Modification of the electric field distribution in a diffuse streamer-induced discharge under extreme overvoltage

Abstract

The present work is devoted to the study of the spatio-temporal distribution of the reduced electric field (REF) in a 10 ns diffuse atmospheric air discharge at very high overvoltage, in a pin-to-plane electrode geometry. The REF is derived through the intensity ratio of two wellknown transitions of molecular nitrogen: N 2 (C-B, v′=2, v″=5) and N 2 + (B-X, v′=0, v ″=0). The achieved temporal resolution is 500 ps, while the spatial resolution is better than 300 μm and 400 μm in the axial and radial direction, respectively. Due to the fast rise time of the voltage pulse, the total electric field is dramatically disturbed by the contribution of the Laplacian field, contrary to low-voltage streamer discharges. Electric field values above the ionization threshold are sustained all along the plasma channel. The dynamics of the high-voltage diffuse discharge seem similar to those of classical streamers with a very high field zone propagating towards the plane electrode then followed by a backward neutralization wave. However, some noticeable discrepancies are reported between the experimentally-obtained distributions of the axial electric field at 65 and 85 kV and those computed by means of a fluid model. They stress in particular the origin and the role of the background electrons in the discharge dynamics. Several limitations of the applicability of the intensity-ratio method for the study of very transient phenomena are also discussed. At first, the effect of the temporal integration of the signals is addressed by comparing them with an artificial averaging of the modeling results. Then, the effect of the non-stationarity of the collected signals is put forward by applying the intensityratio method under steady-state assumption or not. Lastly, the overestimation of the electric field in the discharge front due the relatively long effective lifetime of N 2 (C, v′=2) compared to the discharge dynamics is discussed.

TALIF measurements of atomic nitrogen in the afterglow of a nanosecond capillary discharge

“…The principal mechanism behind such plasmas is that the application of high voltage pulses with a rapid (nanosecond) rise time and short pulse width (tens to hundreds of nanoseconds), creates a system of strong nonequilibrium, allowing access to voltages significantly exceeding the DC breakdown threshold [8]. At extremely high (~ 10 3 Td) electric fields in the front of a nanosecond discharge, the spatial uniformity of these plasmas can be maintained, from moderate pressures (tens of mbar) [9,10] up to atmospheric pressure [11,12]. The discharge propagates in the form of a Fast Ionization Wave (FIW), leaving in its wake a plasma with still relatively high electric fields (200 -400 Td), sustained throughout the duration of the high-voltage pulse.…”

Progresses on the Use of Two-Photon Absorption Laser Induced Fluorescence (TALIF) Diagnostics for Measuring Absolute Atomic Densities in Plasmas and Flames

“…However, the development of those models is based on different assumptions, limiting thus their accuracy. Furthermore, for fast ns-pulsed discharges with voltage pulse durations lower than 10 ns and rise/fall times of the order of few ns [19,32,107], ns-TALIF does not allow investigating species kinetics during the voltage pulse. Thus, ns-TALIF (and LIF) can only be useful to perform time-resolved measurements on longer time-scales than the laser pulse dura-tion, i.e., several tens of ns, μs or ms time-scales [32,36,72,102].…”

Формирование Двух Импульсов Тока Пучка Убегающих Электронов

“…Основное отличие стримера от лавины -это существенное усиление напряженности электрического поля на его фронте. Измерения, проведенные в работах [48,49], показали, что напряженность электрического поля на головке стримера в воздухе атмосферного давления при напряжениях 20−85 kV составляет ∼ 200 kV/cm и зависит от положения стримера в промежутке. Благодаря этому, электроны, двигаясь синхронно с фронтом стримера (волны ионизации), могут набирать дополнительную энергию.…”

“…В это время катод уже экранирован плотной плазмой, и величина E/ p вблизи него уменьшилась. Это подтверждают измерения распределения электрического поля в промежутке при движении стримера для подобных условий в [48,49]. Считаем, что генерация ВИТП происходит благодаря протеканию двух процессов.…”

“…Как обсуждалось выше, ВИТП отсутствует при появлении у катода плотной плазмы за счет взрывной эмиссии электронов, которая уменьшает электрическое поле в этой области, и ВИТП имеет максимум из-за влияния второй волны ионизации. Измерения электрического поля на фронте стримера (волны ионизации) при напряжении ≈ 25 kV дали для воздуха его величину в подобных условиях, не превышающую ∼ 200 kV/cm [48,49]. Из этого следует, что без ускорения электронов из прикатодной области усиления электрического поля на фронте второй волны ионизации не хватит для получения ВИТП.…”