A Study of the Energy of the Fast Ions and Neutrals Using a Time of Flight Spectrometer

Abstract

The work described in this thesis is concerned with the development and application of a time of flight spectrometer for the measurement of the energy of the fast ions and neutrals produced by the B11 saddle field ion source. The thesis includes a review of the literature concerned with the production of fast ions and neutrals and also the principles, characteristics and properties of the saddle field ion sources. The time of flight spectrometer incorporates an E.H.T. clamp circuit which was capable of switching the anode voltage to ground in less than 0.4 pp sec. The circuit employed five thyristors and was operated under pulsed conditions. The ions and neutrals were detected by the secondary electrons produced at a plate collector and the energy spectra were calculated and displayed using a computer. The energy of the fast ions and neutrals has been measured for argon, helium and nitrogen and in all cases the spectra consists of a main peak and a smaller peak at higher energy. The lower energy peak was due to singly charged ions and always occurred at an energy equivalent to 76-78% of the anode voltage which is in good agreement with other workers who used a retarding field analyser. The smaller peak was due to the presence of doubly charged ions at an energy exactly twice that of the singly charged molecular ions. However, only one peak was observed in the energy spectra of the fast neutrals at an energy equal to that of the singly charged molecular ions for all three gases. The latter supports the view that the fast neutrals are produced by a symmetrical resonance charge exchange process occurring inside the source. Theoretical predictions of the formation of the fast neutrals using the appropriate charge exchange cross-sections were in good agreement with the experimental observations.