Direct measurement of the energy spectrum of an intense proton beam

A time-resolved magnetic spectrograph was used to measure the energy spectrum of an intense (0.7 TW/cm2) proton beam. A thin gold foil placed at the focus of an ion-diode Rutherford-scattered protons by 90° into the spectrograph, reducing the beam intensity to a level suitable for magnetic analysis. The scattered protons were collimated and then deflected in a samarium-cobalt permanent magnet. The deflected protons were recorded simultaneously on CR-39 and eight p-i-n diodes. A Monte Carlo computer code was used to calculate the sensitivity and resolution of the spectrograph. Data taken on the Proto I accelerator shows a 150–250-keV-wide proton-energy spectrum at each instant in time.