1. Avoid accidents with superconductive magnets in LHC.
What if protons collide with the magnets?

2. 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.
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CERN HST 2001

3. 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 A, so a temperature below 2 K is needed for safety reasons
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CERN HST 2001

4. 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
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CERN HST 2001

5. This means on the diagram
If the temperature of the spot rises higher than 5 K, Niobium-titanium no longer is superconductive.
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CERN HST 2001

6. 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
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CERN HST 2001

7. 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
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CERN HST 2001

8. 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
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CERN HST 2001

9. 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
04/04/2019
CERN HST 2001