Simple Spectrometer Field Setting (Autopilot Mode)

(All you need when everything is working and power supplies are turned on and ready to go.)

On the Hall A main control screen there is a rectangular box for each spectrometer that looks similar to the illustration (see Figure 4.6).

Figure 4.6: Magnet Portion of Main Hall A Control Screen.

1.

This box displays a brief summary of the status of the spectrometer magnets and their cryogenic systems. The blue fields (with white numbers) give readbacks of the magnetic fields and currents in each magnet. The black fields also give readbacks, however in this case if the text appears green those parameters are OK while if they are red then that parameter is out of tolerance and may indicate a fault condition. For example if the helium level goes below a certain point the magnet will be automatically turned off. In some cases it may be desirable to monitor certain critical quantities on a strip chart (e.g. Magnet settings). A strip chart tool is available for this purpose from the bottom of the main control screen.

To set the spectrometers for a given value of central momentum (P0) type the desired P0 value into the yellow P0 SET box and hit return. The magnets will be automatically set to the correct values. All green numbers in the P0 column indicates that the desired field or current settings have been reached. Caution: Re dipoles, in general it's a bad idea to assume that at the first instant that the P0 display turns green that the desired field has been reached and you can start taking data. Stable field is in general not achieved for from 15 to 30 minutes after reaching the nominal desired field. This settling time depends on the magnet (Hadron is slower than Electron) and the magnitude of the field change (small changes settle faster than big changes). Experimenters are advised to observe both the field reading and current reading on the magnet in question and verify that things are stable to their satisfaction before proceeding.