Electric field determination in transient plasmas: in situ & non-invasive methods

Abstract

One of the primary basic plasma parameters within transient nonequilibrium plasmas is the reduced electric field strength, roughly understood as the ratio of the electrical energy given to the charged species between two collisions. While physical probes have historically been used for electric field measurements, recent advances in high intensity lasers and sensitive detection methods have allowed for non-invasive optical electric field determination in nearly any discharge configuration with time-resolution up to the sub-nanosecond range and sub-millimeter spatial resolution. This topical review serves to highlight several non-invasive methods for in-situ electric field strength determination in transient plasmas ranging from high vacuum environments to atmospheric pressure and above. We will discuss the advantages and proper implementation of (i) Laser induced fluorescence dip spectroscopy for measurements in low pressure RF discharges, (ii) optical emission spectroscopy based methods for nitrogen, helium or hydrogen containing discharges, (iii) electric field induced coherent Raman scattering, and (iv) electric field induced second harmonic generation. The physical mechanism for each method will be described as well as basic implementation and highlighting recent results.

High-resolution electric field and temperature distributions in positive streamers

“…When the previous conditions are satisfied, the dependence R (E/N) relating the intensity ratio and the reduced electric field is given by [5,10]:…”

“…Within this work, we use the intensity ratio of the FNS (0-0) and SPS (2-5) to determine the electric field in synthetic air and pure nitrogen at 33 mbar. A calibration curve for FNS (0-0)/ SPS (2)(3)(4)(5) in synthetic air at atmospheric pressure was determined experimentally by Paris [26] and has the following form:…”

“…For an experiment consisting of 100 radial bins and 25 temporal steps, 2500 spectra are fitted. The rotational and vibrational temperatures are determined from vibrational bands SPS (1-4), (2-5), (3)(4)(5)(6) and FNS (0-0), (1-1) and their entire rotational manifold.…”

“…Two of the main parameters of interest when characterizing streamer discharges are the reduced local electric field strength (E/N) and the electron energy distribution function (EEDF) which describe the electrons accelerated by this field. There are methods of measuring these properties directly and indirectly for plasmas and streamer like discharges [5][6][7][8]. However, it has been proven very difficult to apply these measurement techniques to transient and stochastic phenomena like a streamer discharge, which is exacerbated by the low active species densities found in these types of plasmas.…”

“…A method to measure the electric field which has become popular in recent years is Electric Field Induced Second Harmonic generation (E-FISH). However, this method suffers from complications which make it very hard to use for the quantitative determination of electric fields with unknown spatial distributions [5,9].…”