Cut-away view of the ram wind sensor (RWS), showing the main functional elements.
Basic configuration of the differentially pumped beam expansion chamber used in the validation experiments. High pressures and temperatures within the nozzle lead to supersonic expansion of gas into the vacuum region. The instrument aperture lies on the beam axis, and the rotatable flag can be positioned to block the beam.
Examples of current measured as a function of retarding voltage. The signal of interest is the differential current obtained by subtracting the thermal flux current (beam blocked) from the net beam current (beam open).
(Color) Differential current (as defined in Fig. 3) vs retarding voltage for all test cases. The inset box shows the nozzle pressures and temperatures for each case.
Theoretical retarding potential analysis curves for a flowing gas with constant temperature (top) and constant velocity (bottom).
Example of a nonlinear fit to a typical differential curve using Eqs. (1)–(4). The nozzle temperature and pressure are given in the inset text, as is the velocity inferred from the fit to Eq. (1).
Variation of the velocity inferred from the fits to each of the differential curves shown in Figure 4. The spreads correspond to variations in the nozzle temperature at each pressure.
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