Plasma diagnostics

Plasma diagnostics are methods for measuring plasma properties, including density, temperature, composition, flow, and electromagnetic fields. They range from probes inserted into the plasma to remote optical and electromagnetic measurements.

Langmuir probe: An electrode inserted into a plasma to measure current–voltage characteristics and infer local electron properties. Its current–voltage curve estimates electron temperature and density through direct contact.
Tokamak: A magnetic-confinement device that uses a toroidal magnetic field to confine hot plasma. Its dense diagnostic suite measures profiles, instabilities, and confinement performance.
Plasma frequency: The natural oscillation frequency of electrons displaced relative to ions in a plasma. It sets the cutoff that lets microwave reflectometry infer local density.
Active diagnostic: A measurement method that sends energy or a probe signal into a system and analyzes its response. It contrasts with passive observation by supplying a controlled signal, as in scattering.
Thomson scattering: A laser diagnostic that measures light scattered by free electrons to infer their density and velocity distribution. Scattered laser light yields local electron properties without inserting a probe.
Inertial confinement fusion: A fusion approach that compresses and heats a fuel capsule rapidly using intense energy pulses. Short-lived, dense plasmas require fast imaging and time-resolved spectroscopy.
Debye length: The characteristic distance over which mobile charges screen an electric potential in a plasma. It governs sheath dimensions and whether a probe samples collective plasma behavior.
Passive diagnostic: A measurement method that observes naturally emitted or transmitted signals without deliberately probing the system. It avoids signal injection but depends on radiation the plasma produces or transmits.
Interferometry: A measurement technique that infers changes in a wave’s phase from interference with a reference wave. Plasma-induced phase shifts reveal the integrated electron density along a viewing path.
Solar spectroscopy: The analysis of solar spectra to determine the Sun’s composition, physical conditions, and dynamics. Remote observation uses spectral lines to diagnose plasma inaccessible to probes.

Linked from 2 pages

Laboratory plasmaRelated: Accurate diagnostics remain a central challenge in interpreting laboratory experiments.