Radial segregation and helical instabilities in metal halide HID lamps studied under microgravity conditions in the international space station

The plasma in metal halide HID lamps is characterised by strong acial and radial de-mixing and often by helial instrabilities. These issues compromise the application range and the energy efficacy and the lamps. both phenomena are strongly influenced by convection. Convection itself is driven by gravity. Therefore if one wants to study (radial) de-mixing thoroughly, one has to eliminate gravity. This was the rationale behind the 'ARGES'-experiment which was carried out in the International Space Station during the 'Delta'-Soyux--mission of the Dutch astronaut Andre Kuipers. The plasma was diagnosed with high-resolution optical emission spectrtoscopy and with real-time video imaging. As expected, the axial demixing disappeared under microgravity conditions and radial de-mixing became more prominent. The helical instrabilities no longer rotated.