A summary of the cryogenic work on SCUBA-2 this past winter

SCUBA-2 has been back on the sky for the past month producing excellent data, following both planned engineering down time to work on the instrument cryogenics and unplanned – to fix a vacuum leak.

The end of 2016 was a busy time for the EAO ETIS (Engineering, Technical Information Systems) staff. From the middle of the 2016 we were aware of a change in performance of one of the (two) pulse tube coolers (PTC) that cools the SCUBA-2 inner radiation shields and internal mirrors to below 4K. We were able to continue to use SCUBA-2 without any impact on the quality of the data, while we planned the major task of taking the 3 tonne instrument off the antenna and replacing both of the instrument PTC cold heads with new remote motor models.

The dilution fridge mixture was removed and the warm-up started on October 5th. SCUBA-2 was back on the sky with new PTCs and was operational by November 18th, 1 week ahead of schedule. However, during the subsequent cooldown, the cryostat vacuum was found not to be as good as expected.

Later in December, when we temporarily warmed-up (to 4K) to replace a small pump in the dilution refrigerator (DR) gas handling system – a regular procedure, the poor vacuum became a serious issue. Additional problems with pumps in the GHS and too high a pressure in the DR still prevented cooling below 1K. This is well above the operating temperature of the TES detectors.

The only course was to warm the instrument to ambient temperature and to then carry out extensive leak checking of the cryostat. A leak was found that we could fix. However, on detailed inspection, we discovered that the O-ring between the feedthrough and the top plate of the DR insert was cracked and would fail soon if we did not replace it.

Two weeks of skill and persistence was required to replace this O-ring to enable SCUBA-2 to be yet-again pumped, leak checked and cooled prior to the end of January. With the vacuum leak fixed, the cause of the second issue with the GHS that prevented cooling below 1K became apparent. This issue was caused by a particle filter on the input of the pump. After removing the offending filter SCUBA-2 was operational by February 5th.

The loss of an additional 6 weeks of observing with SCUBA-2 impacted our users. However, by catching the failing O-ring before a total loss of vacuum, we avoided the potential for more serious consequences to the instrument and a bigger disruption of the observing schedule. An extended period of good stable weather in recent weeks has allowed some of the affected programs to makeup for the missed nights.

In addition to the cryogenic work, new improved thermal blocking filters have been installed between the instrument window and the band defining filters for the detector arrays. We are now investigating the change in optical power on the detector arrays, to see if this has modified the stray light environment within the 4K box and improved SCUBA-2’s performance.

Jamie Cookson works on the repair of SCUBA-2.

– 20170407

Blue skies for Venus observations

Over the past two weekends the JCMT has been open and observing during the day. These daytime observations are needed to observe the middle atmosphere (altitude 70-110 km) of Venus.

The aim is to better understand atmospheric physics and chemistry. The way to advance understanding of fundamental atmospheric physics and chemistry in general is to study the atmospheres of individual planets – specifically in this case Venus!

The JCMT is used for this study because sub-millimeter spectroscopy is uniquely powerful for investigations of this altitude range on Venus. JCMT’s location on Maunakea, its ability to safely point arbitrarily close to the sun, and its observation flexibility (capability to modify observing strategies in as little as 5 minutes, during the observations) make it uniquely well-suited to Venus research.

Here is a video of the sky above the EAO office in Hilo – can you spot Venus? If you want to see what the weather is like on Maunakea click here. For a link to the EAO Hilo office weather click here.

-2017/03/28

Electronics Engineer job opening

We are currently recruiting for an Electronic Engineer to join the EAO/JCMT  Engineering Group. This group ensures that the telescopes and associated instruments are at a high level of operational readiness at all times. They apply technical knowledge in support of the testing, modification, maintenance, repair, and upgrading of EAO mechanical, electronic and electrical systems.

CLOSING DATE: March 24, 2017

For more information visit the EAO Jobs homepage.

– 2017/02/24

JCMT 2017 Users Meeting – see you again next year!

The 2017 JCMT Users meeting was held in Nanjing, China. The two day meeting was held on Monday, 13th and Tuesday 14th of February. An additional 1 half-day data reduction workshop was held immediately after the meeting on Wednesday 15th of February. The meeting was well attended and all talks are now available online here. We hope you have a good productive 2017 and hope to see you at our JCMT 2018 Users meeting in South Korea next January.

– 2017/02/21

Call for proposals 17B and Large Programs (II)

The East Asian Observatory is happy to invite PI observing proposals for semester 17B at JCMT (for details see here). Semester 17B runs from 01 August 2017 to 31 January 2018.

In addition the East Asian Observatory is happy to accept proposals for Large Programs – running from 01 August 2017 to 31 January 2019. More details about the Large Programs (II) call can be found here.

You can reach the proposal handling system, Hedwig,  and find complete details of this Call at:

https://proposals.eaobservatory.org/

Any further questions should be directed to our help desk: helpdesk@eaobservatory.org

If this is your first visit to Hedwig, you should go to ‘Log in’ and generate an account. There is a ‘Help’ facility at the upper right corner, and individual Help tags at many other places.

The 17B Call and Large Program (II) call for Proposals closes on the 15th of March 2017.

– 2017/02/13

17B semester Call at the Subaru Telescope is now open

The East Asian Observatory is pleased to partner with the Subaru Telescope to enable astronomers  from an East Asian participant region to have access to Subaru time. The East Asian Observatory proposals are considered by the Subaru scientific panel alongside regular Subaru proposals, with a guaranteed award of time of a total of 3 nights of observing in the semester.

The 17B semester Call at the Subaru Telescope is now open, click here for more details.

– 2017/02/08

Support Astronomer job opening

The EAO/JCMT is currently seeking an astronomer to join its team of support scientists. Duties include: Assists visiting astronomers in obtaining high-quality observational data; provides technical, scientific, and logistical support to astronomers before, during, and after their observing runs, and assists with their data analysis. Performs general and specific support of the telescope operations and/or instruments and their development. Undertakes a program of astronomical research, which may or may not be related to using the James Clerk Maxwell Telescope (JCMT).

CLOSING DATE: February 28, 2017

For more information visit the EAO Jobs homepage.

– 2017/02/02