A Faceted Magnetron Concept Using Field Emission Cathodes

A magnetron concept using field emission cathodes has been modeled with the Air Force Research Laboratory particle-in-cell code ICEPIC and the 2D particle trajectory simulation Lorentz2E. In this approach, field emitters are used to provide a distributed cathode in place of a traditional thermionic cathode. The emitters are placed below the interaction space in a shielded structure. The cathode is comprised of facet plates with slits to protect the emitters. Simulation of an L-band rising sun magnetron shows that the faceted magnetron will oscillate using both five and ten facet cathodes. The startup times are very similar to that of a cylindrical cathode magnetron. The electron trajectories of the shielded slit structure have been modeled, and the results indicate that electrons can be injected through the slits and into the interaction space using lateral edge emitters and a pusher electrode design

Effects of Electromagnetic Stimulation on Soil’s Hydraulic Conductivity

Our research involves the identification of the different effects that electromagnetic (EM) stimulation has on varying soil properties; properties such as hydraulic conductivity. This work could prove to be of importance in furthering our understanding of the effects of EM stimulation with regard to the hydraulic conductivity of soil. A positive correlation between EM stimulation and an increase in hydraulic conductivity could have broad applications for environmental contaminant mitigation in soils and for various geotechnical construction applications such as minimizing soil setup during pile driving operations. EM waves can be used to enhance soil and groundwater remediation in a way that no heat is generated, yet the desired mechanisms in soil are stimulated. Our approach in this project involved the construction of a customized permeameter that enabled us to measure the change in hydraulic conductivity given a tuned EM wave from an antenna. An EM wave with a fixed frequency and varying power output was sent through the permeameter while the hydraulic conductivity was measured in real time. Tests performed for the research project were successful in showing a correlation between hydraulic conductivity and EM stimulation

Electron Hop Funnel Measurements and Comparison with the Lorentz-2E Simulation

Electron hop funnels have been fabricated using a Low Temperature Co-Fired Ceramic (LTCC). Measurements of the hop funnel I-V curve and electron energy distribution have been made using gated field emitters as the electron source. The charged particle simulation Lorentz 2E has been used to model the hop funnel charging and to predict the I-V and energy characteristics. The results of this comparison indicate that the simulation can be used to design hop funnel structures for use in various applications

Hysteresis in Experimental I–V Curves of Electron Hop Funnels

Electron hop funnels provide a method to integrate field emission arrays into microwave vacuum electron devices, to protect the arrays, and to provide a method to study the secondary electron characteristics of dielectrics. A hop funnel is a dielectric material with an electrode, known as the hop electrode, placed around the narrow end (exit) of the funnel to control the current transmitted through the device. Current is transmitted through the funnel via electron-hopping transport. This work investigates a hysteresis observed in the current–voltage characteristic of the device. The experimental results showing the observed hysteresis will be presented. This work will demonstrate that charging on the bottom of the hop funnel is not the fundamental cause of the hysteresis

Simulation of Electron Hop Funnels Using Version 9.2 of Lorentz-2E

Electron hop funnels have been simulated using the new version of the particle trajectory simulation software, Lorentz-2E. Simulations were conducted to determine the validity of the version 9.2 results and the consistency of the results to a previous version of the software, version 8.0. In addition, a new method of injecting a uniform current with all rays of equal charge is discussed, and the results of the method are presented. Version 9.2 of the software was successfully implemented and a new emission model tested. The transition of the software version will allow for faster simulation times of the electron hop funnel simulations to increase the understanding of the device

Combined neutron reflectometry and rheology

We have combined neutron reflectometry with rheology in order to investigate the solid boundary of liquids and polymers under shear deformation. Our approach allows one to apply a controlled stress to a material while resolving the structural arrangements on the sub nanometer length scale with neutron reflectivity, off-specular and small angle scattering at the same time. The specularly reflected neutron intensity of a 20 % by weight solution of the Pluronic F127 in deuterated water is evaluated. We find pronounced changes in the near interface structure under applied deformation for surfaces with different surface energies, which are correlated with changes in the storage and loss modulus

Laboratory Study of the Effect of Electromagnetic Waves on Airflow during Air Sparging

Air sparging is a technique that uses the injection of a gas (e.g., air, oxygen) into the subsurface to remediate saturated soils and groundwater contaminated with volatile organic compounds (VOCs). Contaminant-removal efficiency and air-sparging performance are highly dependent on the pattern and type of airflow. Airflow, however, suffers from air channel formation (i.e., preferential paths for airflow), limiting remediation to smaller contaminated zones. This paper presents the results of experimental work investigating the possibility of controlling and improving airflow patterns through a saturated glass-bead medium using electromagnetic (EM) waves to enhance air sparging. The test setup consists of a resonant cavity made of an acrylic tank covered with transparent, electrically conductive films. Experimental measurement of the electric field component of EM waves is performed at different frequencies. Airflow pattern is also studied at different air-injection pressure levels with/without EM stimulation. The zone of influence (ZOI) during air sparging is monitored using digital imaging. A quantitative approach is then taken to correlate the characteristics of EM waves and airflow patterns

Interaction Between Electromagnetic Waves and Transport in Saturated Media

Air sparging is one of the most popular remediation technologies. However, it is limited to a small radius of influence (ROI) surrounding the air injection well. Hence, there have been several efforts to improve its effectiveness. To study the possibility of improving the effectivity of air sparging electromagnetic (EM) waves, an easily visible analogous problem (dye transport in water) is studied in this paper. In order to quantify the effects of EM stimulation on flow of an inert, nonreactive dye in water, EM-stimulated and unstipulated dye transport experiments tests were performed and compared. To quantify this interaction, both dye transport and EM wave propoagation (only the electric field component Z) are quantified experimentally in lab-scale. In addition to the experimental mapping of the electric field at limited location on depth (i.e., vertical) slices, the electric field is simulated in COMSOL Multiphysics 4.1 in three dimensions (3D) for accurate field analysis. Transport analysis of the dye was performed using digital imaging to determine temporal and spatial concentration variations. The results show a visible effect on the dye transport mechanisms (i.e., fingering and diffusion). However, further study is needed to validate the proposed correlation between the electric field and the transport mechanisms

Study of Mechanisms Governing Electromagnetic Alteration of Hydraulic Conductivity of Soils

Hydraulic conductivity is a measure of the rate at which water flows through porous media. Because of the dipole properties of water molecules, electric field can affect hydraulic conductivity. In this study, the effect of radio-frequency (RF) waves on hydraulic conductivity is investigated. This is important both for the geophysical measurement of hydraulic conductivity as well as remediation using electromagnetic waves. Bentonite clay and sandy samples are tested in rigid-wall, cylindrical permeameters and stimulated using a CPVC-cased monopole antenna vertically centered in the permeameters. The permeameters are encased within RF cavities constructed of aluminum mesh in order to prevent interference from the outside and to confine the RF wave to the medium. Falling-head and constant-head tests are performed to measure the hydraulic conductivity of the clayey and sandy soil samples, respectively. The results show a correlation between the change in the hydraulic conductivity and various characteristics of the RF stimulation. The change is, however, different for sandy and clayey soils

Electromagnetically Induced Transport in Water for Geoenvironmental Applications

Air sparging is a popular soil remediation technique that enables the removal of contaminants through diffusing air into soil. The removal process is, however, slow. The goal of this work is to study the effect of electromagnetic (EM) waves —with minimal heat generation— on transport mechanisms such as diffusion, in order to improve airflow or contaminant transport in order to expedite the cleanup process using air sparging or similar technologies. This effect is studied through an experimental setup that examines the diffusion of a nonreactive dye in water under EM waves at a range of frequencies (50-200 MHz). The electric field was simulated using COMSOL Multiphysics for better three-dimensional (3D) visualization and analysis and then validated using the experimental measurements. A dielectrophoretic study was then performed using the simulated electric field. Various dye flows under EM stimulation at different frequencies were compared. At 65 MHz and 76 MHz, the dye flow was in the direction of the dielectrophoretic forces, which are believed to be the governing mechanism for the EM-stimulated dye transport