Question: How is the electron not getting into the machine?

[Robthebob]

so good news, my boss said i can do it for my phd. Then I remembered, didnt emc2 already do something similar? (like examining geometries)

Anyways, I'm gonna have to come see some of you in person and talk to a bunch of people first before i do any of this.

PS: my boss said he doesnt know where i can get money for this. Air Force?

[KitemanSA]

The cost of the MaGrid should be cheap since you will probably be winding it. It is the RoS cost that gets painful, IIUTC. See if you can find someone in your area that has a fusor.

I am willing to kick in some bucks but this strikes me as prime KickStarter fodder.

[KitemanSA]

so good news, my boss said i can do it for my phd. Then I remembered, didnt emc2 already do something similar? (like examining geometries)?

They did a single and a four turn MPG and the 4 turn did some fusion. But the units suffered from "metalinthewayitis" so didn't prove much. Dr. B wanted to examine the square planform construction before going big, so I guess he thought there was something to prove. Sounds PhD worthy to me.

[ladajo]

I agree. You can do much with a simple exploration of geometry. To my knowledge, EMC2 has focused on basic geometry (Ie. "We know what works, let's go with it"), and someone does need to do some real documented work with geometry alternatives. It has been kicked around here to some degree, even some back-of-the napkin sim work. But not a real concerted effort.

As for money, there are many sources available, you just need to be flexible and creative in what you think of. It may not hurt to ask EMC2 or ONR, and seek to develop a symbiotic relationship.

When you develop your Thesis, remember the Prime Thesis Directive: Keep It Simple Stupid. Many have failed because they unknowingly bit off more than they could chew. Narrow the scope.

We have resources here, you just need to ask.

[D Tibbets]

Rob,

I was thinking about this the other day.

When Bussard's last machine was only full of electrons, it had about 2E12 electrons. Their average energy was 2,500 eV. Now deuterium gas is puffed towards the rings. When it exchanges energy with the electrons, it ionizes. It ionizes if it is hotter than 16 eV. The ions fall into the center. They may hit, they may fuse.


But what happens to the two electrons created?


1. These electrons feel a Columbic repulsive force from the cloud in the center. So they will not necessarily go in that direction.

2. If they fly outside the rings, they will see a 12,500 volt cage field pushing them back towards the rings.

3. They also feel a magnetic field from the rings themselves.



Given all this, I am not surprised we are having problems with electron injection.

Two free electrons are indeed released from the full ionization of a deuterium molecule, but this is perhaps to narrow of a view. A little over a dozen eV is enough to free an electron when hit by another electron at that energy. But, the probabilities are not great. The greatest probability of the bound electron being successfully separated from the deuterium nucleus occurs at ~ 100 eV. This is the peak of the ionization cross section for hydrogen. Thus the average energy of the electrons released by ionization (provided that the colliding free electrons has this energy or more) initially have an energy of ~ 100 eV. Further coulomb collisions with the hot electrons heats these ionization derived electrons to near the energy of the injected electrons. How close the ionized electrons approach the energy of the injected electrons is dependent on confinement conditions. Note that ions are often considered to have confinement times at least 10 times to as much as 100 or more times the electrons. This means that there are ~ 100 injected electrons for each ionization electron. The final temperature of the total electrons will be very close to the temperature of the injected electrons. This is slightly different when ion guns are used. Ideally the contained electron energies (at the bottom of their potential well) will be the injection energy once inside the magrid. In this example the difference may be only about 1 %
With a higher Z fuel like Boron, this will change some. In any case the ionization process is a complex dance of cascading ionizations that happens quickly, but not instantaneously. It takes a few microseconds. Bussard felt that this process was problematic in WB6, because a significant portion of the injected gas would transit the machine without ionization and subsequent entrapment, and this resulted in intolerable accumulation of gas external to the magrid and resultant arcing (which terminated the tests after only a few milliseconds in their setup). Bussard felt that a larger machine would greatly decrease this problem because of the greater transit time. Also, though not mentioned, this should result in a larger percentage of the ionization occurring near the edge of the machine (in relative terms) so that the initial ion population will be more mono energetic (because the steady state potential well is not square). Ion guns changes things, possibly with some advantages and disadvantages.


For small scale Polywell research this may be a good starting point

http://prometheusfusionperfection.com/2 ... the-scene/

Note though that Nebel felt that experiments at size scales less than that of WB6 became much more uncertain as technical difficulties associated with vacuum work, out gassing, etc. became more pronounced.* The resultant signal to noise ratio becomes smaller.

There is a steep learning curve for vacuum research, and measurements in plasma. As represented by Fusor.net , the simple glow discharge fusor is a good starting point for development, especially if you have adaptable equipment lying around the lab (such a the several types of vacuum pumps needed, high voltage power supplies, vacuum chambers with appropriate feed throughs, etc. With the surplus equipment and/ or scrounging, you may need only a few thousand dollars to go a fair distance. If you have university based experts like electrical engineers, machinists, etc. that you can utilize, that is a big plus.
And, of course for theoretical work and computer modeling only brain power and computing power is needed; plus a good internet reference library which can be accumulated through Fusor.net and this site, and "Askmor", etc...

* The problem with smaller size is that things like out gassing is dependent on surface area, while many of the measurements of interest are volume dependent. As machine size increases the volume increases faster than the surface area, so the signal to noise ratio improves, everything else being equal.

Dan Tibbets

[Robthebob]

Whoa now, I'm not even doing any fancy. I just want to measure the well depths. I dont think there's any reason to have ions in the system. I have a lot of questions that needs answering before I even draw up a plan for presenting. But basically I'm asking,

"If I only changed the shape and everything else is the same, does the well depth change (hopefully increase) even in a small machine?"

As far as measurement, I've asked, we can do interferometry. We're gonna do this shoe string on a shoe string style. emc2 has some stuff stored at santa fe, we're gonna ask Dr. Park if I can borrow some stuff, he might want to see what I can come up with. As far as for them to fund me... my boss said they're having problems with money, so probably no.

What I'm hopefully is if they make the significant break through they promised to make before I get my masters and make an announcement, if that, I can actually try to charm the folks at the air force research center to help me.

[hanelyp]

I believe well depth is mostly a function of injected electron energy. wiffleball leakiness as a function of geometry would be of interest. One method to measure that is to put a hot filament emitter in the center of the magrid and measuring current from the emitter to a ground outside as a function of voltage. Current from an emitter positioned over a cusp and a collector inside would also be of interest.

[KitemanSA]

Measure the injector current needed to keep the well depth. Compare the two planforms for loss rates (current).

[Robthebob]

I'm pretty certain that well depth is dependent on loss rates, which is depended on geometry.

[D Tibbets]

I'm pretty certain that well depth is dependent on loss rates, which is depended on geometry.

Geometry and other factors. They pumped a lot of electron current into WB5 but did not come close to the potential well in WB6. The difference was not the geometry, but repellar plates and unshielded structures in WB5. WB6 through the use of spacing of the magnets and small interconnects/ nubs was the difference (along with no repellers/ slow electrons in the cusps) Bussard expressed the importance of magnetic shielding above a certain level ( I think it was 1 part /10,000 as a minumum within the magrid. I believe the spacing did not improve containment (it probably harmed it some), but that electrons could escape confinement and have a good chance of recirculation without an energy penalty and without a high probability of hitting the magnets more than made up the difference by a factor of ~ 10X.

Bussard, etel did believe that increasing the number of faces improved confinement, but that was before WB6, Recirculation considerations may change this (more interconnects. It would be interesting to see some experimental results on this issue.

KitemansSA's championed "X-cuxp" design could improve losses some based on ExY drift in the corner tringular cusps (true point cusps, but the X- cusps still run into metal, and I'm not sure the field lines would always be convex towards the center of the cusp (and the center of the machine)*. That may create macro instabilities. Also the B fields are only 1/2 as strong (wires travel through 4 arms, not just two. Finally the technical winding challenges would be greater. If there is a net benefit, I suspect it would be relatively small.

* As the field lines approach the corner of the X cusp they approach parrelel lines, they never become concave towards the center of the cusp, but would they occasionally become distorted by the plasma and become unstable? The
X- cusps are small, with effectively smaller collection areas. They do not eliminate the Funny cusps, but funny cusps are isolated to this small structure, while the 'corner' cusps are triangular point cusps without funny cusp componets, It is all a matter of field strength locally and the collection area of the corresponding cusps, and how relevant the ExY drift component is compared to the ExB drift component and the underlying cusp leakage.

Finally, I believe interferometry measures the density (very enlightening and important for consideration of Wiffleball formation), not the local voltage/ potential well. I may be wrong, but I believe you need to use a tricky Langmuir probe for that.

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


Dan Tibbets

[happyjack27]

I'm pretty certain that well depth is dependent on loss rates, which is depended on geometry.

weakly. weakly dependant on the level of spherical symmetry. it's much more dependant on size and mag field strength. and unless you have enough money to make a polywell substantially bigger than emc2's wb-8, the mechanics are going to limit you to a truncated cube like wb-6 for max well depth.

[KitemanSA]

Comments in red.

I'm pretty certain that well depth is dependent on loss rates, which is depended on geometry.

KitemansSA's championed "X-cuxp" design could improve losses some based on ExY drift in the corner tringular cusps (true point cusps, but the X- cusps still run into metal, Not sure where, but since there is no field in the metal free center of the X-Cusp, there would be no side drift forces to turn the electrons to nearby metal. and I'm not sure the field lines would always be convex towards the center of the cusp (and the center of the machine)*. They are in my simulation. That may create macro instabilities. Also the B fields are only 1/2 as strong (wires travel through 4 arms, not just two. Finally the technical winding challenges would be greater. If there is a net benefit, I suspect it would be relatively small. Actually, the field is nil in the center of the X-Cusp which makes the gyro radius immaterial. If an electron happens to align with the hole, it exits straight out, and can get sucked straight back it by the MaGrid charge.

* As the field lines approach the corner of the X cusp they approach parrelel lines, ?? they never become concave towards the center of the cusp, but would they occasionally become distorted by the plasma and become unstable? The X- cusps are small, with effectively smaller collection areas. ?? They do not eliminate the Funny cusps, but funny cusps are isolated to this small structure, ?? while the 'corner' cusps are triangular point cusps without funny cusp componets, It is all a matter of field strength locally and the collection area of the corresponding cusps, and how relevant the ExY drift component is compared to the ExB drift component and the underlying cusp leakage. ??
My simulations suggest that all metal is protected by appropriate fields and that the electron will not be drawn into contact with metal. I don't know what Dan is going on about.

BESIDES: my recommendation was that you do side-by-side comparisons of a round and square planform cubeoctahedron unit as Dr. B wanted to do. No X-Cusp involved. That is still my recommendation.

If you want to do a THIRD unit, make it a bow sided square planform. If you want to do a FOURTH unit, then do the "All real, bow sided, square planform cubeoctahedron". Only then do you run into X-Cusps. If you want to jump straight to the fourth, I wouldn't mind from an ego boo stand point, but the better science would be as I have suggested.

NB: The "All real" part means that the triangular magnets would be wrapped like the square ones instead of being "virtual" like the WB6.

PS: Let me know if I can help.

[KitemanSA]

I'm pretty certain that well depth is dependent on loss rates, which is depended on geometry.

In general, I concur. That is why I suggested the two geometries and a simple way to measure loss rate. In detail, the difference between a well depth of 85% and 96% of drive voltage may make a significant difference in final performance and that is the kind of thing I think Dr. B was looking for. Just seems "real world" important to me. PhD fodder for sure?

[Robthebob]

sorry, I didnt mean to make it sound like loss rates only depended on geometry.

imo, with higher order shapes, the confinement can only get better, not worse; this should be true regardless of size, now as the size go down, the well depths of a lower and higher order shapes polywells should converge.

I'm not sure how big it has to be for the geometry to make a significant difference, and I think that would be too much for me to handle by myself.

[KitemanSA]

I'm not so sure the DEPTH would change much but the sphericity (shape) of the well might be much improved with higher order forms.