Vacuum Port Research Articles

Optimal vacuum port placement in vacuum-assisted composite manufacturing for leakage detection and localization: a hierarchical optimization approach

Optimal vacuum port placement in vacuum-assisted composite manufacturing for leakage detection and localization: a hierarchical optimization approach

Design and Implementation of an Energy Selector for Laser-Accelerated Protons

Highly intense bunches of protons and ions with energies of several MeV/u can be generated with ultra-short laser pulses focused on solid targets. In the most common interaction regime, target normal sheath acceleration, the spectra of these particles are spread over a wide range following a Maxwellian distribution. We report on the design and testing of a magnetic chicane for the selection of protons within a limited energy window. This consisted of two successive, anti-parallel dipole fields generated by cost-effective permanent C-magnets with customized configuration and longitudinal positions. The chicane was implemented into the target vessel of a petawatt laser facility with constraints on the direction of the incoming laser beam and guidance of the outgoing particles through a vacuum port. The separation of protons and carbon ions within distinct energy intervals was demonstrated and compared to a ray tracing code. Measurements with radiochromic film stacks indicated the selection of protons within [2.4, 6.9] MeV, [5.0, 8.4] MeV, or ≥6.9 MeV depending on the lateral dispersion. A narrow peak at 4.8 MeV was observed with a time-of-flight detector.

Anaerobic cryoEM protocols for air-sensitive nitrogenase proteins.

Single-particle cryo-electron microscopy (cryoEM) provides an attractive avenue for advancing our atomic resolution understanding of materials, molecules and living systems. However, the vast majority of published cryoEM methodologies focus on the characterization of aerobically purified samples. Air-sensitive enzymes and microorganisms represent important yet understudied systems in structural biology. We have recently demonstrated the success of an anaerobic single-particle cryoEM workflow applied to the air-sensitive nitrogenase enzymes. In this protocol, we detail the use of Schlenk lines and anaerobic chambers to prepare samples, including a protein tag for monitoring sample exposure to oxygen in air. We describe how to use a plunge freezing apparatus inside of a soft-sided vinyl chamber of the type we routinely use for anaerobic biochemistry and crystallography of oxygen-sensitive proteins. Manual control of the airlock allows for introduction of liquid cryogens into the tent. A custom vacuum port provides slow, continuous evacuation of the tent atmosphere to avoid accumulation of flammable vapors within the enclosed chamber. These methods allowed us to obtain high-resolution structures of both nitrogenase proteins using single-particle cryoEM. The procedures involved can be generally subdivided into a 4 d anaerobic sample generation procedure, and a 1 d anaerobic cryoEM sample preparation step, followed by conventional cryoEM imaging and processing steps. As nitrogen is a substrate for nitrogenase, the Schlenk lines and anaerobic chambers described in this procedure are operated under an argon atmosphere; however, the system and these procedures are compatible with other controlled gas environments.

Numerical Study of Thin-Walled Polymer Composite Part Quality When Manufactured Using Vacuum Infusion with Various External Pressure Controls.

The article presents the results of modeling various modes of vacuum infusion molding of thin-walled polymer-composite structures of arbitrary geometry. The small thickness of the manufactured structures and the fixation of their back surface on the rigid surface of the mold made it possible to significantly simplify the process model, which takes into account the propagation of a thermosetting resin with changing rheology in a compressible porous preform of complex 3D geometry, as well as changes in boundary conditions at the injection and vacuum ports during the post-infusion molding stage. In the four modes of vacuum-infusion molding studied at the post-infusion stage, the start time, duration and magnitude of additional pressure on the open surface of the preform and in its vacuum port, as well as the state of the injection gates, were controlled (open-closed). The target parameters of the processes were the magnitude and uniformity of the distribution of the fiber volume fraction, wall thickness, filling of the preform with resin and the duration of the process. A comparative analysis of the results obtained made it possible to identify the most promising process modes and determine ways to eliminate undesirable situations that worsen the quality of manufactured composite structures. The abilities of the developed simulation tool, demonstrated by its application to the molding process of a thin-walled aircraft structure, allow one to reasonably select a process control strategy to obtain the best achievable quality objectives.

Preform Porosity and Final Thickness Variability Prediction after Controlled Post-Infusion External Pressure Application with the FEA Model

One of the reasons for the insufficiently wide use of the low-cost and low-labor vacuum infusion process in the production of polymer composite structures is the uneven distribution of pore pressure, porosity, and preform thickness at the final stage of filling the preform with liquid resin. This article presents the results of a theoretical study of the factors that govern the effectiveness of the known method of external controlled pressure on the preform in order to eliminate or significantly reduce the listed disadvantages. The study includes an analysis of scenarios for the implementation of this method, which differ in the state of the resin gate when external pressure is applied to the preform (open or closed), as well as the pressure in the vacuum vent (maintained unchanged or gradually increased to atmospheric pressure). The research tool was a finite element (FE) model that simulates resin flow according to Darcy’s law and controlled boundary conditions for a thin-walled rectangular preform. The results of the study confirmed the effectiveness of the process in achieving a more uniform distribution of porosity and preform thickness and are good qualitative agreement with the results of borrowed experiments, revealing the conditions for the occurrence of critical situations associated with the possible penetration of air into the preforms through the vacuum port and the reverse flow into the preform of the resin previously forced out through the resin gate.

Computational methods for leakage localisation in a vacuum bag using volumetric flow rate measurements

The localisation of leakages during the vacuum bagging process of a composite is currently time intensive and reliant on human labour. The purpose of this article is to explore four computational methods for leakage localisation using volumetric flow rate (VFR) data to increase the automation of the process. The data used in this article is based on experiments on a square vacuum bag with four vacuum ports. The first method is based on potential flow theory to simulate the flow. In the second method, numerical regression was applied to find a relation between the VFRs and port-leakage distances. The third method consisted of calculating the fractional VFRs for every point on a grid and finding the grid point whose values most closely correspond to the observed fractional VFRs. The last method involved training a machine learning algorithm with experimental data. After the development of the methods, their performance was tested over the entire single-leakage dataset and compared. The results were in the same order of magnitude for all methods, with an area of 10^5 mm^2 for the 95% confidence interval and a distance of 10^2 mm for the average error. Further research is required for application to different vacuum bag shapes and multiple leakages cases. The method with the highest adaptability and performance is the method based on potential-flow theory. Machine learning and the potential-flow method is further applicable to multiple leakage localisation.

Activation analysis and radwaste assessment of CFETR

The materials in the fusion system will be activated by the neutrons generated from D-T fusion reactions, causing the material with activity and decay heat at a variety level among the system. Predicting the amount of radwaste produced in the Chinese Fusion Engineering Testing Reactor (CFETR) and the time-evolution feature of the radwaste is of great importance to the minimization of waste and determine the management strategy. The purpose of this paper is to minimize the quality and quantity of the activated solid waste as low as reasonably achievable via source control, recycling and reuse, clearance, optimization of the management at the designing phase of CFETR. A detailed 3D model for CFETR is created to calculate the neutron spectra and fluxes of all non-void cells of the model. The inventory calculation for each cell with the given irradiation scenario and the cooling scheme was then carried out with FISPACT-II. The extensive calculation, data analysis, and post-processing are performed using a data processing code to calculate the component averaged activation responses and the waste classifications. The results suggest that the in-vessel materials exposed to high level neutron fluxes can hardly meet the clearance and low-level waste requirements, but they can be recycled with an advanced remote handling system shortly after shutdown or a conservative remote handling system after temporary storage within 100 years. The vacuum vessel, port plug, cryostat, and coils can be recycled with a conservative remote handling system with temporary storage. Especially, the port plug, cryostat, and central solenoid are clearable with temporary storage of 100 years. The influence of the operation time of in-vessel components on the radwaste severity and quantity is also evaluated. The severity of the radwaste increases when the operation time increases from 1000 to 3000 MWY, then decreasing with operation times longer than 3000 MWY. The detailed operation plan should be determined with comprehensive consideration of the important factors, including the influence on the radwaste severity. The allowed impurity level is also estimated, finding that the Uranium in the breeding zone and the SS316L used in divertor should be blamed for the intermediate-level waste production of blanket and divertor.

Multi-Criteria Decision Approach to Design a Vacuum Infusion Process Layout Providing the Polymeric Composite Part Quality.

The increasingly widespread use of vacuum assisted technologies in the manufacture of polymer-composite structures does not always provide the required product quality and repeatability. Deterioration of quality most often appears itself in the form of incomplete filling of the preform with resin as a result of the inner and outer dry spot formation, as well as due to premature gelation of the resin and blockage of the vacuum port. As experience shows, these undesirable phenomena are significantly dependent on the location of the resin and vacuum ports. This article presents a method for making a decision on the rational design of a process layout. It is based on early forecasting of its objectives in terms of quality and reliability when simulating its finite element model, on the correlation analysis of the preliminary and final quality assessments, as well as on the study of the cross-correlation of a group of early calculated sub-criteria. The effectiveness of the proposed method is demonstrated by the example of vacuum infusion of a 3D thin-walled structure of complex geometry.

Optimization of liquid resin infusion process (LRI) using finite element simulation software

Infusion processes as LRI (Liquid Resin Infusion) can lead to a significant cost reduction but are not yet so widespread in aeronautical applications. Some of its advantages are: no need of autoclave, lower costs of materials, and the possibility of fabricating integrated structures that reduce the number of joints. However this process still presents some drawbacks such as the need to apply the "Test-Error" method or availability of extensive experience in the design of structures. The risk and cost associated with the infusion process is high, so the industry tends to use more conservative designs or adopt other less competitive alternative technologies and materials. For this reason, a simulation tool is essential to optimize the LRI process. In this work, the optimization and validation of a demonstrator of a wing box of an aircraft has been carried out using the PAM-COMPOSITES simulation software. Firstly, a geometric study and discretization of model has been carried out, secondly, the parameters that govern the process have been defined, and finally an analysis and validation of results have been carried out by means of a experimental infusion of the demonstrator. The obtained results have allowed us to control manufacturing times, improve injection and vacuum ports, and predict dry zones and front flow velocity. Simulations have allowed us to optimise the LRI process of the demonstrator, thus giving continuity to other studies on the viability of the infusion processes in primary structures in the aeronautical sector.

Evaluation of the vacuum infusion process objectives at the early stages of computer simulation

Increasing the quality and reliable reproducibility of large-size composite structures molding using the vacuum infusion method, which is gaining popularity in various industries, is achieved in practice through numerous tests by try and errors that require significant costs and time. The purpose of these tests is to determine the layout of the ports for the resin injection and vacuum supply, as well as the temperature regime that ensures the absence of isolated non-impregnated zones, the minimum porosity and the required reinforcement volume fraction in the composite. The proposed approach removes the simplifying assumptions used in commercial software for modeling the process, which reduce the accuracy of reconstruction of its dynamics and the sensitivity to the formation of unrepairable defects such as dry spots. It involves multiphysics modeling of resin filling in a porous preform by describing the resin front dynamics by the phase field equation, pressure distribution in an unsaturated porous medium by the Richards equation, the evolution of the degree of cure by the convection / diffusion / thermokinetics equation, and thermal processes by the heat transfer equation using modified models of viscosity, the diffusion coefficient of the degree of cure, the boundary condition for the vacuum port. To reduce the finite element computation time of the investigated variants of the process, which is necessary for its computer optimization, the predictive partial sub-criteria were used, which give a reliable prediction before the beginning of the resin gel and solidification. Due to this, a gain in computation time is 30-50% with a significant prediction accuracy of quality objectives and the presence of possible defects.

МОДЕЛИРОВАНИЕ ПРОЦЕССОВ ВАКУУМНОЙ ИНФУЗИИ В ПРОИЗВОДСТВЕ КРУПНОГАБАРИТНЫХ КОМПОЗИТНЫХ КОНСТРУКЦИЙ

The article presents the technology of computer simulation of the vacuum infusion processin the production of large-sized polymeric composite structures, which is attracting more andmore attention in the aircraft industry, due to the ease of implementation and the relatively lowcost of production preparation. The difficulty of industrial implementation of the process and ensuringthe required quality is due to its high sensitivity to modes - temperature, vacuum pressureand the layout of the vacuum ports and resin injection. The purpose of the developed methodologyfor computer modeling of the process with the possibility of its subsequent optimization is to excludethe currently used lengthy and very expensive trial and error method when working out thetechnology. The proposed mathematical model of the process linking the equation of the phasefield, which reconstructs the interface between the resin and the void region of the preform, theRichards equation for the propagating viscous fluid in an unsaturated porous medium, the thermalkinetics of the resin and thermal conductivity, is implemented in the environment of a finite elementpackage. Computer implementation of the model provides an accurate reconstruction of thedynamics of the front of the propagating resin in a porous preform, the possibility of the emergenceand localization of non-impregnated zones of the molded structure, thereby eliminating theformation of irreparable defects. The results obtained demonstrate the ability of the developedtechnique to ensure the stability of the quality of the produced composite structures with increasedrequirements for the continuity of its microstructure and its structural strength.

Tangential hard x-ray diagnostic array on the EXL-50 spherical tokamak.

A tangential hard x-ray (HXR) diagnostic on the newly constructed ENN XuanLong-50 (EXL-50) spherical tokamak for fast electron emission studies is presented. The HXR detection system consists of a symmetrical CdZnTe semiconductor detector array with a spectral sensitivity range of 20-300 keV. 25 channels have been designed on the 270° horizontal vacuum port with 12 sight lines to observe the forward emission, 12 sight lines to observe the backward emission of fast electrons, and 1 for viewing the central. Currently, ten channels have been in operation in the EXL-50 experiments. The systems are designed to measure the x-ray spectra for the estimation of fast electron temperature and electron velocity distribution in the EXL-50 experiment, which will be useful for understanding the dynamics of fast electrons generated by electron cyclotron resonance heating, for plasma instability and transport studies and for the analysis of plasma heating efficiency.

Cryostorage tank failures: temperature and volume loss over time after induced failure by removal of insulative vacuum.

To determine liquid nitrogen evaporation rates of intact liquid nitrogen storage tanks and tanks with their vacuum removed. Donated storage tank performance (LN2 evaporation) was evaluated before and after induced vacuum failure. Vacuum of each tank was removed by drilling through the vacuum port. Temperature probes were placed 2 in. below the bottom of the styrofoam cap/plug, and tanks were weighed every 3 h. Evaporation rate and time from failure to the critical temperature was determined. Storage tanks with failed vacuum have a much higher evaporation rate than those with intact vacuum; evaporation rates increased dramatically within 3 to 6 h in the smaller tanks, and time to complete depletion varied according to starting LN2 volume. Tanks with storage racks/specimens may have altered evaporation profiles compared to tanks without. Locating temperature probes 2 in. below the styrofoam cap/plug suggests that for most applications, alarms would sound approximately 1 h prior to reaching the critical warming temperature, approximately - 130 °C. External signs of vacuum loss were dramatic: vapor, frost, and audible movement of air. For the first time, we have data on how liquid nitrogen storage tanks behave when their vacuum is removed. These findings are conservative; each lab must consider starting volume, tank size/capacity, function (storage or shipping), age, and pre-existing evaporation behavior in order to develop an emergency response to critical tank failure. Times to complete failure/evaporation and critical warming temperature after vacuum loss are different; these data should be considered when evaluating tank alarm systems.

Do remote boundary conditions affect photodetection?

ABSTRACTWe study the photocurrent statistics in a homodyne setup with a mirror in the vacuum port. Conventional photodetection theory predicts a modulation of the photocurrent noise due to the mirror. We show that the mirror changes the quantum efficiency of the detector and affects both the mean and noise of the photocurrent. We discuss detector design parameters that will enhance this effect.

An optimization of water transport through polyurethane silica-nanocomposite membrane

Analysis of water transport through polyurethane silica nano-composite membranes were performed by numerical simulation and experiment. Simulation work was performed using a finite element analysis (FEA) software, COMSOL Multiphysics. Experimental work was performed to validate the simulation model. Through simulation we suggest the minimum membrane-to-membrane distance for stacked membranes to be 2-mm to avoid the membrane concentration polarization effect. The method used to create a concentration gradient between the membrane feed side (humid air) and the membrane permeate side (connected to vacuum) involved with creating a pressure gradient. Water vapor pressure gradient creates a concentration gradient which drives water vapor molecules to diffuse from the membrane feed side to the membrane permeate side. Different membrane configurations including rectangular parallel membranes, perforated cylinder with circular membranes, perforated group of cylinders with circular membranes, and perforated cylinder with curved rectangular membranes were compared in terms of water vapor removal from humid air while connecting all membrane configurations to 47-mm vacuum port. The parallel 22 membranes exhibited maximum water removal. Based on the total membrane area, water vapor removal was maximized at the maximum membrane effective area in contact with humid area. The maximum total water removal was obtained for the 11 cassettes with 22 rectangular membranes with a value of 142 g/(m2·s) while the relative humidity dropped from 60% at the duct inlet to 25.6% at the duct outlet.

Phased array ultrasonic test of vertical defect on butt-joint weld of CFETR vacuum vessel port stub

The CFETR vacuum vessel (VV) main-body and ports are connected via port stub. For the benefits of deep penetration and small deformation, electron beam welding (EBW) was selected for port stub butt-joint welding. Unacceptable defects such as vertical crack, non-fusion and non-penetration might appear in this kind of large depth-to-width ratio weld.In this paper, the phased array ultrasonic testing (PAUT) method was introduced. Reference blocks with artificial defects of different lengths and heights were fabricated, and then tested by 2.5 MHz 64el dual element matrix array probe and 2.25 MHz 64el single linear array probe. Detection sensitivity of 0.2 mm in width was achieved. In the end, the above probes were successfully applied on the detection of the EBW testing blocks with natural defects. The testing results of reference and testing blocks implied the full capability of the selected probes.

Lead shutter for the IFMIF LIPAc accelerator

The International Fusion Materials Irradiation Facility (IFMIF) aims to provide an accelerator-based, D-Li neutron source to produce high energy neutrons at sufficient intensity and irradiation volume for DEMO (Demonstration Fusion Power Plant) materials qualification. As part of the Broader Approach agreement between Japan and EURATOM, the goal of the IFMIF/EVEDA project is to work on the engineering design of IFMIF and to validate the main technological challenges which, among a wide diversity of hardware includes the LIPAc (Linear IFMIF Prototype Accelerator), a 125 mA continuous wave deuteron accelerator up to 9 MeV mainly designed and manufactured in Europe.The LIPAc beam is stopped in a copper cone involving a high production of neutron and gamma radiation and activation of its surface. A lead shutter has been designed to shield against the gamma radiation coming from the copper cone through the beam tube when the beam is off, in order to allow access inside the accelerator vault. The lead shutter is located in a multipurpose chamber that also contains a scraper and two vacuum ports. The function of the scraper is to protect the last part of the beam tube in case of abnormal beams.The requirements imposed on the lead shutter chamber include the motion of the lead shutter to locate it in open (beam on) and closed position (beam off), resistance to the radiation environment, vacuum and leak tightness, alignment capabilities of the scraper and leak tightness of its cooling circuit. In this article the radioprotection calculations demonstrating the shutter performance are presented and the mechanical system of the lead shutter and the layout of the different elements contained in the chamber are described, along with their functions.

Generation of squeezed states at low analysis frequencies

Squeezed states are important sources in quantum physics, which have potential applications in fields such as quantum teleportation, quantum information networks, quantum memory, and quantum metrology and precise measurements. For our interest, the squeezed vacuum will be used in the quantum-enhanced optical atomic magnetometers, filling the vacuum port of the probe beam to improve measurement sensitivity. Based on the sub-threshold optical parametric oscillator (OPO) with PPKTP crystal, the squeezed vacuum at rubidium D1 line of 795 nm is obtained. In our work, we investigate the noise sources in an OPO system. By carefully controlling the classical noise source, the squeezing band extends to the analysis frequency of 2.6 kHz. The flat squeezing trace is 2.8 dB below the shot noise limit. In our work, we focus on the difference between the squeezing results at the analysis frequency of kilohertz regime at two different wavelengths, 1064 nm and 795 nm. The difference mainly comes from the absorption of 795 nm laser and its second harmonic at 397.5 nm in crystal (397.5 nm laser is at the edge of transparent window of PPKTP crystal that has an absorption index much higher than at other wavelength). The absorption induced nonlinear loss and thermal instability greatly affect the squeezing results, which is discussed in our work. Squeezing level at 795 nm is worse than at 1064 nm due to the above-mentioned factors. Noise coupling to the detection system limits the squeezing band. In the audio frequency band, squeezing is easily submerged in roll-up noises and the measured squeezing level is limited. Two factors limit the obtained squeezing:the technical noise induced in the detection and the squeezing degradation by the noise coupling of the control beams. In experiment, we carefully control the classical noise at analytical frequency of kilohertz by means of a vacuum-injected OPO, a counter-propagating cavity locking beam with orthogonal polarization, low noise homodyne detector, stable experimental system and quantum noise locking method for squeezing phase locking. Firstly, to preclude the classical noise from coupling the laser source, we use the vacuum injected OPO. A signal beam helps optimize the parametric gain and is blocked in the squeezing measurement process. In order to maintain the OPO, a counter-propagating beam with orthogonal polarization is used for locking the cavity. Then, a low noise balanced homodyne detector with a common-mode rejection ratio of 45 dB helps improve the audio frequency detection. Finally, the quantum noise locking provides a method to lock the relative phase between the coherent beam and the squeezed vacuum field. With the combination of these technical improvements, a squeezed vacuum of 2.8 dB is obtained at the analysis frequency of 2.6-100 kHz. The obtained squeezing level is mainly limited by the relatively large loss in OPO, which is induced by ultra-violet absorption in PPKTP crystal. The generated squeezed field is used to reduce the polarization noise of probe beam in an optical magnetometer, in order to increase detection sensitivity.

Internal Model Control of a Domestic Microwave for Carbon Composite Curing

This paper outlines the conversion of a domestic microwave oven for use in composite curing applications. It compares several strategies for temperature control. The converted oven has vacuum ports, connectors, and fiber optic thermocouple sensors. Experimental data are provided for each control strategy based on a $200~\text {mm} \times 200$ mm eight-ply prepreg laminate. The degree of cure is established for the test samples by thermal analysis techniques. Multiphysics simulation is used to model the electromagnetic and heating effects in the system, and a common and inexpensive method of approximating the available microwave power is used. The low cost of the microwave components and the ease of conversion are desirable characteristics in this application.

Design and fabrication of a new compound probe for plasma flux measurement in IR-T1 tokamak

A new compound probe is designed, built, and installed on an IR-T1 tokamak to flow measurements in the plasma edge region. The first results of using this probe on the IR-T1 tokamak are presented. The plasma parameters such as plasma current, loop voltage, floating potential, ion and electron saturation currents, electron temperature, plasma potential, and plasma flow velocities are measured in this work. The results show that the electron temperature and the plasma potential in the edge area are 14 eV and 44 V, respectively. The results indicate that the mean value of a parallel Mach number is 0.5 while the mean value of a perpendicular Mach number is almost zero. The large parallel flow velocity (about 17 km/s) and the negligible perpendicular flow velocity are also seen in this work. The most important advantage of using this compound probe is that it can not only save space and vacuum ports but also measure more physical quantities at the same time, contributing to further physical analysis.