Simulation of decelerating streamers in inhomogeneous atmosphere with implications for runaway electron generation

Journal Article · Mon Feb 08 00:00:00 EST 2021 · Journal of Applied Physics

DOI:https://doi.org/10.1063/5.0037669· OSTI ID:1849202

Starikovskiy, A. Yu. ^[1]; Aleksandrov, N. L. ^[2]; Shneider, M. N. ^[3]

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1. Princeton Univ., NJ (United States). Mechanical and Aerospace Engineering Dept.; Princeton Univ., NJ (United States)
2. Moscow Inst. of Physics and Technology, Dolgoprudny (Russia)
3. Princeton Univ., NJ (United States). Mechanical and Aerospace Engineering Dept.

The dynamics of positive and negative streamers is numerically simulated in atmospheric pressure air in the range of parameters corresponding to the streamer deceleration and termination in the middle of the discharge gap. A detailed comparison with experiments in air at constant and variable density demonstrates good agreement between the 2D simulation results and the observations. It is shown that positive and negative streamers behave in radically different ways when decelerating and stopping. When the head potential drops, the negative streamer transits to the mode in which the propagation is due to the forward electron drift. In this case, the radius of the ionization wave front increases, whereas the electric field at the streamer head decreases further and the streamer stops. Its head diameter continues to increase due to the slow drift of free electrons in the residual under-breakdown field. On the contrary, the only advancement mechanism for a positive streamer with a decreasing head potential is a decrease in the effective radius of the ionization wave, leading to a local increase in the electric field. This mechanism makes it possible to compensate for the reduction in the efficiency of gas photoionization at small head diameters. A qualitative 1D model is suggested to describe streamer deceleration and stopping for different discharge polarities. Estimates show that, during positive streamer stopping, the local electric field at the streamer head can exceed the threshold corresponding to the transition of electrons to the runaway mode when the head potential (relative to the surrounding space) decreases to~1.2 kV in atmospheric pressure air. In this case, pulsed generation of a beam of runaway electrons directed into the channel of a stopping positive streamer can occur. The energy of the formed pulsed electron beam depends on the intensity of photoionization in front of the streamer head. This energy can vary from 700 V (when increasing the photoionization rate by a factor of 10 with respect to the value in atmospheric pressure air) to 2.6 kV (when decreasing the photoionization rate by a factor of 1000). It is possible that this behavior of decelerating positive streamers can explain the observed bursts of x-ray radiation during the streamer propagation in long air gaps.

• Research Organization: Pennsylvania State Univ., University Park, PA (United States); Princeton Univ., NJ (United States)
• Sponsoring Organization: USDOE; USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: FE0026825; SC0021330
• OSTI ID: 1849202
• Alternate ID(s): OSTI ID: 1970678
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 6 Vol. 129; ISSN 0021-8979
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Atmospheric radiation
Electrical properties and parameters
Gas discharges
Numerical methods
Photoionization
Physics
Runaway electrons
Streamer discharge
Vacuum ultraviolet radiation