Difference between revisions of "How to operate and monitor the Spectrometer Magnets"

Revision as of 15:05, 19 January 2018

Magnet Controls Screens

• Magnet screen is brought up on any hcdesk machine by the command go_magnets

SHMS Magnets

What SHMS Magnet Settings do I want??

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

go_magnet_SHMS_current P

where P is the desired momentum in [GeV/c]. This will return the current (in Amps) needed to set each of the SHMS magnets. The formulas and program are in sync with the repository. 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. 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.
2. From any computer terminal, run:
   go_magnet_SHMS_current P
This script will ask 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.
In the magnet GUI, you will set each magnet by current. Click on the box for the current to bring up the screen to do this. 
3. If you are increasing momentum, you should first go to Minimum On Loop (MOL) current. Recommendation:  ramp Q1 and HB together, then Q2 and Q3 together. The dipole can be ramped with either pair. 
4. If you are decreasing momentum or have already gone to the MOL current, you should proceed to the set current for each magnet. 

To set the current for the magnet, you will type the current in the current box, hit enter, and then hit the Set Current button. You will see the numbers under I True in the box start to change. If you need to change polarity, first ramp the magnet to 0 [A], and then you can change the polarity. After this change, you will need to ramp the magnet to the MOL current again. The ramp currents for HB, Q2, Q3, and the dipole are 300 [A] above the set current unless this exceeds the maximum current that the magnet has been tested at. For Q1, the set current must always go to at least 1500 [A] and have at least 300 [A] between the set and MOL current. All of these nuances are accounted for when you run the command: go_magnet_SHMS_current. See logbook entry: https://logbooks.jlab.org/entry/3511446

HMS Magnets

What HMS Magnet Settings do I want??

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

  go_magnet_HMS_current P

where P is the momentum in GeV with the corresponding sign (negative for electrons). This one command will run the necessary programs and return the currents for Q1, Q2, Q3 and the dipole's field NMR setting. For precision physics data-taking, the magnets should be put "on loop". The output from the above command will give the Minimum On Loop (MOL) current that should be used first (puts magnet on loop) when increasing in momentum before decreasing to the Iset 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.
2. From any computer terminal, run:
   go_magnet_HMS_current P
This script will ask 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.
In the magnet GUI, you will set each magnet by current. Click on the box for the current to bring up the screen to do this. 
3. If you are increasing momentum, you should first go to Minimum On Loop (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 may also set the quads by momentum using the Standard Tune in the GUI.

To set the current for the magnet, you will type the current in the current box, hit enter, and then hit the Set Current button. Do not use the +/- sign in front of the current- the polarity will take care of this. You will see the numbers under I True in the box start to change. If you need to change polarity, first ramp the magnet to 0 [A], and then you can change the polarity. After this change, you will need to ramp the magnet to the MOL current again. The ramp currents for Q1, Q2, and Q3 are 200 [A] above the set current unless this exceeds the maximum current that the magnet has been tested at. All of these nuances are accounted for when you run the command: go_magnet_HMS_current.

How to set the HMS Dipole

18-JAN-2018 Temporary(?) note: Please see this log entry about the HMS dipole NMR: [1]

• It will tell you that, for now, SET THE DIPOLE BY CURRENT with no NMR regulation.

This is the process that Mike guided us through to change the HMS dipole to the desired NMR field value:

1. On the NMR screen, push the "stop" button and wait for it to be stopped.
2. Enter the desired field in the input box and hit enter.
3. Push "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 readback 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.

If you see a Communication Error, the NMR may need to be power cycled. This can be accomplished by pressing the green button, Power is On, to the right of the field value box in the HMS NMR tab. What for it to say Power is Off. Then click it back on and repeat the above instructions to set the field. You want to see NMR LOCK illuminated green. Note: When the NMR is power cycled it forgets what current the power supply was at, so when the procedure is repeated so is the wait time. Be sure you are in Search mode so that the NMR will look for right setting.

Magnet Cryogenics

• Spectrometer Magnets Cryogenics