Viscosity measurements of dilute solutions of helium 3 in superfluid helium 4 between 0.1 and 1.2 K
Viscosity measurements of dilute solutions of helium 3 in superfluid helium 4
Allen, G.↗
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Cavitation in flowing superfluid helium
Flowing superfluid helium cavitates much more readily than normal liquid helium, and there is a marked difference in the cavitation behavior of the two fluids as the lambda point is traversed. Examples of cavitation in a turbine meter and centrifugal pump are given, together with measurements of the cavitation strength of flowing superfluid helium. The unusual cavitation behavior of superfluid helium is attributed to its immense thermal conductivity .
Daney, D. E.↗
Coupling an Ensemble of Electrons on Superfluid Helium to a Superconducting Circuit
Not Available
Yang, Ge↗
Boiling and cavitation caused by transient heat transfer in superfluid helium-4
Superfluid helium-4 (He II) has been widely utilized as a coolant in various scientific and engineering applications due to its superior heat transfer capability. An important parameter required in the design of many He II based cooling systems is the peak heat flux $q^*$, which refers to the threshold heat flux above which boiling spontaneously occurs in He II. Past experimental and numerical studies showed that $q^*$ increases when the heating time $t_h$ is reduced, which leads to an intuitive expectation that very high $q^*$ may be achievable at sufficiently small $t_h$. Knowledge on how $q^*$ actually behaves at small $t_h$ is important for applications such as laser ablation in He II. Furthermore we present a numerical study on the evolution of the thermodynamic state of the He II in front of a planar heater by solving the He II two-fluid equations of motion. For an applied heat flux, we determine the heating time beyond which the He II near the heater transits to the vapor phase. As such, a curve correlating $q^*$ and $t_h$ can be obtained, which nicely reproduces some relevant experimental data. Surprisingly, we find that there exists a critical peak heat flux $q^*_c$, above which boiling occurs nearly instantaneously regardless of $t_h$. We reveal that the boiling in this regime is essentially cavitation caused by the combined effects of the first-sound and the second-sound waves in He II. Based on this physical picture, an analytical model for $q^*_c$ is developed, which reproduces the simulated $q^*_c$ values at various He II bath temperatures and hydrostatic head pressures. This work represents a major progress in our understanding of transient heat transfer in He II.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
PIP-II Cryogenic System and the evolution of Superfluid Helium Cryogenic Plant Specifications
The PIP-II cryogenic system consists of a Superfluid Helium Cryogenic Plant (SHCP) and a Cryogenic Distribution System (CDS) connecting the SHCP to the Superconducting (SC) Linac consisting of 25 cryomodules. The dynamic heat load of the SC cavities for continuous wave (CW) as well as pulsed mode of operation has been listed out. The static heat loads of the cavities along with the CDS have also been discussed. Simulation study has been carried out to compute the supercritical helium (SHe) flow requirements for each cryomodule. Comparison between the flow requirements of the cryomodules for the CW and pulsed modes of operation have also been made. From the total computed heat load and pressure drop values in the CDS, the basic specifications for the SHCP, required for cooling the SC Linac, have evolved.
43 PARTICLE ACCELERATORS↗
Molecular Tagging Velocimetry in Superfluid Helium-4: Progress, Issues, and Future Development
Helium-4 in the superfluid phase (He II) is a two-fluid system that exhibits fascinating quantum hydrodynamics with important scientific and engineering applications. However, the lack of high-precision flow measurement tools in He II has impeded the progress in understanding and utilizing its hydrodynamics. In recent years, there have been extensive efforts in developing quantitative flow visualization techniques applicable to He II. In particular, a powerful molecular tagging velocimetry (MTV) technique, based on tracking thin lines of He 2 * excimer molecules created via femtosecond laser-field ionization in helium, has been developed in our laboratory. This technique allows unambiguous measurement of the normal fluid velocity field in the two-fluid system. Nevertheless, there are two limitations to this technique: (1) only the velocity component perpendicular to the tracer line can be measured; and (2) there is an inherent error in determining the perpendicular velocity. In this paper, we discuss how these issues can be resolved by advancing the MTV technique. We also discuss two novel schemes for tagging and producing He 2 * tracers. Here, the first method allows the creation of a tagged He 2 * tracer line without the use of an expensive femtosecond laser. The second method enables full-space velocity field measurement through tracking small clouds of He 2 * molecules created via neutron- 3 He absorption reactions in He II.
47 OTHER INSTRUMENTATION↗
Imaging Quantum Vortices in Superfluid Helium Droplets
Free superfluid helium droplets constitute a versatile medium for a diverse range of experiments in physics and chemistry that extend from studies of the fundamental laws of superfluid motion to the synthesis of novel nanomaterials. In particular, the emergence of quantum vortices in rotating helium droplets is one of the most dramatic hallmarks of superfluidity and gives detailed access to the wave function describing the quantum liquid. This review provides an introduction to quantum vorticity in helium droplets, followed by a historical account of experiments on vortex visualization in bulk superfluid helium and a more detailed discussion of recent advances in the study of the rotational motion of isolated, nano- to micrometer-scale superfluid helium droplets. Ultrafast X-ray and extreme ultraviolet scattering techniques enabled by X-ray free-electron lasers and high-order harmonic generation in particular have facilitated the in situ detection of droplet shapes and the imaging of vortex structures inside individual, isolated droplets. Here, new applications of helium droplets ranging from studies of quantum phase separations to mechanisms of low-temperature aggregation are discussed.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Viscosity measurements of dilute solutions of helium-3 in superfluid helium-4 between 0.1 and 1.2 deg K.
Dilute solution of He 3 in He 4 near absolute zero measured for viscosity, showing temperature effect
Allen, G.↗
Superfluid Helium Experiment for Spacelab 2
The Superfluid Helium Experiment is designed to study the properties of superfluid helium in zero gravity and demonstrate the operation of a versatile reusable superfluid helium experiment facility. The superfluid experiment will consist of three subexperiments. The quantized surface wave experiment is intended to contribute to an understanding of the quantum nature of He-2 and the interactions between the normal and superfluid components. The bulk fluid dynamics experiment will determine the response of the bulk helium to known accelerations. The thermal dynamics experiment will attempt to obtain a detailed understanding of the spatial distribution of temperatures and the thermal frequency spectrum in the bulk liquid. In addition, the superfluid helium cryostat will be instrumented to measure its performance in several critical areas.
Mason, P.↗
Superfluid Helium Orbital Resupply Coupling
The resupply of superfluid helium to satellites and other space-based experiment packages can increase the useful longevity of these devices far beyond their present life expectancies which are many times determined by the supply of helium coolant. The transfer of superfluid helium to spacecraft in space will require a reusable coupling that functions at 1.8 Kelvin with little heat leak and low pressure drop. Moog has designed the Helium Resupply Coupling to meet these operational requirements. Initially, the coupling manual mode operation will be demonstrated on orbit by an EVA crew member during the Space Shuttle borne Superfluid Helium On-Orbit Transfer (SHOOT) experiment. The ultimate application will use robotic (automatic) coupling operation to which the present design readily adapts. The utilization of Moog's exclusive Rotary Shut-Off (RSO) technology in the development of the Superfluid Helium Resupply Coupling is described. The coupling not only performs the function of a flow control valve and disconnect but also provides adequate safety features for a shuttle launched man-rated payload. In addition, the coupling incorporates the necessary features to provide the high thermal isolation of the internal flow path from the external environment.
Ryder, M. O.↗
Does one need a 4.5 K screen in cryostats of superconducting accelerator devices operating in superfluid helium? lessons from the LHL
Superfluid helium is increasingly used as a coolant for superconducting devices in particle accelerators: the lower temperature enhances the performance of superconductors in high-field magnets and reduces BCS losses in RF acceleration cavities, while the excellent transport properties of superfluid helium can be put to work in efficient distributed cooling systems. The thermodynamic penalty of operating at lower temperature however requires careful management of the heat loads, achieved inter alia through proper design and construction of the cryostats. A recurrent question appears to be that of the need and practical feasibility of an additional screen cooled by normal helium at around 4.5 K surrounding the cold mass at about 2 K, in such cryostats equipped with a standard 80 K screen. We introduce the issue in terms of first principles applied to the configuration of the cryostats, discuss technical constraints and economical limitations, and illustrate the argumentation with examples taken from large projects confronted with this issue, i.e. CEBAF, SPL, ESS, LHC, TESLA, European X-FEL, ILC.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Superfluid helium orbital resupply - The status of the SHOOT flight experiment and preliminary user requirements
The Superfluid Helium On-Orbit Transfer (SHOOT) flight experiment is designed to demonstrate the components and techniques necessary to resupply superfluid helium to satellites or Space Station based facilities. A top level description as well as the development status of the critical components to be used in SHOOT are discussed. Some of these components include the thermomechanical pump, the fluid acquisition system, the normal helium and superfluid helium phase separators, Venturi flow meter, cryogenic valves, burst disks, and astronaut-compatible EVA coupler and transfer line. The requirements for the control electronics and software are given. A preliminary description of the requirements that must be met by a satellite requiring superfluid helium servicing is given. In particular, minimum and optimum plumbing arrangements are shown, transfer line flow impedance and heat input impacts are assessed, instrumentation is described, and performance parameters are considered.
Dipirro, Michael J.↗
Superfluid Helium Tanker (SFHT) study
Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997.
Eberhardt, Ralph N.↗
Onset phenomena in superfluid helium
Onset phenomena in superfluid helium have been studied by measuring the rotational decay constant of a levitated, superconducting niobium sphere coated with an unsaturated superfluid film. The novel features of onset that were observed are discussed. Previous observations of a two-layer-thick solid phase of helium underlying the film have been confirmed.
Wang, T. G.↗
Liquid acquisition devices for superfluid helium transfer
To transfer superfluid helium (He II) in the milli-g or micro-g environment in orbit, it is necessary to provide a reasonably steady supply of liquid to the inlet of the pump in the supply dewar. To accomplish this without providing an artificial gravity through acceleration requires a liquid acquisition device. Fluid swirl and electrostatic devices have been proposed to orientate the fluid. However, the simplest mechanisms appear to be the use of surface tension or the thermomechanical effect. This paper examines four concepts for providing He II to the inlet of a thermomechanical pump. The devices are a distributed thermomechanical pump, a distributed pump with a main thermomechanical pump, a screened channel system and a vane/sponge combination. Calculations on the efficiency of these types of liquid acquisition devices are made using laboratory data from tests involving small scale devices where applicable. These calculations show that the latter two types of liquid acquisition devices are the most efficient. Questions as to the probability of cavitation and the effect of the residual shuttle acceleration on their operation remain to be answered, however.
Dipirro, M. J.↗
Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets
Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Acquisition system testing with superfluid helium
Minus one-g outflow tests were conducted with superfluid helium in conjunction with a thermomechanical pump setup in order to study the use of capillary acquisition systems for NASA's Superfluid Helium On-Orbit Transfer (SHOOT) flight experiment. Results show that both fine mesh screen and porous sponge systems are capable of supplying superfluid helium to the thermomechanical pump inlet against a one-g head up to 4 cm, fulfilling the SHOOT requirements. Sponge results were found to be reproducible, while the screen results were not.
Anderson, John E.↗