Diffusion Pump Research Articles

Fabrication and characterization of highly enriched thin 176Yb targets for the reaction dynamic studies on fission mass distribution

The fabrication, transfer, and storage of a highly enriched isotopic target is very much crucial because of air gases and moistures being chemically active at room temperature. One must limit the amount of time that the target surface is exposed to the atmosphere during the transfer of air sensitive targets. The highly interactive targets are not easy to store for longer time and demand an in-vacuum transfer facility. Getting an alternative technique to remove all such imperative is a need of the hour specially for the nuclear physics community, more particularly for reaction dynamic studies of fission fragment mass distribution induced by stable and radioactive ion beams. Highly enriched materials are rare and very expensive, so an effective and highly efficient technique is needed to deal with such materials. Here, an attempt has been made to fabricate 96.63% enriched thin targets of 176Yb by evaporation techniques enabling ≈129.1 μg/cm2 thickness with a ≈25.93 μg/cm2 carbon backing to increase its stability and durability. Numerous trials have been performed using natural Yb to optimize the evaporation setup and associated growth parameters for efficient Yb isotope deposition with thin film deposition unit and diffusion pump based coating unit at Inter University Accelerator Centre (IUAC), New Delhi. Thickness and elemental composition of the targets have been analysed using characterization techniques such as X-ray diffraction, α-energy loss technique, Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy. Essentially no significant impurities are found by these measurements, describing high purity and robustness of the fabricated targets. During the nuclear experiments, 30Si and 16O beams of intensity of the order of ≈1010 particles per second were bombarded on the targets for 5–6 days and no ill effects on the target were observed. Isotopic abundance of the target has been obtained experimentally, which ensured the isotopic purity of the target required for the reaction studies. This article will admire our readers about the qualitative nature of the fabrication technique, measurement and characterization citing valuable insights, aiding in a comprehensive understanding of their quality.

Potassium and sodium vapor diffusion pump development for fusion system

An alkali metal diffusion pump, which can meet many requirements for DT fusion system, was developed based on a commercial oil diffusion pump. Using sodium, potassium, and oil each as a vapor source, their evacuation behaviors were compared. The evacuation rate using potassium was comparable to that by original oil, and operation using sodium was found to require higher temperature. The compression ratio and evacuation of deuterium were also investigated. The diffusion pumping system was operated successfully, making this type of evacuation system a potential candidate for the fusion system.

Fabrication and characterization of CaF2 target for multi-nucleon transfer reaction studies

Thin CaF2 targets with carbon backing are fabricated for the first time using physical vapour deposition technique at the target laboratory of IUAC, New Delhi to perform a multi nucleon transfer reaction on 10,11B＋40Ca systems using General Purpose Scattering Chamber (GPSC) facility. Ca being an oxidizing material, we have used molecular CaF2 as the target material instead of Ca. Using turbo-molecular pump based coating unit (TMPU), carbon is deposited on cleaned glass slide and then CaF2 is deposited on diffusion pump based coating unit (DPU). We are successful in fabricating CaF2 targets of thickness ≈264.4μg/cm2 on carbon backing of thickness ≈21.5μg/cm2. The thickness and purity measured by the crystal thickness monitor equipped with the vacuum chamber is verified by different techniques like alpha energy loss, Rutherford Back Scattering (RBS), Electron Diffraction Spectroscopy (EDS) and X-ray Diffraction (XRD). Small impurity level were smeared during the observation and the target is successfully used for nuclear reaction experiment. The fabrication of molecular Ca target is found to be more conducive to experimentation since they exhibit less oxidation and herewith we discuss about fabrication technique, experimentation and characterization.

Study of the Effective Torus Exhaust High Vacuum Pumping System Performance in the Inner Tritium Plant Loop of EU-DEMO

The requirement for a reduction of the tritium inventory of the European demonstration fusion reactor (EU-DEMO) has led to the active research and development of a continuously working pumping process termed “KALPUREX.” This process foresees the direct recycling of a large fraction of the unburnt hydrogen isotopologues via superpermeation in metal foil pumps during the burn phase. The remaining exhaust gas mixture is pumped by continuously operating, mercury-driven linear diffusion pumps. Diffusion pumps are kinetic high vacuum pumps whose pumping principle is based on the momentum transfer from a supersonic mercury vapor jet to the pumped gas mixture. Like many high vacuum pumps, they feature species-dependent pumping speeds. In the present work, we develop a simplified hybrid model of the high vacuum pumping train in order to estimate the effective pumping speed of the integrated system. The results of this model and its implications on the further development of the vacuum system are discussed for the burn and dwell phases of EU-DEMO.

An improved source of spin-polarized electrons based on spin exchange in optically pumped rubidium vapor

We have improved a polarized electron source in which unpolarized electrons undergo collisions with a mixture of buffer gas molecules and optically spin-polarized Rb atoms. With a nitrogen buffer gas, the source reliably provides spin polarization between 15% and 25% with beam currents >4 μA. Vacuum pump upgrades mitigate problems caused by denatured diffusion pump oil, leading to longer run times. A new differential pumping scheme allows the use of higher buffer gas pressures up to 800 mTorr. With a new optics layout, the Rb polarization is continuously monitored by a probe laser and improved pump laser power provides more constant high polarization. We have implemented an einzel lens to better control the energy of the electrons delivered to the target chamber and to preferentially select electron populations of higher polarization. The source is designed for studies of biologically relevant chiral molecule samples, which can poison photoemission-based GaAs polarized electron sources at very low partial pressures. It operates adjacent to a target chamber that rises to pressures as high as 10−4 Torr and has been implemented in a first experiment with chiral cysteine targets.

An in-situ study on surface coloring mechanism of a 12Cr ferrite/martensite stainless steel during vacuum heat treatment

Color changes during oxidation of a 12Cr ferrite/martensite stainless steel were investigated in-situ by using a high vacuum (5 × 10−3 Pa) heating stage where the high vacuum is provided by an oil diffusion pump. The color of the oxide film changed from initial metallic silver to brown, then consecutively to purple, liberty blue, blue-gray and finally to azure blue during the 90 min heat treatment at 690 °C in high vacuum. In contrast to the above changes, during oxidation at 1130 °C, the color changes from metallic silver to brown, then to various blue and finally changed back to metallic silver. The color as a result of thin-film interference mainly depended on the oxide film thickness. The significant reduction of the thickness of the oxide film on the sample vacuum heat-treated at 1130 ℃ is owing to the volatilization of oxide, which is a result of the reaction of the already formed Cr2O3 with residual water vapor and oxygen to generate CrO2(OH)2 and CrO3 gas, which evaporated from the surface at 1130 °C. Ferrite grains have a much lower oxidation kinetics than that of martensite.

Polychlorinated Biphenyl (PCB) in Environment: Contamination, Toxicity, and Carcinogenicity

Polychlorinated Biphenyl (PCB) compounds which are widely used in industry have become a widespread and sustainable environmental problem for decades. PCB is chemically stable, low volatility, non-flammable, and high dielectric constant. Its main uses include heat exchange and dielectric fluids in transformers and capacitors, hydraulic fluids and lubricants, diffusion pump oils, plasticizers for plastics, and so on. PCBs are biologically magnified in the food chain and found in fish, wildlife, and human tissues. PCBs have been identified as contaminants in water, air, and soil, and are distributed up to the polar regions. According to epidemiological studies reporting blood levels of PCBs, the higher the level of exposure, the higher the blood concentration of PCBs, and the higher the environmental concentration or the longer the exposure period (or both), the longer the blood levels of PCBs remain elevated. PCB levels also correlate with race, place of residence (geographical), age, and dietary intake of fish in humans. PCBs have a very low potential to produce acute toxic effects. PCB exposure has been linked to having a particular skin rash commonly referred to as “chloracne”. Liver damage was the most consistent finding among the many laboratory animal species tested. Yusho refers to the epidemic of poisoning by consumption of cooking oil contaminated with PCBs and polychlorinated dibenzofuran. Mothers with Yusho experience stillbirth, abnormal skin pigmentation, or babies tend to be small when compared to the national average. Some PCB compounds are carcinogenic in a number of rodent bioassays, producing liver tumors. Based on the available animal data, PCBs should be considered potential carcinogens for humans. Keywords: Polychlorinated Biphenyl, pollution, contamination, toxicity, carcinogenicity.

65 Years of Turbopumps

SummaryVacuum technology is not necessarily one of the sciences mentioned in connection with groundbreaking inventions. Nevertheless, it is a basic prerequisite for many developments and products that are taken for granted today. The influence of vacuum technology on our lives today can be traced back to the invention of the turbopump 65 years ago. Until then, the diffusion pump was considered the most widely used high and ultra‐high vacuum pump, but with the help of Dr. Willi Becker's invention, it became possible to create hydrocarbon‐free vacuum. It was only through a ‚clean' vacuum that many analyses and manufacturing processes became possible.

Improvement of Ti-6Al-4 V alloy in terms of mechanical and tribological properties by oxidation and nitriding

In this study, we aimed to compare the mechanical properties and tribological properties of specimens after different thermal treatments. We treated specimens in oxidation and nitriding with argon in the chamber with 900 °C and 950 °C respectively. The results of the microhardness showed that the oxidized specimens were observed the highest value of 788VHN (0.05). We found that comparing to oxidized specimens (CoF=0.6 ± 0.09), the nitrided specimens showed lower coefficient of friction (CoF=0.52±0.06). There was around two times improvement of microhardness comparing to untreated specimens. And oxidized specimens (1.61±0.29 μm3/Nmm) showed five times lower value of wear rate than nitrided specimens (4.12±0.79 μm3/Nmm), and around ten times lower value of wear rate than nitrided with mechanic pump (9.54±0.68 μm3/Nmm). We concluded that oxidation could help to achieve the enhancement of hardness and wear properties, but with thinner layer on the surface. Nitriding with diffusion pump increased the efficiency of Ar+ and N+ diffusion than only with mechanic pump.

Simulation of Mercury-Driven Diffusion Pumps for Torus Exhaust Pumping

A new, continuous pumping train has been proposed for the European demonstration fusion power plant (DEMO). Mercury-driven linear diffusion pumps (LDPs) are suggested for use as high-vacuum pumps in this pumping train. In this work, we validate a 2-D simulation framework based on the direct simulation Monte Carlo (DSMC) method with experimental data of a two-stage mercury-driven LDP that was operated at the Lawrence Livermore National Laboratory (LLNL) in the 1950s. The simulation setup and assumed boundary conditions are described and their appropriateness discussed. Numerical results are compared to available experimental data for four different positions of the upper nozzle pipe. We find acceptable agreement between experimental and numerical results for the air pumping speed. This validation paves the way for using the simulation framework as a design and optimization tool in the further development process of the DEMO LDPs.

Effect of Thickness and Deposition Angle on Optical Transmittance of ZnS/Ag Nanostructures

This paper presents the optical transmittance properties of thermally evaporated coatings of ZnS/Ag nanostructures as a function of film thickness and deposition angle designed to mitigate the challenges of indoor heating and their effects on low temperature storage facilities. The nanostructures were deposited on glass by varying the film thickness and deposition angle of both silver and zinc sulphide nanofilms at a pressure of 2.5×10-5 mBars in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). The optical transmittance of the coatings was measured at normal incidence in the wavelength range of 250-2500 nm of the incident electromagnetic radiation. Spectral studies showed that the transmittance decreased with increase in the film thickness of the ZnS/Ag nanostructures and the optical transmittance increased with increase in deposition angle of zinc sulphide in the infrared region. The transmittance of (4 nm)ZnS/Ag, (7 nm)ZnS/Ag, (10 nm)ZnS/Ag and (15 nm)ZnS/Ag samples deposited at normal angle in the visible region had peaks at 61.7%, 66.3%, 54.9%, and 18.0% respectively. The transmittance of the nanostructures increased with the increase in deposition angle of silver nanoparticles. Thus optical transmittance measured at 1800 nm wavelengths for ZnS(0o)/Ag(0o), ZnS(0o)/Ag(30o) and ZnS(0o)/Ag(60o) were 2.8%, 21.7% and 22.1% respectively. The coating of ZnS at high deposition angle decreased transmittance in the visible wavelength. The transmittance peak values in the visible region measured up to 51.1%, 53.5%, and 45.1% for (4 nm)ZnS(0o)/Ag(0o) and (4 nm)ZnS(0o)/Ag(30o) and (4 nm)ZnS(0o)/Ag(60o) samples respectively. However, increase in deposition angle of (10nm)ZnS/Ag nanostructures measured at 1000 nm; ZnS(0o)/Ag(30o), ZnS(30o)/Ag(30o) and ZnS(60o)/Ag(30o) increased transmittance in the infrared wavelengths from 9% to 12% and 34% respectively. Therefore, to increase transmittance in the visible region, the Zinc sulphide nanoparticles should be coated on silver at low deposition angles.

Generation of proton and carbon ion beam from laser ion source using hydrocarbon oil target

The supply of high-flux proton and carbon ions are required for applications such as accelerator-driven neutron sources and heavy ion radiotherapy. So far, it is shown that a laser ion sources using the target of plastics made of hydrocarbons can provide protons and carbon ions. On the other hand, due to the damage of the target by laser irradiation, it is necessary to change the laser irradiation position every time, and the number of ion supply is limited to the area of the laser target. To solve the problem of target damage, we suggest a laser target in which the surface is continuously renewed by flowing hydrocarbon oil instead of solid hydrocarbon. In this study, we demonstrated the generation of protons and carbon ions using the target made of a hydrocarbon oil for a diffusion pump.

Optimization Study of the Diffuser Vane Inlet Angle to Avoid the Diffuser Rotating Stall in a Centrifugal Pump for Liquefied Gas using Computational Fluid Dynamics

Turbopumps are generally operated close to the design specifications, but diffuser pumps such as for the liquid natural gas in particular can be required in a wide range of flow rates. If the flow rate is lower than the design specifications, an unstable phenomenon called diffuser rotating stall(DRS) will occur, which will interfere with the operation of the pump. However, it is difficult to predict the flow rate onset DRS. Unsteady state analysis by computational fluid dynamics is commonly used to investigate the internal flow of DRS to pumps in detail, but the computational cost is huge and the design process is inefficient. In this study, authors investigated the effectiveness of the design method and the optimaized inlet angle of the target pump using the DRS simple prediction method using steady-state analysis of computational fluid dynamics. Then, it was confirmed that the DRS simple prediction method can be used qualitatively in the target pump. It was also confirmed that the optimaized inlet angle of the diffuser vane for the target pump was in the range of 6 degree to 7 degree.

Dependence of reflectance on angular deposition and film thickness of ZnS/Ag nanolayers

This paper presents the spectral reflectance of thermally evaporated ZnS/Ag nanostructures. The coating of ZnS/Ag nanostructures was performed in two steps while varying the film thickness and deposition angle. Silver metal wire (99.99% purity) was heated under vacuum at a pressure of \(2.5 \times 10^{-5}\) mBars and deposited on glass slide substrates in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). Pieces of zinc sulphide (99.99% purity) were heated and deposited to the glass slides previously coated with silver to form the ZnS/Ag/glass composite. The optical reflectance of the samples was studied by the UV/Vis/NIR spectrometer (Perkin Elmer Lambda 19) with UV-WinLab software. The reflectance was measured at angles of incidence between \(15^o\) and \(75^o\). Spectrophotometric studies showed that reflectance decreased with decrease in film thickness and decreased with increase in deposition angle of silver nanoparticles. The reflectance of ZnS/Ag nanostructures decreased with increase in deposition angle of zinc sulphide.

IMPORTANCE OF DIFFUSION PUMPING WHILE PRODUCING AMORPHOUS AND PARTIALLY CRYSTALLISED MATERIALS

It can be state that 1960 was the year when amorphous materials era began. 1989 was the year when bulk materials amorphous were first produced. Since then researchers around the World try to improve or find new correlations according to this group of materials. Sometimes instead of obtaining amorphous materials produced sample may be partially crystallised. During last research, ingots of two different alloys discussed in this work were produced with and without use of diffusion pump. Samples produced in injection method were done under the same condition for both cases of ingots. Then samples were subjected to structure analysis with the use of x-rays and were checked according to magnetic properties. Obtained results are compatible with expectations, however by meet one give promising possibility of further research.

Study of the linear mercury diffusion pump with the fixed mass-flow-rate model by direct simulation Monte Carlo method

The linear mercury diffusion pump is proposed as the primary pump for sustaining the continuous working of KALPUREX (Karlsruhe liquid metal based pumping process for fusion reactor exhaust gases), which is considered as the exhaust pumping solution for reducing the tritium inventory in future fusion reactor with the fuel cycle based on the Direct Internal Recycling (DIR) concept. In this work, a preliminary simulation study of the linear mercury diffusion pump (LDP) is performed based on the Direct Simulation Monte Carlo (DSMC) method. While the dsmcFoam solver in the OpenFOAM platform is used, the inlet model named by fixed mass-flow-rate (FixedMFR) model is developed to control the mass flow rate into the pump, in accord with the condition of the experiment in 1950s. The simulated pumping speeds are in reasonable agreement with the experimental results when the pressure is in the range of 1 × 10−2 ~ 2 × 10−2 Pa, which implies that the DSMC model can be used for simulating the performance of the LDP. It should be noted that in the preliminary DSMC model, the mesh size is too large. Due to the large mesh size, the expansion of the mercury vapor steam is overestimated and the pumping speed is underestimated. Further work is required to find a proper way to generate the computational mesh for predicting the pumping performance of the LDP accurately and effectively.

Particle Simulation of Linear Diffusion Pumps for DEMO Torus Exhaust Pumping

It is currently foreseen to implement Mercury-driven Linear Diffusion Pumps (LDP) in the primary pumping system of the European demonstration fusion power plant (DEMO). Here, a simulation model using the Direct Simulation Monte Carlo (DSMC) method is presented and verified. By a series of simulations the sensitivity of a LDP is analyzed with respect to inlet pressure, compression ratio, gas species dependence, backstreaming and condensation as well as the impact of geometric parameters to explore the operational limits of a LDP. The simulation results confirm that DSMC is a useful tool for the simulation and optimization of LDPs in conditions relevant for fusion reactor exhaust pumping.

О методе расчета параметров откачки ступени диффузионного вакуумного насоса

At present, steam jet vacuum pumps are widely used in various fields of science and technology due to a number of advantages, e.g., reliability, relative simplicity of design, and manufacturability, over other pumping means. The paper analyzes the existing mathematical models of working processes, methods for calculating the pumping parameters of steam-jet vacuum pumps. The problem of improving these methods, which are used in the design, is still urgent. The study attempts to further develop the models in order to increase their practical significance for the pumps design: in particular, the processes of pumping by the first stages of a diffusion pump are considered, since it is they that determine the efficiency of the pump as a whole. Analytical dependences for calculating the main pumping parameters of widely used diffusion vacuum pumps are presented. The obtained equations are a certain clarifying correction of the known provisions on this topic. Findings of research are of practical importance for the design of modern steam-jet vacuum pumps

Rotating stall characteristics in the vaned diffuser of a centrifugal pump

Rotating stall in centrifugal pumps takes place frequently under part-load conditions, along with high pressure pulsation. The major focus for studies is rotating stall inside the impeller, rarely paying attention to that in the vaned diffuser. In this study, rotating stall behavior in a vaned diffuser centrifugal pump has been numerically investigated, and the cross-power spectrum method is adopted to identify low-frequency pressure signals. The applied numerical method has been validated by experimental results including flow structures provided by PIV measurements. For the vaned diffuser pump, a hump region in head curve is observed between 0.25Qd and 0.5Qd conditions. Under 0.41Qd condition, rotating stall occurs in the vaned diffuser of the pump, with three stall cells rotating opposite to the direction of impeller rotation and the rotating frequency being 0.083 Hz equal to 1/600 of the impeller rotating frequency. Rotating stall takes place under 0.5Qd condition as well, whereas only a periodic process of stall cell from inception to disappearance appears in the diffuser channel under 0.35Qd condition. Furthermore, the effect of number of diffuser vanes on rotating stall characteristics has been analyzed in detail.

Investigation of Chemomechanical Effects on Sapphire Surfaces Modified by Ion-Implantation-Induced Carbon Impurities

Modification of the chemomechanical behaviour of the surface of sapphire by ion implantation to improve its near-surface mechanical properties has been investigated. 300 keV Ti+ ions at various doses were implanted and the concentration and damage profiles characterised using Rutherford Backscattering (RBS). At high doses (≥ 3 × 1016 Ti+ cm−2), a surface amorphous layer is formed due to implantation-induced damage. Nanoindentation was used to determine the hardness behaviour of the ion-implanted layer. Hardness increases at low implantation doses, associated with implantation-induced damage, but it is also observed that chemomechanical softening of the surface is reduced due to the removal of adsorbed water. In situ Raman scattering measurements demonstrate this removal at low doses and the re-establishment of the adsorbed water layer at high doses. The adsorption process is changed due to the introduction of carbon into the sapphire surface during implantation. For the optimum-implanted dose, the water readsorption does not recur even several years after the implantation treatment was first carried out. The loss of water adsorption is related to the formation of a non-polar carbonaceous layer on the sapphire surface by cracking of back-streamed diffusion pump oil deposited on the sample surface by inelastic collisions with the ion beam. Based on this study, it is concluded that ion implantation with an appropriate ion species and dose can control the chemomechanical effect and improve the hardness of ceramics, such as sapphire.