Microexplosion initiation by plasma heating of the microprotrusion at the wall

The evolution of fast (~10 ns) overheating of microprotrusion (~1 mum) at the plasma-surface boundary is considered. The heating of surface by plasma ions and electrons, cooling/heating by emission, and Ohmic heating were taken into account. Thermo-field emission current density and average energy of emitted electrons were calculated numerically. Electric field was defined by a Mackeowen-like equation. Considered range of plasma parameters: {10
¹⁴
cm
^-3
-10
²⁰
cm
^-3
}; {0.1 eV-10 keV}. The ability was shown of microprotrusion explosive overheating consistent with emission. The explosive threshold was found to be the power flux to the surface q
_thr
~200 MW/cm
²
. The ldquoexplosiverdquo heating here means both achieving T~10
⁴
K, j~10
⁸
A/cm
²
and increasing of growth: partT/partt>0, part
²
T/partt
²
>0, partj/partt>0 (partJ/partt>0). With plasma density less than (3-5)middot10
¹⁸
cm
^-3
, (with q>200 MW/cm
²
), the emission cooling is insufficient (because of emission restriction by space charge), and overheating occurs much earlier - at ~1 ns. In that case the intense metal vapor ionization lead to the significant density growth at the surface and to transition of heating evolution into the explosive regime. Considered conditions for microexplosion initiation with strong emission pulse - the ecton (~10
¹⁰
-10
¹¹
electrons per pulse), can be realized in plasma interaction with cathode, anode, or isolated wall; and can lead to the arc spots formation.