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# Simulating RF coils within a RF cavity device

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##### Full Member level 4
Hello, I was interested to know whether there is any simple software (or not) or software in general which would show me a few parameters that I am interested in.
namely, I am interested in B field (flux) pathway and field strength within a core air gap that is filled with a RF wire made of individual strips or simply a planar litz wire, there would be many such identical cores assembled in what are normally the side walls of a pillbox RF cavity.
Each core would have it's own field coil.
So in general my aim is to understand how much RF current needs to pass the field coil for given field strength within the core and the airgap and then idealistically calculate the current through the main loop to arrive at the RF field and resulting power within the cavity itself. Also how all of this changes with fixed materials over a range of frequencies from min to max

I have done simple calculations on paper for core cross section and inductance , current through the field coil and resulting approximate airgap field strength but I would need a more complex modelling to understand how all of that comes together when many cores are put in parallel assembled in a cavity.

Can you give me any advice , has anyone had experience with RF electromagnetics simulations?

The term "RF cavity" ususally implies a resonator with of least lambda/4 size. In this case you need a full featured 3D EM solver to analyze it. The core and coil questions rather suggest a simple AC magnetic problem. Please clarify the setup in terms of operation frequency/wavelength and dimensions.

The term "RF cavity" ususally implies a resonator with of least lambda/4 size. In this case you need a full featured 3D EM solver to analyze it. The core and coil questions rather suggest a simple AC magnetic problem. Please clarify the setup in terms of operation frequency/wavelength and dimensions.
Hello, thanks for answering, the idea is this. One cannot approach this as a typical RF cavity where there is the torus and the hollow center through which an electron/proton etc beam passes because such a cavity has the inductor part and capacitor part of it. In my case the cavity is closed, in the sense that it is a toroid in it's form

The image is just for example.

So the litz wire forms a conducting closed toroid cavity, but the litz wire on the axial sides passes through or better said is surrounded by a magnetic core with an airgap and it passes through the airgap.
There are other factors involved but for short there are two types of coils. there are the individual field coils on each core and then there is the toroid loop that has a B field cutting it perpendicularly on the axial sides.
My intent is to get to the field strength within the airgap at certain frequency range and coil amperage and eventually also get to the field within the cavity (in this cavity that would be B field only) and again to know it;s field strength.

The reason why there would be a B field within the cavity is because the cavity would rotate and the lorentz force would form current in the axial parts that have a B field through them from the individual cores.

To be honest, I don't get even an approximate idea what you are designing.

Referring to the original question, if the overall dimensions are small compared to RF wavelength, e.g. < lambda/10, a simple AC magnetic analysis gives acceptable results.

To be honest, I don't get even an approximate idea what you are designing.

Referring to the original question, if the overall dimensions are small compared to RF wavelength, e.g. < lambda/10, a simple AC magnetic analysis gives acceptable results.
Ok let me try to simplify it. Just imagine a torus, one that resembles the pillbox cavity just without a open center, but instead a closed one.
Now imagine the sidewalls of that torus (the ones that are normally perpendicular to the beam that passes the open center) are made from strips of litz wire or similar material. This wire is situated within an airgap. the airgap belongs to the cores I said about. You have multiple cores in parallel.
each core has a small coil that creates field within it, the coil is driven by a small RF amplifier adjacent to the coil.
Drive all these coils/cores together and you should have a B field that permeates the conductors of the cavity sidewalls.

I need to understand whether it is doable at all, the field strength I can achieve within the gaps with the conductor present, the drive current and power for each core field coil, and then the current in the torus loops itself and resulting B field in the cavity.

IIRC such a closed cavity without the center capacitance should not have it's physical dimensions affect the frequency it can be excited with because the cavity becomes a closed loop/short circuit and there is no resonance in it.?

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