A New Method for Longitudinal Emittance Measurements

A procedure for the measurement of beam parameters in the longitudinal phase space has been developed and tested at the Unilac. Approximating the particle distribution in the ¿W-, ¿¿-plane by ellipses the method will be practicable at all rf-accelerators if bunch width can be measured. Taking advantage of the broadband capacitive pick-up system of the Uinilac two different algorithms can be used for the evaluation of the relevant ellipse parameters. One algorithm is based on the measurement of the bunch width at different positions along the accelerator as a function of the drift length. The other one uses an rf-resonator operated at + 90° or - 90° stable phase with different amplitudes to vary the energy spread and therefore the bunch width at one pick-up. The Daper describes both methods and gives some examples from measurements at the Unilac.