Can I Apply Voltage to Non-Conducting Plates?

[kelly0303]

Hello! I have an experimental setup in which I have 2 rectangular aluminum plates on which I apply some voltages (up to $\pm 5000$ V) in order to deflect some ions. Would it be possible to replace them with same sized plates made of a non-conducting material (e.g. ceramics or PEEK). Can I just apply voltage on an insulator the same way I do on a conductor? Just to clarify, I am not driving any current, I just want a voltage difference between the 2 plate in order to create an electric field that will deflect the ions.

 

[Baluncore]

If the potential is DC, then you can use a slightly conductive material for the plates. It cannot be a good insulator, because then stray charges may accumulate on the surface, that will distort the electric field.
Maybe you could use a sparse mesh of very fine carbon fibres.

 

[nasu]

How are you going to apply the voltage to the insulating plates? Will they have a conductive coating on one face?

 

[Baluncore]

How are you going to apply the voltage to the insulating plates? Will they have a conductive coating on one face?

Maybe this is an application for an electret, the electrostatic equivalent of a permanent magnet.
https://en.wikipedia.org/wiki/Electret

 

[kelly0303]

How are you going to apply the voltage to the insulating plates? Will they have a conductive coating on one face?

Currently we have a power supply that can produce up to 5 kV and we just connect it to the aluminum plate with a wire. I was wondering if I can do the same with an insulating plate.

 

[Baluncore]

I was wondering if I can do the same with an insulating plate.

Which bit of the insulated plate would you connect it to?
How is the rest of the insulator connected to the first point?

 

[Nugatory]

Just to clarify, I am not driving any current, I just want a voltage difference between the 2 plate in order to create an electric field that will deflect the ions.

For that you want a conductive plate, not an insulator. A conductor has the nice (for this application) property that when we apply a voltage to it the entire surface is immediately at that voltage.

 

[berkeman]

I was wondering if I can do the same with an insulating plate.

Is there a reason you want to use insulating plates instead of the aluminum plates?

 

[Vanadium 50]

I'm still puzzled as to how one puts voltage on insulating plates. Insulating wire?

 

[berkeman]

I'm still puzzled as to how one puts voltage on insulating plates.

It just takes a little concentration...

https://leadersayswhat.com/2014/09/carnac-the-magnificent-on-strategic-foresight/

 

[kelly0303]

Is there a reason you want to use insulating plates instead of the aluminum plates?

I am still exploring options (and I would really appreciate any advice about that), but the main reason for now is that we want to send microwaves along the beamline (i.e. along the direction of motion of the ions) and the 2 parallel aluminum plates are along this direction, so they would act as an aperture and mess up an otherwise nice propagation space for the microwaves. I was hoping that replacing the aluminum with something that won't disturb the microwaves too much (maybe an insulator?) I can still apply the voltage needed to control the ions and prevent any disturbance of the microwave field.

 

[kelly0303]

For that you want a conductive plate, not an insulator. A conductor has the nice (for this application) property that when we apply a voltage to it the entire surface is immediately at that voltage.

Actually this was one of the questions I have. In my case I don't care about the speed of the voltage distribution i.e. I keep the plates at a fixed voltage for days or weeks after I apply the voltage. While an insulator won't have the same voltage on its whole surface immediately, would it still reach that point after a (reasonably long) while? Or the insulator will never be as uniform as the aluminum plates?

 

[Baluncore]

1. Do the microwaves pass through the high voltage deflection plates, or between them?

2. What wavelength and how much power is in the microwave beam?

3. What is the polarisation of the microwaves, maybe the plates can be a grid that is invisible to the microwaves. Another possibility is that the plates could form a waveguide cavity, that supports and contains the microwave resonance.

 

[davenn]

I am still exploring options (and I would really appreciate any advice about that), but the main reason for now is that we want to send microwaves along the beamline (i.e. along the direction of motion of the ions) a

You never mentioned microwaves in your first or second post
what is the source of the microwaves and their power levels ?
Time for full disclosure and drawings from you

ohhh and I see this is your second thread on the same subject
https://www.physicsforums.com/threads/question-about-microwave-reflections.1063872/

@berkeman maybe a merge is needed ?

 

[kelly0303]

1. Do the microwaves pass through the high voltage deflection plates, or between them?

2. What wavelength and how much power is in the microwave beam?

3. What is the polarisation of the microwaves, maybe the plates can be a grid that is invisible to the microwaves. Another possibility is that the plates could form a waveguide cavity, that supports and contains the microwave resonance.

@Baluncore @davenn Sorry I didn't mention microwaves (indeed the other post is related, but I wanted to keep them separated). I wanted to check if I can use an insulator in general, without further complicating the questions with the microwaves, but probably that would have actually helped.

The microwaves have a wavelength of $15$ GHz (so $~ 2$ cm wavelength), and they pass in between the 2 plates, however the distance between the plates is only $3$ cm and the waist of the microwave beam (sent from a horn) is a bit higher $\sim 4$ cm. The power is $50$ W and they are circularly polarized ($> 95\%$ purity) and we want to keep them as circularly polarized as possible after the aluminum plates, too.

 

[Baluncore]

A ceramic plate will have a dielectric constant that will distort the field in the volume of the plates.

The plates only need to be in the form of a conductive screen that is able to sink any charges that land on it. That screen can have a high resistance since the current is so very small. It is not new technology. Vacuum tubes have been using conductive grids since the first triode was built, and screen grids since the first tetrode.

I would consider supporting each HV plate-grid on two catenary glass fibres that cross the field. I would make the grid from thin carbon fibres running parallel with the microwave propagation. A single fibre could be used to make that plate by winding it back and forth between the two glass fibres to make a zigzag grid. The low mass and volume of material, with the high resistance and orientation, should not distort the microwave field. The distance between the parallel fibres could be one or two millimetres without it changing the electric field.