Vacuum & Cooling

Since March 2008, when the entrance window was replaced, the NOTCam cryostat has behaved well. It has now been kept cold since May 9th 2009 with no incidents, a new record of 1.5 years cold. Apart from the improvement due to the new entrance window, the recent good results are also thanks to 1) an improved alert system and 2) an improved LN2 filling nozzle that does not cause vacuum leaks due to thermal stress, and 3) it probably also benefits from the proper baking of the entire cryostat done in March 2008. We are considering to include a similar baking as a preventive measure during the next opening of NOTCam planned in January 2011.

A minor problem with faulty readings of the cryostat pressure and four temperature detectors still remains unsolved. The Internet plug has been eliminated as a possible cause of the problem. There seems to be a problem with every 1-2 out of 1440 readings on the average, nothing systematically. It is also clear by now that the problem does happen also when NOTCam is mounted at the telescope.

The leakage of the PTR hoses requiring refilling with high-quality Helium about once a month suddenly got worse in June. The leakage was located to be close to the instrument end, and was fixed by cutting the tubes shorter. Mounting instructions were improved to make sure the hoses are treated with more care when moving NOTCam across the dome floor. Quotes were obtained for spare hoses.