The LN2 plunge-tests of the conventional stepper motors was useful, but not sufficient for certifying that the motors would work in Mimir. Based on knowledge of failure modes for other cryogenic motors under vacuum conditions, we wanted to test the motors at low temperature and under vacuum conditions. We built a test chamber, again with parts from our local "Cryogenics-R-Us", which contained our CTI 1050 helium refrigerator cold head and several cold shields. This permitted bringing the motors to under 30K and with good vacuums. The picture shows two test units. At left, two stepper motors are mounted on a common stand. The aluminum disks contain embedded magnets that trigger the magnetic Reed switches mounted in the stand (see the twin sets of wires) once every revolution. So, from outside the test chamber, we could verify that the motors rotated by watching the Reed switch closures.

We also tested various surface treatments, in an attempt to maximize radiative heat transfer between components within Mimir. The stand at right has been bead blasted and hard anodized and is about to be tested for radiative coupling to the inside cold surface of the test chamber.

Dan Eldredge is putting the cover on the internal cold shield in the test chamber.
Eric Tollestrup and Dan Eldredge are completing the assembly of the cold shield before closing the test chamber.