The Madison Symmetric Torus (MST) is a reversed field pinch (RFP) physics experiment with applications to both fusion energy research and astrophysical plasmas.

MST falls into an unconventional class of machine called a reversed field pinch (RFP.)

The RFP is so named because the toroidal magnetic field that permeates the plasma spontaneously reverses direction near the edge.

But for the RFP to be a viable fusion energy candidate the plasma must be sustained by a steady state current source.

[2] A nonlinear reaction in the plasma combines the two oscillations in such a way that, on average, a steady current is maintained.

One of the challenges facing the RFP is fueling the hot core of the plasma directly, rather than relying on the deuterium gas to seep in slowly from the edge.

This peaked current profile serves as a source of free energy for magnetic fluctuations culminating in violent events in the plasma called sawteeth.

A great deal of research on MST is devoted to the study of this effect and its application for enhanced confinement.

Because the magnetic field inside the torus is bent into a circle, the fast ions are hoped to be confined in the background plasma.

It looks like a long silver cylinder laying on its side but tilted slightly downward against the torus near the back of the machine.

Problems would occur if the fast ions aren't confined within the plasma long enough for them to deposit their energy.

Bernstein Wave Mode relates to a method of injecting ion or electron energy (IBW or EBW) into a plasma to increase its temperature in an attempt to reach fusion conditions.

A plasma is a phase of matter which occurs naturally during lightning and electrical discharges and which is created artificially in fusion reactors to produce extremely high temperatures.

The second (and perhaps more scientifically important) goal of the EBW experiment is to drive electric current in a prescribed place within the plasma.

This is an unanswered question for the RFP and will give insight on whether or not this type of machine could be scaled up to a cost-effective, efficient fusion reactor.

Each beam optically pumps a formic acid vapor laser operating at a wavelength of 432.6 mm, and a power of about 20 mW.

In MST, we send multiple probe beams (blue lines in the figure) through the plasma at different radii.

The FIR system measures the Faraday rotation, which is proportional to the line average of the electron density times the magnetic field component parallel to the beam path.

FIR is an essential tool for most of the research topics in MST since it provides information about the basic plasma parameters.

The system measures electron density, toroidal current, poloidal magnetic field, and the spatial profiles of each.

Thomson scattering is the result of a collision between a photon (an electromagnetic wave) and a charged particle, such as an electron.

The Thomson Scattering configuration at MST uses a 1064 nm Nd:YAG laser system, which produces the best time-resolution electron temperature readings in the world.

These exist naturally due to the inability to achieve a perfect vacuum in a fusion reactor before fueling.

Thus, materials such as water vapor, nitrogen, and carbon will be found in small amounts in typical plasma discharges.

Measurements of the impurity ion temperature (Ti) and flow velocity (vi) are obtained on MST using Charge Exchange Recombination Spectroscopy, or CHERS.

During this transfer, the electron typically winds up in an excited state (high energy level) of the impurity ion.

Measurements of the carbon emission line shape are therefore used to extract values for the impurity ion temperature and velocity.

Charge Exchange: H + C+6 → H+1 + C+5 (n=7, l=6) Radiative decay: C+5 (n=7, l=6) → C+5 (n=6, l=5) + h (photon) In a typical fusion device the neutral atom density is small.

Therefore, the amount of radiated emission that results from charge exchange between impurity ions and neutrals is also small.

Perpendicular to the beam path, there exist a number of optical ports for viewing the plasma at different radial positions.