Double-coil magnetic focusing of the electron beam generated by a plasma-cathode electron source.

We present the results of our investigations of magnetic focusing of the electron beam generated by a plasma-cathode electron source in the forevacuum pressure range (10-30 Pa). We show that a magnetic double-focusing system employing two separate field coils with the main magnetic coil located close to the beam collector at the focal plane provides effective and efficient focusing of the electron beam. With our e-beam source, this focusing system produces a power density of more than 1 MW/cm at the electron beam focus with an accelerating voltage of 30 kV and a beam current up to 60 mA. For comparison, the maximum beam power density provided by plasma-cathode electron sources at pressures of less than 0.1 Pa is at the level of 10 MW/cm.