Spallation neutron source target imaging system operation

The Target Imaging System (TIS) at SNS produces images of the proton beam pulses on the target by viewing a luminescent coating on the nose of the target through optics installed on a proton beam window approximately 2 meters upstream. The optics consist of a primary parabolic aluminum mirror which reflects the light vertically through a 25 mm diameter hole in a 1 m thick shield plug to a turning mirror and lens assembly which focuses the light onto a radiation hard fiber optic cable. The cable guides the image out of the shielding monolith to a camera in a low radiation area. The system operated for a year with the first coated target which accumulated 3200 MW-hours. The original optics also worked for four months with a second coated target which incorporated a larger coated area and a fiducial pattern which gave better resolution of position. On-line fitting routines gave beam position, peak density and profile shapes. In addition, spectrum measures were taken for the second target during initial operation while a significant reduction in intensity occurred. Improved optics were installed with a replacement proton beam window during a shutdown starting in December, 2010. This paper will describe the operating experience, comparison to traditional beam diagnostics projections for the beam on target and system improvements.