1. K.T. McDonald DoE Review July 29, 2005 1 E-166 Experiment E-166 is a demonstration of undulator-based polarized positron production for linear colliders. – E-166 uses the 50 GeV FFTB beam in conjunction with 1 m-long, helical undulator ( = 2.4 mm, ID = 0.9 mm) to make 10-MeV polarized photons. –These photons are converted in a ~ 0.5 rad. len. thick target into e+ (and e - ) with ~ 50% polarization. –The polarization of the positrons and photons will be measured. – E-166 was approved in June 2003, for a main data run in 2005.

2. K.T. McDonald DoE Review July 29, 2005 2 (47 Collaborators) E-166 Collaboration (16 Institutions)

3. K.T. McDonald DoE Review July 29, 2005 3 E-166 Beam Measurements Photon flux and polarization as a function of undulator K (P  ~ 75% for E  > 5 MeV). Positron flux and polarization vs. energy for K = 0.17, 0.5 r.l. of Ti (P e + ~ 50%). Positron flux and polarization for 0.1 r.l. and 0.25 r.l. Ti and 0.1, 0.25, and 0.5 r.l. W targets. Each measurement is expected to take about 20 minutes. A relative polarization measurement of 5% is sufficient to validate the polarized positron production processes. The undulator will be pulsed in a random pattern of beam pulses to permit continuous monitoring of undulator-off background levels.

4. K.T. McDonald DoE Review July 29, 2005 4 E-166 Undulator (built at Cornell U. by Mikhailichenko) Two helices wound on a 0.9-mm ID, 1-m-long hypodermic needle. 1.4 kA pulses, ~ 5 μs long provide field of ~ 1 T on axis,  k ~ 0.15.

5. K.T. McDonald DoE Review July 29, 2005 5 Positron Spectrometer (magnets built at Princeton)

6. K.T. McDonald DoE Review July 29, 2005 6 Aerogel Cerenkov Counters (built at Princeton) Two Cerenkov counters with aerogel of index n = 1.0095 are now in the FFTB tunnel. Index measured with a Michaelson interferometer.

7. K.T. McDonald DoE Review July 29, 2005 7 Preliminary Results from First Run of E-166 in June 2005 Linac ran at 46.6 GeV, rather than 50 GeV,  max. positron energy only 8 MeV. Low electron beam emittance, but still significant scraping of beam by undulator,  ~ 3 GeV/pulse backgrounds in the CsI detector. Undulator photons observed in the aerogel and Si-W detectors at roughly the expected rate, and with ~2% asymmetry on reversal of the photon polarimeter iron-core magnet, also as expected. Undulator on-off signal of ~ 2 GeV/pulse of in the CsI detector. Raw, preliminary asymmetry of 0.007  0.002 on reversal of the positron polarimeter iron-core magnet, in rough agreement with expectations.

8. K.T. McDonald DoE Review July 29, 2005 8 Second Run of E-166 in Sept. 2005 Run at 50 GeV if at all possible. Improved position control of the undulator. Improved tuning/collimating of tails in the electron beam. Additional shielding against beam scraping. Improved acceptance of the positron spectrometer. Data with 4 targets, 2 Ti and 2 W.