The motion of solid hydrogen particles in He II thermal counterflow has been measured using the particle tracking velocimetry technique. The tracers can move with the velocity comparable to the velocity of the normal fluid. However, below some transition velocity, the particles can be trapped on individual vortex lines and towed by the vortex tangle in the direction of superfluid flow. Above this transition velocity, the Stokes drag with the normal fluid dislodges the trapped particles from vortex cores and such particles move in the same direction as the normal fluid, albeit with lower average velocity. We discuss the measurement of the transition velocity and the mechanism by which tracers may be trapped by or dislodged from quantized vortices.

The temperature dependence of the effective kinematic viscosity of turbulent $\mathrm{He}\mathrm{II}$, ${\nu }_{eff}\left(T\right)$, is deduced from second sound attenuation data using the late stage of decay of thermally induced counterflow $\mathrm{He}\mathrm{II}$ turbulence in two channels of square cross section. It is shown to qualitatively agree with the published data for ${\nu }_{eff}\left(T\right)$ calculated based on experiments on decaying-grid-generated $\mathrm{He}\mathrm{II}$ turbulence [Niemela et al., J. Low Temp. Phys. 138, 537 (2005)]. Corrections to these data due to the “sine squared” law that describes attenuation of the second sound wave propagating along an arbitrary direction with respect to the direction of the core of a quantized vortex in turbulent $\mathrm{He}\mathrm{II}$ are discussed and applied.

An experimental apparatus has been designed to analyze by visualization cryogenic flows of liquid ⁴He and consequently address unresolved problems of quantum turbulence. The newly implemented flow visualization setup is described and its specific features discussed. Thermal counterflow experiments have been performed and the motion of solid hydrogen and deuterium tracers studied by using the particle tracking velocimetry technique in order to probe the system capabilities. It is shown that the obtained results are consistent with the two-fluid model describing the behavior of superfluid ⁴He. A number of technical and fundamental issues, such as particles’ aggregation, role of rotating particles in counterflow and evidence of non-Gaussian distribution of tracers’ velocities, are also discussed. The apparatus appears to be well-suited to the task of analyzing cryogenic flows and potentially capable of obtaining new results stimulating further understanding of the underlying physics.

Fast solid target delivery and plasma-ion detection systems have been designed and developed to be used in high intensity laser-matter interaction experiments. We report on recent progress in the development and testing of automated systems to refresh solid targets at a high repetition rate during high peak power laser operation (>1 Hz), along with ion diagnostics and corresponding data collection and real-time analysis methods implemented for future use in a plasma-based ion acceleration beamline for multidisciplinary user applications.