Calculations and measurements to a phase-free accelerating stage using electric ac-fields in a triangular shaped electrode system

Abstract

A phase-free accelerating stage for charged particles has been constructed which makes use of electric ac-fields in a triangular shaped electrode system combined with ac-deflecting devices in the MHz-range. An elaborate calculation of the energy gain based on a time dependent Hamiltonian and a simplified calculation assuming perfect shielding within the electrodes were performed. The theoretical results are compared with measurements at a frequency of 13.55 MHz and at peak electrode voltages of 3 kV and 0.5 kV. The maximum energy gain of electrons with an incident energy of 20 keV was measured to be 140 eV at the 3 kV peak voltage. Construction and properties of the retarding-field energy analyzer and of the resonant circuits are given. It is shown that rf-driven magnetic deflecting coils diminish the energy gain due to induced electric fields. Rf-electric capacitor fields seem to be superior to the rf-magnetic fields because they reduce the energy gain very little and furthermore offer a simultaneous phase-free particle acceleration in opposite directions. The possible applications of such a phase-free accelerating stage for heating up a plasma and for producing an intense ring of relativistic electrons are discussed.