Intense Focusing of Relativistic Electrons by Collapsing Hollow Beams

Low-impedance diodes with hollow tapered cathodes produce strong self-pinching in intense relativistic electron beams. Early in the pulse a thin hollow beam is formed, based on evidence of electrons striking the anode. This hollow beam collapses, accelerating toward the diode axis with velocities (1 to 5 mm/nsec) which depend locally on the anode material. An efficient and stable pinch, less than 3 mm in diameter, is formed at the anode. In the center 0.1 ${\mathrm{cm}}^2$, the power rises to ${10}^{11}$ W in less than 3 nsec. About 50% of the total diode energy (∼ 9 kJ) is dissipated within the pinch region.