Cryogenic Design Research Articles

Improvements in noble gas separation methodology: A nude cryogenic trap

A new noble gas cryogenic trap design employing polished stainless steel as the active trapping surface is described and tested. This trap offers significant advantages over the charcoal trap systems now commonly used for the preparation of noble gas samples for mass spectrometric analysis. Aliquots of Ne, Ar, Kr, and Xe are quantitatively trapped at less than 9 K and selectively released (≥99% at 20 K, 85 K, 110 K, 135 K, respectively). These release temperatures are significantly lower than obtained with conventional charcoal traps. The sorption‐desorption characteristics of the trap for the individual gases and neon‐argon mixtures are examined in detail as a function of trap temperature. The low release temperatures and improved separation for these noble gases will decrease processing times, reduce blanks and memory, and enhance the purity of noble gas sample preparation as compared to charcoal traps.

Design and performance of an HTS current comparator for charged-particle-beam measurements

Superconducting direct current comparators are well established for operation at liquid helium temperatures. We have begun investigations into HTS Cryogenic Current Comparator designs, which incorporate a flux concentrator and readout SQUID also made from HTS. This work aims to produce a system capable of high accuracy, non-invasive, measurements of an ion or electron beam current in the range /spl sim/10 nA to 1 mA. We outline a proposal for a precise determination of the faraday fundamental constant, using purely physical systems, and employing an HTS CCC for charged particle beam current measurement. In addition estimates of the potential current sensitivity are reported, based on measurement results of a prototype system, and proof-of-principle measurements of ion beam currents are described. The design and construction of a robust, compact cryogenic unit suitable for further, more realistic, field trials are discussed.

Cryocooled refrigeration for sensitive measuring instrumentation

We describe recent advances in the development of a general-purpose cryocooled dewar designed to eliminate the liquid helium boil-off, as well as provide a low mechanical vibration environment suitable for sensitive measuring instrumentation. Because of the high degree of thermal integration, this system is more efficient in power consumption and cooling requirements than helium liquefaction facilities that recover the helium gas at room temperature. In this report, we outline important elements of the dewar cryogenic design, as well as its ability to operate without degrading the ultimate sensitivity of measuring instrumentation such as a superconductive quantum interference device (SQUID), magnetometer.

Progress in MRI magnets

Since its appearance in the early 1980's, Magnetic Resonance Imaging (MRI) has taken its place as a major player in the noninvasive diagnosis of disease. It is the imaging modality of choice for detecting abnormalities of the brain, spine and musculoskeletal systems. It is on the verge of widespread application in diagnosis of cardiovascular disease and in image guided surgery. While permanent and resistive magnets are used for low field applications (open MRI) most systems use high field superconducting magnets making MRI the largest commercial application of superconductivity. The MRI magnet is the largest and most expensive component in the MRI system. Magnet configuration is the determining factor in MRI system architecture and directly connected to issues such as patient comfort, ease of siting, life cycle cost and functionality. All of these factors drive magnet requirements. Thus, MRI magnet requirements are determined by a combination of MRI system needs, technical requirements and market forces, plus the need for continuous reduction of both magnet-acquisition cost and total cost of ownership. Cost of ownership, in turn, includes siting, installation, operation and service. In this paper we trace the evolution of superconducting MRI magnet systems-taking note of the importance of advances in cryogenic technology and design practice-as they have responded to both market forces and competing magnet technologies.

Cryogenic target design considerations for the production of [ 18F]fluoride from enriched [ 18O]carbon dioxide

Four cryogenic target designs are described for the production of fluorine-18 in the chemical form of fluoride using oxygen-18-enriched carbon dioxide gas utilizing the 18O(p,n) 18F nuclear reaction. The targets are conical in shape and made of copper or silver and the carbon dioxide is frozen into the cone at liquid nitrogen temperatures. Three of the targets (2 copper and 1 silver) have four cooling fins extending radially and are different lengths, and one target has only a single heat sink at the rear of the cone. The targets with four cooling fins could be run with 17.4 MeV protons incident on the target material at a beam current of 25 μA with no detectable volatilization of the target material, although yields did decrease slightly when compared with lower current runs. The target with the single cooling block showed volatilization at about 8 μA. The two copper targets of different lengths did not show a difference in the volatilization of the target material at the beam current limit of our cyclotron (25 μA). The shorter target did maintain production with a lower amount of gas frozen into the target, while the longer target maintained production at higher beam currents. Targets of this type are compatible with low energy, high current accelerators because very thin windows may be used.

Efficient flash calculations for chemical process design — extension of the Boston–Britt “Inside–out” flash algorithm to extreme conditions and new flash types

The effective design of chemical processes requires robust and efficient algorithms for single-stage vapor–liquid flash calculations. These flash calculations represent a critical link between thermophysical properties and process and equipment design. The “inside–out” formulation proposed by Boston and Britt (1978)has proved to be a work-horse algorithm in the in-house software used at Air Products and in commercial process simulators such as AspenPlus TM. In this paper we describe enhancements that improve the efficiency of the Boston–Britt algorithm and extend it to new flash types. A new technique is proposed such that single-phase solutions (either in the vapor or liquid regions, or in the supercritical region) are detected reliably and efficiently. Further, the Boston–Britt algorithm is extended to new flash types, such as pressure-entropy and pressure-internal energy. Our in-house implementation of the proposed enhancements has been validated by application to a wide variety of chemical processes. In the present paper, the efficiency and power of the proposed enhancements are demonstrated by application to cryogenic design calculations.

Acoustic quality factor of 95%-density molybdenum and its application to high frequency cryogenic gravity-wave antennas

The amplitude-independent mechanical quality factor (reciprocal internal friction or Q) of 95%-density (pressed and sintered) polycrystalline molybdenum was measured in the temperature range 50 mK–300 K. Data were obtained from a torsional mode at about 1 kHz and a flexural mode at about 10 kHz of a mechanical resonator configured to minimize extraneous acoustic loss effects. Maximum Q values achieved were 1.0×10 7 at 4 K and 1.6×10 7 at 50 mK. High-resolution frequency measurements gave the temperature dependence of the dynamic shear modulus. The strong effects of various heat treatments on the quality factor are demonstrated. The origin of the acoustic absorption peak observed at about 1 K is discussed. Cryogenic gravity-wave antenna design parameters are calculated for a number of high- Q materials including the 95%-density Mo. The 95%-density Mo is shown to be a suitable choice of resonator material for the local array high frequency cryogenic gravity-wave detector.

A comparison of three-dimensional multimode hydrodynamic instability growth on various National Ignition Facility capsule designs with HYDRA simulations

Three similar cryogenic ignition capsule designs for the National Ignition Facility [J. Lindl, Phys. Plasmas 2, 3933 (1995)] are analyzed to determine surface roughness specifications required to mitigate the growth of hydrodynamic instabilities. These capsule utilize brominated plastic, polyimid and copper-doped beryllium ablator materials respectively. Direct three-dimensional numerical simulations with the HYDRA radiation hydrodynamic code [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)] examine the growth of multimode perturbations seeded by roughness on the outer ablator and inner ice surfaces. The simulations, which showed weakly nonlinear behavior for optimized surfaces, were carried through ignition and burn. A three-dimensional multimode perturbation achieves somewhat larger amplitudes in the nonlinear regime than a corresponding two-dimensional simulation of the same rms amplitude. The beryllium and polyimid capsules exhibit enhanced tolerance of roughness on both the ice and ablator surfaces.

Cryogenic design of a high- T c SQUID-based heart scanner cooled by small Stirling cryocoolers

A heart scanner based on high- T c SQUIDs is currently under development at the University of Twente. It is intended to be used in standard clinical environments without a magnetically shielded room. In order to make the application simple to use, the SQUIDs will be cooled by small cryocoolers, thus realizing a turnkey apparatus. The aimed field resolution is 50 fT RMS Hz − 1 2 in a measuring band of 0.1–100 Hz. The mechanical cooler interference is reduced by incorporating two coolers and operating them in counter phase. The magnetic cooler interference is reduced by positioning the coolers and the SQUIDs in a coplanar arrangement, and by separating the SQUIDs from the cold tips with a solid conducting thermal interface. A design is presented in which a temperature of 55 K is expected with a cool-down time of less than 1 h.

High Temperature Superconducting Space Experiment II (HTSSE II) cryogenic design

At 60 to 80 K large performance gains are possible from high temperature superconducting (HTS) microwave devices for communications applications. The High Temperature Superconducting Space Experiment II (HTSSE II) will demonstrate eight HTS experiments in space for up to 3 years of operation. HTSSE II is the first application of HTS technology to space. In addition to demonstrating HTS devices, an important secondary goal is to demonstrate the cryogenic technologies required for long life HTS space applications. HTSSE II utilizes a British Aerospace 80 K Stirling cycle cryocooler to refrigerate a central cryogenic bus of seven HTS experiments and has an additional stand-alone TRW HTS experiment cooled by a TRW Stirling cycle cryocooler. The HTSSE II flight unit has been assembled and has successfully passed vibration and thermal vacuum environmental tests. HTSSE II was developed on a fixed budget and a fast track schedule of 24 months and is due to launch in March 1997 on the ARGOS spacecraft. This paper presents the design and test results of the cryogenic subsystem, cryocooler integration and a cryogenic coaxial cable I/O assembly.

Cryogenic design of the liquid helium experiment Critical Dynamics in Microgravity

Although many well-controlled experiments have been conducted to measure the static properties of systems near criticality, few experiments have explored the transport properties in systems driven far away from equilibrium as a phase transition occurs. The cryogenic design of an experiment to study the dynamic aspect of critical phenomena is reported here. Measurements of the thermal gradient across the superfluid (He II)-normal fluid (He I) interface in helium under microgravity conditions will be performed as a heat flux holds the system away from equilibrium. New technologies are under development for this experiment, which is in the definition phase for a space shuttle flight.

Design of the superconducting end cap toroids for the ATLAS experiment at LHC

The ATLAS experiment proposed for LHC will use a toroidal magnet system to achieve high efficiency muon momentum resolution. The end cap toroids are designed to provide bending powers in the range 4-8 Tm over the rapidity span 1.5-2.8 in the important forward/backward regions. Each end cap toroid will have an outer diameter of approximately 11 m and an axial length of 5.6 m. This paper presents the magnetic, mechanical and cryogenic design of the end cap toroid magnet systems. Particular emphasis is placed on the interactive design issues imposed by the close proximity of the ATLAS barrel toroid. Proposals for the magnet fabrication and assembly are given.

Efficient cryogenic design, a system approach

With the increasing stress on consumable budgets, the goal of decreasing helium consumption of cryogenic system components has become a major issue. Although much progress has recently been made (improvements in helium Dewar technology and high Tc magnet leads are good examples) the potential to improve efficiency is greater when the entire cryogenic system is viewed as an interacting unit.

Superconducting toroid design for the ATLAS experiment at LHC

The ATLAS Experiment proposed for LHC will use toroidal magnet systems to achieve high muon momentum resolution. The proposal is based on an air-cored superconducting toroid magnet system consisting of a long barrel toroid with a pair of end cap toroids to provide high resolution at large rapidity. Each end cap toroid will have an outer diameter of approximately 11 m and an axial length of 5 m and will provide field integrals in the range 4-8 Tm over the rapidity span /spl eta/=1.5-2.8. This paper presents the magnetic, mechanical and cryogenic design of the end cap toroid magnet systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design study of a thin superconducting solenoid magnet for the SDC detector

A thin superconducting solenoid magnet has been designed for the SDC detector, which is one of major colliding particle detectors for the SSC high energy particle accelerator project. Based on recent R&D efforts to develop a high strength aluminum stabilized superconductor and a honeycomb/isogrid vacuum shell, the thin solenoid has been designed to provide a central magnetic field of 2 T in a tracking volume of 3.4 m phi *8.8 m, with a magnet wall transparency 1.2 Xo. The authors describe the conceptual design and the R&D work. To minimize material in the solenoid, technical guidelines incorporated into the solenoid design are outlined, and material savings are discussed. The cryostat and cryogenic design are considered. A R&D program is in progress to develop a prototype solenoid magnet with a full diameter and a quarter length to verify the SDC solenoid design. >

SQUID systems for non-destructive testing by AC field mapping

The authors describe a low-temperature liquid-helium superconducting quantum interference device (SQUID) system with high spatial resolution and a wider bandwidth than usual for an all-metal cryostat and which also provides access for a mechanism to balance the pick-up coils. They discuss the effects of these properties on AC field measurement and present experimental results from small slits which mimic growing fatigue cracks. Related work on high-temperature superconducting devices indicates that they will offer important advantages over low-temperature SQUIDs, particularly in terms of cryogenic design which has been so restrictive in low-temperature systems. The authors suggest that even relatively poor high-temperature-superconductor SQUID performance will be acceptable if these advantages can be exploited.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Space infrared telescope facility mission and cryogenic design

The Space Infrared Telescope Facility (SIRTF) is the last of the Great Observatory missions. It is presently scheduled for launch in 2001. The mission will study the infrared spectrum from 2 to 1200 μm with three imaging and spectral instruments. The observatory will have a 5 year lifetime and will be placed in a 100 000 km earth orbit. The cryogenic system is based on a 4000 I superfluid helium cryostat. The mission and the cryogenic system are described, and the cryogenic technology issues are discussed.

Comparison of heat transfer correlations for cryogenic engine thrustchamber design

A comparative study of the correlations available in the literature is made to arrive at an appropriate pair for estimating the coolant-side and hot-gas-side heat transfer coefficients in the thrust chamber of a cryogenic engine. Based on this, the thermal analysis of a supercritical liquid hydrogen cooled engine is carried out. Results are presented for axial variation of heat transfer coefficients and temperature distributions for coolant and exposed wall. Tubular as well as milled channel configurations are considered for coolant flow.

Cryogenics: its influence on the selection of the ASTROMAG superconducting magnet coils

ASTROMAG, a particle astrophysics experimental facility proposed for running alongside a space station, has a large superconducting magnet to analyse particles coming from deep space. Several types of magnets were investigated for use in the ASTROMAG central facility. The factors which influence the selection of the magnet coil design include: 1, the upper limit of particle momentum resolved (proportional to the integrated field) as a function of solid angle; 2, cryogenic design and its effect on cryogen lifetime for a given central facility mass; and 3, the overall cost of the magnet coils and cryostat. Four magnet types are analysed in this paper. These include a simple two-coil solenoid (the baseline design), two disc coils at the ends of the helium tank, a two-coil toroid and a thin solenoid plus bucking coil. The superfluid helium cryogenic system must have a cryogen lifetime approaching four years without refilling. (Mechanical coolers on the outer shield may be used to extend this lifetime.) The baseline magnet and cryostat mass (including the helium) is set at 2000 kg. Coils which have extended surfaces will require more helium to keep them cold. Flat surfaces require more mass in the outer vacuum vessel or a greater distance between the coils and the detectors (hence a lower integrated field). A balance must be struck between cryostat lifetime, total mass and the integrated field through the detectors. This balance tends to favour coils which are in the same vacuum vessel as the cryogen. The trade-offs are examined for the four cases given previously.

Experimental Techniques in Condensed Matter Physics at Low Temperatures

Cooling and cryogenic equipment (Dewars and magnets, cryostats for storage Dewars, dilution refrigerators, pumps and plumbing, magnetic cooling) cryogenic design aids (recipes, special materials, vibration isolation, electric and magnetic isolation, cooling the sample) experimental techniques and special devices (bridges, torsional oscillators, cryogenic electronics, nuclear magnetic resonance, ultrasound, high-frequency methods, pressure measurements, electromagnetic compatibility) thermometry (primary thermometry, magnetic thermometry, other secondary thermometers).