SECTIONAL AND PROJECTIONAL EMITTANCE MEASUREMENT

For many applications of ion sources the quality of the generated ion beam plays an increasingly important role. Ion sources consist of the plasma generator and the extraction system. Both parts can, due to hig h ion temperature or various aberrations, contribute to a degrading of the beam quality. Though the beam quality is determined by many more factors, the transverse motion of the particles certainly is one of th e important parameters. Knowledge of it can be obtained by an emittanc e measurement. This is best done in a four-dimensional phase space, yi elding a density distribution as function of the transverse spatial an d momentum coordinates. Often, however, due to practical consideration s, only two dimensions of the four-dimensional ''trace space'' are bei ng measured. This two-dimensional data can be obtained as a section or as a projection of the four-dimensional trace space, where both metho ds have their merits. Projectional emittance measurements can usually be performed much easier and quicker, but by the projection of the fou r-dimensional space onto a two-dimensional plane information is lost. And although not all the particles of the beam are represented in a se ction of trace space, here aberrative distortions of the emittance can be seen most clearly and allow an easier comparison to numerically ob tained data. The advantages and disadvantages of both methods are disc ussed. Numerical and experimental examples are presented. (C) 1996 Ame rican Institute of Physics.