Effect of magnetic field on sustainment of low-current DC vacuum arcs

Effect of magnetic fields on the instability of low current DC vacuum arcs, less than 10A, were examined experimentally. An axial magnetic field less than 100mT composed of a pair of disc magnets, an axial magnetic field by a solenoid coil in a range of 70 to 300mT, and an axial magnetic filed with a radial component by a disc magnet less than 40mT were used. It appeared that the arcs become unstable and the arc voltages rise by applying axial fields. As a result the lifetimes of the arcs rather decreased with increasing magnetic fields.