Measurement of synchrotron beam polarization

摘要

The degree of beam polarization at the end of beam line U3C of the National Synchrotron Light Source has been measured. The polarization was measured at nine photon energy points from 219 to 1136 eV. Scattering from helium gas at 90 degrees was used to separate the beam component polarized with its electric vector parallel to the synchrotron electron orbit from that polarized perpendicular to the orbit. The simultaneous count rates of two gas flow proportional counters, one placed in the orbital plane perpendicular to the beam, the other perpendicular to both the orbital plane and the beam, were taken to be proportional to the intensities of the two components. The measured values of the experiment were lower than originally expected when compared to the theory and similar measurements in the literature. However, if an .8 milliradian vertical offset of the central ray was assumed, the measured values fitted the theoretical curve to within the counting statistics of the measurement. The technique shows promise as a beam line alignment tool.