Best beam configuration for making optimum emittance measurements with three-position method

The transverse emittance in the HIRFL beam line has been measured by using the Three-position Method in which the beam sizes at three different locations in a field-free drift space are measured by three Secondary Emission Multi-wire Profile Monitors. In emittance measurements with this method the error has a great dependence upon the location of a beam waist, the waist size and the separation for three profile monitors. With the standard propagation of error calculations the best beam configuration for making optimum emittance measurements can be found. In making these calculations, it has been assumed that the measurement error of beam size dominates, and the distance measurement can be known to greater precision