Persistent switches

The presence of a persistent switch allows a magnet to remain energized without the need for a constant power source. The model 430 power supply programmer controls transitioning between driven and persistent modes at the press of a button. A magnet operating in persistent mode provides long period field stability and reduces helium boil off in wet systems. Field decay occurs in every magnet operating in persistent mode and the rate varies upon several factors. A persistent field may decay out of homogeneity tolerance over weeks, months or years depending on design. Please note how long you require the magnet to be in persistent mode so that we may consider this during design.

The switch is an integrated superconducting short in parallel to the magnet current leads. While ramping the magnet (driven mode) the short is heated and is driven to a 15 to 20 ohm parallel resistive path. In this mode, the magnet charges and discharges normally. To enter persistent mode, the short is allowed to cool, returning it to the superconductive state. The magnet’s current may then flow through the short, sustaining the field through an integrated path for current. The current leads may then be de-energized and disconnected until the magnetic field needs to be changed.