Laser-wireMeasurement

PrecisionGrahame Blair

Beijing- BILCW07, 6th February 2007

• Introduction

• Overview of errors

• Ongoing technical work in this area

• Plans for the future.

BESSY: T. KampsDESY : E. Elsen, H. C. Lewin, F. Poirier, S. Schreiber, K.

Wittenburg, K. BalewskiJAI@Oxford: B. Foster, N. Delerue, L. Corner, D. Howell, M.

Newman, A. Reichold, R. Senanayake, R. WalczakJAI@RHUL: G. Blair, S. Boogert, G. Boorman, A. Bosco, L.

Deacon, P. Karataev, S. Malton , M. Price I. Agapov (now at CERN)

CCLRC: I. RossKEK: A. Aryshev, H. Hayano, K. Kubo, N. Terunuma, J.

UrakawaSLAC: A. Brachmann, J. Frisch, M. WoodleyFNAL: M. Ross

Laser-wire People

Laser-wire Principle

PETRAII• 2d scanning system• DAQ development• Crystal calorimeter

→ PETRA III• Ultra-fast scanning• Diagnostic tool

The Goal: Beam Matrix Reconstruction

50% Reconstruction success <5% error on σy

NOTE: Rapid improvementwith better σy resolution

Reconstructed emittanceof one trainusing 1% error on σy

Conclude: Essential to measurethe spot-size at the few % level or better

I. Agapov, M. Woodley

x

y u

x

y u

Skew Correction

y

x

1

optimal tan

ILCat 8868

21

222

4

y

y

x

x

u

uyxxy

Error on coupling term:

ILC LW Locations Eb = 250 GeV

x(m) y (m) opt(°) u (m)

39.9 2.83 86 3.9917.0 1.66 84 2.34

17.0 2.83 81 3.95

39.2 1.69 88 2.39

7.90 3.14 68 4.1344.7 2.87 86 4.05

2σscan

2σe

2αJσe

Ntrain bunches

2σL=2cτL

2σe (1 + strain)

αtrainσe

Scan of an ILC Train of Bunches

Not to scale!

Dyx

e HfNN

L4

rep2

train 2train3

1111 s

Need for Intra-Train Scanning

For <0.5% effect, strain<0.12; otherwise, the effect must be subtracted

For 1m bunches, the error after subtracting for any systematic shift (assumed linear ±αtrainalong the train) is:

trainBPM3

nm 100109.1

e

e

For <0.5% effect, αtrain<2.6; otherwise, higher precision BPMs required

Machine Contributions to the Errors

Bunch Jitter

21222scan EeJe

Dispersion

nm1000.5105 BPM

22

J

e

e

2mm/3.2

e

eAssuming can be measured to 0.1%,then must be kept < ~ 1mm

BPM resolution of 20 nm may be required

Alternative Scan Mode• R&D currently investigating ultra-fast scanning (~100 kHz)

using Electro-optic techniques• Alternative: Keep laser beam fixed and use natural beam jitter

plus accurate BPM measurements bunch-by-bunch.Needs the assumption that bunches are pure-gaussian

• For one train, a statistical resolution of order 0.3% may be possible

m10 m,1 exey

Beam jitter fixed at 0.25σ BPM resolution fixed at 100 nm

Single-bunch fit errors for

σeyσexσℓ

xR

laser beam

electron bunch

√2σℓ

xfzy

xfIzyxI

RR2

22

20

2exp1

2,,

ℓℓℓ

For TM00 laser mode:

2

1

RR x

xxf

#2 fM ℓ

2#

2 4 fMxR

Laser Conventions

Compton Statistics

2

21

Detected exp2

11212m

y

m

N

Approximate – shoulduse full overlap integral(as done below…)

Where :

m2.0nm 532102MW 100.05 10

det

fNP eℓ

Laser peak power

Detector efficiency(assume Cherenkov system)

Compton xsec factor

Laser wavelength

e-bunch occupancy

TM00 Mode Overlap Integrals

m10

m,1

ex

ey

m100

m,1

ex

ey

Rayleigh Effects obviousMain Errors:• Statistical error from fit ~ -1/2

• Normalisation error (instantaneous value of ) – assume ~1% for now.• Fluctuations of laser M2 – assume M2 known to ~1%• Laser pointing jitter

2

22

2

#

MMMf

ee

e

%10/

rad10102.2

23

e

e

Y. Honda et al

Estat EM2

TM01

TM00

TM01

TM00

TM01

TM01 gives some advantage for larger spot-sizes

Laser RequirementsWavelength 532 nmMode Quality 1.3Peak Power 20 MWAverage power 0.6 WPulse length 2 psSynchronisation 0.3 psPointing stability 10

rad

ILC-spec laser is being developed at JAI@Oxfordbased on fiber amplification. L. Corner et al

ATF2 LW; aiming initiallyat f2; eventually f1?

TM00 mode

Error resulting from5% M2 change

Statistical ErrorFrom 19-point scan

• Optimal f-num1-1.5 for = 532nm• Then improve M2 determination• f-2 lens about to be installed at

ATF

Relative Errors

Towards a 1 m LW

Wavelength 266 nmMode Quality 1.3Peak Power 20 MWFF f-number 1.5Pointing stability 10

radM2 resolution 1%Normalisation ()

2%

Beam Jitter 0.25BPM Resolution 20 nmEnergy spec. res 10-4

Goals/assumptionsE 2.5

Epoint 2.2

Ejitter 5.0

Estat 4.5

EM2 2.8

Total Error

8.0

Resultant errors/10-3

Could be used for measurement→ E

Final fit, including dispersion

preliminary

Lens Design + Tests

Aspheric doublet

N. Delerue et al.

Vacuum window

• f-2 lens has been built and is currently under test.

• Installation at ATF planned for this year

M. Newman, D. Howell et al.

Designs for f-1 optics are currently being studied, including:

S. Boogert, L. Deacon

ATF Ext

ATF/ATF2 Laser-wire• At ATF2, we will aim to measure micron-scale electron spot-

sizes with green (532 nm) light. • Two locations identified for first stage (more stages later)

1) 0.75m upstream of QD18X magnet2) 1m downstream of QF19X magnet

LW-IP (1) LW-IP (2)

σx = 38.92 m σx = 142.77 m

σy = 7.74 m σy = 7.94 m

Nominal ATF2 optics

ATF2 LW-test optics

P. Karataev

LW-IP (1) LW-IP (2)

σx = 20.43 m σx = 20 m

σy = 0.9 m σy = 1.14 m

Ideal testing ground for ILC BDS Laser-wire system

ATF LW Plans• March 07: Start upgrading ATF LW hardware• April 07: aim to install f2 lens system• May/Jun 07: aim to take first micron-scale scans

Longer term• Upgrade laser system to reduce spot-size further• Install additional LW systems, building towards emittance

measurement system for ATF2.• Investigate running with UV light.• Implement ultra-fast scanning system (first to be tested at

PETRA, funding permitting)• Build f-1/1.5 optical system

Summary• Very active + international programme:

- Hardware- Optics design- Advanced lasers- Emittance extraction techniques- Data taking + analysis- Simulation

• All elements require R&D- Laser pointing- M2 monitoring- Low-f optics- Fast scanning- High precision BPMs

• Look forward to LW studies at PETRA and ATF• ATF2 ideally suited to ILC-relevant LW studies.