American-magnetics Current Leads for Cryogenic Systems Manual Manuel d'utilisateur télécharger pdf (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.

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American-magnetics Current Leads for Cryogenic Systems Manual Manuel d'utilisateur Page 7