Magnetically driven granular gas in low gravity

Experimental investigation of granular gas systems in three dimensions desire the removal of the weight of constituent particles. In a sounding rocket experiment module, such condition is realized and maintained for 6 minutes, allowing 4 rounds of particle excitation and cooling. Varying magnetic force from 8 magnets surrounding the sample cell is adopted as the bulk-driving mechanism to enable a homogeneous spatial distribution of around 3000 particles. Soft ferromagnetic particles are chosen to minimize the long-range interactions between particles once the excitation finishes. The ensuing cooling behavior is thus mainly governed by energy-dissipative particle collisions and the kinetic theory of granular gases becomes comparable with the experimental results. From such comparisons, the prediction of non-Maxwellian velocity distribution is confirmed, while the Haff's cooling law, although qualitatively verified, quantitatively overestimates the cooling time scale significantly.