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K.T. McDonald DoE Review Aug. 10, 2006

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.

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K.T. McDonald DoE Review Aug. 10, 2006

(47 Collaborators)

E-166 Collaboration

(16 Institutions)

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K.T. McDonald DoE Review Aug. 10, 2006

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 (Pe+ ~ 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.

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K.T. McDonald DoE Review Aug. 10, 2006

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.

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K.T. McDonald DoE Review Aug. 10, 2006

Positron Spectrometer(magnets built at Princeton)

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K.T. McDonald DoE Review Aug. 10, 2006

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.

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K.T. McDonald DoE Review Aug. 10, 2006

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 Runsof E-166 in June and Sept 2005

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K.T. McDonald DoE Review Aug. 10, 2006

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.