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Issues calculating magnetic field using multi-turn coils
Posted Mar 10, 2014, 1:18 p.m. EDT Low-Frequency Electromagnetics Version 4.4 1 Reply
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The end goal that I have is to produce a magnetic field map for a superconducting magnet. In my first attempt, I tried to model the magnet coil packages (there are 11 of them) and the result was approximately 0.5 Tesla lower than the measured map and the calculated map from the manufacturer (it should be 5T maximum, but comsol gives something like 4.5T).
I then tried to model a simple system to see if I get an answer that I expect, so I tried Helmholtz coils. I again got a result that was approximately 10% low for the field at the center between the two coils. I then thought that perhaps I was doing something else wrong and tried to use the Helmholtz coil tutorial, but found that it produced a similar result (10% low).
The entire helmholtz geometry is contained inside a 1m sphere with 20cm coils. The sphere is centered on the center between the coils. I added a 10cm thick layer to this outer sphere and then added an infinite element domain to this layer. I re-ran the simulation and the result was once again 10% low. Is there something wrong with my implementation of the infinite element that prevents it from being correctly interpreted?
Thanks for your help.
I then tried to model a simple system to see if I get an answer that I expect, so I tried Helmholtz coils. I again got a result that was approximately 10% low for the field at the center between the two coils. I then thought that perhaps I was doing something else wrong and tried to use the Helmholtz coil tutorial, but found that it produced a similar result (10% low).
The entire helmholtz geometry is contained inside a 1m sphere with 20cm coils. The sphere is centered on the center between the coils. I added a 10cm thick layer to this outer sphere and then added an infinite element domain to this layer. I re-ran the simulation and the result was once again 10% low. Is there something wrong with my implementation of the infinite element that prevents it from being correctly interpreted?
Thanks for your help.
1 Reply Last Post Mar 31, 2014, 5:41 p.m. EDT
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Posted:
1 decade ago
I've continued working on this and have made a small amount of progress both with a basic Helmholtz coil configuration and the real magnet that I have. It seems as though the current density in the coils is incorrect.
The Helmholtz coil tutorial defines a workplane where two square coils of radius R. My current modification of this tutorial uses 1cm square coils of radius 15cm. The coils are defined as multi-turn coils, with 10 turns each and a current of 1Amp.
The current density in each coil should be:
10 * 1 / (0.01)^2 = 1e5 A/m^2.
Comsol instead calculates the current density to be 9.6666e4 A/m^2.
The expected magnetic field for this configuration should be about 5.99e-5 T and comsol gives a result of 5.79e-5 T, for a ratio of about .966. This is exactly the ratio of the calculated current density to the expected current density.
Similarly, for my magnet configuration, which has 11 separate coils, this ratio is approximately 90% for the current density and the magnitude of the magnetic field is also approximately 90% of what it should be.
Is there perhaps something I'm not understanding about how Comsol extracts the current density for a multi-turn coil from the given parameters?
The Helmholtz coil tutorial defines a workplane where two square coils of radius R. My current modification of this tutorial uses 1cm square coils of radius 15cm. The coils are defined as multi-turn coils, with 10 turns each and a current of 1Amp.
The current density in each coil should be:
10 * 1 / (0.01)^2 = 1e5 A/m^2.
Comsol instead calculates the current density to be 9.6666e4 A/m^2.
The expected magnetic field for this configuration should be about 5.99e-5 T and comsol gives a result of 5.79e-5 T, for a ratio of about .966. This is exactly the ratio of the calculated current density to the expected current density.
Similarly, for my magnet configuration, which has 11 separate coils, this ratio is approximately 90% for the current density and the magnitude of the magnetic field is also approximately 90% of what it should be.
Is there perhaps something I'm not understanding about how Comsol extracts the current density for a multi-turn coil from the given parameters?