American Magnetics Current Leads for Cryogenic Systems Brochure - Manual (Page 7)

OTHER TYPES OF CURRENT LEADS (CONT.)
BRASS LEADS
Current leads are also available using brass (Cu/Zn) conductor. Because brass has higher thermal and
electrical resistivity, these leads will have higher losses during charge mode but lower losses in standby mode
compared to copper leads. Brass leads are a good choice for systems operating in standby or persistent
mode for long periods of time.
HIGH CURRENT LEADS
AMI routinely designs and manufactures custom
designed current leads over 10,000 amperes. These
current leads are designed for the same low helium
boil-off and high reliability as our standard leads.
Custom configurations are available for both the
warm and cold end connections.
BUS BARS
Bus bars carry the current between the magnet and the current leads. Unlike
standard NbTi superconducting lead wires, AMI optimized bus bars will carry the
rated current even as the level of helium drops across the full height of the bus
bar. This prevents magnet quenches from being initiated in the lead wires due
to normal fluctuations in liquid helium level and extends your useful helium level
operating range. AMI superconducting bus bars are designed to span the
distance between the cold end of a current lead and the magnet leads.
Resistance heating (I
2 R) is eliminated because the bus bar is superconducting and
thus liquid helium boil off is minimized. Most bus bars are a soldered laminate
of Nb
3
Sn/Cu and will remain superconducting as long as the lower end, closest to
the magnet, is kept at liquid helium temperature. These bus bars are specifically
designed to self supply enough helium boil off so that the operation of an AMI
vapor cooled lead is optimized over the full operating range so long as the cold
end of the bus bars is always in contact with the liquid helium. The choice of
Nb
3
Sn/Cu also provides good critical current performance even in the presence of
high background magnetic field.
High Current Leads with custom upper and lower contact points
80,000 Amp Bus Bar with Vacuum Seal
Current
Lead
Bus Bar
Maximum Liquid
Helium Level