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 on 11-08,09-17 were for the investigation of transverse HOM wakefields on 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. 2 Lumpkin FAST MTG 11-17-17 11/17/2017

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. 4 Lumpkin FAST MTG 11-17-17 11/17/2017

Apparent Correlations at X107 10-26-17 • HOM signal sums done, plotted vs. calculated emittance, projected X107 beam size: 500 pC/b, 50 b. X107 Recalc. Beam Size Emittance vs HOM Sum -2.0 -2.0 -1.8 -1.8 eps-y 500pC/b-50b vs HOM-SUMSC4 beam size Scan 4 -1.6 -1.6 -1.4 -1.4 HOM Sum (V) HOMs Sum (V) -1.2 -1.2 -1.0 -1.0 -0.8 -0.8 -0.6 -0.6 -0.4 -0.4 -0.2 300 350 400 450 500 550 600 -0.2 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Reprojected X107 Beam Size (um) Y-emittance-geom. (10^-2 um) HOMs Sum 10-26-17 -2.0 -1.8 V101 A vs HOM-SUMSC4 -1.6 -1.4 HOM Sum (V) -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 V101 Current (A) 5 Lumpkin FAST MTG 11-17-17 11/17/2017

Suggestions of Centroid Motion Effect at B106PV:10-27-17 • V101=1A; Sub-macropulse centroid motion indicated. V101 Scan, 1.0 A (10-27-17) 60 -1380 STDEV: V101_-1A B106PV STDEV: V101_ 0A -1400 Plot 1 Regr STDEV: V101_+1A Position Standard deviation (um) 50 -1420 -1440 Beam Position (um) 40 -1460 -1480 30 -1500 -1520 20 -1540 -1560 10 -1580 100 101 102 103 104 105 106 107 0 5 10 15 20 25 30 35 40 45 50 55 Vertical BPM Number Bunch Number V101 Scan, 1.0 A 0.2 C1W19 C1W18 0.0 HOM Waveform (V) -0.2 -0.4 -0.6 -0.8 660 670 680 690 700 710 720 730 740 Time (us) 6 Lumpkin FAST MTG 11-17-17 11/17/2017

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. 7 Lumpkin FAST MTG 11-17-17 11/17/2017

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 8 Lumpkin FAST MTG 11-17-17 11/17/2017

Comparison of HOMs 11-08,09-17 • 11-08-17 500pC/b 11-09-17 500 pC/b HOMs 15:57, 11-09-17 HOMs 1715-11-08-17 0.0 0.0 V101 A vs CC1 US Col 3 vs CC1 US V101 A vs CC1 DS -0.2 -0.1 Col 3 vs CC1 DS CC1 HOM signals (V) CC1 HOM Signals (V) -0.2 -0.4 -0.3 -0.6 -0.4 -0.8 -0.5 -0.6 -1.0 -0.7 -1.2 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 V101 Current (A) V101 Current (A) HOMs 1715, 11-08-17 HOMs 15:57, 11-09-17 -0.05 0.0 -0.10 V101 A vs CC2 US V101 A vs CC2 US -0.1 -0.15 CC2 HOM Signals (V) CC2 HOM Signals (V) -0.20 Col 3 vs CC2 US -0.2 Col 3 vs CC2 DS -0.25 -0.3 -0.30 -0.35 -0.4 -0.40 -0.45 -0.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 V101 Current (A) V101 Current (A) 9 Lumpkin FAST MTG 11-17-17 11/17/2017

Comparison at V101=1A, Dramatic Q Effects 11-08,09-17 • 100 pC/b, 1000 shots 500 pC/b, 100 shots Vertical BPM Horiz. BPM Bunch Number Bunch Number 10 Lumpkin FAST MTG 11-17-17 11/17/2017

Comparison at V101=1A 11-08,09-17: Dramatic Effects Seen • 100 pC/b,1000 shots (Top) 500 pC/b,50b,100sh (Bottom) Bunch Number Bunch Number Bunch Number 11 Lumpkin FAST MTG 11-17-17 11/17/2017

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. Bunch Number Bunch Number Bunch Number 12 Lumpkin FAST MTG 11-17-17 11/17/2017

FFT of B121PH Data with V101 scan Show Frequency. • 100-shot BPM data averages of 500 b exhibit ripple effect (L). Bunch Number Nathan’s Vertical BPM Check, 50b 13 Lumpkin FAST MTG 11-17-17 11/17/2017

FFT of 500b Train Shows 855 kHz Peak 11-09-17 • Vertical BPMs 14 Lumpkin FAST MTG 11-17-17 11/17/2017

FFT of 500b Train 11-09-17 • Horizontal BPMs 15 Lumpkin FAST MTG 11-17-17 11/17/2017

CC1 Generated Dipole HOM Kicks (Preliminary) O. Napoly 16 Lumpkin FAST MTG 11-17-17 11/17/2017

CC2 Generated Dipole HOM Kicks (Preliminary) 100 kHz O. Napoly

Summary • 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 oscillation 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. 18 Lumpkin FAST MTG 11-17-17 11/17/2017

Schematic of FAST 50-MeV Beamline Before Chicane. • Linac layout including cavities, correctors, and rf BPMs. X107 slits X111 screen 19 Lumpkin FAST MTG 11-17-17 11/17/2017