Wire scanners for emittance measurements at the 100 keV spin polarized electron beam line at the S-DALINAC

A source of 100 keV spin polarized electrons has been installed at the 130 MeV superconducting Darmstadt linear accelerator S-DALINAC. Circularly polarized laser light excites a GaAs cathode, producing spin polarized electrons in bunches with pulse lengths in the region of 50 ps and smaller at a repetition frequency of 3 GHz. A Wienfilter for spin manipulation and a Mott polarimeter for polarization measurements are installed in the low-energy beam line. Polarizations up to 86% have been shown with strained superlattice GaAs cathodes. Installed wire scanners in the beam line measure beam radius and position and in conjunction with a solenoid with variable focal length a parameter set of beam sizes depending on the focal length can be obtained, allowing for an emittance calculation. The scanning unit, two perpendicular 50 mum tungsten wires for x and y measurements mounted on an insulated frame, is installed at an angle of 45° in a plane perpendicular to the beam. Pneumatic as well as electric translation is used while the data read-out is done by a 24-bit ADC with variable reading speed. Measurements at the S-DALINAC give an indication of the beam quality of the spin polarized electron source, permit a comparison with the already installed thermionic electron source, and allow the measurement of a possible emittance growth from the Wien-filter that is to be excluded. Furthermore, the knowledge of the beam size renders a slit measurement of the beam pulse length possible