Vacuum Envelope Research Articles

Preliminary engineering design of vacuum thermal shielded Pb-Li loop section for potential nuclear fusion application

Nuclear fusion reactor design and engineering has reached into an advanced phase where the issues pertaining to radioactive tritium handling & accountability, divertor heat load mitigation, reactor size reduction & cost minimization are some of the core problems being addressed globally. Tritium breeding blanket is an important sub system of the reactor, which demands the most efficient design from many perspectives including that of tritium handling and accountability. Especially, Liquid Metal Breeder Blanket (LMBB) design consists of a complex network of heated pipes carrying Lead-Lithium (Pb-Li) Eutectic Alloy liquid metal. There are a few major issues with such pipes, namely (1) Large Space required due to substantial increase in diametric size of such pipes covered with heating elements and silica fibre based thermal insulation, (2) Loss of the bred tritium from liquid metal through permeation across the pipe wall and associated radioactive safety issues, and (3) Tritium retention in silica fibre based insulation resulting in tritium accountability problem and health hazard during maintenance duration. One possible solution to these problems could be putting a vacuum envelope over the loop pipe. The vacuum isolation will take care of thermal insulation for convection loss and at the same time, the pumping port of the envelope will collect all the lost tritium. In order to demonstrate the feasibility of the concept from thermal shielding point of view, we have prepared a conceptual and preliminary engineering design of such a vacuum envelope on a segment of the Pb-Li loop of 1 inch diameter. The loop segment includes a straight part as well as one 180° U bend too. The design is to maintain the envelop temperature less than 50 °C while the loop pipe is maintained at 350 °C. Basic calculation of thermal conductivity of low pressure air (vacuum) is done and compared with that of conventional insulation material silica based fibre felt. The fabrication, integration and maintenance schemes are also discussed in this report.

NanoMi: An open source electron microscope hardware and software platform

We outline a public license (open source) electron microscopy platform, referred to as NanoMi. NanoMi offers a modular, flexible electron microscope platform that can be utilized for a variety of applications, such as microscopy education and development of proof-of-principle experiments, and can be used to complement an existing experimental apparatus. All components are ultra-high vacuum compatible and the electron optics elements are independent from the vacuum envelope. The individual optical components are mounted on a 127 mm (5-inch) diameter half-pipe, allowing customizing of electron optics for a variety of purposes. The target capabilities include SEM, TEM, scanning TEM (STEM), and electron diffraction (ED) at up to 50 keV incident electron energy. The intended image resolution in SEM, TEM and STEM modes is ≈ 10 nm. We describe the existing components and the interfaces among components that ensure their compatibility and interchangeability. The paper provides a resource for those who consider building or utilizing their own NanoMi.

The performance enhancement of solar cooker integrated with photovoltaic module and evacuated tubes using ZnO/Acalypha Indica leaf extract: response surface study analysis.

In this study, the effect of employing ZnO/Acalypha Indica leaf extract (ZAE) on the energy absorption of a coated portable solar cooker has been examined using an experimental setup. A prototypical model has been developed to corroborate in associating an investigative outcome per constituents of the experiments. The studied heat transfer process in ZAE is stable for harsh conditions. The design analysis and an estimation of the system performance were done given various parameters including the pressure of the vacuum envelope, bar plate coating digestion, emissivity, and solar rays. The fabricated solar was tested with and without ZAE to investigate the impact of this coating material on the solar cooker's thermal performance. To observe the performance of the new design, two figures of merit (F1 and F2) have been introduced. The factual food cooking assessments were for a family of four people, which operated in ZAE coating (0.8, 1.0, 1.2 μm) of the solar cooker. The values of F1 and F2 for the proposed cooker were obtained as 0.1520 and 0.4235, respectively, which is intact with the BIS values. The results revealed that employing ZAE instead of a thermal NHC-PV solar cooker reduced the time required to boil 2 L of water for about 47 min. The overall thermal energy productivity of the solar cooker with electrical backup was obtained as 42.65%, indicating that the ZAE coating can improve the thermal efficiency by 10.35%.

Исследование влияния состава контролируемой газовой среды и температуры на качество твердофазных соединений проволок при изготовлении пористых сетчатых материалов

Porous mesh materials are designed for the manufacture of products with a given shape and size, as well as hydraulic, filtering, thermal and other properties. At the same time, they must have the necessary mechanical and technological properties, which are formed to a large extent by the quality of weld solid-state bonds of mesh wires. Findings of the research that the increase in the strength of wire bonds during manufacture of porous mesh materials is influenced by the conditions for removing oxide layers by means of choosing the optimal protective gas environment and heating temperature during welding. The analysis of the processes occurring at the boundary of the metal–oxide and oxide–gas phases made it possible to establish that, depending on the structure of the alloy, the heating temperature, the composition and partial pressure of the gas protective environment, not only additional oxidation or thinning of the oxide layers but also gas saturation of the work surface are possible. For the manufacture of sizeable sheet porous mesh materials with high accuracy in thickness, the use of welding by rolling in a protective gas environment is the only possible process. Depending on the chemical composition of the wires, it is possible to carry out mesh briquette rolling welding on vacuum rolling mills, in an argon atmosphere of controlled purity and in evacuated envelopes. Within the research, we studied the influence of the composition of the gas environment and the process temperature on the quality of weld bonds and found that it is advisable to manufacture VT2 alloy sheet porous mesh materials by hot rolling in a vacuum mill and in an inert gas environment with a controlled composition. Porous mesh materials made of 12Kh18N10T steel can be made by hot rolling in vacuum envelopes, and products with limited dimensions can be made by diffusion welding. The study also specifies the modes of technological processes for manufacturing porous mesh materials made of VT2 alloy and 12Kh18N10T steel by rolling welding and diffusion welding.

Failure analysis of leaks due to cracks in hydrogen transfer lines of ESS cryogenic moderator

The ESS cryogenic Moderator System (CMS) has been designed to slow down the high-energy neutrons by means of two hydrogen moderators (to be increased to four in the future) by using forced flow of subcooled liquid hydrogen with a temperature of 17 K at 1.0 MPa. A liquid hydrogen leak is considered the most severe failure for the CMS. A leak scenario from the transfer line to its vacuum envelope through a crack have been analyzed and the expected results will be presented in this paper. An analysis code has been developed and calculated the pressure and temperature changes in the CMS process line and its vacuum envelope. The effect of the crack sizes is clarified. The consequential temperature changes along the vacuum envelope as well as the pressure drops were calculated. The required size of the safety relief device in the hydrogen transfer line and its vacuum envelope have thereby been determined and implemented.

Simulation of nanofluid convective flow inside a complex solar thermal system

Today’s world witnesses an unprecedented augmentation in energy consumption which has tipped the balance of attention toward the renewable energies, especially solar energy as the most promising type. With recent developments in the field of solar heating units, evacuated tube solar units have played a prominent role in solar energy absorption process in recent years due to the existence of a vacuum envelope in the structure of the tubes. Following this, a three-dimensional transient numerical study has been carried out by employing computational fluid dynamics aimed to appraise the water flow, natural circulation process and convective rate inside the evacuated tube along with a storage tank. A comparison has been made using water and CuO/H2O nanomaterial as the operate fluid for the purpose of evaluating the efficacy of nanofluid on the functionality of the system. The results in the form of velocity distribution, temperature and velocity contours served as an array of reasons on serviceability of CuO nanoparticles in the given application. This is evidenced by the natural circulation rate and heat transfer sustaining more desirable magnitudes, while observing an increase in the average temperatures of the tube and tank, respectively. Implementation of CuO/water over plain water has been reasserted categorically and thus justified.

A prototype Multi-X-ray-source array (MXA) for digital breast tomosynthesis

The design and testing of a prototype Multi-X-ray-source Array (MXA) for digital breast tomosynthesis is reported. The MXA is comprised of an array of tungsten filament cathodes with focus cup grid-controlled modulation and a common rotating anode housed in a single vacuum envelope. Prototypes consisting of arrays of three-source elements and eleven-source-elements were fabricated and evaluated. The prototype sources demonstrated focal spot sizes of 0.3 mm at 45 kV with 50 mA. Measured x-ray spectra were consistent with the molybdenum anode employed, and the tube output (air kerma) was between 0.6 mGy/100 mAs at 20 kV and 17 mGy/100 mAs at 45 kV with a distance of 100 cm. HVL measurements ranged from 0.5 mm Al at 30 kV to 0.8 mm Al at 45 kV, and x-ray pulse widths were varied from 20 ms to 110 ms at operating frequencies ultimately to be limited by source turn-on/off times of ∼1 ms. Initial results of reconstructed tomographic data are presented.

Numerical study of a consequence of a vacuum insulation degradation in a cryogenic system

Vacuum is the primary method for a thermal insulation of cold elements in cryogenic systems, tanks and other cryogenic equipment. A dangerous situation arise in the case of vacuum envelope failure when a 300 K air enters the vacuum and the cold elements of cryogenics equipment are exposed to a potentially intense heat fluxes and air velocity. Depending on a mass flow of the air (equivalent to size of an insulation rapture), a different rate of the temperature and pressure growth in the vacuum chamber can promote various mechanisms of the heat transfer to the cold elements. Additionally, it can be limited by the air deposition, condensation and cryosorption. In the present work a simplified numerical model of a typical cryogenics system is developed and different scenarios of vacuum degradation are considered. The current studies aim to identify the development of the different thermal conditions in the cryogenics system in the function of the mass flow of the ventilating air. The present work presents numerical studies of vacuum degradation for various sizes of a rapture hole. Additionally, the work proposes a simplified zero-dimensional model, which includes a deposition of air and its influence on pressure buildup and heat transfer.

Parametric analysis and optimization of a portable evacuated tube solar cooker

In this study, the performance of a portable evacuated tube solar cooker along with a stainless steel tank is analytically investigated. The presented model is validated by comparing the analytical results with those of the experiments. The effect of the important design and weather parameters on the performance of the solar cooker is evaluated. The studied parameters are the absolute pressure of the vacuum envelope, absorber coating absorptivity and emissivity, and solar radiation. In this research, the Taguchi method is applied to optimize the useful thermal power and efficiency of the solar cooker. According to the results, increasing the absolute pressure of the vacuum envelope from 0.01 Pa to 100 Pa reduces the solar cooker efficiency about 23.07%. Moreover, using a material with the absorptivity of 0.95 in the absorber coating of the evacuated tube solar cooker enhances the useful thermal power by about 33.76 W compared to that of the absorptivity of 0.75. Taguchi analysis reveals that the solar radiation is the most effective parameter on the useful thermal power of the solar cooker. Furthermore, in order to optimize the solar cooker efficiency, the most effective parameter of the solar cooker is the absolute pressure of the vacuum envelope.

Innovative compact braze-free accelerating cavity

High energy physics experiments using particle accelerators as well as industrial and medical applications are continuously seeking more compact, robust and cheaper accelerating structures. As of today, stable operating gradients, exceeding 100 MV/m, have been demonstrated by the SLAC group in the X-Band (11.424 GHz). These experiments show that hard structures, fabricated without high-temperature processes, achieve a better high gradient performance in terms of accelerating gradients. Therefore, we present an innovative and compact type of accelerating cavity that avoids any high-temperature processes like brazing or diffusion bonding. All cells are joined together by means of specifically designed and proprietary screws which ensure good vacuum and RF contacts. Two three-cell standing-wave accelerating structures, designed to operate in the pi-mode at 11.424 GHz, have been successfully built and cold tested. In order to guarantee a vacuum envelope and mechanically robust assembly, we used the Electron Beam Welding (EBW) and the Tungsten Inert Gas (TIG) processes. This work has been carried out in the framework of a funded project by the Vth Committee of the INFN for the Laboratori Nazionali di Frascati (LNF), within a large international collaboration between LNF, SLAC and KEK for the development of X-Band accelerating cavities using “hard structure” technology.

Fabrication of Split-Section X-band Structure Using Elastic Averaging

Conventional accelerator structures are manufactured using axial stacks of cylindrical components which, when brazed together, form the accelerator cell structure. Splitting the accelerator structure into two sections along the beam axis allows for a significant reduction in part count and vacuum joint length [1]. The resultant single and coplanar vacuum joint between the two split sections allows for joining techniques such as electron beam welding or brazing of the parts to form the accelerator vacuum envelope. High precision alignment of the two sections is achieved through an elastic averaging interface coupling where improved accuracy is derived from the averaging of errors over a large number of relatively compliant contacting members. The monoblock split sections allow for highly optimized cooling configurations with enhanced heat removal in high heat flux regions, reducing vacuum wall thermal stresses and enabling higher power operation. This paper describes the engineering and manufacturing of four generations of brazed and electron beam welded Xband accelerator structures at both 9.3 GHz and 11.4 GHz frequencies.

Two-stage multi-beam linear accelerator EVT

The concept of the electron multi-beam linear accelerator EVT invokes aspects of a two-beam accelerator. Here, effective transformation of several drive beams energy into the high-voltage accelerated beam energy takes place. It combines an RF generator and essentially an accelerator within the same vacuum envelope. Acceleration occurs in inductively-tuned cavities. The ratios between values of RF beam currents and their voltages are similar to ratios for an electric transformer that allows to designate this device as an Electron Voltage Transformer (EVT). The EVT accelerator properties prove to be true by the example of numerical simulations of two-stage EVT operating in S-band with a 60 kV gun and generating a 1 A, 4.5 MV beam at its output, having efficiency of 25% is presented. ©2001 Elsevier Science. All rights reserved.

Optical Fiber Laser Polaristrobometers and SpectroPolaristrobometers Based on Pr3+-Doped Laser Sources as a Possible Compact Alternative to the Old Type Polaristrobometers Based on Huge Low-Pressure (Mono-chromatic) SodiumVapor Gas-Discharge Lamps

From the pioneering work of H. Wild it is known that the most useful light source for polaristrobometers is a low-pressure sodium-vapor gas-discharge lamp. The high intense yellow band in the emission spectrum of this “pseudo-monochromatic” light source is the atomic sodium D-line (λ=589 nm), comprising about 90% of the visible light emission for this lamp type.But low pressure sodium lamps require an outer vacuum envelope around the inner discharge tube for thermal isolation, and early models of such light sources had a detachable Dewar jacket. But this can significantly increase the size of polaristrobometers which contradictsthe requirements for the modern microminiaturized analyticalsystems (including microfluidic lab-on-a-chip constructions).

Investigation of edge taping method applied to vacuum insulation panels

Vacuum insulation panel (VIP), commonly composed of an evacuated filler material and a vacuum envelope, is drawing attention for the outstanding insulation performance compared with conventional insulators. As an associated problem, however, its effective thermal conductivity may be increased, since additional heat is transferred through the envelope edge; this is called edge conduction. It is significantly large if the envelope includes an Al-foil layer. In this paper, the edge conduction for VIPs with Al-foil envelope is investigated from experiments, numerical results, and theoretical analyses.‘Edge taping method’ is investigated as a means to reduce the edge conduction, where insulation stripes are attached along the edges of the envelope. Numerical analyses and experiments are performed to verify this method and an analytical solution is proposed. The results show excellent agreements among themselves and prove that the edge conduction can be substantially reduced by the edge taping. Also, dimensional analysis is performed and the ‘easy-to-use’ analytical solution is expressed in a dimensionless form. Use of the proposed relation helps one determine a quantitative sizing of physical parameters in the edge taping method.

Design of an Integrated Mechanical Fatigue Test Apparatus for S-Bend Busbar

An integrated test apparatus was designed and constructed in a cryostat in order to qualify the performance of high-voltage (HV) insulation on a mockup ITER TF feeder S-bend (S-shaped) busbar after mechanical fatigue tests at room temperature and low temperature, respectively. The force generator was designed and developed with a hydraulic cylinder as a source of cyclic load. The traveling distance of the hydraulic cylinder can be adjusted between 10 and 100 mm in order to meet different displacement requirements. The fatigue tensile load is transmitted by a reciprocating ball-end shaft at the free end of the S-bend. Welded diaphragm bellows was applied as a flexible vacuum envelope for the transmission rod. The fatigue test displacement and the stretching frequency were set according to the theoretical analysis result. The leakage current in the hipot test of the S-bend busbar after thermal and mechanical cycles was 13.7 μA at 30-kV dc, less than the ITER requirement of 60 μA. The integrated test apparatus has been fully commissioned and is ready for the qualification tests of the HV insulation of the ITER S-bend busbar affected by mechanical and thermal fatigue loads.

Multi-beam linear accelerator EVT

A novel electron multi-beam accelerator is presented. The accelerator, short-named EVT (Electron Voltage Transformer) belongs to the class of two-beam accelerators. It combines an RF generator and essentially an accelerator within the same vacuum envelope. Drive beam-lets and an accelerated beam are modulated in RF modulators and then bunches pass into an accelerating structure, comprising uncoupled with each other and inductive tuned cavities, where the energy transfer from the drive beams to the accelerated beam occurs. A phasing of bunches is solved by choice correspond distances between gaps of the adjacent cavities. Preliminary results of numerical simulations and the initial specification of EVT operating in S-band, with a 60kV gun and generating a 2.7A, 1.1MV beam at its output is presented. A relatively high efficiency of 67% and high design average power suggest that EVT can find its use in industrial applications.

Investigation of Warpage Behavior of Silicon Semiconductor on a Silicon - Adhesive - Ceramic Integrated Structure at Cryogenic Temperatures--STUDENT BEST PAPER $1500

Silicon wafer is widely used as a base material for readout integrated circuit (ROIC) of infrared sensors. There is a heterogeneous component assembly with the silicon wafer material. Warpage behavior of silicon readout integrated circuit is dependent on the material properties and geometrical properties of the integrated materials. Warpage behavior of the silicon material directly affects the warpage of the sensor which must be operated at cryogenic temperatures (around 80 K). There exist a great difference between the operation and storage temperatures (~ 300 K) of these devices. When different materials with different thermal expansion coefficients are used such devices, thermal stresses develop on the components and surface deformations named as “warpage” are observed on the materials. The measurement of excessive thermal stress or warpage formation on the sensor is vital for reliability issues. In this study, warpage behavior of silicon material is examined in the temperature range from room temperature down to cryogenic temperatures (80 K) and under vacuum conditions less than 1 mTorr. The silicon ROIC is integrated on an alumina ceramic by applying an adhesive between these two layers. After the application of the adhesive material, the integration of the silicon to ceramic is accomplished using a pick and place equipment. The warpage of silicon wafer is measured by a Fizeau Laser Interferometer which uses a 633 nanometer wavelength He – Ne laser. The warpage of the diced silicon is measured before and after the integration to the ceramic so that the effect of curing process of the adhesive is determined after which, the warpage of the silicon material is measured at atmospheric pressure and also under vacuum conditions at room temperature. The warpage of silicon material on the integrated structure is measured with increments of 10 K for both cooling from room temperature to 80 K and heating from 80 K to room temperature. In order to reach cryogenic temperatures, a liquid nitrogen cooled vacuum envelope is utilized. The envelope has an optical flat (made of BK7 material and 2.35 mm thick) for interferometric measurements. There are a total of five integrated structures for the warpage measurements. At each of these structures, the silicon material thickness is different. Comparison of the warpage behavior of the silicon material for different thicknesses are performed. Thermal cycling between room temperature and 80 K is also performed up to 5 cycles for each of the integrated structures. Thermal cycling effect on silicon warpage is discussed for silicon - alumina - adhesive trimaterial assembly structure.

Theoretical analysis of a novel, portable, CPC-based solar thermal collector for methanol reforming

In this paper we propose a new solar thermal collector which is suitable for providing heat for endothermic chemical reactions. The particular reaction that is considered is hydrogen production by menthol reforming. The design presented here is based on CPC (compound parabolic concentrator) technology, which can operate without complicated (and costly) tracking systems. It consists of a small, double-sided selective surface receiver in a vacuum envelope comprised of CPC reflectors and a glass aperture cover. Heat absorbed by the receiver is transferred to the working fluid inside micro tubes where the chemical reaction is occurring. This design, to the best of our knowledge, represents the first time that a vacuum package (which creates thermal concentration) has been combined with a CPC-based optical concentrator for thermo-chemical applications. This collector design can convert over 78% of incident solar radiation into heat with a concentration ratio of 1.75, allowing for a high solar-to-fuel efficiency in chemical reactions. This study establishes both the optical and thermal models needed to predict the performance of this type of collector. The results show that the collector stagnates at very high temperatures (up to 600°C), and can provide solar heat in the form of a small collector for a variety of portable applications – e.g. methanol reforming that requires temperatures of around 250°C.

Realistic filter cavities for advanced gravitational wave detectors

The ongoing global effort to detect gravitational waves continues to push the limits of precision measurement while aiming to provide a new tool for understanding both astrophysics and fundamental physics. Squeezed states of light offer a proven means of increasing the sensitivity of gravitational wave detectors, potentially increasing the rate at which astrophysical sources are detected by more than 1 order of magnitude. Since radiation pressure noise plays an important role in advanced detectors, frequency-dependent squeezing will be required. In this paper we propose a practical approach to producing frequency-dependent squeezing for Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and similar interferometric gravitational wave detectors. This work focuses on ``realistic filter cavities'' in the sense that optical losses in the filter cavity and squeezed light source consistent with current technology are considered. The filter cavity solution proposed for Advanced LIGO is ``practical'' in that it considers the nonquantum noise and readout scheme of the interferometer and a potential implementation geometry in the Advanced LIGO vacuum envelope.

Gas Permeation Measurements on Low Temperature Cofired Ceramics

Commercial low temperature cofired ceramic (LTCC) technology is established in microelectronics and microsystems packaging, multichip and radio frequency (RF) modules, and sensors. The ability to combine structural considerations with embedded traces and components using laminated glass-ceramic tapes has created solutions to unconventional packaging requirements of micro-electro-mechanical systems (MEMS) devices. Many MEMS devices such as resonators are very sensitive to pressure and require packaging in a vacuum environment. Attaining and maintaining desirable pressure levels in sealed vacuum packages requires knowledge of the permeation characteristics of the vacuum envelope and the sealing materials. An experimental system to measure the time dependent gas permeation through LTCC at temperatures from room temperature to 500°C has been developed. This system utilizes a membrane technique in which a gas is allowed to permeate through a test sample, held at a constant temperature, into a high vacuum chamber where it is detected using mass spectrometry. The gas permeation value is determined from the steady state gas flux through the sample. The gas diffusivity and solubility in the material were calculated using data from the time dependent approach to the steady state condition. The gas-solid permeation data for helium through DuPont 951 LTCC is presented and compared to the permeation through other common vacuum envelope materials such as glasses and high-purity alumina ceramics. Application of the permeation data to the prediction of vacuum levels inside typical LTCC packaging is discussed. This data can further be utilized in designs to create LTCC packages that meet specific pressure/time operating requirements.