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**THEORETICAL SPHEROMAK:**

Nature uses spheromaks to store energy in rest mass.

This web page makes a few simple assumptions about energy density distributions and based on these simple assumptions shows the existence of spheromaks and derives various spheromak properties. Another web page titled: ELECTROMAGNETIC SPHEROMAK shows that the assumed energy density distributions correspond to the combined electric and magnetic field energy distributions in the proximity of quantized charge that circulates around a stable closed path. The electric and magnetic field energy density distributions indicate the existence of stable charged particles such as electrons and protons, the Planck constant, and particle magnetic resonance. Hence the spheromak properties derived from the assumed energy distributions are the properties of real particles.

This concept can be extended to explain the behavior of electrons around an atomic nucleus. The nucleus provides the central electric field necessary to stabilize the walls of multi-electron spheromaks. As the positive nuclear charge increases the electron spheromaks must change to meet the spheromak wall boundary conditions on the equatorial plane. It is believed that the electron spheromaks of inert gases are exceptionally stable.

As the atomic number increases and electrons are added to the spheromaks the toroidal magnetic fields increase but the poloidal magnetic field cancels. Note that the conditions for existence of a multi-electron spheromak around an atomic nucleus are very similar to the conditions for existence of a discrete electron or proton, so it is not surprising the both systems lead to the Planck constant.

Spheromaks can also form in plasmas, but large plasma spheromaks typically only exist for short times (~ 1 ms) due to complicating factors such as neutral particle interactions with spheromak plasma particles.

**SPHEROMAK WALL CONCEPT:**

Assume that three dimensional space is divided into two regions by a flexible and moveable wall known as the "Spheromak Wall" which totally encloses region **"t"** within region **"p"**. Assume that region **"p"** extends to infinity in all directions. The spacial potential energy density functions in the "p" and "t" regions are different but are dependent on the position of the spheromak wall.

The spheromak wall is free to move. It spontaneously seeks a stable position that results in a system total potential energy minimum. At this stable position the potential energy densities on both sides of the spheromak wall are equal so that there is no force (change in total energy with psition) tending to move the spheromak wall. Since the spheromak wall is at a position corresponding to a stable total potential energy Ett minimum:

dEtt / dX = 0,

where X is the wall position in space.

Spheromaks tend to form because there is a certain degree of random energy motion. If random energy motion results in a spheromak wall configuration with a lower total potential energy and a higher total kinetic energy sometimes part of that kinetic energy becomes a photon that is radiated away. The remaining system is left trapped in a low potential energy (spheromak) state until it absorbs energy (a photon) from an external source. As long as the density of random photons in the system environment is small spheromaks are stable accumulations of potential energy.

**SPHEROMAK GENERAL SHAPE:**

A spheromak has a toroidal shape. The surface of the torus is the spheromak wall. It is shown on this web site that for an electromagnetic spheromak the stable spheromak geometry is a toroid with a round cross section and a ratio of internal radius Rc to external radius Rs of:

**(Rs / Rc) ~ 4.1**

**SPHEROMAK CROSS SECTIONAL DIAGRAM:**

The following diagram shows the cross sectional shape of an ideal spheromak in free space.

Note that an ideal spheromak in free space has a round toroidal cross section whereas a real plasma spheromak in a laboratory may be radially distorted by the proximity of the vacuum chamber metal walls.

**POSITION IN A SPHEROMAK:**

A spheromak wall has cylindrical symmetry about its main axis of symmetry and has mirror symmetry about its equatorial plane. A position in a spheromak can be referenced by:

**(R, H, Theta)**

where:

**R** = radius from the main axis of spheromak cylindrical symmetry;

and

**H** = height above (or below) the spheromak equatorial plane;

and**Theta** = angle around the main axis of symetry;

**GEOMETRICAL FEATURES OF A SPHEROMAK:**

Important geometrical features of a spheromak include:

**Rc** = the spheromak core radius on the equatorial plane;

**Rs** = the spheromak outside radius on the equatorial plane;

**Rf** = the value of R at the spheromak top and bottom;

**(2 |Hf|)** = the overall spheromak length;

The subscript **c** refers to spheromak wall "core" surface at the equatorial plane;

The subscript **f** refers to the "funnel edge" at the spheromak top and bottom;

The subscript **s** refers to the spheromak outer "surface" at the equatorial plane.

In order to understand the material on this web page it is essential for the reader to study the spheromak cross sectional diagram and to identify the above mentioned parameters.

**ENERGY DENSITY FUNCTIONS:**

Assume that inside the spheromak wall the field energy density Ut as a function of position is:

**Ut = Uto (Ro / R)^2**

where **Uto** and **Ro** are situational dependent constants. Note that this energy density function is cylindrically radial.

Assume that outside the spheromak wall the energy density Up as a function of position is given by:

**Up = Uo [(Ro^2 / (Ro^2 + R^2 + H^2)]^2**

Thus for R^2 + H^2 >> Ro^2:

Up ~ Uo [(Ro^2 / (R^2 + H^2)]^2

and for R^2 + H^2 << Ro^2:

Up = Uo

The assumed total energy density function gives perfect matching with the real energy density at both the center of the spheromak and at large distances from the spheromak center. However, there could be some error between the assumption and reality at positions between these two extremes. The choice of this particular energy density function, although it seems simple, required a lot of work.

**SPHEROMAK WALL**

Differential forces on the flexible spheromak wall due to changes in spheromak energy with respect to wall position will cause the wall to spontaneously position itself so that the energy densities on both sides of the wall are equal and so that the wall position is at a total energy minimum. At this wall position at every point on the wall:

**Up = Ut**.

At the intersections of the wall with the equatorial plane:

H = 0

and equal energy densities on both sides of the spheromak wall give:

Uto (Ro / R)^2 = Uo [(Ro^2 / (Ro^2 + R^2)]^2

or

(Uto / Uo) = [(Ro^2 / (Ro^2 + R^2)]^2 (R / Ro)^2

= [(Ro R / (Ro^2 + R^2)]^2

or

(Uto / Uo)^0.5 = [(Ro R / (Ro^2 + R^2)]

or

(Ro^2 + R^2)(Uto / Uo)^0.5 = (Ro R)

or

R^2 (Uto / Uo)^0.5 - Ro R + Ro^2 (Uto / Uo)^0.5 = 0

This is a quadratic equation which provided that:

4 (Uto / Upo) K^2 < 1

has solutions:

R = {Ro +/- [Ro^2 - 4 (Uto / Uo) Ro^2]^0.5} / [2 (Uto / Uo)^0.5]

These solutions are:

Rc = {Ro - [Ro^2 - 4 (Uto / Upo) Ro^2]^0.5} / [2 (Uto / Upo)^0.5]

and

Rs = {Ro + [Ro^2 - 4 (Uto / Upo) Ro^2]^0.5} / [2 (Uto / Upo)^0.5]

The product of these two solutions is:

**Rs Rc** = {Ro^2 - [Ro^2 - 4 (Uto / Upo) Ro^2]} / [4 (Uto / Upo)]

= {4 (Uto / Upo) Ro^2} / [4 (Uto / Upo)]

**= Ro^2**

Thus we have derived the important identity:

**Rs Rc = Ro^2**

where:

Rc < Ro < Rs

The spheromak wall intersects the equatorial plane at both radii R = Rc and R = Rs. It is shown herein that this wall shape defines the surface of a toroid with a round cross section with a minimum inside radius Rc (core radius) and a maximum outside radius Rs. This torus shaped surface is known as the spheromak wall. The wall position corresponds to a stable total energy minimum.

This energy configuration is known as a spheromak.

**SUMMARY:**

Uo = maximum spheromak energy density at the center of the spheromak;

Rs > Ro > Rc;

Ro^2 = Rs Rc;

and

4 (Uto / Upo) < 1

Note that a particular value of Ro^2 defines the product (Rs Rc) but does not define the individual Rs and Rc values. These values depend on other physical parameters.

**SPHEROMAK SIZE:**

The value of Ro is dependent on the total amount of energy present. As shown on the web page titled SPHEROMAK ENERGY integration over all space shows that the total energy present Ett is a few percent less than:

**Efs = Upo Ro^3 Pi^2**

Thus a spheromak can potentially model a real particle or a real plasma with a total energy Ett and a nominal radius Ro.

In order for a spheromak to represent a real physical entity it is necessary to show that a spheromak is an energy stable configuration and that the energy density functions which cause spheromak formation arise from the electric and magnetic field energy densities due to net electric charge and electric charge flow around a closed path that is everywhere tangent to the spheromak wall.

Thus spheromak mathematics explains the existence and behavior of both stable charged atomic particles and semi-stable toroidal plasmas.

Typical plasma spheromaks produced in a laboratory have shape factors of about:

**(Rs / Rc) = 4.2**

**SPHEROMAK GEOMETRY:**

The geometry of a spheromak in free space can be characterized by the following parameters:

**R** = radius of a general point from the spheromak's axis of cylindrical symmetry;

**Rc** = spheromak's minimum core radius;

**Rs** = spheromak's maximum equatorial radius;

**Rf = (Rs + Rc) / 2** = spheromak's top and bottom radius;

**H** = distance of a general point from the spheromak's equatorial plane;

**Hs** = height of a point on the spheromak wall above the spheromak's equatorial plane;

**(2 |Hf|)** = spheromak's overall length measured at **R = Rf**;

**So** = [Rs / Rc]^0.5 = spheromak shape ratio;

**SPHEROMAK STRUCTURAL ASSUMPTIONS:**

1) A spheromak wall is composed of a closed spiral of charge hose or plasma hose of overall length **Lh**;

2) Spheromak net charge **Qs** is uniformly distributed over charge hose or plasma hose length **Lh**.

3) At a particular spheromak energy the charge hose current Ih is constant;

4) The charge hose current causes a toroidal magnetic field inside the hose spiral and a poloidal magnetic field outside the hose spiral;

5) The net charge causes a cylindrically radial electric field inside the charge hose spiral and a spherically radial electric field outside the charge hose spiral;

6) At the center of the spheromak at (R= 0, H = 0) the electric field is zero;

7) Inside the spheromak wall where:

**Rc < R < Rs** and **|H| < |Hs|**

the total field energy density **U** takes the form:

**Ut = Uto (Ro / R)^2**

8) Outside the spheromak wall the total field energy density takes the form:

**Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**;

9) Everywhere at the spheromak surface:

**Up = Ut**

**ROLES OF SPHEROMAK FIELDS:**

The fields of a spheromak serve two important purposes storing energy and acting in combination to position and stabilize the spheromak wall.

**ENERGY DENSITY BALANCE:**

For a spheromak wall position to be stable the total field energy density must be the same on both sides of the spheromak wall. This requirement leads to boundary condition equations that determine the shape of spheromaks.

**SPHEROMAK WALL POSITION POSITION:**

A spheromak is a semi-stable energy state. The spheromak wall positions itself to achieve a total energy relative minimum. At every point on the wall the sum of the electric and magnetic field energy densities on one side of the wall equals the sum of the electric and magnetic field energy densities on the other side of the wall. This general statement resolves into different boundary conditions for different points on the wall. These boundary conditions establish the spheromak core radius **Rc** on the equatorial plane, the spheromak outside radius **Rs** on the equatorial plane and the spheromak length **2 Hf**.

**SPHEROMAK WALL POSITION:**

A stable spheromak charge sheet wall will be located at a position of force balance (energy density balance) which is also a spheromak energy minimum.

Define:

**Ut = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [Rc / R]^2**

= total field energy density inside the spheromak charge wall

**Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**

= total field energy density outside the spheromak wall

**dAs** = element of plasma sheet surface area at wall position **X**

**Ett** = total spheromak energy

**d(Ett)** = change in Ett due to a change in spheromak wall position **dX** normal to spheromak surface at **X**.

**(Rw, Hw)** = an arbitrary point on the spheromak wall;

**SPHEROMAK INSIDE ENERGY DENSITY:**

A spheromak arises from charge moving around a closed spiral that causes an internal toroidal magnetic field and an internal cylindrically radial electric field with a combined energy density **Ut** of the form:

**Ut = Uc (Rc / R)^2**

for:

Rc < R < Rs

and

-Hs < H < = Hs

Note that Ut has both electric and magnetic field components.

**EXTERNAL ENERGY DENSITY APPROXIMATION:**

The sum of the electric field energy density Ue and the magnetic field energy density Um outside the spheromak wall is the total energy density function:

**Up = Um + Ue**

which decreases in proportion to [1 / (distance)^4] in the far field. The external energy density function is chosen so that it matches the magnetic field energy density in the near field and matches the electric field energy density in the far field. Then the spheromak walls occur at the locus of points where:

**Up = Ut**

The external energy density function **Up** is of the form:

**Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**

where the value of Ro satisfies the far field boundary condition where:

(R^2 + H^2) >> Ro^2

and also satisfies the near field boundary condition where:

Ro^2 < (R^2 + H^2).

This external energy density function, while it may not be exact, has the benefit that it yields a practical closed form mathematical model for a spheromak.

At the point **R = Rc, H = 0**, where the inner spheromak wall crosses the spheromak equatorial plane:

**Up = Ut**

giving:

**Uc = Uo [Ro^2 / (Ro^2 + Rc^2)]^2**

Hence:

**Ut = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 (Rc / R)^2**

At R = Ro, Ut = Uto. Hence:

**Uto** = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 (Rc / Ro)^2

= Uo [Ro Rc / (Ro^2 + Rc^2)]^2

= Uo [Ro Rc / (Rs Rc + Rc^2)]^2

= Uo [Ro / (Rs + Rc)]^2

**SPHEROMAK WALL POSITION:**

The spheromak is a semi-stable energy state. The spheromak wall positions itself to achieve a total energy relative minimum. At every point on the spheromak wall the total energy density on one side of the wall equals the total energy density on the other side of the wall. Hence at every point on the spheromak wall the sum of the electric and magnetic field energy densities on one side of the wall equals the sum of the electric and magnetic field energy densities on the other side of the wall. This general statement resolves into different boundary conditions for different points on the spheromak wall. For a spheromak in free space these boundary conditions establish the spheromak core radius **Rc** on the equatorial plane, the spheromak outside radius **Rs** on the equatorial plane and the spheromak length **2 Hf**.

**SPHEROMAK WALL LOCATION:**

The spheromak wall exists on the locus of points where:

**Up = Ut**

or

**Uo [Ro^2 / (Ro^2 + R^2 + Hs^2)]^2 = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 (Rc / R)^2**

or

[(Ro^2 + Rc^2)]^2 (R / Rc)^2 = [(Ro^2 + R^2 + Hs^2)]^2

or

(Ro^2 + Rc^2)(R / Rc) = (Ro^2 + R^2 + Hs^2)

or

Hs^2 = (Ro^2 + Rc^2)(R / Rc) - Ro^2 - R^2

= R (Ro^2 / Rc) + R Rc - Ro^2 - R^2

= - R (R - Rc) + (Ro^2 / Rc) (R - Rc)

= [(Ro^2 / Rc) - R] [R - Rc]

= [(Rs - R)(R - Rc)]

where:

Rs = (Ro^2 / Rc

Hence the general spheromak wall position equation is:

**Hs^2 = [(Rs - R) (R - Rc)]**

or

**Hs = +/- [(Rs - R) (R - Rc)]^0.5**

This equation describes the cross sectional profile of a spheromak in free space.

Note that Hs = 0 at R = Rc and at R = Rs and that in the range:

Rc < R < Rs

Hs has real values that are both positive and negative.

**SPHEROMAK CROSS SECTION:**

Recall that at the spheromak wall:

Hs^2 = [Rs - R][R - Rc]

Make substitution:

R = X + [(Rs + Rc) / 2]

Then:

Hs^2 = [Rs - R][R - Rc]

= [Rs - X - [(Rs + Rc) / 2]] [ X + [(Rs + Rc) / 2] - Rc]

= [[(Rs - Rc) / 2] - X] [X + [(Rs - Rc) / 2]]

= [[(Rs - Rc) / 2]^2 - X^2

or

Hs^2 + X^2 = [[(Rs - Rc) / 2]^2

which is the well known equation of a circle.

Thus the spheromak wall is circular in cross section with a minor radius of [[(Rs - Rc) / 2] and a cross section center at:

R = (Rs + Rc) / 2

**SPHEROMAK SHAPE RATIO So:**

Define spheromak shape factor So by:

**So^2 = (Rs / Rc)**

or

So = (Rs / Rc)^0.5

Recall that:

**Ro^2 = Rs Rc**

Thus:

So = (Rs / Rc)^0.5

= (Rs)^0.5 [Rs / Ro^2]^0.5

= Rs / Ro

Similarly:

So = (Rs / Rc)^0.5

= (Ro^2 / Rc)^0.5 (1 / Rc)^0.5

= (Ro / Rc)

These identities are extensively used in spheromak characterization.

**SPHEROMAK POTENTIAL ENERGY WELL:**

Outside the spheromak wall the field energy density is given by:

**Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**

or

**(Up / Uo) = [Ro^2 / (Ro^2 + R^2 + H^2)]^2
= [1 / (1 + (R / Ro)^2 + (H / Ro)^2)]^2**

At **R = Rc** and **H = 0** **Up = Uc**

giving:

**Uc = Uo [Ro^2 / (Ro^2 + Rc^2)]^2**

Hence the energy density Ut inside the wall is given by:

Ut = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [Rc / R]^2

or

**(Ut / Uo)**

= [Ro^2 / (Ro^2 + Rc^2)]^2 [Rc / Ro]^2 [Ro / R]^2

= [Ro Rc / (Ro^2 + Rc^2)]^2 [Ro / R]^2

= [Ro Rc / (Rs Rc + Rc^2)]^2 [Ro / R]^2

= [Ro / (Rs + Rc)]^2 [Ro / R]^2

= [(Ro / Rc) / ((Rs / Rc) + 1)]^2 [Ro / R]^2

= [(So) / (So^2 + 1)]^2 [Ro / R]^2

= **[(So^2) / (So^2 + 1)^2] [Ro / R]^2**

Thus a stable spheromak results from a central region with a peak energy density:

[Uo]

and a spherical radial decrease in energy density **Up(R,H)** containing within it a region with a cylindrical radial decrease in energy density **Ut(R)**. On the spheromak equatorial plane these two functions are as shown on the below graph where the abcissa is:

**X = [R / Ro]**

and the ordinate

**[Up (R / Ro), 0) / (Uo)]** is the pink line

and the ordinate

**[Ut (R / Ro) / Uo]** for (Rc / Ro) = 0.5 is the dark blue line

and the ordinate

**[Ut (R / Ro) / Uo]** for (Rc / Ro) = 0.4 is the light blue line

On the spheromak's equatorial plane the graph lines intersect at:

**Up(Rc, 0) = Ut(Rc)**

and at

**Up(Rs, 0) = Ut(Rs)**

where:

**Rs Rc = Ro^2**

Note that in the region Rc < R < Rs the energy density inside the spheromak wall is lower than what it would be if the external energy density function:

**Up(R, H) = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**

prevailed everywhere. Hence the spheromak forms a potential energy well. This potential energy well gives a spheromak its inherent stability.

Note that increasing the ratio:

So^2 = (Rs / Rc)

increases the depth of the potential well and hence increases spheromak energy stability. This issue indicates that for highly stable charged atomic particle spheromaks:

**So** is significantly greater than unity. Typically for atomic particle spheromaks the theoretical value of So^2 is:

So^2 = 4.1

and typically for plasma spheromaks the experimental value of So^2 is given by:

So^2 ~ 4.2

Hence from an energy stability perspective an ideal spheromak in free space is defined by its parameters:

**Uo, Ro, So**

where:

**Uo** is the highest field energy density at the center of the spheromak;

and

**Ro^2 = Rs Rc**

and

**So^2 = (Rs / Rc)**

**STABLE SPHEROMAK:**

Note that a spheromak with:

**So = [Rs / Ro] = 2.0**

and

**(1 / So) = [Rc / Ro] = 0.5**

forms a stable potential energy well with a nominal radius of:

**R = Ro**.

Note that a spheromak with:

**So = [Rs / Ro] = 2.5**

and

**(1 / So) = [Rc / Ro] = 0.4**

also forms a stable potential energy well with a nominal radius of:

**R = Ro**.

The difference between these two spheromaks lies in their contained energy. When a spheromak initially forms its energy is too high causing its So^2 value to be either too small or too large. The spheromak must spontaneiously emit photons until it reaches its stable state where:

**So^2 = 4.1**.

Thereafter the spheromak can absorb or emit photons by changing its value of **Ro** while keeping So^2 constant.

**SPHEROMAK WALL POSITION:**

A stable spheromak wall will be located at a position of force balance (energy density balance) which also corresponds to a spheromak total energy minimum.

Define:

**Ut = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [Rc / R]^2**

= total field energy density inside the spheromak charge wall

**Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2**

= total field energy density outside the spheromak charge wall

**X** = wall position vector normal to the plasma sheet

**dAs** = element of plasma sheet surface area at wall position **X**

**Ett** = total spheromak energy

**DeltaEtt** = an element of **Ett** corresponding to element of surface area **dAs**

**d(DeltaEtt)** = change in DeltaEtt due to a change in spheromak wall position **dX** normal to spheromak surface at **dAs**.

**(Rw, Hw)** = an arbitrary point on the spheromak wall;

**EVALUATE DERIVATIVES:**

Ut = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [Rc / R]^2

dUt / dR = Uo [Ro^2 / (Ro^2 + Rc^2)]^2 2 [Rc / R][- Rc / R^2]

= Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [-Rc^2 / R^3]

Note that:

dUt / dH = 0

and

dJ / dR ~ 0

Up = Uo [Ro^2 / (Ro^2 + R^2 + H^2)]^2

gives:

**dUp / dR** = 2 Uo [Ro^2 / (Ro^2 + R^2 + H^2)][- Ro^2 2 R / (Ro^2 + R^2 + H^2)^2]

**= - 2 Uo Ro^4 R / (Ro^2 + R^2 + H^2)^3**

and

**SPHEROMAK WALL POSITION STABILITY:**

The criteria for spheromak wall position stability is that at every point on the spheromak wall:

**d2(Ett / dXw^2) > 0**

**SPHEROMAK WALL POSITION STABILITY AT (Rs, 0):**

At R = Rs:

d(Ett) / dXw = d(Ett) / dRs

= (Ut - Up) dAs

= (Ut - Up) 2 Pi Rs dH

Hence:

**d^2(Ett) / dRs^2** = [d(Ut - Up) / dRs] 2 Pi Rs dH + [Ut - Up] 2 Pi dH

However:

Ut - Up = 0

giving:

**d^2(Ett) / dRs^2 = [d(Ut - Up) / dRs] 2 Pi Rs dH**

Thus wall stability requirement at **(Rs, 0)** is:

[d(Ut - Up) / dR]|R = Rs , H = 0 > 0

or

[dUt / dR] |R = Rs, H = 0 > [dUp / dR]|R = Rs, H = 0

or

Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [-2 Rc^2 / Rs^3] > - 4 Uo Ro^4 Rs / (Ro^2 + Rs^2)^3
or

2 Uo Ro^4 Rs / [Ro^2 + Rs^2]^3 > Uo [Ro^2 / ((Ro^2 + Rc^2)]^2 [Rc^2 / Rs^3]
or

2 Rs / (Ro^2 + Rs^2)^3 > [1 / (Ro^2 + Rc^2)]^2 [Rc^2 / Rs^3]
or

2 [ Rs^4 / Rc^2][(Ro^2 + Rc^2)^2 / (Ro^2 + Rs^2)^3 > 1

or

2 [ Rs^4 / Rc^2][(Rs Rc + Rc^2)^2 / (Rs Rc + Rs^2)^3 > 1

or

2 [ Rs^4 / Rc^2][Rc (Rs + Rc)]^2 / [Rs (Rc + Rs)]^3 > 1

or

2 [ Rs] / [(Rc + Rs)] > 1

Therefore, since Rs > Rc, spheromak wall stability is proven at **(Rs, 0)**

Any disturbance of the wall position at (Rs, 0) causes an increase in total spheromak energy. Hence the outside wall position on the spheromak equatorial plane is at a spheromak energy minimum.

**SPHEROMAK WALL POSITION STABILITY AT (Rc, 0):**

At R = Rc:

d(Ett) / dXw = d(Ett) / dRc

= (Up - Ut) dAs

= (Up - Ut) 2 Pi Rc dH

Hence:

**d^2(Ett) / dRc^2** = [d(Up - Ut) / dRc] 2 Pi Rc dH + [Up - Ut] 2 Pi dH

=** [d(Ut - Up) / dRc] 2 Pi Rc dH**

since:

[Up - Ut] = 0

Thus the requirement for wall stability requirement at **(Rc, 0)** is:

[d(Up - Ut) / dR]|R = Rc , H = 0 > 0

or

[dUp / dR] |R = Rc, H = 0 > [dUt / dR]|R = Rc, H = 0

or

- 2 Uo Ro^4 Rc / (Ro^2 + Rc^2)^3 > - Uo [Ro^2 / (Ro^2 + Rc^2)]^2[1 / Rc]

or flipping sign

Uo [Ro^2 / (Ro^2 + Rc^2)]^2 [1 / Rc] > 2 Uo Ro^4 Rc / (Ro^2 + Rc^2)^3

or

[1 / (Ro^2 + Rc^2)]^2 [1 / Rc] > 2 Rc / (Ro^2 + Rc^2)^3

or

(Ro^2 + Rc^2)^3 / 2 Rc^2 (Ro^2 + Rc^2)^2 > 1
or

(Ro^2 + Rc^2) / 2 Rc^2 > 1

or

(Rs Rc + Rc^2) / 2 Rc^2 > 1

or

(Rs + Rc) / 2 Rc > 1

Hence spheromak wall stability has been proven at **(Rc, 0)**

**SPHEROMAK WALL POSITION STABILITY AT (Rf, Hf):**

At R = Rf, H = Hf:

d(Ett) / dXw = d(Ett) / dHf

= (Ut - Up) dAs

= (Ut - Up) 2 Pi Rf dR

Hence:

**d^2(Ett) / dHf^2** = [d(Ut - Up) / dHf] 2 Pi Rf dR + [Ut - Up] 2 Pi d(Rf dR) / dHf

Note that:

d(Rf dR) / dHf = 0

giving:

**d^2(Ett) / dHf^2** = ** [d(Ut - Up) / dHf] 2 Pi Rf dR**

Thus the condition for wall stability requirement at **(Rf, Hf)** is:

[d(Ut - Up) / dHf]|R = Rf , H = Hf > 0

or

[dUt / dH] |R = Rf, H = Hf > [dUp / dH]|R = Rf, H = Hf

or

0 > - 2 Uo Ro^4 Hf / (K^2 Ro^2 + Rf^2 + Hf^2)^3

which is immediately true by inspection.

Hence we have proven spheromak wall position stability at **(Rf, Hf)**.

**SPHEROMAK GEOMETRY SUMMARY:**

As shown above:

**Lt = Pi (Rs - Rc)**

Hence a spheromak in free space is a round toroid with an core (central hole) radius **Rc** and an outside radius **Rs**. The toroidal region minor diameter is:

**(Rs - Rc)**

and the toroidal region radius equals:

**Hf = (Rs - Rc) / 2**

and the toroidal region centerline is at **R = Rf** where:

**Rf = (Rs + Rc) / 2**

Hence from a structural perspective the poloidal winding turn length **Lp** is given by:

**Lp = 2 Pi Rf
= 2 Pi (Rs + Rc) / 2
= Pi (Rs + Rc)**

However, from the perspectives of determination of the peak central poloidal magnetic field, which determines **Upo**, the effective current ring radius is NOT at **R = Rf**.

p

**NUMERICAL EXAMPLE:**

For a typical spheromak:

**So = [Rs / Rc]^0.5
= 2**

giving:

and

or

= [Rc^0.5 Rc^0.5 2]

= 2 Rc

For this spheromak:

**So^2 = (Rs / Rc)
= 4.0**

and

= (Rc + 4 Rc) / 2

=

Then:

**Lt / Rc = [Pi (Rs - Rc) / Rc]
= Pi (So^2 - 1)
= 3 Pi**

and

= Pi (So^2 + 1)

= 5 Pi

giving:

**TOTAL SPHEROMAK WALL SURFACE AREA As:**

The approximate surface area of a spheromak wall in free space is given by:

**As = [2 Pi(Rs + Rc) / 2] [2 Pi (Rs - Rc) / 2]
= Pi^2 (Rs^2 - Rc^2)
= Lp Lt**

The exact surface area **As** of a spheromak in free space is given by:

**As** = Integral from **R = Rc** to **R = Rs** of:

**2 X d(Lt) (2 Pi R)**

= Integral from **Phi = 0** to **Phi = Pi** of:

**2 X (2 Pi R) [(Rs - Rc) / 2] d(Phi)**

= Integral from **Phi = 0** to **Phi = Pi** of:

**(2 Pi) [(Rs - Rc)] R d(Phi)**

= Integral from **Phi = 0** to **Phi = Pi** of:

**(2 Pi) [(Rs - Rc)][((Rs + Rc) / 2) - ((Rs - Rc) / 2)cos(Phi)] d(Phi)**

= Integral from **Phi = 0** to **Phi = Pi** of:

**(Pi) [(Rs - Rc)][(Rs + Rc) - (Rs - Rc)cos(Phi)] d(Phi)**

= Pi^2 [Rs^2 - Rc^2] - Pi (Rs - Rc) [sin(Pi) - sin(0)]

= **Pi^2 [Rs^2 - Rc^2]**

= **Lp Lt**

Note that the spheromak surface area **As** is smaller than the surface area of a sphere of radius **Rs**.

**CHARGE HOSE LENGTH:**

Define:

Nt = integer number of toroidal charge hose turns; Nt = 1, 2,3,....

Np = integer number of poloidal charge hose turns; Np = 1, 2 , 3, ....

The total charge hose length Lh is given by:

**Lh** = [(Np Lp)^2 + (Nt Lt)^2]^0.5

= [(Np Pi (Rs + Rc))^2 + (Nt Pi (Rs - Rc))^2]^0.5

= Nt Pi [(Nr (Rs + Rc))^2 + ((Rs - Rc))^2]^0.5

= Nt Pi Rc [(Nr ((Rs / Rc) + 1))^2 + ((Rs / Rc) - 1)^2]^0.5

= Nt Pi Rc [(Nr (So^2 + 1))^2 + (So^2 - 1)^2]^0.5

= Nt Pi Ro (Rc / Ro) [(Nr (So^2 + 1))^2 + (So^2 - 1)^2]^0.5

= **Nt Pi Ro (K / So) [(Nr (So^2 + 1))^2 + (So^2 - 1)^2]^0.5**

**SPHEROMAK SURFACE CHARGE PER UNIT AREA:**

Assume that the spheromak net charge is uniformly distributed along the charge hose length **Lh**. Then the spheromak surface charge per unit area **Sa** is inversely proportional to the winding center to center distance **Dh**. However, **Dh** varies in a complex way over the spheromak surface.

Consider a poloidal strip of spheromak surface of length **2 Pi R**, width **dLt** and area **2 Pi R dLt**.

The number of toroidal turns of charge hose passing through this strip is **Nt**.

The number of poloidal turns of charge hose passing through this strip is:

**[dLt / (Pi (Rs - Rc))] Np**

The toroidal length of charge hose in this strip is:

**Nt dLt**

The poloidal length of charge hose in this strip is:

**[dLt / (Pi (Rs - Rc))] Np 2 Pi R
= [dLt / (Rs - Rc)] Np 2 R**

Due to orthogonality of poloidal and toroidal turns, the total length of plasma hose in this strip is:

**{(Nt dLt)^2 + [(Np 2 R dLt / (Rs - Rc)]^2}^0.5
= dLt {Nt^2 + [(Np 2 R) / (Rs - Rc)]^2}^0.5**

Define:

**Rhoh = Qs / Lh**

= charge per unit length on the charge hose.

The total charge on the aforementioned strip is:

**Rhoh dLt {Nt^2 + [(Np 2 R) / (Rs - Rc)]^2}^0.5**

Hence the charge per unit area **Sa** on the strip is:

**Sa** = Rhoh dLt {Nt^2 + [(Np 2 R) / (Rs - Rc)]^2}^0.5 / dLt 2 Pi R

**= Rhoh {Nt^2 + [(Np 2 R) / (Rs - Rc)]^2}^0.5 / 2 Pi R**

**= Rhoh {[Nt / (2 Pi R)]^2 + [Np / Pi (Rs - Rc)]^2}^0.5**

Thus:

At R = Rc:

**Sac** = Rhoh {[Nt / (2 Pi Rc)]^2 + [Np / Pi (Rs - Rc)]^2}^0.5

= (Qs / Lh){[Nt / (2 Pi Rc)]^2 + [Np / Pi (Rs - Rc)]^2}^0.5

= **Qs {[Nt / (2 Pi Rc)]^2 + [Np / Pi (Rs - Rc)]^2}^0.5
/ [(Np Pi (Rs + Rc))^2 + (Nt Pi (Rs - Rc))^2]^0.5**

Hence:

**Sac^2** = **Qs^2 {[Nt / (2 Pi Rc)]^2 + [Np / Pi (Rs - Rc)]^2}
/ [(Np Pi (Rs + Rc))^2 + (Nt Pi (Rs - Rc))^2]**

= (Qs^2 / Pi^2) {[Nt / (2 Pi Rc)]^2 + [Np / Pi (Rs - Rc)]^2}

/ [(Np (Rs + Rc))^2 + (Nt (Rs - Rc))^2]

= (Qs^2 / Pi^4) {[Nt / (2 Rc)]^2 + [Np / (Rs - Rc)]^2}

/ [(Np (Rs + Rc))^2 + (Nt (Rs - Rc))^2]

=

/ [(Nr (Rs + Rc))^2 + ((Rs - Rc))^2]

This equation is of fundamental importance in determination of spheromak wall position on the equatorial plane.

This web page last updated February 28, 2018.

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