test of a two-dimensional optical trap for particle clouds (TPC)

abstract

Long-duration experiments with micro particles in dilute gases are planned for the ICAPS- facility on board the International Space Station ISS. It is, however, even under microgravity conditions, impossible to sustain a cloud of free-floating microscopic particles for an extended period of time, due to thermal diffusion and due to unavoidable external accelerations. To make sure the particles stay within the observational volume, a trap is required to counteract these forces and to provide the experimenters with longer research time for agglomeration and light-scattering experiments. For this kind of trap we are planning to use the photophoretic effect, i.e. the light-induced motion of particles in gases which is due to a temperature gradient across the particles resulting from differential absorption of light. Using absorbing particles, this effect leads to a net motion away from the light source (positive photophoresis), while transparent particles are moving towards the light source (negative photophoresis). For the design of an optical trap for an ensemble of particles embedded in a dilute gas, we plan to utilise the positive photophoretic motion of the particles. The light from a pair of opposing lamps is emitted isotropically from a square surface. The light-emitting surfaces are imaged such that their focal planes form ´light walls´. Thus, any homogeneous particle for which a positive photophoretic effect exists experiences a net force towards the centre of the trap. The relative light intensities of opposite light sources are adjusted such that the net inward photophoretic motion of the particles inside the ´light walls´ is always larger than the thermal diffusion and any residual motion of the dust grains. This kind of trap should also work in two-dimensions by adding a second pair of lamps perpendicular to the first.

• J. Steinbach, J. Blum, M. Krause, Development of an Optical Trap for Microparticle Clouds in Dilute Gases, Eur. Phys. J. E 15, 287-291, 2004.

• J. Blum, Dust Agglomeration, Advances in Physics 55, Nos. 7-8, 881-947, 2006.

• J. Blum, S. Bruns, D. Rademacher, A. Voss, B. Willenberg, M. Krause, Measurement of the translational and rotational Brownian motion of individual particles in a rarefied gas in the transition region between ballistic and diffusive motion, Phys. Rev. Lett. 97, 230601, 2006.

• D. Langkowski. J. Teiser, J. Blum, The Physics of Protoplanetesimal Dust Agglomerates II. Low Velocity Collision Properties, Astrophys. J. 675, 764-776, 2008.

• J. Blum, R. Schräpler, T. Poppe, G. Borst, Handling of Particulate Solids on the International Space Station, Granular Matter 10, 323-328, 2008.

• J. Blum, G. Wurm, The Growth Mechanisms of Macroscopic Bodies in Protoplanetary Disks, Annual Review of Astronomy and Astrophysics 46, 21-56, 2008.

• R. Weidling, C. Güttler, J. Blum, F. Brauer, The Physics of Protoplanetesimal Dust Agglomerates. III. Compaction in Multiple Collisions, Astrophys. J. 696, 2036-2043, 2009.

• P. Hofmeister, J. Blum, D. Heißelmann, The flow of granular matter under reduced-gravity conditions, in: Powders & Grains 2009: Proceedings of the 6th International Conference on Micromechanics of Granular Media, Hrsg.: M. Nakagawa & S. Luding, AIP Conference Proceedings Volume 1145, 71-74, 2009.

• D. Heißelmann, J. Blum, K. Wolling, Laboratory studies of ice-particle collisions in Satur′s dense rings, in: Powders & Grains 2009: Proceedings of the 6th International Conference on Micromechanics of Granular Media, Hrsg.: M. Nakagawa & S. Luding, AIP Conference Proceedings Volume 1145, 785-787, 2009.

• D. M. Salter, D. Heißelmann, G. Chaparro, G. van der Wolk, P. Reißaus, E. de Kuyper, P. Tuijn, R.W. Dawson, M. Hutcheon, G. Drinkwater, B. Stoll, K. Gebauer, F. J. Molster, H. Linnartz, G. Borst, H. J. Fraser, J. Blum, A Zero-Gravity Instrument to Study Low Velocity Collisions of Fragile Particles at Low Temperatures, Rev. Sci. Instrum. 80, 074501, 2009.

• Heißelmann, D., Blum, J., Fraser, H. J., Wolling, K., 2009. Microgravity experiments on the collisional behavior of Saturnian ring particles, Icarus 206, 424–430, 2010.

experiment year: 2004
number of drops: 15