If the grid insulator is a perfect insulator, the E field along the grid support insulator is different from elsewhere in the sphere. Especially where it passes throgh the case (or outer grid).
Has anyone tried coating the support with a resistance (say carbon or graphite) or other method to make the E field more uniform?
Paul
Grid support insulator
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Frank Sanns
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Re: Grid support insulator
Paul,
If you make it conductive then it will have a high E field like the grid and symetry will be very bad then. Ions would be attracted along the entire length of the feed and not just to the inner grid. I think the small insulator occupies a small part of the volume of the fusor and its contribution is minimal. If it has any effect it would be only very close to the inner grid where it physically starts to block ions.
Frank S.
If you make it conductive then it will have a high E field like the grid and symetry will be very bad then. Ions would be attracted along the entire length of the feed and not just to the inner grid. I think the small insulator occupies a small part of the volume of the fusor and its contribution is minimal. If it has any effect it would be only very close to the inner grid where it physically starts to block ions.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Re: Grid support insulator
It depends on the voltage profile along the insulator. If it were a constant resistance per unit length, then E field will be proportional to 1/r. A profiled resistance could make it proportional to 1/r^2 the same as the E field in the rest of the sphere.
(i.e. the spheres of equipotential would pass the insulator without distortion.)
(i.e. the spheres of equipotential would pass the insulator without distortion.)
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Frank Sanns
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Re: Grid support insulator
Paul,
I see what you are trying to do but the problem is that the 1/r is going one direction for the E field of the fusor but the opposite direction for the feedthrough. The highest negative potential is at the inner grid and the lowest is the grounded outer grid or shell.
If you did not use an insulated feedthrough and used a linear resistor for a feed, the greatest negative potential would be at the fusor wall where the feedthrough comes in. The E field would then DROP from the wall to the inner grid becasue the inner grid gets it potential from the feedthrough and not the reverse.
It was a good thought though.
Frank S.
I see what you are trying to do but the problem is that the 1/r is going one direction for the E field of the fusor but the opposite direction for the feedthrough. The highest negative potential is at the inner grid and the lowest is the grounded outer grid or shell.
If you did not use an insulated feedthrough and used a linear resistor for a feed, the greatest negative potential would be at the fusor wall where the feedthrough comes in. The E field would then DROP from the wall to the inner grid becasue the inner grid gets it potential from the feedthrough and not the reverse.
It was a good thought though.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Re: Grid support insulator
Frank,
I envisage connecting one end of the (distributed) R to the case and one to the grid. The potential changes as you move along the support.
An easy way to fabricate this is to coat insulator with carbon from a sooty flame.
Paul
I envisage connecting one end of the (distributed) R to the case and one to the grid. The potential changes as you move along the support.
An easy way to fabricate this is to coat insulator with carbon from a sooty flame.
Paul
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Frank Sanns
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Re: Grid support insulator
Paul,
Yes, that would work to distribute the charge. I could not figure out how you were energizing the inner grid. So what you propose is to use the insulating properties of the alumina tube all the way to the inner grid. Then starting at the grid, provide a somewhat conductive surface on the outside of the ceramic starting at the inner grid. The conductive coating would stop before getting to the fusor wall so that no current could flow in the wrong direction on the outside of the insulator. That will work.
Frank S.
Yes, that would work to distribute the charge. I could not figure out how you were energizing the inner grid. So what you propose is to use the insulating properties of the alumina tube all the way to the inner grid. Then starting at the grid, provide a somewhat conductive surface on the outside of the ceramic starting at the inner grid. The conductive coating would stop before getting to the fusor wall so that no current could flow in the wrong direction on the outside of the insulator. That will work.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Re: Grid support insulator
The distributed resistance has to connect to wall and grid to develop a voltage along it.
Yes it will take some current, but if the R is high enough it should make little difference to power input
Yes it will take some current, but if the R is high enough it should make little difference to power input
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Frank Sanns
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Re: Grid support insulator
I was thinking the circuit would be between the conductive coating to the plasma. If you complete the circuit to the fusor shell, I think you will quickly exceed the breakdown of the ceramic insulator and get curent flowing where you don't want it.
But I think you have much larger problems with the E field effects around the inner grid and elsewhere in the fusor than around the thin insulator.
Frank S.
But I think you have much larger problems with the E field effects around the inner grid and elsewhere in the fusor than around the thin insulator.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Re: Grid support insulator
If the insulator is OK as it passes through the case, It will be OK along its length (assuming the diameters are equal).
Where else do you think E fields are non-uniform?
Paul
Where else do you think E fields are non-uniform?
Paul
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Frank Sanns
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Re: Grid support insulator
They are not uniform around the inner and outer grids. To make matters worse, the fields change with voltage. If you adjust the pressure in the fusor to the point where you get bugle jets, then adjust the power, you will see just how dynamic things are within the fusor. At a constant pressure, the jets will change focus in and out of the inner grid when you change the voltage.
You can see this in even a very simple air demo fusor. Get one together with minimal pieces and try some experiments. Many surprises in the fusor.
Frank S.
You can see this in even a very simple air demo fusor. Get one together with minimal pieces and try some experiments. Many surprises in the fusor.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Re: Grid support insulator
Frank,
Useful feedback thanks.
I would think that the non-uniform E field is due to the inner grid construction. It is not spherically symmetrical.
An earlier post mentioned using a geodesic structure. (i.e. spherical symmetry)
Does anyone know if this improves the bugle effect?
Paul
Useful feedback thanks.
I would think that the non-uniform E field is due to the inner grid construction. It is not spherically symmetrical.
An earlier post mentioned using a geodesic structure. (i.e. spherical symmetry)
Does anyone know if this improves the bugle effect?
Paul