02/18/09 dump line beam steering and beam losses (sept 26, 2008 studies) xiaowei dong & john...
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XFELX-Ray Free-Electron Laser
02/18/09
Dump line beam steering and beam losses(Sept 26, 2008 studies)
Xiaowei Dong & John Carwardine(Argonne)
TTF/FLASH 9mA meeting, 23 February 2009
XFELX-Ray Free-Electron Laser
Outline
• Objectives of the study• Steering, beam loss, beam dump temperatures• Analysis of beam losses and dark current losses
XFELX-Ray Free-Electron Laser
Study objectives
• Need to understand how to keep the beam losses low enough in the dump line for the 9mA run– Assess sensitivities to steering, energy,…
– See what information can be gleamed from the diagnostics
• This step: examine data from the Sept 08 high current run (the subject of this presentation)
• Next will be to analyze the data from parametric scans from the Jan 09 studies period
XFELX-Ray Free-Electron Laser
Notes…
• Analyzed data extracted from the DAQ– Bunch-by-bunch data from each pulse
– BPMs, BLMs, toroids, LLRF waveforms,..
– Some data is not available that could be helpful, eg pulse by pulse thermocouple data from the beam dump
• In most cases we analyzed data bunch-by-bunch
• Short-time (5min) integrals of losses and total number of bunches give a representation of ‘heating power’
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XFELX-Ray Free-Electron Laser
Steering, beam loss, beam dump temperatures
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XFELX-Ray Free-Electron Laser
Sept 26th morning studies(high current studies run)
• Ran at ~900MeV beam with 3nC bunches
• Up to ~8:15, we ran with 30 bunches, then rapidly began increasing the number
• Reached 350 bunches at 500KHz at ~8:20am
• First vacuum trip occurred at ~8:10am
• Reached 550 bunches at 1MHz at ~13:00, then there was the vacuum event
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Beam Dump Temperatures
Dump-line vacuum
Number of bunches per pulse(measured by 9DUMP torroid)
XFELX-Ray Free-Electron Laser
13.2DUMP LM
9DUMP LM
Locations of diagnostics used in the analysis
BPM 92BYP
XFELX-Ray Free-Electron Laser
Steering changes and correlation with beam losses
• Before ~10:40am, losses are relatively high at 13.2DUMP
• Beam power, losses, and dump temperature are well correlated
• Two large steering changes are seen at 9DUMP bpm in x-plane
– Steering at 10:40 reduces the losses significantly.
– Steering at ~11:40 has no obvious effect on beam losses
• Losses at 13.2DUMP almost eliminated at ~12:00pm but not due to steering (energy change?)
• Asymmetrical temperatures on dump…?
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Beam Dump Temperatures
Number of bunches per pulse
XFELX-Ray Free-Electron Laser
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Histograms of bunch locations throughout the morning(measured at 9DUMP bpm)
XFELX-Ray Free-Electron Laser
What’s going on with 15DUMP bpm?
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XFELX-Ray Free-Electron Laser
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Histograms of total bunches vs bunch positionmeasured by BPM 15DUMP
XFELX-Ray Free-Electron Laser
1Hz rotations indicated by 15DUMP bpm
Both planes show 1Hz oscillations that are ~90 degrees apart and ~4cm in diameter
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XFELX-Ray Free-Electron Laser
Slow sweeper
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15DUMP bpm is the only place where the effect of the sweeper magnet could be seen
XFELX-Ray Free-Electron Laser
Can we infer beam position from beam-dump thermocouple data?
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XFELX-Ray Free-Electron Laser
Locations of temperature sensors on FLASH beam dump
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XFELX-Ray Free-Electron Laser
Beam Dump
XFELX-Ray Free-Electron Laser
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Steering information from beam dump thermocouples
1. Faster temperature rises in first ring than the third indicate that more power dissipated at front of dump and that beam is off center to the left
2. After steering change towards the center the temperatures of the first and third rings track each other more closely.
3. Steering change causes the temperature at third ring to increase suggesting that more energy is deposited further into the dump
1
2 31NW1SW3N
XFELX-Ray Free-Electron Laser
Analysis of beam losses and dark current losses vs energy
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XFELX-Ray Free-Electron Laser
Unexpected behavior of 9DUMP beam loss monitor
• Between 8:00am and 9:00am, there are two periods where there was no beam
• Losses on 9DUMP BLM are very high.
• There are no losses detected by 13.2DUMP BLM
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Losses due to dark current?
XFELX-Ray Free-Electron Laser
Correlation with BLMs for two consecutive pulses (First: full 500 bunches; second: MPS inhibit after ~230 bunches)
Large signal on terminated case, that starts after the bunch train terminates (dark current)
V rises when beam loading lost.Falls at end-point of adjustment to FF table for BL compensation
Energy droops at end of bunch train because BL compensation ends before bunch train
BLM signal rises as energy droops. (Energy aperture?)
Green traces: full 500 bunchesBlue traces: terminated early
XFELX-Ray Free-Electron Laser
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Dark current losses at 9DUMP vs energy
Vector Sum vs time
Dark current loss at 9DUMP vs time
Dark current loss vs Vector Sum
Dark current loss vs Vector Sum(overlay of many pulses)
Bunch-train terminated by MPS
Gives an indication of energy acceptance for energies above nominal
Why two peaks?Is the BLM in a shadow?
XFELX-Ray Free-Electron Laser
Beam losses at 9DUMP vs energy
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Vector Sum vs time
Beam Loss @ 9DUMP vs time
Beam loss vs Vector Sum
Beam loss vs Vector Sum(overlay of many pulses)
Droop in vector sum at end of the bunch train is due to LLRF
XFELX-Ray Free-Electron Laser
Inferring energy aperture at 9DUMP(Sept 08 data)
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Combined loss vs Vector SumBeam loss vs VS
Dark current loss vs VS
~1% ΔE/E
XFELX-Ray Free-Electron Laser
Comparison with gradient scan (Jan 09)(approx +/-15MeV out of 720MeV)
Toroid 9DUMP
BLM 2EXP
BPM 92BPY(X)
New Cerenkov
BPM 9DUMP(X)
BLM 9DUMP
BPM 9DUMP(Y)
Radiation Scalar
-30MeV +22MeV ACC1: 128.3MeV; ACC23: 319.7MeV; ACC456: 272.3MeV
Combined loss vs VS(Sept data)
XFELX-Ray Free-Electron Laser
Summary
• There is steering information in the beam dump thermocouple data
• We have estimated the energy aperture using measured beam losses and dark current losses. Result compares well with energy scan performed in January
• The 1Hz oscillation from the slow sweeper is clearly visible in the 15DUMP bpm data
• Data from January study will give more comprehensive information about the dump line aperture and acceptance.
XFELX-Ray Free-Electron Laser
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XFELX-Ray Free-Electron Laser
Comparison of bpms at 92BYP, 9DUMP, and 15DUMP
• 15DUMP both x and y show large pulse-to-pulse excursions
• 15DUMP x and y both respond to steering change at 9DUMP:x. Why does it go the opposite way on the second steering at 9DUMP:x…?
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XFELX-Ray Free-Electron Laser
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Normalized beam loss at 9DUMP vs. position at 9DUMP
Optimum operating region?
Position is equivalent to energy?