Je.I. Sokolovskij - Ph.D. (Eng.), Associate Professor, Department Electronic Engineering and Technology, Ryazan State Radio Engineering University. E-mail: ett@rsreu.ru
V.A. Korotchenko - Dr. Sc. (Eng.), Professor, Department Electronic Engineering and Technology, Ryazan State Radio Engineering University. E-mail: ett@rsreu.ru
Zh.V. Putilina - Post-graduate Student, Department Electronic Engineering and Technology, Ryazan State Radio Engineering University. E-mail: ett@rsreu.ru

Analytical and numerical methods of calculation of thermal conditions of microarea on the anode heated by field-emission current during short (a few μs) time during opening permalloy magnetically operated contacts are developed. Heat sink components from the warmed area connected with heat conductivity, surface emittance and material evaporation are considered in techniques. Changes of heat conductivity factor, thermal diffusivity and permalloy specific resistance with temperature growth are considered in more laborious numerical method. The calculations are performed in the application to the reed switch MKA-14108 with permalloy contacts at breaking the current of 0.1 A and a voltage of 100 V. In this mode, there are short (4 μs) field emission current pulses with an average power per pulse heating spots on the anode of about 2 watts. In calculations it was necessary that on a surface of the cathode there is a land with height 1μm and area of emitting flat top 50 μm2, finishing disconnection of contacts. Found with the help of the developed techniques that the surface temperature of the anode spot quickly (about 0.5 μs) increases to approximately steady-state value, which is determined mainly by the evaporation of the heat sink material and surface radiation. At the heating power of 2 watts depth of distribution of heat through 4 μs makes about 10 μm, and the established temperature value (to 4000 K) much higher than the permalloy boiling point that confirms possibility of intensive evaporation of a material. The mass of the substance evaporating from a surface of an anode spot during heating by field electron current during 4 μs which value makes 5,4∙10-10 g that is equivalent to education on the deepening anode in the form of a hemisphere with a radius about 1 μm is calculated. The obtained data confirm possibility of an erosion of contacts due to field emission.