Use Of Krypton Research Articles

Performance optimization of a krypton Hall thruster with a rotating propellant supply

The use of krypton in the field of electric propulsion has become a key research topic owing to its high specific impulse and high reserves. However, because krypton has features such as a small ionization cross section and high ionization energy, its ionization performance is relatively low, thereby increasing the actual specific impulse loss of the krypton Hall thruster in comparison with its theoretical value. Therefore, to use of krypton as the propellant of the Hall thruster instead of xenon, it is necessary to study the optimization of its ionization process. In this study, a gas distributor with a rotating propellant supply mode is designed, considering factors such as the velocity and density of the velocity of neutral atoms, which affects the ionization process. The distribution of neutral atom parameters in the discharge channel is changed by the rotation; and its influences on the propellant ionization and other performance parameters of the Hall thruster are experimentally analyzed with respect to the magneto-ampere, volt-ampere, and flow rate-ampere characteristics. The results demonstrate that the rotating propellant supply reduces the axial velocity of neutral atoms, increases the density and circumferential motion distance, and thus improves the ionization efficiency of the krypton Hall thruster. Furthermore, the performance parameters, such as thrust and efficiency, are also improved, and the plume divergence angle is reduced. When the discharge voltage is 450 V and the anode flow rate is 60 sccm, the rotating propellant supply can increase the anode efficiency of the axial propellant supply mode from 46.2% to 53.2%. However, the plume divergence half-angle reduces from 39.2° to 35.5°. In addition, an increase in the anode flow rate and discharge voltage continuously increases the performance promotion in the rotating propellant supply mode.

Development of sputtered Nb3Sn films on copper substrates for superconducting radiofrequency applications

Superconducting radiofrequency (SRF) cavities that could provide a higher quality factor as well as a higher operational accelerating gradient at an affordable cost are in high demand for the future generation of particle accelerators. This study aims to demonstrate the potential of Nb3Sn as material of choice for such SRF applications. Due to its brittle nature, the only way to produce an Nb3Sn SFR cavity is to synthesise a thin layer inside a cavity made of niobium or copper. In this work, direct current magnetron sputtering using a stoichiometric target of Nb3Sn was employed to produce films on copper samples. Assessment of the morphology, microstructure and superconducting properties were performed in order to ensure that this approach is suitable for SRF applications. The potential of the method is proven by obtaining films, which exhibit a crack-free surface, dense morphology and critical temperatures (Tc) up to 16 K. The essential properties of the films have also been investigated with respect to the deposition and annealing conditions. The use of krypton as working gas during deposition increases the atomic percent of Sn in the film compared to argon. However, in contrast to argon, higher krypton pressures reduce the atomic percent of Sn. It was also found that long-lasting high-temperature annealing leads to higher superconducting critical temperatures due to an increased crystallographic order. Particular attention was given to the influence of the copper substrate on the film growth as well as the microstructural and superconducting characteristics. We discuss the main constraints introduced by the copper substrate, such as copper interdiffusion during annealing, lattice mismatch and difference in thermal expansion coefficients and methods to overcome them.

Investigation of a Low-power Thruster on Krypton Propellant

Nowadays, higher requirements are set for modern spacecraft,and, in particular, those related to the cost-efficiency of the mission. To ensure a reasonably long period of active life (approximately 10-15 years), stationary plasma thrusters (SPT) are successfully used in propulsion systems. Xenon is the substantial part of the cost of the propulsion system, which is why this could be significantly reduced, were xenon to be replaced with an alternative propellant.On this basis, and taking into account the perspectives for the creation of multi- satellite orbital constellations and the tendency towards spacecraft miniaturizations, there is a demand for the development of a low-power thruster using an alternative propellant to Xenon. It is assumed that krypton is the most suitable replacement, albeit while using krypton there is a considerable decrease in the SPT thrust parameters. Therefore, it is necessary to perform investigations which reduce the negative consequences related to the use of krypton as a propellant.

Krypton for computed tomography lung ventilation imaging: preliminary animal data.

The objective of this study was to assess the feasibility and safety of krypton ventilation imaging with intraindividual comparison to xenon ventilation computed tomography (CT). In a first step, attenuation of different concentrations of xenon and krypton was analyzed in a phantom setting. Thereafter, 7 male New Zealand white rabbits (4.4-6.0 kg) were included in an animal study. After orotracheal intubation, an unenhanced CT scan was obtained in end-inspiratory breath-hold. Thereafter, xenon- (30%) and krypton-enhanced (70%) ventilation CT was performed in random order. After a 2-minute wash-in of gas A, CT imaging was performed. After a 45-minute wash-out period and another 2-minute wash-in of gas B, another CT scan was performed using the same scan protocol. Heart rate and oxygen saturation were measured. Unenhanced and krypton or xenon data were registered and subtracted using a nonrigid image registration tool. Enhancement was quantified and statistically analyzed. One animal had to be excluded from data analysis owing to problems during intubation. The CT scans in the remaining 6 animals were completed without complications. There were no relevant differences in oxygen saturation or heart rate between the scans. Xenon resulted in a mean increase of enhancement of 35.3 ± 5.5 HU, whereas krypton achieved a mean increase of 21.9 ± 1.8 HU in enhancement (P = 0.0055). The use of krypton for lung ventilation imaging appears to be feasible and safe. Despite the use of a markedly higher concentration of krypton, enhancement is significantly worse when compared with xenon CT ventilation imaging, but sufficiently high for CT ventilation imaging studies.

Influence of HPPMS pulse length and inert gas mixture on the properties of (Cr,Al)N coatings

During the production of plastic products by injection molding processes adhesion and abrasion wear as well as corrosion take place in the molding tools. Concerning this, (Cr,Al)N coatings deposited via physical vapor deposition (PVD) have a good potential to be used as protective coatings on injection tools. For an effective protection of coated tools a uniform layer of coating material is also required. In this regard, the HPPMS (high power pulse magnetron sputtering) technology offers possibilities to improve coating thickness uniformity as well as to adapt the chemical and mechanical properties. The present work deals with the investigation of influence of HPPMS pulse length and the argon/krypton ratio in the deposition process on (Cr,Al)N coating properties. For this reason, (Cr,Al)N coatings were deposited with HPPMS pulse length of 40, 80 and 200μs at constant Ar/Kr ratio (120/80sccm). The results were compared with a coating deposited with DC Magnetron Sputtering (DC-MS) with the same Ar/Kr ratio. Afterwards, a (Cr,Al)N coating was deposited with constant pulse length (200μs) without Kr. The chemical composition, morphology and phase composition of the coatings were analyzed by means of EDS (Energy Dispersive Spectroscopy), SEM (Scanning Electron Microscopy) and XRD (X-ray Diffraction), respectively. The composition of the surface near region in the samples was investigated by means of XPS (X-ray Photoelectron Spectroscopy). Mechanical properties were measured by means of nanoindentation. Decreasing of pulse length at constant mean power leads to a considerable increase of cathode current. It could be observed that the deposition rate of the HPPMS process reduces with decreasing pulse length. Nevertheless, short HPPMS pulse lengths and high peak currents lead to an increase of hardness from 25GPa to 32GPa while the DC-MS coating displays a hardness of 18GPa. The use of krypton within the sputter process leads to a marginal increase of the deposition rate while the mechanical properties are not significantly changed. In addition, EIS (electrochemical impedance spectroscopy) was employed to investigate the defect structure of the coatings.

An Approach to Eliminate Initializing Process from Manufacturing of Phase Change Optical Recording Media.

A new method of eliminating the initializing process from phase change recording media production has been proposed. The process is based on the use of krypton instead of argon for the deposition of GeSbTe recording film. By this method the kinetic energy of sputtered atoms can be reduced by collisions with gas atoms. Fairly good recording performance was demonstrated on a non-initialized disc based on the DVD-RAM ver.2.0 format.

High-purity enrichment of [formula omitted

High-purity 84 S r (i.e., >99 at%) is an important tool in many areas of basic and applied research, in particular for spikes used in isotopic dilution/mass spectrometer investigations in geochemistry, cosmochemistry, and paleoclimate-age studies. In nature, the 84 S r abundance is only 0.56%; however, it can be enriched to the specified requirements by using a high-resolution separator, such as the 180°-sector separator, or by completing two passes through a high-production, lower-resolution machine, such as the calutron. The latter option was used for this enrichment to produce ∼1 g of strontium with a final 84 S r concentration of 99.64%. Three innage runs were made, vaporizing a total of ∼17 g of metal feed that had been pre-enriched in the calutron to ∼70% 84 S r. A partial recovery, followed by recycle of the unresolved feed, was made after the second innage run. A process efficiency of 8.44% was achieved, and 4.33 g of the unresolved feed material was recovered. A modified ion-source unit using materials compatible with strontium and the use of krypton as mass markers to aid in operations are described. Standard contamination analyses were performed to evaluate the enrichment and to compare measured results with predicted product purity.

Simulations of constant poloidal beta experiments on ZT‐40M using a one‐dimensional multispecies transport model

A one‐dimensional (1‐D) multispecies transport model for the reversed‐field pinch plasma, which includes neutral deuterium and a coronal nonequilibrium model for impurities, is used to simulate a set of ZT‐40M [Fusion Technol. 10, 307 (1986)] experiments. In these experiments, the radiation fraction is varied from 15% to 95% by use of krypton seeding, while the plasma operating parameters Iφ and ne are constrained to within a small variation from a fixed operating point. In effect, these experiments maintain an almost constant βθe on axis for the range of radiation fractions. The simulations match experimental estimates of particle, energy, and nonradiative confinement times, and of the electron poloidal beta. The results show that the anomalous thermal transport needed to reproduce the observed experimental behavior, i.e., constant βθe on axis, can be modeled by use of a small amount of parallel thermal conduction. Such a model phenomenologically accounts for anomalous heat transport due to fluctuations or stochastic field line diffusion. This model is also used for parametric studies on the design conditions of ZTH [Bull. Am. Phys. Soc. 31, 1546 (1984)]. To achieve the ZTH design values it is necessary for particle and thermal diffusivities to improve by a factor of 10–15 over ZT‐40M.

Collision‐induced dissociation of Cs4I. An Example of Superelastic Collisions?

AbstractThe collision‐induced dissociation (CID) of Cs4I to form Cs3I has been investigated by mass‐analysed ion kinetic energy spectroscopy, When helium was used as collision gas the CID process was accompanied by sizable loss of translational energy in the collisional‐activation step. However, use of krypton or xenon as collision gas yielded product ions with translational energies higher than that observed for unimolecular reaction in the absence of collision gas. Neon and argon provided intermediate behaviour. Extensive experiments designed to investigate possible explanations for these observations left superelastic collisions of an excited state as the only possibility. Since nothing is known about the structures and electronic states of species like Cs4I, the necessarily speculative discussion is based upon general considerations of coupling of translational and electronic energies via crossings between states of the transitory collision complex. These observations emphasise the complexity of the possible processes which can occur as a result of collisions in the keV range.

Surface analysis of griseofulvin powders by krypton adsorption: Evaluation of specific surface area, BET constant C and polanyi adsorption potential

The use of krypton for the analysis of the surface properties of three reference standards and 18 samples of griseofulvin was assessed. A strong correlation (r = 0.9984) was observed between the Brunauer, Emmett and Teller (BET) specific surface areas (S) determined using krypton (S Kr ) and those using nitrogen (S N ). For low sample area (< 0.27 m 2), the estimations of S Kr were more accurate than those of S N . The cross-sectional area of adsorbed krypton, calculated in relation to nitrogen, is independent of the nature of the adsorbents, i.e., is not a function of the BET C constants, determined using krypton adsorption (C Kr ). The values of C Kr were related to the particle morphology. Moreover, the change of surface property upon heat treatment was reflected in a three-fold increase of C Kr . A linear correlation between the Polanyi adsorption potential and ln C Kr was observed suggesting that the entropy of adsorption is either constant or is a linear function of the enthalpy of adsorption. The results support the use of krypton adsorption as a technique of choice that provides valuable information concerning the surface of powders which, in many cases, is difficult to obtain using other experimental procedures.

Right ventricular ejection fraction measured by first-pass intravenous krypton-81m: Reproducibility and comparison with technetium-99m

Study of the effects of various diseases and therapeutic manipulation of pulmonary vascular resistance on the right ventricle has been restricted by methodologic limitations. The radioactive gas in solution, krypton-81m was used to study the right ventricle and the technique was compared with a technetium-99m method. In 22 subjects, first-pass krypton-81m right ventricular ejection fraction, acquired both in list mode and electrocardiogramgated frame mode, correlated well (r = 0.81 and 0.86, respectively, p < 0.01) with that determined by technetium-99m first-pass studies over a broad range of ventricular function. The reproducibility of the technique was excellent (r = 0.84 and 0.95 for each acquisition mode, respectively). Krypton-81m first-pass studies provide accurate and reproducible estimates of right ventricular function. Use of krypton allows multiple measurements, with or without perturbations, over a short period of time.

Glow discharge optical spectroscopy measurements of arsenic-implanted silicon

Recent advances in the glow discharge optical spectroscopy (GDOS) technique have been made, as shown by measurements of implanted arsenic profiles in silicon. The improvements discussed include the use of krypton as a discharge gas, a dual detection system which permits simultaneous measurements of the impurity distribution and the substrate sputtering, and the use of nickel as an overcoat to allow accurate measurements near the surface. Profiles of as-implanted and 1000°C annealed samples are presented which agree substantially with other types of measurements.

Use of Krypton for Surface Area Measurements

WE have recently discussed1 some criteria for the applicability of various gases in measuring the surface areas of solids by the Brunauer–Emmett–Teller2 method. We concluded that the use of krypton in this technique led to valid and useful results and that previous criticism of the use of this gas was unfounded. However, Thomas3 has again suggested that ‘anomalous’ Brunauer–Emmett–Teller plots obtained from krypton adsorption measurements render the use of this gas undesirable. He proposes that the occurrence of phase-changes in the adsorbed film, evidenced by discontinuities in the adsorption isotherm, are associated with these ‘anomalous’ (and presumably suspect) results.

399. On the energetics of physically adsorbed films, with particular reference to the use of krypton for surface area measurement: G. L. Gaines, Jr. and P. Cannon, J. Phys. Chem., 64, 997–1000, Aug. 1960

399. On the energetics of physically adsorbed films, with particular reference to the use of krypton for surface area measurement: G. L. Gaines, Jr. and P. Cannon, J. Phys. Chem., 64, 997–1000, Aug. 1960