High Current Traveling Wave Electron Linear Accelerators

The steady state and stored energy operational regimes of microwave electron linear accelerators are discussed with reference to high current capability. Avoidance of the beam blow-up pulse shortening phenomenon enables long pulse beam currents considerably greater than the maximum conversion efficiency value to be demonstrated. Heavy beam loading effects and choice of frequency are discussed with respect to this steady state operation, and it is shown that conversion efficiencies of greater than 90 per cent can be readily achieved. Stored energy considerations indicate that an increase in peak current of one or two orders of magnitude may be achieved for pulses of short duration with relatively conventional accelerator waveguides. Electron orbit theory including space charge effects for this transient condition is developed. Some experimental data obtained with a 10 Mev linear accelerator using a short pulse inflection system is presented. A concluding discussion deals with design criteria for stored energy operation in high power traveling waye structures and encourages further exploitation by providing higher current high potential sources capable of prebuncher or r-f chopped short pulse injection.