Development of a beamline for photoelectron spectroscopy on INDUS-I

The proposed beamline is centred using a toroidal grating monchromator with three in situ interchangeable gratings to cover the photon wavelength range of 60 to 1600 إ. The monochromator has an entrance arm length of 1500 mm and an exit arm length of 2634 mm. It is preceded by a pre-mirror which accepts radiation with a horizontal and a vertical deflection of 10 and 5 mrad respectively. The glancing angle of the incidence on the mirror is 4.5°. The focus of the mirror is at a distance of 2000 mm from its centre where the entrance slit of the monochromator will be placed. The monochromatised beam is focussed by a post-mirror. The requisite optical parameters of pre- and post-mirrors of ellipsoidal and toroidal types have been worked out. The optical performance of the complete beamline has been evaluated by ray tracing taking into account various errors of optical surfaces. Further calculations for misalignment errors have been carried out showing the critical dependence of the resolution and the throughput on pre-mirror positioning. Based on the numerical studies the design of the pre-mirror chamber including mirror mount and its various kinematic motions in vacuum has been worked out and incorporated in the complete design. Presently, the beamline is under construction.