Rapidin situX-ray position stabilizationviaextremum seeking feedback

Abstract

X-ray beam stability is crucial for acquiring high-quality data at synchrotron beamline facilities. When the X-ray beam and defining apertures are of similar dimensions, small misalignments driven by position instabilities give rise to large intensity fluctuations. This problem is solved using extremum seeking feedback control (ESFC) for in situ vertical beam position stabilization. In this setup, the intensity spatial gradient required for ESFC is determined by phase comparison of intensity oscillations downstream from the sample with pre-existing vertical beam oscillations. This approach compensates for vertical position drift from all sources with position recovery times <6 s and intensity stability through a 5 mm aperture measured at 1.5% FWHM over a period of 8 hours.

Extremum seeking x-ray position feedback using power line harmonic leakage as the perturbation

“…Together with previous work [23], this work constitutes a feedback control in both transverse directions. Intensity fluctuations frequencies are identified with their respective position oscillation axes using time resolved sample and DCM intensities gathered prior to this experiment.…”

“…In this section, an analysis applying extremum seeking feedback to x-ray optics steering is adapted from Ref. [23] to include the HFM steering time response and beam size. The intensity of a Gaussian beam at the sample after passing through a collimating aperture can be approximated as…”

“…While this approach maximizes the intensity immediately downstream from the DCM, the beam intensity at the sample may not be optimal. Recent experiments have demonstrated that oscillations introduced onto the DCM 2nd crystal angle required for ESF intensity optimization of the DCM intensity could simultaneously be used to stabilize the vertical beam position by using ESF optimization of intensity through an aperture immediately upstream from the sample [23]. This approach is favorable compared to position feedback based on quadrant diode beam position monitors (BPM) due to reduced sensitivity to both detector dark currents and parallax errors arising from thermally induced mechanical drifts between the BPM and the source.…”