Variable-Path Magnetic Ion Buncher

Abstract

Following a previously proposed method for producing short intense monoenergetic ion bunches, a complete variable‐path magnetic ion buncher was constructed. Tests in 1958 showed that bunching did occur, but available ion beam intensity and instrumental resolution were too low for detailed measurements at that time. Reconstruction of the available accelerator to give a high current (≥100 μA), well‐focused ion beam, and correspondingly high resolution pulse measuring equipment permitted meaningful resumption of testing by late 1960. Bunching performance in accordance with design predictions was then observed. Measurements with ½‐MeV protons indicated pulse lengths ≤1 mμsec, peak currents ≥4 mA, and a bunching ratio of ≥40. Average bunched current was >30 μA. Although tested with ½‐MeV protons, the design permits operation with protons or deuterons to more than 1 MeV. Bunching is accomplished by deflecting successive portions of a continuous monoenergetic ion beam from an electrostatic accelerator over progressively shorter paths between foci of a multifocusing 103° deflection magnet in a manner such that all ions come together essentially simultaneously at one focal point in high intensity short duration ion pulses. Sinusoidal electrostatic deflection at 8.8 Mc, linearized by cylindrical electrostatic lenses, or through harmonic synthesis, provides the required sweep.