Bagnoud, V.

Blazevic, A.

Cihodariu-Ionita, B.

Helfrich, J.

Kjartansson, E. S.

Ortner, A.

Roth, M.

Sander, S.

Schaumann, G.

GSI Repository

Laser acceleration of small projectiles for hypervelocity impact experimentsE. S. Kjartansson∗2, A. Ortner†2, S. Sander2, J. Helfrich2, B. Cihodariu-Ionita1, G. Schaumann2,A. Blazevic1,3, V. Bagnoud1,3, and M. Roth21GSI, Darmstadt, Germany; 2Technical University Darmstadt, Germany; 3Helmholtz Institute Jena, GermanyA new experimental concept is being developed tomeasure the enhanced momentum transfer during hy-pervelocity impacts of small solid projectiles on solidtargets.Figure 1: Proposed hohlraum target concepts for acceler-ating metal plates (left) and later small particles (right) tohypervelocities with the nhelix laser.The magnitude of the enhanced momentum transfercaused by the ejection of material when a crater is formedon the target during hypervelocity (vrel≈10−15 km/s) im-pacts is not well known for the materials and scales we areinterested in, but it is believed to be at least tenfold [1, 2]compared to elastic collisions. We aim to measure the mo-mentum transfer of dust-size metal particles colliding onlarger metal targets with velocities in the aforementionedregion. The collection of this data is critical e.g. to de-termine the feasibility of ideas proposed by G. Ganguli et.al.[3] for the active removal of space debris in the lowerearth orbit. The experimental challenges of this project areboth the acceleration of such small projectiles to hyperve-locities and the accurate measurement of their velocities.We will use a laser pulse from the nhelix laser system(∼ 30 J energy over ∼ 7 ns @ 532 nm) to drive a plasmaexpansion from a plastic foil mounted at the front of ahohlraum target. The rapidly expanding plasma will beused to accelerate a secondary projectile target to hyperve-locities without melting it. At first we aim at acceleratingsmall metal plates as depicted on the left side in Fig. 1and to measure their velocity and momentum transfer ontoa ballistic pendulum. Ultimately, the goal will be to accel-erate spherical dust-size metal particles to hypervelocitiesand to gather extensive data on the momentum transfer fordifferent materials and parameters. The targets will be fab-ricated in our own target laboratory at the Technical Uni-versity of Darmstadt.To accurately measure the velocity of the projectiles, wehave set up a VISAR (Velocity Interferometer System forany Reflector) at the Z6 experimental area. The VISAR∗ e.s.kjartansson@gsi.de† a.ortner@gsi.deFigure 2: A simulation showing the temporal evolution (y-axis) of the mass density of a target consisting of a 270 µmplastic foil and a 16,5 µm aluminum metal plate, positioned300 µm behind the plastic. The laser hits the plastic foilfrom the left edge at t = 0.can measure velocities in the hypervelocity regime time-resolved on a sub-nanosecond scale with 1% accuracy. TheVISAR requires a laser with high temporal coherence forits measurements. For this purpose we have comissioneda custom Nd:YLF laser by Continuum and modified it tobetter suit our needs. Dichroic mirrors were installed intothe cavity to subdue the dominating 1047 nm lasing linein favour of the more exotic 1320 nm line and a 1320 nmdiode laser which acts as an injection seed for the mainresonator was incorporated into the system to provide therequired temporal coherence.Simulations with the HELIOS 1D hydrodynamic codehave been carried out (see Fig. 2) and are ongoing to helpchoose the initial values for important experimental param-eters such as laser energy, plastic foil thickness and thedistance between plastic foil and metal plate. Preliminaryresults indicate that plastic foils of thickness 50 - 100 µmcombined with a distance of 300 - 600µm between plasticfoil and metal plate is the optimal setup to reach velocitiesin the 10 - 20 km/s range without melting the metal plate.References[1] J. D. Walker and S. Chocron, Int. Journal of Impact Engineer-ing 38, A1-A7, 2011[2] W. M. Alexander and J. A. M. McDonnel, Adv. Space Rev.Vol.2, No.12, pp. 185-187, 1983[3] G. Ganguli et al., Aerospace Conf., 2012 IEEE, pp. 1-9,March 2012GSI SCIENTIFIC REPORT 2013 PNI-PP-18doi:10.15120/GR-2014-1-PNI-PP-18 199

Laser acceleration of small projectiles for hypervelocity impact experiments

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Laser acceleration of small projectiles for hypervelocity impact experiments

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