Diagnostics and modeling of plasma processes in ion sources

Plasma ion sources are constantly growing in importance in the field of atomic mass spectrometry. The idea is to deposit enough energy into the analyte to atomize and ionize a representative part of it and to achieve a plasma state that will endure for some period of time. A fraction of the ions can then be extracted from the plasma and analyzed in the mass spectrometer. The main difference among the methods for plasma ionization lies in the form in which energy is delivered to the sample. Either it is in the form of electric current (glow discharge, spark) or it is mediated by electromagnetic radiation (inductively coupled plasma (ICI’), microwave-induced plasma (MU’), pulsed laser). The present state of the art in using these sources in analytical applications is well summarized in a recent review (1) and in a recently published monograph (2). Plasma ion sources are not only used in mass spectrometers, but have become essential parts of ion implanters, accelerators, nuclear fusion devices, etc. (3). For ion implantation, ion milling, and etching purposes, hollow cathode (4), plasma cathode (5-8), radiofrequency (9) and microwave ion sources (10-12) are under intense investigation. Diligent research is devoted to the ever-improving ion sources for accelerator and nuclear fusion applications. Multicusp (13-16), surface plasma (17), hollow cathode (18), microwave (19), alkaline anode (20-22), radial field discharge (23), and micropinch (24) sources are among the subjects of current interest. We refer to the multitude of these plasma ion source construction efforts only because-as has happened already many times before-new mass spectrometric sources may emerge from such developments. Of these methods hollow cathode sources are familiar to the analytical spectroscopist, and microwave sources are just about to debut in mass spectrometry. The expected properties of the source depend on the particular demands of