i should say that's rather more like (n/2)^2.happyjack27 wrote:i'm 3-sigma statistically and let me tell you it is _hard_ to find a suitable partner, even in a dense n^2 environment!Each time ions don't fuse when they meet (which is 3-sigma statistically all the time!), they loose energy.
Florida lab to pursue Bussard Polywell and IEC fusion resear
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happyjack27
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Come again!!! A touch of irony there!!D Tibbets wrote:This discussion is ignoring Gauss Law.
If the outer edge of the wiffleball is at ground potential and the wall is at ground potential, then there will be a line of equipotential at ground potential that zaps right through the middle of the magrid apertures. They won't be accelerated along that line, but they can run along it, unimpeded. It may be as thin as you like (that's why it is called a 'cusp'), but it will exist. Particles travelling along it will also be travelling parallel to the magnetic fields, and therefore such a particle would experience no electric nor magnetic forces, save for those from the particles around it.
If the outer edge of the wiffeball is NOT at ground potential but at 'V', then any electron that makes a non-collisional route between wiffleball edge and ground will have travelled through V and will therefore loose Vq of energy from the system once it is lost to the wall (and the chamber will also experience Vq's worth of sputtering per electron, which will contaminate it).
chrismb, the point you seem to be missing is that the electrons at the edge of the wiffleball, that are at very high kinetic energy, got that way by travelling through 'V' the other way.
An electron leaving the wiffleball and magrid and heading out towards the wall/Faraday cage/electron emitters is leaving a high positive potential (or ground) and heading towards ground (or a high negative potential), and will thus slow down.
If the point of electron loss is at a similar potential to the (thermionic) electron emitters, electrons lost to that point should have very little kinetic energy to lose as heat, and virtually all of the energy they had on exiting the magrid will be recovered in the circuit.
This is not true for massively upscattered electrons, of course, but hopefully the electron population will not be thermal... I'd rather not get into that right now...
It is also not true for electrons lost to the magrid. Those lose roughly q*V_applied, which is pretty large; this is probably the loss channel that constitutes the bulk of the power losses attributable to the electron population.
An electron leaving the wiffleball and magrid and heading out towards the wall/Faraday cage/electron emitters is leaving a high positive potential (or ground) and heading towards ground (or a high negative potential), and will thus slow down.
If the point of electron loss is at a similar potential to the (thermionic) electron emitters, electrons lost to that point should have very little kinetic energy to lose as heat, and virtually all of the energy they had on exiting the magrid will be recovered in the circuit.
This is not true for massively upscattered electrons, of course, but hopefully the electron population will not be thermal... I'd rather not get into that right now...
It is also not true for electrons lost to the magrid. Those lose roughly q*V_applied, which is pretty large; this is probably the loss channel that constitutes the bulk of the power losses attributable to the electron population.
Last edited by 93143 on Mon Dec 13, 2010 7:58 pm, edited 7 times in total.
Chris,
I don't think anyone is thinking there will be no e- losses in the cusps. The question is how much verses fusion energy produced by ion collisions.
The other consideration that Bussard and Rick have raised is the thought of fuel ionization providing another makeup source of e-. So much so that Bussard mused that it might be enough to self sustain the e-. Now wouldn't that be something...
I don't think anyone is thinking there will be no e- losses in the cusps. The question is how much verses fusion energy produced by ion collisions.
The other consideration that Bussard and Rick have raised is the thought of fuel ionization providing another makeup source of e-. So much so that Bussard mused that it might be enough to self sustain the e-. Now wouldn't that be something...
Assuming that by "ground[/wall]", you mean electron emitters and Faraday cage, the wiffleball edge should be more positive. Simple test: Are the electrons faster there than at "ground[/wall]"? Answer: Yes. Ergo, the wiffleball edge is more positive.
I believe there are supposed to be no points in the wiffleball where the electrons quite get all the way back down to the kinetic energy they had on leaving the thermionic emitters. It is therefore plausible to assert that the entire wiffleball is at a more positive potential than the emitters/Faraday cage.
I believe there are supposed to be no points in the wiffleball where the electrons quite get all the way back down to the kinetic energy they had on leaving the thermionic emitters. It is therefore plausible to assert that the entire wiffleball is at a more positive potential than the emitters/Faraday cage.
My understanding is that the WB6 set-up was ground state as the wall (or there abouts) highly positive at the magrid and then the well gets to about 80% of the positive plateau. The well is RELATIVE to the MaGrid voltage. no?chrismb wrote:Isn't the magrid at the greatest positive potential?!? I thought the magrid was high positive, the edge of the wiffleball was roughly neutral and the centre was high negative, making the wiffleball generally negative wrt magrid so that any loose ions accelerate from magrid-wiffleball region into wiffleball.KitemanSA wrote:The wiffle ball is at (or near) the point of greatest positive potential. It is where the electron has the greatest KINETIC energy.
If this is not so, then I will finally give up any hope of thinking it is possible to comprehend the whole concept of this thing.
Last edited by KitemanSA on Wed Dec 15, 2010 1:12 am, edited 1 time in total.
What he said!happyjack27 wrote:in all this talk i think it's important to distinguish whether you're looking at absolute electric potential energy, or whether you're talking about acceleration along a gradient of electric potential energy. (the latter being the first spatial derivative of the former.) e.g. inside a hollow charged sphere, the gradient may be zero but the electric potential energy is not.
The last few posts from 93143 are reasonable, and also confusing.
The comment about the cross field transport of electrons being the bulk of electron (energy) losses is perhaps excessive. In the 2008 patent application, there is a comment that IF the recirculation can be made very very good, this condition might be approached. It would represent the holly grail of recirculation.
Calling the Wiffleball border an anode is confusing. Of course everything is relative to everything else. But the non neutral plasma inside the Wiffleball border contains an excess of electrons- so it is a cathode- a vertual cathode in this case. This virtual cathode will attract any positive charge outside of it, and it will impead any positive charge trying to leave it. Remember it is simply (?) a substitute for the wire cathode that is placed near the center of a conventional fusor. In an Elmore Tuck Watson type of fusor (like the Polywell), the picture is more vague as the electron containment, distribution, and density is intamitally coupled with a real anode. A wire in the ETW machine, and a magnetically shielded magrid in a Polywell.
Then throw in interactions with ions in which a central vertual anode can form and things become increasing vague, and definitions need to be kept close to the chest.
At its simplest the Wiffleball border and volume of pure electrons is a square potential well so there is only a voltage gradient on the edge (a few Debye lengths wide). With a mixed plasma and resultant parabolic potential well the definitions depend where you are standing within the Wiffleball volume.
From outside the magrid there is a different picture. There is still a negative virtual cathode inside the magrid, but the positive charge on the magrid is greater, and closer, so any negative charge will be attracted towards it and any positive charge will be repelled outwards. If the magrid and Wiffleball volume is added together , it acts as an anode to anything outside it. It is even more vague if the magrid is grounded and the electron guns are at a high negative potential and the vacuum vessel walls are also at ground. Inside the magrid the picture would not change, but I wonder what this version would do to recirculation.
Dan Tibbets
The comment about the cross field transport of electrons being the bulk of electron (energy) losses is perhaps excessive. In the 2008 patent application, there is a comment that IF the recirculation can be made very very good, this condition might be approached. It would represent the holly grail of recirculation.
Calling the Wiffleball border an anode is confusing. Of course everything is relative to everything else. But the non neutral plasma inside the Wiffleball border contains an excess of electrons- so it is a cathode- a vertual cathode in this case. This virtual cathode will attract any positive charge outside of it, and it will impead any positive charge trying to leave it. Remember it is simply (?) a substitute for the wire cathode that is placed near the center of a conventional fusor. In an Elmore Tuck Watson type of fusor (like the Polywell), the picture is more vague as the electron containment, distribution, and density is intamitally coupled with a real anode. A wire in the ETW machine, and a magnetically shielded magrid in a Polywell.
Then throw in interactions with ions in which a central vertual anode can form and things become increasing vague, and definitions need to be kept close to the chest.
At its simplest the Wiffleball border and volume of pure electrons is a square potential well so there is only a voltage gradient on the edge (a few Debye lengths wide). With a mixed plasma and resultant parabolic potential well the definitions depend where you are standing within the Wiffleball volume.
From outside the magrid there is a different picture. There is still a negative virtual cathode inside the magrid, but the positive charge on the magrid is greater, and closer, so any negative charge will be attracted towards it and any positive charge will be repelled outwards. If the magrid and Wiffleball volume is added together , it acts as an anode to anything outside it. It is even more vague if the magrid is grounded and the electron guns are at a high negative potential and the vacuum vessel walls are also at ground. Inside the magrid the picture would not change, but I wonder what this version would do to recirculation.
Dan Tibbets
To error is human... and I'm very human.
Perhaps. It is true that any high-energy thermalization will tend to cause electrons to hit the emitters and Faraday cage harder than they normally would, or even allow them to exit the assembly entirely. The Faraday cage should perhaps be at an even lower potential than the emitters (I seem to recall assuming that at some point), but some portion of the high-energy tail will still make it through, and in a direct-conversion reactor, these escaped electrons will then be accelerated into the collector plates - probably the lowest-level ion leakage collectors at roughly the same potential as the wiffleball edge...D Tibbets wrote:The comment about the cross field transport of electrons being the bulk of electron (energy) losses is perhaps excessive.
It is also true that I was ignoring the magrid supports (though it has been suggested that the insulated sections eventually accumulate enough negative charge to scare away most of the electrons that would otherwise hit them).
On the other hand, it is also true that the nubs are [were?] right in the way of recirculating electrons, and very weakly shielded... I suppose firing a REB at a fridge magnet is technically "cross-field transport"...
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happyjack27
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replace nubs w/supports, on each coil so there are no nubs, only supports where electron transport is minimal.93143 wrote:Perhaps. It is true that any high-energy thermalization will tend to cause electrons to hit the emitters and Faraday cage harder than they normally would, or even allow them to exit the assembly entirely. The Faraday cage should perhaps be at an even lower potential than the emitters (I seem to recall assuming that at some point), but some portion of the high-energy tail will still make it through, and in a direct-conversion reactor, these escaped electrons will then be accelerated into the collector plates - probably the lowest-level ion leakage collectors at roughly the same potential as the wiffleball edge...D Tibbets wrote:The comment about the cross field transport of electrons being the bulk of electron (energy) losses is perhaps excessive.
It is also true that I was ignoring the magrid supports (though it has been suggested that the insulated sections eventually accumulate enough negative charge to scare away most of the electrons that would otherwise hit them).
On the other hand, it is also true that the nubs are [were?] right in the way of recirculating electrons, and very weakly shielded... I suppose firing a REB at a fridge magnet is technically "cross-field transport"...
then you have electron losses to grid, electron losses to cage, and ion losses. ion losses would be a high and very specific energy right through the cusps, esp. w/a charged magrid. you can do direct conversion tuned to that energy level right at cusps (and far from the grid) and recycle most of that energy. this leaves only electron losses to grid and cage. from what i've seen in my sims, the mag field insulates the magrid pretty well, so that it's mostly cage losses. so now you're down to pretty much what the theoretical formula says.