Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 3.9: A CAD image of the rotor as held by the initial spindle. The spindle is
rigidly coupled to the shaft of the ferrofluidic feedthrough. The feedthough attaches
toa10− 4.5 inch zero length reducer, which supports the spinning parts, as well as
the motor, which is mounted above the feedthrough via a flexible coupling. Figure
Courtesy Max Riedel.
forces. Figure 3.8 shows a finite element calculation of the stresses placed on the ro-
tor by rotation at 140 Hz, measured in MPa. This is expressed as a pressure because
the strength of the material is proportional to the cross sectional area, and thus the
relevant number is not the absolute force placed on the rotor, but rather the force
per unit area. The maximum stress placed on the rotor by this speed of rotation is
152 MPa, which is well below the yield tensile strength of the titanium allow used
(880 MPa).
The rotor is held in vacuum by a stainless steel spindle which is rigidly coupled
to the shaft of a ferrofluidic rotary feedthrough [60]. Since an object will rotate stably
around the axis of lowest or highest inertia, one goal in the construction of the spindle
was to ensure that the rotor would be spinning about the axis with the highest moment
of inertia (the lowest moment being rotation about the centerline of the rotor itself).
To do this, a disc was added to the spindle, with most of the mass on the outside
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