QUANTIZATION-ERROR OF SLIT-GRID EMITTANCE MEASUREMENT DEVICES

Slit-grid emittance measurement devices usually do not scan the beam c ontinously. but in fixed linear (x) and angular (x') steps. Thus in an emittance measurement performed with a slit-grid system, the beam is represented by a number of phase space boxes with a constant area or v olume determined by the linear and angular resolution. Considering the emittance as the area in the two-dimensional subspace (x,x') covered by the beam, the quantization error and its dependence on the resoluti on (linear and angular) as well as the influence of the beam parameter s is discussed. Measuring the very low emittance of the high efficienc y source (HIEFS) proved that the quantization error can be unacceptabl y high (much greater than 100%). With an optimized measuring device, t he normalized emittance came down from 10(-1) to 3.6 X 10(-3) pi mm mr ad. Finally, a typical misleading result of an emittance measurement, caused by the quantization error, is presented.