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Lake Shore Model 625 Superconducting MPS User’s Manual
2-2 Magnet System Design
The superconducting wire is wound around a non-magnetic former made from aluminum, brass, stainless steel, or other
material as needed. The individual windings are electrically insulated by the insulation on the wire and by an epoxy that
is applied to the windings. The epoxy is also necessary to keep the individual windings from moving when the magnet is
charged.
Figure 2-1. Typical Superconducting Magnet
2.2.2 Magnet Inductance
The inductance of a solenoid (L) is defined as L = μ
0
n
2
A/l, where μ
0
is the permeability of air, n is the number of turns, A
is the cross sectional area of the coil, and l is the length of the solenoid. The inductance of superconducting magnets is
fairly large, typically between 10 and 100 Henries. The magnet’s inductance limits the rate at which the magnet can be
charged or discharged because of the increased voltage required to change current. The formula V = L (
di/dt ) relates
charging voltage to inductance where V is the charging voltage, L is the magnet inductance, and di/dt is the rate of
change in current. The Model 625 can charge a magnet up to a 5 V rate, although many magnets are not designed to be
charged at that rate. For instance, a 10 Henry magnet can be charged at a rate of 0.5 A/s with a 5 V limit. A rate of 0.1
A/s is more typical.