Video-Based Magnet Operation Tutorial

The following outline provides short descriptions and example video clips illustrating the procedures necessary to install and operate an AMI-provided superconducting magnet. The videos are not intended as a replacement for the provided printed manuals. The intent is to further clarify the required steps for installing and operating a superconducting magnet for inexperienced customers. Click the video clip icon to open a video. DSL, T1, or cable modem bandwidth connection recommended for real-time viewing.

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Page 7: Example Magnet Operation

Charging the Magnet
To charge the magnet to a desired field:
  1. Power-on the Model 420.
  2. Check the Model 420 setup parameters against the provided settings sheet and the magnet specification sheet.
  3. Power-on the power supply.
  4. Check the programmed current, voltage limit, and ramp rate settings. Do not exceed the limits specified on the magnet specification sheet.
  5. Turn on the persistent switch heater and wait until the Model 420 indicates the switch heating time has expired.
  6. Press the RAMP/PAUSE button to begin ramping the magnet current. Note the magnet voltage meter shows an increase to an approximately constant charging voltage during the ramp.
  7. Once the programmed current is achieved, the magnet voltage will decay to zero volts.

Lock-In (Persistent Mode)
The term "lock-in" refers to cooling the persistent switch to a superconducting state so as to circulate the magnet current entirely within a superconducting circuit. Depending upon the design of the magnet, the field may then persist for days, weeks, or months.

To "lock-in" the magnet:

  1. Deactivate the persistent switch heater control of the Model 420 and allow time for the switch to cool to a superconducting state.
  2. Begin ramping down the power supply current by pressing the ZERO button of the Model 420. You may substantially increase the ramp rate since the magnet current is now independent of the power supply (the power supply essentially sees a short-circuit condition across its terminals).
  3. Once the power supply current reaches zero, power-off the power supply followed by the Model 420.
  4. If your magnet system is so equipped, you may retract the vapor-cooled current leads in order to minimize external heat conduction to the magnet (and preserve the LHe).

Discharging the Magnet
In order to discharge the magnet (i.e. remove any stored energy in the magnet), it is necessary to remove the magnet from the "locked-in" or persistent state. Do so by:
  1. Reseat the vapor-cooled current leads if your magnet system is equipped with retractable leads.
  2. Power-on the Model 420 followed by the power supply.
  3. Using the same programmed current and ramp rate stored from the "Lock-In" procedure, ramp the power supply current up to the value at which the magnet was "locked-in".
  4. Once the programmed current is achieved, activate the persistent switch heater control of the Model 420.
  5. Once the switch heating time has expired, the magnet is connected to the power supply system circuit. Decrease the ramp rate setting to the limit specified on the magnet specification sheet.
  6. Press the ZERO key of the Model 420 to initiate a rampdown to zero current.
  7. Once zero current is achieved, power-off the power supply followed by the Model 420.

At this point, all stored energy in the superconducting magnet has been removed. The user may then choose the maintain adequate LN2 and LHe levels in the dewar for future sessions, or the user may choose to remove the magnet and support stand assembly from the dewar.

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