Opinions on the Polywell fusion power system

BrianConlee

I wanted to throw out a question and see what some general consensus/opinion on the Polywell fusion power system is.

After I first read about the precursor (Farnsworth fuser) and was initially interested greatly as I had similiar thoughts before really researching fusion.

Personally, I'm not a big fan of the ITER project being pursued currently... but like us all I have hope that it might work.

So, what are your thoughts, comments, criticism?

Also, why havn't particle accelerators as a method of fusion been pursued?

ZapperZ

Quote by BrianConlee

Also, why havn't particle accelerators as a method of fusion been pursued?

You may want to read this thread:

http://www.physicsforums.com/showthread.php?t=178156

Zz.

BrianConlee

zz,

thanks for replying to my posts and guiding me like this. I tried doing a search on "polywell" but couldn't find any threads.

I'm a second year aerospace engineering student with a weird imagination... (don't we all have one?)

You?

Astronuc

The polywell/fusor systems have been around a long time. They basically use an electrostatic field to accelerate ions (radially) into the center of the chamber, as opposed to magnetic compression. They have drawbacks. Neutron howizters using d+t fusion (in which deuterons are accelerated in electrostatic fields into tritiated targets) were used as neutron sources, but they have very low reaction rates, i.e. low power density.

Accelerators would be inefficient (due to scattering) since one is only looking for 1-300 keV range for fusion temperatures. On the other hand, neutral beam injectors are one method of fueling and adding energy to a magnetically confined plasma. In neutral beam injectors, atoms are stripped and the nuclei accelerated electrostatically, and then neutralized (recombined with electrons) so that they pass through the magnetic field, and the energetic neutrals collide with the plasma and become ionized while dispersing their energy. Obviously the neutral beam energy must be greater than the nominal plasma energy (temperature).

The plasma confinement system is constrained by the strength of materials, which limits the plasma pressure, which limits the plasma temperature and density by virtue of pressure being proportional to nkT, where n is the particle density, k = Boltzmann's constant, T = ion/electron temperature. Also, the plasma temperature limited in order to reduce energy losses due to cyclotron and brehmsstruhlung radiation.

mheslep

R. Nebel of Los Alamos has taken over the Polywell work this past summer. He's been blogging a little about his motivation. Apparently he believes Polywell is worth the time because of its advantages as practical reactor vs a tokamak, mainly in power density. He asserts the Polywell has the potential to magnetically confine electrons per
n*kBolt*Te = B**2/(2*mu0)
That is, where the electron pressure is in balance the with magnetic bottle pressure.
Ions are in turn confined electrostatically by the well set up by the energetic electrons so that the plasma is quasineutral. If Te=10^4eV, B=10T, density is 2.5e22/m**3 which is ~ 10^4 greater than ITER's planned density. Nebel is not counting on any convergence of beam ions in the center here, just a confinement slightly out of LTE. Then there are other advantages like no external neutral beam or RF heating required as for a tokamak, in a Polywell the drive energy is supplied by the electron source. The big unknown appears to be the scale of the losses from the cusps in the quasi spherical magnetic bottle.

TallDave

Lots of relevant discussion at Talk Polywell, in the Theory forum.

http://www.talk-polywell.org/bb/view...ba414b2dece5a9

Art Carlson came by and laid out a lot of objections. Nebel has replied that many of them don't apply in a non-LTE environment, and explained why he believes the others can be solved.

Here's where Carlson originally weighed in before the dicussion moved to T-P.

http://cosmiclog.msnbc.msn.com/archi...36887.aspx?p=1

The relatively recent POPS research that might give an IEC scheme orders of magnitude more ion density also bodes well for Polywell's chances of eventually producing an economically practical fusion reactor, something the ITER path probably can't achieve (due to the poor power density) until competing fission/fossil fuels run out (at least 1,000 years away for the former).

TallDave

Quote by mheslep

The big unknown appears to be the scale of the losses from the cusps in the quasi spherical magnetic bottle.

This is a common point of confusion (and contention). The electron "losses" from the cusps are not losses per se, because the machine recirculates them (they do matter, because the machine must have a 1000:1 ratio inside the "bottle" versus outside). According to Bussard, the only actual losses are electron losses to unshielded areas of the machine, and cross-field transport.

What's really unknown is what losses look like at 1.5m vs 15 cm. Bussard believed they scaled as r^2, but the history of problems with predicting transport scaling in tokamaks suggest this prediction is fraught with uncertainty.

mheslep

Quote by TallDave

...
The relatively recent POPS research that might give an IEC scheme orders of magnitude more ion density also bodes well for Polywell's chances...

Yes I see comments that Nebel still thinks POPs viable, but my impression from the series of POPs paper authored by his team was no, POPs won't work in this case. The last one in series Space charge neutralization in inertial electrostatic confinement plasmas, Nebel et al, Physics of Plasmas 14, 2007
said in essence that while a steady state plasma might achieve compression in the core, oscillating plasmas (ie POPs) can not achieve high density through periodic compression:

Quote by Abstract

...Results indicate that there are limits on the amount of
compression that can be achieved by oscillating plasmas while simultaneously maintaining space charge neutralization and parabolic background potential.

The problem has to do with the spherical geometry chosen by a Polywell/fusor which has a work around

Quote by paper

What cannot be done is to simultaneously completely mitigate space charge effects with large compressions and maintain a pure harmonic-oscillator potential [POPS]in a sphere....
...It is also possible to get around the geometrical convergence limits altogether by using a cylindrical system rather than a spherical one.

But then they are back to the mirror confinement problem of the 70's.

Please comment if TD if you have other information.

mheslep

Quote by TallDave

Here's where Carlson originally weighed in before the dicussion moved to T-P.

http://cosmiclog.msnbc.msn.com/archi...36887.aspx?p=1

Bad link?

TallDave

Oops, sorry, copied the PF abbreviation.

http://cosmiclog.msnbc.msn.com/archi...36887.aspx?p=1

As to POPS, not sure where that stands at the moment. IIRC the original POPS paper stated 10^4 compression was possible, and I'm not sure what the referenced limit worked out to. Even a considerably smaller improvement would be helpful I suppose.

Nebel has said ion focus probably isn't that important in a Polywell. Maybe that obviates the need for a "parabolic" potential well as mentioned above and allows POPS to work better.

Nebel recently commented on another use for resonance: removing ash.

The idea is pretty simple. You oscillate the amplitude of the virtual cathode at the resonant transit frequency for the desired ion species you want to pump energy into. It selects species by q/m. For a harmonic oscillator potential, it's pretty trivial. It's described by Mathieu equations (driven harmonic oscillators). We demonstrated this experimentally (that's what's in the Phys Rev Lett.). This will be more involved for potentials other than harmonic oscillators, but it is probably doable.

Hopefully we'll get to find out how all this works in a larger machine. The funders are reportedly reviewing the WB-7 results.

PolywellGuy

Polywell Links:

A 1 hour 15 minute YouTube Film About the Polywell with Thomas Ligon, which trys to objectively present the Pro's & Con's of the polywell:
http://www.youtube.com/watch?v=1HatE...eature=related

The Talk Polywell Forum, which is filled with lots of discussions:
http://www.talk-polywell.org/bb/index.php

The Polywell Wikipedia page:
http://en.wikipedia.org/wiki/Polywell

A Good Polywell Blog:
http://iecfusiontech.blogspot.com/

Bussard's Big presentation at Google:
http://video.google.com/videoplay?do...le+go+nuclear#

Some of the major arguements against this device working was summarized by Dr. Todd Rider in his 1994 doctoral work "Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium" You can find that here:
http://dspace.mit.edu/handle/1721.1/11412

The Ligon Film does pretty good job of explaining the basic ideas, and the arguements for it working and for it not working,

TallDave

FYI, having reviewed the WB-7 results, they are now building WB-8 with .8T magnets. My rough calc is it wil be expected to produce at least 8W of fusion (that's the power gain if it has the same radius as WB-7 (which produced 2 milliwatts with .1T magnets) with B^4*r*3 scaling).

mheslep

Quote by PolywellGuy

Polywell Links:

A 1 hour 15 minute YouTube Film About the Polywell with Thomas Ligon, which trys to objectively present the Pro's & Con's of the polywell:
http://www.youtube.com/watch?v=1HatE...eature=related

The Talk Polywell Forum, which is filled with lots of discussions:
http://www.talk-polywell.org/bb/index.php

The Polywell Wikipedia page:
http://en.wikipedia.org/wiki/Polywell

A Good Polywell Blog:
http://iecfusiontech.blogspot.com/

Bussard's Big presentation at Google:
http://video.google.com/videoplay?do...le+go+nuclear#

Some of the major arguements against this device working was summarized by Dr. Todd Rider in his 1994 doctoral work "Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium" You can find that here:
http://dspace.mit.edu/handle/1721.1/11412

The Ligon Film does pretty good job of explaining the basic ideas, and the arguements for it working and for it not working,

PWG/TallDave: Several pop background links here. After all this time, is there any publication of actual results from the Nebel (LANL researcher) experiments that we can review?

TallDave

mheslep:

Sadly, no. There is a nondisclosure agreement. We only know the Navy reviewed it and funded the next step, which costs about $12M.

We did manage to dig up the contract for WB-8. There are some details about the equipment but no WB-7 results have been released afaik.

http://www.talk-polywell.org/bb/viewtopic.php?t=1353

Most intriguing is the reference to a design for a 100MW reactor, which is to be delivered at the end of the contract. Also interesting: WB-8 will attempt to fuse p-B11, the first time this has been done in a reactor-type machine than I'm aware of (as opposed to accelerators or the Russian picosecond laser experiment).

Results may be in reviewers' hands as soon as April. When we will see them is, unfortunately, anyone's guess. We may not see any detailed results until either the project is abandoned in failure or WB-100 is producing megawatts of fusion.

mheslep

I find the idea intriguing, but it's some twenty years now since this magnetic wiffle ball was conceived, with no journal published results. I understand non disclosures, and the antagonism from the DoE, but that only goes so far.

Quote by TallDave

...We may not see any detailed results until either the project is abandoned in failure or WB-100 is producing megawatts of fusion.

I hope there are other options, as that's a rather ridiculous way to do science, imo.

TallDave

Bussard dying was inconvenient, too. He was planning to publish something in 2008/2009 iirc.

It is quite frustratiing to know there is experimental data out there we can't access.

It's hard to say how much of is going to remain proprietary. If it works, of course, it could be both a trillion-dollar technology and a fairly significant military advantage, so it's hard to say how open the Navy and/or EMC2 are going to be.

ShotmanMaslo

Polywell is a plasma confinement concept that combines elements of inertial electrostatic confinement and magnetic confinement fusion, intended ultimately to produce fusion power.
The fundamental idea of the polywell device was conceived in 1983. Research was funded by US military and various small-scale prototypes were built.
Today, the development of this approach is funded by Navy but its underfunded because of wars and other projects like Tokamak. Following submission of the final WB-7 results in December 2008, Dr Richard Nebel commented that "There's nothing in there [the research] that suggests this will not work..." Dr. Bussard formed EMC2 Fusion Development Corporation, a non-profit organization, to seek funding for serious continuation of the project.

http://en.wikipedia.org/wiki/Polywell

In September 2009, the US Department of Defense announced further funding of $7,855,504 for Energy Matter Conversion Corp for research, analysis, development, and testing in support of the Plan Plasma Fusion (Polywell) Project. Efforts under this Recovery Act award will validate the basic physics of the Plasma Fusion (Polywell) concept, as well as provide the Navy with data for potential applications of polywell fusion. The project is expected to be completed by April 2011.[38]

Under development also is an "Open Source" Polywell MaGrid, to be found at the "Prometheus fusion perfection" weblog. Having demonstrated the feasibility of a Fansworth-Hirsch fusor recently, the next phase of the project is a Polywell, the parts for which have already been fabricated by 3D Rapid Prototyping.

Another particularly interesting quote from wiki:

With the success of WB-6, Bussard believed that the system had demonstrated itself to the degree that no intermediate-scale models would be needed, and noted, "We are probably the only people on the planet who know how to make a real net power clean fusion system"[8] He proposed to rebuild WB-6 more robustly to verify its performance. After conducting and publishing the results of dozens of repeatable tests, he planned to convene a conference of experts in the field in an attempt to get them behind his design. Assuming his design had been backed, the project would have immediately moved toward a full-scale demo plant. The first step in that plan was to design and build two more small scale designs (WB-7 and WB-8) to determine which full scale polyhedral potential well would be best. He wrote “The only small scale machine work remaining, which can yet give further improvements in performance, is test of one or two WB-6-scale devices but with “square“ or polygonal coils aligned approximately (but slightly offset on the main faces) along the edges of the vertices of the polyhedron. If this is built around a truncated dodecahedron, near-optimum performance is expected; about 3-5 times better than WB-6.” [12] Bussard noted that, "Thus, we have the ability to do away with oil (and other fossil fuels) but it will take 4-6 years and ca. $100-200M to build the full-scale plant and demonstrate it."[8] Bussard said "Somebody will build it; and when it's built, it will work; and when it works people will begin to use it, and it will begin to displace all other forms of energy."[22] There is some evidence of this occurring already, with at least one "Open-Source" project to replicate Dr. Bussard's work already well underway under the project title "Prometheus fusion perfection".

WB-6 prototype:

Polywell links:
http://www.emc2fusion.org/
http://www.talk-polywell.org/bb/index.php - Polywell forum
http://www.strout.net/info/science/polywell/index.html
http://prometheusfusionperfection.com/

This approach looks more promising to me than throwing money at Tokamak. What tokamak has achieved with billions, pollywell has achieved with millions, and first commercial power plants could be producing power as soon as 2020. At prometheus fusion they have already achieved fusion and are going to build a complete polywell.

It is also much smaller and lightweight, and could even be used to power naval or space ships.

Well, I am not nuclear science specialist, so guys, what do you think? Why Tokamak, and not this? :)

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BrianConlee	zz, thanks for replying to my posts and guiding me like this. I tried doing a search on "polywell" but couldn't find any threads. I'm a second year aerospace engineering student with a weird imagination... (don't we all have one?) You?

TallDave	FYI, having reviewed the WB-7 results, they are now building WB-8 with .8T magnets. My rough calc is it wil be expected to produce at least 8W of fusion (that's the power gain if it has the same radius as WB-7 (which produced 2 milliwatts with .1T magnets) with B^4r3 scaling).