Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43a1665m&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43A-1665
Physics
[2194] Interplanetary Physics / Instruments And Techniques, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena, [6213] Planetary Sciences: Solar System Objects / Dust
Scientific paper
Impact physics plays an important role in a variety of fields such as the investigation of matter at extreme pressures and temperature, shock waves in solid bodies or even planetology and cosmic dust research. Impact ionisation is a key part of impact physics, playing an increasingly important role at small scales, e.g. for the impact of micrometer sized dust particles impacting at velocities of some km/s. High velocity impacts of particles on a solid surface produce ions from the particle and the target. To relate the resulting measured values to processes going on during and shortly after the impact and to the hot dense shock state a theoretical model is necessary. The most successful description attempt is the shock wave ionisation model, describing the impact in sequent phases and relates the impact parameters (e.g. impact speed) to the properties of high pressure state. At first, the particle is compressed by a strong shock to high pressures and temperatures. Depending on the impact speed, the particle will be partially or even completely evaporated by the following unloading. For sufficiently high temperatures the atoms are strongly ionised. The plasma cloud emits electromagnetic radiation, measurable for instance as a light flash. This expansion is assumed to be isentropic and the gas quickly reaches local thermodynamic equilibrium. Thus, the hot dense state off the shocked matter can be related to the expanded ideal gas state due to the constant entropy. Finally, the gas expands to infinity in the partially dissociated state with some measurable residual ionisation. There is a wide variety of measurable values providing the opportunity to get a deeper understanding of the processes going on in the plasma cloud during its expansion and of its initial conditions depending on the parameters of the impact. The total charge yield and its temporal evolution are related to the partition of the specific internal energy gained by the impact. The thermodynamical and dynamical characteristics of the emerging plasma, such as the velocity distribution of the ions, and the ion appearance in the mass spectra can be analysed with a linear TOF mass spectrometer. The mass lines act as messengers from different points in the evolution of the plasma cloudlet: The abundance of ions is determined by the state at the end of the isentropic expansion. The shape and width of the same lines were determined earlier at the end of unloading. Together with a deeper theoretical understanding and other experimental approaches, such as the optical spectroscopy of the of the impact flash, this method can offer a powerful tool to investigate the hot compressed state and its dependence on the impact properties.
Close Sigrid
Collette A.
Hornung Klaus
Johnson Tobias L.
Kempf Sascha
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