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Laser-driven Spherically Convergent Plasma Fusion

Posted: Wed Apr 26, 2017 6:34 pm
by Paul W Fontana
A "new" method for producing fusion neutrons has been demonstrated - looks like it's basically a tabletop ICF device: https://physics.aps.org/synopsis-for/10 ... 118.165001.

-- pwf

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 2:30 pm
by Dennis P Brown
So these Chinese researcher's generated a "billion" neutrons - without knowing the laser energy output or wavelength - a rather useless claim. However, NIF produced many orders of magnitude more neutrons then this current effort and still fell short by five orders of magnitude to reach laser energy break even (forget about ignition.) All in all, a rather pointless method and claim that, until they can at the very least achieve levels of uselessness like that of NIF, really just offer's more bad news. Even a superficial review shows that lining a structure with fuel and exploding it (rather than imploding), will achieve no viable method for real gain - as for a neutron source, again, without parameters of the laser(s), a rather worthless claim.

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 4:03 pm
by Richard Hull
Again, it is putt-putt boat fusion! What is the COP? Rep rate? NIF wants to do it but it is falling on its face.

As already mentioned, any laser fusion process must far exceed the laser energy in physically converted electrical output generation before any discussion of any power delivery scenario can even be discussed. There are always pie-in-the sky ideas and hoped for possibilities, but few of the physicists actually look at the system down the road where the bean counter and engineering realm is forced to face a public only interested in how much it will reduce their power bill!

Richard Hull

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 4:37 pm
by Andrew Seltzman
From the PRL: "The SGIII-proto laser is a neodymium glass laser operating at triple frequency with the wavelength of 351 nm. It has eight laser beams with four beams on each end, outputting 8 kJ energy at maximum and a pulse duration from 1 to 3 ns."

I have attached a copy of the paper.

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 5:16 pm
by Dennis P Brown
A 8 kJ(!) laser(s) just for a billion neutrons!? What an utter waste of resources.

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 7:03 pm
by Andrew Seltzman
"maximum deuterium-deuterium (DD) fusion neutron yield of 3.5 × 10^9 with a 6.3 kJ laser."
This is (3.5e9n)/(6.3e3J)=5.5E5 n/J

For a fusor:
The Hirsch 1967 fusor achieved 3e7n/s/kw=3E4 n/J
My best run is 4e6 n/s/kw=4E3 n/J

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Thu Apr 27, 2017 11:22 pm
by Paul W Fontana
Of course, the stated purpose of the device is not to produce energy, but to generate neutrons. To that end, it appears to me to do a pretty good job. Each pulse produces as many neutrons as about 15 min. of operation of a good fusor. What's not clear to me is whether the hohlraum needs to be replaced with every shot - that would be a major cost and drawback and would presumably be the rate-setting step in an industrial application. Nevertheless, producing 10^9 neutrons in 5e-9 s is pretty impressive!

Andrew - thanks for the efficiency estimate, which shows that the system is no slouch. However, the laser is probably only a few percent efficient (most are), so if you were to include the total energy required per neutron it might come out to the same order of magnitude as your fusor.

-- pwf

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Fri Apr 28, 2017 1:24 pm
by Dennis P Brown
Yes, the hohlraum has to be replaced (a rather slow process, I bet; also, coating such a pellet takes a good amount of time) - as for efficiency, never really mattered since this was built just to be an extremely low flux neutron source and publish a useless, pointless paper. Considering the capital cost and running such a laser, this really is pointless for such a low yield system (use these neutrons for what?) Also, the size of this setup - I bet that system occupies a rather large laboratory where as a fusor is extremely small in comparison.

Re: Laser-driven Spherically Convergent Plasma Fusion

Posted: Sat Apr 29, 2017 8:47 am
by Richard Hull
Even with a proposed auto drop, repeating hohlraum setup, what might be a reasonable rep rate? Still, putt-putt boat fusion.

Richard Hull