Sunday 8 July 2012

ALMA Array Operations Site Visit

An early start on Friday  for our second day of ALMA activities. Liliana and Olivier met me at 7:30am and we met Valeria shortly after 8am at the OSF. At the control at the entrance, I had to do an alcohol test - first time I've ever done one of those!! Of course, I had heeded Valeria's advice and hadn't drunk any alcohol the evening before so I had a reading of 0. The guard explained that before 8am, all drivers must do a breathalyser test (and have a reading of 0) and passengers are subject to random testing too.

Although we had all submitted a medical certificate to say we were fit and healthy to go to the 5000m site, ALMA have a policy to do a quick medical check on everyone before they ascend. This involved checking our blood pressure. Mine was a little higher than usual - normally mine is around 120 over 70, but it was 130 over 80- but still within the limits set by the doctors. Thankfully, Liliana and Olivier were both fine too, so we could all go up!

Whilst we were waiting in the medical room, Valeria had gone to get the oxygen cylinders and some food supplies for us to take up to 5000m. She also got us each an ALMA hat, which I was totally delighted with! I'd seen them in the safety video the day before and quite fancied one!

Then we set off - Valeria drove us there, stopping along the way to get some photos and point out some of the traditional Atacameño features which have been preserved along the roadside. One of these was a stancia - a place where nomadic Atacameño people would stay when up in the mountains with their animals. Valeria explained that before construction began, ALMA took an environmental and cultural responsibility and had employed an ecologist and biologist to ensure that native flora and fauna were protected.  

The view was quite stunning on the road up and we also saw some HUGE cacti!
Valeria and I (with my ALMA hat) and a big cactus
All the way up in the car, we had to monitor our blood oxygen levels and heart rate. We did this by putting a little meter thing on our index finger. If our oxygen levels dropped below 80% we had to take oxygen from the cylinder. Valeria also had to radio in every 10km to base. Valeria's and my oxygen levels did indeed drop below the 80% on the journey up, so I had my first experience of inhaling oxygen from the cylinder.

Once we reached the top, we found that once again we were very lucky - one of the North American antennae was being moved down to the OSF for routine maintenance and we were just in time to see this happening. It's quite an incredible feat. Each antennae weighs around 100 tonnes and the transporters (called Otto and Lore - German machinery of course!) are built to carry one antenna each. The transporters have 14 sets of double wheels which can move independently, meaning it can turn in reasonably small areas, despite its huge size!
 We had missed the antennae first being put onto the transporter, but managed to see all the rest of the procedure. All in all, it takes around 5 hours to transport one antenna from the AOS to the OSF.

Seeing the AOS was incredible. Already, even with just over half of the antennae in place, it seems huge - and it can be even bigger too. There are 250 pads where the antennae can be moved to for different observations. All the proposals requiring the same configuration of dishes will be gathered together and the dishes moved into the positions and the observations done.

I certainly felt the altitude in terms of lack of oxygen - it made me feel very sleepy at times, although it's not really much wonder. My oxygen level at one stage was 65% and my heart rate 94 bpm. So, needless to say, I needed a bit more supplementary oxygen.
Oxygen please!
Once we had watched the antenna being lifted onto the transporter and the transporter started to move off (Olivier and Liliana even had a go in the drivers cabin!) we headed inside to the technical building to speak to some of the computer engineers who handle the correlators.

We met 2 guys, who were attached to a permanent supply of oxygen. I asked if they always had this when working up at the AOS and they said they did. They normally spend around 4 hours there, and because they need to use their brains a lot, they need their oxygen levels to be at a reasonable level.

They showed us the super computers which are the correlators. First the one which is just for the Atacama Compact Array, so only the 16 East Asia dishes, and then the second super computer for the wider array.
Atacama Compact Array correlator
The job of the correlator is to collect all the signals from the antennae. In the 'Base' correlator (the one for the wider array) there are 4 quadrants, each one working in a different wavelength range. Each quadrant has an energy consumption of 40kW per hour. To compare, typically, your television uses 0.2kW per hour. There are 1250 cables for each quadrant (see picture) and each quadrant receives approximately 120gigabytes of data per antennae per second!

The room where the correlators are must be kept at a stable temperature (less than 20°C) and with reasonably high humidity (around 30 - 40%). These conditions help to avoid electrostatic charges.

On our way back down to the OSF we caught up with the transporter and American antenna number 11 on its journey:

Another fascinating day, and so amazing to see the Array Operations Site itself. I really don't know how the people work up there - it is absolutely freezing outside with the antennae and the lack of oxygen made me so tired! Whilst we were up there some of the work actually got stopped because the wind was picking up again. Just a clear example of the challenges this huge project faces.

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