December 18, 2009, South Pole Station –
Four Phases of the IceTop Deployment Season
As the first IceTop crew leaves South Pole, the most hectic time of the IceTop deployment season is over: 28 tanks are laid out, 28 Freeze Control Units (FCUs) are calibrated and installed, about 19,600 gallons of filtered water poured in 28 tanks, sunshades installed, power cables laid out and connected, 56 Digital Optical Modules (DOMs) are installed, connected and checked. Aah! This is amazing work in such a short time and under unearthly temperatures of -50C with the wind chill, or worse.
The second phase of the deployment is mostly about babysitting the tanks, making sure all are behaving normally, excess water is discharging regularly, water is freezing properly without many bubbles and cracks. Emergencies can still happen, especially during the nasty storms. It never snows at South Pole, but gusts can drift a lot of snow and cover everything in no time. Even a couple of inches of snow inside the tank insulates the ice and slows down the freezing process. We can not go out to clean off the snow during the storm, but we have a lot of fun “playing” with a lot of snow afterwards!
Here is a freezing history of a tank from the 2008–2009 deployment season. Each color is a temperature profile of a sensor on the side of the tank. Red is the top sensor above the ice, green is the first one inside the ice, blue is 6 inches below that. Can you tell the dates of the storms? Just watch the temperature of the sensor shown with green symbols. On Dec. 23, 2008, a new record was broken in South Pole history for that day--31 mph gusts were recorded, lasting two days. The crew, led by Len Shulman, did a good job clearing the snow off of the tank, but three days later the storm came right back, covering the ice yet again. Nevertheless, the tank froze completely on time by Jan. 20, 2009.
The third phase of the deployment starts when all the tanks are frozen. The IceTop pits are backfilled, sunshades are taken off, 40 cm of insulation is poured on top of the ice, tank lids are closed, and the freeze control units are removed. During these operations, we get to drive the IceCube van, which adds extra excitement on its own. Even when driving it at careful speeds of 20 mph the speedometer shows 100 mph due to its track system!
The excitement reaches its apex in the final phase. It is time to turn on the power to the DOMs. Will they all talk to us? Will they all give good quality signals? Each DOM is checked one by one, calibrated, and commissioned. They are then declared to be ready to take data.
By this time, the sun starts to circle lower and lower above the South Pole, the colors change. When the shadows get really long, we know it is time to leave South Pole. The last plane is usually around Feb. 15, and we make sure we are on it.