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Bunch length measurement

Bunch length measurement at PBPL is a difficult mission, as our beams are measured in the picoseconds or below. These types of measurements are often performed in the frequency domain, as the spectrum of coherent radiation (e.g. coherent transition radiation, CTR) follows that of the beam. Such measurements can achieve resolution of the rms bunch length at the 10's of fs level, but do not easily yield detailed information available about the exact profile of the beam.

Alternatively one may use a fast "sweeping" measurement, such as a streak camera. In a streak camera, the time profile of the beam is encoded first in photons (from, say Cerenkov radiation or OTR), and then converted back to electrons in a tube that is swept quickly in time. The resolution obtained from this type of measurement is ps or above, but one may also exploit the non-sweeping dimension to perform type dependent imaging, which gives rise to very powerful techniques. To extend the reach of this typeof measurement to the fs level, we are now developing rf sweepers, where the relativistic beam itself is swept using a deflection mode cavity.