Research Groups - Laboratory

Accelerator Laboratory

The Institute has extensive laboratory equipment to conduct experimental tasks in the field of micrometeoroid simulation and dust research. A plasmadynamic high-velocity accelerator (particle size: 20 Âµm up to approx. 100 Âµm; speeds of up to approx. 12 km/s), an electrothermal accelerator (projectiles up to 30 mg, speeds of up to 5.5 km/s) and an electromagnetic accelerator (particles with a mg range; speeds of <500 m/s) are available for particle acceleration. The capacitor banks required for operating the individual accelerators have a capacity of 352 ÂµF, 60 ÂµF and 10 ÂµF, and they provide the corresponding surge currents of up to 450 kA, 100 kA and 30 kA. The samples are bombarded in vacuum tanks with a vacuum of max. 10-5 mbar. The largest tank is equipped with a length of 85 cm and a diameter of 80 cm.

The measuring technology required for operation and control of the accelerator facilities comprises high-voltage sensing heads (up to 40 kV), high-current probes (up to 500 kA), pressure gauges (up to 6 kbar) and high-speed photography (single frame with exposure time of at least 10 ns).

A small scanning electron microscope, different optical microscopes, a contactless 3D surface analyser as well as a microhardness tester are available for the analysis of the bombarded samples. Sensitive samples can be handled on a clean-room workbench.

The experimental tasks are supported by a precision-engineering workshop, which has extensive metal working possibilities, as well as by an electronic workshop. We have specific skills for manufacturing vacuum and high-voltage components (e.g. high-current vacuum bushings, magnetic field probes, Rogowski coils).

In the following you will find some examples of projects to illustrate the laboratory work:

ICAPS - Technology Support with Dust Experiments under Microgravitation

The physical interactions of particles with each other, with gas, and light are important in a large number of scientific questions. Within the framework of the experiment proposal ICAPS six areas have been qualified central scientific issues, like aerosol physics, the simulation of regolith, or the agglomeration of dust particles. The latter scientific focus is critically important to understand how our solar system was formed. It is assumed that the planets formed out of a dense gas-dust slice around the new-born sun. When these so-called protoplanetesimals are very small (< 1 km), it is assumed that the main process of planetary growth is the dust agglomeration (collision of dust particles with subsequent adhesion). Under the management of Prof. JÃ¼rgen Blum (formerly Jena University; now Technical University Brunswick) experiments regarding the investigation of dust clouds and particle agglomerates are carried out. The simulation material is glass balls with a typical diameter of 1 micron. As these micro-particles are susceptible to clogging, deagglomeration mechanisms have to be developed, that also work under conditions of vacuum and weightlessness. The Institute of Astronautics developed such a deagglomeration and dust injection device on the basis of the turbo-molecular pump (very fast rotating blade wheels). The picture shows a dust agglomerate created with this device at the Astrophysical Institute of the Jena University.

The Institute of Astronautics also works on other tasks related to ICAPS. These tasks are the automated handling of microparticles, and the defined generation of macroscopic dust agglomerates. Dust cakes with a size of some ccm need to be handled and produced reproducibly especially for planned research on regolith. The goal is to produce loose structures that would break down on Earth because of their own weight.

HVL Development - Development of High Velocity Launchers

Plasmadynamic particle accelerator:
More than 25 years ago the Institute started building a high-velocity accelerator to simulate micrometeoroids and space debris. This accelerator has been improved, upgraded and supplemented with new components. The plasmadynamic accelerator installation can accelerate particles with a diameter of about 30 Âµm up to 100 Âµm until they reach a speed of a little bit more than 12 km/s. The particles that are used are glass balls, which are aerodynamically accelerated by means of a very fast plasma jet. The plasma jet is generated and accelerated by ionising injected He gas in a coaxial arrangement of electrodes (diameter: 33 mm; length: 160 mm). This is done with a surge current discharge of a capacitor bank (capacity: 352 ÂµF). A charging voltage of the capacitor bank of up to 16 kV leads to peak currents of up to 450 kA. At the end of the coaxial electrode arrangement the plasma is compressed in a self-excited conical coil (compressor coil). This plasma jet, which has been bundled, interacts with the quiescent microparticles and accelerates them. The picture above shows the arrangement of electrodes with the compression coil.
The accelerator is operated in a vacuum tank (diameter: 85 cm; length: 220 cm). This tank is connected with the impact chamber (diameter: 90 cm; length: 80 cm) by means of a tube. This chamber can be evacuated to up to 10-5 mbar. Typical fields of application of this accelerator are the simulation of micrometeoroids, basic research on high-velocity impacts, and the calibration of space experiments for dust research.

Electrothermal Particle Accelerator:
The accelerator is based on the following principle: Energy saved in a capacitor bank (60 ÂµF; 12 kV) is used in order to generate a high pressure plasma (up to 10 kbars) between two electrodes by means of a current discharge in a very narrow capillary (length: 20 to 40 mm). One of the two electrodes is formed as a barrel (diameter: 4 mm) with a projectile of the same calibre. The high plasma pressure in the capillary accelerates the projectile. Maximum speeds of up to 5.5 km/s were achieved in the vacuum for projectile masses of approx. 25 mg. These are extremely good figures for a single-stage accelerator. Although we have to use a new barrel and a new capillary for every experiment in order to achieve these speeds (because of component erosion caused by the plasma), the accelerator is characterised by a relatively easy use with very different applications (like demonstration accelerators for teaching; impact research in heat shields; DOD research in turbine blades; impact experiments in water ice).

Electromagnetic Accelerator:
The eddy-current accelerator is very easy to use in order to accelerate any dust particles to a speed of some hundred m/s. The strong change of current during the discharge of a capacitor bank by means of the accelerator coil generates a vigourously changing magnetic field in the coil. A thin aluminium slice is placed above the coil (e.g. d = 30 mm, t = 0,5 mm); a current is induced in this slice which produces a field opposed to the original magnetic field and thus leads to the acceleration of the aluminium slice. In the centre of the slice (sabot) is a centre punch to take up the projectile. Sabot and projectile are accelerated together; the sabot is kept back by a massive stopper, whereas the projectile continues moving in the direction of the experiment. If the projectiles are too heavy, the aluminium slice is destroyed under very high accelerations (typically 10 6 g) because of the high inertia force of the projectile. The shape of the sabot was optimised during the last two years, which led to a considerable efficiency increase of the accelerator. Steel balls with a diameter of 2.5 mm can be accelerated reliably to up to 280 m/s.
Typical applications for this accelerator are basic research with low impact speeds, research of dust adhesion, and the simulation of abrasive particles in jet engines.