Design of Coronagraph for the Observation of Beam Halo at LHC

In the LHC, the beam halo due to higher beam energy and intensities will increase the impact on LHC machine protection and on luminosity performance. Measurement of the beam halo distribution is therefore important for understanding and controlling the beam halo. A coronagraph was designed for the observation of the beam halo population. A new optical design of the coronagraph is made for the halo observation in the LHC. For convenience of masking the core image, we need a large transverse magnification. For this purpose, a telephoto lens arrangement is applied to the adjective lens to extend the focal length to obtain a large transverse magnification. The result of diffraction analysis, the contrast is estimated better than 10⁶. Since the beam halo is estimated to 10⁴ -10⁵ of the core intensity, the coronagraph is estimated to have enough contrast for the observation of beam halo distribution at LHC. This paper describes the detail study of the coronagraph for the LHC for the observation of transverse profile of the beam halo with a contrast down to a level of 10⁻⁶ compared to the peak intensity of the beam core.