Abstract: Modern large-scale X-ray sources such as synchrotrons and high-repetition-rate X-ray Free-Electron Lasers generate high-power radiation heat load on primary X-ray optical components. While dissipating the overall heat load (total absorbed power from few Watts to ~1 kW) is straightforward using cryogenic or water cooling, heating optical materials with energetic, penetrating (mm-sized) X-ray beams generates non-uniform volumetric heat sources, which results in thermoelastic distortion of the optics across the beam footprint. This distortion (even at a level of just a few microradians) can affect the optics performance (e.g., reduced efficiency of the optics and/or wavefront distortions of the reflected radiation [1,2]). The thermoelastic distortion can be reduced by proper choice of the optics shape and its boundary conditions (heat transfer coefficient, thermal contact surface area and coolant temperature).

Abstract: A low-voltage (30 kV) cryogenic DC gun has recently been built at Cornell University for use as a photocathode measurement test stand. When complete, the system is expected to be capable of performing mean transverse energy (MTE)/intrinsic emittance measurements on photocathodes with an MTE as low as ~1 meV (0.044 um/mm) and at temperatures down to ~20 K. Space charge and non-linear forces from the beamline elements degrades MTE measurements and a detailed study of the system is required to understand and mitigate their effects. In this project, particle tracking simulations are used to quantify the accuracy of measurements in the new cryogenic gun. Limits are placed on bunch charge and pulse shape based on acceptable errors in the MTE of the photocathode. From this simulation experience, multi-objective genetic optimization will be used to evaluate the performance of the gun as a high-brightness electron source for ultrafast electron diffraction applications with an emphasis on measurements with 2D materials.

Abstract: Particle tracking is a standard and very important simulation method to study the linear and nonlinear beam dynamics in accelerators. Simulation tools with tracking have been extensively used to evaluate storage ring properties, such as dynamic aperture, resonant lines in tune plane, and injection efficiency, and also to study impedance effect. The normal method of tracking is performed by element-by-element. However, this tracking job will take a long time when tracking multiple-particles for many turns in a large accelerator with enormous elements. An alternative method is to use 1-turn Taylor map to replace the entire ring structure for tracking, which will be extremely fast. Since the Taylor map is an approximation to the accelerator, the higher the order of the map is, the more accurate the approximation will be but taking more computation time. The student will learn how to generate the Taylor map of a CESR lattice, evaluate different order maps, and use them for tracking and compare with normal tracking method. Eventually, an appropriate ordered Taylor map for partial CESR ring is needed for tracking a Optical Stochastic Cooling (OSC) lattice and to study the OSC process.

Abstract: Single-shot ultrafast electron diffraction has the potential to measure physical phenomena at unprecedented levels of spatial and temporal resolution. In order to realize this potential, it is necessary to produce electron beams with extremely low emittance, i.e., beam sizes at the single micron level and angular spreads at the single milli-radian level, as well as bunch lengths of less than a picosecond. The primary difficulty in producing beams of sufficient quality is packing enough electrons into a single bunch to create an image, as the electrons experience Coulomb repulsion, causing the beam to expand. This REU project will consist of investigating the viability of emitting more charge than needed and collimating the bunch by clipping it with a downstream pinhole, instead of preserving the full charge of a bunch through the beamline.

Abstract: High brightness electron sources are required for many accelerator-based applications ranging from Ultrafast Electron Diffraction experiments to high power Energy Recovery Linacs and Free electron lasers. In particular they will play an important role in the realization of the Electron Ion Collider (EIC), the next premier large-scale accelerator experiment to be built in the US. The design of these sources requires detailed simulations and optimization of the space charge (self-field) dynamics which occur when creating a beam at low energy. Here we will investigate and optimize the electron sources used for beam cooling in the EIC, as well as optimize the settings of the CBETA machine, a novel accelerator built at Cornell University..

Abstract: High-brightness laser-driven electron sources for applications in next-generation electron accelerators or next-generation ultrafast electron microscopy require high-quality photocathodes. High-quality photocathodes must have (1) high quantum efficiency (QE), the number of emitted photoelectrons per incident photon, and (2) low mean transverse energy (MTE), the average kinetic energy of the photoelectrons parallel to the photocathode surface. Searching for high-quality photocathodes with high QE and low MTE requires understanding of the underlying fundamental physics behind the photoemission process. Such fundamental physics include, but not limited to, the crystal structure of the photocathode material, the electronic structure of the photocathode material, and the photoemission process itself. In this project, the student will be involved in active research on ab initio (first-principles) computational studies of photocathode materials for next-generation high-brightness applications. Possible topics include studies on equilibrium ground-state crystal structures of alkali-antimonide photocathodes, studies on surface electronic states or defect states in cesium-telluride photocathodes, or code development for MTE and QE calculations using new ab initio photoemission frameworks. Required skills: (1) some familiarity with (or willingness to learn about) Linux terminal commands for navigation and basic text editing; (2) some experience in data analysis using Python, Octave/MATLAB, or similar languages.