University of Wisconsin-Madison

First Year Performance Paper - Section 2.3.1

2.3.1 Drilling and deployment

Strings of modules are deployed into holes drilled with hot water. The most critical and demanding component of the IceCube deployment process is the forced hot water drill system. The plant for producing the drill water comprises a total of 15 buildings that host the hot water heaters, generators, pumps and storage tanks. These buildings are set up in a temporary equipment camp during each season.

A supply hose from the equipment camp to the drill site connects to the hose winch, which can support a single 2.5 km long drill hose. The nozzle of the hot water drill is connected to the end of the drill hose and lowered into the hole at the rate ice is melted by the hot water. A return hose carries cool water from the hole back to the heating system. Cables for both drilling and deployment are fed through a hole in the roof of a tower operating structure, which is a building located over the hole. The tower is heated and contains a control room for drilling and deployment operations. A water-filled hole is prepared to a depth of 2.5 km with a minimum diameter of 60 cm. This is wide enough to insure a 45 cm diameter cylinder of water remains when the string of DOMs is later deployed. The drill hose is removed and rewound on the hose winch, and the tower is then available for deployment.

After building up the equipment site and assembling the tower and drill system for the first time, the hole was ready for string deployment on January 27, 2005. The deployment of String-21 took a total of 18 hours. The following day, the string was connected to the junction box, and commissioning began.

Soon after deployment the PMT rates rose dramatically because of triboluminescence caused by stresses in the ice forming near the DOMs as the water in the borehole refroze. The time for the water in the hole to refreeze varied with depth, from 5 days at 1.5 km to more than two weeks at 2.5 km. After the refreeze was complete, DOM rates decreased to a typical noise level of 650 Hz. When a dead-time interval is enforced to remove pulsing correlated in time within the same PMT, the noise is reduced further. This is shown in Fig. 4. Such a low noise rate is favorable for searches for low energy neutrinos from stellar collapse, the detection of which would follow from an observation of a simultaneous increase in the overall counting rate [29].

Noise Rates when after-pulsing is suppressed. DOMs are numbered in sequence from 1 (highest) to 60 (lowest).
Noise Rates when after-pulsing is suppressed. DOMs are numbered in sequence from 1 (highest) to 60 (lowest).