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13.2 Emittance measurements method

The Method of Wiedmann, use three screens, to determine the emittance with three measure of sigma x. In reality, this is done with one screen and by varying a quadrupole, and fitting a curve. This requires the knowledge of the transport matrix, which is not a problem, but space charge effects are not taken into account by the transport matrix.

Methode of slits: Slits are introduced in the beam line so that part of the bunch goes through. The ``holes'' are proportionnals to the dispersion at point A, so by moving the slits the dispersion is known at several locations and thus, an ellipse can be fitted.

At a0, the small intermediate camera are used to measure sigma x and sigma y. For the emittance, Sigma z is measured. The bunch reflects on a metal screen and thus emit a really fast radiation. The radiation is proportionnal to the duration of the bunch. This radiation, goes into a yag screen which emit electrons, who are then deflected by an electric field. Their image is then screened by a camera. The image is fitted with a gaussian, providing us with sigma z. This is called a streak camera. To determine the energy spread, we use a spectrometer. But this is done three meteres after the streak camera, so charge effects during the drift might strongly affect the dispersion. Moreover the influence of the term sigma z delta is not studied.

Emmanuel Branlard
http://emmanuel.branlard.free.fr/