Utilization of an Electron Beam for Density Measurements in Hypersonic Helium Flow

S methods have been investigated for making nondestructive measurements of various wind tunnel parameters. Herein is described a study to determine the feasibility of using an electron beam to measure the freestream static density of gaseous helium over a range of hypersonic flow conditions. Measurements were made for a range of stagnation pressures and temperatures which produced freestream number densities of 1.53xl0 to 1.25x IO molecules/m and static temperatures from 2 to 80 K. The results showed the collision quenching cross section to be 4.4 x 10 ~ cm at 1 K and to have a weak temperature dependence of T'. Knowing these values, the freestream number density can be determined quite accurately. These results are reported in more detail in Ref. 1.