1. Charge Measurements on VELA
Alex Brynes

2. BPM (stripline)
ICT
WCM
FCUP

3. In Practice
Signals from all devices are fed into here – we need to interpret these and convert them into pC, shot-to-shot.
We don’t want to have to take cables in and out, twiddle knobs etc. – this can, and should (?) be done remotely.
Prototype system working – needs many improvements.
WCM / FCUPs – only the first peak of the signal ( x conversion factor ) is needed.
ICT – the entire area under the curve – a bit more tricky.

4. Hardware Controllers
In order to make the interface to hardware more user-friendly, controllers for various VELA components were written.
Currently have: scope, BPM, magnets, RF, screens, shutters, vac valves, cameras.
See guide for more info:
\\fed.cclrc.ac.uk\Org\NLab\ASTeC\Projects\\VELA\documentation\notes\VELA_Hardware_Controllers_Guide_v1.docx
Type
Function
void
monitorTracesForNShots
monitorNumsForNShots
std::vector<std::vector<double>>
getScopeTrace
std::vector< double >
getMinOfTraces
getMaxOfTraces
getAreaUnderTraces
getAvgNoise
double
getScopeP1-4
getWCMQ/ICTQ/FCUPQ/EDFCUPQ
std::vector< std::string >
getScopeNames

5. Scope
Currently less than ideal – scope traces are written to EPICS via this console and then interpreted using a hardware controller.
This depends on a Python script which is prone to crashing.
We can’t write all four full scope traces to EPICS at 10Hz this way – this was sufficient last year but may not be enough for 100Hz operation
Also depends on scope setup, especially for ICT.
Ideally, Diagnostics / Controls should do this – this may be the case in future but we will have to rely on this for now!

6. BPMs
If we can correctly interpret the voltage induced on the four BPM pickups for a given resistance (attenuation), we can calculate the current, and thus the charge.
To get the charge, we need to know: the four voltages, two attenuations ( + two delays ), and a “calibrated” charge value ( BPMs are most accurate in a given charge range ).
Then to calculate charge for each shot.
BPM hardware controller does all this – prototype working as of last year.
See

7. Screens
Given a gain, and a known charge reading, the pixel intensity on a screen can be calibrated and then used as another diagnostic.
Not absolute, but still useful.
Needs more work before this can be used routinely.
\\fed.cclrc.ac.uk\Org\NLab\ASTeC\Projects\VELA\documentation\notes\VELA Wall Current Monitor Charge Measurement Monitoring in EPICS.docx

8. Examples BPM-to-charge GUI (also plots WCM / ICT / FCUP)
RF auto-crest (prototype)
BPM re-calibrator
VELA status monitor

9. Plans for next run
SP1 Fcup should be the most accurate, and so should be used to calibrate all other devices.
All new BPMs, ICTs, etc. need calibrating – better procedure for ICTs.
Sort out scope interface with help from Controls/Diagnostics.
Controller interface to multiplexer.
Discuss scope setups for planned experiments.

10. Software Improvements
Everything is a prototype at the minute, lots of improvements are needed to current software.
Operators should try these out, suggest improvements.
Also try writing software using the hardware controllers – charge should be monitored for most experiments.

11. Desired Software
Auto-setting of charge using laser – if we are ever allowed to control laser.
Robust calibration procedure.
Beam intensity on screen -> charge.
Suggestions?