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

Rev. 5, July 2003 Page 7 of 10
V. BREAKAWAY CURRENT LEADS
Break-away vapor cooled current leads (Figure 2) represent a popular configuration for long-
term, persistent magnet operation. Break-away leads are supplied in two sections so that the
upper section can be disconnected from the lower section during persistent magnet operation.
Helium consumption is significantly reduced because the 300K to 4K thermal conduction path
through the current leads is eliminated.
A. DISCONNECTING THE CURRENT LEADS:
WARNING: All AMI current leads are designed to be connected
and disconnected with zero current flow. NEVER connect or
disconnect current leads whileany current is flowing through them.
Attempting to do so could result in FATAL ELECTRIC SHOCK.
WARNING: Breakaway leads should be connected and
disconnected only by qualified personnel.
1. Ensure a zero current state exists and verify with an appropriate instrument.
2. Disconnect power supply cables from the warm terminals of the breakaway
current leads.
3. Loosen the brass fitting on the upper section of the breakaway current lead. It
may be necessary to warm the fitting with a heat gun to melt any ice or frost
which may be present.
4. Lift up on the upper section of the breakaway current lead, while slightly rotating
it back and forth. You should be able to feel the current lead disconnect from the
lower section. (Do not use excessive force if the current lead cannot be
disconnected as ice may be present at the connection point. Ice can be removed
by flowing room temperature helium gas through the top of the lead into the
cryostat where the connection is located.)
5. At this point the current lead can be lifted another few inches and the fitting can
be re-tightened. (Alternatively, the current lead can be completely removed and
replaced with NPT pipe plugs.)
6. Seal off the vapor exhaust from the current leads to prevent air from entering the
cryostat. This could cause ice formation on the male connector and make
reconnection of the current lead difficult or impossible.