Sectional and projectional emittance measurements (abstract)a)

Abstract

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 high 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 the important parameters. Knowledge of it can be obtained by an emittance measurement. This is best done in a four-dimensional phase space, yielding a density distribution as function of the transverse spatial and momentum coordinates. Often, however, due to practical considerations, only two dimensions of the four-dimensional ‘‘trace space’’ are being measured. This two-dimensional data can be obtained as a section or as a projection of the four-dimensional trace space, where both methods have their merits. Projectional emittance measurements can usually be performed much easier and quicker, but by the projection of the four-dimensional space onto a two-dimensional plane information is lost. And although not all the particles of the beam are represented in a section of trace space, here aberrative distortions of the emittance can be seen most clearly and allow an easier comparison to numerically obtained data. The advantages and disadvantages of both methods are discussed. Numerical and experimental examples are presented.