EPFL revamps the CERN's power supply

A new electricity supply system enabling the provision of all the necessary energy to the particle accelerators and their magnets has recently been commissioned at CERN. Within a few seconds, it can generate a current surge of 60 megawatts; the same combined power that 600 car engines at full throttle would produce.

The result of cooperation with EPFL’s Industrial Electronics Laboratory, this installation is essential for the smooth running of the experiments conducted in the various accelerators at CERN. These instruments – of which the most impressive and well-known is the Large Hadron Collider (LHC), 27km long, lying at 100 meters underground in the Geneva area – use electric or magnetic fields to raise the speed of the particles so that they are fully charged with energy, and to make them collide. They are used to study the ultimate components of matter within the framework of fundamental research in physics.

The new electric system, called POPS – which stands for “POwer for PS” – supplies the proton synchrotron (PS). The first ever to have been put into operation, in 1959, the PS belongs to CERN’s current group of accelerators. Its 101 electromagnets supply mainly the electrical impulses enabling the acceleration of the particle beams in the super proton synchrotron (SPS) and the LHC. A breakdown would therefore mean that almost all the experiments would stop.

The main challenge was that the PS must very rapidly deliver very powerful electric impulses and then absorb the energy again at each cycle of the accelerator two seconds later in order to obtain a constant and highly stable supply of energy. To quickly establish a current of the order of 6 kA in the magnets, a power level of 60 megawatts (MW) is required; a power surge which would be very difficult to take directly from the grid.

In modules of six

These new installations operate according to the principle of “supply by multilevel converters with integrated storage”, a concept developed at EPFL, and which is being patented. It is based on the use of capacitors grouped in six modules and connected in a circuit. A topology supplies the magnets, powered to approximately 10kV, and enables them to store and exchange energy more easily and in a more continuous manner with the magnets, obtaining the immense stability required for efficient particle flow in the circuit.

This system replaces the one which was installed over forty years ago. The principle of storage adopted then used a bigger momentum wheel, that was much less reliable, incurred more energy loss, and was very expensive to maintain.

For more information, read Claude Fahrni’s thesis, “Principe d’alimentation par convertisseurs multiniveaux à stockage intégré – Application aux accélérateurs de particules” (Principle of supply by multilevel converters with integrated storage – Applied to particle accelerators)