A closed loop feedback system for synchrotron radiation double crystal monochromators

Feedback system of a liquid-nitrogen-cooled double-crystal monochromator: design and performances

“…Various feedback systems have been detailed in the literature which maximize the output from a double-crystal X-ray monochromator or stabilize it at a given offset from its maximum to improve the harmonic rejection. These systems are suitable for stepper motors (Siddons, 1998;Jemian, 2002), piezoceramic electrostrictive actuators (Shard et al, 1998) or piezoelectric transducers (PZT) (Bridges, 1987;Ramanathan et al, 1988;Jemian, 2002). The optimization of the angle between the two crystals is then achieved by maximizing either the signal proportional to the intensity of the monochromatic beam measured after the monochromator (I 0 ) or the intensity of the transmitted beam (or of the fluorescence current) through (or delivered by) the sample.…”

“…This kind of adjustment is now used to maximize the intensity of the sample diffracting peaks measured during diffraction anomalous fine-structure experiments (Cross et al, 1998;Renevier et al, 2003). The direct optimization of the monochromator transmittance can also be achieved by maximizing the I 0 value (Shard et al, 1998), the I 0 value normalized by the intensity of the electron storage ring (Ramanathan et al, 1988;Siddons, 1998) or that normalized by the intensity of the white beam before the monochromator (Jemian, 2002).…”

Beam and sample movement compensation for robust spectro-microscopy measurements on a hard X-ray nanoprobe

“…Beam position can also be used as an indicator of monochromator alignment and is controlled using piezo actuators in the monochromator. If the source of intensity loss or beam movement is misalignment of the second crystal with respect to the first, a position-based feedback will bring the beam back to the same position, and consequently the monochromator crystals into a parallel alignment (Ramanathan et al, 1988).…”

Nanoradian angular stabilization of x-ray optical components

“…The signal is extracted from intensity of x-rays reflected from the monochromator crystals using a so-called null-detection principle. Previously, this technique has been widely used for stabilization of double crystal x-ray monochromators with typical energy resolution of about 1 eV [4][5][6][7][8]. An angular stability in the µrad regime is required for such monochromators due to a few µrad angular widths δΘ of the commonly used low index Bragg reflections (e.g., for Si(111) and C(111) δΘ > ∼ 10µrad for E < ∼ 23.7 keV).…”