# Diagnostics

Diagnostics are the eyes and ears of fusion reactors. They return vital parameters such as the temperature, the density, the impurity content, the magnetic field et cetera. A distinction can be made between active diagnostics (requiring the injection of light beams, particles, or probes and the observation of an induced effect), and passive diagnostics (based on the observation of radiation and particles emitted spontaneously by the plasma). Below follows a list of different diagnostics, together with their main measurement parameters.

## Passive diagnostics

Name Abbreviation Measurement parameters
Mirnov coils, pickup coils - Magnetic field components and fluctuations (outside plasma)
Flux loops - Magnetic field (outside plasma)
Electron Cyclotron Emission ECE, ECEi Electron temperature $T_e$, electron temperature fluctuations (turbulence) $\tilde{T}_e$ (local)
Soft X-Ray Emission SXR A combination of electron temperature $T_e$, electron density $n_e$, and effective charge $Z_{eff}$ (line integral)
Bolometry - Broad spectrum emission (line integral)
Hα monitors - Emission of specific Hα radiation
Spectroscopy - Monitoring of impurities, etc. (line integral)

## Active diagnostics

Name Abbreviation Measurement parameters
Thomson Scattering TS Electron temperature $T_e$, electron density $n_e$ (local)
Charge Exchange Recombination Spectroscopy CXRS, CXS, CHERS, CER Ion temperature $T_i$, toroidal and poloidal plasma rotation velocity $v_\phi$, $v_\theta$, impurity density $n_Z$
Motional Stark Effect MSE Magnetic pitch angle $\tan(\gamma) = B_\theta/B_\phi$
Heavy Ion Beam Probe HIBP Electron density $n_e$, plasma potential $\phi$ (local)
See TJ-II:Heavy Ion Beam Probe
Interferometry - Electron density $n_e$ (line integral)
Polarimetry - Magnetic field pitch (line integral)
Reflectometry - Electron density $n_e$ (local, fluctuations)
Langmuir probes - Ion saturation current, plasma potential, Mach number, etc. (local, fluctuations)
Diagnostic beams - Injection of Helium, Lithium, etc., and observation of emitted radiation (local, fluctuations)

A special bi-annual conference on fusion diagnostics is held in the U.S.: The Topical Conference on High Temperature Plasma Diagnostics (HTPD)

## References

• I.H. Hutchinson, Principles of Plasma Diagnostics, Cambridge University Press; 2nd edition (2002) ISBN 978-0521803892