well yes. The point is that it doesnt have to run continously. What counts for spallation is peak energy, so a bunch of supercapacitors could be the source of the one microsecond petawatt pule.
Probably destroy any smart phones nearby of course, from EMP, but that is a positive advantage :-)
Let's face it a petawatt in and two petawatts out, for a microsecond, every second is a gigawatt! you only need about 200KW for a decent car
so you would just fire the onmce in a while, creating a tiny nuclear explosion that would run the boiler for hours..
And probably good design to very accurately focus the laser beam would get peak power down a lot.
I only said petawatt laser because that is what they are using in the lab. The important thing is not the average power in, its the peak power concentrated on the spallation target. That is one of the design challenges that may be a show stopper, or not.
As I said, we started with tonnes of U235/238 to create free neutrons then moved on to particle accelerators to fire protons at spallation targets, now we are looking at using lasers..its getting smaller.
And that is really key. smaller means a lot less hazard and a lot less cost.
I am not going to say this is going to work, but it is certainly worth a sub million grant to look into laser induced fission. Its only been possible in the last few years as laser design has progressed up to the sort of peak power levels needed.
and yes, they are being used for fusion research, BUT the reason why they are useful for fission, is that fission is a lot easier to get working than fusion.
I have explained that.
High phopton energy on a spallation target produces free neutrons. Eseentially if you heat up stuff enoiughh it undergoes a sort orf raioactive decay to a digferent isotope and pops out neutrons.
neutrons are what you need and particlee accelertaytors do not produce neutrons directly, so they had been using proton beams to hit spallation targets to get neutrons out.
Normally if you uwant neutrons you use a radioactive material that produces them.
But this is a beter way to do it.
It doesn't have to be petawatts all it has to do
AS I have explained., you need to get above a critical energy density in the spallation target to make those neutrons. Lasers can just about do that.
No, that's more what they do for fusion...
here is a paper from 2005 using the vulcan petawatt laser at Rutherford labs to investigate ultra high enegegy laser induced spallation.
Note that the pulse is less than a picosecond here.
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The other refrences I have seen on prototype laser driven fission seem to suggest a foil spallation target backed by a film of (e.g.) thorium to soak up the spare neutrons and do the fission bit.
Its all very new. acceletrator ignition reactors have been proposed but accelerators are huge beasts.
The fact that lasers can do similar things is the fundamental key..in fusin they are somply interested in a very hot plasma and a shock wave, in fission its the neutrons you need.
And I think some of te effort that went into star wars to make incresdibly high powered lasers may be leaking out into fusion and fission research areas now.
hence the 'pocket fusion reactor' and this pocket fission reactor being burbled about.
What is sure is that high peak power lasers can create particles - neutrons and protons - on spallation targets. I think the use of those to promote fission in thorium has been demonstrated but its hard work googling it - I found a reference and lost it again.
What has not been demonstarted yet is a positive energy coefficient, although lacking the reference I have lost, I cant be sure of that, or indeed a sensible way to package all this into a commercially viable product.
So waht these car peopel are probably doing is saying 'if we had a relaible source of 200KW of theremal energy as heat, how could we make a far to run off it' rather in the same way that electric car devlopment happened on the premiss that one day a relaiable cheap 200KWh battery weighing less tha a tonne would appear. Which to daye it has not.
So a bit pie in the sky, but not totally.
Which is why, with respect, I am interested enough to reserach the area, and sceptical enough not to invest..yet :-)
sober scepticism, but not derision.
Those of us who watched 'tomorrows world' for years and years can recall perhps one or two out of several hudred 'scientific breakthroughs' actually dong something useful in later years.
Remember lasers? I saw my first laser at a rock concert. That seemed all it was useful for. I remember reading they were a 'solution without a problem'...
Now they are the back bone of the internet, behind all 'optical media' will cut wood and metal, and possibly initiate a fission or fusion reaction.
Fusion power was always possible, but the practical difficulties of doing it were monumental.
Here's another paper clearly demostrating laser induced thorium 232 and uranium 238 fission from 2003, but no hint of any positve energy out at that point.
But that's the point, that's as far as a research lab can go on a small budget. Yes we can split thorium with a laser...
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Note that the massively powerful laser ONLY generates 12 watts on average.
It is desinged to charge up, and fire a very short pulse of very high peak power, but only modest energy up, to ten times a second.
up till now accelerator driven systems (ADS) for nuclear fission have been proposed, but accelerators are big expensive beasts.
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Lasers are a lot less expensive.
If the billions thathave been watsed on 'renewable' energy had gone into half a dozen projects in this area, we might have tabletop nuclear reactors by now.
My point was that if the 8 grams was the fuel for life and you leave the fission products in place, like you do on modern subs, you might (by the end of life) need something like the same shielding of a current road transport flask for spent nuclear fuel from a civil nuclear power station. Roughly, a two metre cube weighing 50 tons.
The fuel in a typical UK flask has delivered something like 40,000 MWh of electrical energy, so my original assertion was probably wrong, this looks to me like a couple of orders of magnitude more than the car would need. So you might only need a ton of shielding (although in a fuel flask it turns out that the other uranium fuel makes a very significant contribution to the shielding).
Of course, current international regs for shipping used nuclear fuel require the "container" to remain its integrity after a 30 metre drop followed by an engulfing petrochemical fire for half an hour, which might impose some interesting design challenges.
That is the nature of Q Switching lasers - they produce gigantic instantaneous powers, but only for tiny fractions of a second. The average is often nothing to write home about.
No: thayts the WHOLE POINT of using an energuy ampolifier. Yu need peanuts of fuel and there arent that many fission products to speak of - most get burned up by fissions.
THuis is utterly irrelevant to a thorium reactor.
Because its a sub critical desighn it doesnt need 50 tonnes of uranium to get going. The laser does that. The 8 grams of thorium are all that it has in it.
yes there's some vicious alpha beta and gamma, BUT that doesn't need tonnes of lead, because the reactor itself is probably no bigger than a test tube.
Gamma is the most difficult to shield really. But most of what comes out is beta - electrons. And those are stopped by a few millimeters of aluminium - no big shielding required.
the reason for tonnes of conmcrete and lead is simply to stop gamma. But I am pretty sure that the only gamma a pure thorium reactor would produce is from decay of U233.
This is where my understanding of nuclear phsyics is starting to run out. as far as I can tell the cycle would be that thorium absorbs a spallation neutron and immedately turns into Throium 233, which decays rapidly into Proactinium 233, then uranium 233, (emitting electrons on the way) which when hit with another neutron actually fissions to provide most of the energy output.
Ultimately its the U233 or U235 that fissions. producing non radioactive end products.
The chief danger seems to be residual U233 and U232 in a reactor that's off line - that will spontaneously decay quite quickly producing a lot of gamma.
So that would need shielding BUT we are talking tiny amounts of radioactive material in a car or ship sized reactor. Maybe the whole thing would be a cube of lead smaller than a tea cup, with a heat exchanger in it, a laser in it, and thats it.
The whole point is that a critical reactor needs tonnes of partiually enriched uranium to work. And the rest of the fuel - U238 - gets turned into nastiness by neutron absorbtion. A laser ignited reactor doesn't have a critical mass - its always sub critcal - so the sheer volume of material to transute simply isn't there, and most of what is there gets burnt up.
It has to be said that all this is highly speculatve, because no one has built a laser ignited fission reactor yet.
So it might be that the original article is pure BS. Nevertheless acceleratator driven reactors have been built, and the approach in general seems valid enough to be worth looking at.
What a load of bollocks. The reason cities are warmer is the effect of solar insolation is greater and there is no evaporative cooling effect from vegetation. Compared with that, the amount of energy we use is utterly insignificant.
Amazing the number of people that lap up this crap because it's what they want to hear. Why they believe any indiviadual should be able to do this when government programmes have failed beats me.
Maybe it's the picture of the (photocrap?) stupid car that deludes their tiny minds. They believe/don'tbelive stuff because they are living in a dream world. I blame the DM/DT.
You only have to use your common sense. All the easy things that an individual can discover in their garden sheds have been done. What's left is difficult and expensive. Especially in the field of nuclear research.
And especially when you see a stupid impractical car. This is just an attention seeker/hoaxter. Preying on the gullible.
I expect there were halfwits here believed in cold fusion too.
Well that's a claim that has been made many many times in the past. Its sure to be as wrong now as it ever was.
My comments were general in nature and not specifically related to the subject in this thread. Your posting MO seems to have degenerated into waiting for TNP or one of your other favoured perceived nemesis to post, and then chip in with a well thought out and deeply reasoned "that's bollocks" or similar.
Either he has found a new group to haunt, or croaked...
It's your physics which is letting you down. For each little bit of energy you get from one fission, you get two fission products. And
*these* are the dominant source of radiation. To a good approximation it's independent of what you are fissioning. The level of radioactivity is more or less linear with the energy generated.
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