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Wire Scanner for Swiss FEL

Supported primarily by Paul Scherrer Institute, Contract 8446-T1
and supplemented by College of Arts and Sciences, Mississippi State University
& Shackouls Honors College, Mississippi State University
Fig.1. The wire scanner in the electron beam's perspective (© Advanced Instrumentation Group, Swiss FEL PSI)

    Wire Scanners can be used for many things such as measuring beam profile and beam emittance. One way of measuring beam transverse profile using a wire scanner is to move the wire through the beam and observe the induced current in the wire. The other way is to move the wire through the beam and observe the beam lost using a dipole and a spectrometer with a couple of beam position monitors.

The later method has been employed at SwissFEL. For this method to work, we demonstrated that the Swiss FEL injector test facility beam jitter was minimal and so was the vibration of the wire scanner.

While the wire is being moved through the beam, some particles interact with the wire and undergo a change in trajectory and energy. Since the beam has a well-known energy, the beam is bent with a dipole. But most of those particles that interacted with the beam do not bend with the beam and are lost. By observing the beam that is lost, one can measure transverse beam profile. Also by introducing a transverse deflection cavity (TDC), longitudinal bunch length information can be converted to a transverse beam profile. Using the TDC and wire scanner in the setup described, the longitudinal bunch length could also be measured.