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

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


Outline

• Objectives of the study• Steering, beam loss, beam dump temperatures• Analysis of beam losses and dark current losses


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


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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Steering, beam loss, beam dump temperatures

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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)


13.2DUMP LM

9DUMP LM

Locations of diagnostics used in the analysis

BPM 92BYP


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


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Histograms of bunch locations throughout the morning(measured at 9DUMP bpm)


What’s going on with 15DUMP bpm?

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Histograms of total bunches vs bunch positionmeasured by BPM 15DUMP


1Hz rotations indicated by 15DUMP bpm

Both planes show 1Hz oscillations that are ~90 degrees apart and ~4cm in diameter

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Slow sweeper

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15DUMP bpm is the only place where the effect of the sweeper magnet could be seen


Can we infer beam position from beam-dump thermocouple data?

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Locations of temperature sensors on FLASH beam dump

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Beam Dump


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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


Analysis of beam losses and dark current losses vs energy

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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?


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


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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?


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


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


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)


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.


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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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Normalized beam loss at 9DUMP vs. position at 9DUMP

Optimum operating region?

Position is equivalent to energy?

Documents

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