DESIGN, PERFORMANCE, AND CALCULATED ERROR OF A FARADAY CUP FOR ABSOLUTE BEAM CURRENT MEASUREMENTS OF 600-MeV PROTONS

摘要

A mobile self-contained Faraday cup system for beam current measurements of nominal 600-MeV protons has been designed, constructed, and used at the NASA Space Radiation Effects Laboratory. The cup is of reentrant design with a length of 106.7 cm and an outside diameter of 20.32 cm. The inner diameter is 15.24 cm and the base thickness is 30.48 cm. The pri¬mary absorber is commercially available lead hermetically sealed in a 0.32-cm-thick copper jacket.nSeveral possible systematic errors in using the cup are evaluated. The largest source of error arises from high-energy electrons which are ejected from the entrance window and enter the cup. All other errors are at least 1 order of magnitude lower. A total systematic error of -0.83 percent is calculated to be the decrease from the true current value.nFrom data obtained in calibrating helium-filled ion chambers with the Faraday cup, the mean energy required to produce one ion pair in helium is found to be 30.76 ±0.95 eV for nomi¬nal 600-MeV protons. This value agrees well, within experimental error, with reported values of 29.9 eV and 30.2 eV.