A New Wide Band Wall Current Monitor

Wall current monitors (WCM) are commonly used to observe the time profile of particle beams. In CTF3, a test facility for the CERN Linear Collider study CLIC, high current electron beams of 1.5 microseconds pulse length are bunched at 3 GHz and accelerated in a Linac working in fully loaded mode, for which a detailed knowledge of the time structure along the pulse is mandatory. The WCM design is based on an earlier version developed for CTF2, a previous phase of the test facility, in which the beam duration was only 16 ns. Due to the longer pulse width the low frequency cut-off must be lowered to 10 KHz while the high frequency cut-off must remain at 10 GHz. The new WCM therefore has two outputs: a direct one for which an increase of the inductance results in a 10 GHz to 250 kHz bandwidth while the second one, using an active integrator compensating the residual droop, provides a 10 kHz to 300 MHz bandwidth. The new WCM has been installed in CTF2 late 2002 in order to test its high frequency capabilities prior to its use in CTF3. Design considerations and first results are presented.