Liquid Nitrogen Reservoir Research Articles

High-efficiency, fifth-harmonic generation of a joule-level neodymium laser in a large-aperture ammonium dihydrogen phosphate crystal.

High-energy deep ultraviolet (UV) sources are required for high-density plasma diagnostics. The fifth-harmonic generation of large-aperture neodymium lasers in ammonium dihydrogen phosphate (ADP) can significantly increase UV energies due to the availability of large ADP crystals. Noncritical phase matching in ADP for (ω + 4ω) was achieved by cooling a 65 × 65-mm crystal in a two-chamber cryostat to 200 K. The crystal chamber used helium as the thermally conductive medium between the crystal and the crystal chamber, which was surrounded by a high-vacuum chamber with a liquid nitrogen reservoir. A temperature variation of 0.2 K across the crystal aperture was obtained. The total conversion efficiency from the fundamental to the fifth harmonic at 211 nm was 26%.

Experimental study on coal permeability and cracking characteristics under LN2 freeze-thaw cycles

Liquid nitrogen (LN2), a new and effective reservoir stimulating medium, has been widely used to boost coal bed methane (CBM) production. In this study, the damage mechanism and permeability evolution of the coal during LN2 freeze-thaw cycles are explored. The permeability tester was used to obtain the permeability of coal under different confining pressure and freeze-thaw cycles; the camera and scanning electron microscope (SEM) were respectively employed to observe cracks in the coal from the macroscopic and microscopic perspectives, and the ultrasonic wave was used to monitor the wave velocity of the coal. The experimental results showed that initial defects in the coal were firstly destroyed, forming the main fracture network; with the increase of cycles, the cracks were generated in coal matrix and gradually expanded and intersected with the main fracture network, then a complex fracture network was formed. The above results are consistent with the results of wave velocity. The wave velocity decreased about 40% after 10 cycles. Thus, the permeability of coal increased with the increase of cycles. Under the confining pressure of 9 MPa, the permeability reached 1.216 mD with an increase of 1200 times after five cycles. Besides, the coal sample with the small initial wave velocity had the most obvious improvement of permeability. The increase of confining pressure led to the decrease of permeability, and the sensitivity of permeability to confining pressure increased with the increase of cycles. Especially, under the low confining pressure, there was the biggest decrease of 3.44mD on the permeability for 1 MPa increment of confining pressure. During the freeze-thaw cycles, the temperature stress was the main factor of the damage on cracks and cementation structures, and LN2 gasification can cause the secondary propagation of cracks. Moreover, the uncoordinated deformation of matrix and mineral particles was the main factor promoting the initiation of cracks.

In-Situ Characterization of Lithium Native Passivation Layer in A High Vacuum Scanning Electron Microscope.

A technique to characterize the native passivation layer (NPL) on pure lithium metal foils in a scanning electron microscope (SEM) is described in this paper. Lithium is a very reactive metal, and consequently, observing and quantifying its properties in a SEM is often compromised by rapid oxidation. In this work, a pure lithium energy-dispersive x-ray spectrum is obtained for the first time in a high vacuum SEM using a cold stage/cold trap with liquid nitrogen reservoir outside the SEM chamber. A nanomanipulator (OmniProbe 400) inside the microscope combined with x-ray microanalysis and windowless energy dispersive spectrometer is used to fully characterize the NPL of lithium metal and some of its alloys by a mechanical removal procedure. The results show that the native films of pure lithium and its alloys are composed of a thin (25 nm) outer layer that is carbon-rich and an inner layer containing a significant amount of oxygen. Differences in thickness between laminated and extruded samples are observed and vary depending on the alloy composition.

μCHILL: a lightweight, modular system for handling crystalline samples at low temperatures under inert conditions

A procedure for preparing and mounting crystals under inert conditions is demonstrated, using a specialized apparatus (μCHILL) to provide a cold gas stream fed from a liquid nitrogen (LN2) reservoir or an open bath heat exchanger. A second, dry gas stream at room temperature enwraps the cold gas, protecting the sample preparation zone from ambient moisture. The technique is extremely flexible, requiring only a single operator, little practice and almost no preparation time. The device enables operation in a wide temperature range (at least 213 K to room temperature), providing temperature control and very stable conditions with no icing for extended time periods. The flexible, modular and low-cost design is based on three-dimensional-printed parts and readily available standard components, potentially making the device available to a wide range of users and applications not limited to single-crystal studies.

Megacam: A Wide-Field CCD Imager for the MMT and Magellan

Megacam is a large-format optical camera that can be operated at the f/5 Cassegrain foci of the MMT on Mount Hopkins, Arizona, and the Magellan Clay telescope at Las Campanas Observatory, Chile. Megacam’s focal plane is composed of 36 closely packed e2v CCD42-90 CCDs, each with 2048 × 4608 pixels, assembled in an 18,432 × 18,432 array. Two additional CCD42-90s are provided for autoguiding and focus control. The CCDs have 13.5 μm square pixels that subtend at the f/5 foci, yielding a 25′ × 25′ field-of-view. The camera system includes a focal plane shutter, two filter wheels, two liquid nitrogen reservoirs, a central chamber that holds the CCD mosaic array, and two electronics boxes. Megacam is equipped with a variety of broadband and narrowband filters. Software features include automatic calculation of twilight flat exposure times.

Pore Size Reduction in Directional Crystallization Processing of Porous Polymeric Membranes

Although various prep technologies of porous polymeric materials have evolved, the versatile control of pore morphology still remains as the most demanding subject. Herein, we applied the engineering principles of crystal habit by directional crystallization to the fabrication of porous PVDF (polyvinylidene fluoride) membranes. Pores of low tortuosity and relatively high porosity (80-90%) were successfully fabricated by the directional crystallization of DMSO (dimethyl sulfoxide) under a temperature gradient imposed by the controlled movement of a sample toward a liquid nitrogen reservoir followed by subsequent solvent removal. Pore size was controlled across a wide range by mixing DMSO with dioxane. Notably, nanoporous structures could be prepared at a 1:1 mixing ratio, in which the multi-step crystallization of solvents restricted by highly concentrated solutes enabled the preparation of nanomembranes. The homogeneous dispersion of TiO2 nanoparticles into PVDF, which are often used to improve hydrophilicity and antifouling performance, was easily achieved by this method. This novel prep technology based on the directional crystallization of solvent mixtures is a potentially viable solution to the limitations of current porous materials research.

Directional crystallization of dioxane in the presence of PVDF producing porous membranes

Melt crystallization methods offer high purity and energy-efficient purification for many chemicals. The solubility of solutes in a crystal phase is extremely low, but they can be engulfed by crystal phases. Therefore, the control of crystal morphology and size is critical in melt crystallization. In this work, we investigated the crystallization behavior of dioxane in the presence of a polymer solute under a controlled temperature gradient. By controlling the movement of a sample toward a liquid nitrogen reservoir, the nucleation and growth of crystals were regulated to produce uniformly distributed cylindrical crystals. Upon cooling, two crystallization steps were observed. While the first crystallization step mainly involved solidification of the bulk solution, the second crystallization at a lower temperature was accompanied by a further reduction in transparency and micro-cracking. This two-step crystallization behavior was used to make defect-free polymer structures with a unique cylindrical morphology of through-thickness pores, regardless of the dioxane removal method. Such understanding of directional crystallization will facilitate the future development of melt crystallization routes for dioxane and novel preparation methods for porous polymeric materials.

Ice particles trapped by temperature gradients at mbar pressure

In laboratory experiments we observe that ice particles (≤100 μm) entrained in a low pressure atmosphere (~1 mbar) get trapped by temperature gradients between three reservoirs at different temperature. Confining elements are a peltier element at 250 K (bottom), a liquid nitrogen reservoir at 77 K (top), and the surrounding vacuum chamber at 293 K. Particle levitation and trapping is modeled by an interplay of thermophoresis, photophoresis, and gravity. A number of ice particles are trapped simultaneously in close spatial distance to each other at least up to minutes and are accessible for further experiments.

Cryogenic thermal simulator for testing low temperature thermophotovoltaic cells

Thermophotovoltaic (TPV) devices convert infrared electromagnetic radiation into electricity. The authors’ research involves the use of strained-layer superlattices to enable TPV devices to operate at longer wavelengths than the current state of the art designs. To determine the performance of these devices, a novel test apparatus was designed and constructed. Here, the authors present a custom-built, cryogenic vacuum chamber for the testing and characterization of TPV samples. As TPV cells become sensitive to longer wavelength photons (lower source temperatures) in the infrared, the need to control the sample’s ambient temperature becomes critical for accurate testing; thus, the tester includes two copper heat shields cooled via conduction with two liquid nitrogen reservoirs. A calibrated blackbody source is used to illuminate a temperature controlled sample in high vacuum (∼10−6 Torr). The chamber temperature is extensively monitored and is designed to generate current-voltage (I-V) curves for TPV samples at different temperatures and input radiation in order to determine cell conversion efficiency. The system is evaluated based on the performance of its component systems.

Development of a 20 Tesla Superconducting Magnet

A 20 T superconducting magnet was designed and developed for studying physical properties. The cryostat is an open neck Dewar vessel with a liquid nitrogen reservoir and radiation shield. A lambda plate is built into the magnet support assembly. The operating temperature can be reduced from 4.2 K to 2.2 K by pumping liquid helium through a throttle valve under the lambda plate. The central magnetic field is 20 T at 2.5 K (18 T at 4.2 K). The field homogeneity is less than +/-0.1% in a 10 mm diameter sphere volume. The inner diameter of the cold clear bore is 52 mm. The outer diameter of the coil is 349 mm. The height of the coil, excluding the magnet protection circuit, is 560.5 mm. The coil is wound with the specially developed wires for use in high magnetic fields. In the case of Nb3Sn wires, a marked increase of the critical current density is achieved with higher tin content in the bronze matrix. The wires are more resistant to external stress with a rectangular cross section. We hung the magnet into the Dewar vessel and energized it. At first the magnet was operated at liquid helium temperature 4.2 K. As a result, the magnetic field rose to over 18 T with no training quench. The maximum magnetic field was 18.5 T. Then we energized the magnet after reducing the operating temperature to 2.2 K. Finally, the magnetic field rose to over 20 T with no quench. The result of this study shows that this magnet delivers a high magnetic field stably and easily

A Short-Period High-Field<tex>$rm Nb_3rm Sn$</tex>Undulator Study

With the intention to develop a technology suitable for a 2.4 m magnetic length, superconducting undulator with 0.8 T on the beam and a 15 mm period for the IXS beam line at the Advanced Photon Source at the Argonne National Lab, USA, a 0.6-m Nb3Sn undulator demonstration magnet is under development at the NHMFL. The intent is to investigate the applicability of Nb3Sn superconductor, in combination with soft magnetic materials, for a 15 mm period planar superconducting undulator. The demonstration requirements include a peak undulator magnetic field of at least 0.8 T and a vertical stay-clear aperture for the beam of at least 7 mm. In concept, the beam tube will be thermally isolated from the windings and operated at LN2 temperature to promote system reliability. Liquid helium and nitrogen reservoirs provide conduction cooling and the former also acts as a basic structural element. A brief description of a design is presented. A comparative study of fully and partly iron yokes and their effect on the required current density is performed. The results have implications for the yoke assembly procedure. Finally, a new yoke-winding geometry is presented

The set-up of a high temperature superconductor radio-frequency SQUID microscope formagnetic nanoparticle detection

SQUID (superconducting quantum interference device) microscopes are versatileinstruments for biosensing applications, in particular for magnetic nanoparticle detection inimmunoassay experiments. We are developing a SQUID microscope based on an HTS rfSQUID magnetometer sensor with a substrate resonator. For the cryogenic set-up, aconfiguration was realized in which the cryostat is continuously refilled and kept at aconstant liquid nitrogen level by an isolated tube connection to a large liquid nitrogenreservoir. The SQUID is mounted on top of a sapphire finger, connected to theinner vessel of the stainless steel cryostat. The vacuum gap between the coldSQUID and room temperature sample is adjusted by the precise approach of a50 µm thin sapphire window using a single fine thread wheel. We investigated possible sensing tipconfigurations and different sensor integration techniques in order to achieve anoptimized design. A new scheme of coupling the rf SQUID from its back to aSrTiO3 substrate resonator was adopted for the purpose of minimization of the sensor-to-sample spacing.By SQUID substrate thinning and washer size reduction, the optimum coupling conditionsfor back coupling were determined for different rf SQUID magnetometers prepared onLaAlO3 and SrTiO3 substrates. The SQUID microscope system is characterized with respect to its spatialresolution and its magnetic field noise. The SQUID microscope instrument will be used formagnetic nanoparticle marker detection.

Design and Development of a Pair of 10 kA HTS Current Leads for the NHMFL 45 Hybrid Magnet System

During a planned replacement of one of the three superconducting coils in the outsert magnet of the 45 T Hybrid, there is an opportunity to replace the existing pair of standard helium-vapor-cooled current leads with a pair of leads incorporating high-temperature superconductor (HTS) sections. A conceptual design for these leads has been completed, and various critical components have been modeled and tested. The design includes an integral liquid-nitrogen reservoir at the interface between resistive and HTS sections, automatic liquid-nitrogen level control, a resistive heat-exchanger section cooled by nitrogen vapor, an HTS section with integral stainless-steel shunt for protection, and an interface to the low-temperature superconductor bus. A detailed design is presently underway and fabrication tooling and techniques are being developed. We present design details, projected performance, results of development testing, and plans for manufacturing and acceptance testing.

Low-Cost Temperature Control from 160 K to Ambient Temperature Using Liquid Nitrogen Evaporation

A low-cost temperature controller that allows variation from 110 K to room temperature of liquid, gas, or solid samples is described. The desired stabilized temperature is obtained within a few minutes by controlling the current through an electrical resistor immersed in a liquid nitrogen reservoir. The stability of the temperature ranges from less than ± 0.5 K at temperatures higher than 230 K to ± 1.1 K at 160 K. The maximum consumption of liquid nitrogen for cooling a glass photochemical reactor was less than 0.60 liters per hour at temperatures lower than 160 K, about 0.4 liters per hour at 160 K to 190 K, and decreases considerably over 200 K. A linear dependence of the temperature with a flow of evaporated gas was found (240–285 K). This device can be used easily in experiments that need low temperature regulation, involving gas–surface interactions, adsorption–desorption processes, heterogeneous atmospheric chemistry, thermodynamics of gases, and so forth.

A cryostat for low-temperature spectroscopy of condensable species

A simple experimental setup for the production of cold samples for spectroscopy is described. The samples are deposited under vacuum on a cold metallic surface whose temperature is controlled between 80 and 323 K by varying the heat flow balance between a liquid nitrogen reservoir and a power transistor. Tests of temperature stability and thermal inertia, as well as a set of reflection–absorption infrared and thermal desorption spectra, are reported as a demonstration of the performance of the system.

Performance of a 1-MVA HTS demonstration transformer

We report on test results for a single phase, 60-Hz, 13.8 kV/6.9 kV, 1-MVA high temperature superconducting (HTS) transformer which was completed in February, 1998. This transformer models in many ways a full scale section of a 30-MVA HTS commercial transformer design. The transformer windings are cryocooled in the range of 25 K and are made with a low-cost, surface-coated BSCCO-2212 conductor. Heat leaks are reduced using a liquid nitrogen thermal ballast and reservoir. The use of high temperature superconductors can substantially reduce transformer losses, weight, size, noise and potential fire and environmental hazards. Designs promise stable operation through faults without thermal degradation, and at temperatures that allow efficient and reliable refrigeration.

Long Pulse Fusion Physics Experiments without Superconducting Electromagnets

Long pulse fusion physics experiments can be performed economically via resistive electromagnets designed for thermally steady-state operation. Possible fusion experiments using resistive electromagnets include long pulse ignition with DT fuel.1,2,3,4 Long pulse resistive electromagnets are alternatives to today's delicate and costly superconductors.5 At any rate, superconducting technology is now evolving independent of fusion, so near-term superconducting experience may not ultimately be useful.High magnetic field copper coils can be operated for long pulses if actively cooled by subcooled liquid nitrogen, thermally designed for steady state operation. (Optimum cooling parameters are characterized herein.) This cooling scheme uses the thermal mass of an external liquid nitrogen reservoir to absorb the long pulse resistive magnet heating. Pulse length is thus independent of device size and is easily extended. This scheme is most effective if the conductor material is OFHC copper, whose resistivity at liquid nitrogen temperature is small. Active LN2 cooling also allows slow TF ramp-up and avoids high resistance during current flattop; these factors reduce power system cost relative to short pulse adiabatic designs.

A flexible, self-contained germanium spectrometer for the in-situ measurement of gamma-ray emitting radionuclides in and around piping

In order to certify that process and drain lines which had been used for transporting radioactive materials, and their surrounding environments, are now free of residual contamination, it is both desirable and cost effective to make in situ measurements during the decontamination and decommissioning process. A 4.83-cm diameter modular proble consisting of a liquid nitrogen reservoir, a preamplifier, and a high-resolution germanium gamma-ray spectrometer with flexible connections between the modules has been developed for the measurement of gamma rays in and around piping. The assembly is sufficiently flexible to navigate through a “3-inch diameter p-trap.” The probe design and specifications are discussed. Results from an application are presented.

Ammonium Bisulfate/Water Equilibrium and Metastability Phase Diagrams

is monitored continuously using a capacitance manometer. The change in the particle’s composition as the temperature or relative humidity (RH) is varied is determined by measuring the mass-to-charge ratio (with an accuracy of1%). A vertically polarized HeNe laser is focused on the particle. The intensity of the scattered light is continuously monitored at a9 0 °angle from the incident laser, and the phase (solid or liquid) is determined from the Mie scattering. To assure uniform temperature, the electrodynamic trap and the interaction chamber are constructed of copper. The chamber is insulated with a vacuum shroud and is in contact with a liquid nitrogen reservoir via heat transfer straps. An automated feedback heating loop is used to control the temperature to better than 0.2 K. The temperature is monitored at two points, above and below the particle, with the difference kept to less than 0.3 K. The reported temperature is the average between the two points. The system can be used to perform experiments at constant temperature or to scan temperature at a prescribed rate. Both modes were utilized to obtain the data presented here. When the temperature was scanned, the water vapor pressure was maintained at equilibrium with ice, by coating the cell walls with ice. The entire pressure and temperature monitoring system was calibrated against the ice frost line. The results reported here represent observations of over20 particles.

Clouds of ammonia ice: Laboratory measurements of the single-scattering properties

This work presents scattering measurements and photographs of ammonia ice crystals grown at temperatures from 130 to 180 K. The prime candidate for the material making up the visible clouds of Jupiter and Saturn is ammonia ice. Spacecraft observations of these planets have constrained the single-scattering properties of the cloud particles. To further investigate the nature of these particles, ammonia ice crystals were grown at temperatures occuring at the relevant levels of the atmospheres of Jupiter and Saturn. The experimental apparatus used to make these measurements has a glass-walled cylindrical chamber which permits measurement of the scattered light over a wide range of scattering angles and a temperature control system which uses a liquid nitrogen reservoir combined with heaters. The chamber is illuminated by a tungsten lamp through a rapidly spinning filter/polarizer wheel which yields measurements of intensity and linear polarization in each of three colors. A photographic record of the crystals is obtained with a microscope objective, and six linear array detectors measure the scattered light. Representative scattering measurements and photographs are presented, showing a variety of phase functions and crystal shapes. The data cannot be reproduced by theoretical calculations for ammonia clouds composed purely of cubic, tetrahedral, or octahedral crystals. The data appear similar to microwave analog measurements of the scattering by a mix of particles shapes and also by fluffy particles. The ammonia measurements fall into two groups: one has wavelength-dependent polarization and for size parameters up to about seven the scattering properties can be fit by Mie theory. The second group has wavelength-independent phase functions, implying size parameters of 10 to 50, and has a characteristic signature of polarization varying from - 10% to +10%. The data can be used to rule out some models for Jupiter's and Saturn's atmospheres and to guide future modeling efforts. For Jupiter, models with a cloud of ammonia crystals of size parameter equal to about 5 (in the red) are suggested. For Saturn, a model is suggested that has a thin layer of small ammonia crystals (in the Mie range) over a thicker ammonia cloud with the wavelength-independent polarization that is characteristic of larger crystals.