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18
Technical Information
Pump used in Presence of Magnetic Fields
298/306 Turbo-V 903 Pumping System User Manual / 87-901-016-01 (A)
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 dependent 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, than the case should be carefully reviewed by
Agilent
specialist. As a matter of fact, in case of high magnetic fields, also
important forces might be generated and applied to the rotor.