HOM Transverse Wakefield Studies for CC1 and CC2 (11-08,09-17 Run) - - PowerPoint PPT Presentation

HOM Transverse Wakefield Studies for CC1 and CC2 (11-08,09-17 Run)

Alex Lumpkin, Chip Edstrom, Jinhao Ruan, Randy Thurman-Keup, Olivier Napoly (TD), Kip Bishofberger (LANL), Bruce Carlsten (LANL) FAST/IOTA Dept. Mtg. 17 November 2017

Introduction

• Primary goal is to reduce beam steering offsets and

possible emittance dilution by monitoring and minimizing higher order modes (HOMs) in the cavities.

• Two HOM couplers are installed in both CC1 and CC2:

upstream (US) and downstream (DS).

• Studies
• n

11-08,09-17 were for the investigation

• f

transverse HOM wakefields

• n

beam centroids via V101,H101 scans.

• Used Chip’s scripts for stepping corrector currents while

tracking HOM signals, rf BPMs, etc. and Randy’s script for 100 shot BPM array acquisitions.

• Searching for sub-macropulse effects on beam centroids

correlated with HOMs.

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Beamline Layout (50 MeV)

Transverse Wakefield Shifts Summary-1

• 10-18-17: Preliminary HOM studies with H,V101 and H,V103
• scans. Good minimization of CC1 HOMs and CC2 US for

corrector set. This was precursor to longitudinal wake study.

• 10-26-17: First V101 study with X107 multi-slits emittance
• technique. Calc. y emittances grow with HOM strength,

projected size back to X107 increases with HOMs. Reported.

• 10-27-17: First study with X111 beam sizes vs. V101 scan.

Projected peak shoulder seen to shift with V101 corrector strength and HOMs. Averaged over macropulse. Reported.

• 10-31-17: First framing camera tests at X121. V101 scan on

X121 YAG images. Weak effect. Reported.

• 11-02-17: Machine downtime, Lost transverse study. Only

took one longitudinal data set with Kip B.

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Apparent Correlations at X107 10-26-17

• HOM signal sums done, plotted vs. calculated emittance,

projected X107 beam size: 500 pC/b, 50 b.

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Emittance vs HOM Sum

Y-emittance-geom. (10^-2 um)

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

HOMs Sum (V)

• 2.0
• 1.8
• 1.6
• 1.4
• 1.2
• 1.0
• 0.8
• 0.6
• 0.4
• 0.2

eps-y 500pC/b-50b vs HOM-SUMSC4

X107 Recalc. Beam Size

Reprojected X107 Beam Size (um)

300 350 400 450 500 550 600

HOM Sum (V)

• 2.0
• 1.8
• 1.6
• 1.4
• 1.2
• 1.0
• 0.8
• 0.6
• 0.4
• 0.2

beam size Scan 4

HOMs Sum 10-26-17

V101 Current (A)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

HOM Sum (V)

• 2.0
• 1.8
• 1.6
• 1.4
• 1.2
• 1.0
• 0.8
• 0.6
• 0.4
• 0.2

V101 A vs HOM-SUMSC4

Suggestions of Centroid Motion Effect at B106PV:10-27-17

• V101=1A; Sub-macropulse centroid motion indicated.

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V101 Scan, 1.0 A (10-27-17)

Bunch Number

5 10 15 20 25 30 35 40 45 50 55

Beam Position (um)

• 1580
• 1560
• 1540
• 1520
• 1500
• 1480
• 1460
• 1440
• 1420
• 1400
• 1380

B106PV Plot 1 Regr

V101 Scan, 1.0 A

Time (us)

660 670 680 690 700 710 720 730 740

HOM Waveform (V)

• 0.8
• 0.6
• 0.4
• 0.2

0.0 0.2 C1W19 C1W18

Vertical BPM Number

100 101 102 103 104 105 106 107

Position Standard deviation (um)

10 20 30 40 50 60 STDEV: V101_-1A STDEV: V101_ 0A STDEV: V101_+1A

Transverse Wakefield Shifts Summary-2

• 11-08-17: Framing camera studies with our first double

column sampling with 2 µs x 100 µs. First 100 shot BPM averaging with Randy’s Matlab program. 500 pC/b, 50 b.

• 11-09-17: Framing camera run on active area of beam

motion, but images missed. Further BPM averaging sets done, including 1000 shot averages for 100 pC/b in V101 scan, 500 b data taken. Various effects seen (Randy), but post analysis showed upstream correctors (and HOMs) were not set properly on this date.

• 11-13-17: Whole shift lost to downtime. Planned X107 vertical

slits, X107 YAG images, and targeted framing camera in 15- 45 bunch number area.

• Need X107 camera working and time for critical data.

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V101 Scan: Framing Camera Mode Test 11-08-17

• 61b, 1000 pC/b, 2 µs vertical, 100 µs Horiz., ~16 µs gap.
• Bunches 3-9, 55-61. Later time is down and leftward on axes.
• 1.0 A 0.0 A 1.0 A

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Comparison of HOMs 11-08,09-17

• 11-08-17 500pC/b 11-09-17 500 pC/b

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HOMs 1715-11-08-17

V101 Current (A)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

CC1 HOM Signals (V)

• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

0.0 V101 A vs CC1 US V101 A vs CC1 DS

HOMs 1715, 11-08-17

V101 Current (A)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

CC2 HOM Signals (V)

• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

0.0 V101 A vs CC2 US V101 A vs CC2 US

HOMs 15:57, 11-09-17

V101 Current (A)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

CC1 HOM signals (V)

• 1.2
• 1.0
• 0.8
• 0.6
• 0.4
• 0.2

0.0 Col 3 vs CC1 US Col 3 vs CC1 DS

HOMs 15:57, 11-09-17

V101 Current (A)

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5

CC2 HOM Signals (V)

• 0.45
• 0.40
• 0.35
• 0.30
• 0.25
• 0.20
• 0.15
• 0.10
• 0.05

Col 3 vs CC2 US Col 3 vs CC2 DS

Comparison at V101=1A, Dramatic Q Effects 11-08,09-17

• 100 pC/b, 1000 shots 500 pC/b, 100 shots

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Bunch Number Bunch Number

Vertical BPM Horiz. BPM

Comparison at V101=1A 11-08,09-17: Dramatic Effects Seen

• 100 pC/b,1000 shots (Top) 500 pC/b,50b,100sh (Bottom)

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Bunch Number Bunch Number Bunch Number

V101 Scan, Vertical BPMs Show Damping Effect 11-09-17

• Centroid oscillation seen over first ~100 b, then damps out.

V101= -1A (T) and 1A (B), but HOMs are different. 500 pC/b.

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Bunch Number Bunch Number Bunch Number

FFT of B121PH Data with V101 scan Show Frequency.

• 100-shot BPM data averages of 500 b exhibit ripple effect (L).

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Bunch Number

Nathan’s Vertical BPM Check, 50b

FFT of 500b Train Shows 855 kHz Peak 11-09-17

• Vertical BPMs

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FFT of 500b Train 11-09-17

• Horizontal BPMs

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CC1 Generated Dipole HOM Kicks (Preliminary)

• O. Napoly

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CC2 Generated Dipole HOM Kicks (Preliminary)

100 kHz

• O. Napoly

Summary

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• Transverse wakefield studies’ results are consistent with a

sub-macropulse centroid motion correlated to HOM strength.

• Vertical

position bunch-by-bunch data suggest centroid motions of 150 um in subset of bunches. Variances about 40 µm in B106PV while ~25 µm at B102PV on 10-27-17.

• Vertical position bunch-by-bunch data with 100-shot averages

show clear centroid

• scillation

at some BPMs with V101=±1A. Effect seems to be directional.

• Horizontal

position bunch-by-bunch data with 100-shot averages show centroid oscillation at some BPMs with H101=±1A.

• Mode measurements and modeling underway by Olivier N..
• Confirming data with X107 YAG images, emittances, framing

camera, and 100-shot averages needed. 3 shifts requested.

Schematic of FAST 50-MeV Beamline Before Chicane.

• Linac layout including cavities, correctors, and rf BPMs.

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X107 slits X111 screen