Finding Beam after the Mass Separator Magnet (IMS:MB2).

This section describes the process of locating beam after the Mass Separator Magnet.  It assumes that the beam transmission from IMS:FC3 to IMS:FC10A is ~100%, IMS:YSLIT0=2.00mm, IMS:YSLIT10A=0.80mm, and IMS:YSLIT11=0.80mm.

- Insert IMS:FC14 and a Faraday Cup upstream of IMS:MB2.

- If you are setting up a tune from scratch, set the IMS:MB2 field to theory using the 'Mass Change' utility (EPICS Main Menu => left click 'Beam Modes' => select 'Mass Selection' => left click '"Chris' Mass Scaling"' => select 'Chris' Mass Scaling').

The example below shows the theoretical magnet number for 7Li at 28kV (in this case, -629.97G).

 

 

 Set the Mass Separator magnet to the theoretical magnetic field

-  Open the IMS:MB2 EPICS device panel (shown below):

 

- Enter the theoretical magnetic field value to the right of 'Field Set' and press 'Enter' on your keyboard.  If the magnet power supply is on and "Ready" (green LED on the right), press '"Go!"'.  A control loop will regulate the supply current to produce the desired magnetic field.  Depending on how far the starting magnetic field is from the desired setpoint this could take up to 10 minutes.

 

Set the Alpha and Beta trim coils (roughly) 

-  Search the ISAC eLog for the last time the desired beam was transported at the appropriate energy (in the case above, 7Li at 28kV).  Use the saved Alpha / Beta numbers to set IMS:ALPHA and IMS:BETA (this should get you "close" to the optimized values -- good enough for this procedure).

 

-  Once IMS:MB2 has finished 'moving', remove all upstream Faraday cups and look at IMS:FC14.

 

If you see beam on IMS:FC14, your task is simple.  With an increment of 0.001A, adjust the IMS:MB2 current to maximize the Faraday Cup reading.  Proceed with the instructions outlined in "Tuning -- Front-End to IMS:FC34".

 

If you don't see beam on IMS:FC14, first ensure steerers between the magnets are neutral then try scanning IMS:MB2 using increments of 0.001A to +/- ~50G.  

 

If you still don't see beam on IMS:FC14, restore theoretical IMS:MB2 field & make sure all IMS:DB11 devices are set to transmit beam (see image below).  Press the appropriate 'set' buttons if required.

 

 

- At the bottom of the IMS2 Optics Summary Page, left click on 'Correlations' and select 'IMS:FC11CI vs position'.  Insert IMS:FC11 by pressing the Faraday Cup 'in' button (see image below).  The Faraday cup (& slit 11) will move to the 135.00mm position (the expected center position).

 

 

- Set the IMS:FC11 position to 0.00mm by typing manually typing '0' in the 'Motor Control' text entry field (or send the platform 'left').  Once the platform has stopped moving, right click on the plot area and select 'Clear Plot'.  Ensure speed is set to 2.5 (button selection right of 'Platform'), & 'fix FC11 bias' is enabled.  Move the IMS:FC11platform to 250.00mm (or send platform 'right').  The IMS:FC11 platform will now move horizontally through the beam plane.

 

- Take note of the beam profile generated (if still can't find beam, try tapping IMS:MB2 toward the old 'Probe 2' field on the magnet page).  We want the beam to be centered at 135.00mm, so if the profile position is less than 135.00mm, the Mass Separator Magnet current will need to be decreased (it is bending 'too much'), the opposite is true if the profile position is greater than 135.00mm (it isn't bending 'enough').  The beam profile is expected to be fat (for mass separation), but centering is important.

 

- Move the Faraday Cup to the 'out' position, and ensure that DB11 is set to Transmit beam, as above.

 

With an increment of 0.01A, quickly 'tap' the IMS:MB2 current in the appropriate direction until beam becomes visible on IMS:FC14.  Once you see beam on IMS:FC14, change the current increment to 0.001A and fine-tune.  Proceed with the instructions outlined in "Tuning -- Front-End to IMS:FC34".

 

-- Jon Aoki on December 05, 2009

-- Edited for text by Rene Tanaja, July 22, 2010