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
||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
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
||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).
N2 warm-up coils atop the clean room.
||N2 flow meter
during cooldown. Flow rate is about 100 SCFH.