Actual Polywell News!

[Joseph Chikva]

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.
..... No open line cusps.

For your reference:

An FRC (field reversed configuration) is an elongated plasma ellipsoid conducting an azimuthal current which reverses the direction of an externally applied magnetic field.

Yes, there is not open lines. But for forming of FRC rather strong azimuthal current is required. Have you an azimuthal current?

[Torulf2]

It may not form an FRC plasma. Only the B-field geometry is resemble of a FRC devise but is not elongated.
The inner coil have the place of the FRC plasma in the B-field.
The plasma confinement in this devise may be located as in my pictures.

[Joseph Chikva]

It may not form an FRC plasma. Only the B-field geometry is resemble of a FRC devise but is not elongated.
The inner coil have the place of the FRC plasma in the B-field.
The plasma confinement in this devise may be located as in my pictures.

I did not see your pictures.
But:
1. Endless "like FRC" lines to which you came is the same torus. Does not matter with central hole (donut) or without. Simply, torus machines always have endless field lines
2. But mentioning FRC you must to know that its (FRC’s) sense namely is in "reversation" of field used for better confinement first thought up by Nick (Nicholas) Christofilos in his Astron machine: http://w3.pppl.gov/ppst/docs/coleman.pdf And by its geometry FRC is a torus (a surface of revolution generated by revolving a circle in three-dimensional space about an axis coplanar with the circle)

[Torulf2]

This may make it more easy to understand. The plasma is red, coils are black.

[D Tibbets]

...
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?

First, you second point, I'm uncertain of your assertion. The Debye length is dependent on the density, but also the temperature. For convenience consider the Polywell as operating at 10 X the average temperature of a Tokamak. So if you are using that as your baseline you need to adjust.


Debye length and shielding are widely used in plasma physics ionics in general. Capacitor behavior, plasma behavior, etc. are usefully represented by this parameter. The definition of the Debye length is dependent on mobile charge carriers and the difference in their mobility (speed Any current flow atomic nuclei are not.- in effect the ion) Thus a potential results in a flow of electrons only (ignore concepts like holes or plasmons that are used to explain some processes). In a plasma the ions can move and this changes things in some ways, but still the lighter/ faster electrons determine the build up of charge separation. And at some point this charge separation will result in opposing electrical fields that counteracts the potential on a fixed electrode (fixed in space or time) and the initial current flow (redistribution of mobile charge carriers) stops and a new equilibrium is established. This is where my uncertainty and belligerence enter the picture. The Debye length is an equilibrium state, which means there is no input or output of energy in the system. Things change when there is an outside influence, such as an applied electrical bias, either via a fixed electrode or by introduction of an excess of negative or positive charge carriers. The system is again in a non equalibrium state and current flow will occur until a new equilibrium is established. If input is maintained the equilibrium will never be reached and current flow will be continuous through the system (in one side and out the other).
Statements that Debye shielding prevents current flow is miss leading. This only occurs in the static or equilibrium condition. Static means unchanging- which means no current flow through the system. Debye length/ shielding is a static consequence of mobile charge distribution. It describes the distance at which an unbalanced charge will communicate in a static time frame (or a zero system current frame (actually time of the speed of light considerations)). This is useful for describing the scale of influence of local charge imbalance in an larger plasma or other substrate - the limits that a local charge imbalance can exist- such as islands of charge separation in an overall neutral plasma.

These interactions applies to many systems, not just plasmas. Take a liquid salt solution. The ions will mix together through well defined processes till they are evenly distributed (in equilibrium). The solution is neutral both globally and locally (at scales greater than a few times the average ion separations). There might be local variations that arise due to random/ chaotic behavior, but the maximum extent of these are limited by Debye shielding in the system. Again this reflects the solution at equilibrium- a closed system. The kicker is when the system is influenced by an external force- a potential applied by electrodes. The ions start moving dependent on the potential and their mobility. The lighter ions will move faster and this sets up the Debye length relationship. This imbalance is a temporary though. The ions will continue to redistribute (the system is perturbed) until the potential applied to one side of the system reaches the other side and there will be net flow of current through the entire system. Statements that suggest this will not occur if the distance is greater than the Debye length is what annoys me. It is just nonsense.
Of course the Debye length is involved with a lot of behavior in a plasma, gas, liquid, or solid. It is tied to other parameters like plasma frequency, conductivity, density, temperature, etc. But this static definition being applied to dynamic situations (non equilibrium) without consideration of modifications is inappropriate.

In the Polywell, if you consider Gauss Law simply, then any electrons inside the radius of the ion will have a net attraction on the ion, while those electrons outside the ions radius will not have a net attraction because they all cancel out. If you apply the static Debye shielding distance, then only those electrons within this local radius will effect the ion. This limits things and changes the ion acceleration characteristics. But this ignores the electrons beyond the Debye shielding distance to the ion, but within this distance to other electrons, or ions. Thus this electron is moving due to influences of the test ion and any other ions or electrons within it's specific Debye shielding distance. Thus indirectly, electrons (and ions) at distances greater than the Debye length are effecting the test ion. Since this interaction is dependent on interactive motions, it is time dependent, so of course temperature and other plasma motion and collision perimeters apply. It is a complicated picture but directly or INDIRECTLY every electron effects every ion, not only those within the Debye length of that electron. If the system is closed- in equilibrium things settle down until the distributions become static- defined quasi neutral definitions, etc. But so long as there is a potential applied (represented here by the excess energetic electron injection) things remain dynamic and equilibrium is never reached.
In effect (at least in my mind) the potential well is a global thing, made up of many local Debye length dependent interactions, but still overall a global process, much like the current conducted though a salt solution due to the potential between two distant fixed electrodes.

The mention of the time dependance/ current dependance upon the Debye length definition and its significance are hard to find but some hints may be found in these links:

http://www.tf.uni-kiel.de/matwis/amat/e ... 2_4_2.html

http://www.google.com/url?sa=t&rct=j&q= ... V8hpNNPzrw

Dan Tibbets

[DeltaV]

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.

Based on the blue field lines in your drawing, you are showing the current in the central coil flowing in the opposite direction from the currents in the outer coils.

EDIT - Oh, you meant the exterior field lines of the central coil have the same direction as the interior field lines of the outer coils. OK. The wording implied the poles pointed in the same direction, which they do not.

A "synthetic" FRC... interesting.

[D Tibbets]

...
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...

To answer this question, it has to be rephrased. The Debye length assigned to the Solar Wind (which is indeed a dynamic system), is a near static slice of that system. As defined, the Debye length is dependent on the current and the time. The charge separation is dependent on the different speeds/ acceleration rates of the two species (primarily electrons and protons in the Solar Wind). It takes time for the separation to occur. I'm not certain how much time is necessary, but it is dependant on the greater mobility- speed of the electrons relative to the protons. So time cannot be set to zero. Alternately, you can vary the current but this changes the results for any change in current. You cannot use zero current as this would result in zero as your result. But a tiny current that is much less than than other considerations will give you a result that is consistent within a tiny range of error. If the current is not insignificant, the results change. The Debye length could be defined as the distance over which the counterbalancing forces cancel out the potential with 1 Coulomb of current through the system, but then you would have Debye length variations dependent on the current. It would no longer be a constant.

The current in the Solar wind is not zero, nor is it infinitely small, but the Debye length assigned to it does assume the current is infinitely small (at least in proportion to other parameters). My descriptions may be confused, but the end result is obvious. The Earth is not shielded from the current flowing from the Sun despite the fact that it is much further away than the Debye length for the solar Wind. There is a tremendous amount of current flow through this tenuous plasma. Why? Because the current flow into the system is considerable, and the current flow out of the system must match it otherwise intolorable conditions will develop. It is the same argument about the limits on charge separation in a system such as a Polywell. The charge separation will drive a potential and this potential will increase rapidly until one of two things happen, Either input will be choked off due to opposing forces, or insulation will break down and current will flow out of the system. Some seem to consider the Debye length equivalent to the absolute insulation capacity of the system, but this is misleading. It is the insulating capacity of the system under defined charge separation conditions. The charge separation is a dynamic process dependent on the current flow.

To say it another way, Debye length / shielding describes the accumulation of electrons around a positive fixed electrode until the crowd of electrons repel any more electrons moving towards the electrode. This ignores any electrons that leave the system through hitting the electrode and being carried away. If one electrode leaves, then one electrode must move to replace it in the shielding cloud. If 1 million electrons leave, then one million electrons must replace them. These electrons come from the plasma beyond the Debye length . This gradient replacement will continue until the other side is reached, the plasma would then be in equilibrium- and also non neutral globally. This condition would persist until a new source of electrons was obtained, and this would be from a negative electrode. There is net current/ electron flow through the entire length of the plasma. It is this continuous replacement of mobile charge carriers that results in trans plasma current flow/ conductivity, despite the local Debye shielding which would seem to prevent current flow- but only, of course, under (almost) static conditions where there is (almost) no current flow into or out of the system. Do not confuse local current flow under narrowly defined parameters as being determinate of global current flow under all conditions.

Dan Tibbets

[D Tibbets]

There is a tremendous amount of current flow through this tenuous plasma.

This quote from my preceding post might be considered in another light. The Debye length limits the current flow to only a short distance within the plasma. If you accept that and accept that charge is transmitted through a global plasma (just as through a wire, liquid solution, etc) then something else must be occuring.
One perspective is that the entire medium is moving. The current is not moving through the plasma beyond Debye lengths, but the entire plasma is moving. In someways this is like considerations of light speed limits versus space expansion. Space expansion is not limited by the speed of light.

Interesting consideration.

In plasmas, the oppositely charged species may move in opposite directions at different rates, but so long as replacements are supplied the plasma could expand/ flow/ conduct a current independent of any Debye limits. The Debye length limits communication within the plasma, but not communication across the plasma ...


Dan Tibbets

[Joseph Chikva]

First, you second point, I'm uncertain of your assertion. The Debye length is dependent on the density, but also the temperature. For convenience consider the Polywell as operating at 10 X the average temperature of a Tokamak. So if you are using that as your baseline you need to adjust.

Ok. Let’s adjust.
We have:
2 orders of magnitude higher than in TOKAMAK plasma density (10^22 vs. 10^20)
1 order of magnitude higher average energy (so only 3-4 times higher average speed)
So, we should estimate Debye Length in desired for you Polywell (parameters: Diameter= 3m, Density = 10^22 m^-3, Ion average energy calling by you as “temperature” 150 keV) Right?
So, if plasma in TOKAMAK has 10^−4 m order Debye Length, in desired for you Polywell number will have 3-4/100. So, not 10^-6 m but 2.5-3E-5 m instead 1E-6.
Is this so helpful for you?

When you have statement that charge separation is possible on distances exceeding Debye Length in 10-20 times, this means that separation goes under influence of field technically we know to create. So, instead of required separation on 1.5 m you would get separation on 20 * 2.5E-5 m = 5E-4 m = 0.5 mm
That’s all, Dan. Without necessity to write long texts.

PS: the same problem for you when you and others here state that there is possible to create compact direct energy converter. So compact that can be fitted on medium size ships.
I am state that impossible. Again due to the small Debye length of dense plasma not allowing us required charge separation before expansion.