K.T. McDonald DoE Review 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.
Download ReportTranscript K.T. McDonald DoE Review 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.
K.T. McDonald DoE Review
E-166 Experiment
July 29, 2005
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 ( polarized photons.
= 2.4 mm, ID = 0.9 mm) to make 10-MeV – 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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(47 Collaborators) (16 Institutions) 2 K.T. McDonald DoE Review
E-166 Collaboration
July 29, 2005
K.T. McDonald DoE Review July 29, 2005
E-166 Beam Measurements
• Photon flux and polarization as a function of undulator K (P g ~ 75% for E g > 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.
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K.T. McDonald DoE Review July 29, 2005
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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Positron Spectrometer
(magnets built at Princeton)
July 29, 2005
Two Cerenkov counters with aerogel of index n = 1.0095 are now in the FFTB tunnel.
K.T. McDonald DoE Review July 29, 2005
Aerogel Cerenkov Counters
(built at Princeton)
Index measured with a Michaelson interferometer.
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K.T. McDonald DoE Review July 29, 2005
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.
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8 Run at 50 GeV if at all possible.
K.T. McDonald DoE Review July 29, 2005
Second Run of E-166 in Sept. 2005
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.