By favoring the L-peak emission over the bremsstrahlung part, direct quasi-monochromatic soft x-ray emission has been obtained with a field emission (FE) x-ray source. The electron impact x-ray setup uses an arrayed cathode of carbon nanopearl FE tips as a stable cold electron source within a vacuum of 10(-6)-10(-7) Torr. The high brightness of the FE e-beam coupled with the array structure of the cold cathode allows a smoother control of the x-ray emission intensity. The wavelength of the x-ray source can be modified by the choice of target materials. Using Mo as the target material, the x-ray emission shows a peak centered at 2.45 keV with a monochromaticity between 75% and 55% and a FWHM in the range of 450 eV.

A prototype based on the Electron Beam Fluorescence (EBF) Technique is being developed for in- §ight measurements in the shock layer of a reentry demonstrator. The measurement objectives are rotational and vibrational temperatures of N 2 as well as the densities of N 2 and NO at di¨erent positions in and outside a shock layer. There is a renewal of interest in extending the technique to higher densities and to probe CO/CO 2 §ows (Mars atmosphere studies). The present paper gives a brief description of the status of the instrument with details on the optimization work performed to miniaturize the electron gun, the study of induced §uorescence in some gases and mixtures in laboratory vacuum chamber.

We present a new compact electron gun based on the secondary emission through ionic bombardment principle. The driving parameters to develop such a gun are to obtain a quite small electron gun for an in-flight instrument performing Electron Beam Fluorescence measurements (EBF) on board of a reentry vehicle in the upper atmosphere. These measurements are useful to characterize the gas flow around the vehicle in terms of gas chemical composition, temperatures and velocity of the flow which usually presents thermo-chemical non-equilibrium. Such an instrument can also be employed to characterize the upper atmosphere if placed on another carrier like a balloon. In ground facilities, it appears as a more practical tool to characterize flows in wind tunnel studies or as an alternative to complex electron guns in industrial processes requiring an electron beam. We describe in this paper the gun which has been developed as well as its different features which have been characterized in the laboratory.