Physics of magnetic insulation failure of charge streams in crossed electric and magnetic fields

The collective oscillations of the charge streams occur at gap with the E×B-field (crossed electric and magnetic fields) by means of the exchanges by momentum and energy between the electrons (ions) and the E×B-field. The crossed field contains the energy density (εE
²
/2) and the momentum density (εE×B). The auto-excitation and self-organization of the streams occur due to secondary emission of the electrons from the cathode (ions from the anode). This instability was called as the back-bombardment instability (BKB). The physical model for the BKB - instability is proposed. The results of numerical simulation ((r,θ)-geometry) are given for dynamics of the back-bombardment instability (BKB) inside the magnetron diode (coaxial diode in magnetic field, B≡B
_0z
≡B
₀
). A <;<;quasi-stationary>;>; regime has been got for the electron leakage across the strong magnetic field (B
₀
/B
_cr
>; 1.1, B
_cr
- insulation critical field). The electron streams in the gap are self-modulated like the series bunches in an azimuthal direction. The modulated charged streams create attendant waves of the gradδV(r,θ,t) = δE(r,θ,t) electrical field. This field accelerates additionally some electrons and they get excess energy and whereupon they bombard a cathode producing the electron secondary emission. The others electrons are losing kinetic energy and they come to the anode. The instability is taking place, if primary emission of the cathode is small and a secondary emission factor is the k
_es
= I
_es
/I
_eBKB
>; 1.