HSX Alumni

Stefan Gerhardt

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 is currently the Principal Research Physicist at the Princeton Plasma Physics Lab in Princeton, NJ.

John Canik


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 Ph.D. in Spring of 2007 and went to work at Oak Ridge National Laboratory under a prestigious Wigner Fellowship. John now heads the ORNL plasma physics theory group.

Walter Guttenfelder

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 currently works at the Princeton Plasma Physics Lab in Princeton, NJ.

Ali Abdou

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 in the 2005, and currently works as an Associate Professor at Zewail City of Science and Technology, Egypt.

Jeremy Lore


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 in the Spring of 2010, and currently works at the Oak Ridge National Lab

John Schmitt


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 in 2011 and currently works at the Princeton Plasma Physics Laboratory in Princeton, NJ.

Alexis Briesemeister


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 currently employed by the Oak Ridge National Laboratory Fusion Energy group and works at the General Atomics Fusion Group/DIII-D Laboratory in San Diego, CA.

Chris Clark


Chris while at HSX was investigating 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 joined the ranks of Google and currently works in Madison, WI.

Bob Wilcox


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.

Bob is currently employed by the Oak Ridge National Laboratory Fusion Energy group and works at the General Atomics Fusion Group/DIII-D Laboratory in San Diego, CA.

Gavin Weir


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.

Gavin is currently working at the Heliotron-J stellarator in Kyoto, Japan.

Enrico Chlechowitz

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 is currently working with Roland Berger Strategy Consultants in Germany.

Jerahmie Radder

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 is currently working in Minneapolis, MN.

Laurie Stephey

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.

Carson Cook

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 will be extremely useful for equilibrium analysis in perturbed tokamaks and stellarator modeling and design.

Adrian Akerson

Adrian studyied 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 verifications 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


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


Tom is implementing a polarimetry system to evaluate the Stark shift from the diagnostic Hydrogen neutral beam to allow better Electric field determination.
Tom is currently working at GE in Minneapolis, MN.