Protection of Mirrors

The most essential optical device is the mirrors. They are "sealed" in the mirror box. To protect them from being oxidized, the whole mirror box is filled with helium gas constantly. You should notice the tube that is hooked up between a helium gas cylinder at a corner of the R-AXIS mounting base and the mirror box. A gauge tells you whether there is still helium gas floating through the tube and into the mirror box. The gauge can be switched to either constant flux or slow purge. Whenever the mirror box is opened (don't try it yourself!) for service, the switch should be turned to constant flux for 30 minutes or so and then turned to slow purge. Set the flow rate at the highest (65) value on the gauge. Also, you should check the pressure of the helium gas cylinder from time to time. Replace it when you can't get the maximum float rate no matter how you adjust the float gauge.

In case you seriously suspect that the mirrors have been oxidized, which should hardly be the case, contact MSC immediately and schedule a service.