Diamonds for 3rd and 4th Generation X-ray Sources P. Van Vaerenbergh # , M. Mattenet, J. Härtwig, J. Hoszowska, T. Mairs, J. Morse European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble, France S.H. Connell, M. Rebak, D. Dube, L. Mkhonza, R. Setshedi University of the Witwatersrand, P.O WITS 2050, Johannesburg, South Africa R.C. Burns, J.O. Hansen Element Six Technologies, Booysens Reserve rd, Theta Johannesburg, South Africa H.P. Godfried Element Six BV, P.O. Box 119, 5430 AC Cuijk, The Netherlands Abstract The 3 rd and 4 th generation sources are characterised by their high brilliance. This may induces a high heat load and a high local power density on the beamline optical elements such as monochromators, filters, phase plates, beam splitters, lenses, vacuum windows and on beam position monitors. Optical components are often made of silicon (available in large dimensions, grown with high crystal perfection and with very good surface quality). Instead of silicon we can use diamond, a material that has excellent thermal characteristics and thus considerable advantages compared to silicon. Nevertheless, up to now, the diamond material available had small dimensions and many defects in the bulk and often an insufficient surface quality. Nowadays, the diamond industry can produce highly pure type IIa Single Crystal diamonds made by the High Pressure High Temperature synthesis method. This results in a considerable reduction of the number of crystallographic defects within the material. The key parameters of a diamond crystal for the majority of X-ray applications are the perfection of his bulk and also of its surface. In the most advanced application it should conserve the coherence of the X-ray beam. Industry efforts must be focused on these directions as well as on increasing the crystal dimensions. In a successful collaboration project between the authors, many diamond samples have been studied over the last years. At the ESRF, X-ray topography is the most important and effective experimental method used to characterise the defects structure in diamond crystals. Some of the topographs are presented below. It appears that for most of the future practical diamond applications the efficiency of crystal cooling methods has to be improved; this will reduce the thermo-mechanical deformation of the crystal. We are working at the ESRF on two complementary approaches. The first is to increase the surface of thermal exchange with the cooled support. The size of available single crystal diamond plates is about 7x7 mm 2 (with a perfect central region of about 4x4 mm 2 , (100)-orientation). Such single crystal diamonds can be brazed on larger CVD diamond plates. Brazing tests have been initiated in order to qualify the different brazing techniques and to measure the stress induced within the single crystal material by this process. The second approach is to increase the efficiency of the cooling support structure. The design and manufacture of dedicated support are in progress. 1. Introduction The ESRF is a third generation high energy light source that has been in operation since 1994. Component upgrade and optimisation are key issues for the future of this source. Among the present R&D programmes, diamonds’ characterisation and development are of primer importance at the ESRF. At present, many of the optical elements (in particular the monochromators), located on the synchrotron beam path, are made of silicon. This material was selected due to the high crystalline perfection and the easiness of his processing to obtain large optical surfaces of good quality. The third, # Corresponding author: vanvaer@esrf.fr