Two-dimensional Brownian motion of active particle on superfluid helium surface

Abstract We report an experimental study of the 2D dynamics of active particles driven by quantum vortices on the free surface of superfluid helium at T = 1.45 К. The particle motion at short times (< 25 ms) relates to anomalous diffusion mode typical for active particles, while for longer times it corresponds to normal diffusion mode. The values of the rotational and translational kinetic energies of the particle allow to determine for the first time the intensity of the particle-vortex interaction and the dissipation rate of the vortex bundle energy. Strong bonding between a particle and a vortex is explained by coupling of normal and superfluid components

Spectra, Line Intensities of the C1 ∑+g --> A1 ∑+u and c3 ∑+g --> a3 ∑+ uTransitions in Liquid Normal He, and Rotational Level Populations of the C1 ∑+ g and the c3 ∑+g Terms

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On the Efficiency of Infrared Filters in Optical Cryostats

8 pagesInternational audienceIn an optical cryostat, the sample temperature is limited by the 300 K ther- mal radiation transmitted through the observation windows. As discussed in this pa- per, the corresponding heat load should be brought much below the μW level by using suitable cold IR filters. However, there are situations where one wants to di- rectly check the absence of IR heating by running the same experiment with the cold observation windows either open or totally blocked. We describe a particular example which is the study of helium condensation in a silica aerogel. On this aim, we devel- oped a simple and compact magnetic system able to move metallic shutters inside our optical cryostat. This allows us to set an upper bound of 1 μW for the effect of 300 K thermal radiation on our sample. We discuss the relevance of this result to the operation of optical dilution refrigerators

Dust-Acoustic Nonlinear Waves in a Nanoparticle Fraction of Ultracold (2K) Multicomponent Dusty Plasma

The nonlinear dust-acoustic instability in the condensed submicron fraction of dust particles in the low-pressure glow discharge at ultra-low temperatures is experimentally and theoretically investigated. The main discharge parameters are estimated on the basisof the dust-acoustic wave analysis. In particular, the temperature and density of ions, as well as the Debye radius, are determined. It is shown that the ion temperature exceeds the temperature of the neutral gas. The drift characteristics of all plasma fractions are estimated. The reasons for the instability excitation are considered