Ion Traps for Single Particle Imaging

X-ray Free Electron Lasers (XFELs) are used for diffractive x-ray imaging of the structure of many biological particles, such as viruses and proteins. The ultimate goal for XFEL-based microscopy is atomic resolution images of non-crystalline particles. However, data collection efficiency as well as the limited amount of measurement time given annually to researchers, such high-resolution images are presently impossible to attain. Here, we consider two potential solutions to the single-particle hit rate problem; the first looks at applying static electric fields to existing aerodynamic particle injectors, and the second looks at the viability of using time-varying electric fields associated with ion traps to create high-density regions of particles. For the static solution, we looked at applying a constant electric potential to the nozzle, as well as applying a high voltage to a ring electrode in close proximity to a grounded nozzle. We considered the breakdown field strength of the helium gas used to determine how closely the ring electrode could be placed without creating an arc that could potentially destroy expensive equipment. Then, we considered the possibility of using electrodynamic ion traps to increase particle densities. We first characterized how charged particles behave in oscillating electric fields using a simple electrode geometry. Using the general results from this, we then constructed a rudimentary ion trap to test if our experiment agreed with the theory. Finally, we conducted a literature review to determine what particle densities other scientists have been able to measure using ion traps. We then compared existing ion traps to what we expect from the nozzle injectors to determine which method may be the better solution.