Actual Polywell News!

[D Tibbets]

I'm explaining how it's supposed to work.

Motion of ions can be considered as combination of two:
· harmonic oscillation around the center
· chaotic (thermal) motion
Because they are going to increase B-field strength from 0.8 to 10 T, so in12 times, and expect that number density will increase in 144 times (also dubious expectation), chaotic motion intensity will become comparable with harmonic (so called thermalization) faster.

Due to permanent neutralization of electron cloud the depth of potential well will decrease by entering of new portion of ions.
So, amplitude of harmonic oscillation of ions entered machine later will be slower than initially.

etc. etc. etc.

Important point, the thermal motion is not totally chaotic. There are two considerations. Coulomb scattering collisions can result in two processes- up scattering and down scattering collisions, and transverse or angular momentum changing collisions. One aspect of the Polywell is that there is some confluence or central focus of the ions. How much is debatable, but there will always be some. As such , any Coulomb collisions that occur near the center cannot induce as much angular momentum randomization, compared to collisions away from the center. With confluence in the spherical geometry, the density in the center is greater and thus the collision frequency is greater. This distorts the angular momentum randomization rate and thus the angular momentum thermalization times (it takes longer relative to the total number of collisions occuring in the system. Again, whether this non random/ non chaotic bias is minor or major depends on your assumptions about the confluence of the average ion over it's lifetime.

For up/ down scattering , non chaotic effects are several fold. First the issue of edge annealing can be very important. The density in various regions of the machine and associated MFP considerations vs machine diameter are important. There is some density limit where the MFP is much (or mildly?) less than the machine diameter, so that edge annealing becomes meaningless- full thermalization occurs in one pass of the ion through the core and mantle regions. Raising the KE of the particles retards this, while increased density favors this.The balance is the issue. I believe that the density and ~10 KeV potential well in WB6 allowed for average MFP's great enough for annealing to work. How this would extend into larger, more plasma dense and energetic systems is more challenging. Nebel commented on this and admitted that in larger machines this threshold might be exceeded. It doesn't mean that edge annealing stops, but that it cannot keep up with global thermalization. With D-D this does not preclude success, though it does increase Bremmstruhlung issues for P-B11 fusion.
Another process that impeads full thermalization is that the high energy tail ions will leave through the cusps faster than the average ion. Once the potential well energy is exceeded by the up scattered ions the confinement becomes magnetic, and losses through cusp exit (or ExB diffusion) is more rapid both from a number of passes perspective and from a time perspective. . The up scattered ions have a lower collisionality (scales as the 1/KE squared) and ythus less opportunity to share their energy with the average ion. The effect may be trivial or significant, but it is present. In a Tokamak the confinement time is huge (hundreds of seconds) versus the 10's of millisecond lifetimes in the Polywell (even much less for highly up scattered ions). There is no provision for preferential extraction of the up scattered ions so the full high thermalization tail has sufficient time to form. This is not the case in the Polywell. Again, the significance of this difference is debatable, but real. I think the confinement time for ions in WB6 was ~ 10-20 milliseconds. This was due to the electrostatic confinement, and at ~ 10 KeV energies this correlated to ~ 160,000 M/s. With 10,000 passes confinement, the distance traveled would be ~ 3,000 meters, so this distance would be traveled in ~ 18 ms. which is consistent with statements*.
An up scattered ion in isolation whith twice the velocity (4 times the KE) would have a confinement time shorter by this amount except that the electrostatic confinement is lost, so that the number of passes would be closer to the Wiffleball trapping factor which is closer to 1000. So the net confinement time for this up scattered ion might be ~ 1 ms. This depletes the high energy tail of the thermalization distribution to a degree. Compare this to a Tokamak with eg: 800 to 1000 second confinement time. The difference is ~ 1 million. The density in the Polywell might be 100 times greater with a resultant conditionality 10,000 times greater. This still leaves a 100 fold difference in dwell time in which the up scattered ion can continue to contribute to the thermalization process. The difference in average temperature also plays a role. A Tokamak might struggle to reach an average temperature of 10 KeV, while the Polywell might be operating at 100KeV. This results in an average thermalization time- collision frequency of 10^2 or 100 times less in the Polywell. The net result is that the Polywell density- energy conditions results in thermalization profiles that is up to ~ 10,000 less less relative to the ion lifetimes, compared to a Tokamak. Even with a 1000X difference in density, the Polywell still trails by a factor of ~ 100.
Thus claims that the Polywell ions do not thermalize over the lifetime of the ions does not seem to be an outrageous claim, at least on the surface. I again point out the the often used term- monoenergetic energy is misleading. Of course there is some spread. The important point is that it is not full thermalization. Even with annealing overwhelmed, the high energy thermalized tail is truncated to an uncertain amount.


* A clearification for me and others(?). The ion confinement time may be represented as time to escape, of number of passes till escape. Electron confinement time is often stated as ~ 100,000 with recirculation, or ~ 10,000 passes without. Ions are considered confined better with the electrostatic potential well, and I have sometimes considered confinement of perhaps 1,000,000 passes as representative. But this is wrong. The deuterium ions travel ~ 60 times slower than the electrons, so it takes 60 times longer to complete one pass. Bussard mentioned ~ 10,000 passes being required to achieve adequate fusion rates. Multiplied by 60 results in ion confinement times of ~ 6 times that of the electron confinement times (with recirculation). 12-18 ms for the ions vs 2-3 ms for the electrons. Again the numbers are consistent.
This also gives a representation of the energy costs of electron vs ion losses. Ion losses account for ~ 20% compared to the electrons (accounting for ion acceleration as they pass beyond the magrid). It is safe to say the electron losses dominate the picture.

Dan Tibbets

[Joseph Chikva]

Important point, the thermal motion is not totally chaotic.

First wrong statement. As definitely thermal motion is totally chaotic.

The ion confinement time may be represented as time to escape, of number of passes till escape.

The second wrong statement. When you have dense enough set of particles, in which Debye length is lower than geometric dimensions of system (this is one of definition of plasma), confinement time of ions can be define as confinement time of plasma (ions and electrons taken together and not separately). And more likely that you can not organize harmonic motion of ions at all. As inevitably strong electrostatic fields are needed for separation of particles for low Debye length set of particles. And so the maximum you can do is to organize the harmonic oscillation of total plasma with its fast thermalization. So increasing density to claimed 10^22 m^-3 (and even 10^19 m^-3) you will get a thermal machine.

[D Tibbets]

And of course in the Polywell thermalization of the fusion ions with the fuel ions is insignificant.

Of course insignificant?
At what number density? In which form energy of electrons injected by electron guns will be converted? If I recall correctly you mentioned desired number density of future Polywell as 10^22 m^-3. Can you separate spices at this number density with the help of electrostatic field forcing e.g. ions to oscillate around electron cloud? If to recall that debye length at this number density will have micrometers order of magnitude.
Are you sure that injected energy will be converted in harmonic motion energy and not in thermal?

Relative number- density and fusion ions thermalizing with fuel ions? Forget electrons, energy exchange between alphas and electrons will be ~ 60 times less than between the alphas and fuel ions.

Well, using some assumptions/numbers. A 100 MW P-B11 reactor might produce ~10^20 fusions per second.
~ 1 billion fusions produce roughly 1 milliwatt of power., so 100 MW implies ~ 10^9 *10^8 or 10^20 fusions per second.
If a fusion produced alpha is at ~ 3 MeV, the speed will be ~ 160,000 M/s (for a deuterium ion at 10 KeV) * the difference in energy to the 1/2 power or ~square root of 300. The speed of the alpha would be ~ 160,000 *17.5 = 2,800,000 M/s
Assume a 5 meter diameter machine. The alpha would complete 1000 passes (the expected lifetime) in 2,800,000 M/s / 5000 M = 5,600 /s or a dwell time of ~ 0.0002 seconds. This dwell time multiplied with the alphas produced per second results in a population of ~ 10 ^16 alpha particles in the machine at any given time.

This compares to fuel ion populations of ~ 10^22 /M^3 or a total fuel ion in a ~ 100 cubic Meter machine of 10^25 fuel ions.

The alpha population in the machine at any given time is 1 billionth that of the fuel ions.

The collisionality of the alphas may be ~ 1 % that of the fuel ions.
Using these ratios, if you assume a fuel ion lifetime ~ 100 ms (purely arbitrary number) for the fuel ion mixture in a Polywell, then the contribution from the alphas would be ~ 100 *1,000,000,000 of 10^12 times less than the inter fuel ion thermalization processes. There is a tremendously small contribution by the alphas to the average fuel ion temperature over either the assumed fuel ion lifetime. If you accept the assertion that the ions do not thermalize over there lifetime due to inter fuel ion collisions, then the contribution from the alphas is relatively tiny compared to that. Even if you claim the ions thermalize among themselves in only eg:10 micro seconds, the contribution from the alphas would still be insignificant. Using this comparison, it would take alpha dwell times of thousands of seconds to thermalize with the fuel ions. The alpha collision frequency and relative numbers is just totally insignificant. Ignition/ internal plasma heating by fusion products is completely insignificant in the Polywell system. Even with lower energy D-D fusion ions, the contribution is trivial.

Also, consider that the alpha energy will have very small changes while it dwells within the machine. This has implications for direct conversion issues.

Compare this to a Tokamak. The alphas (assume your Tokamak can run on P-B11 fuel) are confined for ~ 1000 seconds just like the fuel ions. This alpha dwell time is ~ 10,000,000 times longer than in the Polywell. The density of the fuel ions is perhaps 1000 times less in the Tokamak. The volume is greater, but so is the anticipated fusion output, so conveniently assume this cancels out the fuel density vs volume differences. This leaves the dwell time and the number of alphas produced per second. The alpha production may be 100 times greater (10 GW of power) so the net population of alphas in the Tokamak at any given time relative to the fuel ions is greater by a factor of ~10^9. Now factoring the available dwell time and the relative numbers of the fuel ions to alphas, and the thermalization process time available and the difference between the two systems is obvious. In the Tokamak, the alpha contribution to thermalization about a common average occurs about 1 billion times more efficiently, or even several orders of magnitude beyond this.

Compare this with ignition in other machines. The critical elements are density (including relative densities), energy with associated Coulomb collisionality, and lifetimes of the particles (both the fuel and fusion products).

Short confinement times not only effect the energy balance, it has consequences in other areas such as this.

Dan Tibbets

[D Tibbets]

I'm explaining how it's supposed to work.

Motion of ions can be considered as combination of two:
· harmonic oscillation around the center
· chaotic (thermal) motion
Because they are going to increase B-field strength from 0.8 to 10 T, so in12 times, and expect that number density will increase in 144 times (also dubious expectation), chaotic motion intensity will become comparable with harmonic (so called thermalization) faster.

Due to permanent neutralization of electron cloud the depth of potential well will decrease by entering of new portion of ions.
So, amplitude of harmonic oscillation of ions entered machine later will be slower than initially.

etc. etc. etc.

You have no concept of annealing or distanve traveled as a measure of confinement.

Nor does debye length have anything to due with confinement efficience, or at least not with measured confinement time. You can do all sorts of manipulation with different perameters to predict something, but that is mot experimental results. I have repeatedly stressed measured results. You can denied the validity of the results, but igtnoring them is foolish.

You statement of ion and electron flows being equal is of course absolutely true within very limited margins. The Coulomb pressure (volts) very quickly becomes enormus as you seperate increasing amounts of electrons and positive ions. Bit, this is also a very foolish assertion in this context. A neutral plasma is just that. Equal numbers of opposite charges. But this says nothing about the dynamics. A plasma can be non neutral provided you input energy. If an electron lasts 1/10th as long in a system as an ion, plasma neutrality is still maintained, provided you introduce electrons into the system at 10 times the rate of the ions. Beyound this the rates have to be maintained, but there can be an offset. You can initially introduce more electrons and within Coulomb limits maintain this excess by subsequent input at relatively constant rates. Thus the often mentioned one part per million excess of electrons in the Polywell.

I again use the example of an ion engine. Electron and ion flows do not have to follow a common path- charge seperation is possible. Eventually the input must equal the output, with some fixed offset thatis maintained by applying a potential. This is the whole basis of electronics.

I know that debye length is often involked when talking about plasma, along with quasi neutrality and global effects.

One important point that you seem incapable of appreciating is that Debye length is a term defined by a static situation. To define it at all you have to assume an almost infinatly small current. This is extreamly close to a completely static situation. I have struggled with this concept and it's application to dynamic situations. A fixed electrode and a cloud of free electrons and positive ions will respond almost instatainously to it , but once there is any movement of the particles, things have to be recalculated. In an unchanging population as one species moves it sets in play other actions, thus things like Debye shielding. But, discriptions often seem to imply that this prevents current flow or transmission of potential driving forces. But, obvously plasma conducts electricity between fixed electrodes, it is not a static situation.

Sorry for the ramble, but misconceptions about plasma physics seem to abound.

Points:
1) Plasma does not have to be neutral so long as there is some input of energy such as excess injection of some species. Eventually neutrality will be reached as this is the lowest energy state but time is the critical component.

2) Charge seperation is a must if anything electronic is to work, including but not limited to muscles, nerves, ion engines, vacuum tubes, etc. Note that these charge seperations are local within the system. If you wish to go large enough you can say the universe is charge neutral, but that does not preclude local imbalances. In the Polywell the charge seperation is local, the system overal is certainally neutral, but by biasing one way with electron guns outside the machine, the neutrality inside the magrid can be biased.

Consider a Penning trap confining a few anti protons. Your absolute viewpoint obviously implies that this is impossible. The anti protons in this plasma would have to be balanced by an equal number of protons, yet it occurs. The system must be balanced (over long times) but this can be achieved while maintaining the charge seperation by having an opposing equal force. That is what voltage is all about. There are so many examples as this is what makes the universe work. Consider a thunderstorm. Charge seperation occurs and is maintained up to the point where insulation breaks down, the lightening occurs. It is all a matter of charge separation(which you claim is impossible , insulation and time. Debye definitions is tied up with time and insulation, and this can place limits on charge seperation ( distance and/ or duration) but it is a snap shot of a dynamic process. Thus terms like quasi neutral which understand limits the scope of local charge seperation, but does not absolutely prevent it.

Enough ranting...

Dan Tibbets

[Joseph Chikva]

If you accept the assertion that the ions do not thermalize over there lifetime due to inter fuel ion collisions, then the contribution from the alphas is relatively tiny compared to that.

Why I should accept it if physics (and not me) gives another assertion?
At high densities (IIRC desired goal is 10^22 m^-3) you can not separate charges with the help of electrostatic field presenting in Polywell.
And if so, if to neglect instabilities, all the energy being pumped by electron guns will be converted into heat and not into energy of harmonic motion of ions. Denser plasma - faster thermalization.

[Joseph Chikva]

One important point that you seem incapable of appreciating is that Debye length is a term defined by a static situation.

Dan, do numbers correctly. Think hydrogen or debye length in dynamics too.
You are wrong Dan.
And there is not a necessity to write so long texts.

[paperburn1]

I prefer that someone explain their process than just say "no your wrong"
It helps those of us that this is not their field of expertise. It also helps me understand their point of view.

[Joseph Chikva]

I prefer that someone explain their process than just say "no your wrong"
It helps those of us that this is not their field of expertise. It also helps me understand their point of view.

Ok
http://www.plasma-universe.com/Quasi-neutrality

The magnitude of the size of the violation of quasi-neutrality is typically a few 10s times the Debye length. In other words, if the Debye length for a particular plasma is about 1cm, then charge separation regions around 10 - 20 cm may occur.

Debye lengths for different plasmas:
Gas discharge tube 10^−4 m
Tokamak 10^−4 m
Ionosphere 10^−3 m
Magnetosphere 10^2 m
Solar core 10^−11 m
Solar wind 10 m
Interstellar medium 10 m
Intergalactic medium 10^5m

And Dan is wrong for example when says that Debye length is defined only for static systems.
If so please explain how solar wind with typical value of Debye length 10 m we can cosider as static?
And so on.

Also for reference at 10^22 m^-3 number density plasma in Polywell will have about 10^-6 m Debye length. So, order of magnitude of charge separation will be equal to 10^-5 m = 0.01 mm. Now understand?

[paperburn1]

On a better note
http://www.livescience.com/8058-levitat ... ality.html
showing its possable to control the plasma instability

[paperburn1]

I prefer that someone explain their process than just say "no your wrong"
It helps those of us that this is not their field of expertise. It also helps me understand their point of view.

Ok
http://www.plasma-universe.com/Quasi-neutrality

The magnitude of the size of the violation of quasi-neutrality is typically a few 10s times the Debye length. In other words, if the Debye length for a particular plasma is about 1cm, then charge separation regions around 10 - 20 cm may occur.

Debye lengths for different plasmas:
Gas discharge tube 10^−4 m
Tokamak 10^−4 m
Ionosphere 10^−3 m
Magnetosphere 10^2 m
Solar core 10^−11 m
Solar wind 10 m
Interstellar medium 10 m
Intergalactic medium 10^5m

And Dan is wrong for example when says that Debye length is defined only for static systems.
If so please explain how solar wind with typical value of Debye length 10 m we can cosider as static?
And so on.

Also for reference at 10^22 m^-3 number density plasma in Polywell will have about 10^-6 m Debye length. So, order of magnitude of charge separation will be equal to 10^-5 m = 0.01 mm. Now understand?

In a low density plasma, localized space charge regions may build up large potential drops over distances of the order of some tens of the Debye lengths. Such regions have been called electric double layers. Would this effect occur in a polywell and provide the needed Charge seperation to reach q>1?

[Joseph Chikva]

In a low density plasma, localized space charge regions may build up large potential drops over distances of the order of some tens of the Debye lengths. Such regions have been called electric double layers. Would this effect occur in a polywell and provide the needed Charge seperation to reach q>1?

Low density plasma is less interesting as power density is proportional to square of number density.
Here people talk about achivable 10^22 m^-3 number density at 10 T mag field, while for charge separation number density at resoanable dimensions of machine should not be more than 10^17 -10^18. So, in 100'000'000 - 10'000'000'000 times lower power density if they do not want to get again a thermal machine.
Are you still interested in Q?

[paperburn1]

Has anyone read this paper? Some of the asertion are very promising. http://ssl.mit.edu/publications/theses/ ... Thomas.pdf

[D Tibbets]

If you accept the assertion that the ions do not thermalize over there lifetime due to inter fuel ion collisions, then the contribution from the alphas is relatively tiny compared to that.

Why I should accept it if physics (and not me) gives another assertion?
At high densities (IIRC desired goal is 10^22 m^-3) you can not separate charges with the help of electrostatic field presenting in Polywell.
And if so, if to neglect instabilities, all the energy being pumped by electron guns will be converted into heat and not into energy of harmonic motion of ions. Denser plasma - faster thermalization.

You have little appreciation for what is claimed. The charge separation is not 10^22 charged particles per M^3. With a ~ 1ppm excess of electrons you have a charge separation of ~ 10^16 charged particles per /m^3, or ~ 10^10 charged particle / cc. This deviation from net and global charge balance is what has to be maintained (by continous injection of appropriate numbers of excess electrons). This may or may not exceed the Brillion limit and such excess may or may not be achievable. Read the multiple references that have been given concerning this issue.

Your mention that adding ions decreases the potential well is of course correct, but this ignores the simultaneous injection of energetic electrons in comparable numbers in order to stay ahead. It is not a question of whether you can stay ahead, but of how much power is needed to do so. EMC2 tried to stay ahead by increasing the electron injection 10 fold in WB5 and ignoring other problems with the design, this ~ doubled the potential well duration/ depth results. The recognition of this punishingly slow gain in part led to the WB6 design (Recirculation is a game changer).

You mention that the deep potential well cannot long survive, and of course this is true for many experiments. Many experiments have shown (again see previous references) the short duration of the potential well- times of a few 10's of milliseconds at best. But WB5 and then WB6 showed the path to overcoming this shortage. It is not further improvements in electron confinement so much (because while this can probably be done with repellars in the cusps, it results in additional ion losses due to compromises to the central potential well dominance) as it is recirculation (efficiently recovering most of the energy of the escaping electrons). This allows for determined input of energetic electrons at energy costs that are reasonable. Any potential well is simply the dynamic process of maintaining energetic electron populations in small excess to the ions. This could be done in even a simple biconic opposing magnet machine, but only with stupendous electron input currents/energy (possibly ~ several thousand times higher). This would preclude reaching Q>1 even with D-D or maybe even D-T fuel. Other things also might worsen.

Everything in the Polywell is based on accepted physics. There are interpretations, and just like the Field reversed concept views have changed. Even Riders's paper, which is often used as an argument against Polywells, admits that the physics does not exclude the Polywell working with D-D fuel.

Dan Tibbets

[Joseph Chikva]

The charge separation is not 10^22 charged particles per M^3. With a ~ 1ppm excess of electrons you have a charge separation of ~ 10^16 charged particles per /m^3, or ~ 10^10 charged particle / cc.

So, are you stating that 1.000001N electrons will force N ions to move harmonically with amplitude 1.5 m?
And it is enough to write 10^16 particles/m3. As if needed everyone can convert: 10^16 m^-3 = 10^10 cm^-3 = 10^7 mm^-3 and so on. Would you not like to convert this density in particle/cubic inch?

[Torulf2]

New thoughts about the Lockheed Skunkworks reactor.
If the central coil is relatively small and have the same direction of its B field as the outer coils. It should take the please as the plasma in a FRC.
The plasma may look as in my pictures. No open line cusps.
The point cusps may be plugged threw the waffelbal effect or some other ways.
Watt dos the magnet simulation tell about this?