ABSOLUTE VELOCITY MEASUREMENTS IN A RAREFIED GAS FLOW BY MEANS OF AN ION TIME-OF-FLIGHT TECHNIQUE.

A method developed to measure the absolute velocity in a rarefied gas flow is described. A short pulsed 20 keV electron beam is used to ionize the flow within a thin volume. A small tungsten wire collects the ions at a given distance downstream of the electron beam for time-of-flight measurements. Both the starting pulse of the electron beam and the amplified ion signal of the collector were recorded by a dual trace sampling oscilloscope. The time-of-flight was determined by varying the repetition frequency of the starting pulse in such a manner, that the (n plus 1)th starting pulse coincided with the peak value of the nth ion signal.