1. A Short History of Nearly Everything Michele Viti

2. 07 August 2009Michele Viti2 Outline Myself About my work in Zeuthen –ILC overview –Beam energy measurement –An brief overview of my work and results Magnetic measurements Relative beam energy resolution Laser Compton energy spectrometer

3. 07 August 2009Michele Viti3 Myself I was born 31 years ago somewhere in Italy I studied physics at the Perugia university

4. 07 August 2009Michele Viti4 Myself Master degree in 2004. Title of the thesis : “Evaluation of a Tracking Algorithm for the Trigger of KOPIO Experiment on the Decay ”. I continued working on this topic until the project was canceled by the DOE.

5. 07 August 2009Michele Viti5 Myself I moved then to Germany and started in February 2006 my PhD. I joined the Linear Collider working under the supervision of H.J. Schreiber. Title of the thesis “Precise and Fast Beam Energy Measurements at ILC”.

6. 07 August 2009Michele Viti6 ILC 30 Km electrons/positrons linear accellerator Total energy in the cms 500 Gev (upgradeable 1 Tev) High luminosity (2*10^34 /cm^2*s) A machine for precise measurements

7. 07 August 2009Michele Viti7 ILC: Precise Top Mass Measurements Many Standard Model depends strongly on the value of the Top Mass. Well understood background, clean experimental environment Best direct measurement of the top mass will be at ttbar threshold –Vary the beam energy (Precise Beam Energy Measurements) – Count number top-antitop events.

8. 07 August 2009Michele Viti8 Basic Requirements for Beam Energy Measurements In order to make a precise measurement of the top quark mass we need to know some “input” parameters very well such as the mean energy of the bunch We need to have a fast (bunch-by-bunch), precise and non-destructive monitor for beam energy Direct measurement of energy at the IP is very difficult. We want to measure the beam energy upstream, downstream the IP plus a slow monitoring at the IP Relative Energy precision required for upstream measurements

9. 07 August 2009Michele Viti9 Magnetic Chicane Energy Spectrometer Electrons are deflected in this chicane and the offset in the mid-chicane is anti-proportional to the energy. Measuring this position with some special devices (Beam Position Monitor, BPM) together with B-field integral we have access to the beam energy Method well tested used at LEP with a precision of offset d magnets L BPM

10. 07 August 2009Michele Viti10 Experiment T474/491 At the End Station A (ESA) a 4-magnet chicane energy spectrometer was commissioned in 2006/2007 (experiment T474/491). The goal is to demonstrate the feasibility of the system.

11. 07 August 2009Michele Viti11 End Station A Characteristic: –Parasitic with PEP II operation –10 Hz and 28.5 GeV –Bunch charge, bunch length energy spread similar to ILC Prototype components of the Beam delivery System and interaction Region.

12. 07 August 2009Michele Viti12 End Station A ParameterSLAC ESAILC-500 Repetition Rate 10 Hz5 Hz Energy 28.5 GeV250 GeV Bunch Charge 2.0 x 10 10 Bunch Length 300-500  m300  m Energy Spread 0.2%0.1% Bunches per train 1 (2*)2820 Microbunch spacing (20-400 ns*)337 ns Beam Parameters at SLAC ESA and ILC

13. 07 August 2009Michele Viti13 Experiment T474/491 Institutes involved: SLAC, U.C. Berkeley, Notre Dame, Dubna, DESY, RHUL, UCL, Cambridge 2006: –January (4 days): commissioning steering BPMs –April(2 weeks): commissioning cavity BPMS, optimization digitization and processing –July(2 weeks): commissioning interferometer and stabilty data taken with frequent calibrations 2007: –March(3 weeks): Commissioning and installation magnets: first chicane data!!! –July(2 weeks): Additional new BPM in the centre of the chicane.

14. Magnetic measurements

15. 07 August 2009Michele Viti15 Magnetic measurements B-field Integral, essential parameter for beam energy measurement. Need to be measured with an accuracy of 50 ppm.

16. 07 August 2009Michele Viti16 Magnetic measurements Between November 2006 – February 2007 measurements on these magnets were performed in the SLAC laboratories (DESY, Dubna, SLAC). Purpose of the measurements: –General understanding and characterization of the magnets Stability of the B-field and B-field integral with fixed current and switching the polarity. Monitoring of the residual B-field. B-field map. Measurement of the temperature coefficient for B-field and B-field integral. –Development and test a procedure to monitor the B-field integral.

17. 07 August 2009Michele Viti17 Magnetic measurements Monitor of the B-field integral: in ESA no device was available to measure directly this quantity. Solution: measure the B-field in one point and from that determine the integral. –Basic assumption When the field is changing in one point, changes everywhere by the same amount. The field shape stay constant

18. 07 August 2009Michele Viti18 Magnetic measurements To measure the B-field in one point an NMR probe was used. Flip coil technique to measure for B-field integral. Calibration of the NMR: determination of the slope and intercept for the relation. Comparison of the prediction with the measurement.

19. 07 August 2009Michele Viti19 Magnetic measurements The total error on the estimation of the B- field integral using the one-point B-field measurement was Main contributions are alignment errors of the devices. Several suggestions were given to improve the results.

20. Relative beam energy resolution

21. 07 August 2009Michele Viti21 Relative Beam Energy Resolution At the End Station A several problems occurred for 4-magnet chicane prototype A complementary method to cross-check the absolute energy measurement was not implemented Only relative energy measurement possible at ESA

22. 07 August 2009Michele Viti22 Relative Beam Energy Resolution The offset d in the mid-chicane point is determined by two points, namely Xb and X0 Xb is measured by the BPMs the mid-chicane and X0 is extrapolated using BPMs upstream and downstream of the chicane. Beam direction

23. 07 August 2009Michele Viti23 Relative Beam Energy Resolution BPMs, Beam Position Monitors. They measure the transverse position (X and Y) and angle (tilt) in the X-Z and Y-Z plane (X’ and Y’). Accuracy on position measurement < 500 nm.

24. 07 August 2009Michele Viti24 Relative Beam Energy Resolution X0 can be written as For zero current magnet Xb=X0, the BPM measures directly X0. The coefficients in Eq. above can be determined with a minimization.

25. 07 August 2009Michele Viti25 Relative Beam Energy Resolution One fundamental condition: the magnetic chicane must work symmetrically The upstream path must be restored downstream Beam direction

26. 07 August 2009Michele Viti26 Relative Beam Energy Resolution Unfortunately this was not the case of the 4-magnet chicane in ESA For a given current the magnet fields were different up to ~3% BPMs downstream could not be used to determine X0. This resulted in a worse resolution for d.

27. 07 August 2009Michele Viti27 Relative Beam Energy Resolution A resolution of 24 MeV was found (Resolution -- the smallest amount of energy change that the instrument can detect reliably) For a beam energy of 28.5 GeV this corresponds to a relative resolution of ~ The largest contribution to this number comes from the resolution on d (>2 microns).

28. Laser Compton Energy Spectrometer

29. 07 August 2009Michele Viti29 Laser Compton Energy Spectrometer At LEP it was possible to have redundant beam energy measurement devices  cross check!!! At ILC so far, complementary methods for upstream beam energy measurements not implemented. Studying the feasibility of an upstream energy spectrometer based on Compton backscattering (CBS) events.

30. 07 August 2009Michele Viti30 Laser Compton Energy Spectrometer Compton process with initial electron not at rest. Energy spectrum for electrons (photons) present a sharp cut-off (Compton edge). Scattered particles collimated in forward region.

31. 07 August 2009Michele Viti31 Laser Compton Energy Spectrometer

32. 07 August 2009Michele Viti32 Energy measurement, is the center of gravity of the scattered photons, or, equivalently, the end point of the SR fan., position of beam, possible to measure with BPMs, position of the electrons with minimum energy.

33. 07 August 2009Michele Viti33 Laser Compton Energy Spectrometer Beam parameters –Beam energies 50-500 GeV –Beam size in x (y) 20-50 (2-5) microns Geometrical parameters –Drift distance 25-50 m –B field 0.28 T, magnet length 3 m Laser parameters –Smaller wavelength preferable (e.g. green laser) –Pulsed laser with 3 MHz frequency –Laser spot size 50-100 microns –Laser pulse energy must ensure 10^6 scatters (e.g. 30 mJ per pulse) –Crossing angle ~8 mrad Accuracy required to achieved – < 1-2 microns – < 20 microns

34. 07 August 2009Michele Viti34 Laser Compton Energy Spectrometer Beam position can measured with a normal BPM (very well know and precise technique). Edge position: Diamond strip detector or quartz fiber detector. Basic simulation shows that this feasible. Photon detection: Basically 2 possibilities, using the backscattered photons or the synchrotron radiation photons.

35. 07 August 2009Michele Viti35 Laser Compton Energy Spectrometer Number of backscattered photons (BP) 4 order of magnitude less than SR photons BP ~100 GeV, SR photons ~3 MeV. 2 possibilities –Place a thick absorber in front of detector and measure the profile of shower (signal from BP dominant), quartz fiber detector suitable. –No absorber, detector in front of the photon beam (signal from SR photons dominant). Novel detector under development in DUBNA (Xenon gas detector). Main problem for both configurations: very high radiation dose (10-100 GGy per year).

36. 07 August 2009Michele Viti36 Conclusions A prototype of 4-magnet chicane was built in ESA. The absolute value of the B-field integral can be monitored with an accuracy 184 ppm (ESASLAC note and PAC poster) The resolution of the chicane was found to be ~24 MeV, where the main contribution is the resolution on the beam offset in the mid-chicane (to be published…) A novel method based on Laser Compton events was studied(NIM publication). An experiment is under study to proof the feasibility (proposal in preparation).