1. FACET Tests Update A. Latina, J. Pfingstner, D. Schulte,
D. Pellegrini, and E. 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 * * * * (*) Emittace measurements:
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 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

5. 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

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 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 / x 10-5 m
Y = 0.54 / x 10-5 m
Emittance after correction
X = 3.38 / 1.01
Y = 0.12 / 1.16 ; 0.17 / 1.20

11. 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 = / 1.63
w = 40, vertical emittance = / 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

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

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

14. 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!

15. 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 = / 1.1
Y = / 1.06
Emittance before BBA (6h later)
X = / 1.19
Y = 0.91 / 1.12
Emittance after correction:
X = 9.50/1.04
Y = 1.06/2.40
(improvement in X)

16. 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)

17. 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

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

19. 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

20. Extra

21. 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

22. Response 0: nominal orbitX Y

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

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