JCMT shutdown in the summer of 2002

Plans are firming up for a service shutdown of the JCMT in the summer of 2002. Why are we having a service shutdown? One issue to be addressed by the shutdown is the problem of the sticking filter drum on SCUBA. This problem started in December 1999, making it impossible to use any other filter than the 850/450-wideband combination. Repairing the filter drum will take SCUBA out of action for several weeks and is not risk free. ITAC has weighed the scientific motivation for a repair against the outage and risk. It was decided, at the June 2001 ITAC meeting, to do the repair during the summer 2002. During the shutdown, we will also replace the bad indium seal. Other SCUBA work under discussion are fridge repair/maintenance, replacing the 850 micron filter with new edge filter, wide-band 850-750 micron filter, new 850 micron array feed horns and fixing broken or noisy pixels.

We also need to shut down the telescope in order to do preparation work for the B-band array HARP-B. The array has a K-mirror for image rotation that will be located in the cabin. In order to install the K-mirror the cabin needs to be modified. Further, all helium lines for the closed-cycle coolers in the cabin need to be rerouted. The work will involve electrical welding as well as cutting metal burs. Due to the risk of damaging the SIS junctions and receiver optics, all heterodyne receivers will be removed from the cabin during this work. The antenna will be immobilized during this work stopping all observations allowing for extended working days to complete the task as quickly as possible - making the antenna ready for SCUBA observing each night would be very inefficient if even possible.

To minimize the loss of SCUBA observing time we plan to overlap the shutdowns as much as possible. We have insufficient staff to do all work in parallel. Other factors affecting the planing is availability of ATC staff needed for the SCUBA work and avoiding other labor intensive work at the JAC such as the move of Michelle to Gemini. The current plan, which not is final, is outlined below.

June 13^th SCUBA work starting with warmup.

June 24^th Heavy engineering starts, heterodyne receivers removed and antenna is closed.

July 15^th SCUBA work finished and cool-down starts.

July 22^nd Heterodyne receivers returned to cabin, pumping and preparation for cool-down starts.

July 23^rd SCUBA observing starts - still extended day work.

July 26^th Extended day work ends - 16 hours observing starts.

Aug 2^nd All instruments in operation.

The final schedule will depend on the amount of SCUBA work attempted as well as need for contingency time.

Per Friberg

2001/08/30

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