Detector alignment for X-ray crystallography using Millepede-II.

Area of Science:

• Crystallography
• High-energy physics
• Detector physics

Background:

• Accurate geometrical parameters of X-ray area detectors are crucial for precise serial crystallography.
• Previous methods for detector calibration suffered from bias and slow convergence.
• Simultaneous refinement of detector and crystal parameters is necessary to avoid these issues.

Purpose of the Study:

• To introduce and validate the Millepede algorithm for refining segmented X-ray area detector geometry in serial crystallography.
• To demonstrate the method's ability to accurately and efficiently correct detector parameters, including tilts and distances.
• To improve the indexable fraction of data and enable real-time calibration.

Main Methods:

• Adaptation of the 'Millepede' algorithm, originally from high-energy physics, for serial crystallography.
• Simultaneous refinement of detector geometrical parameters with individual crystal parameters.
• Utilizing the structure of least-squares normal equations for rapid computation.

Main Results:

• Simulated data showed panel shifts within 7% of correct values after one iteration, and near-perfect accuracy after two.
• A simulated out-of-plane panel rotation was determined to within 0.001°.
• Experimental data from an X-ray free-electron laser saw the indexable fraction of frames increase from 30% to 91% in one iteration, reaching 96% after further iterations.
• Geometry updates for 2060 crystals took only 0.819 seconds on desktop hardware.
• The method was successfully integrated into a real-time feedback system at a synchrotron beamline, correcting a 0.04° detector tilt.

Conclusions:

• The Millepede method provides a fast, accurate, and practical solution for refining X-ray area detector geometry in serial crystallography.
• This technique significantly enhances data quality and efficiency in X-ray diffraction experiments.
• The method's speed and accuracy allow for frequent recalibration, maintaining optimal detector performance without specialized alignment.