A RADIAL-FIELD MASS-SPECTROMETER WITH T-2 DEFLECTION VOLTAGE

Mass analysis of ions emanating from a laser-produced plasma requires some means of overcoming their wide energy spread, such as, for exampl e, through the use of an ion reflector in time-of-flight spectrometers . An alternative approach to this problem is to allow the ions to move freely from the plasma into a spectrometer in which a radial deflecti on field varies in time in such a way that the deflection trajectory o f an ion is independent of its energy. This paper describes the theory of such a spectrometer and investigates the focusing properties of th e system. It is found that the required time-varying field does not de stroy the focusing features known for a radial field system except tha t under these new conditions first-order focusing occurs at a turning angle of 144-degrees, which contrasts with a focusing angle of 127-deg rees for a radial-field spectrometer operating with a constant deflect ion field. The ion trajectories for the time-varying field have been s tudied using numerical methods and results from these are presented. A n approximate theory is also included which is in excellent agreement with the numerical computations and which yields simple results for us e in spectrometer design.