How to set a high beam current > 200 nA
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If you already know how to do this the old way then scroll down to see an easier way.
The old, tedious way to set the current
The commands set_current and adjust_beam fail above ~ 150 nA and so to get a beam current of 350 nA we can follow this tedious procedure:
Load the closest beam archive file, eg
pg arc rest beam 200na_400
then display the setting of the electrostatic lens aka "C1" with
pg get cc1 --bin
then set a higher value, realign the gun, and measure the current
| pg set cc1 --bin xxxxx |
| pg adj beam align |
| mcur |
Repeat this lens poking until you overshoot the desired value. Then move to a marker to re-focus with the condenser lens, aka C2:
| mvm |
| pg get cc2 --bin |
| pg set cc2 --bin xxxxx |
Now the beam current will be wrong, so you must return to the Faraday cup to re-adjust C1. Loop through this about 3 or 4 times. Then confirm that the settings work by doing an auto-focus and a field calibration:
| afa |
| pg adj ebpg 500 |
BUT NO! THIS IS THE HARD WAY. NOW THERE IS AN EASIER WAY!
The easy way to set a high current
Instead of typing lens values by hand, you can use two little python programs: adjust_c1 and focus_c2. These scripts let you use the arrow keys to adjust the lenses, just like the "manual_focus" program.
Load the closest archive, as before
pg arc rest beam 200na_400
Then start the C1 program
adjust_c1
This program will automatically move to the Faraday cup to measure the current. Now pop up a SECOND terminal window and then start the C2 program at the same time:
focus_c2
This program will prompt you to move to a focus location, such as the corner of a standard marker. Once you move there, the program will remember the stage location so that it can zip back there. Or, you can start the two scripts in the opposite order. It doesn't matter.
You should click on the C1 terminal, adjust the current with the arrow keys, then click on the C2 terminal and adjust the focus (with the arrow keys). The python scripts will move the stage to the Faraday cup and to the focus location automatically. It's so convenient!
Loop back and forth from C1 to C2 a few times, until the current hits the desired value. Finish by checking auto-focus and field calibration:
| afa |
| pg adj ebpg 500 |
| pg arc save beam 350na_400 |
Installing the programs
The programs adjust_c1 and focus_c2 are available in the ebpg funpak. Move the python scripts to someplace like /home/pg/bin or some other place in your command path. You can add /home/pg/bin to the command PATH with
export PATH=$PATH:/home/pg/bin
This could be a line in /home/pg/.bashrc or in /home/pg/pg_local
The python programs require the "blessed" package, which can be installed with
| su |
| pip install blessed |