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
SHMS Magnets
What SHMS Magnet Settings do I want??
- For the Fall 2017 run, the SHMS magnets can be set by current from the desired momentum in [GeV]. From any computer, run:
go_magnet_SHMS_current P
where P is the desired momentum in [GeV]. This will return the current that each SHMS magnet should be set to. 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 magnet and putting on loop. The procedure to put the magnet on loop is described here:
Ensure beam is off. 1. Select polarity for electrons or positrons in the magnet gui. 2. Ramp each magnet to the maximum current (see table below for SHMS). Rampe no more than three magnets at one time. Once magnets are ramping down, then proceed to ramp the other magnets. Recommendation to ramp Q1 and HB together, and Q2 and Q3 together. The dipole can ramp with either. 3. Ramp each magnet down to its desired current (the output of go_magnet_SHMS_current).
| SHMS Magnet | Max current [A] |
|---|---|
| HB | 3600 |
| Q1 | 2400 |
| Q2 | 3660 |
| Q3 | 2480 |
| Dipole | 2100 admin (previously 3440) |
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 maximum again.
HMS Magnets
- For HMS magnets, the current limits are shown in the following table:
| HMS Magnet | Max current [A] |
|---|---|
| Q1 | 1000 |
| Q2 | 600 |
| Q3 | 600 |
| Dipole | 3000 |
Do not exceed these limits! HMS magnets are put "on loop" by going 200 A above the desired set point and then reducing current to desired (see below).
What HMS Magnet Settings do I want??
For a desired momentum setting, the currents for the HMS quads and the needed NMR field for the dipole are all obtained by running the command
goHMS_all_magnet_settings x.x
where x.x is the momentum in GeV. This one command will run the necessary programs and return the currents (Q1, Q2, Q3) and the NMR setting.
How to set the HMS Dipole
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 a certain time for the power supply to reach the initial current, then it will start trying to get NMR lock. You just have to wait for it... it was almost 10 minutes for the change from 1.6162 GeV setting to 1.3773 setting. Once it gets NMR lock, it will 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.
How to set the HMS Quads
If HMS momentum is being decreased:
1) Set HMS magnets by momentum at main screen
If HMS momentum is being increased:
1) Set HMS magnets by momentum at main screen 2) Bring up control screens for Q1, Q2, and Q3. 3) Go to “Current Input Mode” (click on “Momentum Input Mode” button to switch to Current mode). NOTE: All magnets will change mode at the same time, and the setpoints on the main screen will show the “current mode” setpoint, even though that value is not being used. 4) Increase the set current to 200A above nominal (the “set current” button on the left). [Note: do NOT put a '+' or '-' sign in the current setpoint box.] 5) When all quads reach the increased current, go back to “Momentum Input Mode” and set to the correct momentum separately for each individual quad. 6) When all are set, verify that the main screen shows “using standard tune” and that all magnets are at desired current/field
