MEASUREMENT OF GAS DENSITY BY ELECTRON SCATTERING

Abstract
It is theoretically possible to infer the density of a gas from the rate at which particles are scattered out of a beam of subatomic particles which is passed through the gas. This technique offers the possibility of a probeless density measurement which is independent of the state of the gas. Previous research verified that this technique could be implemented using a gamma ray beam, but that the best spatial resolution and measuring time which could be achieved were inadequate to allow the technique to be applied to a low density test facility. In the research reported, the technique was applied using a 50, 000-v electron beam. It was found that excellent spatial resolution and measuring time could be achieved at densities as low as 6 x 10 to the -8th power gm/cc. Density profiles were measured in a low density wind tunnel with a nozzle exit diameter of 18 in. and an open jet test section.A spatial resolution of about 1 cm was achieved, and measurements required 10 sec per point. This measuring time can probably be reduced by several orders of magnitude if necessary. The densities measured were repeatable within 1 percent. Accuracy, spatial resolution, and measuring time are found to be interrelated. The constraint on the combination is discussed in detail. The design of equipment is discussed.

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