Beam propagation options for intense electron beams in welding and materials processing applications

Summary form only given. A typical high-intensity electron-beam device for welding and materials processing applications might produce beams with energies of several MeV, currents of 0.1-10 kA, radii as small as 1 mm, pulse lengths of tens of nsec, and pulse repetition rates up to several kHz. This dramatic increase in beam energy and peak power offers several new capabilities, including the potential for self-pinched propagation in ambient air over distances of a few tens of cm. This capability would eliminate the need for vacuum pumping and magnetic focusing required for most present-day electron beam welders. The choice of beam parameters in the high-power regime is found to be constrained mainly by gas scattering and the resistive hose instability. For applications such as welding which would require very tight beams, the emittance tailoring techniques often used to control the instability in present experiments are not expected to be effective in this regime, and the stable propagation range is expected to be only a few betatron wavelengths. Nevertheless, a wide range of acceptable parameters is available, especially when use is made of a narrow conducting pipe to guide the beam to the workpiece.