Another KOS Diary On IEC/Bussard

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

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Keegan
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Location: Brisbane, Australia

Post by Keegan »

Tom Ligon wrote:The "wiffleball" effect is possible because pushing back the magnetic field is so stable. The compression effect tends to squash the cusps closed as an added benefit.
If one could modulate the B fields with precision, i envisage that one could open and close the cusp flow analogous to the valves found in an internal combustion engine.

At the moment any uncooled device will be extremely limited. I always knew there were going to be thermal problems but the "thermos bottle" analogy really hits home the fact that there is absolutely no where for the heat to go = Big Problems.

Longer duration pulsed experiments on simple actively cooled coils are the next logical steps, which is what my AC polywell comments were directly aimed at. It could take some time to get cooled coils up to spec, but when you do you will find your going to need some fresh power supply topology to get the most out of the coils. Just trying to think one step ahead.

Ageed the 100 microsecond to 1 millisecond time discharges are longer than the plasma timescales, but im designing a specific experiment that require times scales of 1/100th of second (More to come :) )

Dr Mike Do you feel like scanning any exerts from "Stability of a Plane Plasma-Magnetic Field Interface: Energy Principle Analysis". Sounds Good but i just dont feel like giving Amazon $117 especially if Dr Krall isn't going to see any of it.
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jmc
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Post by jmc »

When I referred to the ion-electron collissional timescale I wasn't referring to instabilities that could creep in, I was reffering to the effect of ions heating the electrons causing cusp losses to increase.

I think that was Rider's main concern in his Phd. thesis, reducing the net transfer of energy from ions to electrons. I don't think this can be experimentally refuted until we have a machine that can run on the ion-electron collissional timescale.

drmike
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Post by drmike »

Keegan - I just ordered a digital camera yesterday so I can put drawings into the math. You've just given me the perfect excuse for it now! :D

When it gets here that will be my first experiment.

Keegan
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Post by Keegan »

Sweet :wink: if its just black and white once they are on your puter reduce the bit depth to 2bit. Great way to shrink and clean up ebooks.
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gblaze42
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Post by gblaze42 »

Tom Ligon wrote: Looking from the perspective of a confined plasma or electrons pushing at a field, a concave field will be stretched when you push on it. Picture air pushing out a balloon. As it stretches, the field or balloon skin becomes weaker. This setup is prone to instability. The ultimate example of a stretched magnetic field would be a loop-shaped solar prominence. When one of those stretches too far, it ruptures with a stupendous release of energy.
Not being a plasma physicist, this sounds like magnetic reconnection, and to clarify for my feeble mind to grasp, your saying that the polywell uses a convex gradient coil? pardon the questions.

rnebel
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Joined: Mon Dec 24, 2007 12:15 am

Post by rnebel »

to JMC:

Since you are worried about Rider, let me suggest the following exercise. Let's assume that a Polywell reactor is in the wiffleball mode, namely that:

n*kBolt*Te = B**2/(2*mu0)

to make it simple, let's use mks units and assume B = 10 Tesla, mu0 =4.0e-7*pi, Te = 1.0e4 eV and kBolt = 1.6022e-19 Joules per eV.

Calculate what n is and compare it to the ITER value at

http://www.iter.org/a/index_nav_4.htm

Tell me what you get.

MSimon
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Post by MSimon »

gblaze42 wrote:
Tom Ligon wrote: Looking from the perspective of a confined plasma or electrons pushing at a field, a concave field will be stretched when you push on it. Picture air pushing out a balloon. As it stretches, the field or balloon skin becomes weaker. This setup is prone to instability. The ultimate example of a stretched magnetic field would be a loop-shaped solar prominence. When one of those stretches too far, it ruptures with a stupendous release of energy.
Not being a plasma physicist, this sounds like magnetic reconnection, and to clarify for my feeble mind to grasp, your saying that the polywell uses a convex gradient coil? pardon the questions.
Here is a picture of the fields:

http://www.mare.ee/indrek/ephi/polywell ... ld_log.png

you can see they bulge into the center.

More:

http://www.mare.ee/indrek/ephi/polywell ... _lines.jpg

http://www.mare.ee/indrek/ephi/polywell ... gcolor.jpg

http://www.mare.ee/indrek/ephi/polywell_cube_lint.png

Go here:

http://forum.nasaspaceflight.com/forums ... =5367&mid=

and search for Indrek for more.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
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Post by MSimon »

Engineering is the art of making what you want from what you can get at a profit.

gblaze42
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Joined: Mon Jul 30, 2007 8:04 pm

Post by gblaze42 »

MSimon wrote:
gblaze42 wrote:
Tom Ligon wrote: Looking from the perspective of a confined plasma or electrons pushing at a field, a concave field will be stretched when you push on it. Picture air pushing out a balloon. As it stretches, the field or balloon skin becomes weaker. This setup is prone to instability. The ultimate example of a stretched magnetic field would be a loop-shaped solar prominence. When one of those stretches too far, it ruptures with a stupendous release of energy.
Not being a plasma physicist, this sounds like magnetic reconnection, and to clarify for my feeble mind to grasp, your saying that the polywell uses a convex gradient coil? pardon the questions.
Here is a picture of the fields:

http://www.mare.ee/indrek/ephi/polywell ... ld_log.png

you can see they bulge into the center.

More:

http://www.mare.ee/indrek/ephi/polywell ... _lines.jpg

http://www.mare.ee/indrek/ephi/polywell ... gcolor.jpg

http://www.mare.ee/indrek/ephi/polywell_cube_lint.png

Go here:

http://forum.nasaspaceflight.com/forums ... =5367&mid=

and search for Indrek for more.
Thank you!

jmc
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Location: Ireland

Post by jmc »

rnebel wrote:to JMC:

Since you are worried about Rider, let me suggest the following exercise. Let's assume that a Polywell reactor is in the wiffleball mode, namely that:

n*kBolt*Te = B**2/(2*mu0)

to make it simple, let's use mks units and assume B = 10 Tesla, mu0 =4.0e-7*pi, Te = 1.0e4 eV and kBolt = 1.6022e-19 Joules per eV.

Calculate what n is and compare it to the ITER value at

http://www.iter.org/a/index_nav_4.htm

Tell me what you get.
I couldn't find the density on the website, I could however find the normalized beta, which varied between 1.8% and 3%, while the normalized beta of a polywell in WB mode even without convergence and assuming ion and electron temperatures are in equilibrium can be up to 100%. It can be somewhat less if the energy of the well is significantly higher than the energy of the ions inside. (i.e. with a deeper well the effective ion beta of a non-covergent device in WB mode becomes sqrt((T_i)^2/T_e*E_well) ) and if you have convergence the effective beta is amplified by twice the square root of the convergence ratio.

Since the fusion power a device of a given magnetic field is proportional to the square of the value of beta it is quite clear the Polywell blows the tokamak away on this front.

This is why I'm interested in the Polywell, infact. Given two magnetically confined fusion devices with lawson triple products confortably above breakeven, the device with the highest beta wins economically, as the two things that cost most in a such devices are the magnetic field and the volume and beta is a meassurement of the square root how much power a device of a given volume with a given magnetic field may deliver. With convergence, a Polywell blows every other magnetic confinement device out of the water, without convergence, I believe mirror machines and cusp machines are still credible rivals betawise. Tokamaks are far behind in this respect.

But beta is only a meassure of efficiency for two fusion reactors with the required lawson triple product to produce net energy, if the device can't give you net energy then all the beta in the world won't save it. So you need to take another factor into account, the energy confinement time. I believe that this quantity is the reason why tokamaks recieve so much funding in comparison to other devices, they have empirical proved themselves to be better at holding energy in them then any other magnetic fusion device built to date, that is in part due to the fact that they recieved more funding and so could be made bigger than any other fusion device built to date. But if a Polywell is to be a valid fusion concept then it needs to reach the lawson breakeven criterion at least and that requires knowledge about the confinement time.

I completely agree there is an awful lot of useful question to be answered by running Polywell on the electron-electron collission time and indeed on the ion-ion collission time, but the ion-electron collission time will be the time it takes the ions to heat the electrons, and once the electrons are heated they will flow out of the bulk and through the cusps at a much faster rate then before they are heated by the ions, whats more, if the electrons are heated by the ions then as they flow out of the cusps they will deposit more energy on the emmitters. It just strikes me that the ion heating of electrons could turn a device that is above breakeven to one that is below this threshold. That's another reason I'm interested in the convergence of a polywell. From the point of view of electrons flowing out the cusps of the device they don't care whether the polywell converges or not (assuming they are at the same temperature as the ions anyway), so the electron loss power would be constant from that point of view. But convergence could very significantly enhance the fusion power and if you keep the loss power constant while increasing the fusion power, then you've just got that bit closer, or even surpassed, breakeven.

MSimon
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Post by MSimon »

jmc,

I think beam annealing solves (sufficiently) the upscattering of electrons and ions. Also the down scattering. Provided they do not happen too fast.

See my speculations here:

viewtopic.php?p=4934#4934
Engineering is the art of making what you want from what you can get at a profit.

rnebel
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Joined: Mon Dec 24, 2007 12:15 am

Post by rnebel »

JMC and MSimon:
Actually, you need to click on “read more” under the design section, then “main parameters” then on the “more” button. What you will find is that the average density of ITER is ~ 1.0e20/m**3. If you use the formula I sent you for the Polywell, you will get a density ~ 2.5e22/m**3. The upshot of this is that the Polywell has a power density that is ~ 62500 times bigger than ITER EVEN IF THERE IS NO ION CONVERGENCE! Thus, a Polywell should far outperform a Tokamak even with a constant density Maxwellian plasma. Even if Rider and Nevins were correct (which Chacon has pretty clearly shown they aren’t) this isn’t a show stopper. It has a lot more significance for Hirsch/Farnsworth machines that have low average densities than it does for the Polywell.
The best analogy that I can think of is that the wiffleball mode is the jet engine and the ion convergence is the afterburner. The 2.5e22/m**3 density is what the Polywell should have on the edge, and then it hopefully goes up a few orders of magnitude as it goes into the interior. I don’t mean to imply that ion convergence isn’t important. This power density boost is what enables the Polywell to be built in small attractive unit sizes and to easily use advanced fuels.
However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction. Does this kind of make sense?

MSimon
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Post by MSimon »

However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction. Does this kind of make sense?
Yes.
Engineering is the art of making what you want from what you can get at a profit.

jmc
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Post by jmc »

rnebel wrote:JMC and MSimon:
However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction. Does this kind of make sense?
Yes, it makes perfect sense to start with the biggest challenge and then try to enhance the device from there. I have, infact done some handywavy calculations myself that suggest that an isotropic plasma in an open box design would probably get beyond breakeven with 8 point cusps (diameter 2m, field 1 Tesla) or so (I'm not sure whether it would still be the case with line cusps and funny cusps though)

How is the wiffleball thing going? I was told by a former EMC^2 researcher that in WB4 any attempt at wiffle ball formation in steady state mode while he was working there, invariably led to well blowout. He attributed it to an uncontrollable increase in density which resulted in a current to the magrid that was too great for the power supplies to cope with.

If stable wiffleball formation is a problem then it might be interesting to just try and achieve a stable wiffleball at a few hundred volts rather that 10KV, leave fusion to the side for awhile and see how high you can push up the density. At lower voltages your magrid might be able to handle higher currents for longer.

I was also wondering what would happen if instead of fuelling the device through gas breakdown, the device was fuelled by exploding a pellet in the centre. When gas breaks down throughout the device I imagine the electrons would hug onto the magnetic fieldlines where they were first ionized throughout the device, but if a pellet exploded in the centre they would push back the magnetic fieldlines as the cloud expanded. If you weren’t focussed on making fusion maybe you could use a small pellet of water ice or something easier to handle then cryogenic deuterium. And if the final temperature was to be 100eV then perhaps the energy required to explode a small pellet would not be prohibitive.

I can imagine that the WB6 pulsed mode might have achieved wiffle ball formation, if the thermionic emitters were bang on the cusps then the electron from them would only ionize the gas in the low field centre maybe then the ions formed in this low field region, pushed back the field enabling the plasma to swallow up yet more gas, ionizing it and forming a wiffleball.

Another way of obtaining the wiffleball might be to start with no field, or a very weak field, an ionize the gas in this state and then slowly increase the field while the gas is already ionized, the new field lines from the increasing magrid current will not penetrate the plasma on timescale below the resistive time.

Perhaps it was the effect of pushing the plasma out of the field by alternating the octahedral and truncated cube formations that allowed Keller and Jones in their 1966 Laussane paper to achieve good plasma confinements in their Polyhedral magnetic field configuration (albeit at 7eV).

I still prefer exploding the pellet though, it will allow you to control the precise quantity of material that goes into the plasma, push back the fieldlines and lower the neutral density in the tank outside the plasma which will in turn reduce charge exchange losses.

Tom Ligon
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Post by Tom Ligon »

jmc,

Several of Dr. Bussard's papers have a pair of figures that show the wiffleball forming by two routes. What you describe sounds familiar. One form of that figure is, in fact, the inspiration for the name of the phenomenon.

WB4 had square cross-section coils that were welded where they touched, so it was the lossy configuration WB6 overcame by going to round cross-section coils spaced apart several gyroradii. Both of those flaws would have directed some electrons into magrid metal, causing hydrogen evolution. I'm sure that's where the pressure increase came from. But even so, WB4 did supposedly manage a little fusion, so I suspect it could produce a wiffleball for a moment before the gas flooded it out.

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