A beam signal1 can be provided to users for the purposes of logging or triggering experimental equipment. This is routinely provided in one of two forms, which we call “beam possible” and “beam present”.
Beam Possible
The Beam Possible signal is a nominally +5V TTL logic signal which is synchronized to the extraction timing of the accelerator and goes high whenever the extraction magnets are enabled. The signal goes high well before the actual beam spill starts and goes low after the spill has ended, but it is not possible for any beam to be delivered during the time when the signal is low.
It is called “Beam Possible” because the magnets continue to function during that window whether or not beam is actually being delivered, even if beam is inhibited by a user, disabled by a safety system, or simply not being injected into the accelerator in the first place. This signal requires little to no manual intervention by NSRL staff to maintain during operations after it is initially set up.
This signal can be made available in the target room or setup area. The actual voltage of the signal in the target room can often be as low as +3.5V due to attenuation through the long cable.
A cartoon timing diagram of the Beam Possible signal is shown below.
Beam Present
The Beam Possible signal is routinely augmented into a form that is more useful to many users, especially those that require real time logs. This signal, called “Beam Present” is also a nominally +5V TTL signal that goes high during the time beam is being delivered to the target room.
This is accomplished by inserting a scintillation detector into the edge of the beam, outside of the uniform area, and only generating a logical high when the scintillator is currently detecting particles AND the Beam Possible signal is high.
This setup ensures the signal is not enabled if the scintillator is ever triggered by a stray background particle outside of the extraction timing window. The signal does occasionally require some manual tuning by NSRL staff so the scintillation detector can be adjusted to optimize for different ion species or energies.
Timing Diagram
A full timing diagram of both the Beam Possible and Beam Present signals, as well as all the intermediate signals used to generate them, is shown below.
[Timing diagram under construction]
Custom Signal
NSRL staff can work with users to develop a custom beam signal should neither the Beam Possible nor Beam Present signals be sufficient for their needs. There are many NIM-based signal processing modules available for this use, including logic level translators, as well as a pair of Stanford Research Systems DG535 pulse generators.
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- This is sometimes referred to as a “shutter signal” at cyclotron facilities. ↩︎
