Cryovac test chamber with internal test box. The test box has both temperature sensors and a heater block as well as a strap up to the 2nd stage of the CTI refrigerator. This allows measuring the cooling/warming rates of the test box or controlling the test box temperature.

A new series of tests was run to try to determine the maximum safe rates at which the various lens materials (LiF, ZnSe, ZnS, BaF2) could be cooled without breakage. These were performed on 1 inch dia flats, resting on G10 pillars so they could cool radiatively. One flat, the ZnSe one, had a temperature diode taped to it to monitor how the test crystals cooled.

Motor test jig previously used in cryovac test chamber. Two motors are mounted, each with a wheel on its shaft. Embedded in each wheel is a samarium cobalt cylindrical magnet (the ends of which are the black dots on each wheel). As the motors turn, the wheels rotate, sweeping their magnets across the face of two reed switchs mounted against the vertical part of the L-bracket holding the motors. Monitoring the reed switch closures and openings outside the cryovac test chamber allowed us to verify operation of the motors to 27K in a full vacuum environment. This is a distinctly different cold test than the LN2 plunge testing.
Side view of motor test jig. Reed switches are epoxied to the vertical part of the L-bracket; switch wire leads trail off to lower right
Mimir configuration during second cold test. Notice the LN2 hose is now MLI wrapped over the two layers of neoprene rubber insulation. Also note that the copper pipe connected to the LN2 loop outlet is frost covered, produced by cold N2 gas cooling the pipe and condensing, then freezing ambient water vapor.
Front view detail. Orange vertical line at right is the twin fiber connecting the electronics rack to the control computer (via the matching Blackbox 8-to-1 multiplexers).
Cooldown, showing N2 warm-up coils atop the clean room.
N2 flow meter during cooldown. Flow rate is about 100 SCFH.