Operational Experience with ATF2 Beam Diagnostics Glen White, SLAC On Behalf of ATF2 Collaboration TIPP, Chicago, June

KEK 2

ATF International Collaboration 3

ATF2 Project Goals Experimental verification of the ILC FFS scheme – Development of beam tuning procedures – Goal A: focus vertical spot at IP to ~37nm (single bunch) – Goal B: maintain IP vertical position with few-nm precision (multi-bunch) Development of ILC beamline systems & instrumentation – BPMs, movers, high-bandwidth feedback, Laserwire, – beam size monitor, HA-PS, fast pulser, bckg monitors, SC- FD etc. Education of young generation for future linear colliders – Active participation of graduate students and post-docs. 4

Scale Test of ILC FFS Optics Scaled design of ILC local-chromaticity correction style optics. Same chromaticity as ILC optics. At lower beam energy, this corresponds to goal ~37nm IP vertical beam waist. Typical DR Parameters  x  y  = 1.3nm / 8- 10pm E  GeV ATF2 IP parameters  x  y = 4cm / 0.1mm  x /  y = 6um / 37nm Rep. Rate = 1.56 Hz 5

KEK Accelerator Test Facility (1.3 GeV) 6

Beam Diagnostic Systems for ATF2 Beam Position Monitors Stripline BPMs 12 in EXT + 1 in FFS 2-10 um resolution Cavity BPMs (20-200nm res.) 41 C-band (EXT, FFS & IP) 4 S-band (final doublet) Beam Position Monitors Stripline BPMs 12 in EXT + 1 in FFS 2-10 um resolution Cavity BPMs (20-200nm res.) 41 C-band (EXT, FFS & IP) 4 S-band (final doublet) Beam Size Monitors Solid-wire wirescanners 10um tungsten 5 in EXT, 1 post-ip 5um carbon IP assembly, 1 post- ip Pulsed laser-wire EXT, goal 1um measurement ability OTR monitors 4 in EXT close to wirescanner locations. IPBSM IP Interference “Shintake” laser monitor for vertical IP waist sizes 2um -> 20nm Beam Size Monitors Solid-wire wirescanners 10um tungsten 5 in EXT, 1 post-ip 5um carbon IP assembly, 1 post- ip Pulsed laser-wire EXT, goal 1um measurement ability OTR monitors 4 in EXT close to wirescanner locations. IPBSM IP Interference “Shintake” laser monitor for vertical IP waist sizes 2um -> 20nm High-Bandwidth (intra- pusle)Feedbacks FONT 2 phase feedback in EXT Stripline BPMs, stripline kickers, FPGA FB logic IP FB IP BPM c-band cavity BPM doublet or special low-Q cavity close to IP High-Bandwidth (intra- pusle)Feedbacks FONT 2 phase feedback in EXT Stripline BPMs, stripline kickers, FPGA FB logic IP FB IP BPM c-band cavity BPM doublet or special low-Q cavity close to IP Background Monitors Fibre loss monitor EXT+FFS (digitized) Multiple scintillator dector system for source ID Background Monitors Fibre loss monitor EXT+FFS (digitized) Multiple scintillator dector system for source ID 7

Beam Operation Modes Single bunch operation – 1 x e/bunch, 1.56 Hz (max 2 x Hz) Multi-bunch operation – 1-3 bunches, 154ns spacing with conventional DR kicker system – 1-30 bunches, 308ns spacing with ILC-spec fast (5ns rise-time) kicker system 30 Bunches DR -> EXT 8

Beam Size Monitors - Requirements Emittance determination, matching & coupling correction in EXT – Fast O(1 min) for emittance scans – <2% beam size measurement accuracy for good 4D emittance reconstruction – 4 OTR system taking over as primary measurement system due to speed of operation with Hz beam ops – Beam sizes ~10um Linear matching at IP – 5um C-wire scanners give ~1.25um measurement ability, can check approx matching with quad scans for relaxed IP beta configurations (nominal y size >1um) Tuning of IP beam size to goal A (~37nm) – C-wire used until beam size within capture range of IPBSM – IPBSM tunes down from 2um to goal size – Need low backgrounds at IP (<10GeV) Good BBA and steering in EXT AND FFS – To get optimal performance (few % at goal spot sizes), need either low jitter or knowledge of shot-shot jitter beam w.r.t. laser fringes at 10nm-level. 9

EXT OTR Monitor System 4 OTRs at different beam phases along EXT. Triggered CCD acquisition of OTR light. Online model software controls sequential target insertion, image acquisition, data quality checks and processing to obtain twiss parameters and emittances. Full automated emittance measurement <2min for 1.56Hz beam. 10

Emittance Measurements with OTR Automated scripts for acquition of 4 OTR images and processing into Twiss/Emittance data via EPICS link to online model data server (flight simulator). Coupling correction currently via scans of skew-quads versus emittance. Working on algorithms for automated measurement and correction via 4D emittance determination method 11

IPBSM 12

IP Beam Size Tuning with IPBSM After initial beam preparation, remaining aberrations at IP removed using orthogonalised multi-knobs based on offseting FFS Sextupole magnets. Good, stable beam at IP with good signal:background noise ratio critical for timely application of tuning knobs. Good S:N Poor S:N 13

Beam Position Monitors - Requirements General requirements – Beam based alignment Get BPM electrical offset -> quad/sext field centres – Steering Maintain accurate steered orbit (to BBA) for good IPBSM backgrounds and low-dispersion trajectory. Good maintenance of steered orbit (slow orbit FB) for stability when tuning IP beam size. – Dispersion measurements – Monitoring of IP vertical position offset – Good gain+offset calibration and monitoring (<10% level) Need good reproducibility of steered orbit, minimising repetition frequency of calibration and BBA determination. EXT stripline – 2-10um resolution (3 types of stripline installed) – Continuous self gain calibration – Scale calibration by orbit bump EXT & FFS c & s-band cavities – nm resolution (few um – few mm dynamic range) Depending on selected final stage attenuation – Integrated calibration tone monitoring – Calibration by orbit bump or magnet mover system for FFS IP c-band cavity doublet – ~8nm experimentally determined resolution – Need routine, robust operation at <10nm for goal A if jitter with respect to IPBSM fringe larger than this – Need ~10% vertical IP spot size measurement accuracy for Goal B (<3nm) Theoretically possible given thermal noise limit calculations, but need solid R&D to experimentally realise 14

EXT Stripline BPM System 15

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Stripline Resolution and Gain Monitoring Gains constantly calculated, monitored and self-corrects position readbacks. Also monitor resolution via SVN measurement method 17

Cavity BPM System 18

Digital DDC Processing of Cavity Waveforms 19

Cavity BPM Calibration 20

Calibration Tone for System Monitoring Monitor gain and phase differences for I/Q channels. Would like ~<1 degree and ~<10% drifts over 2 week timescales for stable operations. See this in cal system, but larger variations with repeated calibrations which are currently under investigation. 21

Resolution Monitoring 22

Cav BPM Controls Comprehensive user-friendly panel for BPM control and diagnostics. Setup + calibration with links to online model software. Diagnostic plots etc. 23

Dispersion Measurement and Correction 24

EXT and FFS BBA Data Quad-BPM offsets determined by “Quad shunting” technique. Resolutions achieved ~10um at best. Need to study stability of BPM offsets. 25

Model Checkout First requirement for any ATF2 tuning shift Sweep selection of corrector magnets, check response in downstream BPMs and check against online model. Checks BPMs well calibrated, magnets reading into online model correctly, control system linkages ok etc… 26

Orbit Steering Online s/w automated 2-stage orbit correction. Uses live model to compute and invert BPM->corrector / BPM -> magnet mover response matrices. +/- 500um orbit w.r.t. Magnet centre essential For low IP bkg condition +/- 500um orbit w.r.t. Magnet centre essential For low IP bkg condition FFS magnet-mover based steering EXT corrector- based steering 27

High-Bandwidth Feedbacks - Requirements Typical pulse-pulse orbit fluctuations are observed at the 10-20% σ x/y/E level. – Pulse-pulse distributed feedbacks are capable of maintaining this orbit with specified BPM hardware and conventional dipole correctors. – This preserves beam quality at IP to manageable levels (e.g. dispersion, coupling, waist shift etc) Beam motion at IP dominated by ground motion and mechanical vibration effects in key quadrupole magnets (mostly final doublet) – Ground motion and vibration measurements and theoretical studies suggest 10-30nm jitter w.r.t. IPBSM interference fringe likely. Control of IP vertical position at ~<10nm – level only possible by using MHz bandwidth feedback to control trailing edge of multi-bunch pulse (like ILC/CLIC style fast-feedback). – Need low-latency multi-bunch processing of IP cavity BPMs ~<2nm resolution and processing latency ~bunch spacing (~ ns) Low-Q or high-Q bpm systems required? will test both. – Test of high-bandwidth, low-latency BPM signal processing and driving of stripline corrector tested by FONT experiment in test region in EXT with stripline BPMs. 28

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IP Beam Position Monitor System 30

Cavity BPM Hardware R&D for IPBPM Low Q and High Q Approaches With multi-bunch ops, helpful to have ring-down time of cavities small wrt bunch spacing. New low-Q cavities produced, low resolution not yet demonstrated however. Alternative approach, separate pulses using digital processing algorithms to fit and subtract contributions from proceeding pulses. Continue to pursue both approaches. “High-Q” “Low-Q” 31

Background Monitoring - Requirements Provide online monitoring of beam loss events and approximate position reporting. – Fibre strung close to EXT & FFS beamline. Manufactured by Toray, 960mm core (PMMA), 1000um fluorinated polymer cladding. – PMT readout digitized and timing information provides few-m position resolution of loss events. – Useful for initial steering, alerts to beam loss events (e.g. when screen inserted) and sensitive enough to be used as backup system for wirescanner system detector. Distributed system of scintillator detectors for background type identification and source location. – Offline analysis, tied in with GEANT4 modelling of beamline, currently under development. – Will be very useful to understand IPBSM background sources. 32

Fibre Loss Monitor Display Beam loss position information available online during running. 33

Summary ATF2 employs a wide range of beam diagnostics for its main program and is testing many others. We are trying to push the stability, reproducibility and accuracy limits to serve the ATF2 program and to better understand the limitations of the instrumentation for future high-energy collider projects. The main program suffered a setback as a consequence of the March 11 th Mag. 9 earthquake in Eastern Japan. – Current status is most major repair work is completed and first beam restored to the main ATF2 beam dump Friday last week. – Substantial re-alignment work is needed in the DR before nominal emittance can be achieved but we expect the resumption of low-emittance beam to ATF2 this Autumn. 14:46 March