"Why superconducting magnets? - PowerPoint - PowerPoint"
Avoid accidents with superconductive magnets in LHC. What if protons collide with the magnets? An important diagram Only under the 2 dimensional surface in a 3 dimensional space the material used for the wires of the magnets, niobium- titanium, is superconductive This surface is determined by temperature, magnetic induction and current density. 11/06/2012 CERN HST 2001 An important diagram(2) To be save it is necessary to stay far from the surface, it limits current densities, magnetic induction and temperature. In LHC B must be some 9 T, current some 13 000 A, so a temperature below 2 K is needed for safety reasons 11/06/2012 CERN HST 2001 What happens if a proton hits the magnet? Sometimes a proton could hit de side of the tube, hitting a superconducting magnet The collision point heats up This spot is no longer superconductive 11/06/2012 CERN HST 2001 This means on the diagram If the temperature of the spot rises higher than 5 K, Niobium-titanium no longer is superconductive. 11/06/2012 CERN HST 2001 Catastrophy? Heat due to Ohm’s law is generated This causes the non-superconductive spot to become larger quickly, and more heat is generated Etc... The experiment breaks down 11/06/2012 CERN HST 2001 Unless... The heat of the initial collision spot is taken away. Superfluid helium takes care of that: it flows all over, the magnets swim in this fluid the heat capacity of helium becomes larger with lower temperatures, one of the reasons why the temperature is so low 11/06/2012 CERN HST 2001 As a consequence The helium must flow constantly and cool permanently, taking the heat of accidental collisions away The circuit should continuously be able to cool all helium to this low temperature They will need 5000 tons of helium in this giant magnet, the production of the whole world during one year 11/06/2012 CERN HST 2001 If this is not enough The beam must be taken out of the tubes A kicker magnet kicks the 2850 bunches of protons into a larger magnetic field, allowing the protons to bend into a pipeline of 100m long. Another magnet disperses the proton bunches to bigger surfaces to collide with, the energy is absorbed by special materials (mainly graphite) at the end of the tunnel 11/06/2012 CERN HST 2001