Long-range propagation of high-power, pulsed electron beams for welding and materials processing applications

The electron beams used commercially for welding and materials processing operate either in vacuum or at very short range in air, which limits system productivity and the types of applications allowed. We show here that these restrictions can be relaxed considerably by raising both the beam energy and current, from under 200 keV to a few MeV and from under 1 A to a few kA, respectively, with the beam chopped into short pulses to preserve average beam power. This technology is made possible by the recent development of high-power generators that produce low-emittance beams with radii as small as 1 mm, pulse lengths of tens of ns, and pulse repetition rates up to several kHz. After studying the constraints imposed by gas scattering and the resistive hose instability, we conclude that high-power beams can propagate and remain tightly pinched over tens of cm in ambient air, without need of external guide fields. Equally important, the propagation requirements can be significantly relaxed by using a narrow conducting pipe filled with air or another gas to guide the beam to the workpiece.