1. The E166 Experiment K. Peter Schüler e+ source options for the ILC undulator source scheme for ILC E166 – proof-of-principle demonstration of the undulator method undulator basics transmission polarimetry results & conclusions The E166 Experiment: Undulator-Based Production of Polarized Positrons K. Peter Schüler (DESY) - on behalf of the E166 Collaboration PSTP 2007 at BNL 10-14 Sep. 2007

2. The E166 Experiment K. Peter Schüler e+ source options for the ILC 2 existing/proposed positron sources: ILC 3 Concepts: large amount of charge reqd ! conventional laser Compton based (see M. Kurikis talk) undulator-based (this talk) PSTP 2007 at BNL 10-14 Sep. 2007

3. The E166 Experiment K. Peter Schüler 3 conventional positron source (as used with SLC at SLAC) PRO: established technology (although not at reqd level) CON: pushing technical limits of target materials; reqs multiple targets and beamlines; very high activation levels no polarization option PSTP 2007 at BNL 10-14 Sep. 2007 thick W-Re target: strong multiple scattering, less efficient e+ capture

4. The E166 Experiment K. Peter Schüler undulator source scheme for ILC 4 PRO: photoprod. in thin target 0.4 X 0 Ti-alloy lower e+ beam emittance less energy deposition in target (1/5) and AMD (1/10) less neutron induced activation (1/16) polarized positrons CON: need high-energy electron drive beam (coupled e+/e- operation) long undulator (150-300 m) reqd positron beam profile PSTP 2007 at BNL 10-14 Sep. 2007

5. The E166 Experiment K. Peter Schüler undulator source scheme for ILC 5 PSTP 2007 at BNL 10-14 Sep. 2007 auxiliary keep-alive source

6. The E166 Experiment K. Peter Schüler E166 – proof of principle demonstration of the undulator method 6 PSTP 2007 at BNL 10-14 Sep. 2007

7. 7 The E166 Experiment K. Peter Schüler PSTP 2007 at BNL 10-14 Sep. 2007

8. The E166 Experiment K. Peter Schüler undulator basics 8 PSTP 2007 at BNL 10-14 Sep. 2007 E166 ILC (RDR) electron beam energy (GeV) 46.6 150 field (T) 0.71 0.86 period (mm) 2.54 11.5 K value 0.17 0.92 photon energy 0 max (MeV) 7.9 10.0 beam aperture (mm) 0.89 5.85 active length (m) 1 147 M (no. of periods) 394 12800

9. The E166 Experiment K. Peter Schüler undulator basics 9 PSTP 2007 at BNL 10-14 Sep. 2007 E166 Photon SpectrumE166 Photon Polarization Spectrum:Angular Distribution:Polarization: first harmonic (dominating) expressions: E166 Photon Yield: = no. of photons per high-energy beam electron 0 max = 7.9 MeV

10. The E166 Experiment K. Peter Schüler The E166 Experiment 10 PSTP 2007 at BNL 10-14 Sep. 2007 2004/2005 setup and checkout Oct. 2005 4 weeks of data taking

11. The E166 Experiment K. Peter Schüler E166 experimental setup 11 PSTP 2007 at BNL 10-14 Sep. 2007 46.6 GeV 4 – 8 MeV C1 – C4: photon collimation AG1, AG2: aerogel detectors AG1Si, AG2Si: silicon detectors GCAL: Si/W-calorimeter DM: electron beam dump magnets T1: g e+ prod. target (0.2 X 0 W) T2: e+ g reconv. target (0.5 X 0 W) PosSi: e+ flux monitor (Silicon) CsI: Cesium Iodide calorimeter SL: solenoid lens J: movable jaws < 8 MeV

12. The E166 Experiment K. Peter Schüler E166 photo gallery 12 PSTP 2007 at BNL 10-14 Sep. 2007

13. The E166 Experiment K. Peter Schüler transmission polarimetry 13 1.Compton Transmission Polarimetry for Low-Energy Photons relies on spin dependence of Compton effect in magnetized iron: 2.Positron Polarimetry: (a) transfer e+ polarization to photon via brems/annihilation process (b) then infer e+ polarization from measured photon pol. as in method 1. PSTP 2007 at BNL 10-14 Sep. 2007

14. 14 analyzer magnets: overview active volume Photon Analyzer: 50 mm dia. x 150 mm long Positron Analyzer: 50 mm dia. x 75 mm long The E166 Experiment K. Peter Schüler P e 0.07 ΔP e /P e < 0.05 (aim of experiment) electron polarization of the iron: M = (B–B 0 )/ 0 magnetization n = electron density μ B = Bohr magneton g = magneto-mechanical factor PSTP 2007 at BNL 10-14 Sep. 2007

15. 15 spin and magnetization The E166 Experiment K. Peter Schüler g = magneto-mechanical factor: obtained from Einstein - de Haas type experiments, related to gyromagnetic ratio: γ = (g/2) (e/m) the principle … and its ultimate implementation (Scott 1962) g = 1.919 ± 0.002 for pure iron i.e. orbital effects contribute about 4% Note: g = 2 M s / M = 1 (pure spin magnetization) γ = e/m g = 1 M s / M = 0 (pure orbit magnetization) γ = ½ (e/m) PSTP 2007 at BNL 10-14 Sep. 2007

16. 16 analyzer magnets The E166 Experiment K. Peter Schüler CsI-Detector e+ Analyzer Pickup Coils e+ Analyzer Analyzer PSTP 2007 at BNL 10-14 Sep. 2007

17. 17 field distribution modeling (Vector Fields OPERA-2d) The E166 Experiment K. Peter Schüler R = 0 mm 10 15 22.5 B z (T) Z (mm) longitudinal field distribution: B z (R,Z) field drops gradually towards the ends: L eff / L < 1 center end PSTP 2007 at BNL 10-14 Sep. 2007 20 5

18. 18 field distribution in 2d (Vector Fields OPERA-2d) The E166 Experiment K. Peter Schüler longitudinal field distribution: B z (R,Z) (shown for one quadrant) R (mm) Z (mm) PSTP 2007 at BNL 10-14 Sep. 2007

19. 19 flux measurements: The E166 Experiment K. Peter Schüler measure voltage transients in pickup coils upon current reversals Positron Analyzer (-60 +60 amps) PSTP 2007 at BNL 10-14 Sep. 2007 voltage transient

20. 20 flux and field measurements: results The E166 Experiment K. Peter Schüler Note: polarimetry was always done at full saturation over the central region (±60A) Z = 0 (center) PSTP 2007 at BNL 10-14 Sep. 2007

21. 21 electron polarization of the iron The E166 Experiment K. Peter Schüler PSTP 2007 at BNL 10-14 Sep. 2007 P e /P e ~ 2%

22. 22 photon asymmetries The E166 Experiment K. Peter Schüler PSTP 2007 at BNL 10-14 Sep. 2007 detector asymmetry (%) (%) AG2Si (silicon) 3.883 0.062 AG2 (aerogel) 3.307 0.123 GCAL (Si/W-calo) 3.665 0.071 AG2Si AG2 GCAL measured photon asymmetries are in reasonable agreement with simulation results (3.2-3.5%) based on the theoretical undulator polarization spectrum and detector response functions, but no detailed spectral shape analysis is possible.

23. The E166 Experiment K. Peter Schüler e+ analysis: energy deposition in CsI crystals 23 good signal/background separation in central crystal background comes from beam halo hitting the undulator undulator on/off measurements were taken on alternating machine pulses for effective background separation PSTP 2007 at BNL 10-14 Sep. 2007 undulator on: signal + background undulator off: background

24. The E166 Experiment K. Peter Schüler 24 central crystal asymmetry vs. run cycle number for e+ spectrometer setting at 140 A positron asymmetries PSTP 2007 at BNL 10-14 Sep. 2007 data samples and spectrometer settings

25. The E166 Experiment K. Peter Schüler positron asymmetries & beam polarizations 25 PSTP 2007 at BNL 10-14 Sep. 2007 e+ / e- results for the central CsI crystal = analyzing power from simulations = electron polarization of the iron

26. 26 conclusions successful demonstration of the undulator method undulator functioned as predicted successful polarimetry of low-energy and e+ confirmed expected γ e+ spin-transfer mechanism measured high positron polarization with ~ 80% max. The E166 Experiment K. Peter Schüler PSTP 2007 at BNL 10-14 Sep. 2007