Time resolved proton focus studies on a radial applied B-field diode

The focus of a 4.5 cm radius applied B-Field diode powered by the Proto I (1.5 MV, 500 kA, 25 ns) accelerator has been studied on a time resolve basis. The focus was observed with an 11 channel PIN diode-array pinhole camera system. This system observes protons which are Rutherford scattered from a planar gold target located at the center of the diode and oriented at 450 to the diode axis. The PIN array is configured in a cross geometry with linear arrays of PIN's observing the axial focus and 5 PIN's observing the horizontal focus. In this experiment a 280 segment of the beam is observed in the azimuthal direction together with the full 280 axial extent of the beam. This minimizes target geometry corrections. The 0.3 diameter pinhole is located 2.5 to 3.5 cm from the target and the 1 mm diameter PIN's at 15.6 cm from the target. This allows observing the beam profile at intervals of 0.7 to 1.3 mm. A sample of CR-39 with eleven holes to transmit portions of the beam was mounted in front of the PIN's to observe the time-integrated focus and allow checks on the absolute ? of protons detected. A 4 μm aluminum filter excluded visible light and UV from the PIN's. The gold was 5cm thick and mounted on 1.5μm mylar. The beam was observed after passing through the mylar and gold. An inverted target geometry allowed the variation of the target thickness with beam angle of incidence to partially cancel the variation of the Rutherford scatter cross section with angle of incidence