1. 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

2. Outline Objectives of the study Steering, beam loss, beam dump temperatures Analysis of beam losses and dark current losses

3. 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

4. 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’ 02/18/09

5. Steering, beam loss, beam dump temperatures 02/18/09

6. Sept 26 th 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 02/18/09 Beam Dump Temperatures Dump-line vacuum Number of bunches per pulse (measured by 9DUMP torroid)

7. 13.2DUMP LM 9DUMP LM Locations of diagnostics used in the analysis BPM 92BYP

8. 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…? 02/18/09 Beam Dump Temperatures Number of bunches per pulse

9. 02/18/09 Histograms of bunch locations throughout the morning (measured at 9DUMP bpm)

10. What’s going on with 15DUMP bpm? 02/18/09

11. Histograms of total bunches vs bunch position measured by BPM 15DUMP

12. 1Hz rotations indicated by 15DUMP bpm Both planes show 1Hz oscillations that are ~90 degrees apart and ~4cm in diameter 02/18/09

13. Slow sweeper 02/18/09 15DUMP bpm is the only place where the effect of the sweeper magnet could be seen

14. Can we infer beam position from beam-dump thermocouple data? 02/18/09

15. Locations of temperature sensors on FLASH beam dump 02/18/09

16. Beam Dump

17. 02/18/09 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 3 1NW 1SW 3N

18. Analysis of beam losses and dark current losses vs energy 02/18/09

19. 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 02/18/09 Losses due to dark current?

20. 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 bunches Blue traces: terminated early

21. 02/18/09 Dark current losses at 9DUMP vs energy Vector Sum vs time Dark current loss at 9DUMP vs time 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?

22. Beam losses at 9DUMP vs energy 02/18/09 Vector Sum vs time Beam Loss @ 9DUMP vs time Beam loss vs Vector Sum (overlay of many pulses) Droop in vector sum at end of the bunch train is due to LLRF

23. Inferring energy aperture at 9DUMP (Sept 08 data) 02/18/09 Combined loss vs Vector Sum Beam loss vs VS Dark current loss vs VS ~1% ΔE/E

24. 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)

25. 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.

26. 02/18/09

27. 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…? 02/18/09

28. Normalized beam loss at 9DUMP vs. position at 9DUMP Optimum operating region? Position is equivalent to energy?