Figure 1: Proton probing of EM pulse.

(a) Schematic representation of the setup for diagnosing the EM pulse propagation along a folded wire. A small bent was made in one of the wire segments to act as a fiducial. The corresponding proton radiographs obtained at three different times (as labelled on each image) are shown in b–d. In these images, the film darkness is proportional to the proton flux. The red arrows in the images indicate the direction of charge flow in the folded wire pattern. The red dotted lines are eye guides for the width of the proton deflected region. The scale bar (solid red line) shown in b refers to 1 mm in the plane of the folded wire pattern. (e) Temporal profile of the positive charge pulse travelling along the folded wire. The x axis of the graph corresponds to the relative probing time, t=t_charge−t_proton, where t_proton is the probing time of a given point on the folded wire by the protons reaching the Bragg peak in the given RCF layer, and t_charge is the time of arrival of the peak of the charge pulse at that point. The experimental uncertainty in time is determined by the transit time of protons through the electric field region and the energy resolution of the active layers of RCF (ref. 25). The uncertainty in the charge density is estimated from the uncertainty in measuring the width of the proton deflection from the RCF data. The red arrow in the graph indicates the direction of propagation of the pulse.