1. VELA BPMs
Alex Brynes

2. Position Measurement
EM field of bunch induces travelling wave at four strips.
Combination of signal from two H / V pickups yields bunch position.
Signal is amplified, digitised and then passed into EPICS.
Beam Trigger
pickup
Front-End
Transmission cable
T/4=13.83ns spacing
Analog Processors ADCs & FIFOs

3. BPM Timing 2 stages: Pre-trigger (“AWAK”) - <1us before WCM signal
Delays – ns level control
Pre-trigger not fully understood – see wiki and shift #323 log.
Timing of BA1 BPMs was an issue.

4. Attenuations + Delays
Raw voltage at each pickup (inc. pedestal) should be ~0V.
So attenuation needs to be set correctly for accurate measurement.
Range of 20dB for 20 < q < 250 pC.
Beam trigger pulses, synchronous with front-end BPM signals, trigger ADC clock pulses.
Maximum BPM resolution and sensitivity is achieved when the timing of output pulses is maximised.
Range of 512ns.

5. 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
monitorDataForNShots
std::vector< double >
getXVec / getYVec / getQVec
std::vector<std::vector<double>>
getBPMRawData
getTimeStamps
reCalAtt
setSA1/2 / setSD1/2
long
getRA1/2 / getRD1/2
double
getXFromPV / getYFromPV
getX / getY / getQ
std::vector< std::string >
getBPMNames

6. Calibration - Attenuation
Set charge (at WCM) to 50 < q < 80 pC.
Measure U1,2,3,4.
Change ATT1,2 so that U1+U2 / U3+U4 ~2V
These are ATTcal values for each BPM.
Value for each BPM is incorporated into Hardware Controller.
Now we can measure q at WCM and adjust attenuation accordingly using:
And calculate q at each BPM using:

7. Calibration - Delay
Prototype program implemented last year – results not very well understood.
Lots of improvements could be made.
Should only need calculating once to ensure optimal signal at each BPM.

8. Planned Improvements Improve DLY calibration program.
Incorporate offset, jitter + resolution calculations into controller.
Cross-calibration between BPMs and screens.
Auto-centre program.
Orbit monitoring / correction.
Histogrammer – could be made generic to monitor any EPICS PV.
Suggestions?