Electron Emission from Tungsten under Proton Bombardment

The yield of electrons from clean polycrystalline tungsten under bombardment by protons at normal incidence has been measured as a function of proton energy in the range 50 to 225 keV. The maximum value of the yield is 1.65±{}0.03 electrons per proton at a proton energy of 125 keV. The tungsten surface was cleaned by flash heating a tungsten ribbon to 2400^∘{}K in a vacuum chamber in which the total pressure was about 2×{}10^-10 Torr. The yield was measured with the surface at room temperature, about two minutes after the surface was cleaned, while the time for a monolayer of residual gases to form on the surface was greater than two hours.