Difference between revisions of "CIS OnCall and Troubleshooting"
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'''Fall 2015 and Spring 2016 Instructions to Change Laser Rep Rate''' | '''Fall 2015 and Spring 2016 Instructions to Change Laser Rep Rate''' | ||
* [[media:160128_LaserFrequency.pptx]] | * [[media:160128_LaserFrequency.pptx]] | ||
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| + | == Gun Current Monitoring == | ||
| + | |||
| + | The gun current is calculated from the HVPS analog output that reports a voltage proportional to current output. We typically calibrated this HVPS output against beam well centered in PCUP (assumes no loss). The equation EPICS uses is a bit odd but Gun_Current = (HVPS - Offset)/Gain. The Offset is typically 0.15-0.25 V depending upon power supply and the Gain is typically 0.001 V/uA, i.e. ~1V/mA. Here are some examples with 150 kV Glassman supply from [http://www.example.com Feb 2016] and [https://logbooks.jlab.org/entry/1565373 Jan 2011]. | ||
Revision as of 16:47, 3 February 2016
No good solution is too small to go undocumented!!!
OnCall Responsibilities
CIS on-call share responsibilities for supporting the NP program goals.
Typical activities include ... * Pay attention to source operation and performance * Have a presence at daily discussion (7:45am and 8:00am) and weekly scheduling (1:30pm Wednesday) meetings * Participate in discussions, planning and testing of delivered beam performance e.g. transmission, stability, requirements or improvements
Gun High Voltage Interlock Faults
* AC Line Volt Fault does not clear: you may want to recycle PSS system or reboot iocin3, see [1] for more details.
250V Gun High Voltage FSD Comparator Faults
Use comparator circuit in ISB monitoring HVPS output to set window (range about +/- 500V) about gun high voltage. Faults can be real (gun HV is out of range) or false (comparator is drifting).
To check if the gun HV is actually drifting the following archived read backs are useful to view ... * Precision read back of Ross probe * HVPS lock set point * Horizontal orbit at IPM1I02
To determine if the gun HV window comparator is drifting or set incorrectly ... * Window drift during SAD can be found at startup * Window drift sensitive to temperature variation e.g. seasonal temperature swing * Window set too tightly by Ops
To set gun HV window comparator window ... * While clicking FSD clear button vary POT until resets to find a good region * High Limit : Increase POT while clicking until fault occurs, then decrease until fault clears and record new high value * Low Limit : Decrease POT while clicking until fault occurs, then increase until fault clears and record new low value * Set POT at center of new low and high values; maybe repeat to get consistent values
Diagnosing Beam Intensity and Position Noise
Use FastSEE BPM Mode to diagnose intensity and position from injector BPM's with 4 microsecond sampling
To start the fastSEE EPICS screen ... * To start : Accel Menubar => EDM => BPM => New FastSEE Control * MAC or Channel Access is required * Choose a BPM mode and BPM by selecting corresponding ioc e.g. iocse11
Notes for BPMSEE mode ... * Non-invasive * BPM spikes update correctly * Less samples limit to lower frequency * Make sure FastSee Light is ON
Notes for FastSEE mode ... * Invasive * BPM spikes update erratically * More samples for higher frequency ~60kHz
QE Measurement Script
It is useful for Operations or CIS staff to perform a daily measurement of photocathode QE using an automated script.
To configure and test QE Measurement Script ... * Determine laser attenuator values that generate same bunch charge from each laser e.g. in the 5-15 uA range * Load and save these values into the Injector Expert Script * Run QE measurement script selecting all lasers * Laser power and PCup current are measured for each laser in sequence * QE = (124 * I[uA]) / (P[mW]*Wavelength[nm)
Laser Related Issues
To change the laser pulsewidth ... * To start : PGun Main (John's laser control screen), then click Fiber Laser Super User, another screen appears. * From Fiber Laser Super User, click "Frequency Division Controls". Yes, this name no longer makes sense. It is now the screen to adjust the laser dc bias current. * From "Frequency Division Controls", adjust the dc bias current by following the instructions outlined by John Hanskencht, see link Media: laser dc bias_DAC instructions.pdf
Resetting LLRF quadrant detection : use with care ! * To start : JTABS => Tools Screen (right side of menubar) => Laser Quadrant Init Pulse (lower left related display) * Pick some diagnostic (separator viewer is best if setting phase of 250MHz rep rate e.g. invisible effect at chopper) * Choose laser A/B/C and cycled button from from 0=>1=>0 (i.e. leave at zero); repeat until phase is correct
Fall 2015 and Spring 2016 Instructions to Change Laser Rep Rate * media:160128_LaserFrequency.pptx
Gun Current Monitoring
The gun current is calculated from the HVPS analog output that reports a voltage proportional to current output. We typically calibrated this HVPS output against beam well centered in PCUP (assumes no loss). The equation EPICS uses is a bit odd but Gun_Current = (HVPS - Offset)/Gain. The Offset is typically 0.15-0.25 V depending upon power supply and the Gain is typically 0.001 V/uA, i.e. ~1V/mA. Here are some examples with 150 kV Glassman supply from Feb 2016 and Jan 2011.