The Helically Symmetric eXperiment (HSX) is an optimized stellarator operated by the College of Engineering at UW-Madison. 3D shaped coils are arranged in a torus-like configuration to produce a 1Tesla magnetic field that confines high temperatures plasma with temperatures higher than 10 Million degree C. The goal of the experiment is to contribute to the physics basis of a future  power plant which produces energy by fusing Hydrogen isotopes to Helium.

HSX rendering, vessel cutaway, isometric view.
CAD drawing of the HSX stellarator


08/31/23: HSX successfully resumes plasma operation after a first wall reset.


Video of a fast-framing camera during conditioning discharges showing hot-glowing particles that are accelerated when the plasma touches the plasma vessel for the first time.

What is helical symmetry?

HSX is the only device in the world that has a magnetic field structure described as Quasi-Helically Symmetric (QHS) where high and low-field regions of the magnetic field structure wrap around the device helically (see picture above). This allows particles to “see” a quasi-symmetric magnetic field structure which provides excellent confinement properties.


Plasma physics research at HSX focuses on studies of turbulent transport, as well as the generation and damping of plasma flows in the 3D magnetic field geometry.


Video showing the perturbed electrostatic potential inside HSX, as simulated by the turbulence code GENE.

Device Parameters

Major Radius (machine center to Plasma center): 1.20 meters
Average Plasma Minor Radius: 0.12 meters
Aspect Ratio (Major Radius/Plasma Radius): 10
Plasma Volume: 0.44 cubic meters
Number of Field Periods (symmetry around torus): 4
Rotational Transform on axis: 1.05