Pure Kr Research Articles

Argon admixture-driven enhanced ionization and performance of a 5 kW Hall thruster on krypton

Utilizing alternative propellants has been recognized as a strategy to reduce the total cost of propellants in electric propulsion-based missions. The aim of this study is to quantify the Hall effect thruster (HET) performance and operating characteristics using a Kr–Ar mixture to enable mission designers to evaluate the impact on mission and spacecraft design. We present the performance and plume plasma properties of the P5 5 kW-class HET operated with a Kr–Ar mixture with Ar volumetric flow rate fractions from 0 to 100%. The thruster is characterized at discharge power levels of 2.6 kW and 4.1 kW at constant discharge current and voltage over the range of Ar fractions. Despite higher ionization energy and lower mass of Ar, the thruster exhibited a similar level of thrust within 2% when comparing the pure Kr and 26%-Ar mixture cases. The derived ion energy distribution functions and analytical modeling suggest that the characteristic length for the ionization region is extended as the Ar fraction increases. The increased residence time of Kr at the extended ionization region and background energetic electrons from the ionized Ar neutrals are considered to cause this enhanced ionization of the injected Kr neutrals. This leads to a 6% higher Kr ion density at the 26%-Ar case even at the 16% less injected Kr neutral density than in the pure Kr case. The enhanced Kr ionization and generated Ar ions in the 26%-Ar case consequently led to a comparable thrust with that of the pure Kr case. The study indicates that mixing Ar with approximately 26% volumetrically with Kr can provide a similar or even higher thrust performance at the same discharge power. This will be particularly advantageous for various space missions that require high impulses by reducing the total cost of the propellant.

Xe Recovery from Nuclear Power Plants Off-Gas Streams: Molecular Simulations of Gas Permeation through DD3R Zeolite Membrane.

Recent experimental work has shown zeolite membrane-based separation as a promising potential technology for Kr/Xe gas mixtures due to its much lower energy requirements in comparison to cryogenic distillation, the conventional separation method for such mixtures. Such a separation is also economically rewarding because Xe is in high demand, as a valuable product for many applications/processes. In this work, we have used Molecular Dynamics (MD) simulations to study the effects of different conditions, i.e., temperature, pressure, and gas feed composition, on Kr/Xe separation performance via DD3R zeolite membranes. We provide a comprehensive study of the permeation of the different gas species, density profiles, and diffusion coefficients. Molecular simulations show that if the feed is changed from pure Kr/Xe to an equimolar mixture, the Kr/Xe separation factor increases, which agrees with experiments. In addition, when Ar is introduced as a sweep gas, the adsorption of both Kr and Xe increases, while the permeation of pure Kr increases. A similar behavior is observed with equimolar mixtures of Kr/Xe with Ar as the sweep gas. High-separation Kr/Xe selectivity is observed at 50 atm and 425 K but with low total permeation rates. Changing pressure and temperature are found to have profound effects on optimizing the separation selectivity and the permeation throughput.

Molecular dynamics study of flow of Ar-Kr mixture across a smooth walled nano channel with and without obstacles

Nanofluidics has emerged as an interesting field involving science and engineering, in which a fluid is made to flow across the structures having diameter in the nanometers range such as nanochannels. Nanochannels are channels having any one or all dimensions in the range of nanometers. As a flow in the reduced-size dimensional system, the nanochannel flow manifests a series of special properties and has gained a large attention. The understanding of different properties and dynamic behavior of fluid flows across a nanochannel has great impact on the study of fluid dynamics and various applications in the field of physics, chemistry, medicine and electronics. In the current study, we have studied fluid flow in smooth walled nanochannel, with and without obstacles introduced in the path of fluid flow. For both the cases we studied the velocity profiles of the system and analyzed the effect of varying channel width, varying force field, and varying densities on the velocity profile of the system. It is inferred that there is variation in the mean velocity of system in all cases. The mean velocity of the system increases with increase in the channel width, and applied force and decrease in density of mixture. We have taken pure Ar, pure Kr and Ar-Kr binary mixture as a fluid for the study. The velocity profile of the Ar-Kr mixture lies between that of pure Ar and pure Kr. For Ar system, the value of mean velocity is highest and for Kr system the value is lowest. There is a decrease in the mean velocity of the system with introduction of obstacles in the path of flow of the nanochannel. The value of viscosity of the system remains constant even with the introduction of obstacles in the path of the flow of system.[Copyright information to be updated in production process]

Comparison of NaX and NaA Zeolites as Absorbents in Purification Units of Pure Kr and Xe Production Plants

Comparison of NaX and NaA Zeolites as Absorbents in Purification Units of Pure Kr and Xe Production Plants

Повышение эффективности генерации многозарядных ионов высоких энергий при взаимодействии фемтосекундных релятивистских лазерных импульсов со смешанными кластерами KrXe

A new approach is proposed to the production of high-energy ions from a cluster jet irradiated with relativistic (5×10^18 W/cm2) femtosecond laser pulses, based on the formation of mixed clusters with an Xe core surrounded by a Kr shell. The appearance of distinguished charge states of accelerated ions was registered: instead of low-charge Kr2+, Kr3+, Kr4+, Kr5+ for pure Kr clusters, there are three components Kr8+, Kr14+, Kr20+ for mixed KrXe clusters. The energy range of detected ions expands significantly: from 1–6 MeV for Kr clusters to 2–16 MeV for KrXe clusters.

Development of a fully analytical equation of state using ab initio interaction potentials. Application to pure simple fluids: Noble gases Ne, Ar, Kr, and Xe

In this work, we have extended the first-order mean spherical approximation (FMSA) equation of state (EOS) of Tang and Lu [J. Chem. Phys., 99, 9828 (1993)] in order to predict accurately fluid phase diagrams using ab initio potentials. At this level of development, we restricted to simple spherical compounds.The original equation based on hard-core two-Yukawa (HC2Y) was improved by the following:•Adding a new approximate simple correction to include higher orders in the development of Tang and Lu to get an analytical model closer to the full MSA.•Including a term to a better account for the long-range behavior of two-body potentials.•Adding a three-body interaction term (1st order perturbation) based on Axilrod-Teller potential.A general recommendation for setting the hard-sphere diameter value was also given.The predictive capability of the EOS was tested in a systematic manner. First, we checked that various simple theoretical potential (Mie n-6 and Exp n-6) phase diagrams are well reproduced. Second, the EOS was used for predicting fluid phase diagrams of the pure noble gases fluid series Ne, Ar, Kr, and Xe using realistic (i.e. derived from ab initio) two-body and three-body interaction potentials. The model is in good agreement with the experimental phase diagrams.As a conclusion, the simple statistical-mechanics-based fully analytical EOS developed in this work predicts accurately fluid phase diagrams of simple spherical compounds using ab initio potentials. No adjustable parameter was used. This EOS constitutes a strong basis for future development of a predictive model based on ab initio potentials and applicable to more complex compounds.

Phase equilibrium modeling for confined fluids in nanopores using an association equation of state

The conventional cubic‒plus‒association equation of state (CPA EoS) is extended to describe the phase behavior of non‒associating and associating fluids in nanopores. To consider the effects of molecule‒wall interaction, a new pressure term was introduced into the CPA EoS. The modified Laplace equation was used to describe the capillary condensation in confined space. A thermodynamic model, i.e., mCPA/Laplace, based on modified CPA EoS and Laplace equation was presented. Furthermore, while correlations among the tensile strength, fluid critical point, and liquid spinodal point were discussed, the negative pressure for the mCPA/Laplace and mSRK models was studied. The calculations of the mCPA/Laplace model for pure O2, Ar, N2, Kr, CO2, C2H6, C3H8, n‒C4H10, n‒C5H12, n‒C6H14, n‒C7H16 and certain binary mixtures agreed with experimental data. Using the parameter database from the experimental data, this promising study can be extended to both shale oil and shale gas.

A study on 85Kr measurement with an internal gas proportional counter

A measurement method of 85Kr using an internal gas proportional counter (IGPC) is presented in this study. The operation conditions of the IGPC were determined and optimized, including the operating voltage, pressure, sample volume, interference from other gas components such as nitrogen or air, and mitigation of the memory effect. The IGPC was calibrated using certified standards, and the detection efficiency was approximately 58% for typical samples. A lower limit of detection of approximately 0.11 MBq/m3(Kr) was achieved after counting for 5 h with 1 mL pure Kr, corresponding to the atmospheric activity concentration of 0.18 Bq/m3 (air). It was shown that the IGPC could be used effectively for measuring 85Kr.

Study of pure and mixed clustered noble gas puffs irradiated with a high intensity (7 × 1019 W/cm2) sub-ps laser beam and achievement of a strong X-ray flash in a laser-generated debris-free X-ray source

AbstractWe present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

THCOBRA X-ray imaging detector operating in pure Kr

MicroPattern Gaseous Detectors (MPGD) have been explored for X-ray imaging, namely for photon counting imaging which allows the improvement of image quality and the collection of more information than the conventional commercial systems. A 2D-THCOBRA based detector was developed, studied and used to acquire X-ray transmission images. The 2D-THCOBRA structure used has an active area of 2.8 × 2.8 cm2 and allows obtaining the position and energy information of each single photon that interacts with the detector. It is filled with pure Kr at 1 bar operating in a sealed mode. Within this work the performance of the detector is evaluated in terms of charge gain, count rate, time stability, energy and spatial resolutions. The detector presents a charge gain of 2 × 104 and an energy resolution of 23% for 5.9 keV, showing gain stability along time for a count rate of about 1 × 105 Hz/mm2. It presents a spatial resolution of 600 μm (σ = 255 μm) and 500 μm (σ = 213 μm) for x and y directions, respectively, and, considering energy bins about 650 μm (σ = 277 μm) for approximately 16.5 keV. X-ray transmission images of some samples presented here show good prospects for X-ray imaging applications.

Numerical simulations of gas mixing effect in electron cyclotron resonance ion sources

The particle-in-cell MCC code NAM-ECRIS is used to simulate the ECRIS plasma sustained in a mixture of Kr with O2, N2, Ar, Ne and He. The model assumes that ions are electrostatically confined in ECR zone by a dip in the plasma potential. Gain in the extracted krypton ion currents is seen for the highest charge states; the gain is maximized when oxygen is used as the mixing gas. A special feature of oxygen is that most of singly charged oxygen ions are produced after dissociative ionization of oxygen molecules with the large kinetic energy release of around 5 eV per ion. Increased loss rate of energetic lowly charged ions of the mixing element requires building up of the retarding potential barrier close to ECR surface to equilibrate electron and ion losses out of the plasma. In the mixed plasmas, the barrier value is large (~1 V) compared to the pure Kr plasma (~0.01 V), with the longer confinement times of krypton ions and with the much higher ion temperatures.

Theoretical and experimental investigation of Electron Transfer Mediated Decay in ArKr clusters

We investigate the electronic decay of an Ar 3s-1 vacancy in medium sized ArKr clusters. The only energetically accessible, radiationless decay mechanism is Electron Transfer Mediated Decay Three (ETMD3). Here, the argon vacancy is filled by an electron from one krypton atom, and the excess energy is transferred to a second krypton atom which consequently emits an electron. For the theoretical calculation of ETMD3 spectra, in a bottom-up approach, we study the dependence of the decay width on the geometry of elementary sets of three atoms, from which any cluster can be composed. We simulate the ETMD3 spectra of medium sized ArKr clusters and compare the resulting spectra to experimental ETMD electron spectra presented earlier (Förstel et al, 2011) and in this work. We show that ETMD3 is the dominating relaxation mechanism for the cases studied here. Experimental secondary electron spectra from ArKr clusters are compared to pure Ar and pure Kr clusters.

Recent developments on field gas extraction and sample preparation methods for radiokrypton dating of groundwater

Summary Current and foreseen population growths will lead to an increased demand in freshwater, large quantities of which is stored as groundwater. The ventilation age is crucial to the assessment of groundwater resources, complementing the hydrological model approach based on hydrogeological parameters. Ultra-trace radioactive isotopes of Kr ( 81 Kr and 85 Kr) possess the ideal physical and chemical properties for groundwater dating. The recent advent of atom trap trace analyses (ATTA) has enabled determination of ultra-trace noble gas radioisotope abundances using 5–10 μ L of pure Kr. Anticipated developments will enable ATTA to analyze radiokrypton isotope abundances at high sample throughput, which necessitates simple and efficient sample preparation techniques that are adaptable to various sample chemistries. Recent developments of field gas extraction devices and simple and rapid Kr separation method at the University of Chicago are presented herein. Two field gas extraction devices optimized for different sampling conditions were recently designed and constructed, aiming at operational simplicity and portability. A newly developed Kr purification system enriches Kr by flowing a sample gas through a moderately cooled (138 K) activated charcoal column, followed by a gentle fractionating desorption. This simple process uses a single adsorbent and separates 99% of the bulk atmospheric gases from Kr without significant loss. The subsequent two stages of gas chromatographic separation and a hot Ti sponge getter further purify the Kr-enriched gas. Abundant CH4 necessitates multiple passages through one of the gas chromatographic separation columns. The presented Kr separation system has a demonstrated capability of extracting Kr with > 90% yield and 99% purity within 75 min from 1.2 to 26.8 L STP of atmospheric air with various concentrations of CH4. The apparatuses have successfully been deployed for sampling in the field and purification of groundwater samples.

Unusual morphology of equimolar Ar–Kr alloys

The transmission high electron energy diffraction (THEED) technique was employed for studying the structure of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase separation. Deposition of preliminarily cooled gas mixtures was performed onto substrates cooled to 6 or 20 K. All diffraction patterns contained several sets of reflections against an appreciable background. Analysis of the data obtained during a warm-up from 6 to 33 K (at which the major part of argon was removed due to sublimation) as well as of the diffraction pattern from the “sandwich” (two successively deposited film of pure Ar and Kr) provided reliable arguments for the following conclusions. Actually, we have documented for the first time a phase separation of an Ar–Kr mixture, manifestations of which turned out to be oddly asymmetric as far as the behavior of the components involved is concerned. Upon deposition both onto 6 or 20 K the emerging sample contained two crystal phases of virtually pure argon with a small admixture of krypton. One of the Ar phases (fcc) did not cause a surprise, whereas the other was hcp with the a/c ratio close to the ideal value. The krypton component separated as a fine-grained glass-like state, possibly, with a low admixture of argon.

Crystal Phase Boundaries of Structure-H (sH) Clathrate Hydrates with Rare Gas (Krypton and Xenon) and Bromide Large Molecule Guest Substances

Phase equilibrium pressure–temperature (pT) boundaries of structure-H clathrate hydrates (sH hydrates) with rare gas (Kr and Xe)-bromide large molecule guest substances (LMGSs: bromocyclohexane, BrCH and bromocyclopentane, BrCP) were measured. The phase boundaries for the sH hydrates in the Kr–LMGS–water systems shifted to lower pressures than those for the pure Kr hydrate in the temperature range of (273.2 to 279.3) K. In this study, sH hydrate formation was not confirmed in the Xe–BrCP–water system, but sH hydrates were found in the Xe–BrCH–water system. At temperatures below 277 K, equilibrium conditions were observed at lower pressures for the Xe–BrCH–water system than for the pure Xe hydrate. However, the equilibrium pT curve for the Xe–BrCH–water system crossed over the equilibrium pT curve for the Xe hydrate at around 277 K. Intersections between the equilibrium pT curves for the Xe hydrates and the sH hydrates (Xe + LMGS) have also been found in Xe–methylcyclohexane–water systems. Using the Kr–and Xe–bromide LMGS–water systems showed that the sH hydrate phase stabilities are strongly related to the encaptured LMGS.

Electronic spectroscopy of I2–Xe complexes in solid Krypton

In the present work, we have studied ion-pair states of matrix-isolated I(2) with vacuum-UV absorption and UV-vis-NIR emission, where the matrix environment is systematically changed by mixing Kr with Xe, from pure Kr to a more polarizable Xe host. Particular emphasis is put on low doping levels of Xe that yield a binary complex I(2)-Xe, as verified by coherent anti-Stokes Raman scattering (CARS) measurements. Associated with interaction of I(2) with Xe we can observe strong new absorption in vacuum-UV, redshifted 2400 cm(-1) from the X → D transition of I(2). Observed redshift can be explained by symmetry breaking of ion-pair states within the I(2)-Xe complex. Systematic Xe doping of Kr matrices shows that at low doping levels, positions of I(2) ion-pair emissions are not significantly affected by complexation with Xe, but simultaneous increase of emissions from doubly spin-excited states indicates non-radiative relaxation to valence states. At intermediate doping levels ion-pair emissions shift systematically to red due to change in the average polarizability of the environment. We have conducted spectrally resolved ultrafast pump-probe ion-pair emission studies with pure and Xe doped Kr matrices, in order to reveal the influence of Xe to I(2) dynamics in solid Kr. Strikingly, relaxed emission from the ion-pair states shows no indication of complex presence. It further indicates that the complex escapes detection due to a non-radiative relaxation.

Lattice parameters of CO2-Kr cryoalloys

The structure of the cryoalloys CO2-Kr has been studied in the entire range of relative concentrations by means of transmission electron diffraction. Gaseous samples were deposited from a tank at room temperature onto substrates cooled to 30K. The filling channel was thermally insulated from the cryogenic screens. An anomalous dependence of the lattice parameter a on the molar content x of krypton in the initial gas mixture was observed; specifically, the function a(x) contains a section which can be regarded as a minimum to within the limits of error. The maximum solubility of the krypton in the carbon dioxide crystal is 38mol.%, and the solubility of CO2 in a Kr crystal is low. The experimental data taken together give us a basis for supposing that the phase composition as a function of x has the following regions: 1) 0⩽x⩽0.38—regular solution of Kr in CO2; 0.38⩽x⩽0.6—mixture of a regular solution with critical concentration xcr=0.38 and nano inclusions of almost pure Kr; 3) 0.6⩽x⩽1—mixture of almost pure Kr with nano inclusions of a solution with xcr. A theoretical explanation is given for the anomalous behavior of the function a(x) for x≲20mol.%; the explanation is based on a cluster model and takes account of three mechanisms of interaction of Kr clusters with the crystalline environment of CO2.

Method for Purification of Krypton from Environmental Samples for Analysis of Radiokrypton Isotopes

Radiokrypton isotopes ((81)Kr and (85)Kr) are ideal tracers and chronometers of various environmental processes. Atom trap trace analysis (ATTA) is capable of determining the ultralow isotopic abundances of radiokryptons (<10(-12)) provided that 50 microL of pure Kr is available. The analysis by using ATTA of (81)Kr in naturally occurring gases of interest, e.g., dissolved gases in hydrological reservoirs, requires separation of parts-per-million (ppm) level Kr from chemically airlike bulk gas. A newly developed Kr purification system is based on conventional cryogenic distillation and gas chromatography to which continuous monitoring of gas effluent composition using a quadrupole mass spectrometer brings significant advantages. Simple cryogenic distillation is controlled based on the evolution of N2/Ar ratio that is relatively constant in naturally occurring, inorganic gas. Gas chromatographic separation of parts-per-million by volume (ppmv) level Kr from up to a few liters of bulk gas can be achieved by concentrating the Kr under the chromatographic tails of major components. The system described here is capable of extracting Kr of >98% purity from 5-125 L STP (standard temperature and pressure) of bulk gas with >90% yield within several hours. This system is generally useful for separation of microliter amounts of unreactive trace volatile compounds from large-volume gas samples.

Kr과 Xe 원자기체의 전자수송계수의 해석

Accurate sets of electron collision cross sections and the electron transport coefficients for atoms and molecules are necessary for quantitative understanding of plasma phenomena Kr and Xe atom are used in many industrial applications, such as in PDP and fluorescent induction lamps(FILs). Therefore, we analysed and calculated the electron transport coefficients, the electron drift velocity W, the longitudinal and transverse diffusion coefficient and , and the ionization coefficient /N in pure Kr and Xe gases over the wide E/N range from 0.001 to 500[Td] at 1[Torr] by two-tenn approximation of the Boltzmann equation.

Transport Properties of Ar-Kr Mixtures: A Molecular Dynamics Simulation Study

Equilibrium molecular dynamics (EMD) simulations are used to evaluate the transport coefficients of argon-krypton mixtures at two liquid states (state A: 94.4 K and 1 atm; state B: 135 K and 39.5 atm) via modified Green-Kubo formulas. The composition dependency of the volume at state A obeys close to the linear model for ideal liquid mixture, while that at state B differs from the linear model probably due to the high pressure. The radial distribution functions for the Ar-Kr mixture (x = 2/3) show a mixing effect: the first peak of g 11 is higher than that of g(r) for pure Ar and the first peak of g 22 is lower than that of g(r) for pure Kr. An exponential model of engineering correlation for diffusion coefficient (D) and shear viscosity (η) is superior to the simple linear model for ideal liquid mixtures. All three components of thermal conductivity (λ pm , λ tm , and /λ ti ) at state A and hence the total thermal conductivity decrease with the increase of x. At state B, the change in λ tm is dominant over those in λ pm and λ ti , and hence the total thermal conductivity decrease with the increase of x.