Low surface distortion monochromator

Abstract

A monochromator 18 has a thin faceplate which reduces temperature-induced distortion in a strain-free region by placing it close to a two-level heat exchanger 46, 64. The heat exchanger has a first level 46 in juxtaposition with the faceplate 22 for efficient heat extraction, and a second level 64 which establishes a constant temperature plane along a neutral bending axis of the monochromator 18. The first level heat exchanger is operated at a temperature below the zero CTE point of the silicon faceplate so that the integrated CTE of the faceplate is approximately zero. Pumps 30 and 32 are disposed respectively at the coolant inlets 26 and outlets 28 for fine-tuning the coolant pressure so that a minimal pressure across the faceplate 22 may be established to minimize bending moments on the thin faceplate. The upper and lower heat exchangers 46, 64 are comprised of a plurality of micro-channels which are divided into groups, each group associated with a macro-channel 40, 60 and a return plenum 48, 68 which tapers down to an orifice 50, 72, which is connected to a return header 52, 74. The sizes of the orifices 50, 72 may be adjusted to control the amount of coolant flow through each macro channel so that the cooling provided may be matched to the heat absorbed by the faceplate.