Talk-Polywell.org

In a recent post, and occasionally quoted, is the idea that polywell will run with 10T.

It is also said that it can run at beta=1.

A 10T field at beta=1 is capable of confining [limiting] a 9MeV plasma at a micron pressure.

Why would the outer edge be a 9MeV plasma, and has anyone even contemplated the brems from such a plasma edge?

chrismb wrote:In a recent post, and occasionally quoted, is the idea that polywell will run with 10T.

It is also said that it can run at beta=1.

A 10T field at beta=1 is capable of confining [limiting] a 9MeV plasma at a micron pressure.

Why would the outer edge be a 9MeV plasma, and has anyone even contemplated the brems from such a plasma edge?

Admittedly pure speculation, but if a 10 Tesla will contain 9 MeV charged particles, that is good. It means you have plenty of surplus to contain the several MeV alphas till they hit a cusp. Dr. Nebel mentioned once the strength needed to contain the alphas- I forget, but I think it was around several Tesla, with a size to accommodate the subsequent gyro radius of the alphas. With other fuels, the fusion produced charged particles (like protons, tritons and He3 nuclei would also be contained, allowing for similar (but more challenging) direct conversion of that portion of the fusion eneryy, and protect the mag casings from that thermal load, even if the fusion charged particles end up hitting the walls for thermal conversion. Also, as the fusion gain is supposed to scale as the 4th power of the magnetic field, the stronger fields have a gain advantage, within thermal load and insulating limits*.
And, that capacity does not mean you have to pump in particles at that energy, only that this is the maximum the field could contain.
The actual quoted 10 Tesla fields is arbitrary and , I think, based on a quote from Dr Bussard for a demo machine. There may be some engineering considerations with copper magnets that allows this magnet strength scaling with size. Coil cases that are increased by a factor of 10 (15 cm to 150 cm radius) in size would have an internal volume 100X


*Increasing the magnetic field strength is supposed to increase yield by increasing the contained density. Since the volume of the Wiffleball would be decreasing a proportionate amount(?), I guess that the Wiffleball trapping factor and/ or ion electrostatic confinement must be increasing enough to provide this gain despite smaller volumes. Or, perhaps the rate increases as d ^2, while volume effects are linear. I don't know.

PS: I'm not sure, but I believe the pressure within the Wiffleball will be closer to ~ 1000 microns (~ 0.001 atmospheres) if densities of 10^22 particles/ M^3 is obtained. How would that effect the Tesla vs particle energy picture?

[EDIT] Actually, I think the volume of the reactor is not derived by the above calculations, as volume is already incorporated in the density variable. The volume is user selectable within engineering limits. And since gain scales as only r^1.5, pushing the reactor size is a poor choice over pushing magnetic field strength (gain scales as ~B^4), as M. Simon said.


Dan Tibbets

So you are describing when it isn't a beta=1. I'm saying I thought it was to operate in beta=1 condition.

Bear in mind that, supposedly, this is only the magnetic field experienced by the outer edge of the wiffleball, because the magnetic field is pushed back and screened within it - according to the theory. So if you were to argue that this is actually a 10keV plasma at n=10^22, then fair enough but this is by no means a 'low-density' nor 'cool' plasma at the edge.

These conditions are virtually free of resistance, and if it only gets more dense and hotter towards the centre, there is no way this'll hold up an electric field. This can't be had both ways, you either have a high beta and near-immediate negation of the electric field, or you have a low beta and reduced charge transportation.

So what are the edge conditions supposed to be; what is the mag field strength, beta, electric field, density and electron and ion temps. Can anyone actually put some figures to these, or am I now about to witness either a blank of responses, or a load of pontificating subjective and inconclusive hot air about what may or may not be what is intented and envisioned.

Micron - A metric unit of length equal to one millionth of a meter.

Do you guys have any idea what you are saying? If so, please put it into consistent units for the rest of us.

Velocities need to be in consistent nukular units, root-barns per microshake.

Aero wrote:Micron - A metric unit of length equal to one millionth of a meter.

It is a standard term used. 1 atmosphere = 760mm of mercury. 1 micron is 1 micron of mercury.

Call it 76mPa - if you must.

Call it 76mPa - if you must.

The above statement is wrong.

"How many pascal in 1 micron of mercury [0 °C]? The answer is 0.13332239."

http://www.convertunits.com/from/pascal ... %C2%B0C%5D

I might add that the inconsistent use of units and worse usage of upper/lowercase for magnitudes (m-milli, k (small k!)-kilo, M- mega, etc) is going to take building a fusion reactor that much longer .... and so much wasted verbiage.

icarus wrote:

Call it 76mPa - if you must.

The above statement is wrong.
"How many pascal in 1 micron of mercury [0 °C]? The answer is 0.13332239."
http://www.convertunits.com/from/pascal ... %C2%B0C%5D
I might add that the inconsistent use of units and worse usage of upper/lowercase for magnitudes (m-milli, k (small k!)-kilo, M- mega, etc) is going to take building a fusion reactor that much longer .... and so much wasted verbiage.

OK, so I did one millionth of 0.76 instead of one millionth of 1/0.76. Big FLICKING difference - OH MY GOD THIS TOTALLY INVALIDATES EVERYTHING I'VE EVER SAID!!!

No, sir. It is a failure to understand the principles of plasma physics [and being too much up one's own posterior that a person quotes 8 decimal places on conversion of a 1sf number (darn - I knew I should've just put 0.1Pa)] that will cause the building of a fusion reactor to be longer than necessary.

However long it takes to build a polywell, I cannot see how that would ever have any impact on the timeline of the first Q>1 fusion reactor.

I haven't looked too hard at the Beta=1 question chris so correct me if I'm in error.

The Pressure at Beta=1 is a product of particle energy and particle density. If you can't raise the energy then density must go up to get the desired Beta.

MSimon wrote:I haven't looked too hard at the Beta=1 question chris so correct me if I'm in error.

The Pressure at Beta=1 is a product of particle energy and particle density. If you can't raise the energy then density must go up to get the desired Beta.

If it is to function at a given beta, then yes, that's right. But I'm just asking as I thought polywell was supposed to function at beta=1, and if so then 10T is more than overkill.

The scaling with respect to B is, I presume, only true up to the point that it is still useful to increase it. If you put up two umbrellas then you don't get any less wet in the rain, providing one umbrella is big enough for the job. Or, if you have two 1 litre bottles and the second has a thicker wall than the first, it doesn't contain more fluid! So if polywell can work at beta=1, and works at a lower beta at higher mag fields because it doesn't need to work at higher betas with a big field then you will find your notions of B scaling goes to pot.

chrismb wrote:

MSimon wrote:I haven't looked too hard at the Beta=1 question chris so correct me if I'm in error.

The Pressure at Beta=1 is a product of particle energy and particle density. If you can't raise the energy then density must go up to get the desired Beta.

If it is to function at a given beta, then yes, that's right. But I'm just asking as I thought polywell was supposed to function at beta=1, and if so then 10T is more than overkill.

The scaling with respect to B is, I presume, only true up to the point that it is still useful to increase it. If you put up two umbrellas then you don't get any less wet in the rain, providing one umbrella is big enough for the job. Or, if you have two 1 litre bottles and the second has a thicker wall than the first, it doesn't contain more fluid! So if polywell can work at beta=1, and works at a lower beta at higher mag fields because it doesn't need to work at higher betas with a big field then you will find your notions of B scaling goes to pot.

Higher density makes for smaller reactors. And for greater internal vs external density. Both useful.

chrismb wrote:

MSimon wrote:I haven't looked too hard at the Beta=1 question chris so correct me if I'm in error.

The Pressure at Beta=1 is a product of particle energy and particle density. If you can't raise the energy then density must go up to get the desired Beta.

If it is to function at a given beta, then yes, that's right. But I'm just asking as I thought polywell was supposed to function at beta=1, and if so then 10T is more than overkill.

The scaling with respect to B is, I presume, only true up to the point that it is still useful to increase it. If you put up two umbrellas then you don't get any less wet in the rain, providing one umbrella is big enough for the job. Or, if you have two 1 litre bottles and the second has a thicker wall than the first, it doesn't contain more fluid! So if polywell can work at beta=1, and works at a lower beta at higher mag fields because it doesn't need to work at higher betas with a big field then you will find your notions of B scaling goes to pot.

One equation I found for Beta is:
Beta= n * K (subscript B) * T / B^2 /2* Mu (subscript 0).
Disregarding the constants this essentially reduces to :
n * T / B^2.
So Beta is the density * temperature / magnetic field strength.
If I have not made an error in translation., the relationship is straight forward. B=1 condition can be any situation in which these variables balance out.
A B= 10 Tesla, can be matched easliy by appropiate temperatures and densities. Actually achieving these conditions involve engeenering considerations, not physics issues.
And, as M. Simon said pushing the density (by pushing more charged particles into a stroer magnetic shell is the best way to increase power. The volume occupied is a derivative of of these primary conciderations.

I wonder how the numbers would play out (how close to Beta= 1 you get using approximatuions of the following variables in a D-D reactor.
n= 10^22 particles / M^3
T= ~ 80 KeV,
B= ~ 10 Tesla

The volume where this would happen should be somewhat less than a1.5 meter radius sphere if I'm thinking right.
I'm not sure how to handle the constants. I guess that K (subscript B) is Boltzman's constant- I don't know how this would apply to a nonthermal plasma.
Mu (subscript 0) is, I believe, the dielectric constant of free space and should not require modification.

Dan Tibbets

MSimon wrote: Higher density makes for smaller reactors. And for greater internal vs external density. Both useful.

Sorry, you're still missing the point. If you run a small, compact device (Polywell, tokamak, whatever...) at beta=0.01 but you *could* run it at beta=1, then you've got no means to assess the scaling law of the device whilst you're p*ssing around running it at a low beta. All you are doing is floating around in multiple variables. The only way to understand the limit of the device is to run it at its limit then change the boundary conditions. But if Polywell *can* run at beta=1, then WB8 is gonna push out megawatts, because you only need a few kG at beta=1 to confine some real hot plasma - and I mean plasma so hot that it will definitely be unsustainable due to brems.

So either Polywell *can do* beta=1, or it can only do what it can only do.

.. or it can ONLY do, what it can do, "at beta=1".

ie. how important is 'beta=1' for 'polywell' operation - i had always considered it quintessential to the device concept, from by brief perusing of Bussard's papers. (Wiffleball inflation).

though i also understand MSimons argument that it is just one dimension of the matrix, providing roots to the radius of a 'real-sized' physical object.

(btw. i agree with you chris on the anoyying red herring and digressions that people keep injecting - by all means point out errors, but please try and keep the flow constructive).

i think this discussion might identify some further useful answers for the FAQ's section, on beta=1 in particular.