CLASSE: Student Opportunities

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CORNELL LABORATORY FOR ACCELERATOR-BASED SCIENCES AND EDUCATION — CLASSE

Remote REU 2020 Projects

MENTOR STUDENT 2020 PROJECT
Michelle Kelley and Nathan Sitaraman Benjamin Cheung
Mentor Intro, Presentation, Final Report
"Computational electrochemistry of tin binding to niobium surfaces during Nb3Sn growth"

Abstract: Next-generation superconducting radio-frequency (SRF) cavities for particle accelerators consist of a thin layer of Nb3Sn grown on the surface of a niobium SRF cavity. The superconducting properties of this thin layer can exceed those of niobium, but are highly sensitive to the details of layer growth, especially during the initial nucleation phase. In this project, we will use the first-principles computational method of density functional theory to study how tin binds to niobium and niobium oxide surfaces in an electrochemical environment. These calculations will aid the development of new Nb3Sn growth procedures that are a subject of ongoing* experiments at Cornell.

Zeming Sun Gabriel Mohideen
Mentor Intro, Presentation, Final Report
"Simulation of focused ion beam (FIB) nanofabrication on Nb and Nb3Sn thin films for ion milling and implantation. "

Abstract: Focused ion beam (FIB) is a powerful technique for multiple sample preparation processes that include milling samples down to very thin thickness (~100 nm) for transmission electron microscopy (TEM), etching sample cross-section to achieve a polished surface for scanning electron microscopy (SEM), and implanting or depositing ions for device fabrication. An accurate control of the ion-material interaction, however, is challenging due to the low engineering tolerance of tens of nanometers. This is especially true for thin films whose cross-sectional height is so small as a few micrometers or hundreds/tens of nanometers. Moreover, the Nb and Nb3Sn materials are mechanically hard, which significantly differs the milling rates between the film and substrate. Thus, the FIB processes require to be optimized on Nb and Nb3Sn thin films, and a parameter map for different processes should be generated. In doing this, simulations will be carried out to investigate the sputtering yields for ions on films, substrates, and protection layers under different beam conditions. These data would later be compared with experiments.

Stanislav Stoupin, Carl Frank Liana Shpani
Mentor Intro, Presentation, Final Report
"Understanding how X-rays can deform crystals: Thermoelastic response of optical materials under penetrating heat load of X-rays"

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).

Luca Cultrera & Jai Kwan Bae Jeanne Garriz
Mentor Intro, Presentation, Final Report
"Modeling of photoemission from heterojunction GaAs based photocathodes"

Abstract: GaAs based photocathodes are the most popular options for spin polarized electron sources, but suffer from short operational lifetimes due to the Negative Electron Affinity (NEA) layer at the surface. Recently, NEA activation on the GaAs surface was achieved with semiconductor materials such as Cs2Te or Cs3Sb and showed significant improvements in lifetime without any adverse effects on photoelectron spin polarization. In this project, a REU student will participate in constructing a simulation of photoemission using Monte Carlo techniques based on the photoemission three-step model.

Chris Pierce & Alice Galdi Menaka Kumar
Mentor Intro, Presentation, Final Report
"Study of a cryogenic DC gun for beam emittance and ultrafast diffraction measurements"

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.

Jim Crittenden Co-mentor: Suntao Wang Nicole Verboncoeur
Mentor Intro, Presentation, Final Report
"Numerical Design of Electromagnets and Application in Lattice Development for the Cornell Electron Storage Ring"

Abstract: The design, fabrication and detailed understanding of static magnetic fields are essential components of the development and operation of storage rings such as the Cornell Electron Storage Ring. Material properties and space constraints are among the considerations contributing to the magnet engineering design procedures. This project will take the participant through the magnet design process, modeling calculations, and the implementation of these used either as field maps or in parameterized form in the lattice model both for beam optics development and for optics correction algorithms during operation of the storage ring.

Suntao Wang and David Sagan Brian Jiang
Mentor Intro, Presentation, Final Report
"Particle tracking with high-order Taylor maps in CESR"

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.

Kirsten Deitrick Rachel Ratvasky
Mentor Intro, Presentation, Final Report
"Accelerator Ring Operation with Large Radial Shift"

Abstract: The Electron-Ion Collider (EIC) is the next large accelerator planned in the United States. The Accelerator Ring (AR) allows for the full-energy injection of hadrons into the Collider Ring (CR), which goes on to collide the hadrons with electrons for the benefit of fundamental scientific research. Currently, we anticipate that the operation of both AR and CR will require that the beams are capable of operating with a large radial offset, in order to change the path length of the beam without changing the hardware of the accelerator. This project will work on simulating the beam dynamics of a beam with a large radial offset in the accelerator ring, working to identify and solve problems that limit this operation, and contribute towards the design of the AR.

William Li Pedro Rivera-Cardona
Mentor Intro, Presentation, Final Report
"Viability of post-emission collimation of photoemitted electron beam"

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.

Ryan Porter Sam Ginnett
Mentor Intro, Presentation, Final Report
"Modeling 2-Gap Superconductivity in Nb3Sn Superconducting RF Cavities"

Abstract: Description: Superconducting Radio Frequency (SRF) cavities are utilized in most modern particle accelerators to accelerate particles. These cavities are typically made out of the superconductor niobium, but this material is nearing the theoretical limits of performance. Cornell has been developing niobium-3 tin (Nb3Sn) as a superconductor for SRF cavities. Measurements of these cavities have indicated the existence of 2 superconducting “gaps” in the material. The superconducting gap of a material is an important parameter that determines much of the behavior of a superconductor. The project will entail investigating the source of the behavior. This will include exploring literature for possible mechanisms, developing mathematical models, and fitting models to data.

Colwyn Guliford Jamie Boyd
Mentor Intro, Presentation, Final Report
"Modeling and Optimization of Advanced Electron Sources"

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..

Jacob Ruff & Purnima Ghale Kathleen (Katie) Chang
Mentor Intro, Presentation, Final Report
"Hunting for hidden orders via numerical analysis of x-ray diffraction"

Abstract: The QM2 beamline at CHESS specializes in collecting comprehensive diffraction data from complex quantum materials. This instrument collects about 30 million distinct measurements each second. The information content of these datasets is too large to be effectively analyzed using traditional means. Collaborating with staff scientists and postdocs at CHESS, an REU researcher will apply strategies from data science and high performance computing to uncover "hidden" ordered states within the deluge of data from QM2. Developing workflows to transform, visualize, and analyze QM2 data, the REU researcher will hunt for physically interesting needles in multidimensional haystacks. Interests in python, scientific computing, and machine learning, and quantum physics are assets for this position.

Kevin Nangoi Emilie LaVoie-Ingram
Mentor Intro, Presentation, Final Report
"Ab initio computational studies of next-generation high-brightness photocathode materials"

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.