Demonstration of cavity field mapping by falling drops of liquid

Experimental mapping of the electric field of a cavity is usually through bead-pull measurements. These require quite long times to align the bead and are generally restricted to the beam axis. Here, the bead has been replaced by drops of liquid falling through the cavity. Together with efficient compression and noise reduction techniques, the method allows for fast and precise measurements. The launching position of the droplets is controlled by a motor driver, thus allowing for automated 3d-field mapping around the axis. Results from mapping a 36 MHz buncher cavity are presented.