An apparatus for studying electrical breakdown in liquid helium at 0.4 K and testing electrode materials for the neutron electric dipole moment experiment at the Spallation Neutron Source.

We have constructed an apparatus to study DC electrical breakdown in liquid helium at temperatures as low as 0.4 K and at pressures between the saturated vapor pressure and ∼600 Torr. The apparatus can house a set of electrodes that are 12 cm in diameter with a gap of 1-2 cm between them, and a potential up to ±50 kV can be applied to each electrode. Initial results demonstrated that it is possible to apply fields exceeding 100 kV/cm in a 1 cm gap between two electropolished stainless steel electrodes 12 cm in diameter for a wide range of pressures at 0.4 K. We also measured the current between two electrodes. Our initial results, I < 1 pA at 45 kV, correspond to a lower bound on the effective volume resistivity of liquid helium of ρV > 5 × 10(18) Ω cm. This lower bound is 5 times larger than the bound previously measured. We report the design, construction, and operational experience of the apparatus, as well as initial results.

Electrical breakdown in helium cells at low temperature.

Electrical breakdown of partially filled helium cells below 0.5 K is shown to be the result of Penning ionization of metastable triplet helium excimers bound to the surface of the liquid.

Magnetic levitation-based Martian and Lunar gravity simulator.

Missions to Mars will subject living specimens to a range of low gravity environments. Deleterious biological effects of prolonged exposure to Martian gravity (0.38 g), Lunar gravity (0.17 g), and microgravity are expected, but the mechanisms involved and potential for remedies are unknown. We are proposing the development of a facility that provides a simulated Martian and Lunar gravity environment for experiments on biological systems in a well controlled laboratory setting. The magnetic adjustable gravity simulator will employ intense, inhomogeneous magnetic fields to exert magnetic body forces on a specimen that oppose the body force of gravity. By adjusting the magnetic field, it is possible to continuously adjust the total body force acting on a specimen. The simulator system considered consists of a superconducting solenoid with a room temperature bore sufficiently large to accommodate small whole organisms, cell cultures, and gravity sensitive bio-molecular solutions. It will have good optical access so that the organisms can be viewed in situ. This facility will be valuable for experimental observations and public demonstrations of systems in simulated reduced gravity.

Coalescence of viscous liquid drops.

We report on studies of the early stage of coalescence of two liquid drops. The drops were high viscosity silicon oil immersed in a water-alcohol mixture of the same density in order to eliminate the effects of gravity. The viscosity was sufficiently large that measurements could be made under the conditions of Stokes flow. Measurements were made of the radius of the neck between the drops as a function of the time from the onset of coalescence, and the results compared with theoretical predictions.