Physics – Nuclear Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43a1660l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43A-1660
Physics
Nuclear Physics
[6015] Planetary Sciences: Comets And Small Bodies / Dust, [6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena
Scientific paper
Small meteoroids and dust particles in the Solar System routinely impact larger planetary bodies. Upon impact on an airless body such as Earth's moon or an asteroid, the impactor's kinetic energy is converted over a very short time into vaporization and ionization, resulting in a small, dense plasma. The impact of dust particles has implications for the generation of the plasma sheath and residual magnetic signatures on the moon. The formation of the lunar plasma sheath is attributed to energetic particle impacts - an unanswered question is whether impact-generated plasma could be a significant contributor. Through hypervelocity impact tests at a dust accelerator, we study impacts of dust particles impacting on different material surfaces in order to answer these questions. At the Max Planck Institute for Nuclear Physics, we conducted two experimental campaigns studying the impact-generated plasma and the associated EM emission in the optical and RF regimes. We used a 2 MV Van de Graaff generator to accelerate positively-charged iron dust particles to speeds of 1-50 km/s. The targets included a variety of metals that are electrically isolated, grounded, or biased to +1 kV or -1 kV. In future testing we plan to incorporate natural target materials including silicates to better represent lunar impacts. Unlike most tests at this type of facility, we did not use an accelerating grid to separate plasma species and direct them to a sensor; instead we allowed the plasma to expand freely before it encountered the sensor. Preliminary results show that the characteristics of the impact-generated plasma depend both on the material and electrical bias of the target. The average plasma expansion speed measured was 20.8 km/s, faster than the projectile speed. Impacts from higher-speed impacts (above 10 km/s) have shown evidence of oscillatory behavior (shown in the figure), which may be attributed to several mechanisms. These results shed light on the behavior of plasmas generated by hypervelocity dust impacts, and through further study will lead to insight on the lunar plasma and magnetic environment.
Bugiel S.
Close Sigrid
Lauben Dave
Lee Namkyung
Mocker Anna
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