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Energy security is becoming increasingly important from both a civilian and national defense perspective. From a civilian point of view, energy resilience is coming under threat from the rise of AI companies demanding more power which threaten to strain the energy grid1 and increasingly severe storms are knocking out power grids2. Added to trade tensions putting strain on energy related supply chains (oil, rare earth elements, etc), there is an immediate need to consider a multitude of energy sources to meet current and future power needs. Current energy sources powering the electric grid include fossil fuels, nuclear (fission), and renewables.3
Absent from this list is fusion energy production – where nuclei are fused together, releasing energy and neutrons which can then be exploited to generate heat and subsequently electricity. Fusion energy has long promised to deliver the “power of the stars” as a useable energy source. Because of this, a significant amount of research has gone into developing a working fusion reactor over the past several decades. As of 2025, different reactor designs being pursued include tokamaks (ITER, SPARC, EAST), stellarators (LHD, HSX), z-pinch devices (FuZE), and laser-based inertial confinement (NIF, LMJ). While none have succeeded in delivering energy onto the grid, yet, this has not stopped a significant surge in interest in studying the potential of the above fusion designs with both governments and private corporations actively participating in the development of fusion reactor technology.4
As progress marches on towards realizing fusion energy, a significant amount of R&D remains to optimize reactor specific fusion parameters, develop novel plasma-facing materials, and understand the fundamental physics of plasma generation and stability. Contributing to this research are a variety of optical diagnostics that can monitor neutron generation, plasma evolution, contaminant concentrations, and material breakdown of plasma-facing components.
In this application note we present several optical methods contributing to the progress in fusion reactor development and highlight the imaging and spectroscopy technology Oxford Instruments Andor manufactures that empower these methodologies.
Through various optical diagnostics one can measure plasma’s electron density and temperature, detect impurities, probe energy loss mechanisms, and understand plasma evolution. The available optical tools span the X-ray to the UV/Vis and include bremsstrahlung radiation, optical emission spectroscopy (OES), and Thomson Scattering, to name a few.
Bremsstrahlung radiation provides an opportunity to both measure electron density/temperature5 and understand an energy loss mechanism for a fusion reactor6. Often emitting soft x-rays up to a few keV, a detector is required that can detect photons in this energy regime. At Andor we manufacture several direct detection x-ray cameras that are sensitive up to ~15 keV that can be fit onto a vacuum spectrometer to study Bremsstrahlung radiation. The open-fronted Newton-SO and iKon-SO CCDs have spectroscopy/imaging sensors, respectively, that can be utilized to detect EUV and soft X-ray photons up to 15 keV. For lower energy experiments the Marana-X is an sCMOS based camera that offers near 100% quantum efficiency from 80 eV to 1 keV for sensitive detection at full frame rates over an order of magnitude faster compared to conventional CCD technology. In the event that photon energies higher than 15 keV need to be detected, several FO coupled scintillator cameras are available (iKon-L HF and Zyla HF). If an experimental design calls for scintillators to be lens-coupled, then the entire visible wavelength camera portfolio becomes available.
Optical emission spectroscopy can be a broadly applicable optical diagnostic to study plasma impurities7, helium accumulation8, and even measure internal electric fields via the stark effect9. Dependent on experimental specifics, sensitive detection across the UV and into the near infrared (~200-900 nm) could be required. For the UV-NIR spectral regions, Andor provides Czerny-Turner spectrographs with resolution down to 0.02 nm and an echelle spectrograph that can measure high resolution (R~5000) spectra across the whole UV-NIR region in a single shot. Coupled to these spectrographs are high QE (>95%) CCD and sCMOS spectroscopy cameras that provide sensitive detection across the whole potential OES spectrum. OES experiments in the EUV/VUV can be used to detect carbon impurities in hydrogen/deuterium plasmas. Experimentally, these can take advantage of the same open-fronted cameras mentioned above.
Thomson scattering in fusion plasmas is the elastic scattering of laser light by the free electrons, which carries information about the number and temperature of free electrons in the plasma. This is contrasted to the inelastically scattered Raman signal, where coherent anti-Stoked Raman scattering can be used to measure plasma temperature through the ro-vibrational spectra of molecular plasma gases. Using a spectrograph to spectrally resolve scattered laser light, an intensified CCD or sCMOS is the camera of choice to detect the Thomson scatter.10 This is because the nanosecond gating of an intensified camera can isolate the Thomson scatter from stray light sources while amplifying weak signatures, increasing the accuracy and sensitivity of a Thomson scattering setup. Andor’s iStar sCMOS also enables particle image velocimetry (PIV) experiments where a double frame image is recorded with an interframe gap possible down to several hundred nanoseconds. In a Thomson scattering experiment, PIV experiments would allow the study of the evolution of electron density and temperature with sub-microsecond temporal resolution.
Since the primary fusion reaction being pursued for commercial fusion systems is deuterium and tritium, there is interest in understanding the evolution of the following reaction as a function of reactor operating conditions:
2H + 3H à (4He + 3.5 MeV) + (n + 14.1 MeV)
The neutrons (n) emitted in this reaction carry an energy of 14.1 MeV, so understanding their production rate requires neutron detection at this energy. Due to the intense energy, a neutron scintillator (ex. LaBr3(Ce))11 is required. This scintillator can be placed in the neutron path and its emission lens-coupled to a camera outside of the neutron path. Imaging format CCD or sCMOS cameras provide robust detection solutions to image scintillator emission. For faster acquisition rates sCMOS or EMCCD technology are a preferred choice for sensitive scintillator emission detection due to the low read noise or EM gain to overcome CCD read noise, respectively.
As important as understanding the physics of plasma evolution within a reactor is developing plasma-facing materials that can withstand the intense heat and magnetic fields of the plasma reaction. During the fusion reaction the materials thermo-mechanical properties can change under exposure to the plasma, plasma fuel can embed in the wall, and plasma-facing material can leach into the plasma as an impurity effecting the continual operation of the fusion reaction. Several plasma-facing materials under consideration include Tungsten, Molybdenum, various carbide ceramics, and liquid lithium layers coating other wall materials. As the fusion reaction proceeds OES can be used to monitor contamination of plasma-facing materials into the plasma by looking for contaminant emission lines. Post-exposure, laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy are two optical diagnostics that can be used to study the material composition after reacting with the hot plasma.
LIBS is an optical diagnostic that uses an intense laser to generate a small plasma from the material surface under consideration. As the laser-induced plasma cools, the emission can give information about the composition and relative quantities of atoms in the plasma-facing material. Examples of relevant spectral targets that could be considered include the 7S3 and 5D0 lines of tungsten at 400.88 nm and 498.26 nm, respectively,12 the 247.83 nm line of atomic carbon,13 and the 670.78 nm line of lithium. Changes in LIBS spectra pre- and post- exposure to plasma can provide important information into the generation of contaminants from, and breakdown of, plasma-facing materials. Popular for LIBS experiments are Echelle type spectrographs that enable spectral measurements that simultaneously have high resolution and large bandpass. At Andor the Mechelle spectrograph coupled with the iStar CCD or iStar sCMOS provide the necessary detection equipment for LIBS experiments spanning 200-950 nm and a resolving power up to R~5000.
Raman spectroscopy provides another avenue for studying plasma-sidewall interactions for a wide range of materials. Examples of relevant materials and their Raman shifts include amorphous carbon with shifts observed from 500-3000 cm-1, while crystalline beryllium and tungsten oxides have Raman shifts found in the fingerprint region (below 1000 cm-1).14 Extending the use of Raman spectroscopy, Raman microscopy can be used to study the distribution of specific materials and their chemical properties by spatially resolving specific Raman shifts. Andor spectrographs and spectroscopy cameras enable the construction of both custom Raman spectroscopy and microscopy systems. The modularity of the spectrographs allows for flexibility of the detection hardware to suit a user’s present needs while leaving room to adapt the system overtime. If a turn-key microscopy solution is required Oxford Instruments Witec can provide a variety of confocal Raman microscopy solutions.
Date: November 2025
Author: Andrew P. Carpenter
Category: Application Note
