K.T. McDonald DoE Review Aug. 10, 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.

K.T. McDonald DoE Review Aug. 10, (47 Collaborators) E-166 Collaboration (16 Institutions)

K.T. McDonald DoE Review Aug. 10, 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.

K.T. McDonald DoE Review Aug. 10, 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.

K.T. McDonald DoE Review Aug. 10, Positron Spectrometer (magnets built at Princeton)

K.T. McDonald DoE Review Aug. 10, Aerogel Cerenkov Counters (built at Princeton) Two Cerenkov counters with aerogel of index n = are now in the FFTB tunnel. Index measured with a Michaelson interferometer.

K.T. McDonald DoE Review Aug. 10, Linac ran at 46.6 GeV, rather than 50 GeV,  max. positron energy only 8 MeV. Positron asymmetries observed of order 1%. Preliminary calculation of analyzing power implies that positron polarizations of up to 80-90% were observed. Preliminary Results from Runs of E-166 in June and Sept 2005

K.T. McDonald DoE Review Aug. 10, Implications The use of undulator-based production of positrons was accepted as the ILC baseline at SNOWMASS’05. The use of a helical undulator for production of polarized positrons is the recommended option. This option must now be established as cost effective.