Linde Kryotechnik, the Swiss-based cryogenic specialist and part of the Linde Group’s Engineering Division, has developed a ground-breaking refrigeration system used to cool extreme temperatures in an experiment to create fusion fuel.

The Max Planck Institute for Plasma Physics (IPP), developed the Wendelstein 7-X (W7-X) fusion device in Greifswald, Germany, which successfully generated hydrogen (H2) plasma for the first time in a fusion experiment.

The objective of the project, which will run for the next four years, is to demonstrate the ability of continuous operation under plasma conditions. Ultimately, this will enable the harvest of energy from the fusion of atomic nuclei to create fusion fuel.

The IPP suggest that as little as one gram of fusion fuel can deliver the same amount of energy as 11 tonnes of coal, and could potentially power the world’s energy needs indefinitely.

Linde Kryotechnick developed the pioneering refrigeration system used in the experiment, which is capable of cooling the W7-X’s 50 magnetic coils to super-conduction temperature (close to absolute zero) with supercritical helium (He). The unique cooling system, which began being developed in 1997, is one of the most sophisticated and complex refrigeration plants ever built.

One gram of fusion fuel can deliver the same amount of energy as 11 tonnes of coal, and could potentially power the world’s energy needs indefinitely.

With fusion running within the plasma superheated to around 100,000,000°C, strong magnetic fields are vital in order to prevent the plasma from coming into contact with the fusion chamber wall and cooling down. Confined in the magnetic cage generated by W7-X, the charged particles levitate, and therefore maintain their temperature.

Due to the unique properties of He, the start-up of the system leaves no scope for the slightest error, so the revolutionary developments of the procedure lie primarily in the control of the system, especially the starting sequence of the cold compressors and He pumps. 

The industrial gas giant also supplys an on-site 10,000 litre Dewar for the experiment, which allows for temporary storage of liquid He and enables fast transition between operating modes. The He refrigeration system, consisting of 15 machines, is self-adjusting, having the capability to quickly connect or disconnect from each W7-X consumer via 100 control valves and 500 analogue signals.

Linde’s refrigeration operation was designed to service multiple components including magnetic coils, coil housings and support structures, cryo-vacuum pumps and shield and the cryostat heat radiation shield, in order to successfully cool the W7-X.

Since the start of its operation on 10th December 2015, the W7-X has produced more than 300 discharges with He, which served primarily to clean the plasma vessel as the plasma temperature increased, and finally attained a temperature of 6,000,000°C.

This current experimentation phase will last until next month, when the plasma vessel will then be opened in order to install carbon tiles for protecting the vessel walls and a ‘divertor’ for removing impurities. Subsequently, successive extensions are planned for the project.