SCUBA Update

Users are no doubt still drumming their fingernails waiting to get their hands on SCUBA at the earliest possible opportunity. In order to keep you informed the current situation is as follows: Delivery has been delayed because of two major problems which the team spent most of 1994 solving. The first was noise instability caused by rf interference. This has now been solved by a more or less brute force technique of careful shielding and filtering of every line going into and out of the cryostat. The noise performance and characteristics of the detectors are now extremely stable and within specification. The second problem was microphonic noise caused by the closed-cycle cooler mounted on the cryostat. This has been a very difficult and subtle problem (SCUBA is the first bolometer system to use a hybrid cryostat) and although the effect has been greatly reduced to a more or less acceptable level within the signal band there are still some residual effects which are being worked on. However, the best news of all is that the instrument performance now allows optical commissioning, which has begun in the lab at ROE. SCUBA is now mounted in its frame and the JCMT telescope simulator optics have been set up and are currently being used to check the SCUBA optics and beam patterns. After this all the observing modes will be commissioned in turn. Work to eliminate the residual microphonic effects continues in parallel.