3D simulations of positive streamers in air in a strong external magnetic field
Zhen Wang, Anbang Sun, Saša Dujko, Ute Ebert, Jannis Teunissen
Abstract
Abstract We study how external magnetic fields from 0 to 40 T influence positive streamers in atmospheric pressure air, using 3D PIC-MCC (particle-in-cell, Monte Carlo collision) simulations. When a magnetic field B is applied perpendicular to the background electric field E , the streamers deflect towards the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>+</mml:mo> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> directions which results in a branching into two main channels. With a stronger magnetic field the angle between the branches increases, and for the 40 T case the branches grow almost parallel to the magnetic field. Due to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="bold-italic">E</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> drift of electrons we also observe a streamer deviation in the opposite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mi mathvariant="bold-italic">E</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> direction, where the minus sign appears because positive streamers propagate opposite to the electron drift velocity. The deviation due to this <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="bold-italic">E</mml:mi> <mml:mo>×</mml:mo> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> effect is smaller than the deviation parallel to B . In both cases of B perpendicular and parallel to E , the streamer radius decreases with the magnetic field strength. We relate our observations to the effects of electric and magnetic fields on electron transport and reaction coefficients.