Secondary electron flight times and tracks in the carbon foil time pick-up detector

Abstract

Carbon foil time pick-up detectors used in the time-of-flight measurements of MeV energy ions have been studied in connection to time-of-flight-energy spectrometer used for heavy ion elastic recoil detection analysis. In experimental coincident TOF-E data characteristic halos are observed around light element isobars, and the origin of these halos were studied. The experimental data indicated that these halos originate from single electron events occurring before the electron multiplication in the microchannel plate. By means of electron trajectory simulations, this halo effect is explained to originate from single electron, emitted from the carbon foil, hitting the non-active area of the microchannel plate. This electron creates a secondary electron from the surface and which ends up to the microchannel plate pore, is multiplied and create now a detectable signal. Other general timing gate parameters such as wire-to-wire spacing of the grids, acceleration potential of the 1st grid and the mirror grid potential gradient were also studied in order to improve the detector performance.