Advanced Simulation Methodology for Optimizing Aerodynamic Lenses used for Single-Particle Diffractive Imaging

Supervisors: Prof. Michael Breuer (HSU), Prof. Philipp Neumann (HSU), Prof. Jochen Küpper (DESY, UHH), Dr. Muhamed Amin (DESY)

Single-particle diffractive imaging (SPI) relies on high-density streams of individual aerosolized particles to collect sufficient numbers of diffraction patterns with short x-ray pulses. As the intense x-ray pulses destroy the intercepted particles, a constant, focused stream of particles is decisive for the recording of many high-quality diffraction patterns. Aerodynamic lens stacks (ALS), a series of orifices, are a widespread technique for obtaining collimated particle beams in SPI experiments, but optimization for certain parameter sets, e.g., particle sizes, flow rates, pressures, is difficult. The development of advanced aerosol injection techniques for better selectivity of the injection and particle control exploiting novel operation regimes, including very low temperatures is thus an important issue.
Numerical simulations are an important tool to better understand and optimize ALS, guiding experimental optimization of the injection process. Due to the multiscale character and the wide range of flow states, e.g., continuum vs. free molecular regime, these calculations require advanced simulation methodologies and high-performance computing techniques. Multiscale and multiphysics simulations for a huge number of particles over a large phase space lead to a vast amount of data requiring efficient simulation as well as on-line and off-line data analysis. Simulations of actual experiments on the fluid-dynamic transport and manipulation of nanoparticles/biomolecules over wide ranges of temperatures (4–300 K) and particle sizes (3–300 nm) will utilize particle methods such as molecular dynamics and direct simulation Monte Carlo methods to solve the Boltzmann equation for finite Knudsen numbers Kn; new and more appropriate modeling assumptions will be derived. Further challenges include calculations of actual cooling rates/temperatures of particles in the cold-gas fields and additional simultaneous forces on the particles, e.g., external electric fields, requiring variable multiphysics approaches.