### Stefan Gerhardt

Position title: PhD Alumni

Stefan’s research on HSX concentrated on examining flows and flow damping in HSX which because of the quasi-symmetry was predicted to allow flows similar to tokamaks.

Stefan received his PhD in 2004, and began work at the Princeton Plasma Physics Lab in Princeton, NJ as the Principal Research Physicist. View a paper from his presentation of his dissertation at the 2004 IAEA Fusion Energy Conference here.

### John Canik

Position title: PhD Alumni

John studied the effects of quasisymmetry on particle and heat transport in HSX. He did this by measuring the plasma density and temperature profiles using a Thomson scattering system. He also performed extensive three-dimensional modeling of the neutral gas in HSX plasma, which has yielded the particle source rate and neutral density.

John received his PhD in Spring of 2007 and went to work at Oak Ridge National Laboratory under a prestigious Wigner Fellowship. John then headed the ORNL plasma physics theory group.

### Walter Guttenfelder

Position title: PhD Alumni

Walter’s research on HSX concentrated on examining fluctuations and anomalous transport in HSX especially through comparisons of edge fluctuations measurements with 3-D gyrokinetic modeling.

Walter received his PhD in the Winter of 2007, and began work at the Princeton Plasma Physics Lab in Princeton, NJ.

### Ali Abdou

Position title: PhD Alumni

Ali’s research on HSX concentrated on examining superthermal electron dynamics in HSX especially through hard X-ray measurements of the electron superthermal tail produced through second harmonic X-mode ECRH.

Ali received his PhD (link to Ali’s dissertation) in the 2005, and began work as an Associate Professor at Zewail City of Science and Technology, Egypt.

### Jeremy Lore

Position title: PhD Alumni

Jeremy’s focus area, during his time at HSX, was stellarator transport, specifically the measurement and modeling of transport at HSX. Jeremy currently developed the PENTA code with Don Spong from ORNL, which calculates neoclassical transport quantities in stellarators or tokamaks while conserving parallel momentum. Neoclassical calculations predict a large “electron root” radial electric field (Er) in the core of HSX plasmas, with strong radial shear. The neoclassical simulations, coupled with turbulent transport calculations performed by Walter Guttenfelder have been successful in simulating the strongly peaked electron temperature profiles measured during ECR heating. The predicted electric fields and in-surface flows will be compared to ChERS measurements in the near future.

In 2006 Jeremy implemented a displacement sensor system on HSX and performed structural modeling and testing to ensure safe operation at B=1T. Jeremy also performed analysis of data from the Thomson scattering diagnostic.

Jeremy received his PhD (link to article) in the Spring of 2010, and began work at the Oak Ridge National Lab.

### John Schmitt

Position title: PhD Alumni

John worked on the design, installation, and analysis of the magnetic diagnostics on the HSX stellarator in order to measure the the equilibrium plasma currents present during the plasma discharge. The pressure-driven Pfirsch-Schluter current is helical in nature because of lack of toroidal curvature in the QHS magnetic spectrum, and reduced by the high effective transform (3). The net toroidal current is predominantly bootstrap-driven. The bootstrap current is modeled by PENTA, and the time and spatial evolution is modeled by a diffusion equation that includes the 3-D nature of the plasma column.

John received his PhD (link to his dissertation) in 2011 and began work at the Princeton Plasma Physics Laboratory in Princeton, NJ.

### Alexis Briesemeister

Position title: PhD Alumni

Alexis explored the effects of quasi-symmetry on flows. To do this she led the implementation of a charge exchange recombination spectroscopy (ChERS) system on HSX. Her research focused on improving the ChERS system and using it to measure plasma flow velocity, ion temperature, and impurity ion density profiles. The radial electric field, which can be deduced from flow and pressure gradient measurements, was compared to the values predicted by neoclassical theory.

Alexis received her PhD in 2012 and began work at the Oak Ridge National Laboratory Fusion Energy group and then joined the General Atomics Fusion Group/DIII-D Laboratory in San Diego, CA.

### Chris Clark

Position title: Alumni

Chris investigated impurity transport in the HSX Stellarator. He led the development and construction of a laser blow-off impurity injection system, which is currently being used to introduce controlled quantities of impurities into HSX for analysis. Data from this was analyzed using the STRAHL code modified for the non-axisymmetric stellarator geometry.

Chris did not complete his PhD but began work at Google in Madison, WI.

### Bob Wilcox

Position title: PhD Alumni

Bob studied the interaction of turbulence and flows in HSX and the effects of quasi-symmetry on the determination of the radial electric field in a stellarator. This was mainly done by using multi-tipped Langmuir probes to measure the radial electric field, density and potential fluctuations in the plasma edge, and then comparing these measurements with neoclassical calculations.

Bob received his PhD in 2014. Visit this link for his full dissertation, and visit this link for his article.

Bob is began work at the Oak Ridge National Laboratory Fusion Energy group and then joined the General Atomics Fusion Group/DIII-D Laboratory in San Diego, CA.

### Gavin Weir

Position title: PhD Alumni

The primary area of Gavin’s work centered on the design, construction and implementation of the second ECH quasi-optical power transmission system for delivering power from the second 28 GHz gyrotron to HSX. The mirror is manually steerable to permit off-axis power deposition control. His research included examination of the heat propagation from modulated ECH heating, as compared to the overall the overall thermal diffusivity – a measure of the profile stiffness or resiliency, especially as this relates to the axisymmetric tokamak devices.

Gavin received his PhD in 2014. Visit this link to view his full dissertation.

Gavin is began work at the Heliotron-J stellarator in Kyoto, Japan.

### Enrico Chlechowitz

Position title: PhD Alumni

Enrico worked to extend the design of magnetic diagnostics on the HSX stellarator. Optimization of the coil placements and field components measured was carried out to guide the implementation of a new array of in-vessel coil diagnostics used for equilibrium reconstruction of the plasma density, pressure and current profiles.

Enrico received his PhD in 2014 and began work with Roland Berger Strategy Consultants in Germany.

### Jerahmie Radder

Position title: Alumni

Jerahmie’s primary research area was in RF heating and the design and fabrication of a quasi-optical launching system for the high-power electron cyclotron resonance heating microwaves – 2 gyrotrons, 100-200 kilowatts each, for 50 to 75 milliseconds. His research concentrated on measurement and modeling of power deposition and coupling to the electrons under ECH, and predictions of a resultant non-Maxwellian distribution in the electron population.

Jerahmie did not complete his PhD but began work in Minneapolis, MN.

### Laurie Stephey

Position title: PhD Alumni

Laurie studied plasma fueling and the HSX neutral population. She used H-Alpha measurements and the DEGAS and DEGAS 2 neutral Monte-Carlo codes to study the 3D neutral particle density, radial particle flux, and impacts of various fueling scenarios in HSX. Her work also included looking at the particle and energy balance at limiters placed at the edge of the HSX plasmas.

Laurie recieved her PhD (link to her full dissertation) in 2017.

### Carson Cook

Position title: PhD Alumni

Carson worked on the SIESTA (Spectral Iterative Equilibrium Solver for Toroidal Applications) code development project with Steve Hirshman and Raul Sanchez of ORNL. SIESTA is a magnetohydrodynamic equilibrium code used for modeling toroidal plasmas in 3D systems. Unlike VMEC, SIESTA does not assume nested magnetic flux surfaces, so equilibria involving magnetic islands and stochastic regions can be computed. The code is very scalable, a necessary feature for ITER-relevant calculations. SIESTA is useful for equilibrium analysis in perturbed tokamaks and stellarator modeling and design.

### Adrian Akerson

Position title: PhD Alumni

Adrian studied the edges of the plasmas in HSX, with a strong emphasis on divertor flows, particle edge fluxes and edge plasma parameters. In particular, comparisons and verification of models of the plasma divertors (EMC3-EIRENE) which at present do not include the effects of local electric fields on the flows and particle fluxes.

### Carlos Ruiz

Position title: PhD Alumni

Carlos studied the the diagnostic neutral beam used in HSX for CHERS flow measurements which is intended for use in Motional Stark Effect determination of the plasma electric field.

### Tom Dobbins

Position title: PhD Alumni

Tom implemented a polarimetry system to evaluate the Stark shift from the diagnostic Hydrogen neutral beam to allow better electric field determination. His thesis was on the addition of neutral damping to the model used to calculate plasma flows and explains the differences seen between the model and the experimental measurements.

Tom began work at GE in Minneapolis, MN.

### Jason Smoniewski

Position title: PhD Alumni

Jason has studied edge flows and field structure with a Gundestrup probe, the monoenergetic approximation in neoclassical transport calculations, neoclassical viscosity with a bias probe, and calculations of neoclassical impurity transport at HSX. Jason’s thesis compares turbulent transport in the quasi-helical symmetry and broken symmetry configurations of HSX in both experiment and simulation using the GENE code, power balance calculations, and reflectometry measurements.

Jason received his PhD in 2021 and began work on an electron-positron tabletop optimized stellarator at the Max Planck Institute for Plasma Physics in Greifswald, Germany.

### Paul Willis

Position title: Associate Instrumentation Technologist

Paul Willis worked at HSX from September 2019 to September 2021. He maintained the HSX computers and data acquisition system, and assisted in the addition of new diagnostics and data analysis.

### J. Fernando Castillo

Position title: PhD Alumni

Fernando earned his PhD in electrical engineering in 2022, and is now a fusion scientist at Helion Energy.