Latest results of our Beam-based alignment tests

at FACET

Andrea Latina,

for the E-211 team: myself, Erik Adli, and Dario Pellegrini

CLIC Beam Physics meeting, March 26 2014

Week 1 Week 2 Week 3 Week 4

Mon A E-211 A-D ½ E-211

Tue A A-D A back!

Wed A A-D A

Thu A-D E-211 A

Fri A-D A-D A

Sat A-D E-211 A

Sun A-D E-211 A

A=Andrea ; D=Dario; Erik was also there

Main Goals

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) Deploy a set of new tools:friendly, robust, flexible, complete, portable

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-)

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

* * * *

Recap of BBA: 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 shifts

Shift 1 – Monday – Sectors LI02-04Goals Wake free steering (WFS) tests is Sectors 02-04:

• Measure orbit response, R0• Measure test-charge response, Rwake (we call it R2)• See the impact of WFS on the orbit and if possible on the emittance

Progress- Studied orbit difference for different charge variations- Studied orbit difference for different energy variations (offset phase of klystron LI02:21, by 45 degrees)- Measured R0 and R2 for S02 and S03- Performed WFS for one parameter set: vertical wakefields seem reduced, results will be analyzed in more detail

Data:• We used 88 correctors• Same number of BPMS

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

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Horizontal Wakefield orbit = X_test_charge – X_nominal

Sectors LI02-04

Comparing the matrices afterthree months time

LI02-04 – Nov 13 vs. Mar 14Horizontal orbit response

LHS = March 2014 ; RHS = November 2013;

LI02-04 – Nov 13 vs. Mar 14Vertical orbit response

LHS = March 2014 ; RHS = November 2013;

Difference in LI02 – LI04from Nov 2013 to Mar 2014

Relative difference of the orbit responses from November 2013 to March 2014

• norm(Rx_nov - Rx_mar) / norm(Rx_mar)= 8.25 %

• norm(Ry_nov – Ry_mar) / norm(Ry_mar) = 9.22 %

Matrices look quite similar. Need to evaluate the impact of BPM noise w.r.t. machine drifts.

Shift 2 – Thursday – Sectors LI02-04

Goals Wake free steering (WFS) tests is Sectors 02-04.

Based on the experience during Shift 1, the goals for Shift 2 are:• Test different parameters, and understand why we could correct in Y and not in X.

Did nonlinearities play a role during Shift 1?

• Plot the emittance vs the WFS weight, to locate the best working point[theoretical value is for w=40 (assuming ~3 micron BPM resolution)]

Shift 2 – Thursday – Sectors LI02-04Convergence plot.

Apply WFS with optimal weight=40.

Emittance at start of our shift was:X = 2.79 / -Y = 0.54 / -

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

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 LI02-04

Goals1) Apply simultaneous DFS+WFS

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

Progress:- Achieved goal 1)- Achieved goal 2). With the help of Nate we improved the speed in both the

measurements, and in the steering (Sectors 02 03 and 04 - speed up by 30%)- Achieved goal 3). An alternative stabilizing scheme was implemented an tested.

The old feed-forward scheme could not be used, since LI06 orbit feedback was on during the measurements on Monday

- Dispersion diverged during correction, to be understood why.- Goal 4) was not achieved- Goal 5) Not attempted

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.

Measured time to set corrector and read bpms

SPEED UP OK!

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 4 – Sunday – Sectors LI05-11Goals1) Measure orbit, dispersion and wake responses LI05-LI09 (bpms up to LI11)2) Apply DFS + WFS in same sectors, fine tune feed-forward scheme3) Measure effectiveness of correction by looking at both orbit and emittance

Progress-Achieved goal 1)-Achieved goal 2)-Goal 3). We verified that the algorithms perform as they should from the point of view of reducing the wake field orbit difference and the energy orbit difference. However, we did not manage to see significantly improved emittances in LI11 after correction.

Response 0: nominal orbit

X Y

Dispersion response: R1-R0

Wakefield response: R2-R0X Y

X Y

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

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 = 4.6 (4.186 * 1.1)- Y = 0.47 (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)

Analysis of BBA

Sectors LI05-11

Trying to address the divergenceShift 4 – Sunday – Sectors LI05-11Example of convergenceTest of DFS+WFS: LI02-LI04w1_w0 = 40

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

Singular values for X and Y

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

Correcting a simulated LINACwith the measured response matrices

…including:

• Injection jitter• Misalignments• BPM resolution error (3 microm)• Transverse and Longitudinal Wakefields

Picking N progressive singular values at time

N=1 singular value

N=2 singular valuesnorm_OrbitX = 8.13995norm_OrbitY = 25.8351norm_DispX = 1.29383norm_DispY = 2.99051norm_WakeX = 0.905165norm_WakeY = 1.17392

N=3 singular valuesnorm_OrbitX = 10.3687norm_OrbitY = 22.6852norm_DispX = 1.53973norm_DispY = 3.02105norm_WakeX = 0.729164norm_WakeY = 0.998268

N=4 singular valuesnorm_OrbitX = 7.61432norm_OrbitY = 19.1609norm_DispX = 1.03749norm_DispY = 1.40887norm_WakeX = 0.50546norm_WakeY = 0.734156

N=5 singular valuesnorm_OrbitX = 6.72384norm_OrbitY = 22.656norm_DispX = 0.811785norm_DispY = 1.34545norm_WakeX = 0.380037norm_WakeY = 0.869225

N=6 singular valuesnorm_OrbitX = 7.31326norm_OrbitY = 23.0469norm_DispX = 1.04246norm_DispY = 1.38634norm_WakeX = 0.435169norm_WakeY = 0.917698

N=7 singular values

Shift 5 – Mon-Tue – Sectors LI05-11GoalsBased on the experience during our first four shifts, we want to apply simultaneous DFS WFS correction on the axes X and Y independently, using a (very) small number of singular values on each axis, while keeping the other axis hold on the golden orbit.

1) Test 1• Keep X trajectory on the golden orbit• Correct Y axis with 4 different singular value cuts (tentatively: 1, 2, 4, 8

singular values)• Check convergence over 10 iterations

2) Test 2• Keep Y trajectory on the golden orbit• Correct X axis with 4 different singular value cuts (tentatively: 1, 2, 4, 8

singular values)• Check convergence over 10 iteration

3) Measure the emittance whenever the convergence looks promising.

Progress• In Y: applied correction for singular values using up to 1,3,5,7,10 and

15 SVs - while holding X orbit constant with orbit correction – Result in Y: some emittance correction for 3,5 SV. Measurable but degraded

emittance for 1,7,10 singular values. 10, 15 SVs included: indications of divergence

• In X: applied correction for singular values 1,3,5 - while holding Y orbit constant with orbit correction – Result in X: more divergent than Y, and very poor emittances after correction

• Speed: improvement in correction speed. Now less than 2 min per iteration.

Shift 5 – Mon-Tue – Sectors LI05-11

• I wanted to try the new tools that we have developed for BBA.

• I tried a few interesting things:1) simultaneous X and Y correction (after one shift focused on 1 axis at the time)2) use of 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

Y:--> from 1.58 was 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

Some Conclusions

• We learned that our matrices seem still valid after months

• We see reasonable orbit / dispersion / wake control (many free parameters to tune, difficult to find the optimum)

• We managed to measure improved emittance almost systematically

• We still have a lot to learn from the data

• We have developed some fantastic new tools

Additionally: new tools developedSystem Identification User Interface

Additionally: new tools developedBeam-Based Alignment User Interface

(under development)

Extra

Sectors LI05-11

Evaluating the jitter

Response 1: X-excitations, absolute orbits (raw data)

Y-excitations

X ax

is [m

m]

Excitation numberBpms

From the Y-exctiations we can extract jitter in the X direction.

X-excitations

Response 1: Y-excitations, absolute orbits (raw data)

X-excitations Y-excitations

Y ax

is [m

m]

Excitation numberBpms

BPM 46 seems faulted.

From the X-excitations we can extract jitter in the Y direction.

Response 0: rms jitter vs max excitation

Removed vertical BPM 46

Response 1: rms jitter vs max excitation

Response 2: rms jitter vs max excitation