Volume 77, Issue 2, February 2006
Index of content:
- PARTICLE SOURCES, OPTICS AND ACCELERATION; PARTICLE DETECTORS
77(2006); http://dx.doi.org/10.1063/1.2168676View Description Hide Description
The proposed experiment E-166 at SLAC is designed to demonstrate the possibility of producing longitudinally polarized positrons from circularly polarized photons to be used in future linear collider. The experimental setup utilizes a low emittance electron beam passing through a helical undulator in the final focus test beam line of the SLAC accelerator. Circularly polarized photons generated by the electron beam in the undulator hit a target and produce electron-positron pairs. The purpose of the post-target spectrometer is to select the positron beam and to deliver it to a polarimeter while keeping the positron beampolarization as high as possible. This article analyzes positron transmission and polarization in the E-166 spectrometer experiment. The positron transmission has a maximum value of 7% for a positron beam energy of , while positronpolarization is approximately 60%.
77(2006); http://dx.doi.org/10.1063/1.2170078View Description Hide Description
A low energy electron diffraction(LEED) instrument incorporating a delay line detector has been constructed to rapidly collect high-quality digital LEEDimages with low total electron exposures. The system uses a position-sensitive pulse-counting detector with high bias current microchannel plates. This delay-line detector combined with a femtoampere electron gun offers a wide range of flexibility, with electron dosing currents ranging from . Using the highest current setting and collecting counts per image, individual LEEDimages can be completed in with an acquisition rate of and a total electron exposure of electrons. Under the latter conditions, images can be collected in with an acquisition rate of with a total electron exposure of electrons. An angular width of 0.13° at is demonstrated, which means that domain sizes as large as can be resolved, depending on the surface quality of the crystal. The system electronics collect images with a spatial resolution of about . The dynamic range of this system is (limited only by physical memory). The construction of the detector results in a “plus”-shaped artifact, which requires that, for a given sample orientation, two images be taken at a relative angle of 45°. Identical current-voltage curves from an terminated sample, taken during several hours of exposure to the low current electron beam, demonstrate minimal electron induced H desorption.