Is it true that there is no recirculation, just bounce of the electrons? I watched the Google video again and Bussard specifically said that electrons recirculate through another cusp. Without the math or a strong (err... small) grounding in magnetic theory, I may be thoroughly confused, but that's never stopped me before. In various threads, it's mentioned that the electrons bounce back unless they have enough kinetic energy to get past the magnets- then they are lost to the vessel wall- ie- on a hyperbolic orbit (or intercepted elliptical orbit). Why can't it be on an elliptical orbit? With the round magnetic tube as opposed to the square tube the really close magnetic flux lines do not hit the metal, so that where the flux lines are densest and the most curved there is greater chance that the electron will bounce back. That I can follow, and is what seems to be the consensus here. But, those electrons that make it past this point are still traveling along a flux line, and as the flux line becomes less curved it speeds up, but in an isolated system I'm thinking it should orbit the magnet. The question is if this magnetic flux line reaches the vacuum vessel wall before the vector of the electron has swung around so that it is traveling back towards the inside of the magrid. I'm uncertain what happens in this part of the inbound orbit. In an isolated system I'm thinking that it would be a stable orbit (ignoring gravity waves, etc). If traveling from a corner cusp to a center cusp the returning flux line is less curved ( more space between magnets, and does the ' wiffleball' effect play a part here?) so if the electron didn't bounce on it's way out, it should be even less likely to bounce on it's way back in. But in the Polywell, once back inside the magrid the electron would see strong electrostatic forces from nearby ions and sibling electrons and be knocked off its orbit and perhaps rejoin the general electron population (effectively losing some of it's energy to the average energy of the electrons). This would have the effect of recovering some of the highest energy electrons (is this part of the 'annealing' process?).
And, I have not seen any discussion on how much the positively charged magrid effects the electrons path through the cusps. I assume that the pos. charge would pull the electron into an even tighter orbit- more dense, curved magnetic field lines leading to a greater chance of bouncing ( or before the round geometry of the WB6 magrid, of smacking into the magrid), or if it gets outside the magrid then the orbit again would be tighter so the electron would be less likely to reach the vacuum chamber wall .
Hopefully, I've explained my conclusions without too much deviation from reality due to lacking mathematical arguments, and ignoring things like debye length, mean free path, etc.
Dan Tibbets
ps: I can see why having the spacing between the magnets set at two gyro radius apart might be advantageous. The compressed and tightest magnetic field lines there have the greatest chance of bouncing the electron, while minimizing the chance that the electron would hit the maggrid. I'm guessing that adding additional magnets would increase the area of the corner/ funny cusps that approach this condition. But, with more magnets, each would be smaller and the density / curvature of the flux lines between the corner cusps and center cusps would be less, so recirculation might decrease ( as my argument above). So, there may be a break even point somewhere. eg: a 36 ( or whatever fits the geometry requirements) face my work as well as a 500 face magrid...
Does Recirculation real?
Does Recirculation real?
To error is human... and I'm very human.
Howdy Dan,
You aren't the only one confused. I think Bussard changed his mind between 1991 when wrote the first papers and 2007 when he did the Google video. It makes sense to me that particles that escape the center will have a hard time getting back, but if the MaGrid is far enough from the walls then it will attract the electrons back.
What makes this problem hard is that the cusps are non symmetric. The inside mirror is a tighter field than the outside, so it is easier to enter and harder to escape. That helps with recapturing. But at the neck it will be pretty darn close, so any external collisions will make recapture almost as hard as escape from the center.
It could be we need to play with that field, and it could be the internal currents will do it for us. If the internal cusp looks tight and the re-entry cusp looks loose, then recapturing lost electrons may be pretty easy. It is a pretty complex problem though and hand waving won't solve it.
You aren't the only one confused. I think Bussard changed his mind between 1991 when wrote the first papers and 2007 when he did the Google video. It makes sense to me that particles that escape the center will have a hard time getting back, but if the MaGrid is far enough from the walls then it will attract the electrons back.
What makes this problem hard is that the cusps are non symmetric. The inside mirror is a tighter field than the outside, so it is easier to enter and harder to escape. That helps with recapturing. But at the neck it will be pretty darn close, so any external collisions will make recapture almost as hard as escape from the center.
It could be we need to play with that field, and it could be the internal currents will do it for us. If the internal cusp looks tight and the re-entry cusp looks loose, then recapturing lost electrons may be pretty easy. It is a pretty complex problem though and hand waving won't solve it.
Getting past the magnets isn't enough, they would also have to overcome the gradient between the positively charged Magrid and the walls. I doubt many ever do. Bussard did not seem to regard this as a significant loss mechanism. Nebel has said the behavior outside should be adiabatic, so what goes out comes back in.In various threads, it's mentioned that the electrons bounce back unless they have enough kinetic energy to get past the magnets
You end up with an interior density a thousand or more times the exterior density. There's some speculation this works because at beta=1 the wiffle-ball effect causes the geometry of the field lines to be much friendlier to returning electrons than to those exiting.
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...
Which Spects?
TallDave,
Is it more helpful to we wearing our energy spectacles rather than our particle spectacles? It seems the energy is hopefully retained even if charge is lost to the reaction area, such that electrons that do escape have little energy left and carry little energy away from the reaction area at least this way. A slight continuous inexorable charge loss won't break Miss Polly, but energy loss will. Is this right?
Isn't that the "wiffleball works" that we're hoping for in these first renewed set of experiments (WB7)?
Is it more helpful to we wearing our energy spectacles rather than our particle spectacles? It seems the energy is hopefully retained even if charge is lost to the reaction area, such that electrons that do escape have little energy left and carry little energy away from the reaction area at least this way. A slight continuous inexorable charge loss won't break Miss Polly, but energy loss will. Is this right?
Isn't that the "wiffleball works" that we're hoping for in these first renewed set of experiments (WB7)?
To expand on my impression of asymetry of the magnetic fields, I'm thinking that the line- edge-corner- funny (?) cusps outside the magnet donut have more dense and curved field lines due to compression by the adjacent magnets, and that difference is magnified by the 'Wiffle Ball' effect(?).
viewtopic.php?t=650&postdays=0&postorder=asc&start=15
So, electrons escaping through these cusps might orbit back through the center- point cusps more easily. Those electrons escaping through the central point cusps would have a harder time recirculating- orbiting back through the edge cusps. But, as Art Carlson has reveiled to me in his posts, the losses through the line cusps far exceed those through the point cusps. Perhaps that is why the U-Tube vidio showing recirculation only shows the electons exiting the edge cusps and reentering through the center cusps .
http://www.youtube.com/watch?v=jmp1cg3-WDY
from TallDave ... "Getting past the magnets isn't enough, they would also have to overcome the gradient between the positively charged Magrid and the walls. I doubt many ever do"...
Once past the magnet (outbound) the electron would be slowed by the positively charged magrid. I'm thinking that this would help, not hinder the chances of the electron turning around before hitting the vessel wall (tighter orbit). I'm assuming that once back inside the magrid the interactions with the much more dense electron and ion clouds would knock the recirculated electrons off of this narrow ' flux line orbit' that otherwise would allow it to again exit through an edge cusp. Also, if neutral gas accumulates outside the magrid, which is apparently one of the concerns, the potentially recirculating electrons could hit them and be perminatly lost.
from Helius ..."Is it more helpful to we wearing our energy spectacles rather than our particle spectacles? It seems the energy is hopefully retained even if charge is lost to the reaction area, such that electrons that do escape have little energy left and carry little energy away from the reaction area at least this way"...
Hmm... sort of like what is needed to capture the energy of the alpha particles in a p-B11 reactor. This could reduce the energy that is needed to maintain the potential on the magrid. I don't know how much this would contribute, but every little bit would help.
Dan Tibbets
viewtopic.php?t=650&postdays=0&postorder=asc&start=15
So, electrons escaping through these cusps might orbit back through the center- point cusps more easily. Those electrons escaping through the central point cusps would have a harder time recirculating- orbiting back through the edge cusps. But, as Art Carlson has reveiled to me in his posts, the losses through the line cusps far exceed those through the point cusps. Perhaps that is why the U-Tube vidio showing recirculation only shows the electons exiting the edge cusps and reentering through the center cusps .
http://www.youtube.com/watch?v=jmp1cg3-WDY
from TallDave ... "Getting past the magnets isn't enough, they would also have to overcome the gradient between the positively charged Magrid and the walls. I doubt many ever do"...
Once past the magnet (outbound) the electron would be slowed by the positively charged magrid. I'm thinking that this would help, not hinder the chances of the electron turning around before hitting the vessel wall (tighter orbit). I'm assuming that once back inside the magrid the interactions with the much more dense electron and ion clouds would knock the recirculated electrons off of this narrow ' flux line orbit' that otherwise would allow it to again exit through an edge cusp. Also, if neutral gas accumulates outside the magrid, which is apparently one of the concerns, the potentially recirculating electrons could hit them and be perminatly lost.
from Helius ..."Is it more helpful to we wearing our energy spectacles rather than our particle spectacles? It seems the energy is hopefully retained even if charge is lost to the reaction area, such that electrons that do escape have little energy left and carry little energy away from the reaction area at least this way"...
Hmm... sort of like what is needed to capture the energy of the alpha particles in a p-B11 reactor. This could reduce the energy that is needed to maintain the potential on the magrid. I don't know how much this would contribute, but every little bit would help.
Dan Tibbets
To error is human... and I'm very human.
The fields outside the Magrid have to be consistent with the Faraday cage that is located out there, "far" from the Magrid, but close to the vessel wall. This cage allows for adjustment (i.e. control) of voltage potential in the far-field from the Magrid.
It is, IMO, a very simple but clever innovation of Dr. B's that many are over-looking in why recirculation IS real and controllable.
Only the cusp lines (not the line cusps) will actually terminate on the cage, all others must close back into the Magrid internal field.
It is, IMO, a very simple but clever innovation of Dr. B's that many are over-looking in why recirculation IS real and controllable.
Only the cusp lines (not the line cusps) will actually terminate on the cage, all others must close back into the Magrid internal field.
The electric fields will be affected by the Faraday cage, but the magnetic fields won't.
The cusp losses are complicated. You have both ions and electrons spinning around the B field lines, with different radius for each species and energy level. You have electrons being accelerated into the cusps by the MaGrid and ions being repelled away from it. So electrons that leave the MaGrid want to come back, but ions that leave the MaGrid never want to. Because the ions have a lot of momentum, they will drag the electrons away. But if the electrons shield the MaGrid enough, they can bring some ions back.
That sets you up for oscillations and arcing. It's the same problem ITER has. But if you set up the oscillations on purpose, you may be able to prevent arcing. Accepting losses for part of the cycle may really help maintain an over all steady state. Seeing the system as a dynamic one which is constantly changing means "stability" is not a constant state - but it also means taking hits on efficiency.
It'd be fun to do a lot of experiments on it anyway!
The cusp losses are complicated. You have both ions and electrons spinning around the B field lines, with different radius for each species and energy level. You have electrons being accelerated into the cusps by the MaGrid and ions being repelled away from it. So electrons that leave the MaGrid want to come back, but ions that leave the MaGrid never want to. Because the ions have a lot of momentum, they will drag the electrons away. But if the electrons shield the MaGrid enough, they can bring some ions back.
That sets you up for oscillations and arcing. It's the same problem ITER has. But if you set up the oscillations on purpose, you may be able to prevent arcing. Accepting losses for part of the cycle may really help maintain an over all steady state. Seeing the system as a dynamic one which is constantly changing means "stability" is not a constant state - but it also means taking hits on efficiency.
It'd be fun to do a lot of experiments on it anyway!