Energy Extracting and Quench Protection System in the LHC

quadrupole magnets. The electromagnets are built of special cables that operate in superconducting state by cooling them to 1.9K (-271.3℃); the superconducting magnets of the LHC are powered in about 1700 electrical circuits. A phenomenon called quench can spontaneously occur in superconducting magnets, which means that the superconductivity is lost in part of their windings. The energy stored within the magnet, up to 1.3 GJ, can cause severe damage. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into a dump resistor installed in series with the magnet chain that is switched into the circuit by opening circuit breakers. The system described above is utilized for magnets installed in the LHC that operate under currents ranging from 600A up to 13kA. For the next LHC upgrade (High Luminosity) there is a need for circuit breakers capable of interrupting high DC currents in a solely inductive circuit within one millisecond and under development of very high voltage across it, therefore specially designed DC- breakers are developed at CERN. Mechanical circuit breakers can withstand a DC current up to 600A, by splitting it in 3 parallel branches with 200A each, but for higher currents (7.5 – 30 kA), another approach was developed using solid state switches to ensure an ultra-fast energy extraction system that prevents overheating of the magnet during quench process. The energy extraction system of the 600A concept is based on three, series connected, fast, mechanical 3-phase AC breakers, specifically equipped with a DC arc chutes. The three, simultaneously operated poles are connected in parallel to carry the 600A DC. For the 30kA system illustrated in figure 1, 16 IGBTs are used, each 8 IGBTs are grouped together in parallel with a 15kA current that is supplied by a power converter, and each 4 IGBTs are mounted within one rack that takes 7.5kA (with ~1.9 kA/IGBT). The total current (30kA) will be fed to the superconducting magnets in order to bend or focus the beams. The present system will be used on a stand where magnets for a future upgrade of LHC will be tested.