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

3

Beam-based alignment testsWe 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:• 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 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

Orbit feedbacks (slow):• S03-04, S06, S11, S15: orbit correction• S09, S17-18: energy correction

* * * *

Main goals of the last tests

1) Study of Wakefield-Free Steeringin sectors LI02 – LI04

2) Study of Wakefield-Free Steering and Dispersion-Free Steering simultaneously

in sectors LI02 – LI04

3) Apply WFS and DFS over longer sections of the LINACsectors LI05-11

4) 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

Simulation: WFS weight scanSimulation: DFS weight scan

woptimal = ~40

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

Shift 1 – Monday – Sectors LI02-04Vertical Wakefield orbit = Y_test_charge – Y_nominal

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Shift 2 – Thursday – Sectors LI02-04WFS convergence plot.

Apply WFS with optimal weight=40.

Emittance at start of our shift was:X = 2.79 / 1.07 x 10-5 mY = 0.54 / 1.12 x 10-5 m

Emittance after correctionX = 3.38 / 1.01Y = 0.12 / 1.16 ; 0.17 / 1.20

Nominal emittances should beX = 2.5 x 10-5 mY = 0.2 x 10-5 m

Shift 2 – Thursday – Sectors LI02-04Weight 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 / 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

Conclusion:• Emittance scan gives expected

results• No time to measure more points

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

Shift 3 – Saturday – Sectors LI02-04Test of DFS alone: DFS LI02-LI04gain = 0.5svd = 0.7w1_w0 = 40

Shift 3 – Saturday – Sectors LI02-04

1) Measure the response of dispersion in S02-S042) Optimize speed in measurements3) Test a feed-forward system to stabilize the orbit during correction4) Measure effectiveness of correction by looking at both orbit and

emittance5) Extend measurements of system to S05 and downstream

Work with Nate Lipkowitz to speed up the overall procedures.

Overall 30% speed up measured in acquiring the response.

Time required to set corrector and read bpms

SPEED UP OK!

Shift 4 – Sunday – Sectors LI05-11Problems:• 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)

• Test of the new tools that we developed for BBA.

• Tried a few interesting things:1) simultaneous X and Y correction2) with all coupled information3) 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 correction1) down to 0.50 after few iterations of fully coupled correction2) to further 0.40 after resetting the target orbit during the correction

(equivalent to correct without orbit constraint)

Shift 5 – Mon-Tue – Sectors LI05-11Extra test

The new toolsobject: 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)

• 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

Response 0: nominal orbit

X Y

Dispersion response: R1-R0

Wakefield response: R2-R0X Y

X Y

Singular values for X and Y

2 very large singular values – we need to understand what they do represent