1

Operational Experience with ATF2 Beam Diagnostics

Glen White, SLACOn Behalf of ATF2 Collaboration

TIPP, Chicago, June 2011

2

ATF2 @ KEK

3

ATF International Collaboration

4

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.

5

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 Parametersex / ey = 1.3nm / 8-10pmE = 1.282 GeVATF2 IP parametersbx / by = 4cm / 0.1mmsx / sy = 6um / 37nmRep. Rate = 1.56 Hz

6

KEK Accelerator Test Facility (1.3 GeV)

7

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 Size Monitors•Solid-wire wirescanners

• 10um tungsten• 5 in EXT, 1 post-ip

• 5um carbon• 1 @ 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

Background Monitors•Fibre loss monitor• EXT+FFS (digitized)

•Multiple scintillator dector system for source ID

8

Beam Operation Modes• Single bunch operation

– 1 x 1010 e/bunch, 1.56 Hz (max 2 x 1010 @ 3.02Hz)• 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

9

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 1.56-3.02 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.

10

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.

11

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

12

IPBSM

13

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

14

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– 20-200nm 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

15

EXT Stripline BPM System

16

17

Stripline Resolution and Gain Monitoring

• Gains constantly calculated, monitored and self-corrects position readbacks.

• Also monitor resolution via SVN measurement method

18

Cavity BPM System

19

Digital DDC Processing of Cavity Waveforms

20

Cavity BPM Calibration

21

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.

22

Resolution Monitoring

23

Cav BPM Controls

• Comprehensive user-friendly panel for BPM control and diagnostics.

• Setup + calibration with links to online model software.

• Diagnostic plots etc.

24

Dispersion Measurement and Correction

25

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.

26

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…

27

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 essentialFor low IP bkg condition

FFS magnet-mover based steering

EXT corrector-based steering

28

High-Bandwidth Feedbacks - Requirements

• Typical pulse-pulse orbit fluctuations are observed at the 10-20% σx/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 (~100-300 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.

29

FONT

30

IP Beam Position Monitor System

31

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”

32

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.

33

Fibre Loss Monitor Display

• Beam loss position information available online during running.

34

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 11th 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 11 2011