Vacuum & Cooling

NOTCam has been running cold for two years without opening. This is a new record, but we have started to noticed that the holding time has become short and the average pressure has increasing from 2E-4 mbar to 5E-4 mbar, while also the pressure variations have a higher amplitude with temperature fluctuations (i.e. between LN2 filling cycles). Thus, there is a need to warm-up NOTCam and open it in the service building clean room, in order to bake the charcoal and pump NOTCam warm.

The opportunity should be taken to install some optical components for testing, and take out a filter for proper characterising. In particular, there is an interest in having an additional warm filter wheel for the NTE IR imager. This requires blocking the thermal emission somehow. As a preparatory exercise it has been suggested to test a narrow-band filter (VISTA NB118, centred on 1.1185 microns and 0.012 micron wide) in front of NOTCam, i.e. outside the Cryostats in the cookie box, and using the J-band filter as a blocker. In addition, because it is not well known to what extent the J-band does not leak, thermal blocking through a KDP (potassium dihydrogen phosphate) crystal and its deuterated analog DKDP will be tested. These will need to be surface treated, as they don't like water vapour. In order to minimise the effect of a non-perfect optical surface, the KDPs will be put in the aperture wheel, and to reduce the cost, the small (18mm) slots will be used as this is sufficient for testing. (It should be noted that if the KDPs are working well, they will also solve the problem we are facing with our leaking Z-band filter.) Two small test KDPs have been ordered for testing and we hope they will arrive by Christmas such that they can be installed in NOTCam when we open it.

We should also exchange/check the gear wheel bearings as it will be 4.5 years since they were previously exchanged (May 2011). This is part of our maintenance plan.

The opening is scheduled for January 2016, and a detailed plan is being made.