The flux of backstream electrons to the source plasma region increases significantly with the acceleration voltage of an ion beam, so that the back plate in the arc chamber should be broken for quasi‐dc operation. The flux of backstream electrons is estimated at the acceleration voltage of 50–100 kV for a proton beam with the aid of ion beam simulation code. The power flux of backstream electrons is up to about 7% of the total beam output at the acceleration voltage of 75 kV. It is pointed out that the conventional ion sources such as the duoPIGatron or the bucket source which use a magnetic field for source plasma production are not suitable for quasi‐dc and high‐energy ion sources, because the surface heat flux of the back plate is increased by the focusing of backstream electrons and the removal of it is quite difficult. A new ion sourc which has an electron beam dump in the arc chamber is proposed.