Routine POMPOM sensor test procedure

The POMPOM (polarity monitor) sensors must be checked annually for radiation damage. This is done by ramping up the dipoles and measuring directly the output voltage via the breakout box in the trench. Access to the magnets themselves is not required.


  • Powering the dipoles requires the Muon Beam Permit from the PPS, as well as the usual ATW, RA/MS (probably 001), trained operator, etc.
  • Voltmeter - the large orange one from the Rack Room
  • Pair of 4mm-4mm test leads
  • Printout of attached test form: POMPOMsTestForm-1.0.pdf


  • Prepare magnets for use following usual procedure and checklist
In Trench,
  • Measure power supply voltage between "+12 V" and 0V outputs on breakout box:
    Power supply and breakout box
    • The "+12 V" socket is covered by a flap of masking tape to keep out dirt. Take care not to knock the nearby webcam when working with the breakout box.
  • If necessary, adjust power supply to get as close to 12.00 V as possible. Note value on form.
  • Ramp dipole to each current indicated on the test form, and note down sensor output voltage at breakout box
    • Ensure the current has stabilised. It is not necessary to wait the full 60 s for the field to settle, as the error is negligible for this task
    • Expected voltage ~5.8 V at 0 A. At operating current (>50 A) 1 - 1.1 V in negative polarity and 9.4 - 9.5 V in positive polarity.
    • The dipole controls are not stable at low current. If the current starts to oscillate about the set point:
      • switch OFF,
      • set current to 0 V
      • switch ON
      • skip troublesome setting and move on to next point
Once complete,
  • Check power supply voltage between "+12 V" and 0V outputs on breakout box
  • Shut down magnets according to usual procedure
  • Return results form to Henry

Updated by Nebrensky, Henry over 10 years ago · 5 revisions