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CORNELL LABORATORY FOR ACCELERATOR-BASED SCIENCES AND EDUCATION — CLASSE

REU 2015 Projects

MENTOR STUDENT 2015 PROJECT (click on link to see abstract)
Richard Gillilan Marissa D'Amelio Presentation Final Report
In-situ Microfluidic High Speed Mixing for Biological X-ray Small Angle Solution Scattering at a Synchrotron Beamline
X-ray small angle solution scattering on biological systems (BioSAXS) is a rapidly growing field in structural biology that has proven to be a powerful tool both in answering fundamental questions about living systems and in advancing drug development and delivery. As technology improves, researchers are interested in moving beyond a single snapshot to time-dependent phenomena. The student will help design new sample mixing devices for time-dependent BioSAXS by simulating the fluid dynamics of mixing at microscopic scales. The project will involve learning to use the commercial program COMSOL Multiphysics to numerically solve the Navier-Stokes and Convection Diffusion equations for full 3-dimensional models of various microfluidic chips. The student will explore possible chip designs that minimize sample consumption while maximizing speed and completeness of mixing. An important fundamental question will be addressed: can rapid enough mixing be achieved without turbulence?
Adam Bartnik Joseph Burnett Presentation Final Report
Laser Development and Control for the Cornell ERL Injector
Abstract: The Cornell prototype photoinjector is the highest brightness electron source in the world. As a photoinjector, i.e. a machine that uses photons to create electrons via the photoelectric effect, the laser system is integral for this machine, since the properties of the laser beam directly determine the initial properties of the electron beam. This summer, the photoinjector itself is being upgraded and rebuilt, so it is a key opportunity to upgrade the laser. A variety of modifications and upgrades to the laser system are planned. New laser oscillators to reach new regimes of laser pulse length and frequency are needed, and these will need to be designed and built. A new method of transport is needed to deliver the laser to its target. And, time permitting, a tunable-color laser needs to be built. The student will work closely with others to help reach these goals.
Ivan Bazarov/
Jim Sethna/
Dave Rubin
Mikhail Gaerlan Presentation Final Report
Innovations in optimization and control of accelerators using methods of differential geometry and genetic algorithms
Modern particle accelerators, representing the frontier of applied science and technology, serve as a testing-ground for new ideas and sophisticated methods of design, control, and optimization. The remarkable performance of modern accelerators would not be possible without sophisticated optimizations and feedback in both the design stage and in active online control. Our goal is to develop and test new optimization algorithms including methods of hybrid optimization (e.g. genetic algorithms combined with local steepest descent) and also new algorithms inspired by the recent information-geometric discoveries. These new algorithms will be tested with implementation in the control system of the Cornell Electron Storage Ring (CESR) to optimize the machine performance. Broadly speaking, we will use new advanced optimization algorithms and strategies and apply them to the control of modern and future accelerators for the widest range of applications. The successful REU student must be comfortable with computers. A working knowledge of Python/MATLAB by the start of the REU term is essential. The mentors will provide guidance with the rest of the project.
Michael Billing Naomi Gendler Presentation Final Report
Analysis of Methods to Excite Head-Tail Motion of Bunches within the Cornell Electron Storage Ring
In storage rings it is important to be able to study the motion of the bunched beam. This includes dipole motion where the center of the bunch oscillates up/down, or right/left. It also includes head-tail motion where the particles in the leading portion of the bunch move in one direction and those at the trailing part in the opposite direction. The dipole motion is relatively easy to excite, using deflecting magnets or stripline kickers, and to detect with conventional beam position monitors (BPMs), but the excitation and observation of head-tail motion is much more difficult. However, the diagnosing of head-tail motion can be very important in understanding beam stability when studying intensity-dependant effects in the storage ring. The most common example occurs when the electro-magnetic fields traveling with the bunch interact with discontinuities in the vacuum chamber walls in the storage ring CESR and these interactions cause differential deflections of the head and tail of the bunch. As a second example, the CESR-TA project studies the effects of Electron Clouds, generated by photoemission from the synchrotron radiation emanating from trains of circulating positron bunches in a storage ring. The electron clouds can produce transverse deflections, which cause particles travelling near the head of the bunch and those near the tail of the bunch to move in opposite transverse directions. Studies of the BPM signals and simulations of these signals strongly suggest that we have observed the head-tail shape oscillation. There is also evidence that we have been able to excite this mode of oscillation by first driving large amplitude longitudinal oscillations, using phase modulation of the RF accelerator cavities, and then driving the vertical stripline kicker at the vertical head-tail oscillation frequency. The observations suggest that this method does excite the head-tail motion, but we do not have an understanding of the exact mechanism, by which this process functions. There are also two other and presently untested methods for possibly exciting the head-tail motion: 1) Change the delay of the driving RF pulse for the vertical stripline kicker to be on the rising edge of the drive signal, causing a difference in deflection between the head and tail of the bunch. 2) Excite a deflecting RF cavity mode already present in CESR's longitudinal feedback kicker and time the bunch's arrival to be at the zero-crossing of the deflecting field, again to produce a differential deflection between the head and tail. This REU project will include a) the analysis of data, which has been acquired in the accelerator physics studies, b) the use of a beam in CESR, to acquire further data during one or more machine studies periods, c) possibly performing RF measurements of the deflecting mode in the feedback cavity and d) creating simulations to investigate and further our understanding of the methods for the excitation of head-tail motion within a bunch. The REU student's work includes analysis of data from a BPM during the excitation of head-tail motion and then using a combination of simulation, analytic and possibly RF measurement techniques to model and compare the head-tail signals.
Jim Crittenden/
John Sikora
Kellie Olear Presentation Final Report
R&D for Future Accelerator Facilities with the Cornell Electron Storage Ring Test Accelerator
The buildup of low-energy electron densities resulting from synchrotron-radiation-induced photo-electron production, followed by secondary emission processes, has been shown to be an important factor limiting the performance of storage rings such as the B-meson factories KEK-B in Japan and PEP-II at the SLAC National Laboratory. An international collaboration of a dozen laboratories involving hundreds of physicists has been concentrated on solving the problem of understanding and reducing the buildup of such electron clouds since the 1990's. In particular, the Cornell Electron Storage Ring (CESR) was reconfigured as a test accelerator in 2008 in order to study cloud buildup and its effects on beam dynamics in a controlled setting where beam energy, bunch configuration and bunch population can be varied. Custom vacuum chambers with various types of mitigating techniques such as material choice, coatings and groove patterns have been installed and tested. In early 2013 we installed a cloud-sensitive shielded pickup detector inside a quadrupole magnet. It had long been surmised that cloud electrons may become trapped in the quadrupole field, but no measurements of the effect were available to validate modeling codes. With the first analysis of the measurements of cloud buildup in the quadrupole magnet, we realized we had discovered the trapping effect when 20-bunch-long positron trains showed signals for the first 10 bunches larger than those measured for a 10-bunch train. How do those leading 10 bunches "know" that another 10 bunches are coming? They must produce the measured signal using electrons which have been trapped since the previous passage of the bunch train, a full 2.3 µs earlier. This work has now been accepted for publication in Physical Review Special Topics - Accelerators and Beams. The preprint is available here: http://arxiv.org/abs/1309.2625. Since this is the first ever quantitative measurement of such a trapping phenomenon in a positron storage ring, and owing to its potential for imposing operational limitations on the Super KEKB e+e- collider to be commissioned next year, as well as on the positron damping ring for the proposed International Linear Collider, plans are underway to install an additional quadrupole magnet and detector in the CESR ring to make possible an expanded measurement program. This REU project will concentrate on analyzing and modeling the existing data in view of design considerations for future experiments.
Luca Cultrera Udit Gupta Presentation Final Report
Growth and Characterization of Cs-K-Rb-Sb Photocathodes
Photocathodes with very high Quantum Efficiency, possibly larger than 30%, in the blue region of the visible spectrum are important for detection of Cherenkov radiation in large neutrino detection experiments. High QE in the visible range is also of interest to generate high average current (several mA) in modern photoinjector. Multi-alkali antimonides photocathodes based on Cs-K-Rb-Sb are promising candidates for such applications. Early results reported for non optimized growth conditions that QE approaching 40% can be obtained from this material when illuminated with light at 400 nm. The candidate will attempt to grow this material and to characterize its emission properties leveraging the existing photocathode lab infrastructure.
Ralf Eichhorn Conrad Smart Presentation Final Report
Accurate Measurement of Surface Temperature of a Superconducting Cavity by Means of Vapor Pressure
The radio frequency (RF) losses of a superconducting accelerator cavity, described by the BCS theory, is a strong function of the temperature. To calibrate measured data one typically measured the temperature of the helium bath that cools the cavity. this is, however, the temperature of the outer surface of the cavity, while the RF and the losses exists on the inner surface. given the limited heat transfer through the niobium, there is a small temperature difference between these two surfaces. depending on the cavity field, this can amount to 50-100 mK and thus influence the data analysis. Within this project, you will investigate a newly proposed method to measure the temperature of the inner surface, using a high resolution pressure gauge and relating the vapor pressure inside the cavity to the temperature. You will learn the fundamentals of SRF (superconducting radio frequency), vacuum technology and some fundamental RF measurement techniques
Ken Finkelstein/
David Sagan
Sydney Jupitz Presentation Final Report
X-ray Beam Line Simulation
We want to build a next generation x-ray topography capability, that is simple to operate and much more flexible than we currently have. The REU student will contribute by helping to optimize the facility by simulating performance of alternative x-ray optical designs. He or she will learn basic principles of x-ray diffraction, and apply them using the BMAD suite of programs for photon ray-tracing developed at Cornell by David Sagan. BMAD allows us to define a realistic source of x-rays in CESR, follow photons through optical components, and map beam phase space distribution when it arrives at the topography sample.
Matthias Liepe Isaac Packtor Presentation Final Report
Field Dependence of the RF Surface Resistance of Superconductors
Abstract: Recent measurements of the superconducting microwave surface resistance of impurity-doped niobium have revealed an unexpected strong dependence of the BSC resistance on surface magnetic field. As part of this project you will participate in the cryogenic testing of superconducting RF cavities to measure the field dependent BCS surface resistance. You will participate in data analysis, and compare the experimental results with predictions by new theories aiming to explain the source of the field dependence. This project will involve a wide range of activities ranging from hands-on experimental work to theoretical modeling.
Matthias Liepe Waverly Gorman Presentation Final Report
Improving Diffusion Model for Nitrogen Doping of SRF Cavities
Abstract: Nitrogen doped superconducting radiofrequency cavities have been shown to have atypically high quality Q values and reverse medium field Q-slopes. The diffusion of nitrogen into niobium in the temperature range typically utilized in the cavity doping process is currently not very well understood. This paper solves an equation for the uptake of nitrogen into niobium derived by Clenny and Rosa (1980) for temperatures of 800C and 900C, and relates the solution to furnace pressure data at the corresponding temperatures.
Chris Mayes Dillon Berger Presentation Final Report
Dark Current tracking for the Cornell-BNL ERL Test Accelerator (CBETA)
Cornell University and Brookhaven National Laboratory are currently designing a small Energy Recovery Linac (ERL) to be built at Cornell that utilizes the existing prototype injector and main linac cryomodule, called CBETA. This machine is driven by a high-voltage electron gun and superconducting accelerating cavities which can accelerate (in addition to the intended electrons) stray electrons which can be lost in unwanted locations. Together these stray electrons, called 'dark current', can create a radiation hazard and damage the machine. This project will utilize the existing Bmad accelerator simulation library and related programs to simulate dark current in the current CBETA design. It will also develop related visualization tools. For this project the student must be familiar with programming in a Linux environment and have a good knowledge of classical electrodynamics.
Chris Mayes Mariel Tader Presentation Final Report
Multi-turn Beam Breakup studies for the Cornell-BNL ERL Test Accelerator (CBETA)
Cornell University and Brookhaven National Laboratory are currently designing a small Energy Recovery Linac (ERL) to be built at Cornell that utilizes the existing prototype injector and main linac cryomodule (MLC), called CBETA. This machine will have four acceleration passes and and four energy recovery passes through the MLC. On each pass, a particle bunch can excite and be affected by so-called higher order modes (HOMs) in the accelerating cavities. Depending on the properties of these HOMs, a steady stream of bunches can set up a feedback loop that limits the current that can be sent through the machine, called beam breakup (BBU). This project will write simulation software based on the existing Bmad accelerator subroutine library to study multi-turn BBU in the current CBETA design, and compare with analytic estimates. For this project the student must be familiar with programming in a Linux environment and have a good knowledge of classical electrodynamics.
Jacob Ruff Leon Otis Presentation Final Report
Modeling Three-Dimensional Diffuse X-ray Scattering Patterns from Disordered Materials
A triumph of 20th century materials science was the development of robust techniques for x-ray crystallography, which allows the arrangement of atoms inside a solid to be directly measured with exquisite levels of detail. Direct methods crystallography can readily define a unit cell for materials wherein the electron densities of the average structure are determined to a precision smaller than the size of the individual atoms. However, the spatial deviations away from this average structure, and the effects of various types of disorder, are not readily derived using existing techniques. Researchers at CHESS are working to develop a complementary "crystallography" for disordered phases of matter, which will collect, visualize, and understand the diffuse portion of the x-ray diffraction pattern than is typically ignored in direct methods. To help improve our intuition for diffuse scattering, an REU researcher will develop tools to forward model scattering patterns based on known crystal structures and categories of structural defects. This software project will start from the ground up, with simple systems, but the emphasis will be on scalability to harder problems down the line. Strong computer science abilities (c++, python) would be advantageous. Students interested in visualization and "big-data" are especially encouraged.
John Sikora Anjuli Jones Presentation Final Report
Measurement of Electron Cloud (Plasma) Density in Accelerators With Resonant Microwaves
An accelerator beam will often leave behind a "dust" of low energy electrons called Electron Cloud (EC). When the EC density is high enough, it can produce beam instabilities that limit accelerator performance. One technique for the measurement of EC density is the use of resonant microwaves, where the shift in the resonant frequency of the beam-pipe is proportional to the EC density within it. This project will include bench measurements and simulations of prototype sections of beam-pipe that are planned for future measurements as well as some analysis of existing accelerator data.

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