Slalom Focusing

Abstract

In the search for a scheme of electron focusing which would permit a beam to weave in and out through an rf structure, it was discovered that a linear array of line charges in free space produces two equipotential surfaces which contain exact electron trajectories. The field about such an array may be nearly duplicated by an array of positive wires sandwiched between two negative plates. It has been found that such a structure will effectively focus a ribbon type electron beam of surprisingly high perveance. A backward-wave oscillator was built which utilized this "slalom" type focusing. Although this tube was of the rough, experimental variety, oscillations were obtained throughout the range of 3.3 to 4.3 kmc. A beam tester was constructed which has a beam-focusing structure just ten times the size of that of the oscillator's. Ninety-seven per cent transmission through 27 wires of a beam of perveance (2×10-6) has been achieved with this tester. Slalom focusing may also find application in the field of switching.