1. 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 F Poirier, B Foster, D Howell N Delerue, C Driouichi, F Poirier, B Foster, D Howell DESY K Balewsk, H C Lewin, S Schreiber, M Wendt, K Wittenburg, BESSY T Kamps University College London S Boogert, S Malton Rutherford Laboratory I. Ross SLAC J. Frisch, M. Ross

2. 12/12/04 2 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

3. 12/12/04 3 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

4. 12/12/04 4 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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 ~10 3 photons

5. 12/12/04 5 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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 M 2 ~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

6. 12/12/04 6 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF Laser light transport

7. 12/12/04 7 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

8. 12/12/04 8 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF Post interaction diagnostics optics ● Transverse profile of laser measured using CCD camera – Basler A300/A600 series cameras – Firewire readout – ~10  m pixel size ● Need to measure laser beam size at collision – Re-image laser spot using 4f relay

9. 12/12/04 9 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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%

10. 12/12/04 10 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

11. 12/12/04 11 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF Profile measurements at PETRA ● Exponential background and Gaussian approximation of beam shape, fit results in –  m = (68 ± 3 ± 14)  m  at low current –  m = (80 ± 6 ± 16)  m  at high current

12. 12/12/04 12 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF Compton rate (J. Carter) Particles NOT passing through beam pipe: 99.7% Particles passing through beam pipe: 0.3% Using the ENTIRE spectrum gives: ~ 4200 photons This spectrum for a single photon being generated at the IP was used to extrapolate to N photons Mistake in the code meant that only the Particles passing through were used. Therefore only simulating what passes through the beam pipe - not what was created at the IP This gave ~7.6 photons arriving in detector Good agreement with Shintake-san, with given laser power and beam sizes (electron and photon)

13. 12/12/04 13 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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 – M 2 and sigma improve after beam transport to tunnel ● Errors large in tunnel due to ambient light

14. 12/12/04 14 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

15. 12/12/04 15 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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)

16. 12/12/04 16 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF ATF extraction line laserwire

17. 12/12/04 17 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF ATF extraction line laserwire ● Test laserwire optics concept in the extraction line – Install chamber before summer 2005 ● Standard system with laser spot size ~5  m – Or during shutdown fall 2005 ● Advanced system ~1  m 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 10 10 – Beam size at IP : down to 1x70  m ● Laser parameters – 300 mJ per pulse – 200 ps pulse length – Wavelength : 532 nm – Rep. rate 10 Hz

18. 12/12/04 18 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

19. 12/12/04 19 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

20. 12/12/04 20 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF 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

21. 12/12/04 21 Stewart Boogert (UCL) Second Mini-workshop Nano project at ATF ATF laserwire conclusions ● Recent discussions favour production of an optical system capable of producing 1  m 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