Beam-Based Feedback in LCLS-II P. Emma March 30, 2017

Beam-Based Feedback Loops Beam-Based Feedback is Separate from RF-Based Feedback Transverse Feedback (LCLSII-2.7-PR-0075) Read 5-10 BPMs (X & Y) with ~p/2 net b-phase separation Control 2 XCOR’s and 2 YCOR’s upstream of the BPMs (also ~p/2) Maintains ref. beam position (DX & DY) at BPMs & collimators Longitudinal Feedback (LCLSII-2.7-PR-0076) Read 4 bend system BPMs and 2 relative bunch length monitors Control RF voltage and phase of each upstream main linac section Maintains e- energy and peak current at each location Timing Feedback (LCLSII-2.7-PR-0076, no cavities in baseline) Fast vs. Slow Feedback At commissioning time we need mainly slow drift-feedback (~1 Hz) Upgrade to fast-feedback may be justified later (operations exp.) Slow feedback is very useful at re-start, or during tuning Some concern of cross-talk over various loops (diff. time scales?)

LCLS-II Transverse Feedback Stations (DRAFT) “28NOV16” m-wall BC2 LTUS SXR L2 L3 Sec. 11-20 Linac Sec. 21-30 Linac L3 BSYDMP  Bypass LTUH HXR 3 HTR CM02 CM03 BC1 L1 CM01 3.9 Gun Launch  L1 L2  heater  IR  UV DIAG0

Beam-Based Trajectory Feedback LCLSII-2.7-PR-0075

Gun-Launch Angle (X & Y position only) F-Cup BPM02 SOL01 YAG01 SOL02 BPM X or YCOR Gun-Launch keeps e- centered at CM01-entrance

Heater-Launch Loop CM01 HTR BPM X or YCOR Don’t use cold magnets in feedback loops due to hysteresis? Heater-Launch keeps e- aligned with heater IR beam

DIAG0-Launch Loop (low rate, off-axis beamline) Kicker BPM X or YCOR DIAG0-Launch keeps e- centered on diagnostics

L1-Launch Loop Keeps beam centered on 4 collimators Kicker STC0 BPM X or YCOR Collimator c=45 Keeps beam centered on 4 collimators Still works when OTRC006 or STC0 stopper are inserted Should correctors be downstream, of DIAG0 kicker?

L2-Launch Loop BC1 L2 Keeps beam centered on 4 collimators BPM X or YCOR Collimator

Maintains launch into long L3-linac L3-Launch Loop L3 BC2 BPM X or YCOR Maintains launch into long L3-linac

Bypass-Launch Loop c=45 Keeps beam centered on 4 collimators BPM X or YCOR Collimator

LTUS-Launch Loop BY2 c=45 Keeps beam centered on 4 wire-scanners BPM X or YCOR Collimator

SXR-Launch Loop (fast loop?) TDUND BPM X or YCOR Keeps beam launched into SXR undulators Last loop before und. so might convert to fast loop later?

BSY-Dump Loop Keeps beam on BSY dump Need both position and angle? new XCOR & YCOR needed BSY Dump BPM X or YCOR Keeps beam on BSY dump Need both position and angle? If yes, needs 2 new correctors Fast raster-coils are separate

Beam-Based Longitudinal Feedback Slow (drift) feedback initially (Matlab) Read energy BPMs & bunch length monitors Adjust RF phases and amplitudes (global) Also holds bunch charge constant Maybe upgrade to high rate later Similar system works well at LCLS-I E V0 j1 V1 j2 V2 j3 CM01 CM02,3 3.9GHz CM04 CM15 CM16 CM35 Gun 750keV L0 12A LH 100MeV L1 12A HL BC1 250MeV L2 80A BC2 1.6GeV L3 (10) 1.0kA BYP/LTU 4.0 GeV BPM Bunch Length LCLSII-2.7-PR-0076