超导物理学3.ppt

Lecture 3: Cables and quenching
Cables
why cables?
coupling in cables
effect on field error in s
Quenching
the quench process, internal and external voltages
decay times and temperature rise
propagation of the normal zone
quench protection schemes
protection of LHC
Rutherford cable
used in all superconducting accelerators to date
Martin Wilson Lecture 3 slide1
Superconducting s for Accelerators JUAS Feb 2003
Why cables?
for good tracking we connect synchrotron s in series
if the stored energy is E, rise time t and operating current I , the charging voltage is
V = 2E / (I t)
the RHIC tunnel
RHIC E = 40kJ/m, t = 75s, 30 strand cable
cable I = 5kA, charge voltage per km = 213V
wire I = 167A, charge voltage per km = 6400V

SIS at GSI E = 40kJ/m, t = 4s, 30 strand cable
cable I = 5kA, charge voltage per km = 4kV
wire I = 167A, charge voltage per km = 120kV
so we need cables and high currents!
a single 5mm filament of NbTi in 6T carries 50mA
posite wire of fine filaments typically has 5,000 to 10,000 filaments, so it carries 250A to 500A
for 5 to 10kA, we need 20 to 40 wires in parallel - a cable
Martin Wilson Lecture 3 slide2
Superconducting s for Accelerators JUAS Feb 2003
Types of cable
like the filaments posite wires, cables must be twisted to reduce coupling
because cables are so large, they generate a significant self field and it is necessary to 'twist' against this self field,
note how in this cable there are flux linkages between the inner and outer wires 
Bself
thus it is necessary for the wires to be fully transposed, ie every wire must change places with every other wire along the length of the cable
three types of fully transposed cable have been tried in accelerators
- rope
- braid
- Rutherford
Martin Wilson Lecture 3 slide3
Superconducting s for Accelerators JUAS Feb 2003
Rutherford cable
the cable is insulated by wrapping 2 or 3 layers of Kapton. The outer layer is treated with an adhesive layer for bonding to adjacent t