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I need to produce a magnetic field that goes from 0 - 80 kA/m (0 - 100 mT), which I can control the amplitude of, and change its polarity.
The diagram below outlines a couple of pieces of laminated transformer core I was given (blue), with a winding (red) and the green is where I need to place what I want to measure. This was apparently used by someone before to do the same things, but the rest of the set up is lost.

I am hoping somebody could advise me as to what to use to drive the coil to reach the the field I need and to control reasonable steps (5-10 kA/m) of the field, or any other set up or modifications that I could make to improve things.

I put 4 amps through the coil and measure 8 kA/m (10 mT) in the gap. This is the limit of the power supply I have, and the coil heated up quite a bit. I have some worry of the coil heating up and the limits. If I assumed a relatively linear increase that would require 40A, which seems like a lot.

There is a gap between the cores under the coil, and the calculation I have come across for these setups usually there is only one gap placed opposite the coils.

Any advice would be greatly appreciated, even if it is an alternative set up.

enter image description here

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  • \$\begingroup\$ More windings will get you more field with the same current. \$\endgroup\$ – Cristobol Polychronopolis Aug 7 '18 at 12:05
  • \$\begingroup\$ The core will behave as if there was a single gap equal to the total of the two gaps. You don't want the gap under the coil. \$\endgroup\$ – Spehro Pefhany Aug 7 '18 at 12:47
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To make the magnetic field in the outside gap stronger, you can

  • Add more windings to the coil.
  • Remove the gap in the coil; fill it with something ferromagnetic (doesn't need to be laminated, that's only important in AC applications)
  • Make the outside gap smaller.

It's also possible that there's some short-cut across some of the windings, that would make them useless.

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    \$\begingroup\$ A shorted turn would only affect an AC setup. Its effect with DC would be negligible. \$\endgroup\$ – Dave Tweed Aug 7 '18 at 12:41
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    \$\begingroup\$ @DaveTweed I think he means that those shorted turns would not carry current rendering them useless for producing DC mag fields. \$\endgroup\$ – Andy aka Aug 7 '18 at 12:46
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I put 4 amps through the coil and measure 8 kA/m (10 mT) in the gap. This is the limit of the power supply I have, and the coil heated up quite a bit.

I'm assuming you are talking about DC current here. With 4 amps and 8 kA/m it sounds like you have several hundred turns and if those turns are producing too much heat your only feasible options are either to cool the winding or use thicker copper wire.

Any advice would be greatly appreciated, even if it is an alternative set up

I might also add that the core gap under the coils does not make much sense.

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