Here's a simple idea on how to magnetically confine a plasma ball without loosing particles like magnetic mirrors usually do.
For simplicity let's assume mass density and pressure of the plasma approximately follow a normal distribution around the center.
Apply a strong magnetic field which accelerates the plasma in x direction towards its own center.
While the plasma is due to inertia compressing itself in x direction, rotate the magnetic field lines a ninety degrees to confine the plasma in y direction. Now the plasma is accelerated in y direction towards its center. Meanwhile the plasma pressure causes acceleration away from the center in x direction. Now of course rotate the magnetic field lines another 90 degrees and so on...
This cycle should be repeated in at high frequency.
During the entire process the plasma can constantly be magnetically confined in z direction.
Is this idea new or has it already been discussed or is there a reason it wouldn't work ?
Magnetic Confinement using Oscillating or Rotating Fields
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Re: Magnetic Confinement using Oscillating or Rotating Field
A solenoid field rotated about an axis normal to the field...
To work it would have to rotate faster than the plasma can spread. Mechanical rotation would be fiercely fast. Electronic rotation by quadrature phased AC coils would be an interesting situation to see simulated. Coil inductance may be prohibitive. The rotating magnetic field would drag on the plasma, making it spin as well.
To work it would have to rotate faster than the plasma can spread. Mechanical rotation would be fiercely fast. Electronic rotation by quadrature phased AC coils would be an interesting situation to see simulated. Coil inductance may be prohibitive. The rotating magnetic field would drag on the plasma, making it spin as well.
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Re: Magnetic Confinement using Oscillating or Rotating Field
You're probably picturing straight field lines, which is fine, but helical or circular field lines should also be considered.hanelyp wrote:A solenoid field rotated about an axis normal to the field...
There are differences between them and I don't know yet which of them would be optimal.
I was thinking of using LC-circuits.hanelyp wrote:To work it would have to rotate faster than the plasma can spread. Mechanical rotation would be fiercely fast. Electronic rotation by quadrature phased AC coils would be an interesting situation to see simulated. Coil inductance may be prohibitive.
The shape of the plasma would certainly make it look as if it was spinning.hanelyp wrote:The rotating magnetic field would drag on the plasma, making it spin as well.
I'm not so sure if it would really spin though.
One effect which could make the plasma really spin would be its viscosity, but I know nothing about plasma viscosity.
In case the rotation of the plasma is a too much of a problem, there are some alternatives which use oscillating fields without rotating.
Re: Magnetic Confinement using Oscillating or Rotating Field
Spining of periodically compressing the plasma (aka POPS) may have some interesting effects.I'm guessing the rotation , etc would have to be at some resonate frequency of the plasma frequenccy. Prehaps at frequwencies at resenant frequencies faster than the plasma frequency (if a plasma frequency can be figured in this dynamic system). Two monkey wrenches might be one: ExB drift issues and two; eddies, in the plasma magnetic field interaction- if macro instabilities form, confinment will suffer.
I don't know, but some of this may be similar to the complex magnetic patterns used in spheromaks, and I think that these are considered inferior to tokamaks in current thinking.
The Polywell confinement and possible central confluence (central focus) is, I think, based on spherical and symetrical influence of both the magnetic fields and the potential well. Swirling/ twisting fields might have some interesting effects and also might gum up the works. Again- Periodic Oscillating Plasma Sphere (POPS) is a pulsating application of force that may concentrate the plasma in regions and have beneficial effects on fusion rates. This work by Nebel, etel though is, I believe, a symetrical effect. No rotation or twisting componet.
Another concern of twisting the plasma and creating a swirling complex plasma motion is that some of the benefits of the opposing potential wells for the electrons and the ions would result in greater Bremmstruhlung penalties. In the quasi spherical distribution of positive and negative charge, the electrons are fast on the edge (greatest radii) and slow in the center.It is the opposite for ions. This effects time dependant concentration of charged particlesin different regions/ radii of the machine. The ions are most concentrated and fastest in the center- this aids fusion rate. The electrons may also be more concentrated towards the center, but they are much slower here. This profoundly effects the Bremmstruhlung process.
Keep in mind that the Polywell is a non neutral plasma. The effects can be appreciated in a symetrical near spherical geometry with both potential wells oriented radially. With a swirling helical or other complex plasma motion, the potential well shapes become much more complex. Also if there is any preferred motion to the charged particles- such as along a helix, then the plasma has its own magnetic field, the plasma is magnatized. This is completly different that in the Polywell. It is a different animal.
Finally, consider that cusp confinement losses is nessisary foe several reasons. Manip[ulating the cusps with complex B fields/ repellars may do more harm than good- WB5 is an example of this. Recirculation is not really an improvement in electron confinement , it is a mechanism for energy confinement. The electrons outward KE is recovered, so actual electron particle losses are much less painful. From an energy perspective it is much better to lose 1000 electrons at 10 eV each, than it is to lose 10 electrons at 10,000 eV each. of course there are trade offs, engineering concerns, Pashin arc breakdown concerns, etc. But, the conditions represented by WB 6, seems to be the best compromise possible (at least that Bussard, etel was able to determine with 20 years of work). Anything that adversly effects recirculation, near spherical symetry, radial electron energy distribution, etc may help in some regards, but possibly do more overall harm than good. I think this is why POPS may be a viable option for boosting Polywell performance as things are kept spherically symetrical.
Dan Tibbets
I don't know, but some of this may be similar to the complex magnetic patterns used in spheromaks, and I think that these are considered inferior to tokamaks in current thinking.
The Polywell confinement and possible central confluence (central focus) is, I think, based on spherical and symetrical influence of both the magnetic fields and the potential well. Swirling/ twisting fields might have some interesting effects and also might gum up the works. Again- Periodic Oscillating Plasma Sphere (POPS) is a pulsating application of force that may concentrate the plasma in regions and have beneficial effects on fusion rates. This work by Nebel, etel though is, I believe, a symetrical effect. No rotation or twisting componet.
Another concern of twisting the plasma and creating a swirling complex plasma motion is that some of the benefits of the opposing potential wells for the electrons and the ions would result in greater Bremmstruhlung penalties. In the quasi spherical distribution of positive and negative charge, the electrons are fast on the edge (greatest radii) and slow in the center.It is the opposite for ions. This effects time dependant concentration of charged particlesin different regions/ radii of the machine. The ions are most concentrated and fastest in the center- this aids fusion rate. The electrons may also be more concentrated towards the center, but they are much slower here. This profoundly effects the Bremmstruhlung process.
Keep in mind that the Polywell is a non neutral plasma. The effects can be appreciated in a symetrical near spherical geometry with both potential wells oriented radially. With a swirling helical or other complex plasma motion, the potential well shapes become much more complex. Also if there is any preferred motion to the charged particles- such as along a helix, then the plasma has its own magnetic field, the plasma is magnatized. This is completly different that in the Polywell. It is a different animal.
Finally, consider that cusp confinement losses is nessisary foe several reasons. Manip[ulating the cusps with complex B fields/ repellars may do more harm than good- WB5 is an example of this. Recirculation is not really an improvement in electron confinement , it is a mechanism for energy confinement. The electrons outward KE is recovered, so actual electron particle losses are much less painful. From an energy perspective it is much better to lose 1000 electrons at 10 eV each, than it is to lose 10 electrons at 10,000 eV each. of course there are trade offs, engineering concerns, Pashin arc breakdown concerns, etc. But, the conditions represented by WB 6, seems to be the best compromise possible (at least that Bussard, etel was able to determine with 20 years of work). Anything that adversly effects recirculation, near spherical symetry, radial electron energy distribution, etc may help in some regards, but possibly do more overall harm than good. I think this is why POPS may be a viable option for boosting Polywell performance as things are kept spherically symetrical.
Dan Tibbets
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Re: Magnetic Confinement using Oscillating or Rotating Field
Thanks for your answer. I still don't get how POPS works.
Here's my idea for a fusion reactor (you can tell me how POPS is similar or different.):
Use the system I described in the first post to magnetically confine a normally distributed "cold" plasma cloud.
Use sensors and computers to keep the shape of the plasma under control.
Once the optimal shape is achieved, increase the field strength to compress the plasma cloud.
During the process of compression the field is still oscillating/rotating many times to keep up the spherical symmetry of the cloud.
Now the spherically symmetric plasma is imploding at high speed.
This implosion concentrates the plasma in the center and increases the temperature to fusion conditions.
At the center the plasma is for a short time confined under its own inertia,
(the magnetic field is too weak to have influence on such a small dense plasma cloud.)
Then the plasma explodes at a higher speeds than it imploded.
(The fuel has been chosen to produce a lot of ions instead of neutrons)
This explosion compresses the surrounding field such that the surrounding coils can act as a flux compression generator to produce electrical power. During the expansion of the plasma cloud the field still oscillates/rotates many times.
The plasma expands until it is cold again.
Here's my idea for a fusion reactor (you can tell me how POPS is similar or different.):
Use the system I described in the first post to magnetically confine a normally distributed "cold" plasma cloud.
Use sensors and computers to keep the shape of the plasma under control.
Once the optimal shape is achieved, increase the field strength to compress the plasma cloud.
During the process of compression the field is still oscillating/rotating many times to keep up the spherical symmetry of the cloud.
Now the spherically symmetric plasma is imploding at high speed.
This implosion concentrates the plasma in the center and increases the temperature to fusion conditions.
At the center the plasma is for a short time confined under its own inertia,
(the magnetic field is too weak to have influence on such a small dense plasma cloud.)
Then the plasma explodes at a higher speeds than it imploded.
(The fuel has been chosen to produce a lot of ions instead of neutrons)
This explosion compresses the surrounding field such that the surrounding coils can act as a flux compression generator to produce electrical power. During the expansion of the plasma cloud the field still oscillates/rotates many times.
The plasma expands until it is cold again.
Re: Magnetic Confinement using Oscillating or Rotating Field
POPS works independent of the magnetic field surrounding the plasma. It involves the ions oscillating as a group in the electric potential well. Since fusion reaction rate scales with density squared, in theory the density peaks when the ions converge in mass more than makes up for the lack of reactions when the center is depleted of ions.
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Re: Magnetic Confinement using Oscillating or Rotating Field
Abstractness, my understanding of POPS is also limited. As pointed out it involves inducing grouping of ions into wave like bunches (?), such as standing waves, etc. Essentially instead of ions flying towards the center in a average mixture- some traveling inward some traveling outward and distributed in a smooth gradient, the ions travel more in bunches at some radius from the center (note no induced angular momentum), and as a result at times the effective density in a given region may be much higher- with resultant greater gains in overall fusion...I think... It may also have some significant effects on the shape of the potential well.
Your inertial central density picture sounds somewhat like the Dense Plasma Focus/ Pinch- the ions are accelerated inwards by the collapsing magnetic field and are confined inertially long enough for significant fusion to occur. This is on time scales of less than a microsecond. The hot fusion ion and electron plasma then squeeze out the polar cusps(?) of the plasmoid and can give up their kinetic energy to a direct conversion process. The process also sounds like it may have some similarity to the General Fusion approach of having a rotating lead blanket to help maintain spherical symmetry during compression (?). In the Polywell the sphericity (or at least quasisphericity is maintained naturally by the centrally directed ion potential well. I do not think any other mechanism is needed and may actually be harmful. As for electron confinement, a magnetic field spinning faster that the electron's transition time through the cusps might effect confinement, but also the distribution of the electrons overall and especially in the cusps. It might distort the electron generated central virtual cathode, which may be very bad. The interactions would be complex at the very least and again be a different beast than the electrostatic potential well which is the ion driving force in the Polywell.
Also, keep in mind that the electromagnet generated B field does not effect the ions (in the ideal picture) The ions do not see the magnetic field, their behavior is (almost) totally governed by the electrostatic potential well. This is one of the keys of the Polywell that much different than magnetic confinement of ions- such as a Tokamak or Spheromac. ExB drift limits the ion confinement if magnetic fields are the dominate confining mechanism for those ions. That is why Bussard quoted that "magnetic fields are no darn good for ion confinement " (qualifier- for fusion plasmas that are of necessity collisional plasmas- they work very good for confining a few ions like a Penning trap for a noncollisional plasma of a few antiprotons, etc.). What this means is that if you are needing to use magnetic confinement, whether static or rotating, to effect the ions directly the Polywell is already a failure. The Polywell magnetically confines the electrons, but not (to a significant extent) the fuel ions. The trick is that the electrons are maintained at a small excess compared to the ions and this decouples the ions from the need for magnetic confinement. They are confined electrostatically.
In inertially confined devices, the plasma is so dense that a significant portion of the ions will fuse before they can escape from the core. The confinement time is measured in nanoseconds. In the Polywell, the density is much less so only the rare ion will fuse during the time they are in the core. The trick is to turn the escaping fuel ions around and direct them back towards the center (or at least a confined volume) again and again until the rare fusions per pass add up. Inertially confined plasmas may have densities of 10^27 ions per M^3 or more. Polywells may manage densities of ~ 10^22 ions per M^3 while Tokamaks may be ~ 10^19 or 10^20. Fusion scales as the square of the density so inertially confined devices like bombs, laser inertial confinement or pinches need this high density since the material flies apart very quickly- nanoseconds. The Polywell needs to keep the fuel ions confined for ~milliseconds, and Tokamaks require confinement times of hundreds of seconds. Things can become much more complicated when you consider convergence, POPS, thermal spread, average temperature, other loss mechanisms, etc. , but that is the basic principle (the triple product consideration).
Dan Tibbets
Your inertial central density picture sounds somewhat like the Dense Plasma Focus/ Pinch- the ions are accelerated inwards by the collapsing magnetic field and are confined inertially long enough for significant fusion to occur. This is on time scales of less than a microsecond. The hot fusion ion and electron plasma then squeeze out the polar cusps(?) of the plasmoid and can give up their kinetic energy to a direct conversion process. The process also sounds like it may have some similarity to the General Fusion approach of having a rotating lead blanket to help maintain spherical symmetry during compression (?). In the Polywell the sphericity (or at least quasisphericity is maintained naturally by the centrally directed ion potential well. I do not think any other mechanism is needed and may actually be harmful. As for electron confinement, a magnetic field spinning faster that the electron's transition time through the cusps might effect confinement, but also the distribution of the electrons overall and especially in the cusps. It might distort the electron generated central virtual cathode, which may be very bad. The interactions would be complex at the very least and again be a different beast than the electrostatic potential well which is the ion driving force in the Polywell.
Also, keep in mind that the electromagnet generated B field does not effect the ions (in the ideal picture) The ions do not see the magnetic field, their behavior is (almost) totally governed by the electrostatic potential well. This is one of the keys of the Polywell that much different than magnetic confinement of ions- such as a Tokamak or Spheromac. ExB drift limits the ion confinement if magnetic fields are the dominate confining mechanism for those ions. That is why Bussard quoted that "magnetic fields are no darn good for ion confinement " (qualifier- for fusion plasmas that are of necessity collisional plasmas- they work very good for confining a few ions like a Penning trap for a noncollisional plasma of a few antiprotons, etc.). What this means is that if you are needing to use magnetic confinement, whether static or rotating, to effect the ions directly the Polywell is already a failure. The Polywell magnetically confines the electrons, but not (to a significant extent) the fuel ions. The trick is that the electrons are maintained at a small excess compared to the ions and this decouples the ions from the need for magnetic confinement. They are confined electrostatically.
In inertially confined devices, the plasma is so dense that a significant portion of the ions will fuse before they can escape from the core. The confinement time is measured in nanoseconds. In the Polywell, the density is much less so only the rare ion will fuse during the time they are in the core. The trick is to turn the escaping fuel ions around and direct them back towards the center (or at least a confined volume) again and again until the rare fusions per pass add up. Inertially confined plasmas may have densities of 10^27 ions per M^3 or more. Polywells may manage densities of ~ 10^22 ions per M^3 while Tokamaks may be ~ 10^19 or 10^20. Fusion scales as the square of the density so inertially confined devices like bombs, laser inertial confinement or pinches need this high density since the material flies apart very quickly- nanoseconds. The Polywell needs to keep the fuel ions confined for ~milliseconds, and Tokamaks require confinement times of hundreds of seconds. Things can become much more complicated when you consider convergence, POPS, thermal spread, average temperature, other loss mechanisms, etc. , but that is the basic principle (the triple product consideration).
Dan Tibbets
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Re: Magnetic Confinement using Oscillating or Rotating Field
The reactor I described above works similar to a Diesel engine.
First Compression, then Ignition and then the energy is harnessed by Expansion.
But instead of pistons we use magnetic fields and maintain spherical symmetry.
During one Compression the magnetic field rotates several times.
And during one Expansion the magnetic field also roatates several times.
First Compression, then Ignition and then the energy is harnessed by Expansion.
But instead of pistons we use magnetic fields and maintain spherical symmetry.
During one Compression the magnetic field rotates several times.
And during one Expansion the magnetic field also roatates several times.
What rotating lead blanket ?D Tibbets wrote:The process also sounds like it may have some similarity to the General Fusion approach of having a rotating lead blanket to help maintain spherical symmetry during compression
Re: Magnetic Confinement using Oscillating or Rotating Field
There is no ignition in a Polywell. As Bussard described it, it is an amplifier. Heating is through accelerated electrons which in turn lead to a potential well that accelerates ions, and importantly does so in a way that the ions are hot in the center and cold on the edge. Microwave heating may also be employed. There is no significant heating by the fusion products. Because of their high energy the Mean Free Path (MFP) of the fusion ions is longer than the confinement time/ distance traveled before they escape through a cusp. They are not contained by the potential well as their KE is way greater than the potential well, which differentiates them from the fuel ions . They are contained by the cusp magnetic field (Wiffleball trapping)just as the electrons are.The MFP of the fusion product ions may be relatively ~ 100 times as great, and the number of passes (related to the confinement time) is perhaps 100-1000 times less. They simply do not have time to thermalize with the fuel plasma- or with each other for that matter. If you are pursuing fusion ignition conditions you are diverging from Polywell principles by a huge amount. I'm guessing that the confinement for the fuel ions is in the 10's or even the hundreds of milliseconds. For the fusion generated high energy ions (eg:alphas) the containment time is perhaps in the neighborhood of a microsecond.
As for General Fusion, this link presents more than what I know of them:
http://en.wikipedia.org/wiki/General_Fusion
Dan Tibbets
As for General Fusion, this link presents more than what I know of them:
http://en.wikipedia.org/wiki/General_Fusion
Dan Tibbets
To error is human... and I'm very human.
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Re: Magnetic Confinement using Oscillating or Rotating Field
I'd like to simulate the reactor which I described in the 1st, 5th and 8th post on this thread.
Does anyone know which free software to use to do 1D, 2D or 3D simulations?
Does anyone know which free software to use to do 1D, 2D or 3D simulations?
Re: Magnetic Confinement using Oscillating or Rotating Field
This D.K.Taylor, Jan 1961 paper suggests confinement gain from rotating the magnetic field in a cusp configuration.
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Re: Magnetic Confinement using Oscillating or Rotating Field
That's awesome, thanks.polyill wrote:This D.K.Taylor, Jan 1961 paper suggests confinement gain from rotating the magnetic field in a cusp configuration.
Re: Magnetic Confinement using Oscillating or Rotating Field
No time for studying your idea, but maybe there is something useful here:
Actively Controlled Rotating Magnetic Flux Compressor
viewtopic.php?f=4&t=4521
Double-helix / multi-helix magnets
viewtopic.php?f=4&t=2496
(many dead links; basic idea here - http://amlsuperconductivity.com/capabil ... echnology/ )
Actively Controlled Rotating Magnetic Flux Compressor
viewtopic.php?f=4&t=4521
Double-helix / multi-helix magnets
viewtopic.php?f=4&t=2496
(many dead links; basic idea here - http://amlsuperconductivity.com/capabil ... echnology/ )
Re: Magnetic Confinement using Oscillating or Rotating Field
Reminds me of an electrodeless lorenz force thruster:
https://www.aa.washington.edu/research/ ... s/elf.html
https://www.aa.washington.edu/research/ ... s/elf.html
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Re: Magnetic Confinement using Oscillating or Rotating Field
on the point of spinning field inducing drag on the plasma, two solutions:
* since you'd be slowly adding in new plasma and draining off old plasma, the spin will reach an average equilibrium spinning speed omewhat below that of the field.
* you can add acceleration to the field, rather than just velocity, to keep it from reaching equilibrium - or at least first-order equlibrium. using an oscillating field would be an example of this. sinusoidal would be another - e.g. spinnning in one direction, then switching back to the other direction, flipping the direction. whatever the approach, adding accelleration would mean more power drain, since the acceleration would be applying force.
on the difficulty in creating such a spin:
* you could invert it, so to speak - spin the plasma rather than the field. e.g. you could have angled gas - puffers. not sure how well that would work and you'd have to offset them to maximize central convergence. maybe you could also do something with rf fields to accellerate the plasma to a spin. still, though, you might have to get it pretty fast to get it to sort of smooth out the effects of the cusps, as it were. then again, presumably at the outer ends of the cups, the ions are near 0 KE - so you might actually get a good bang for your buck.
* since you'd be slowly adding in new plasma and draining off old plasma, the spin will reach an average equilibrium spinning speed omewhat below that of the field.
* you can add acceleration to the field, rather than just velocity, to keep it from reaching equilibrium - or at least first-order equlibrium. using an oscillating field would be an example of this. sinusoidal would be another - e.g. spinnning in one direction, then switching back to the other direction, flipping the direction. whatever the approach, adding accelleration would mean more power drain, since the acceleration would be applying force.
on the difficulty in creating such a spin:
* you could invert it, so to speak - spin the plasma rather than the field. e.g. you could have angled gas - puffers. not sure how well that would work and you'd have to offset them to maximize central convergence. maybe you could also do something with rf fields to accellerate the plasma to a spin. still, though, you might have to get it pretty fast to get it to sort of smooth out the effects of the cusps, as it were. then again, presumably at the outer ends of the cups, the ions are near 0 KE - so you might actually get a good bang for your buck.