Poster prÃ¤sentiert anlÃ¤sslich der EGS2003 in Nizza, Frankreich:
We built a prototype of a sensor for the direct measurement of the interstellar gas. The prototype sensor includes energy and time-of-flight analysis of the ions generated on the conversion surface upon impinging of neutral particles and thus provides unambiguous mass determination. This combination allows the distinction between intrinsic background, sputtered ions and truly converted primary neutrals. Both the positive and the negative ion fraction generated on the conversion surface was analyzed and the resulting sensor performance compared. We investigated three different candidate conversion surfaces (CVD diamond, barium zirconate and magnesium oxide) for the ionisation of the interstellar neutral gas. A beam of neutral oxygen and neutral hydrogen in the energy range 20-300eV was used. This energy range is typical for interstellar gas flow as seen from a spacecraft in the inner eliosphere. For all three surfaces a substantial conversion was observed that extended to the lowest energies under investigation. The overall detection efficiencies are sufficient to collect typical interstellar H and O distributions with meaningful statistics within reasonable integration times (one to a few days).