SOLUTION TO THE HIGH HEAT LOADS FROM UNDULATORS AT 3RD GENERATION SYNCHROTRON SOURCES - CRYOGENIC THIN-CRYSTAL MONOCHROMATORS

We have developed a new design for a cryogenically cooled monochromato r employing a thin-crystal strategy which is capable of handling the c entral-cone power of the advanced photon source's undulator A at machi ne currents up to 300 mA. The key to the proposed design is to machine two opposing narrow channels in a large, indirectly cooled block of S i crystal, leaving a thin, similar to 0.6-mm-thick strip of Si. The th in section absorbs only a fraction of the incident beam power so that the operating temperatures of the crystal are in the range where Si ha s both a very high thermal conductivity and a very small or slightly n egative thermal expansion coefficient. The fact that the crystal is op erated in the negative range of thermal expansion means that the cryst al surface illuminated by the x-ray beam is always under tension and t herefore will not buckle.