficiency to be gained, 20% is definitely achievable but not for a long time (maybe only when using a non frequency doubled laser), currently the most efficient diode pumped lasers are about 10% efficient. At 20% this means a 20x improvement (if you can deliver the 4MJ rather than 2MJ to target. It is hard to imagine much more improvements over that, but there is a huge ceiling for improvements in the fusion yield. They need both to get the 5 or so orders of magnitude they need between both. I would point out though that the demands on the laser are different for the different purposes, technology translates but not without adaptation.
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I 100% agree that one of the few (maybe only significant?) advantages of ICF is the target chamber being very simple. They actually also benefit from a smaller neutron blanket being necessary but it isn't all positives, the number of laser beam paths needed to evenly heat the holhraum makes fitting the blanket around the outside comparatively tricky.
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I don't believe this is either true or an advantage. NIF uses less tritium because it does tiny shots once a day. Jet pulses every 20-30 minutes with much higher amounts of tritium in each shot because it generates far more energy (50-100x more roughly) so requires far more fuel on site. Fundamentally I disagree there is a proliferation problem, tritium is not the limiting step in making a hydrogen bomb (the fission warhead is far harder) nor is it essential, DD is sufficient. Lastly, we don't like having it around because it is hard to handle, and extremely radioactive, I don't think it is in particular due to proliferation fears.
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So NIF is a weapons lab but it is somewhat supported by the fusion-for-power cause too. It does what it is designed to do very well (test equation of state of high density matter, test x-ray ablation of hydrogen targets, test compression and fusion of hydrogen targets). It does fusion for power reasonably badly. Without going off on paragraphs of text, MCF problems are numerous but they are mostly understood, we know we need different divertor designs and what they should be, we know we need better ELM control, we know we need to conquer tritium breeding and material science under neutron bombardment. ICF has similar problems and then 100 other ones - in the context of fusion for power. There is no sensible plan to get a 2-10Hz repeat rate on it (versus the 0.000001Hz of NIF), there is no sensible plan to get fabrication costs down by a factor of 1000. And on top of all of that MCF machines built in the 90's are about 1-1.5 order of magnitude away from our goal in terms of raw power output. (JET at 30MW versus ITER at 500MW with the same heating). ICF is 3 or 4 away (Again alongside the 6 orders in repeat rate). The disclaimer here is that ICF is extremely new science and MCF is established so there is plenty if time for ICF to mature. I'll leave it with saying that the steady state nature of a tokamak (maybe 1000s flat top burns not being out of the realms of possibility for ITER) just makes so much more sense as a power plant than pulsed explosions.
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Funding both of them makes 100% sense to me, I have no issues with ICF or with laser plasma physics in general and as I've said all over the place, NIF is an incredible feat of plasma physics and engineering. I doubt a commercial reactor will ever use both in my lifetime (in fact I doubt one will use ICF in my lifetime) but I am 100% certain there will be a tokamak power plant.
zbobet2012 t1_j078rk0 wrote
Incredible reply, and thank you!
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