American Magnetics 420 Power Supply Programmer - Manual (Page 78)

60 Rev. 7
Operation
Persistent Switch Heater
3.4.1 Procedure for Entering Persistent Mode
In order to enter the persistent mode of magnet operation, the operator
should perform the following steps:
1. Use either the programmed or manual ramping modes of the Model
420 to achieve the desired current or field.
2. The Model 420 should be in either the HOLDING or PAUSED
mode at the desired current or field.
3. Record the desired current or field setting.
4. Deactivate the switch heater control (the LED indicator should
extinguish).
5. Wait until the switch heater is completely cooled before changing
any parameters. Most persistent switches cool to superconducting
state in a few seconds if completely submerged in liquid helium.
6. Once the switch has cooled, the Model 420 may be used to ramp the
current to zero at an increased ramp rate (since the magnet is no
longer in the circuit). Using the ZERO mode is recommended since
it allows the programmed current/field to remain unchanged for
future sessions.
7. Once at zero current, de-energize the power supply first, then
power-off the Model 420 instrument.
3.4.2 Procedure for Exiting Persistent Mode
To exit the persistent mode of magnet operation, the operator should
perform the following steps:
1. If the Model 420 has been powered-off, then first energize the
Model 420. After the Model 420 has been energized, energize the
power supply.
2. Using the value of current or field recorded when the magnet last
entered the persistent mode, use either the programmed or manual
ramping modes of the Model 420 to achieve the last recorded value
of current or field.
3. The Model 420 should be either in the HOLDING or PAUSED
mode at the last recorded value of current or field.
4. Activate the switch heater control (the LED indicator should
illuminate). Note that the Model 420 will enter the HEATING