p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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TheRadicalModerate
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p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby TheRadicalModerate » Sat Nov 21, 2015 2:30 am

Here's a group that's claiming they can get ponderomotive acceleration of blocks of plasma in a magnetized target:

http://docs.google.com/viewer?url=http% ... .02465.pdf

Seems like a long shot to me, but it's kinda interesting. I think this is old (70's and 80's) theoretical work from Hora that's been revived with better laser technology. Over my head, frankly. Any opinions?

Skipjack
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby Skipjack » Sat Nov 21, 2015 3:30 am

Seems like another variation of the giant NIF. PB11 would make more sense with something like that than DT I suppose, but I am still skeptical of the concept.

mvanwink5
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby mvanwink5 » Sat Nov 21, 2015 9:19 am

This ain't NIF.

This is not thermal compression of the pellet, but electromagnetic compression induced using two picosecond lasers; and the claimed gain is enormous.

A coil is used to generate the cylindrical kiloTesla field via laser 1 on figure 2 and that coil looks expendable. So each shot from what I am gathering will involve a PB11 pellet and sacrificial coil.

No costs associated with the pellet and coil are given, but there is one per second expended in this scheme. Still, without showing operating costs, the claim is a net $300 million for grid power per year. And further, no capital costs are shown. However, it would seem the capital costs would involve two PS lasers and the alpha collection grid.

There is no 'first wall' problem.

It seems the physics of their scheme is understood theoretically and has experimental backing. Are they asking for money yet?
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

TheRadicalModerate
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby TheRadicalModerate » Sat Nov 21, 2015 10:26 am

mvanwink5 wrote:This ain't NIF.
A coil is used to generate the cylindrical kiloTesla field via laser 1 on figure 2 and that coil looks expendable. So each shot from what I am gathering will involve a PB11 pellet and sacrificial coil.


I suspect that the coil/copper sleeve is sacrificial, but note that it's picking up its current from the laser pulse itself. If they actually fry the coil, they're going to have a copper contamination problem (which almost certainly hasn't been simulated yet).

One of the problems with MagLIF (which is kinda similar, albeit thermal) is that the Z-pinch + laser pulse is so violent that it fries the Helmholtz coils that generate the axial containment field. That kinda makes frying a simple copper sleeve look pretty good, although I have no clue what kind of tolerances are required. I'd guess they're fairly moderate--all they need to do is inhibit electron and alpha transport long enough for this cascade effect to build up.

I think they've confirmed the ponderomotive effects on solid flat targets, but it sounded to me that they haven't done a test on a cylindrical target yet, nor have they built the axial B-field. These guys are mostly optics folks--I don't think they've started looking for fusion money yet.

mvanwink5
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby mvanwink5 » Sat Nov 21, 2015 11:11 am

I would expect that the entire event takes place so fast that there is no possibility for the coil to contaminate the pellet.
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

Skipjack
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby Skipjack » Mon Nov 23, 2015 2:15 am

mvanwink5 wrote:This ain't NIF.

It still needs giant lasers and has other similarities. As I said. I think it is better than the NIF concept, but I am not convinced.

mvanwink5
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby mvanwink5 » Mon Nov 23, 2015 9:40 am

That is just being argumentative, like saying a mouse and an elephant are both mammals. And everyone is skeptical. Come on. :roll:
Near term, cheap, dark horse fusion hits the air waves, GF - TED, LM - Announcement. The race is on.

djolds1
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby djolds1 » Wed Nov 25, 2015 4:58 am

mvanwink5 wrote:This ain't NIF.

This is not thermal compression of the pellet, but electromagnetic compression induced using two picosecond lasers; and the claimed gain is enormous.
A gain of several hundred. So a Q of several tens in hardware.

Close to the claimed gain for Winterberg's 2003 design, which also used electromagnetic compression.

http://www.21stcenturysciencetech.com/a ... rview.html
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby TheRadicalModerate » Thu Nov 26, 2015 8:00 pm

djolds1 wrote:
mvanwink5 wrote:This ain't NIF.

This is not thermal compression of the pellet, but electromagnetic compression induced using two picosecond lasers; and the claimed gain is enormous.
A gain of several hundred. So a Q of several tens in hardware.

Close to the claimed gain for Winterberg's 2003 design, which also used electromagnetic compression.

http://www.21stcenturysciencetech.com/a ... rview.html


The Winterberg design is still thermal--it's just using an electron beam for heating, and then you get a thermal shockwave propagating forward.

The Hora scheme is using ponderomotive acceleration of the ions, into the center of the target, because the the laser pulse is so large and so sharp that it produces a big honkin' E field gradient that drives the ions down the gradient (toward the center of the target). The argument here is that you've got a dynamic pressure term, produced by heating, and a ponderomotive term. With wide pulses, the pressure term swamps the ponderomotive term. But if you get the pulse short enough and powerful enough, the pondermotive term swamps the pressure term and produces much more efficient acceleration of the plasma.

RERT
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby RERT » Thu Nov 26, 2015 10:39 pm

I'm quite surprised that there has been no comment on one thing which caught my eye in the paper: they talk of an 'avalanche' reaction with energetic alphas provoking further reactions.

Isn't that a chain reaction? Is the gain so high because they have managed to provoke a small (ok very small!) explosion, and is that of any significance?

R.

D Tibbets
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Re: p-B11 Fast Ignition Scheme Using PW, ps-scale Laser Pulses

Postby D Tibbets » Fri Nov 27, 2015 4:14 pm

I don't believe it is a chain reaction like a supercritical fision reactor. The alphas from P-B11 fusion are hot and in the dense inertially confined plasma they heat the plasma sufficiently so that the fuel does not require continuous heating from outside. This is the typical ignition process envisioned for fusion reactors where the plasma is dense enough and contained long enough for the hot alphas to thermalize (heat) with the cooler fuel plasma. The alphas don not contribute to any further fusions themselfs. This is a qualified statement as alphas can fuse with each other. This is the triple alpha process in stars. But there are constraints on this process such that I do not think it will occur significantly in typical man made reactors.

Note that in the Polywell, the hot alphas do not hang around long enough to significantly heat the plasma. The alpha containment time is not long enough at the expected densities in a Polywell. They escape through the cusps. I have wondered though, if there is sufficient confluence (focus) of fuel ions in the center, the density in this small volume might be enough for some alpha heating, especially if one of the alphas produced is much lower energy than the other two alphas in the fusion chain. There is some information that one of the alphas may be close to or less than one MeV, and it's thermalization time will be faster than ~ 4 MeV alphas by a factor of ~ 16.

Dan Tibbets
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