Google Polywell Fusion Counter

[KitemanSA]

Well here may be where our understandings of the unit depart. It seems that you are looking to the cusps to do some sort of confinement. Not so. The cusps just provide directed leakage and re-entry paths that avoid the MaGrid can. The confinement is the positive charge on the MaGrid.

Not quite. You don't need 1e5 confinement from the cusps, but you do need 1e3 containment.

As previously noted, no Polywell can operate at all if arcing occurs outside the machine, between the walls and the machine, because this destroys the ability of the driving power supplies to produce deep potential wells. Thus the mean free path for ionization outside the machine (inside the container) must be much greater than the external recirculation factor, times the machine-to-wall distance.

Since the mfp for ionization is inversely proportional to the product of the local neutral density and the ionization crosssection, this condition can ALWAYS be satisfied, IF the external neutral gas pressure is made sufficiently small. In order to avoid external arcing, the densities thus required are very much too low to be of interest for fusion, thus the density inside the machine (at its boundary) must be very much higher than that outside. This ratio is the Gmj factor, which is the ratio of electron lifetimes within the machine with B fields on, to that without any B fields.

In contrast, in order to be of interest for fusion, the interior density must be above some numerical value for any given size of machine. Typically this requires electron densities at the interior boundary of order 1E13/cm3, or higher. While the exterior densities (of neutrals able to be ionized) must typically be below 1E10/cm3 or less. Thus a minimum value exists for Gmj (here, typically 1E3), below which no machine can give significant fusion or net power, independent of the unprotected wall loss problem. Both must be solved simultaneously

The magnetic fields don't just shield the Magrid. They also provide enough confinement that you have a 1000:1 ratio inside:outside.

This section you quote of Dr. B is perhaps one of the most confusing I have run across, exemplified by the apparent concretion of two completely different concepts (electron lifetime and ion density ratio) into one variable.

First and primarily, he defines Gmj as the "ratio of electron lifetimes within the machine with B fields on, to that without any B fields". Now this variable has absolutedly no fundimental connection to population density. If an electron passes thru the grid 10 times before quenching on something when the magnet is OFF and passes thru the grid 10,000 times with the magnet ON, the Gmj is 1000, but the population ratio for the electrons is still 1:1. However, because you can now maintain a decent potential well, the population ratio of ions can be maintained at a much higher value, which is needed to prevent arching.

At least that is how I have come to interpret it.

[KitemanSA]

Doc B kept saying no unshielded metal in the paths of the electron flows. I'd stick with that until we know something better.

That is why I'd like to get that stub, the crossover, away from the funny cusp. While it may have a bit of magnetic field due to the power flow thru it, it surely won't prevent the electrons from reaching it, will it? I mean the field can't be all that strong with only one wire thru it.

[TallDave]

Doc B kept saying no unshielded metal in the paths of the electron flows.

He did also say the interconnects could be shielded with internal currents, so maybe he was doing that.

Tom Ligon might know for sure.

It does seem odd he would put the interconnects right in the path of the funny cusp, if he thought electrons were recirculating through that area.

If an electron passes thru the grid

I think Bussard was actually referring to internal transits, but anyway...

but the population ratio for the electrons is still 1:1. However

No, because you're constantly feeding it electrons at a given rate, and the electrons are spending more time inside than out. To the extent you can keep the holes small or plugged enough, you can maintain higher density ratios inside. It's like filling a sieve with a garden hose.

the population ratio of ions can be maintained at a much higher value, which is needed to prevent arching.

He's talking about external arcing. The ions should be trapped inside.

In a recirculating MG machine, this factor is important since
it sets the minimum density that can be maintained outside
the machine, for any given interior edge density, as required
for sufficient fusion production. It is desired to keep this
outside density low, in order to avoid exterior Paschen curve
arcing, which can prevent machine operation. To have low
exterior density of electrons, and high interior density
requires large Gwb factors, thus, good Wiffle Ball
confinement is essential to system operation at net power

It is confusing. Art had some harsh words for Bussard on this well. Rick Nebel said a little while back that there is a complicated relationship between the various factors for external arcing, and that it wasn't a simple Paschen equation.

Of course, it may actually be electron plugging/oscillation and not recirculation happening around the cusps.

[KitemanSA]

By your interpretation, I read this to mean that an Elmore Tuck Watson machine would never work, even if it had a 100% transparent grid, since the population of electrons outside would always be equal to the population inside. This seems odd to me.

Does anyone know if an ETW machine has ever been made to work at any efficiency level?

[TallDave]

the population of electrons outside would always be equal to the population inside.

Not equal, but not in a very high ratio either. They form a cloud around the anode grid. A Polywell simultaneously compresses the cloud inside the grid and shields the grid.

An ETW can never achieve net power, and a Polywell will greatly outperform an ETW at similar drive levels. Of course, most of that is due to the losses to the grid in an ETW, but there's also the WB effect.

Initially, when the electron density is small, internal B field
trapping is by simple “mirror reflection“ and interior
electron lifetimes are increased by a factor Gmr, proportional
linearly to the maximum value of the cusp axial B field.
This trapping factor is generally found to be in the range of
10-60 for most practical configurations. However, if the
magnetic field can be “inflated“ by increasing the electron
density (by further injection current), then the thus-inflated
magnetic “bubble“ will trap electrons by “cusp confinement“
in which the cusp axis flow area is set by the electron gyro
radius in the maximum central axis B field. Thus, cusp
confinement scales as B2. The degree of inflation is
measured by the electron “beta“ which is the ratio of the
electron kinetic energy density to the local magnetic energy
density, thus beta = 8(pi)nE/B2.

The highest value that can be reached by electron density is
when this ratio equals unity; further density increases simply
“blow out“ the escape hole in each cusp. And, low values of
this parameter prevent the attainment of cusp confinement,
leaving only Gmr, mirror trapping. When beta = unity is
achieved, it is possible to greatly increase trapped electron
density by modest increase in B field strength, for given
current drive. At this condition, the electrons inside the
quasi-sphere “see“ small exit holes on the B cusp axes,
whose size is 1.5-2 times their gyro radius at that energy and
field strength. Thus they will bounce back and forth within
the sphere, until such a —hole“ is encountered on some
bounce. This is like a ball bearing bouncing around within a
perforated spherical shell, similar to the toy called the
“Wiffle Ball“. Thus, this has been called Wiffle Ball (WB)
confinement, with a trapping factor Gwb (ratio of electron
lifetime with trapping to that with no trapping).
Analyses show that this factor can readily reach values of
many tens of thousands

Snice ion density is dependent on electron density (I can hear Art yelling "quasineutral!" somewhere) and power density is roughly the ion density squared, doing a few orders of magnitude better on electron density has big ramifications for the size of a device that could reach net power.

You can get some fusion out of an ETW, and probably more from an ETW with a shielded grid. But as Rick put it:

If we can’t get the wiffleball, then we can kiss our behinds goodbye.

[PolyGirl]

Current figures are:


Robert Bussard gives 167,000
Bussard Fusion gives 32,100
Polywell Fusion gives 18,500
Bussard Polywell gives 12,800
Bussard Polywell Fusion gives 12,300


Regards
Polygirl

[TallDave]

I used to get a hit on my Polywell Fusion alerts a couple times a week, and I tried to check on them all. Now there are several a day and I can't keep up.

Interest is growing. It's still hard to say whether this is going to end somewhere commercially useful (and propenents should be careful about their claims), but Rick has apparently found some very promising confinement data and the research is increasingly visible.

[KitemanSA]

the population of electrons outside would always be equal to the population inside.

Not equal, but not in a very high ratio either. They form a cloud around the anode grid. A Polywell simultaneously compresses the cloud inside the grid and shields the grid.

An ETW can never achieve net power, and a Polywell will greatly outperform an ETW at similar drive levels. Of course, most of that is due to the losses to the grid in an ETW, but there's also the WB effect.

Actually, given a perfectly transparent grid, the population outside would probably be GREATER that the population inside. Each electron would transit from outside to inside to outside... and becasue the outside parts are all much slower than the inside parts, each electron would spend more time outside. Any general population wherein the elements spend more time outside will have more units outside.

An ETW with a perfectly transparent grid SHOULD be able to make net power. If not, the problems with Polywell may go beyond cusps.

[TallDave]

An ETW with a perfectly transparent grid SHOULD be able to make net power.

Doubtful, at least at any reasonable size (would anyone like to volunteer to do the math given 1e-3 smaller ion densities?). Thus Rick's comment.

[KitemanSA]

An ETW with a perfectly transparent grid SHOULD be able to make net power.

Doubtful, at least at any reasonable size (would anyone like to volunteer to do the math given 1e-3 smaller ion densities?). Thus Rick's comment.

I take it you mean the bit about wiffleballs and kissing one's nether regions...

I think he is talking about the real world of non-transparent grids, while I am asking about the hypothetical world of 100% transparent grids. Totally different animal.

I don't see why we would not be able to get the same ion density with a perfect ETW as with a wiffleball. Heck, maybe even higher!

[TallDave]

I don't see why we would not be able to get the same ion density with a perfect ETW as with a wiffleball.

With no magnetic confinement?

Remember, the power scaling law works as B^4 * R^3, where B balances against the electron pressure (beta = 1). You would be removing the B^4 from the equation.

[KitemanSA]

I don't see why we would not be able to get the same ion density with a perfect ETW as with a wiffleball.

With no magnetic confinement?

Remember, the power scaling law works as B^4 * R^3, where B balances against the electron pressure (beta = 1). You would be removing the B^4 from the equation.

I suspect there would be an equivalent type of scaling law using drive voltage or something rather than B. With a perfect ETW, what would be to stop flooding the well with HUGE amounts of electrons in order to get huge (minus a bit) ions and have a great power ratio?

I guess I am just not sure why the exterior population of electrons amounts to anything. What is important is the maintenance of a good well and the removal of neutrals from the outside, no?

[derg]

Interest is growing. It's still hard to say whether this is going to end somewhere commercially useful (and propenents should be careful about their claims), but Rick has apparently found some very promising confinement data and the research is increasingly visible.

People- potential investors- who are good at making and saving money tend not to be science enthusiasts. It is a broad and difficult gulf to bridge between the understanding of physics and engineering and the resources to take it to the next step. We're at a fortunate crossroads now in that it's mostly an engineering not an experimental problem- most of the the theory and experimentation has already been done. What is needed now is people who can bridge the gap- (like Bussard did in his Google talk, only better) between the engineering requirements and the understanding of potential investors.

[hanelyp]

Actually, given a perfectly transparent grid, the population outside would probably be GREATER that the population inside. Each electron would transit from outside to inside to outside... and becasue the outside parts are all much slower than the inside parts, each electron would spend more time outside. Any general population wherein the elements spend more time outside will have more units outside.

I'd expect the electrons to be fastest passing through such an ideal grid, slowing with distance on either side.

An ETW with a perfectly transparent grid SHOULD be able to make net power. If not, the problems with Polywell may go beyond cusps.

I agree, assuming a perfectly transparent grid an ETW fusor could be a net energy producer. Probably not a lot of power, but more than the zero lost to the perfect grid.

[TallDave]

I suspect there would be an equivalent type of scaling law using drive voltage or something rather than B.

The drive power is dependent on B. The drive basically functions to replace the lost electrons and keep the machine at beta=1.

With a perfect ETW, what would be to stop flooding the well with HUGE amounts of electrons in order to get huge (minus a bit) ions and have a great power ratio?

In addition to the arcing problem Bussard mentioned, you would need a hell of a potential on the anode, and at some point you would melt the grid with cross-field diffusion even with shielding. Bussard believed losses could only be held to r^2. I'll punt on the math again, but the things would be huge.

What you're talking about is basically like running a Polywell at a beta =/= 1 condition.

An ETW with a perfectly transparent grid SHOULD be able to make net power. If not, the problems with Polywell may go beyond cusps.

I agree, assuming a perfectly transparent grid an ETW fusor could be a net energy producer. Probably not a lot of power, but more than the zero lost to the perfect grid.

I assumed we were still counting cross-field diffusion losses, but if we're being entirely fanciful and imagining a grid that needs no shielding, catches no electrons, and therefore needs no drive then yes that's true. Even if it only produces a milliwatt of fusion, it's still at net power because it has no losses. Of course, you might as well ask for a fusion-crapping unicorn while you're at it. And we're ignoring the dynamic effects.