In early January ALICE’s time projection chamber (TPC) moved 300 m from the assembly hall to the experiment cavern, taking four days to complete the journey. This 5 m wide, 5 m diameter cylinder weighs 8 tonnes and is extremely fragile.
The first steps included lifting the TPC with an overhead crane from the cleanroom in the assembly hall and positioning it onto four hydraulic jacks, which raised the TPC to 80 cm. Then a flatbed truck gently slid under the structure and carefully carried it to the entrance of the cavern, making sure not to tilt it more than 2°. The next step was to lower the cylinder 50 m into the ALICE cavern. This proved challenging, with just 10 cm of leeway between the delicate TPC and the shaft walls. Finally, a gantry crane moved the TPC close to its final position within the solenoid magnet, where work will begin on installing the internal tracking system.
The TPC consists of very light, fragile carbon-fibre. The surface structure, or field cage, is covered with 30,000 mylar strips secured with the utmost precision. The two endcaps carry electronic read-out channels. These are connected by several thousand flat cables to two service support wheels, which provide support for the electrical, electronic and gas-supply systems. In May, the TPC will be tested in its underground location using cosmic rays.
