The effects of incident electron current density and temperature on the total electron emission yield of polycrystalline CVD diamond

International audienceEffects of the temperature and the incident electron current density on the total electron emission yield (TEEY) of polycrystalline diamond deposited by chemical vapor deposition technique (CVD) were investigated at low electron beam fluence. It was found that the TEEY reversibly increases with the temperature and reversibly decreases with the current density. This behavior is explained on the basis of a dynamic completion between the holes accumulation which (positive space charge) that internally diminish the secondary electron (SE) emission and the thermally activated conductivity that tends to reduce the space charge formation

Development status of triple-junction solar cells optimized for low intensity low temperature applications

Latest results of 3G28 triple-junction solar cells manufactured by AZUR SPACE Solar Power GmbH under low intensity low temperature (LILT) conditions are reported. Excellent beginning of life (BOL) efficiencies in the order of 35% at 50W/m2 and -150°C have been realized on a large number of cells with standard and LILT optimized design. Furthermore, temperature dependent irradiation tests with 1 MeV electrons and 1 MeV protons have been performed on LILT optimized 3G28 solar cells. Initial results show some indications of temperature annealing but also other stabilization effects already present at LILT conditions

Performance analysis of AZUR 3G28 triple-junction solar cells optimized for operation in Jupiter environment

The results of electrical characterization of AZUR 3G28 solar cells and solar cell assemblies (SCAs) at low intensity low temperature (LILT) conditions are reported. In order to avoid flat spot effect appearance, solar cells were optimized for operation at LILT conditions by modification of the front grid metallization. Superior BOL efficiency of about 35% at 0.037AM0 and -150degC was demonstrated on a large number of SCAs. In-situ characterization after electron irradiation at -150degC has shown that the illumination and the temperature result in the improvement of the cell voltage and current. These recovery effects have to be taken into account for correct determination of degradation coefficients for solar cells for missions at low intensity low temperature conditions

Measurements of physical parameters characterizing ESDs on solar cell and correlation between spectral signature and discharge position

International audienceElectrostatic discharges on solar cells are possible cause of dramatic consequences such as secondary arcs responsible of definitive power losses. To cope with these significant implications, different approaches are followed such as design rules reducing voltage between adjacent cells, conductive layers or grouting to try to reduce ESDs triggering. However, ESDs on solar cells cannot be completely avoided and having a good knowledge of their characteristics is essential for prevention, prediction and modelling. In this paper, we describe how the plasma emitted during an electrostatic discharge on solar cell can be analyzed with dynamic tools such as triple probes and time-resolved optical spectroscopy. These techniques are used to obtain results on plasma density and electron temperature that can be compared with outputs from ESDs and flashover propagation models. While time-resolved optical spectroscopy is used on a single point (the point where optical fiber is focused on), triple probe is also used for spatial measurements. With this technique, electron density is measured at several distances from the discharge point providing both temporal and spatial information. In a second time, the optical signature measured by optical spectroscopy is correlated with SEM observations showing the existence of two kinds of triple points at the cell's edge. These two kinds of discharges have different optical signatures showing either elements from the active junction or from the substrate and rear electrode. These discharges are also distinguished by SEM observations and images of cell's edges confirm the previous results. These results show the importance of the silver back electrode and also of the eventual presence of covering glue on the position of the discharge. They provide information for models but let us also imagine possible mitigation methods

Preliminary flight data from the Materials Exposure and Degredation Experiment (MEDET)

The Materials Exposure and Degradation Experiment (MEDET) was recently launched to the ISS on Space Shuttle Flight IE, as part of the EuTEF payload on the external payload facility of ESA's Columbus module. The experiment will operate in-orbit for at least 1.5 years, and has the overall objectives of evaluating the effects of the complex low Earth orbit space environment on material properties, investigating material degradation due to contamination, characterising the local ISS environment and measuring the local micro-particle flux. This paper gives a brief overview of the experiment function and the material samples which are being exposed, before presenting some of the early flight data. In this phase of the mission, all of the instruments are operating successfully, and continuously acquiring data. The preliminary results mainly concern the environmental sensors, which are operating at relatively high acquisition rates (e.g. one reading every few seconds). It has been shown that the docking of the Space Shuttle to the ISS has a significant effect on the local pressure environment. The more complex degradation experiments are acquiring at much slower rates (e.g. one reading per day) and several more months of space exposure will be required before sufficient data is generated to reach conclusions about the behaviour of the materials. However, preliminary data is presented. ©2009 American Institute of Physic