How to operate and monitor the Spectrometer Magnets

Magnet Controls Screens

• Magnet screen is brought up on any hcdesk machine by the command go_magnets
  • Note: only ONE copy of the magnet control GUI screen can be running. Creating a new one will cause the old one to disappear.

SHMS Magnets and HMS Quads

• The SHMS magnets are set by current from the desired momentum. From any hcdesk computer, run:

go_magnets_SHMS_current P

• The HMS quad magnets are set by current from the desired momentum. From any hcdesk computer, run:

go_magnets_HMS_current P

where P is the desired momentum in [GeV/c]. This will return the current (in Amps) needed to set each of the magnets.

• This script will ask if alarm limits should be set. If you answer yes, then the alarm handler will show an alarm for any magnet with a set current that does not agree with the desired momentum. Also, the MOL (Minimum On Loop) and Target (desired) currents will load in the individual magnet GUIs for each magnet.
• For precision physics data-taking, the magnets should be put "on loop". Turn off the beam prior to ramping the magnets to put them on loop.
• From the main magnet GUI, click on the box for the current to bring up the screen to set each magnet by current. The procedure to put a magnet on loop is described here:

Ensure beam is off.
1. Select polarity for electrons or positrons in the magnet GUI. If you need to change polarity, first ramp the magnet to 0 [A], and then you can change the polarity.
2. Run the go_magnets_XXX_current P command as described above.
3. If you are increasing momentum, you should first go to MOL current. You can type in the current, press enter and then click Set Current or you can click (twice) the Go command next to the MOL current.
4. If you are decreasing momentum or have already gone to the MOL current, you should proceed to the set current for each magnet. You can type in the current, press enter and then click Set Current or you can click the Go command next to the Target current.

• The program for the magnet settings is in sync with the repository.

HMS Dipole

• We set the HMS dipole first by current, and then adjust the current to get the desired magnetic field as given from the command above ("go_magnet_HMS_current P"). To do this without field regulation, ensure the Start command in the HMS dipole NMR screen is not selected/illuminated.

1. Run the go_magnets_HMS_current P command to see the MOL and Target currents as well as the B-field we will set the magnet to.
2. If changing polarity, ramp to 0 A first, then change the polarity.
3. In the HMS PSU screen, go to the MOL current if increasing momentum or after having changed polarity (this is at least 1500 A, with 300 A buffer above the set current).
4. In the HMS PSU screen, after reaching the MOL current (or if descending in momentum), decrease the current to the Target current.
5. Make sure you have an NMR Lock (NMR Lock will be illuminated bright green). Wait 5 minutes at the Target current, and begin to slowly adjust the current in small steps to reach the desired B-field setting. The field read back is in the HMS dipole NMR screen. This process will take approximately 10-15 minutes for the dipole to settle. Be sure to agree with the desired B-field from the program to within 5E-5 T.
6. After the dipole settles and the field read back agrees with the desired field, proceed to take data (approximately 5 more minutes).

Troubleshooting the dipole NMR lock

• If the dipole NMR Lock does not illuminate, ensure that Search Mode is turned off (if the box to the left of the words is illuminated, then it is on. It can be toggled off by clicking this box), and select Manual .
• Click on the probe to the left in the NMR GUI that corresponds to the desired field in units of Tesla. Wait 1-2 minutes.
• If NMR Lock illuminates, then all is well.
• If the NMR Lock does not illuminate, call an expert.

Communication Error

• If you see a Communication Error, the NMR may need to be power cycled. This is accomplished by clicking the green button, Power is On to the right of the field value box in the HMS NMR tab. Wait for it to say Power is Off.
• Next, click it back on and proceed to set the current to obtain the desired field. You want to see NMR LOCK illuminated green.

Old Instructions for Setting the HMS dipole by NMR

1. On the NMR screen, click the "Stop" button and wait for it to be stopped.
2. Enter the desired field in the input box and Enter.
3. Click Start and wait. The system will calculate the initial current to set the dipole, and you should see the current setting change. This ought to be close to what you see from "go_magnet_HMS_current".
4. The system is now going to wait about 1 second/amp for the power supply to reach the initial current, then it will start trying to get NMR lock.
   1. Do not do anything with the dipole controls for at least 20 minutes. Patience is important at this stage.
   2. You can watch the current read back in the lower-left of the Dipole NMR window. It needs to get close to the current reported by the 'go_magnet_HMS_current' command before it will start searching for an NMR lock.
   3. Eventually it should get an NMR lock and begin making adjustments in the current. You can watch the dipole current stripchart to see when it begins regulating.
5. Once the current and NMR values stabilize you should be good to go.

Magnet Cryogenics

• Spectrometer Magnets Cryogenics