12/12/04 1 stewart boogert (ucl) second mini-workshop nano project at atf lbbd-collaboration...

12/12/04 1 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF

LBBD-collaboration Laserwire update

Adams Institute (Oxford/Royal Holloway)G Blair, G Boorman, J Carter

N Delerue, C Driouichi, F Poirier, B Foster, D HowellF Poirier, B Foster, D HowellDESY

K Balewsk, H C Lewin, S Schreiber, M Wendt, K Wittenburg,K Balewsk, H C Lewin, S Schreiber, M Wendt, K Wittenburg,BESSYBESSY

T KampsT KampsUniversity College London

S Boogert, S MaltonRutherford Laboratory

I. RossI. Ross

SLAC

J. Frisch, M. Ross


Introduction

● Outline of the PETRA laserwire system and recent results

– PETRA

– Laserwire setup

– Scan results

– Compton signal

– Laser measurements

● Plans for ATF extraction line laserwire

– Chamber design

– Scanning

– Compton calorimeter

– Readout and control


PETRA

● Injector for HERA and will be upgraded to a SR light source

● Long free straight section

● IP camber with viewports and button BPM

● Operation

– Dedicated running during HERA fills

– Possible parasitic running during SR runs (HASYLAB)

– Beam bump to bring electron and photon beams into overlap

4.5 to 12

~100

3 to 20

1000 to 100

100 to 10

E/GeV

z/ps

nC

x/m

y/m

Energy

Bunch Length

Charge/bunch

Hor. beam size

Ver. beam size


PETRA laserwire

● Compton scattering of laser beam with electron beam

– Detect Comton photons colinear with electron beam by bending the electron beam out of the way

– Compton signal modulated by the spatial overlap of the beam distributions

– For the exisiting system at 7 GeV beam energy expect Compton rate ~103 photons


Nd:YAG Laser

● Old LEP polarimeter laser

– Q-switched Nd:YAG with SHO

– Externally triggered from PETRA bunch clock

– Rep. rate 30Hz

– Complete refurbishment at Oriel, new YAG crystal

– Transverse mode quality poor M2~10 (see later)

– Longitudinal mode quality also poor, GHz mode beating

1064/532 nm

250/90 mJ

10 ns

up to 30 Hz

≤ 1 mm

Wavelength

Energy

Pulselength

Rep rate

Beam size


Laser light transport


Scanning and focusing optics setup

● Scanner

– PI piezoelectric stack

– 2.5 mrad tilt range and ~kHz scanning frequency

● Focusing lens

– 125 mm, air spaced doublet from CVI

SCANNER

125 mm

IMAGINGLENS

TODUMP

VIEWPORTMIRROR

SPLITTER

CCD

BEAM

LENS


Post interaction diagnostics optics

● Transverse profile of laser measured using CCD camera

– Basler A300/A600 series cameras

– Firewire readout

– ~10m pixel size

SCANNER

125 mm

IMAGINGLENS

TODUMP

VIEWPORTMIRROR

SPLITTER

CCD

BEAM

LENS

● Need to measure laser beam size at collision

– Re-image laser spot using 4f relay


Compton calorimeter

● Requirements for detector material

– short decay time (avoid pile up)– short radiation length– small Moliere radius

● Cuboid detector crystals made of PbWO4

● 3x3 matrix of 18x18x150 mm crystals

● Energy resolution better than 5%


Fast scanner operation (December 2003)

● Positron beam in PETRA – 7 GeV

– Low current setup 7.1 mA, first bunch 0.458 mA (3.9 nC)

– High current 40.5 mA, first bunch 2.686 mA (22.3 nC)

● Find compton signal via beam bump in x and y

● Varied the voltage to the piezo scanner from 0 to 100 V

– corresponding to 2.5 mrad tilt

– taking 5000 calorimeter readings at each point

● Complete scan took 40 mins

● Background signal 20k events without laser pulse

● Large variations in the signal due to the laser mode beating


Profile measurements at PETRA

● Exponential background and Gaussian approximation of beam shape, fit results in –

m= (68 ± 3 ± 14) mat low current

– m= (80 ± 6 ± 16) mat high current


Compton rate (J. Carter)

Particles Particles NOTNOT passing through beam pipe: passing through beam pipe: 99.7%99.7%

Particles passing through beam pipe: 0.3%Particles passing through beam pipe: 0.3%

Using the ENTIRE spectrum Using the ENTIRE spectrum gives:gives:

~ 4200 photons~ 4200 photons

This spectrum for a single This spectrum for a single photon being generated at the photon being generated at the IP was used to extrapolate to N IP was used to extrapolate to N photonsphotonsMistake in the code meant that only Mistake in the code meant that only the Particles passing through were the Particles passing through were used.used.

Therefore only simulating Therefore only simulating what what passes through the beam pipe passes through the beam pipe - - not what was created at the IPnot what was created at the IPThis gave This gave ~7.6 photons~7.6 photons arriving in arriving in detectordetector

Good agreement with Shintake-san, Good agreement with Shintake-san, with given laser power and beam sizes with given laser power and beam sizes (electron and photon)(electron and photon)


Laser beam profile measurements (S. Malton)

● Laser beam size significant systematic error in size determination– Create IP focus before and

after laser transport down to tunnel

● Measure laser beam size as function of distance along beam using CCD cameras

● Beam waist 35-40 microns– M2 and sigma improve after beam

transport to tunnel● Errors large in tunnel due to

ambient light


DAQ and software upgrade (S. Boogert & G. Boorman)

● Previous running

– Totally manual system, calorimeter/scanner/bpm readout

– ~1 hour to take a scan

– Incomplete data format and unsyncronised

● Upgrades since December 2003

– Scanner motion triggered from PETRA trigger

– General trigger fanout card with programmable delays, 0.5ns resolution

– National instruments (NI) DAQ slow trigger system for triggering components

– Fast photodiodes and power meter digitisation

– PETRA data server, beam currents, BPM positions, vacuum status

● Integrated Labview DAQ program


PETRA conclusions and outlook● Last scans performed December 2002

– No new scanning data since then, only runs to understand the Compton spectrum success

– Problems with laser/access to PETRA

● Low Compton rate

– Total flux now consistent with expectations

– DESY has designed a new beam pipe with window

– Should increase Compton rate by ~two orders of magnitude

● Laser beam transverse size

– Measured using CCD cameras, consistent with measured electron beam size

● Next PETRA laserwire shift next week at DESY

● New laser (Modern Nd:YAG, Mode locked system?)

● Vertical optical system for x and y size measurement (being designed now)


ATF extraction line laserwire


ATF extraction line laserwire

● Test laserwire optics concept in the extraction line

– Install chamber before summer 2005

● Standard system with laser spot size ~5m

– Or during shutdown fall 2005

● Advanced system ~1m spot size

● Pulse structure and ILC timing

– Must wait until extraction kicker issue is resolved

● ATF parameters

– Energy : 1.28 GeV

– Bunch length : 26 ps

– Charge : > 0.5 1010

– Beam size at IP : down to 1x70m

● Laser parameters

– 300 mJ per pulse

– 200 ps pulse length

– Wavelength : 532 nm

– Rep. rate 10 Hz


Chamber design (D. Howell & N. Delerue)

● Design underway at Oxford

– Knife edge scanner

– OTR screen

– Optics probably inside vacuum vessel

– First design ready in the next few weeks, according to Nicolas

● Scanning

– Initially no active scanning, allow position jitter to scan electron beam across laser beam

– Electo-optic scanning

– Acoustic-optic scanning

● Custom lens design (1 m spot design)

– f>25mm

– D/f > 0.933

– Pure silica, due to radiation damage

– Compound lens, have to worry about glues in UHV

● Local diagnostics

– Traditional wire scanner

– ATF BPMs


Read out and control

● ILC bunch timing

– Transfer experience from PETRA

– Similar concepts for

● Compton detector● Tiggering● Readout and DAQ

– We are currently discussing how much of the existing PETRA system can be transferred directly to ATF extraction line

● Interface to existing diagnostics

– Nicolas has already done the ATF_CONTROL for FEATHER project

● BPM measurements● Corrector control

– Wire scanner control

● good to use same detector for laser and wire scanners


Issues related to ATF beam

● Position jitter in the extraction line

– Could use stripline BPMs to reconstruct electron beam position at laserwire IP

● ~1 m resolution possible?

● Laser performance

– Operational stability

– Must obtain characteristics, such as

● longitudinal profile● transverse profile

– Does this data exist?

● Laser light delivery optics

– Assume mostly in place for the polarised e+ measurements

● Compton detector

– Lead glass calorimeter, a la PETRA

– Air Cerenkov detector with APD for visible photon detection


ATF laserwire conclusions

● Recent discussions favour production of an optical system capable of producing 1m spot sizes

– Chamber design well underway at Oxford

– Lens design will start soon

– but later installation

● Compton calorimeter and DAQ

– Cold technology choice, short bunch spacing not an issue

– Developments at PETRA more applicable to the ATF

● UK laserwire collaborators are looking forward to a successful collaboration and many visits to Japan

12/12/04 1 stewart boogert (ucl) second mini-workshop nano project at atf lbbd-collaboration...

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