Physics Seminar by Dr. Kyuil Cho, Thursday (3/28) at 11 am – VDW104

Title: Room temperature superconductor! Is it possible?
Abstract: Superconductor is a material that shows two special properties: zero resistance and Meissner effect (expulsion of magnetic field) below its critical temperature. Thanks
to these special properties, this material has been used in many applications such as
superconducting wires, medical device MRI, superconducting magnets in particle
accelerators and plasma Tokamak reactors, and qubits for quantum computers.
Recently there has been a rapid development on high temperature superconductors
and their superconducting critical temperatures approach almost room temperature.
In this seminar, this exciting development will be reviewed, and the possibility of room
temperature superconductors will be discussed. Furthermore, the recent research
obtained by Hope College superconductivity research group will be discussed with
some exciting superconductivity demos (zero resistance and magnetic levitation).

Speaker: Dr. Kyuil Cho


B.S., Physics, Hanyang University, South Korea, 1998
M.S., Physics, Hanyang University, South Korea, 2000
Ph.D., Physics, Clark University, USA, 2009
Postdoc at National High Magnetic Field Laboratory, USA, 2009-2010
Postdoc at Ames National Laboratory, USA, 2010-2014
Staff scientist at Ames National Laboratory, USA, 2014 – 2021
Assistant Professor at Hope College, USA, 2022 – present

Physics student presentations #2 (summer research in 2023), Thursday (3/21) at 11 am – VDW104

1. “Turbulence and Zonal-Flow Impact in the Madison Symmetric Torus in Quasi-Single Helicity” by Nick Kaipainen, Mentor Zach Williams

Reversed-Field Pinches (RFPs) operating in the Quasi-Single-Helicity (QSH) magnetic geometry exhibit significant improvements in confinement time as compared to standard discharges due to the efficient saturation of large-scale tearing modes. This modification to the magnetic geometry and profiles introduces new instabilities which drive transport. This work focuses on diagnosing the microinstabilities and microturbulence in a non-reversed Madison Symmetric Torus QSH experiment. Local gyrokinetic simulations are conducted with the GENE code to identify the dominant instabilities as ion-temperature-gradient (ITG) and density-gradient-driven trapped-electron-mode (TEM) at core and edge radial locations, respectively. It has been previously observed in the RFP (Williams PoP 2017) that residual tearing fluctuations in RFPs degrade zonal flows; the degree to which this affected turbulence and transport in that work depended on the driving instability. While initial investigations reveal strong zonal flow activity, an ad-hoc magnetic perturbation is employed to model magnetic fluctuations present in the RFP. These fluctuations degrade the zonal flow structure, resulting in a more substantial increase in electrostatic fluxes for the TEM-dominated position than for its ITG counterpart.

2. “Exploring Properties of YBCO Superconductors Using Proton Irradiation” by Joey Fogt, Hope Weeda, Trevor Harrison, and Nolan Miles, Mentor Kyuil Cho

We studied the effect of 600 keV proton irradiation on thin film Cuprate superconductors. Using the Hope Ion Beam Accelerator Laboratory, a 580 nm thick YBCO-1237 sample was subjected to a series of proton irradiations totaling a fluence of 7.2 x 1016 p/cm2. The superconducting critical temperature (Tc ) of the YBCO sample decreased drastically, from 90K towards 0K, while normal state resistivity increased with increasing irradiation dose. These changes in sample properties will be used to discuss fundamental properties of the superconductor.

Physics student presentations #1 (summer research in 2023), Thursday (3/7) at 11 am – VDW104

1. “Efficient Techniques for Calculating the Energy Widths of Cyclotron Resonance in Strong Magnetic Fields”
By Will Vance and Matt Stowe, mentor Peter Gonthier
Abstract: It is believed that Compton scattering is the reason for the high-energy radiation observed in the X-ray spectra of magnetars. These are neutron stars that have the strongest inferred magnetic fields. Our main objective is to conduct Monte Carlo simulations of the magnetosphere emission of magnetars and compare them with actual observations. To achieve this, we need to compute the Compton Scattering cross-section frequently using a C++ code. Therefore, improving efficiency is crucial. The QED spin-dependent resonance cyclotron energy widths are necessary for this code. Our study aimed to improve the efficiency of the energy widths calculation code using four methods – numerical methods, interpolation, extrapolation, and parallelization. We mainly focused on implementing the Baring method, which is a numerical method that can speed up the computation of the energy widths. It was found that this method lost accuracy outside certain bounds, but nevertheless proved beneficial in reducing computation times. In order to reduce the number of energy widths being calculated, we devised a bilinear interpolation method. This interpolation method afforded the ability to interpolate between every fifth energy width while retaining less than 1% fractional error. We aim to extend the extrapolation of the energy widths beyond the high Landau states, where numerical issues arise. Lastly, in order to complete as many computations at a time as possible, we focused on parallelizing our code across both CPUs and GPUs. As modern computers have multiple cores, and GPUs are common, it was feasible to achieve lower computation times using CPU and GPU parallelization. However, we discovered during our research that GPU parallelization was impractical for our application. Therefore, the CPU alone provides faster computation times.

2) “Investigation of convection cells via truncated eigenmode decomposition”
By Gillian Donley, mentor Zach Williams
Abstract: Convection cells are found in a variety of contexts throughout physics, including plasmas within the stellar interior and in neutral fluids such as planetary atmospheres. Rayleigh Benard Convection (RBC) is the most well studied model for this behavior, describing convection in fluids that are heated from below and cooled from above, resulting in a temperature gradient which can drive instabilities. Under the right conditions, this instability develops and drives convective heat transport, which is still actively researched in fluid and plasma dynamics today. We study the neutral fluid configuration of this system using a novel modeling approach that approximates the solutions of the 2D nonlinear Boussinesq equations via a truncated sum of linear eigenmodes. The contribution of each eigenmode to the nonlinear state is determined by an appropriately defined inner product, which we discuss. The effectiveness of this approximation is assessed by calculating the error between the truncated sum and the full nonlinear solution. Importantly, we find that a number of stable eigenmodes contribute significantly to the nonlinear state. As a physical application of this new modeling approach to describe RBC, we calculate the Nusselt number time averaged over the saturated dynamics.

3) “β-decay strength function of 53Ni and 52Co”
By Gabe Balk, mentor Paul DeYoung
Abstract: The p process is believed to be responsible for the formation of heavy proton-rich nuclei in the universe. Because p nuclei are short-lived, the specific properties of their reaction and decay paths are difficult to measure. This work deals with the decays of two nuclei, 53Ni and 52Co. β+ decays for each isotope were recorded with the Summing NaI(Tl) detector at the National Superconducting Cyclotron Laboratory. A preliminary β-decay Intensity Function was derived with Total Absorption Spectroscopy. Total energy spectra, β-particle spectra, individual γ-energy spectra, and multiplicity spectra for decays to levels in the child nucleus were modeled with GEANT4 based on information from the National Nuclear Data Center. The measured spectra, when fit with the simulated spectra, give the probability that a particular child level is populated during decay. Refined results, when compared to theory, will provide insight into the formation of p-nuclei elements.