On the performance of a straight acceleration tube with axial gradient modulation

Abstract

An earlier inclined field configuration has been replaced by a straight field configuration in the acceleration tube of the 5 MV electrostatic accelerator at the Institute of Nuclear Research, with the aim of improving lateral position stability of the beam at the tube exit. Making use of the so-called decoupling sections proposed by Herb [1], axial gradient modulation has been introduced by conic electrodes arranged periodically in shorted sections along the tube axis, in order to prevent secondary electrons from travelling long distances towards the terminal. Good beam stability has been achieved at high, medium and very low beam currents as a result of this modification. The voltage holding properties did not show any observable change. The results obtained from a series of bremsstrahlung measurements performed with thermoluminescent dose meters in the stack of the machine and around the vessel clearly indicate the main electron suppression properties of this tube geometry.