A reactor comprising {HEAD ~ an annular iron core} constituting a closed magnetic path and {TAIL ~ a conductor wound} on the annular core, said iron core being formed of particles of iron or an iron based magnetic material each covered with an insulative oxide film which contains 0.3 to 0.8% of oxygen by weight based on the particle 
A reactor comprising { HEAD ~ an annular iron core } constituting a closed magnetic path and { TAIL ~ a conductor wound } on the annular core , said iron core being formed of particles of iron or an iron based magnetic material each covered with an insulative oxide film which contains 0.3 to 0.8 % of oxygen by weight based on the particle
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