Technical Information
Pump Used in Presence of Magnetic Fields
TwisTorr 74 FS User Manual / 87-901-053-01 335/342
Pump Used in Presence of Magnetic Fields
Magnetic fields induce eddy currents in the rotor of a turbomolecular
pump that tend to oppose to its rotation.
The result is increased electrical power consumption by the motor,
most of which is dissipated in the rotor.
Since the rotor is not in contact with the stator the above power can
leave the rotor mainly by radiation and hence the rotor may be
overheated while static parts of the pump remain cool.
This effect is strongly dependant from the intensity, time function
and distribution of the magnetic field.
In general, therefore, an increase in pump current can be expected.
If this increase is lower than 50 % of the current value drawn by the
motor in high vacuum operation, no particular problem should be
expected.
However if the effect is greater, then the application should be
carefully reviewed by Agilent's specialist. As a matter of fact, in case
of high magnetic fields, also important forces might be generated and
applied to the rotor.
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