scholarly journals (ECS 234th) Fluid Flow and Current Distribution during Pulse-Reverse Electropolishing of Niobium Superconducting RF Cavities

2018 ◽  
Author(s):  
Brian Skinn ◽  
Stephen Snyder ◽  
Tim Hall ◽  
Maria Inman ◽  
Jennings E. Taylor
Keyword(s):  
Fluid Flow ◽  
Oxide Film ◽  
Current Distribution ◽  
Material Removal ◽  
High Speed Photography ◽  
Actual Distribution ◽  
Current Distributions ◽  
Pulse Reverse ◽  
Srf Cavities ◽  
Passive Materials

The International Linear Collider (ILC) is a 200–500 GeV center-of-mass linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency accelerating technology. This installation will require ~16,000 RF superconducting cavities operating within two linear accelerators at near absolute zero [[1]]. These SRF cavities are fabricated from pure Nb; to take full advantage of the Nb superconducting properties, the inner surface must be polished to a microscale roughness, and cleaned to be free of impurities that could degrade performance. Current methods use high viscosity electrolytes containing hydrofluoric acid, which is not conducive to low-cost, high volume manufacturing and is potentially harmful to workers. Faraday is developing an electropolishing process for niobium SRF cavities, based on a new and evolving paradigm of non-viscous dilute acid processing, enabled by a pulse-reverse electric field. Based on our understanding to date [[2]], we have speculated that the process works via oxide film formation controlled during a designed anodic pulse, followed by an off-time to remove heat and waste byproducts, followed by a cathodic pulse that removes the oxide film from the surface. This cycle is repeated many times per second, effectively removing niobium. The waveform design is such that the niobium is preferentially removed from the peaks on the surface, thus smoothing the surface.This talk will describe two recent efforts undertaken to improve understanding of various factors influencing the uniformity and speed of pulse-reverse electropolishing of niobium SRF cavities. The first is a flow study performed in a transparent plastic model of a single-cell (single-bell) cavity, to examine the flow dynamics in the absence and presence of an axisymmetric baffle fixed to the rod counter-electrode within the cavity bell. High-speed photography clearly shows the presence of a slow-moving eddy in the equatorial region of the bell, which is appreciably reduced in size when the baffle is present. Furthermore, rapid clearance of electrolysis gases and niobium oxide precipitates from the bell is expected to be strongly dependent on a proper configuration of flow throughout the bell.The second effort to be discussed comprises multiphysics modeling of the actual distribution of material removal in the EP process, as a function of position within the cavity. Modeling of EP of passive materials is complex, as numerous coupled phenomena must be accounted for, including: primary, secondary and tertiary current distributions; multi-phase effects, including fluid flow; and oxide formation/removal at the working surface. The strongest effects appear to be the primary and secondary current distributions, along with the surface oxide dynamics, inclusion of these physics (or semi-empirical approximations thereof) provides a significantly improved match between the model to the experimentally observed distribution of material removal, as compared to simulations incorporating only the primary current distribution.[1] http://www.linearcollider.org/ILC/What-is-the-ILC/The-project[2] M. Inman et al “Electropolishing of Passive Materials in HF-Free Low Viscosity Aqueous Electrolytes, J. Electrochem. Soc., 160 (9) E94-E98 (2013).

Experimental Research of Cluster Magnetorheological Finishing on Anodic Oxide Film of Aluminum

2016 ◽  
Vol 874 ◽  
pp. 158-166
Author(s):  
Run Chen ◽  
Jia Bin Lu ◽  
Qiu Sheng Yan ◽  
Xiao Lan Xiao ◽  
De Yuan Li
Keyword(s):  
Surface Roughness ◽  
Oxide Film ◽  
Material Removal Rate ◽  
Material Removal ◽  
Removal Rate ◽  
Anodic Oxide ◽  
Anodic Oxide Film ◽  
Magnetorheological Finishing ◽  
Machining Time ◽  
Good Surface

The polishing experiments of anodic oxide film of aluminum were performed to research the influence of polishing parameters on the surface roughness and material removal rate in the cluster magnetorheological finishing (MRF). Experimental results demonstrate that a mirror effect can be reached when the anodic oxide film of aluminum is polished by the Cluster MRF. The roughness of the workpiece surface after polishing for 15 min is decreased from Ra 0.575μm to Ra 4.13nm and the material removal rate is 0.653mg/min. With the extension of the polishing time, the surface roughness rapidly declines at first and then slowly decreases. When the machining time is more than 15min, the anodic oxide film of aluminum is easily worn out, resulting in a sharp increase in the surface roughness. The machining gap between the workpiece and the polishing plate influences the polishing effect of anodic oxide film of aluminum. With the increase of the machining gap, the material removal rate decreases and the surface roughness increases. A good surface quality can be got at the machining gap of 1.1mm. The type and size of abrasive particles will directly affect the polishing effect of anodic oxide film of aluminum, and when using CeO2 abrasive with the particle size of W3, a higher material removal rate and a smaller surface roughness can be obtained.

scholarly journals Influence of Discharge Gap On Material Removal and Melt Pool Movement in EDM Discharge Process

2021 ◽  
Author(s):  
Xiaoming Yue ◽  
Ji Fan ◽  
Qi Li ◽  
Xiaodong Yang ◽  
Zuoke Xu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Material Removal ◽  
High Speed ◽  
Electrical Discharge Machining ◽  
External Pressure ◽  
High Speed Photography ◽  
Discharge Process ◽  
Melt Pool ◽  
Discharge Gap ◽  
Gap Width

Abstract In electrical discharge machining (EDM), gap control is the key to stable processing; the discharge gap plays a significant role in EDM. To determine the influence of the discharge gap on material removal and melt pool movement, which are two fundamental issues in EDM, high-speed photography and molecular dynamics (MD) simulations were used to study the discharge process. Research results demonstrate that the discharge gap has a significant influence on material removal during the discharge process. A smaller gap width produces more and larger removed materials. The influence mechanism of the gap width on material removal is explained as follows. A smaller gap width produces discharge plasma with a smaller diameter and greater heat flux. Discharge with a greater heat flux generates more material removed during the discharge process. In addition, a smaller gap width and greater heat flux produce a stronger interaction of metal vapor jets, generating a stronger shear force acting on the melt pool. The discharge gap also influences the movement of the melt pool and the final topography of the discharge crater through external pressure acting on the melt pool. Smaller gap width produces greater external pressure acting on the melt pool, generating a bowl-shaped melt pool and a discharge crater with a depression in the center and a bulge around the edge. A larger gap width produces less external pressure acting on the melt pool, generating a flat melt pool and a discharge crater with swelling in the center and a depression around the edge.

scholarly journals (ECS 236th) Multiphysics Modeling of the Tertiary Current Distribution in Pulse/Pulse-Reverse Electrochemical Processing of Microstructured Workpieces

2020 ◽  
Author(s):  
Brian Skinn ◽  
Alan C West
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Current Distribution ◽  
Surface Finishing ◽  
Workpiece Surface ◽  
Structured Surfaces ◽  
Electrochemical Processes ◽  
Pulse Reverse ◽  
Primary Current ◽  
Primary Current Distribution

The physical phenomena governing the current distribution on an electrode of arbitrary shape are typically categorized as falling into primary, secondary, and/or tertiary effects. Primary current distribution effects are defined by the geometry of the system and the electrical properties of the relevant materials, whereas secondary and tertiary effects incorporate additional position-dependent polarizations that respectively arise from electrochemical-kinetic and mass-transfer/concentration physics. In industrial electrochemical processes, the uniformity of the current distribution across a workpiece is of vital concern. In electrodeposition processes, for example, it is usually desirable for the deposited metal to be as uniformly distributed as possible, regardless of the form of the workpiece. Conversely, in electropolishing processes, it is critical to focus the current density onto the tops of asperities on the workpiece surface, in a highly non-uniform fashion, in order to minimize material removal irrelevant to the goal of decreased surface roughness. In general, the primary current distribution leads to the most non-uniform current distribution possible for a given geometry, from which the secondary and tertiary effects tend to have varying degrees of a “leveling” effect, leading to a comparative increase in processing uniformity.In electrodissolution processes, saturation of the dissolved metal at the workpiece surface is an important mechanism by which the tertiary current distribution effects influence practical electrochemical processes. This saturation phenomenon leads both to an increase in the local overpotential, via concentration polarization, and also has the potential to occlude locally a fraction of the workpiece exposed area due to the formation of insoluble precipitates. As noted, both of these effects tend to increase the uniformity of the resulting overall current distribution, and thus it is important to be able to predict, even if approximately, when a given process will be operating in this regime and to what extent the uniformity of the current distribution might be affected.This talk will summarize results from multiphysics simulations developed to represent this occluded-surface aspect of the tertiary current distribution, in addition to primary and secondary current distribution effects. These simulations incorporate pulse/pulse-reverse waveforms applied to workpieces with structured surfaces, in an attempt to approximate a surface finishing application of industrial relevance. In particular, focus was placed on simulating a “microprofile,” the scenario where surface structures have characteristic dimensions much smaller than the hydrodynamic boundary layer for mass transfer—this choice simplifies the modeling by obviating consideration of the macroscopic fluid dynamics of the system. The effect of pulse waveform parameters on the uniformity of the overall current distribution will be discussed, and simulation results will be shown illustrating the tendency of suitably-chosen waveform parameters to “collapse” toward the workpiece surface the subdomain of the boundary layer in which the local concentration of dissolved material oscillates significantly in response to the applied electric field.

scholarly journals Simulations of fluid flow, mass transport and current distribution in a parallel plate flow cell during nickel electrodeposition

2020 ◽  
Vol 873 ◽  
pp. 114359 ◽  
Author(s):  
Tzayam Pérez ◽  
Luis F. Arenas ◽  
Daniel Villalobos-Lara ◽  
Nan Zhou ◽  
Shuncai Wang ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Mass Transport ◽  
Current Distribution ◽  
Parallel Plate ◽  
Flow Cell ◽  
Nickel Electrodeposition

Method of Moment Determination of Current Distribution on Elements of Yagi-Uda Array

2017 ◽  
Vol 2 (9) ◽  
pp. 23-29
Author(s):  
Raji A. Abimbola
Keyword(s):  
Integral Equation ◽  
Method Of Moments ◽  
Current Distribution ◽  
Tangential Component ◽  
The Other ◽  
Induced Current ◽  
Method Of Moment ◽  
Current Distributions ◽  
Complex Coefficients

Presented in this paper is the numerical solution to the current distributions on two forms of Yagi-Uda antenna designs. One form consists of twelve elements while the other consists of fourteen elements. Employing method of moments technique in which the unknown current is expanded in terms of known expansion function and complex coefficients which are to be determined. It is demonstrated that, when the integral equation that expresses tangential component of an impressed field in terms of induced current on the elements of Yagi-Uda array is reduced into matrix form, the current distribution of interest becomes known. The profiles for the current distributions on elements of those arrays represented in graphical forms reveal that, the currents are symmetrical about the length of the element in each case. It is found that the highest magnitude of the current exists on the driven element. Furthermore, the characteristic profiles of the currents on elements of those arrays exhibit sinusoidal type of waveform and are largely similar when the frequencies of operation are 200MHz and 665MHz, respectively.

Corrosion of Pure Copper in Flowing Seawater Under Cavitating and Noncavitating Flow Conditions

1990 ◽  
Vol 112 (2) ◽  
pp. 218-224 ◽  
Author(s):  
R. J. K. Wood ◽  
S. A. Fry
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Incubation Period ◽  
Current Distribution ◽  
Material Removal ◽  
Pure Copper ◽  
Corrosion Current ◽  
Cavitating Flow ◽  
Flow Conditions ◽  
Working Section

This paper investigates the corrosion of pure copper in flowing seawater under cavitating and non-cavitating flow conditions. Experiments were conducted in a 10 mm × 20 mm working section with a 60 deg symmetrical wedge cavitation source. A copper sidewall specimen was held under potentiostatic control and its average corrosion current was measured under different flow conditions. To facilitate a detailed investigation of the flow field upon the current distribution over the specimen surface, further tests were carried out using a sidewall incorporating 24 mini-electrodes. Apart from some indication of cavity shielding, corrosion currents were little affected by the presence of cavitation during the incubation period (when no material was being removed). However, under similar cavitation conditions (but with material removal under steady-state erosion conditions) the corrosion currents approximately doubled.

scholarly journals Two Novel Information Entropy Indices for Analysis of the Eddy Current Distribution

Entropy ◽  
2018 ◽  
Vol 20 (9) ◽  
pp. 699 ◽  
Author(s):  
Guolong Chen
Keyword(s):  
Current Distribution ◽  
Eddy Current ◽  
Radial Direction ◽  
Current Sensor ◽  
Koch Curve ◽  
Intersection Angle ◽  
Current Distributions ◽  
Exciting Frequency ◽  
Exciting Coil ◽  
Lift Off

The Koch curve exciting coil eddy current sensor is a kind of novel flexible planar eddy current probe. In this study, an intersection angle spectrum entropy index and a radial direction energy spectrum entropy were proposed to evaluate the eddy current distribution. Eddy current distributions induced by one turn of a circular coil and one turn of a second order Koch curve coil feed with different exciting frequency alternative currents and at different lift-off distances, were simulated and the eddy current distributions varying with lift-off distance in different exciting frequencies were compared by the two proposed indices. With the increase of the lift-off distance or the decrease of exciting frequency, the similarity between the shape of the Koch curve and the eddy current distribution became weakened and the degree of the concentration of the eddy current distribution in the specimen under the exciting coil was loosened.

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