Ion beam figuring of nickel mandrels for x-ray replication optics

The x-ray telescopes foreseen for future x-ray missions will need an high number of mirrors. Using for their production the replication method, an high number of mandrels will be necessary. A cost-effective approach that offers accurate control of the mandrels shape is the ion beam figuring. Using this procedure the aluminum-kanigen mandrels are initially optically figured by diamond turning or by other means, superpolished to the specified microroughness and then ion beam figured to the required shape. An ion beam facility has been built to test the concept. A small test mandrel has been measured obtaining the map of its surface. From this map and from the beam removal function of the ion head a time matrix has been computed to remove the shape errors. Using this time matrix as input to the program that control the movement of the ion head, the mandrel has been corrected from the errors. In this paper is given a description of the im beam facility and the results obtained figuring the surface of the test mandrel.