Preparations for operation of Wendelstein 7-X now in full swing

Target temperature of four kelvin attained / evacuation of plasma vessel started

Preparations for operation of the Wendelstein 7-X fusion device at Greifswald are in full swing: A decisive stage is cooling the superconducting magnet coils, which will later generate the magnetic cage for the hot plasma. This step has been preceded by extensive preparations, including cleaning and flushing the numerous helium cooling pipes and starting up of the previously thoroughly tested cryo-plant. It produces the low-temperature liquid helium by means of which the coils and their insulating cryostat vessel are to be cooled to four kelvin, i.e. minus 269 degrees Celsius or four degrees above absolute zero.

On 13 February a start was made to cooling the cryo-plant slowly along with the device. During this stepwise refrigeration all systems were carefully monitored. Especially checking for leaks in the piping or cooling system was a matter of great suspense.

Four weeks later, on 10 March, the target temperature of four degrees kelvin was attained, this being an essential milestone and the prerequisite for making the magnets superconductive. In this state the current can flow in the magnets with almost no loss; no energy is needed for the magnetic field. Checking the cooling system will still take some time yet; presumably in May the magnets will be tested for the first time while powered.

On 12 March the last of the over 200 ports in the plasma vessel were sealed vacuum-tight and evacuation of the vessel could start. At present the search for vacuum leaks at the numerous connections and seals is proceeding. Also the periphery of the device is being completed and work is being done on the switchgear and cabling. Finally, the measuring equipment is being made ready for operation, which later is to diagnose the properties of the plasma. The first plasma in Wendelstein 7-X is expected by the end of 2015 at the latest.