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FACET Tests Update

FACET Tests Update. A. Latina , J. Pfingstner , D. Schulte, D. Pellegrini , and E . Adli (Univ. of Oslo). CLIC Project Meeting – April 11, 2014 – CERN. Overview. Motivations and objectives Summary of the results Progress and future p lans. Beam-based alignment tests.

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FACET Tests Update

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  1. FACET Tests Update A. Latina, J. Pfingstner, D. Schulte, D. Pellegrini, andE. Adli (Univ. of Oslo) CLIC Project Meeting – April 11, 2014 – CERN

  2. Overview • Motivations and objectives • Summary of the results • Progress and future plans

  3. Beam-based alignment tests We propose to test automated beam-steering methods that improve a linac performance correcting orbit, dispersion,and wakefields simultaneously. Our technique is: • Model independent • Global • Automatic • Robust and rapid It is a considerable step forward with respect to traditional alignment techniques. Brief recap of the previous results.

  4. The SLAC linac • Divided in 100m long sectors • Energy = from 1.19 GeV to 20.3 GeV • Bunch length = from 1.0-1.5 mm in S02 to 20 μm in S20 • Nominal charge = 2e10 e- (test charge = 1.3e10 e-) • Nominal emittances: X = 2.5 x 10-5m ; Y = 0.2 x 10-5m * * * * • (*) Emittace measurements: • S02: 7 wires (only 5 used) • S04: quad-scan (1 wire) • S11: 4 wires (only 3 used) • S18: quad-scan (1 wire) • Orbit feedbacks (slow): • S03-04, S06, S11, S15: orbit correction • S09, S17-18: energy correction

  5. Main goals of the last tests • Study of Wakefield-Free Steeringin sectors LI02 – LI04 • Study of Wakefield-Free Steering and Dispersion-Free Steering simultaneouslyin sectors LI02 – LI04 • Apply WFS and DFS over longer sections of the LINAC sectors LI05-11 • Develop a set of new tools:friendly, robust, flexible, complete, and portable

  6. Recap of DFS and WFS • DFS: measure and correct the system response to a change in energy(we off-phased one klystron either in sectors S02 or in S04, depending on the case) • WFS: measure and correct the system response to a change in the bunch charge (this time we used 70% of the nominal charge, 2e10 e- and 1.3e10 e-) Recap of the equations woptimal= ~40 Simulation: DFS weight scan Simulation: WFS weight scan

  7. Highlights from the (four and a 1/2) shifts

  8. Shift 1 – Monday – Sectors LI02-04 Vertical Wakefield orbit = Y_test_charge – Y_nominal <<< Steps of corection <<<

  9. Shift 2 – Thursday – Sectors LI02-04 WFS convergenceplot. Apply WFS with optimal weight=40. Nominal emittances should be X = 2.5 x 10-5m Y = 0.2 x 10-5m Emittance at start of our shift was: X = 2.79 / 1.07 x 10-5 m Y = 0.54 / 1.12 x 10-5 m Emittanceafter correction X = 3.38 / 1.01 Y = 0.12 / 1.16 ; 0.17 / 1.20

  10. Shift 2 – Thursday – Sectors LI02-04 Weight scan vs. emittance. We tried w = 4, 40, 160, 400. • Vertical emittance measured in sector 04 (quad scan) • w = 0 initial vertical emittance: 0.56 / 1.10 • w = 4, vertical emittance = 0.36 / 1.63 • w = 40, vertical emittance = 0.12 / 1.16 (re-measured: 0.17 / 1.20) • w = 160, emittance not measurable • w = 400, emittance not measurable From simulation, one expects something like the black line in the plot: • Conclusion: • Emittance scan gives expected results • No time to measure more points

  11. Shift 3 – Saturday – Sectors LI02-04 First test of combined DFS+WFS

  12. Shift 3 – Saturday – Sectors LI02-04 Test of DFS alone: DFS LI02-LI04 gain = 0.5 svd = 0.7 w1_w0 = 40

  13. Shift 3 – Saturday – Sectors LI02-04 Measure the response of dispersion in S02-S04 Optimize speed in measurements Test a feed-forward system to stabilize the orbit during correction Measure effectiveness of correction by looking at both orbit and emittance Extend measurements of system to S05 and downstream Time required to set corrector and read bpms Work with Nate Lipkowitz to speed up the overall procedures. Overall 30% speed up measured in acquiring the response. SPEED UP OK!

  14. Shift 4 – Sunday – Sectors LI05-11 • Problems: • Very unstable machine • Damping ring extraction kicker • NRTL energy jitter • Earthquake ? • Initial config problems with scavenger line (3h to recover) • Emittance at start of our shift: • X = 4.186 / 1.1 • Y = 0.445 / 1.06 • Emittance before BBA (6h later) • X = 11.21 / 1.19 • Y = 0.91 / 1.12 • Emittance after correction: • X = 9.50/1.04 • Y = 1.06/2.40 • (improvement in X)

  15. Shift 5 – Mon-Tue – Sectors LI05-11 Extra test • Test of the new tools that we developed for BBA. • Tried a few interesting things: • simultaneous X and Y correction • with all coupled information • re-measurement of the golden orbit after 5 or 6 iterations, to update the reference for the orbit correction The emittance measurements from 4am to 5am witness the result: an improvement in both horizontal and vertical emittance, with quite satisfactory numbers in Emittance Y: --> from 1.58 x 10-5m, the last vertical emittance measured before correction • down to 0.50 after few iterations of fully coupled correction • to further 0.40 after resetting the target orbit during the correction(equivalent to correct without orbit constraint)

  16. The new tools • object: Interface • FACET • PLACET • object: State • Complete machine information • Persistent • GUI: SysID • Excite correctors • Acquires orbits • Store state files • GUI: BBA • Acquires orbits • Computes and apply correction • Displays orbits / convergence • Stores everything on disk • Compute Response matrices • R0: orbit • R1: dispersion • R2: wakefiels

  17. New tools developed “CERNBBA” Tools (top) System Identification (bottom) Beam-Based Alignment

  18. Conclusions and future plans • Applying DFS and WFS the emittance got reduced almost systematically • We are analysing the data to understand the performance limitations, and separate out what is due to peculiarities due to FACET and what is a genuine limitation • E.g. why sometimes BBA did not converge? (especially in the horizontal axis) ? dispersion? Jitter? Ill-conditioned system? • A session dedicated to CERNBBA is being organized at the Americas Workshop on Linear Collider at FNAL in May, involving SLAC, KEK, FNAL: • to discuss what else can and should be done, also thinking ahead to FACET2 and what may be possible with that beam in LI11-20; • to examine what hardware upgrades could be desirable at FACET • We are pursuing other experimental tests (ATF2 ? Fermi in Trieste ? … ) • An effort to revive the other two CLIC beam physics experiments at SLAC is on going: (i) ASSET and (ii) Collimator wakefields

  19. Extra

  20. Shift 4 – Sunday – Sectors LI05-11 • Test of DFS+WFS followed by WFS only • Iteration 1-7 (including): DFS+WFS • corresponding to previous plot blow) • Iteration 8-10 (including): drift (gain=0) • corresponding to previous plot blow) • Iteration:11-18 (including): WFS (setting DFS gain to 0) • Iteration 13: some kind of machine hickup (not identified). Algorithm recovers afterwards • Emittance non measureable in Y – we stopped

  21. Response 0: nominal orbit X Y

  22. Dispersion response: R1-R0 Wakefield response: R2-R0 X Y X Y

  23. Singular values for X and Y 2 very large singular values – we need to understand what they do represent

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