Microfields

Microfields are the local electric fields produced at a point by the surrounding charged particles in a plasma or similar many-body system. At any instant, the net field results from the instantaneous positions and motions of nearby ions and electrons, and it fluctuates in time as the particles move.

In idealized theories, the ions are treated as a random, uncorrelated distribution around a probe particle, leading to statistical descriptions such as the Holtsmark distribution for the static ion microfield. In real plasmas, electron screening, ionic correlations, finite temperature, and dynamical effects modify the distribution and its time dependence. The field is often described by its probability distribution and autocorrelation functions, which determine how the microfield influences atomic energy levels over short timescales.

A primary physical role of microfields is in spectroscopy. Local electric fields cause Stark shifts and broadening of atomic and ionic spectral lines. The resulting line shapes depend on plasma parameters such as electron density, ion composition, and temperature, and thus microfield analyses provide diagnostic tools for inferring these parameters in laboratory and astrophysical plasmas.

Modeling and measurement approaches include analytic distributions with their extensions and numerical simulations, notably molecular dynamics and Monte Carlo methods, to compute microfield distributions and time autocorrelations. Experimental diagnostics compare observed spectral line profiles with predictions to extract plasma conditions, making microfields a foundational concept in plasma spectroscopy and related fields.