Center for Advanced Diagnostics

The Center is dedicated to advancing measurement science and diagnostics

Laser-based plasma diagnostics

Laser-based plasma diagnostics like interferometers, Thomson scattering systems, polarimeters, absorption spectrometers, and emission spectrometers are powerful tools used in both fusion and industrial plasma settings. These instruments obtain spatially and temporally precise information about the plasma temperature, density, magnetic fields magnitude and direction, and ion presence. The Diagnostics Center is actively pursuing multidimensional interferometric devices as well as compact and simplified versions of standard interferometer architecture. Contact us to explore how General Atomics’ expertise in these areas can enable valuable diagnostic measurements in your plasma environment and expedite your research and development.


  • Toroidal Interferometer Polarimeter (TIP)

    Designed for the ITER facility, TIPprovides a robust, high-resolution, steady-state, interferometry and polarimetry solution that can be applied to a wide range of plasma applications measuring plasma density and magnetic field direction.

  • Two-Color Interferometer at DIII-D

    The two-color interferometer is a standard diagnostic tool on DIII-D that employs a combination of CO2 and HeNe lasers to compensate for beamline vibrations. By utilizing the relative phase shift between these lasers, the interferometer accurately measures the electron density, making it an indispensable instrument in DIII-D diagnostics.

  • Dispersion Interferometer for Atmospheric Plasma Diagnostics and Controls

    Funded by the Department of Energy, this project explores the use of advanced interferometry techniques, specifically dispersion interferometry, in atmospheric plasmas. These plasmas, used in industries from medical cleaning to surface functionalization, will be studied using high-speed diagnostics developed for fusion machines. The project aims to enhance understanding of plasma structure and develop control schemes for direct stabilization, moving away from traditional methods that rely on correlated parameters like flow-rate or voltage or disturbing methods like Langmuir probes.

  • Dispersion Interferometers at DIII-D

    General Atomics has extensive experience with building and developing dispersion interferometers (DI). DIs measure plasma density by extracting the phase shift created between fundamental and doubled laser beams that have passed through a plasma of interest. After passing through the plasma, these beams combine to form an interference pattern, which is analyzed to determine the phase shift and thus the plasma density. A DI is less sensitive to mechanical vibrations that other interferometer designs and less affected by perturbations by inhomogeneous air. The instrument can feature a wide bandwidth and fast measurement response time.

  • CO2 Laser Polarimeter

    In a collaborative project between General Atomics and the Large Helical Device in Japan, a polarimeter was built to measure the electron density via measurement of the Faraday rotation angle of a linearly polarized CO2 laser. This method proved to be a reliable diagnostic tool for electron density due to its immunity to fringe jump errors, a common issue in interferometers.

  • Fiber Interferometer

    General Atomics built a fiber interferometer and tested it in a laboratory-based plasma. The instrument is a compact, turn-key system that leverages fiber optics to conduct heterodyne interference between two lasers to measure electron density in plasmas. It achieves vibration compensation through the use of common path DFB lasers with all functions, including beam combining, splitting, frequency modulation, and collimation, being facilitated by shared single-mode fiber optical components, contributing to the system's compactness and ease of use.

  • Upper Wide Angle Viewing System (uWAVS)

    The uWAVS consists of five large periscope assemblies that will monitor the lower divertor (the particle and heat exhaust) sector of the interior surface of the ITER tokamak. It includes infrared and visible cameras that will monitor the surface of the tokamak components and relay their status to the operators.