LHRS for GMn

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Nominal Settings

The nominal current for the LHRS is X A

  • When starting a shift, it is prudent to verify that the magnets are set correctly. If it's not right, consult the RC. Currents should be within about 0.5 A of the values. Also, note that "readback" values are slightly different from "set point" values.
  • The LHRS dipole NMR doesn't lock. Need to set manually to match the field value (iterative procedure, see the instruction below)
  • Below are set points. Readbacks will be a bit lower.

Setting the LHRS Magnets

If one can not reset the magnet remotely: Do NOT go into the hall to reset by yourself. Contact RC and then tech on-call/magnet expert. Regulators for Q1, Q2, Q3 are always OFF. Q1, Q2, Q3 magnets will be set by current.

0. Clear all faults (if there are still problems with flows or liquid levels there is no point ramping back up to crash again).


  1. Regulator OFF (because of NMR multiplexer problems. Directions to proceed are here)
  2. Set the current to 744.0 followed by the procedure
  3. Wait until the field is stable (watch the strip chart). Check that the Hall probe matches the target value (XYZ ± XYZ) when it is stable
  4. Adjust the current if they do not match. Repeat step 3.

If the dipole turns off, to turn it back on:

  1. Zero
  2. Reset
  3. On
  4. Type in the desired current and hit enter

If this does not work, notify the RC.


  1. Check that the regulator is OFF for Q1, Q2, and Q3
  2. Turn on the Q1 power supply if it is not ON already
  3. If turning a quad magnet down, we do not need to cycle the magnet. Just set the set point.
  4. If turning a quad magnet up, it must be cycled to always follow the same hysteresis curve
    1. Q1: The LQ1 should be run to 900 A. Let it stay at 900 A for roughly 2 minutes before loading the desired set point.
    2. Q2: The LQ2 should be run to 1600 A. Let it stay at 1600 A for roughly 2 minutes before loading the desired set point. First ramp to 100 A. If it does not trip, then ramp to 1600 A.
    3. Q3: The LQ3 should be run to 1600 A. Let it stay at 1600 A for roughly 2 minutes before loading the desired set point.


Bringing Up the GUI

The LHRS GUI can be found at:

OPS Menu -> EDM (HLA) -> Hall A -> Tools Display

Checking Polarity

LHRS dipole polarity changes require an access. The rest can be changed with the power supply GUI.

One should check the polarity with Gaussmeter. The Hall probes should read positive for positive particles and negative for negative particles (with current in the magnets)

show image

Checking and Controlling Drifts

Notes from Javier

  • The L-HRS NMR is not currently working, so one should go by the Hall probe field, which however is not as accurate as NMR.
  • When an IOC is rebooted, the set points are put to the observed read-back values, and this might not be what you want! (probably not, in fact)
  • The dipole is an iron dominated magnet so its actual field will change with current history (the reason to define hysteresis cycles) so, neither set or read-back currents are reliable. After a large current change, you will see both Hall probe and NMR (if it was working) changing (dp ~ several 10-3) over many hours.So, you want to use the Hall probe if the NMR is not available and adjust by hand as needed. Unfortunately, the Hall probe was not calibrated vs NMR measurements - you have to find a previous setting, preferably near to desired setting. Also, keep in mind that the Hall probe has lower precision than the NMR probe.
  • Rebooting an IOC. Note that there are differences between the set and read-back currents of the power supplies. There are many reasons for these differences. We use the read-back currents to determine the momentum of the quads based on cross checks done long time ago. The dipole currents are nor really relevant for the reasons described above. When an IOC is rebooted, it needs to initialize all its variables (these IOCs do not have such thing as an entire image of the system from x -time ago). One thing that it needs to do is to initialize the set current variables. It uses the read back currents to do so which will cause some changes in the magnets currents