1. Summary Shifts 8th Oct – 12th Oct
Jack Roberts
28/11/2018
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2. Overview Beam status. Shifts 8th-12th October. Beam schedule.
Beam setup
Phase monitor calibrations
R56
Slow feedback setup
Slow feedback runs
Slow feedback + feedforward attempts
Feedforward only attempts.
Kicker timing scans.
Beam schedule.
IPAC abstract.
28/11/2018
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3. Beam Status
The gun has been stable for last few weeks the gun tripped this morning and is still not completely stable at 145 kV (nominal). At 140 kV it does appear to be stable.
However, large improvement in downstream beam/phase at 145 kV.
Last week/early this week: Beam downstream with gun at 140 and 145 kV. Eventually fairly similar stability to July, but generally quite a bit worse.
New accelerating structures have been conditioned and were powered in time with the beam first time this week.
Now running with ~10% higher energy and higher current -> beam sent as far as combiner ring so far.
Should gain from lower relative energy spread.
28/11/2018
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4. Phase Monitor Output Levels
I haven’t had time to revisit the phase monitor output vs. input attenuation tests -> hope to focus on that next couple of weeks.
But the phase monitor calibration factor (max output) has changed by more than a factor 3 over the past week with different beam setups!
Thursday 8th: 0.5 V.
Friday 9th: 1.3 V.
Thursday 15th: 1.6 V
NB: Voltages after amplifier prior to SiS digitisers.
28/11/2018
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5. Change in Monitor Output Levels
THURSDAY 8th: 0.5 V (upstream)
Gun at 140 kV, pre-buncher etc. changed to optimise.
28/11/2018
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6. Change in Monitor Output Levels
NB: Mon1 and Mon2 give same calibration constant.
FRIDAY 9th: 1.3 V (upstream)
Gun HV increased to 145 kV, setup most similar to July.
28/11/2018
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7. Change in Monitor Output Levels
THURSDAY 15th: 1.6 V (upstream)
Gun current increased.
28/11/2018
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8. R56
Have not run a complete scan, but optimal R56 point seems to have been around 0.3 m. In July it flipped between 0.2 and 0.05 m.
28/11/2018
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9. R56
Have not run a complete scan, but optimal R56 point seems to have been around 0.3 m. In July it flipped between 0.2 and 0.05 m.
28/11/2018
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10. Drifts: Amplification downstream
2 degrees
6 degrees
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11. Drifts: correlation with energy
Drifts (in particular gun current) lead to high correlation with energy which had to be fixed quite regularly.
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12. Drifts – gun current 5.57 A (4pm)
5.67 A (set point of morning, set in afternoon)
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13. Slow Correction
Two magnetic correctors installed neighbouring feedforward kickers.
Can be used to correct drifts in the mean phase.
Correctors take as much as 5 pulses to change -> realistically fastest that correction can be updated is every 10 pulses .
Tried various averaging times and gains.
Tests with slow correction by itself and slow correction + feedforward together.
Limited benefit with current feedforward setup: can only take out what feedforward system can’t, i.e. slow uncorrelated component or when feedforward correction is saturating the amplifier.
28/11/2018
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14. Slow Correction – Phase shift per amp
Around 15 degrees phase shift per amp on 465 (1.2 A on 765 for orbit closure).
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15. Slow Correction
Gain 0.5, average 20 pulses.
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16. Slow Correction
Gain 0.25, average 10 pulses.
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17. Slow Correction
Gain 0.75, average 50 pulses
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18. Feedforward and Slow Feedback Together
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19. Feedforward and Slow Feedback Together
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20. Feedforward Attempts FF OFF
Large wiggles in jitter as well as mean phase along pulse.
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21. Feedforward Attempts FF ON
Oscillations along pulse don’t seem to be reduced by FF but are correlated with upstream phase.
28/11/2018
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22. Possible causes of wiggles along pulse not being removed
Wiggles not correlated.
Looks like they are by eye but maybe there are differences.
Wiggles out of bandwidth.
Wiggles seem to be ~12 MHz, amplifier should be 50 MHz.
Wiggles out of correction range.
Definitely has an effect. Central region was near saturation on amplifier to be able to correct as much as the pulse as possible.
Correction applied out of time.
Took data yesterday with both kickers on in same direction / one kicker at a time with added delays to be able to see applied kick on BPMs and compare.
28/11/2018
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23. Kicker Timing Scans
Large (unwanted) wiggles in upstream phase are actually perfect for performing a check of the alignment of the correction with the beam.
Three combinations of kicks which don’t close the orbit after the chicane thus the phase (via the applied feedforward correction) can be seen on BPMs after the chicane:
K1 and K2 both kicking in the same direction.
K1 only.
K2 only.
Compare the relative location of the wiggles along the pulse in a BPM downstream of the chicane to the location of the wiggles in the upstream phase.
Repeat for different output delays on the correction.
28/11/2018
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24. Applied Delay: 0 ns
Interleaved data: BPM is KickOn-KickOff. Phases with FF off.
Alignment function works on diode/BPM sum signal, using the end of the pulse. Error maybe up to 2 samples = 10 ns.
Transient lost downstream.
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25. Applied Delay: 28 ns
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26. Applied Delay: 56 ns
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27. Applied Delay: 84 ns
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28. Fitted Offset vs. Applied Delay
Correction being applied ~40 ns early!
Either:
This has always been the case.
FONT5a board + new firmware has much lower latency (but should be about the same).
Difference in time of flight between monitors with different beam conditions (unlikely to be ns level).
To be checked: relative timing between kickers.
Last year found should delay K2 output by one clock cycle (2.8 ns.
Not immediately clear that this is present in this data (with K1, K2 only).
28/11/2018
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29. Traces Aligned (in data analysis)
Possibly only a normalisation effect but different phase sags between upstream, downstream, and BPM.
Overall agreement between upstream phase and kick seen in BPM is good.
28/11/2018
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30. CTF Beam Schedule/Planning
Discussed schedule for the rest of the year in a meeting yesterday.
High priority for time critical PhDs (me and Davide for the drive beam, Jack Towler CALIFES).
Other activities: Injector feedback performance tests (Tobias/Lukas), beam instrumentation tests, combined beam setup and related experiments.
The majority of these (especially high priority) require 3 GHz, uncombined beam.
General plan is to focus on 3 GHz beam first, with 1.5 GHz / combined beam taking priority towards end of year (initially taking 1-2 days per week for setup work).
Beam time requested by me/Davide:
I estimated a total of around 3 weeks beam time needed for phase monitor, phase propagation and feedforward tests.
Davide estimated a similar amount for tests of tomography, dispersion free/target steering, orbit feedbacks etc.
Parasitic tests with upstream phase monitors can be done in parallel with a lot of what Davide wants to do.
For phase feedforward: focus on phase monitors/beam setup before first feedforward tests with new amplifier in November.
For phase monitor tests we are depending on Stephane Rey to help install new phase shifters etc. He is now working on AWAKE but I have talked to him and Steffen/Roberto will arrange to get a few days of his time for this and other CTF3 activities.
28/11/2018
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31. IPAC Abstract
Submitted to go through the various stages of CERN approval:
Title: Demonstration of CLIC Level Phase Stability Using a High Bandwidth, Low Latency Drive Beam Phase Feedforward System at the CLIC Test Facility CTF3 Authors: J. Roberts (CERN, Geneva, Switzerland; JAI, Oxford, UK), P.K. Skowroński, R. Corsini (CERN, Geneva, Switzerland), P.N. Burrows, G.B. Christian, C. Perry (JAI, Oxford University, UK), A. Ghigo, F. Marcellini (INFN/LNF Frascati, Italy). Abstract: The CLIC two beam acceleration scheme, in which the RF power used to accelerate the main high energy beam is extracted from a second high intensity but low energy beam, places strict requirements on the phase stability of the power producing “drive” beam. To limit luminosity loss caused by energy jitter leading to emittance growth in the final focus to below 1%, 0.2 degrees of 12 GHz, or 50 fs, drive beam phase stability is needed. A low-latency drive beam phase feedforward correction with bandwidth above 17.5 MHz will be used to reduce the drive beam phase jitter to this level. The proposed scheme corrects the phase using fast electromagnetic kickers to vary the path length in a chicane prior to the drive beam power extraction. A prototype of this system has been installed at the CLIC test facility CTF3 to prove its feasibility. The latest results from the system are presented, demonstrating phase stabilisation in agreement with simulations given the beam conditions and power of the kicker amplifiers. Necessary improvements in the phase monitor performance and optics corrections made to remove the phase-energy dependence via R56 in order to achieve this level of stability are also discussed.
28/11/2018
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32. Summary Phase monitors: Slow correction: Timing: Schedule:
Change in calibration factors over the last week show how sensitive we are to beam setup changes (if we don’t recalibrate).
Stephane Rey contacted r.e. installing new phase shifters etc.
Slow correction:
Trying to do what it should but possibly too slow to remove the drifts we have.
Limited benefit with current setup.
Timing:
Correction applied 40 ns early. Was it always like this?
Schedule:
Phase feedforward a priority. Preference to complete 3 GHz, uncombined beam tests earlier this year before moving on to 1.5 GHz combined beam.
28/11/2018
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33. Backup
28/11/2018
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34. Slow Correction
Gain 0.5, average 30 pulses
28/11/2018
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