scholarly journals Controlled Phase Interactions Between Pulsed Electric Fields, Ultrasonic Motion, and Magnetic Fields in an Anodic Dissolution Cell

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Curtis Bradley ◽  
Johnson Samuel
Keyword(s):  
Magnetic Field ◽  
Anodic Dissolution ◽  
Electric Fields ◽  
High Frequency ◽  
Performance Metrics ◽  
Removal Rate ◽  
Ultrasonic Transducer ◽  
Three Dimensional ◽  
Electrochemical Machining ◽  
3D Printed

This paper presents the design of a novel testbed that effectively combines pulsed electric field waveforms, ultrasonic velocity, and magnetic field waveforms in an anodic dissolution electrochemical machining (ECM) cell. The testbed consists of a custom three-dimensional (3D)-printed flow cell that is integrated with (i) a bipolar-pulsed ECM circuit, (ii) an ultrasonic transducer, and (iii) a custom-built high-frequency electromagnet. The driving voltages of the ultrasonic transducer and electromagnet are calibrated to achieve a timed workpiece velocity and magnetic field, respectively, in the machining area. The ECM studies conducted using this testbed reveal that phase-controlled waveform interactions between the three assistances affect both the material removal rate (MRR) and surface roughness (Ra) performance metrics. The triad-assisted ECM case involving phase-specific combinations of all three high-frequency (15.625 kHz) assistance waveforms is found to be capable of achieving a 52% increase in MRR while also simultaneously yielding a 78% improvement in the Ra value over the baseline pulsed-ECM case. This result is encouraging because assisted ECM processes reported in the literature typically improve only one of these performance metrics at the expense of the other. In general, the findings reported in this paper are expected to enable the realization of multifield assisted ECM testbeds using phase-specific input waveforms that change on-the-fly to yield preferential combinations of MRR and surface finish.

scholarly journals Induced telluric currents play a major role in the interpretation of geomagnetic variations

2020 ◽  
Author(s):  
Liisa Juusola ◽  
Heikki Vanhamäki ◽  
Ari Viljanen ◽  
Maxim Smirnov
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Three Dimensional ◽  
Image Data ◽  
Geomagnetically Induced Currents ◽  
Ionospheric Currents ◽  
Geomagnetic Variations ◽  
Near Surface ◽  
Telluric Currents

Abstract. Geomagnetically induced currents (GIC) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents as well as the three-dimensional distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH/dt) is closely related to the electric field via Faraday's law, and provides a convenient proxy for the GIC risk. However, forecasting dH/dt still remains a challenge. We use 25 years of 10 s data from the North European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that instead of the primary ionospheric currents, the measured dH/dt is dominated by the signature from the secondary induced telluric currents nearly at all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to highly-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the involved stations. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible, i.e., a dense observation network is available.

scholarly journals Induced currents due to 3D ground conductivity play a major role in the interpretation of geomagnetic variations

2020 ◽  
Vol 38 (5) ◽  
pp. 983-998
Author(s):  
Liisa Juusola ◽  
Heikki Vanhamäki ◽  
Ari Viljanen ◽  
Maxim Smirnov
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Three Dimensional ◽  
Geomagnetically Induced Currents ◽  
Ionospheric Currents ◽  
Geomagnetic Variations ◽  
Near Surface ◽  
Induced Currents ◽  
Telluric Currents

Abstract. Geomagnetically induced currents (GICs) are directly described by ground electric fields, but estimating them is time-consuming and requires knowledge of the ionospheric currents and the three-dimensional (3D) distribution of the electrical conductivity of the Earth. The time derivative of the horizontal component of the ground magnetic field (dH∕dt) is closely related to the electric field via Faraday's law and provides a convenient proxy for the GIC risk. However, forecasting dH∕dt still remains a challenge. We use 25 years of 10 s data from the northern European International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer network to show that part of this problem stems from the fact that, instead of the primary ionospheric currents, the measured dH∕dt is dominated by the signature from the secondary induced telluric currents at nearly all IMAGE stations. The largest effects due to telluric currents occur at coastal sites close to high-conducting ocean water and close to near-surface conductivity anomalies. The secondary magnetic field contribution to the total field is a few tens of percent, in accordance with earlier studies. Our results have been derived using IMAGE data and are thus only valid for the stations involved. However, it is likely that the main principle also applies to other areas. Consequently, it is recommended that the field separation into internal (telluric) and external (ionospheric and magnetospheric) parts is performed whenever feasible (i.e., a dense observation network is available).

Energy conversion by electron beam-driven waves in a compressed reconnection separatrix

2020 ◽  
Author(s):  
Justin Holmes ◽  
Rumi Nakamura ◽  
Owen Roberts ◽  
Daniel Schmid ◽  
Takuma Nakamura ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Energy Conversion ◽  
Electric Fields ◽  
Spatial Configuration ◽  
Three Dimensional ◽  
Lower Hybrid ◽  
Magnetic Compression ◽  
Rotational Discontinuity ◽  
Highly Correlated

<p>We investigate magnetic compression near the reconnection separatrix observed by Magnetospheric MultiScale (MMS) on July 11<sup>th</sup> 2017. A clear transition between inflow and outflow in both ions and electrons is observed across an ion gyro-scale region of enhanced magnetic field. Multispacecraft techniques for magnetic curvature and local gradients along with timing of highly-correlated wave packets are used to determine the spatial configuration of the compressed region. Structure of the system is found to be inherently three dimensional; electron beam-driven modes propagating parallel to the magnetic field are observed concurrent with perpendicular-propagating lower hybrid waves. Larger scale surface waves are also present behind the compression front. Transforming to a deHoffmann-Teller frame across the boundary results in a distinctly non-rotational discontinuity with structure similar to a quasi-2D, Petschek-like slow shock. However, MHD jump conditions are not satisfied, indicating kinetic dissipation may occur within the thin layer. The largest amplitude measurements of $\mathbf{J}\cdot\mathbf{E}$ energy conversion are associated with an inflowing electron beam and parallel electric fields near the magnetic peak. Spikes in $\mathbf{J}\cdot\mathbf{E}$ are predominantly negative, suggesting electron-scale mixing between the reconnection inflow and outflow is partially responsible for the observed magnetic compression.</p>

Proton acceleration in three-dimensional non-null magnetic reconnection

2016 ◽  
Vol 82 (5) ◽  
Author(s):  
Z. Akbari ◽  
M. Hosseinpour ◽  
M. A. Mohammadi
Keyword(s):  
Magnetic Field ◽  
Energy Distribution ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Three Dimensional ◽  
Null Point ◽  
Proton Acceleration ◽  
Electric And Magnetic Fields ◽  
Field Lines ◽  
The Magnetic Field

In a three-dimensional non-null magnetic reconnection, the process of magnetic reconnection takes place in the absence of a null point where the magnetic field vanishes. By randomly injecting a population of 10 000 protons, the trajectory and energy distribution of accelerated protons are investigated in the presence of magnetic and electric fields of a particular model of non-null magnetic reconnection with the typical parameters for the solar corona. The results show that protons are accelerated along the magnetic field lines away from the non-null point only at azimuthal angles where the magnitude of the electric field is strongest and therefore particles obtain kinetic energies of the order of thousands of MeV and even higher. Moreover, the energy distribution of the population depends strongly on the amplitude of the electric and magnetic fields. Comparison shows that a non-null magnetic reconnection is more efficient in accelerating protons to very high GeV energies than a null-point reconnection.

Parametric Instability of Plasma Waves in a Magnetic Field, Due to High-Frequency Electric Fields

1972 ◽  
Vol 28 (4) ◽  
pp. 206-209 ◽  
Author(s):  
R. P. H. Chang ◽  
M. Porkolab ◽  
B. Grek
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
High Frequency ◽  
Parametric Instability ◽  
Plasma Waves

Three-dimensional microscopic and high frequency magnetic field measurement

1990 ◽  
Author(s):  
H. Shinada ◽  
S. Fukuhara ◽  
S. Seitou ◽  
H. Tohokoro ◽  
S. Omoto ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Measurement ◽  
High Frequency ◽  
Three Dimensional ◽  
Magnetic Field Measurement ◽  
Frequency Magnetic Field ◽  
High Frequency Magnetic Field

scholarly journals An Analogy Between the Effects of Fluctuating Electric Fields and Steady Magnetic Fields in Isotropic Conductors when a Universal Relaxation Time Cannot Be Defined

1960 ◽  
Vol 13 (1) ◽  
pp. 95
Author(s):  
EJ Moore
Keyword(s):  
Magnetic Field ◽  
Relaxation Time ◽  
Electric Field ◽  
Electric Fields ◽  
High Frequency ◽  
Present Note ◽  
Isotropic Solid ◽  
High Frequency Electric Field ◽  
Circular Frequency ◽  
Steady Magnetic Field

It is well known that when a " universal" time of relaxation ("t') exists, the influence of a harmonically varying electric field (F cceiOlt) on the transport properties of a solid may be taken into account by replacing "t' by "t'/(l +iCil"t'). Dingle (1956a) demonstrated that, for an isotropic solid, the effect of a steady magnetic field may similarly be obtained by replacing "t' by "t'/(l+j~l"t') with an applied d;c. electric field, and by "t'/[l+(iCil+jO)"t'] with an a.c. field. (Here j2= -1, ij -=1= -1, and 0=( -e)H/mc is the circular frequency of precession of an electron.) The object of the present note is to show that this analogy between a high frequency electric field and a steady magnetic field still exists, even when a " universal" relaxation time cannot be defined.

scholarly journals Experimental investigation of the electrochemical micromachining process of Ti-6Al-4V titanium alloy under the influence of magnetic field

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
T. Praveena Gopinath ◽  
J. Prasanna ◽  
C. Chandrasekhara Sastry ◽  
Sandeep Patil
Keyword(s):  
Magnetic Field ◽  
Titanium Alloy ◽  
Removal Rate ◽  
Electrochemical Machining ◽  
Machining Process ◽  
Electrochemical Micromachining ◽  
Machining Accuracy ◽  
Micro Hole ◽  
Neodymium Magnets ◽  
Pulse On Time

Abstract An attempt has been made to study the influence of magnetic field on the micro hole machining of Ti-6Al-4V titanium alloy using electrochemical micromachining (ECMM) process. The presence of magneto hydro dynamics (MHD) is accomplished with the aid of external magnetic field (neodymium magnets) in order to improve the machining accuracy and the performance characteristics of ECMM. Close to ideal solution for magnetic and nonmagnetic field ECMM process, the parameters used are as follows: concentration electrolyte of 15 g/l; peak current of 1.35 A; pulse on time of 400 s; and duty factor of 0.5. An improvement of 11.91–52.43% and 23.51–129.68% in material removal rate (MRR) and 6.03–21.47% and 18.32–33.09% in overcut (OC) is observed in ECMM of titanium alloy under the influence of attraction and repulsion magnetic field, respectively, in correlation with nonmagnetic field ECMM process. A 55.34% surface roughness factor reduction is ascertained in the hole profile in magnetic field-ECMM in correlation with electrochemical machined titanium alloy under nonmagnetic field environment. No machining related stress is induced in the titanium alloy, even though environment of electrochemical machining process has been enhanced with the presence of magnetic field. A slight surge in the compressive residual factor, aids in surge of passivation potential of titanium alloy, resulting in higher resistance to outside environment.

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