of Filter Box. Two filter wheel drive stepper motors are installed
below the hub mount, two are on the table awaiting installation. The
large round opening below the mounted motors is the receptacle that
will hold the collimator. The long screws surrounding the opening
hold the collimator to the filter box.
gears on the two motors, seen from within the Filter Box.
batch of lenses shipped from Lambda Research Optics. ZnSe and ZnS
cover with heater tape wrapped around it. The purpose of the heater
tape was to try to warm the shell and the enclosed MLI in order to
boost outgassing and deepen the vacuum achieved.
heater tape wrapping details. In addition to the tape, temperature
sensors (thermocouples) were attached to the shell in two places.
temperature controllers for the shell heaters. Two independent circuits
were used, each supplying up to about 300 W of heat. Here the setpoints
are at 104F and the thermocouple sensors report 101 F.
pumping and heating set up. Heater control in foreground, turbo vacuum
pump controller behind it, multirange vac gauge readout at right.
after two weeks of heating and vacuum pumping. Value shown is about
In the end,
we abandoned the shell heater system for routine Mimir work. We
found that the MLI refills with water and other contaminants promptly
upon reopening, that the adhesive backing of the aluminum tape used
to hold the heater tape against the cryostat shell went soft with
heating and left a sticky mess on the shell. Alex spent a couple
of long days cleaning the outside of the cryostat shell and we retired
the shell heating system for good.