An Ultra-violet Light Monitor for Spear3

A synchrotron light monitor is an essential tool for operating a storage ring. For SPEAR3, the upgrade of the SPEAR storage ring, the light monitor was designed not only for monitoring the beam presence but also to measure beam parameters. To minimize diffraction effects, UV light around 200 nm is used to image the electron source rather than visible light. At 200 nm, the rms diffraction spot is 14 μm, much smaller than the rms beam sizes 180 μm horizontally and 51 μm vertically. A mask will absorb the x-ray fan of synchrotron radiation. The outer core of the light cone is reflected by a 9 degrees grazing incidence flat silicon mirror coated with rhodium. A telescopic system, of the Cassegrain type, with 2 onaxis spherical mirrors, images the source. The magnification can be varied from 1:1 to 8:1 but the system is optimized for a 3:1 magnification. Reflective optics was chosen to maximize the flux by permitting large bandwidth in a chromatic aberration-free system. Tolerances on the optics needed for high quality imaging are discussed. 1 SOURCE AND BEAMLINE