Beam Tests of DFS & WFS at FACET Andrea Latina, J. Pfingstner, D. Schulte, D. Pellegrini (CERN), E. Adli (Univ. of Oslo) With the help of F.J. Decker, and N. Lipkowitz (SLAC) AWLC 2014 – Fermilab – May 14, 2014

Overview Motivations and objectives Summary of the results Analysis of the results Conclusions 2

Beam-based alignment tests We proposed automated beam-steering methods to improve the linac performance by correcting orbit, dispersion, and wakefields simultaneously. Our technique is: Model independent Global Automatic Robust and rapid We base our algorithms operate in two phases: automatic system identification, and BBA It is a considerable step forward with respect to traditional alignment techniques. 3

Recap on Dispersion-Free Steering and Wakefield-Free Steering 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 Simulation: WFS weight scan Simulation: DFS weight scan w optimal = ~40 4

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

Overview of the tests performed 2013: 1)Dispersion-Free Steering in sectors LI04 – LI : 1)Wakefield-Free Steering in sectors LI02 – LI04 2)Wakefield-Free Steering and Dispersion-Free Steering simultaneously in sectors LI02 – LI04 3)WFS and DFS over longer sections of the LINAC in sectors LI05 – LI11 6

March 2013: Tests of DFS Sectors LI04 thru LI08 (500 meters of Linac) 52 correctors and 52 bpms (one every two) Dispersion created off-phasing one klystron in sector LI03 by 90 o 7 Dispersion got reduced by a factor 3-4 in X and Y

Before correctionAfter 3 iterations Incoming oscillation/dispersion is taken out and flattened; emittance in LI11 and emittance growth significantly reduced. After 1 iteration S19 phos, PR185 : March 2013: DFS and Emittance Reduction Emittance at LI11 (iteraton 1) X: 43.2 x m Y: x m Emittance at LI11 (iteration 4) X: 3.71 x m Y: 0.87 x m 8

March 2014: Tests of WFS in LI We measured the wakefield effects by using a test beam with 80% of the nominal value We used all correctors and all bpms. Notice: The wakefield is measured as orbit distortion due to the difference in bunch charge

Tests of WFS in LI02-04, March 2014 Vertical Wakefield orbit = Y_test_charge – Y_nominal <<< Steps of corection <<< 10

Tests of WFS in Sectors LI02-04 Horizontal Wakefield orbit = X_test_charge – X_nominal <<< Steps of corection <<< 11

Tests of WFS in Sectors LI02-04 WFS convergence plot. Apply WFS with optimal weight=40. Emittance at start of our shift was: X = 2.79 / 1.07 x m Y = 0.54 / 1.12 x m Emittance after correction X = 3.38 / 1.01 Y = 0.12 / 1.16 ; 0.17 / 1.20 Nominal emittances should be X = 2.5 x m Y = 0.2 x m 12

WFS weight scan Weight scan vs. emittance. We tried w = 4, 40, 160, 400. From simulation, one expects something like the black line in the plot: Vertical emittance measured in sector 04 (quad scan) -w = 0 initial vertical emittance: 0.56 / w = 4, vertical emittance = 0.36 / w = 40, vertical emittance = 0.12 / 1.16 (re-measured: 0.17 / 1.20) -w = 160, emittance not measurable -w = 400, emittance not measurable Conclusion: Emittance scan gives expected results No time for measuring more points 13

Sometimes in Sectors LI02-04 First test of combined test of DFS+WFS. Notice machine “hiccups”. 14

Sometimes in Sectors LI02-04 Test of DFS: LI02-LI04. Divergence. gain = 0.5 svd = 0.7 w dfs = 40 15

Tests of simultaneous DFS + WFS in LI05-LI11 Problems: Very unstable machine Damping ring extraction kicker NRTL energy jitter Earthquake ? Initial config problems with scavenger line (3h to recover) Emittance at shift start: -X = / 1.1 -Y = / 1.06 Emittance 6h later, before applying BBA -X = / Y = 0.91 / 1.12 Emittance after correction: -X = 9.50/1.04 -Y = 1.06/2.40 (improvement in X) Not conclusive 16

Tried a few interesting things: 1)simultaneous X and Y correction 2)with all coupled information 3)re-measurement of the golden orbit after 5 or 6 iterations, to update the reference for the orbit correction, y 0 Emittance Y: --> from 1.58 x m vertical emittance before correction 1)down to 0.50 after few iterations of fully coupled correction 2)to further 0.40 after resetting the target orbit during the correction (equivalent to correcting without orbit constraint) Further tests in Sectors LI05-11 Extra beam-time 17

Analysis Try to understand divergence in simulation (see next slides) Stability analysis proved that the choice of gain, g was correct, and that the system is stable even in presence of potential corrector errors: – b n : bpm readings at iteration n – δ n : relative correction – R: ideal response matrix – R tilde: erroneous matrix representing eventual corrector erroes if the absolute value of all eigenvalues of (I-gRR) < 1, the system is stable 18

Singular Values, DFS+WFS, w=40 19

Correcting a simulated LINAC with the measured response matrices …including: Injection jitter Misalignments BPM resolution error (3 microm) Transverse and Longitudinal Wakefields Picking N progressive singular values at time 20

Correction using N=2 singular values norm_OrbitX = norm_OrbitY = norm_DispX = norm_DispY = norm_WakeX = norm_WakeY =

N=3 singular values norm_OrbitX = norm_OrbitY = norm_DispX = norm_DispY = norm_WakeX = norm_WakeY =

N=4 singular values norm_OrbitX = norm_OrbitY = norm_DispX = norm_DispY = norm_WakeX = norm_WakeY =

N=5 singular values norm_OrbitX = norm_OrbitY = norm_DispX = norm_DispY = norm_WakeX = norm_WakeY =

N=6 singular values norm_OrbitX = norm_OrbitY = norm_DispX = norm_DispY = norm_WakeX = norm_WakeY =

N=7 singular values 26

Singular Values, DFS+WFS, w=40 27

FACET-specific problems The response matrix measurement is very slow – Takes ~2 hours for 48 correctors / 1 matrix Large jitter in the horizontal axis makes the X axis harder – Damping ring extraction kicker – RF system of NRTL bunch compressor Machine “hiccups“, LEM – LEM (linac energy management) – Impact to be studied 28

Speeding up the response matrix measurement 1)While measrung the response of dispersion in S02-S04 2)Optimize speed in measurements 3)Test a feed-forward system to stabilize the orbit during correction Worked with Nate Lipkowitz to speed up the system identification procedure. Overall 30% speed up measured Time required to set corrector and read bpms SPEED UP ACCOMPLISHED. Still quite slow. 29

New tools developed “CERNBBA” Tools: (top) System Identification (bottom) Beam-Based Alignment Tests foreseen at Fermi (Elettra) and ATF2 (KEK), … 30

Conclusions and future plans Applying DFS and WFS, the vertical emittance got reduced almost systematically Horizontal axis more difficult Sometimes observed instability/divergence: Might be related to noise in the measurement of the response matrices (counteracted with SVD cuts) Tests of convergence showed that the matrices are not ill- conditioned We are pursuing tests at other facilities (Fermi in Trieste, ATF2) We will learn a lot from these tests Further tests at FACET should surely be envisaged Need to speed up the system identification phase 31

Extra 32

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 33

Response 0: nominal orbit XY 34

Dispersion response: R1-R0 Wakefield response: R2-R0 XY XY 35

Singular values for X and Y 2 very large singular values – we need to understand what they do represent 36

Response 0: rms jitter vs max excitation 37

Removed vertical BPM 46 Response 1: rms jitter vs max excitation 38

Response 2: rms jitter vs max excitation 39

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