PURPOSE: To stably and easily obtain an indirectly-heated cathode heater which dissipates a low power and starts quickly by electroanalyzing a heater foot end with no electric field applied in an electrolyte which selectively dissolves only an Mo wire with an electric field for electroanalysis applied but does not dissolve either a W wire or an Mo wire with no electric field applied.

CONSTITUTION: A W.Re alloy wire is formed in a combined winding of condensation and rarefaction with an Mo wire serving as a mandrel, then it is formed in a double helical winding to form a heater. Next, after performing processes such as forming, annealing, and alumina coat sintering on the secondary coil section 3, an adequate number of them are clipped and immersed in an electrolyte up to a position 8 to selectively electroanalyze only Mo. In this case, an electrolyte is used which does not dissolve W and Mo with no electric field applied but selectively dissolves only Mo with an electric field applied. 85% concentrated sulfuric acid or an aqueous solution of 15g/l of sulfanic acid+ 30g/l of chromic acid, for example, can attain this purpose.