Two-dimensional SR Interferometer for PLS-II

A synchrotron radiation (SR) interferometer was used for beam size measurements at the Pohang Light Source (PLS). It was an one-dimensional (1D) interferometer, and the horizontal beam size was only available for real time measurements of the user service. In the PLS upgrade project (PLS-II), a 2D interferometer was tried for simultaneous measurements of the horizontal and the vertical beam sizes. Various sizes of the 2D slits were tried to find an optimum condition by considering the SR characteristics and the instrument's limitations. Measurement results of the beam size were cross-checked in three different ways and showed good agreements with each other. After optimization, the measurement accuracy of the beam size was improved significantly, and a vertical beam size change was noticed when the gap distance of the elliptically polarized undulator (EPU) was changed.