Changes in the composition of the ion current in the process of field evaporation of tungsten at high temperatures

Field evaporation of tungsten at $T\sim$ 2000 K was studied using a sector magnetic mass spectrometer with a field ion source and a field emission microscope. Only low-charge ions W$^{+2}$ and W$^+$ of all W isotopes were observed in the process of evaporation. The mass distribution of ion currents of isotopes agreed roughly with the standard isotopic ratio for natural tungsten, although certain deviations from it, which were attributed to fluctuations and the erratic nature of evaporation process, were also detected.