SCUBA event log

12th July 2006: SCUBA IS OFFICIALLY RETIRED FROM SERVICE.

16th June 2006 We have produced a report on our ongoing search for new Secondary Calibrators for SCUBA. Thanks to all those whose observing time was interrupted to take observations for this project. Four candidates are suggested as potential calibrators for SCUBA and/or SCUBA-2, and the rejected sources are also discussed.

10th June 2006 Unfortunately, SCUBA's blockage has definitely returned again. We now believe that we have reached the end of the road with in-house repair of SCUBA, and hence SCUBA will not now be available for observing until further notice. Clearly, the problems with the instrument are serious, and we believe that the only remedy will involve major engineering work on the cryogenic insert. We are in negotiations with a UK firm in regards to this. If a repair is deemed feasible SCUBA will still likely be out of service for several months. Various other options are being explored as well, but none will return SCUBA to operations in less than a few months.

3rd June 2006 SCUBA as been back for a week now and so far is still working. It has been through two ~ 3-day cycles and has cooled down without problems each time. FCFs look ok at ~ 210 Jy/V (850 µm) for 60" chop jiggle maps. We had an initial noise problem of an electronic nature but checking the grounding and shielding of the cables seems to have removed that. So the remaining issue is what the pressures are going to do - we may be seeing some evidence of them rising, indicating a blockage, but we do not yet have a consistent picture. Probably we will have a clearer idea after the weekend.

13th May 2005 Too optimistic. The pressures soon rose back again, suggesting the (apparently) mechanical blockage returned. Some observing was attempted during the night but was abandoned as the array temperatures rose. Now an extended full warmup, aiming to dislodge permanently the blockage, is planned to start on the 16th, with return to service no sooner than the 25th.

12th May 2005 During the regular LHe fill, before the scheduled mini-warmup the pressures suddenly dropped back to a normal range and SCUBA quickly cooled to basetemp. We have never observed this kind of behaviour before. Subsequent noise observations look good. The mini-warmup was cancelled. Let's hope the situation will hold this time!

11th May 2005 After a few days of regular use, albeit with the return of the spontaneous 3-day cycle, SCUBA's pressures shot up on 05/10 indicating another cryo blockage is developing. SCUBA went through the 3-day cycle on the 11th, but was unable to maintain a proper operational temperature afterwards. A mini-warmup is scheduled for the 12th, but, frankly, the outlook is bleak.

5th May 2005 SCUBA was used successfully throughout the nights! Its performance was acceptable for a first night after a cooldown with a FCF of about 215 Jy/V (60" beam). As was noticed before, 5 pixels on the SW array don't see any signal: A1, A6, B11, C3, and D4. C3 is a nuisance since it is part of the R1 ring. All bolometers, including G9, are working in the LW-array.

4th May 2005 SCUBA reached basetemp at 2pm HST.

27th April 2005 Some good and some bad: SCUBA has reached 4K and the throughput test indicates a clear path. At this point all indications are that a cooldown to basetemp should be successful. However, after scrubbing the mixture overnight prior to inserting it into the system today, the circulation pump was found to be leaking. It will need to be replaced by its spare. This will put us back a few days: the next cooldown to basetemp will be attempted on Monday May 2.
Update: the necessity to clean and re-install a contaminated oil-filter has delayed the cooldown to Wednesday May 04.

19th April 2005 Now available on the SCUBA website: SCUBA chop throw - FCF relations. Using archive data, we've established some relations for the dependence of the FCF on the chop throw used. We hoe this will help those without suitable calibration data make use of other measurements taken on the same night.

15th April 2005 SCUBA is now passing its throughput test at room temperature. An extended cool-down process will be started next week, with tests along the way to make sure SCUBA remains unblocked. On the proposed schedule, SCUBA is expected to reach base-temp on Wednesday 27th April.

11th April 2005 With SCUBA back at room temperature, the throughput test failed, suggesting that the blockage is physical instead of cryogenic. The system will be flushed and back-flowed and put on directly on the turbo-pump overnight in a further attempt to remove the blockage.

8th April 2005 SCUBA is still not available. When cooled to 15K on Wednesday (the 6th March), a standard throughput test failed repeatedly, indicating a further blockage problem. A subsequent throughput test the next day with SCUBA at 3K also failed. Hence SCUBA has been warmed back up completely and will now be turbo pumped for a further week. We will then attempt a repeat of the cooldown procedure, meaning that the first possible return will be on the 20th April.

28th March 2005 Well, still not a clear picture, just an update: The short story is that SCUBA has been fully warmed up, and will not be available until at least the 6th April. The details: on the 15th March (UT) and again on the 20th March, SCUBA warmed itself up and cooled back down again. Since these corresponded to two different timescales, which were also different again to the previous regular 3.2 day cycle, we have been reluctant to take these as evidence of the return of the cycling behaviour, at least until a few more cycles are seen and the timing settles down. However, the second time around, the cooldown did not progress quite all the way and the temperature stalled at slightly too high a temperature. Following a mini-warmup on the 22nd March (UT), SCUBA again cooled down but again had trouble reaching stable cold temperatures and low pressures, although it went further than it had done before. It has slowly warmed up by itself since then (as would be expected with the high pressures) and so today it has been fully warmed up, in the hope of clearing out whatever blockage has prevented the complete cooldown. It should be back next Wednesday evening, the 6th April (7th UT). We will then need to watch again for further cycling behaviour.

18th March 2005 The FCO was carried out last night and appears to have been broadly successful. The FCFs at both 450 and 850 microns are good and all observing modes seem to work fine. There is some odd behaviour in a few 450 micron bolometers which we will continue to investigate. We are still maintaining a cautious position regarding the cryogenics though ...

17th March 2005 The electronic problem has been fixed, and SCUBA's noise values have returned to more normal levels. We will hopefully be able to carry out a proper FCO tonight and thus get a more quantitative handle on SCUBA's performance. However, we suspect there may be some residual cryogenic issues at the moment and will be watching it all very carefully for the next week or so still.

14th March 2005 (An update: we don't have a final picture yet but we know there are plenty of people waiting to hear what's happening!)
SCUBA cooled down last week, although much more slowly than expected. It finally reached base temp at about 0200 UT on 20050311 (i.e. about 4pm HST on the 10th, nearly 24 hours later than expected) and it appears to be holding this temperature so far. However the noise performance is far worse than expected, and we are in the process of investigating various potential electronic causes. We had some initial communications problems which were mainly caused by an overly-aggressive ACSIS computer (!) but these have been solved. Unfortunately bad weather at the summit (snow, ice and extremely high winds) are hampering our ability to work on SCUBA for the time being, but we hope to have some progress in the next few days. For the time being, SCUBA remains unuseable.

7th March 2005 SCUBA is now been cooled down to hopefully return on the 9th (weather permitting). A full summary of the work done will follow when complete, but signs are currently good.

3rd Feb 2005 SCUBA has been warmed up for its 5-week shutdown, during which time the problems with the Indium seals will hopefully be solved. Current expected return date is March 9th.

23rd Dec 2004 SCUBA has clearly returned to its 3.2 day cycle again. FCFs have been somewhat varied but again it looks like about a 10 - 15% increase over ideal values is representative for the two good days of its cycle. Our next plan is to work on replacing/retightening of the Indium seals; this will be done in February, with SCUBA unuseable from 2nd February - 8th March 2005.

10th Dec 2004 SCUBA is cool again. Immediate results look good with low FCFs ~ 210 for photometry and ~ 240 for jiggle maps (both 850; 450 also looks good). Now we wait to see what happens over the next few days - our expectation is for it to revert to its 3-day cycle, which would imply a warm up sometime on the 12th.

28th Nov 2004 SCUBA has warmed itself up to 68 K; this has been traced to the turbopump tripping off during a power outage. Since SCUBA was planned to have a standard warmup anyway in two days' time, it will now not be cooled back down again. During the warmup, as well as the standard cycling of the cryogenic mixture, we plan to attempt the installation of a He leak detector which will hopefully give us a better idea of what was causing the 3-day cycle. SCUBA is expected to return to use on the 9th of December.

8th Nov 2004 SCUBA is continuing to warm itself up every ~ 3.2 days. It takes approximately 18 hours to warm to ~ 1K and then only 2 hours to cool back down again. Investigations continue!

17th Oct 2004 SCUBA has warmed itself up again. We appear to be following a three-day cycle. This doesn't correlate with any other activities at the telescope. SCUBA seems to recover itself each time.

14th Oct 2004 SCUBA has warmed itself up again. This time, the outlet valve from the mixing chamber relief dump was left open, allowing the cryogenic mixture to return by itself to the mixing chamber. The chamber then cooled very rapidly by itself again, although we note that the sensitivities and general noise levels take a couple of extra hours to calm down as well.

8th - 11th Oct 2004 SCUBA has warmed itself up again. Cooled down by pumping mixture out of the relief dump back into the mixing chamber, produces a very rapid re-cooling.

5th Oct 2004 Initial signs are that the mini-warmup cycle was successful; temperatures have returned to the normal operating range, in fact quite rapidly. Noise levels stabilised during the night, although the sensitivities still look low.

4th Oct 2004 SCUBA has warmed itself up, during the course of about 24 hours. Pressures all stayed sensible but the temperature just rose by itself. We do not understand this behaviour - this wamrup is much faster than we've seen on previous occasions. We will carry out a mini-warmup and cooldown as a first attempt to remedy the situation.

1st Oct 2004 SCUBA has reached base temperature again. Sensitivities still look to be quite low, but the pressures have returned to sensible levels.

22nd Sept 04 Sensitivities are still low by ~ 20%. Furthermore, SCUBA's pressures and temperatures have risen, which suggest it may be preparing to warm itself up anyway. Hence we have started a full warmup today. Return date expected to be the 29th Sept.

7th Sept 04 The migrating noise has now completely cleared both arrays. It appears to have reduced the sensitivity of both by perhaps as much as 25%. We need some good weather to test this accurately.

30th Aug 2004 SCUBA has been suffering from a migrating noise event which began on the 28th of August. It appears to have now cleared the centre of the LW array but has yet to reach the centre of the SW array, as is typical. We are watching sensitivity levels to see how they are affected once the noise has moved off the array.

26th Aug 2004 SCUBA is back! SCUBA achieved base temperature during the early hours of the 25th August. We then carried out a full FCO last night and all looks good. FCFs and NEFDs are good so far, although poor weather prevents us from trusting the 450 micron results too much. But, so far so good ...

6th Aug 2004 Further delays ... the "replacement" pump sent to us was the wrong pump - we are now awaiting the return of our original, fixed pump. Unfortunately this clashes with a long-planned shutdown at UKIRT and as a result SCUBA will not be available now before the 19th August.

23rd July 2004 So near, yet so far ... just as we were getting optimistic, a rotary pump was found to have seized. A new one is on order, which puts the new date for SCUBA's return back to July 29th at the earliest.

8th July 2004 SCUBA's return has been delayed further, again. However, we do now have some real progress to report: the gas handling rig has returned to the summit, and hopefully we're now onto the final leak checking stage. Expected return date, if no major leaks are found now, is July 21st.

1st July 2004 SCUBA's return has been delayed further, again. Expected return is now July 14th/15th.

24th June 2004 SCUBA's return has been delayed further, again. Expected return is now July 8th.

17th May 2004 SCUBA's return has been delayed further. The gas handling rig has been brought down to Hilo for some extensive parts replacements. Expected return is now July 1st.

1st May 2004 A message has been sent to the JCMT user list concerning a new analysis for the SCUBA secondary calibrators and discussing the A7/A16 crosstalk problem. Click here to see the message.

15th Apr 2004 SCUBA's cooldown has failed to go as planned. It appears that more valves need replacing than was originally realised, and these will need to be ordered. Current expected return date is around May 12th.

5th Apr 2004 SCUBA has again started to significantly warm up of its own accord. Warm up starts today. Some valves will also be replaced which it is hoped will help prevent this happening again.

31st Mar 2004 A quick fix for SCUBA's noise looks hopeful: activating the rad shield fill for as few as 10 seconds (during which time no fluid flows) seems to have a calming effect on the noise levels.

30th March 2004 B card seems to be having intermittent problems. Unclear what the cause is - seating of the card has been checked.

13th Feb 2004 SCUBA has returned from an enforced full warm-up after it started to lose vacuum. FCFs look nominal again, although the weather has prevented any NEFD measurements yet.

29th Jan 2004 (Log restarted for first time since 2002! Will try to fill in some information on intervening years ...)
450 micron bolometers A7 and A16 have been found to have some crosstalk. Tests are ongoing to determine degree of this effect.

13th Dec 2003 Noise monitoring campaign ends. Data analysis begins ...

5th Nov 2003 SCUBA FCO after full warm-up. FCFs and NEFDs all appear nominal. 450 micron cal signal has recovered to normal level.

20th Sept 2003 SCUBA noise monitoring campaign begins in an attempt to understand the variation in SCUBA's noise on a night-to-night basis. Very frequent noise measurements will be taken during heterodyne observations, and TSSs and observers will be asked to insert more during SCUBA observations.

9th Sept 2003 450 micron FCF cal signal appears low in noise ref observations. FCFs and NEFDs correspondingly slightly higher.

2nd July 2003 SCUBA FCO after full warm-up. FCFs and NEFDs all appear nominal. 2-bol photometry checked-out and works fine.

13 Mar 2002 Suspected problems with 2bol chop: the calibration on H5 and H7 differs

   MARS:
                          H5/H7 = 0.8755  (226812/259068)
   CRL618:
             both nights  H5/H7 = 0.8398  (3812.55/4540.08)
             first night  H5/H7 = 0.8535  (3902.11/4571.70)
             second night H5/H7 = 0.8310  (3721.29/4478.02)

06 Mar 2002 On LW-array H10, H11, I1, I3, and I8 are still intermittent noisy. The effect appears to become more permanent. Start contemplating mini-warmup.

10 Feb 2002 On LW-array H10, H11, I1, I3, and I8 are intermittent noisy in addition to the regular G9,I2, and I9. Decided against mini-warmup at this point.

07 Feb 2002 FCFs are back to nominal after full warmup and pump-out.

30 Jan 2001 The mini-warmup on the 24'th and another one on the 28'th (clean cold load) were not successful in restoring the FCFs as far as we can conclude from the internal calibrator signal from 'noise_ref'. Problems with the He fill and the arrival of inclement weather prompted us to move the planned full warmup forward from the end of february. SCUBA is expected to be available again for 20020207 UT.

30 Dec 2001 - 25 Jan 2002 FCFs are higher than normal (FCF_850 ~ 250-300 Jy/V). This was eventually traced to a mini-warmup on 27 Dec 2001 and a non-standard behaviour of the migrating noise sweeping across the arrays during the 2/3 days following. Present status: attempted to cure it by mini-warmup on 24 Jan 2002 UT. Click here for a detailed description of the problem.

12 Jul 2001 Equivalence of raster and discrete skydips

25 Oct 2000 New relationships between SCUBA opacities and those from CSO

03 July 2000 Noise migrates across arrays - but is low and stable through August and September.

22 June 2000 Clock error and fix

• An error in the time held by SCUVAX was discovered earlier in the year. The message provides links to a full description of the problem and to algorithms for fixing it.

07 March 2000 Filter Drum still stuck

• The filter drum has again failed to respond and will be left at the 450w:850w position until at least Aug 2000. Scheduling of any repairs after that date will be possible in about June 2000, once the demand for SCUBA during Semester 00b is known.

06 Dec 1999 Filter Drum stuck

12 Feb 1999 Telescope tracking error.

• From 4th to 9th February 1999 a problem was intermittently present in the telescope tracking. A full explanation and the likely effect on the data is provided.

31 Jul 1998 Chop tracking error.

• In July 1998 a problem with chop tracking was discovered for photometry and jiggle map observations. This is only likely to have affected a very small number of projects, and only those which employed RA-dec or LO chopping. A full explanation is provided.