Nitrogen Helium Research Articles

Measurement of output characteristics of Tm:YAG laser at 25–300 K

In this paper, output characteristics of a laser diode end-pumped Tm:YAG laser in a wide temperature range were investigated. In this laser system, a Tm:YAG crystal was cooled in a cryostat with liquid helium or liquid nitrogen as coolant. At the temperature of 88K, a maximum output power of 4.68W is achieved when the incident pump power is 8.9W, and the optical–optical conversion efficiency is 52.6%, with a slope efficiency of 56.1%. The dependence of the output characteristics of Tm:YAG on temperature was experimentally studied in the temperature range of 25–300K.

Fast Sensitive Ultra-Low Power Micro Thermal Conductivity Gas Sensor

A miniature, ultra-low power, sensitive, microbridge-based thermal conductivity gas sensor has been developed. The batch fabrication of the sensors was realized by CMOS compatible processes and surface micromachining techniques. Doped polysilicon was used as the structural material of the suspended sensing element with critical dimension of 500 nm. To understand the design of the sensors, a model of the suspended element was simulated in COMSOL that couples electrical and thermal physics together and includes minimal simplifications. Modeling results coincide with experimental data in predicting resistance changes. The sensor was tested with nitrogen, carbon dioxide, helium and methane.An electronic circuit was developed to measure very fine changes in the signal output and to keep the signal to noise ratio such that ppm detection is possible, while exciting the sensor at minimal power levels. The sensor was able to detect ppm levels of helium, methane, or carbon dioxide in nitrogen at room temperature. The sensor can make a measurement in less than 2 ms consuming only 5 nJ or power per reading.The transient as well as steady state response was investigated as potential indicator of gas thermal capacity; as thermal conductivity and thermal capacity are independent properties of a gas, this new approach may enable MicroTCD sensors to make detections in gas mixtures by thermal analysis [1].[1]U.S. Patent 8,426,932 B2, April 23, 2013, Apparatus and Method for Microfabricated Multidimensional Sensors and Sensing Systems, Joseph R. Stetter.

Analysis of the anisotropic critical current behaviour of HTS coated conductors

In order to generate fields of more than 20 T using pure superconducting magnets, the implementation of HTS coated conductors (CCs) is an option. Amongst the characteristics of the REBCO is its intrinsic anisotropy which means its critical current, Ic, varies as a function of its orientation with respect to the external magnetic field, ϕ, as well as being dependent on external field, B, and temperature, T. For the design of the high field insert coils for the experimental magnet facility HOMER II, the behaviour of Ic at fields of about 24 T and at ϕ approximately 80 ° is required. Within our JUMBO facility it is possible to measure the U(I) behaviour of commercial CCs at liquid helium and liquid nitrogen temperatures. The free bore available is 100 mm at 4.2 K; the applied magnetic field can be varied up to 10 T, and ϕ can be set between 0 and 180 °. Measurements were carried out on commercially available CCs with emphasis on ϕ values near to 90 °. The critical current was determined by means of a power law function fitted to the resulting U(I) curves using specially written Matlab® programs. A number of different three dimensional functions were fitted to the measurement data and compared with each other.

Simulation and Fabrication of an Ultra-Low Power Miniature Microbridge Thermal Conductivity Gas Sensor

A miniature, ultra-low power, sensitive, microbridge-based thermal conductivity gas sensor has been developed. The batch fabrication of the sensors was realized by CMOS compatible processes and surface micromachining techniques. Doped polysilicon was used as the structural material of the bridge with critical dimension of 500 nm. A model of the microbridge was simulated in COMSOL that couples electrical and thermal physics together and includes minimal simplifications. Modeling results shows that the majority of heat is transferred via conduction through the gas gap under the bridge. Heat loss from constant voltage application was observed to be a function of the thermal conductivity of the gas ambient, resulting in different magnitude of resistance change. Maximum temperature occurs at the center of the bridge and could be as high as 800 K. Modeling results coincide with experimental data in predicting resistance changes. The sensor was tested with nitrogen, carbon dioxide, and helium. The response of the sensor to the mixtures of helium fractions in nitrogen was tested. We demonstrated that the sensitivity for helium in nitrogen was 0.34 mΩ/ppm when operated at 3.6 V supplies (at power level of 4.3 mW). With a Wheatstone bridge with ac excitation and a lock-in amplifier the sensor limit of detection was ∼700 ppm helium in nitrogen. The stability of the sensor was excellent achieving over 30 billion measurements before failure.

Recent operational experience of cryogenic system for sst-1

Prior to the SST-1 device integration, all the TF as well as some of the PF superconducting coils were tested in a dedicated cryostat in respective rated parameters. Many of new auxiliary cryo sub-systems were made functional as per the design parameters prior to SST-1 cooldown activities. Recently the cool-down attempts of SST-1 machine has been carried out for the engineering commissioning. SST-1 cryogenics system comprises of cryogenic helium and liquid nitrogen systems. IPR has an operational 1.3 kW at 4.5 K custom designed cryogenic helium refrigerator-liquefier (HRL). In order to minimize the static heat loads from ambient (300 K), double embossed type thermal shields system has been provided. The major new auxiliary cryo-systems include the current feeders system (CFS) and 80 K thermal shields system. These auxiliary cryo-systems have demonstrated their rated performance during the recent cool-down of SST-1. This paper will elaborate the recent experience of SST-1 cool-down results.

Liquid nitrogen distribution for pelletronlinacfacility, Mumbai

Low temperature facility of Tata Institute of Fundamental Research Mumbai provides liquid helium and liquid nitrogen along with the various other cryogenic support services to many facilities and laboratories of the institute. On the total annual liquid nitrogen consumptionover 3,00,000 liters, majority supply is utilized by the Pelletron LINAC Facility, for cooling the thermal shields of the quarter wave resonating cavities, distribution line of the cryostats, precooling of helium refrigerator and for the beam hall experiments. Liquid nitrogen is produced by STIRLIN-8 plant with a liquefaction rate of 110 liter per hour at an elevated pressure of 2barg. The vacuum jacketed and super-insulated liquid nitrogen transfer line of about 310 meters long interconnects plant and SC LINAC accelerator. The paper present the in depth details about the cryogen distribution, VJ piping and also the technical modifications and various automation carried out by us on the liquid nitrogen plant.

High purity multi-walled carbon nanotubes: Preparation, characterization and performance as filler materials in co-polyimide hollow fiber membranes

Functionalized MWCNTS were used as filler materials for the preparation of composite polymeric hollow fiber membranes based on the BTDA-TDI/MDI (P84) co-polyimide. As a first step high purity multi-walled carbon nanotubes (MWCNTs) were synthesized using a novel catalytic CVD (chemical vapor deposition) technique, which enables large-scale production at low cost, while maintaining high purity and exceptional material properties at the same time. Covalent modification of pristine MWCNTs was applied in order to optimize both their nanoscale morphology and their dispersion in organic solvents. The functionalization process introduced certain functional groups, namely phenol groups, on the external surface of the nanotubes. Both pristine and functionalized MWCNTs with phenol groups were characterized using a variety of techniques such as XRD, SEM, TGA and Raman spectroscopy. The functionalized nanotubes were found to result in a uniform dispersion in NMP solvent. The best dispersion was observed in the case of phenol-functionalized MWCNTs. The effect of the concentration of carbon nanotubes on the composite membranes was investigated by carrying out DSC, SEM and gas permeability experiments. The prepared composite membranes were crack free and they presented high permeability values and ideal helium–nitrogen selectivities. In addition, the gas permeance coefficients increased linearly with the MWCNT concentration suggesting an increase of the free volume of the polymer matrix.

Isobaric expansion based regenerative trilateral thermal cycle with helium hydrogen and nitrogen as working fluids

The work aims feasible structures of regenerative trilateral thermal cycles (RTTC). The RTTC differs from the conventional quadrilateral Carnot based thermal cycles (Carnot, Otto, Diesel, Rankine, Brayton, Stirling, Ericsson, and variants of these cycles) in that the conversion of heat to mechanical work is performed during an isobaric expansion process, in which thermal energy absorption and conversion to mechanical work is simultaneously performed, contrary to what happens in conventional quadrilateral based Carnot engines.An analysis of the RTTC is carried out and results compared with that of a Carnot cycle operating under the same ratio of temperatures. Into the range of operating temperatures high thermal efficiency is achieved for hydrogen, helium and nitrogen as optional working fluids. These results combined with a cost effective and structural simple and compact engine open the way towards a new generation of power conversion engines.

Enhanced data‐independent analysis of lipids using ion mobility‐TOFMSE to unravel quantitative and qualitative information in human plasma

Lipids are involved in various biochemical and signaling pathways, cell structure and function, and the pathophysiology of many diseases. We took advantage of ion mobility spectrometry (IMS) in conjunction with ultra-performance liquid chromatography (UPLC) and high-resolution mass spectrometry to gain quantitative and deeper qualitative structural insight within a single experiment. Human plasma lipid extracts were analyzed using an Acquity UPLC system coupled to a Synapt G2-HDMS mass spectrometer system. The ion mobility gas employed was helium for the helium cell (150 mL/min) and nitrogen (80 mL/min) for the T-wave drift tube. The wave height for the T-wave cell was ramped in a linear fashion between 5-40 V. The mass spectra were acquired in an electrospray positive ionization mode. We resolved chromatographically co-eluting lipids further by ion mobility tube drift time and then subjected them to low- and high-energy fragmentation without pre-selecting respective precursor species. The fragment ions produced in a high-energy mode were aligned with their precursor ions in a low-energy mode. By aligning intact molecular spectra and fragment spectra for these lipids at a given ion mobility drift time and chromatographic retention time, we were able to obtain much cleaner fragment ion spectra for structural elucidation. For quantitative analysis we obtained a dynamic linear range from 0.002 to 2 µg/mL with and without an additional dimension of IMS. The additional dimension of IMS allowed us to perform quantitative and qualitative analysis within a single experiment in a relatively high-throughput manner thus providing deeper structural insights into lipids of biological interest and resulting in an information-rich dataset.

A molecular dynamics analysis of homogeneous bubble nucleation with a noncondensable gas in cryogenic cavitation inception

In this paper, homogeneous bubble nucleation in liquid oxygen (as one of the cryogenic fluids) with a noncondensable gas of nitrogen or that of helium was investigated using molecular dynamics method employing a fitted Lennard-Jones potential. We evaluated the influence of nitrogen gas and helium gas on the SATuration line (SAT) and the spinodal line as the thermodynamic limit of stability (TLS), and on the kinetic limit of stability (KLS) defined from a bubble nucleation rate. As a result, it was obtained that the influence of the noncondensable gases on the SAT and the TLS was negligible at molar fraction less than 1% although helium gas had several times stronger action to decrease the KLS compared with nitrogen gas. On the other hand, it was also indicated that the actual influence of both noncondensable gases on the cavitation inception in liquid oxygen might be negligible at least at standard conditions where the fluid starts to flow around or less than the atmospheric pressure.

Comparative study of thermo-stimulated luminescence and electron emission of nitrogen nanoclusters and films

We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those detected from N2 films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates.

Tailoring of the interfacial properties of polymeric single fibre-reinforced epoxy composites by non-oxidative plasma treatments

The interfacial properties of epoxy composites reinforced with a single, plasma-treated fibre of either poly(p-phenyleneterephthalamide) (PPTA) or poly(p-phenylenebenzobisoxazole) (PBO) have been investigated with a focus on evaluating the effect of two non-oxidative (He and N2) microwave plasma treatments on interfacial adhesion properties. Tensile testing of single filaments revealed that their tensile strength does not diminish with the plasma treatments, despite the fact that their surface properties have been both physically and chemically modified. Interfacial characterisation by Raman spectroscopy indicated that the quality of adhesion was substantially enhanced following exposure of the fibres to microwave plasma treatment in either pure helium or pure nitrogen flows for just one minute. Such improvement was higher than that attained when O2 was used for blowing the plasma, under the same operational conditions. Moreover, no swelling effect was observed by AFM after exposure of the He or N2 plasma-treated fibres to ambient conditions for as much as 24h.

Real Time in Situ Chemical Characterization of Submicrometer Organic Particles Using Direct Analysis in Real Time-Mass Spectrometry

Direct analysis in real time mass spectrometry (DART-MS) is used to analyze the surface chemical composition of nanometer-sized organic aerosol particles in real time at atmospheric pressure. By introducing a stream of particles in between the DART ionization source and the atmospheric pressure inlet of the mass spectrometer, the aerosol is exposed to a thermal flow of helium or nitrogen gas containing some fraction of metastable helium atoms or nitrogen molecules. In this configuration, the molecular constituents of organic particles are desorbed, ionized, and detected with reduced molecular ion fragmentation, allowing for compositional identification. Aerosol particles detected include alkanes, alkenes, acids, esters, alcohols, aldehydes, and amino acids. The ion signal produced by DART-MS scales with the aerosol surface area rather than volume, suggesting that DART-MS is a viable technique to measure the chemical composition of the particle interface. For oleic acid, particle size measurements of the aerosol stream exiting the ionization region suggest that the probing depth depends upon the desorption temperature, and the probing depth is estimated to be on the order of 5 nm for a 185 nm diameter particle at a DART heater temperature of 500 °C with nitrogen as the DART gas. The reaction of ozone with submicrometer oleic acid particles is measured to demonstrate the ability of this technique to identify products and quantify reaction rates in a heterogeneous reaction.

Pore structure and permeability of hardened calcium aluminate cement pastes of low w/c ratio

The conversion of hydrated calcium aluminate cement (CAC) leads to an increase of its porosity which results in lower strength and higher permeability. Due to particular failures in the past, caused by conversion of CAC concretes, their use is sometimes considered to be not reliable. To evaluate the durability of converted CAC, pastes of two CACs were prepared at low w/c ratios (0.25 and 0.35), heated to 105 °C for 15 days and investigated by means of helium pycnometry, mercury porosimetry and nitrogen adsorption as well as by air permeability measurements. The results were compared to the pore structure properties and permeabilities of hardened Portland cement (OPC) pastes. At identical w/c, CAC pastes and OPC pastes exhibited similar open and total porosities. The threshold radii of the CAC pastes were about one order of magnitude greater while the hydraulic radii of their open pore system were smaller. The CAC pastes possessed somewhat smaller permeabilities than the OPC pastes and can thus be regarded as being as durable as the latter in this respect. From comparison of pore structure parameters and permeabilities it was furthermore concluded that significant pore structure damage occurs in the CAC pastes during mercury porosimetry measurements and therefore the measured threshold radii have to be considered as unreliable.

ESR studies of nitrogen atoms stabilized in aggregates of krypton–nitrogen nanoclusters immersed in superfluid helium

Impurity–helium condensates (IHCs) containing nitrogen and krypton atoms immersed in superfluid 4He have been studied via CW electron spin resonance (ESR). The IHCs are gel-like aggregates of nanoclusters composed of impurity species. It was found that the addition of krypton atoms to the nitrogen–helium gas mixture used for preparation of IHCs increases the efficiency of stabilization of nitrogen atoms. We have achieved high average (5 · 1019 cm−3) and local (2 · 1021 cm−3) concentrations of nitrogen atoms in krypton–nitrogen–helium condensates. The analysis of ESR lines shows that in krypton-nitrogen nanoclusters three different sites exist for stabilization of nitrogen atoms. Nitrogen atoms are stabilized in the krypton core of nanoclusters, in the nitrogen molecular layer that covers the Kr core, and on the surface of the nanoclusters. High concentrations of nitrogen atoms achieved in IHCs provide an important step in the search for magnetic ordering effects at low temperatures.

Mechanical tests of the conduit tubes of a conductor for the Toroidal winding of the International Thermonuclear Experimental Reactor (ITER)

Extremely stringent requirements, which include the impact toughness at the liquid-helium temperature, are imposed on the material of the conduit tubes for International Thermonuclear Experimental Reactor (ITER) Toroidal Field (TF) conductors. Modified 316LN-IG stainless steel is recommended as the conduit tube material. Steel 316LN-IG tube samples (both full-size samples and sub-sized samples) are subjected to mechanical tests at various stages of the process of conductor production: in the as-recieved state and after compacting, preliminary elongation by 2.5% at room temperature, and annealing at 650°C for 200 h in a pure helium gas atmosphere. The tests are carried out at room, liquid nitrogen, and liquid helium temperatures and satisfy the standards of the American Society of Mechanical Engineers (ASME and ASTM). The results of sub-size and full-size samples testing show that the last one gives more representative results to qualify the weld joints in liquid nitrogen. When the temperature decreases or the strain increases, the magnetization of the samples increases, especially in the weld area. Strain measurements with an extensometer demonstrate that the intracrystal processes occurring at the liquid-helium temperature can lead to a significant change in the local load, up to complete unloading in a deformation zone. Unusual local serrated deformation is observed with an extensometer installed in the weld area during tests in liquid helium: this deformation is the result of compressive jumps opposite to the loading direction.

Amplifying the VUV radiation of atomic nitrogen in helium, argon, krypton, and xenon

This paper discusses the spectral features of the amplification of narrow-band radiation of atomic nitrogen in the excimeric media of inert gases, including helium, argon, krypton, and xenon. Appreciable short-wavelength shifts (up to 0.026 nm) are detected in the spectra of the amplified radiation relative to the atomic emission lines of nitrogen that initiate this radiation. The observed shifts exceeded the instrumental resolution of the spectrometer that we used, were determined by the composition of the amplifying medium, and were independent of its excitation parameters under the experimental conditions. An explanation of the observed effect is proposed.

Thermal fluids along the East Anatolian Fault Zone (EAFZ): Geochemical features and relationships with the tectonic setting

A geochemical investigation has been carried out on the gas phase associated to thermal fluids discharged along three different segments of the East Anatolian Fault Zone (EAFZ, Turkey) running from Malatya to the Triple Junction area (Karlıova) where the East and North Anatolian Faults cross each other. CO2 is always the major gaseous component in both bubbling and dissolved gases with variable amounts of nitrogen helium and CH4. The isotopic ratios of helium range from 0.44 to 4.41Rac (values corrected for the atmospheric contamination) and cover a range spanning from crustal to magmatic-type values. The isotopic composition of carbon (CO2) shows values in the range from −5.6 to −0.2‰ vs PDB for the bubbling gases in contrast with the positive values (from 0.3 to 3.4‰ vs PDB) detected for the Total Dissolved Inorganic Carbon (TDIC). Coupling the information from the isotopic and chemical compositions, it results that mantle-derived fluids are driven to the surface by lithospheric structures. Despite the absence of outcropping volcanic products, the tectonic setting of the different segments plays a major role in releasing mantle-type fluids. The mantle derived fluids interact at shallower levels with circulating waters and originate geothermal systems which equilibration temperatures are estimated to be up to 360°C. The collected thermal fluids show different geochemical features consistent with processes occurring at two different levels: a deep level where mantle-originated fluids are taken either from the upper mantle or from intruded magma batches, and a shallower level, in the upper crust, where Gas Water Interactions (GWI), secondary CO2 production, and fractionation processes induced chemical and isotopic modifications of the pristine gas composition.

THE TIGHT DANIAN EKOFISK CHALK RESERVOIR FORMATION IN THE SOUTH ARNE FIELD, NORTH SEA: MINERALOGY AND POROSITY PROPERTIES

In the Danish North Sea, the chalk of the Danian Ekofisk Formation is largely pelagic and includes horizons of clay‐sized quartz and/or clay minerals. The upper part of the Ekofisk Formation (“Ekofisk Porous”) has reservoir potential, whereas the lower part of the formation (“Ekofisk Tight”) is of low permeability. The Ekofisk Formation was studied in wells Rigs‐1, Rigs‐2 and SA‐1 in the South Arne field in the Danish North Sea. Clay‐poor and clay‐rich horizons were sampled in order to evaluate the effect of the mineralogical composition on the reservoir properties of the Ekofisk Formation. The Ekofisk chalk samples were investigated by scanning electron and atomic force microscopy, by thermal analysis and for isotopic composition. Helium porosity, gas permeability and nitrogen adsorption (for specific surface area and fine porosity) were measured to characterize the chalk structure. Calcite was removed by titration and the residues investigated by X‐ray diffraction and atomic force microscopy. The clay layers consisting of nano‐quartz, clay minerals and carbonates have He‐porosity similar to that of the tight chalk matrix and have a large amount of fine pores (<200 Å diameter) which favour diffusion. This diffusion has dissolved calcite in the layers and has resulted in the formation of low‐porosity chalk due to recrystallization of calcite adjacent to the layers.The chalk matrix of the Ekofisk Formation contains a considerable amount of non‐calcite residue, of which the major part (∼2/3) is nano‐quartz. The nano‐quartz is assumed to have formed by sedimentation. For the samples investigated, there is no clear correlation between mineralogy (% residue, % nano‐quartz, % clay minerals) and porosity/permeability. However, samples with <20% residue have high He‐porosity and relatively high permeability; whereas samples with >25% residue have permeability <0.4 mD. The effect on He‐porosity is due to the content of both nano‐quartz and clay minerals, whereas the effect on permeability is mainly due to the content of nano‐quartz, because the nano‐size quartz particles pack between the coccoliths and thereby reduce the effective pore throat size. Consequently, for reservoir evaluation purposes, it is important to distinguish between the clay minerals and the nano‐quartz in the clay fraction. However, the high proportion of nano‐quartz in the Ekofisk Formation in general, and the relative high content in the Ekofisk Tight in particular, suggest that nano‐quartz may have a major impact on the reservoir properties.

Self-consistent two-dimensional modeling of cold atmospheric-pressure plasma jets/bullets

A computational modeling study of streamer propagation in a cold, atmospheric-pressure, helium jet in ambient air is presented. A self-consistent, multi-species, multi-temperature plasma model with detailed finite-rate chemistry and photoionization effects is used to provide fundamental insights into the structure and dynamics of the streamers. A parametric study of the streamer properties as a function of important discharge geometric and operating conditions is performed. The fluid mechanical mixing layer between the helium jet core and the ambient air is instrumental in guiding the propagation direction of the streamer and gives the plasma jet a visibly collimated appearance. The key chemical reactions which drive the streamer propagation are electron-impact ionization of helium neutral and nitrogen molecules. Photoionization plays a role in enhancing the propagation speed of the streamer, but is not necessary to sustain the streamer. The streamer yields a large radical concentration through chemical reactions in the streamer head and the body. The streamer propagation speed increases with reduced helium jet radius and increased helium–air mixing layer width. Impurities in the helium jet result in a significant increase in the discharge propagation speed within the tube through photoionization, but not after the streamer propagates into the open ambient region. It is also observed that thinner electrodes produce stronger electric-field concentrations that increase discharge propagation speeds within the tube but have a smaller influence on the discharge after it emerges out of the tube as a streamer.