Direct measurement of beam-induced fields in accelerating structures

We have developed a new method for measuring the electromagnetic fields (wake fields) induced in high-frequency accelerating devices by intense relativistic electron bunches. These fields are probed by a second collinear electron bunch which follows the primary bunch at a variable delay. Initial results for several iris-loaded rf structure geometries are presented. This technique is expected to be important for the study of new acceleration methods such as the plasma wake-field accelerator. Another possible application is the measurement of parasitic wakes in conventional accelerator components