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Laser fusion again...

Posted: Tue Dec 29, 2015 7:18 pm
by Munchausen

Re: Laser fusion again...

Posted: Tue Dec 29, 2015 9:09 pm
by Giorgio
It's a theoretical simulation, so the results is strongly correlated to the starting assumptions and starting experimental/theoretical data-set that was chosen when making the simulation. They didnt go much in details into the paper, but based on the reported results (and on the point that the thermal transfer efficiency in the simulation is in the range of 0.0X %), it does not seem to have any real practical application fusion wise.

Anyhow it is a nice paper and I am sure some one will take the challenge to test it in the lab to see if the experiments will mirror the simulation of if any interesting differences will arise.

Re: Laser fusion again...

Posted: Wed Dec 30, 2015 11:20 pm
by TheRadicalModerate
This sounds a little bit like the paper I referenced here. Lasers might start to get interesting as the pulse width starts to approach the wavelength.

Re: Laser fusion again...

Posted: Thu Dec 31, 2015 10:43 pm
by hanelyp
as the pulse width starts to approach the wavelength ...

... Electric fields associated with the pulse become an important element in driving the implosion.

Re: Laser fusion again...

Posted: Fri Jan 01, 2016 1:50 am
by Skipjack
As long as they need to have huge lasers and a gold plated hohlraum, I seriously doubt that this is the path to economic fusion reactors.

Re: Laser fusion again...

Posted: Fri Jan 01, 2016 7:03 am
by TheRadicalModerate
hanelyp wrote:
as the pulse width starts to approach the wavelength ...

... Electric fields associated with the pulse become an important element in driving the implosion.


Exactly. Ponderomotive effects start to swamp thermal effects.

Re: Laser fusion again...

Posted: Fri Jan 01, 2016 5:41 pm
by hanelyp
This talk of a very short coherent light pulse driving implosion has me pondering monopulse millimetre wave driven implosion, the longer wavelengths being far easier to generate efficiently. I'm also reminded that you can't "comb a hairy ball flat", suggesting a not entirely symmetrical implosion.

One arrangement that comes to mind involves filling a circular waveguide with fusion fuel then firing through a transverse magnetic microwave pulse to ionize and compress the fuel.

One drawback to photon electric field driven implosion is the electrons being driven the opposite direction from the ions.

Re: Laser fusion again...

Posted: Fri Jan 01, 2016 6:50 pm
by TheRadicalModerate
hanelyp wrote:This talk of a very short coherent light pulse driving implosion has me pondering monopulse millimetre wave driven implosion, the longer wavelengths being far easier to generate efficiently.

Remember that the way you get these ultra-short pulses is by compressing a relatively long pulse (or pulses) using weird optical tricks. Not sure how well those tricks work at longer wavelengths. However, a long-ish soliton would be the ponderomotive ideal.

I'm also reminded that you can't "comb a hairy ball flat", suggesting a not entirely symmetrical implosion.

Several schemes (e.g. MagLIF and the Hora paper cited above) use a cylinder of fuel in a coaxial solenoid magnetic field and then just heat one end, eliminating the topology problems. If you're just driving one population of ions near one end of the cylinder into another population closer to the middle of the cylinder, then spherical symmetry isn't important. You just need to contain the (remaining) electrons and ions radially to avoid cooling.

One arrangement that comes to mind involves filling a circular waveguide with fusion fuel then firing through a transverse magnetic microwave pulse to ionize and compress the fuel.

I don't think you can do all the chirping/compression of the pulse inside the resonant cavity. But if what you're saying is that the target is one end of a cylinder, then that's pretty much what they're doing.

One drawback to photon electric field driven implosion is the electrons being driven the opposite direction from the ions.

If the idea is to drive one non-maxwellian population of ions into another (stationary) population, then the heat loss from the electrons is pretty trivial. Also, note that there are plenty of electrons in the center, where you've ultimately got thermal conditions triggering ignition.

The nice thing about these ponderomotive schemes (assuming they actually show up in real hardware) is that they provide really nice energy sources for heating stuff in a solenoid field, which is simple and presumably requires very simple pellet design with no hohlraum. Just toss the lil' sucker into the solenoid field and zap it.