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Laue-Laue crystal monochromator is a horizontally scattering fixed exit Si (111) monochromator operating under high heat loads has been installed on the ID11 beamline at ESRF. The energy is tuneable in the range 22.7 to 141.7 keV (~5.0° to 0.8°). The main construction issues are: 1) the very compact configuration. Crystals can be driven along the beam path very close to each other; 2) The axes of the 3 rotations converge in the middle of both crystals to minimize parasitic displacements during adjustment; 3) Crystal benders have been designed to accept different crystal shapes. Both crystals can translate out of the beam in the transverse direction since the white beam has to be used for experiments with different devices. Piezoelectric actuators have been mounted on both crystals to enable energy scans and active feedback. Both crystals are water cooled and are in contact with an InGa bath in a vacuum chamber. Between the two stages there is a protective tungsten beam mask to stop the straight pink beam. Two additional linear stages are provided for filter selection and diode insertion or removal.

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The monochromator consists of a channel cut crystal cryogenically cooled by means of lateral absorbers. The second diffracting surface can be bent by means of an high resolution detuning systems.
The Bragg angle rotation stage has some particular features: it is completely backlash free and has a central opening through which the cryogenic tubes can pass through. This makes the system instability free in case a closed loop configuration on the high resolution encoder is adopted (different choices
available). The coils of the cooling circuits have just to compensate for fine alignment movements.
The crystal mount is designed in order to be thermally insulated from the support structure and is kinematically mounted over a support bracket that allows a straightforward crystal substitution.
Different configurations of support are selectable. The stiffer one is based on a granite block that has to be adjusted in both transversal position and height, levelled and adjusted in its angle around the vertical axis. The table that sustains the whole monochromator, can be then finely adjusted on all the degree of freedom with the exception of the two horizontal translations.
The detuning system act on a silicon lever arm of the crystal itself that has a flexible hinge dimensioned by F.E.A. that allows the listed angular stroke.

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Two goniometers are installed: the first on a fixed support, the second on a movable support translating along the beam direction. On the movable support a vertical stage adjusting the vertical position of the goniometer itself has been implemented. Each goniometer supports a bracket carrying a linear stage for the stripe selection. Each crystal (multilayer) has two different coatings and a bare stripe (Si 111). Rotating encoders detecting angular positions are installed.
Both crystals are equipped with motorized roll adjustment; the second one has also a motorized yaw adjustment. All these fine adjustments are based on flexures in order to get the maximum sensitivity.
The first mirror is water cooled by means of a water circuit completely surrounded by an air guard independently pumped to limit the loads transmitted by three flexible hoses and to guarantee an higher precision. All stepper motors are water cooled too, in order to improve the thermal stability of the system.

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