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 plans

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.

The SLAC linac * * * * (*) Emittace measurements: 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 10-5 m ; Y = 0.2 x 10-5 m * * * * (*) 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

Main goals of the last tests Study of Wakefield-Free Steering in sectors LI02 – LI04 Study of Wakefield-Free Steering and Dispersion-Free Steering simultaneously in 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

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

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

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

Shift 2 – Thursday – Sectors LI02-04 WFS convergence plot. Apply WFS with optimal weight=40. Nominal emittances should be X = 2.5 x 10-5 m Y = 0.2 x 10-5 m 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 Emittance after correction X = 3.38 / 1.01 Y = 0.12 / 1.16 ; 0.17 / 1.20

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

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

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

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!

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)

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 10-5 m, 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)

Compute Response matrices 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

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

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

Extra

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) 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

Response 0: nominal orbit X Y

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

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