Magnets

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In the process of editing and updating this page. Please contact Juliette Mammei crowder@jlab.org with questions or suggestions.

PREX Main<< HOW TOs


Nominal Settings

PLEASE READ HOW-TO BEFORE SETTING THE MAGNETS!!!!!

  • 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.
  • 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.
  • CREX LHRS
Dipole Q1 Q2 Q3
Hall Probe: -0.7775 225.387 A 934.273 A 981.301 A
  • CREX RHRS
Dipole Q1 Q2 Q3
p0 = 2.18350 230.916 A 925.955 A 981.301 A
PREX Tune P
LHRS Dipole LQ1 LQ2 LQ3
p0 = 0.95285 118.50 A 407.70 A 450.76 A
RHRS Dipole RQ1 RQ2 RQ3
p0 = 0.95284 118.55 A 404.07 A 446.90 A

Setting the 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.

Set HRS Magnets

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

RHRS Dipole

  1. Regulator ON
  2. Set the target momentum and hit enter. The dipole should start moving towards that setting.

LHRS Dipole (New instruction for CREX)

  1. Regulator OFF (why not using NMR? https://logbooks.jlab.org/entry/3747901)
  2. Set the current to 774.576.
  3. Wait until the field is stable. Check the Hall Probe if it matches the target value (nominal CREX: -0.7775 +/- few 1.e-4) when it is stable.
  4. Adjust the current if they don't match. Wait until it gets stable and repeat #3 if needed.

Quads

  1. Check regulator OFF for Q1, Q2 and Q3
  2. Turn on the Q1 power supply if 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. Right:
      1. Q1: The RQ! should be taken to 900A. Let it stay at 900A for about 2 minutes before loading the desired set point. (NB in the past the RQ1 has had problems reaching 900A so if you cannot do that make a log entry and go to 700A)
      2. Q2: The RQ2 should be run to 1400A. Let it stay at 1400A for about 2 minutes before loading the desired set point.
      3. Q3: The RQ3 should be run to 1400A. Let it stay at 1400A for 1 minute before loading the desired set point. Do NOT leave RQ3 at 1400 A more than 5 min (but leave it there for 1 min)!!
    2. Left:
      1. Q1: The LQ1 should be run to 900A. Let it stay at 900A for about 2 minutes before loading the desired set point.
      2. Q2: The LQ2 should be run to 1600A. Let it stay at 1600A for about 2 minutes before loading the desired set point.
      3. Q3: The LQ3 should be run to 1600A. Let it stay at 1600A for about 2 minutes before loading the desired set point.

Set Septum Magnet

CREX Septum SBS power supply
CREX Septum HES power supply
  • The polarity of the septum is positive
  • Instructions for setting the current Jack's elog entry.
  • CREX set points determined here.


To check/set the septum current:

  • In JMenu:
    • Operations < Magnets < Special Hall Magnets < Septum Magnet (Hall A)
    • The Hall A Septum screen will come up (see Figure 1)
  • From the Hall A Tools screen:
    • Find the HES power supply link in the top right of the GUI
  • For CREX we are running high, with negative polarity in both the SBS and HES power supplies
    • Cycle the magnet to 400 A (PREX), -900 A (CREX)
    • Set it to 333 A -- nominal Tune (PREX), -801.2474 A (CREX)


To reset the Septum magnet power supplies (CREX) after some problem (from Jack's log entry):

  • Auxillary switches on the main contactors are wired in series with a relay
    • Relay contacts are wired to fault inputs on the supplies
    • Turning one supply OFF, or the supply faulting OFF, will fault both supplies to OFF
  • To turn the supplies ON you need to open the GUIs for the HES supply and the Super BigBite supply (above)
    • On the HES GUI you need to click on the Handshake Bypass button
      • This will short out the contactor switches for two minutes, 120 seconds
      • State will change to On and Counter will change to 120 and count down to 0
    • You now have 120 seconds to do the following:
      • Reset a supply and the fault should clear
      • Turn the supply ON
      • Reset the other supply and its fault should clear
      • Turn the supply ON. After this point, if the Counter reaches 0, the supplies will not trip off unless there is a fault or one is turned OFF
    • Please note that the Super BigBite supply is not stable at 0A
      • If it needs to sit for some time while ON, it is best to have it set to 150A or higher
      • Brief periods at 0A are not too bad, though

Monitoring the Magnets

HRS

GUI can be found at:

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

How to check polarity

LHRS dipole, RHRS 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)

  • PREX polarity and CREX polarity (Signs of field should be the same!)

Septum

GUI can be found at:

OPS Menu -> EDM (HLA) -> Hall A -> Magnets -> Super Big Bite
OPS Menu -> EDM (HLA) -> Hall A -> Tools Display -> Top Right of GUI has HES Dipole button