Experimental Medical Physics

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Levitating Targets

Daniel, Peter, Tobias_web

Current Paul Trap team in front of the Phelix laser target area, from left to right: Daniel Haffa, Peter Hilz and Tobias Ostermayr

A multitude of theoretical publications in the past decade have demonstrated that targets with a limited mass and volume promise a more detailed understanding of the dynamics of the laser-plasma interaction itself as well as enhanced properties of the resultant particle beams and radiation. Levitating and thus fully isolated targets in the size-range of the laser focal spot size or even smaller (nano- to micrometer-scale) constitute the ideal case for this scenario. Even though isolated targets are promising in theory, they are challenging to provide in practice and thus widely unexplored. Already small supporting structures for the target have been shown to disturb the interaction significantly. With our Paul Trap we are now for the first time capable to access this regime experimentally. We levitate single truly isolated spherical targets of various materials in the size-range between 100 nm and 50 μm, thereby covering a range of 7 orders of magnitude in terms of particle numbers and mass. Our setup includes a set of sophisticated techniques to charge, trap, damp and monitor the targets in the trap and thereupon enables precise target positioning with an accuracy of better than 1 micrometer is enabled, even in UHV environments. Another advantage of the Paul Trap is its accessibility for diagnostics. With the Paul Trap it is possible to have optical as well as ion and electron diagnostics in any direction relative to the laser beam. Especially the ability to look at 90° is unique for solid targets and offers new possibilities to understand the laser-plasma interaction. The setup has been designed to be transportable and easily adoptable to the specific needs at different laser facilities. This enables us not only to cover a wide range of target parameters but also a wide range of laser parameters. Successful experiments have been carried out at the Max-Born-Institut at Berlin, the Phelix Laser at GSI Darmstadt and the Texas Petawatt Laser at the University of Texas at Austin. The results of those beam-times prove the huge potential of the Paul trap concept and mark the beginning of further efforts to explore mass limited targets. Related publications are in preparation. Near future beam-times are planned at Phelix and LEX Photonics. Besides that we have started efforts to provide isolated non-spherical targets with our system as well.


Experimental Setup of the Paul Trap Experiment at the Phelix Laser in GSI

The following video shows particles that are injected into the trapcenter and get charged. An active damping system extracts energy from the particle until it is at rest.