One method of measuring the transverse phase-space distribution of a particle beam is to intercept the beam with a slit and measure the angular distribution of the beam passing through the slit using a parallel-strip collector. Together the finite widths of the slit and each collector strip form an acceptance window m phase space whose size and orientation are determined by the slit width, the strip width, and the slit-co distance. If a beam is measured using a detector with a finite-size phase-space window, the measured distribution is different from the true distribution. The calculated emittance is larger than the true emittance, and the error depends both on the dimensions of the detector and on the Courant-Snyder parameters of the beam. Specifically, the error gets lager as the beam drifts farther from a waist This can be important for measurements made on high-brightness beams, since power density considerations require that the beam be intercepted far from a waist In this paper we calculate the measurement error and we show how the calculated emittance and Courant-Snyder parameters can be co for the effects of finite sizes of slit and collector.
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