External Publications

Improved design of a high-voltage vacuum-insulator interface

PHYSICAL REVIEW SPECIAL TOPICS - ACCELERATORS AND BEAMS 8, 050401 (2005)

W. A. Stygar, J. A. Lott, T. C. Wagoner, V. Anaya, H. C. Harjes, H. C. Ives, Z. R. Wallace, G. R. Mowrer,
R.W. Shoup, J. P. Corley, R. A. Anderson, G. E. Vogtlin, M. E. Savage, J. M. Elizondo, B. S. Stoltzfus,
D. M. Andercyk, D. L. Fehl, T. F. Jaramillo, D. L. Johnson, D. H. McDaniel, D. A. Muirhead, J. M. Radman,
J. J. Ramirez, L. E. Ramirez, R. B. Spielman, K.W. Struve, D. E. Walsh, E. D. Walsh, and M. D. Walsh

We have conducted a series of experiments designed to measure the flashover strength of various azimuthally symmetric 45° vacuum-insulator configurations. The principal objective of the experiments was to identify a configuration with a flashover strength greater than that of the standard design, which consists of a 45° polymethyl-methacrylate (PMMA) insulator between flat electrodes. The thickness d and circumference C of the insulators tested were held constant at 4.318 and 95.74 cm, respectively. The peak voltage applied to the insulators ranged from 0.8 to 2.2 MV. The rise time of the voltage pulse was 40–60 ns; the effective pulse width [as defined in Phys. Rev. ST Accel. Beams 7, 070401 (2004)] was on the order of 10 ns. Experiments conducted with flat aluminum electrodes demonstrate that the flashover strength of a crosslinked polystyrene (Rexolite) insulator (18 +/- 7)% higher than that of PMMA. Experiments conducted with a Rexolite insulator and an anode plug, i.e., an extension of the anode into the insulator, demonstrate that a plug can increase the flashover strength by an additional (44 +/- 11)% The results are consistent with the Anderson model of anode-initiated flashover, and confirm previous measurements. It appears that a Rexolite insulator with an anode plug can, in principle, increase the peak electromagentic power that can be transmitted across a vacuum interface by a factor of [(1.18)X(1.44)]² = 2.9 over that which can be achieved with the standard design.

Electric and Magnetic design of the g-2 magetic kicker

APAC98 Proceedings

W. Feng, Nanjing University, Nanjing 210093, China
E. B. Forsyth and G. C. Pappas, Brookhaven National Laboratory, Upton, New York 11973, U.S.A.

The ultra-high precision g-2 experiment requires a fast kicker to deflect incoming muon beam with a momentum of 3.094 Gev/c. A magnetic kicker was selected since this approach requires the lowest excitation voltage of all designs considered. However, a higher driving current (>6000A) is required which leads to more residual eddy current field to influence the main dipole magnetic field. Several possible magnetic kicker designs were investigated to determine their effects on kicker field quality, driving efficiency (B/I) and inductance per unit length. A satisfatory construction is a two plate kicker with shaped edges for the two electrodes. Using the transient eddy current analyses (Opera 2d/TR)[1], the authors studied a variety of factors which affect the eddy current residual field. This paper presents the electric and magnetic parameters of the magnetic kicker which was completed in 1996 and has been put into operation now.

∗ references ELECTRO for electric field results.

Critical Cavity Size Producing Internal Discharges in Stator Bar Ground Wall Insulation

2011 Electrical Insulation Conference, Annapolis, Maryland, 5 to 8 June 2011

Turgeon, A., Hudon, C., and Nguyen, D.N.

Partial discharges (PDs) cause degradation of the generator stator bars insulation. The use of mica in this insulation system prevents small internal PDs from reducing the expected life of the equipment. However, some cavities may be the cause of a more significant PD presence and accelerate the aging of the insulation system. A method that uses the Paschen law and numerical simulations is presented for determining critical cavity sizes that produce significant PDs.

∗ COULOMB was used in this work.

Characteristics of a dust trajectory sensor

Review of Scientific Instruments, Volume 79, Published: August 4, 2008

Siegfried Auer, Eberhard Grün, Sascha Kempf, Ralf Srama, André Srowig, Zoltan Sternovsky, and Valentin Tschernjawski

Trajectories of cosmic dust particles are determined by the measurement of the electrical signals that are induced when a charged grain flies through a position-sensitive electrode system. A typical dust trajectory sensor has four sensor planes consisting of about 16 wire electrodes each. Two adjacent planes have orthogonal wire directions. The sensor is highly transparent and mechanically robust, provides a large sensitive area, large field of view, and can, at least in principle, achieve unlimited precision. While a sensor model had already undergone limited testing in the dust laboratory, its response as a function of position and angle of incidence of the trajectory and as a function of sensor dimensions was generally unknown. To better understand its characteristics, the operation of a sensor model consisting of three planes and seven wires per plane was simulated using the COULOMB computer program. We show that the response of the reduced model can be applied to a model with more planes and more wires per plane. The effect of a trajectory's position and angle on the signal strength is discussed as well as the influence of geometrical parameters such as wire diameter, distance between wire planes, and wire length. We found a greater effect of the wire diameter on the signal strength, and a lesser effect of the plane distance, than expected. A set of similarity rules is provided for the design of a larger sensor. Finally, we discuss the optimization of the sensor for different applications.

∗ COULOMB was used in this work.

Planar Electrode Dielectrophoresis Systems

A Thesis Submitted to the Faculty of Graduate Studies in Partial Fulfillment of the Requirements for the Degree of Master of Science at The University of Calgary

Lee Fason Hartley

Demand from the biosciences continues to increase for systems able to assist in the preparation and analysis of biological samples. Appropriately, dielectrophoresis continues to emerge as a valuable technique for characterizing a diverse array of particles. Particle processing systems capable of autonomously executing various operations on samples may offer cost effective means for such tasks. Dielectrophoretic microelectromechanical systems technology is well positioned to participate in this growing industry...

∗ references obtaining results from COULOMB.

Three-dimensional modeling of potential and electric-field distributions along an EHV ceramic post insulator covered with ice - Part I: Simulations of a melting period

IEEE Transactions on Power Delivery, Publication Date: July 2005 Volume: 20, Issue: 3, page(s): 2006- 2013

Volat, C. Farzaneh, M., Univ. of Quebec-Chicoutimi, Chicoutimi, Que., Canada

The main objective of this paper is to determine the potential and electric-field distributions along a typical ceramic extremely-high-voltage post insulator covered with atmospheric ice during a melting period. Commercial software, Coulomb 3D, based on the boundary element method (BEM), was used for all of the three-dimensional modeling and simulations. It was demonstrated that the BEM is well suited for evaluating the effect of ice shedding on the potential and electric-field distributions along an ice-covered insulator during a melting period. The results obtained show that the length and number of ice free zones, also called air gaps, are the major parameters that affect the applied voltage distribution along an ice-covered insulator. The mean electric field per arcing distance, affected mainly by the air-gap lengths, can provide a good indication of the presence of partial arcing along the different air gaps.

∗ references obtaining results from COULOMB.

Five parametric resonances in a microelectromechanical system

Letters to Nature, NATURE | VOL 396 | 12 NOVEMBER 1998

Kimberly L. Turner, Scott A. Miller, Peter G. Hartwell, Noel C. MacDonald, Steven H. Strogatz & Scott G. Adams

The Mathieu equation governs the forced motion of a swing, the stability of ships and columns, Faraday surface wave patterns on water, the dynamics of electrons in Penning traps, and the behaviour of parametric amplifiers based on electronic or superconducting devices. Theory predicts that parametric resonances occur near drive frequencies of 2v₀=n, where v₀ is the system's natural frequency and n is an integer > 1. But in macroscopic systems, only the first instability region can typically be observed, because of damping and the exponential narrowing of the regions with increasing n. Here we report parametrically excited torsional oscillations in a single-crystal silicon microelectromechanical system. Five instability regions can be measured, due to the low damping, stability and precise frequency control achievable in this system. The centre frequencies of the instability regions agree with theoretical predictions. We propose an application that uses parametric excitation to reduce the parasitic signal in capacitive sensing with microelectromechanical systems. Our results suggest that microelectromechanical systems can provide a unique testing ground for dynamical phenomena that are difficult to detect in macroscopic systems.

∗ this paper uses COULOMB for electrostatic force and torque computations.

Passive superconducting shielding: experimental results and computer models

AIP Conference Proceedings - June 23, 2004 - Volume 710, pp. 1754-1762
ADVANCES IN CRYOGENIC ENGEINEERING: Transactions of the Cryogenic Engineering Conference - CEC

B. A. Warner and K. Kamiya

Cryogenics Branch, Goddard Space Flight Center, Greenbelt, Maryland 20771
Tsukuba Magnet Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan

Passive superconducting shielding for magnetic refrigerators has advantages over active shielding and passive ferromagnetic shielding in that it is lightweight and easy to construct. However, it is not as easy to model and does not fail gracefully. Failure of a passive superconducting shield may lead to persistent flux and persistent currents. Unfortunately, modeling software for superconducting materials is not as easily available as is software for simple coils or for ferromagnetic materials. This paper will discuss ways of using available software to model passive superconducting shielding.

Progress on a 4 K to 10 K Continuously Operating Adiabatic Demagnetization Refrigerator

AIP Conference Proceedings -- April 27, 2006 -- Volume 823, pp. 969-976, ADVANCES IN CRYOGENIC ENGINEERING: Transactions of the Cryogenic Engineering Conference - CEC

M. DiPirro, J. Tuttle, M. Jackson, E. Canavan, B. Warner, and P. Shirron
NASA/Goddard Space Flight Center, Code 552, Greenbelt, MD 20771

An adiabatic demagnetization refrigerator (ADR) is under development for use in cooling relatively large loads (10–100 mW) at 4 K and rejecting that heat to a cryocooler operating at 10 K. ADRs can operate in this temperature range with an efficiency of 75% of Carnot, saving as much as 2/3 of the required overall input power. In addition this ADR can provide cooling down to 0.4 K. The ADR magnet consists of 8 short coils wired in series and arranged in a toroid to provide self-shielding of its magnetic field. Eliminating passive or active shields saves 30% of the mass of the system. The average field is 3 Tesla using 5 amps. In the first model the coils are wound with ordinary NbTi superconducting wire and operated at 4 K. A second version will then use fine Nb3Sn wire to provide complete 10 K operation. As a refrigerant for this temperature range we are using readily available gadolinium gallium garnet (GGG) crystals, which provide suitable performance. In the future we will switch to either GdLiF4 or GdF3, which have 13% or 30%, respectively, more cooling power per volume than GGG. We use gas gap heat switches to alternately connect the toroid to the cold load and the warm heat sink. A small continuous stage maintains the cold end at 4 K while the main toroid is recycled. Data on toroid , magnet performance with respect to central field vs. current and fringing field vs. current are given. Data on the transient heating due to hysteresis losses within the superconductor are also presented.

∗ although it isn't mentioned by name, AMPERES produced all 3D magnetic modeling presented in this paper

Chicane compressor development for BNL ATF- applications to SASE FEL

22nd International Free Electron Laser Conference, 2001

R. Agustsson,J. Rosenzweig

A chicane compressor is being designed and constructed at UCLA for implementation at the BNL Accelerator Test Facility. The beam optics, including collective fields, and expected performance of the device has been simulated using TRACE3D and ELEGANT. Based on these studies, as well as constraints due to downstream ATF optics, the chicane magnet specifications were determined. The dipole magnets were designed using AMPERES 3D magnetostatic modeling, and have been constructed. Implementation of this device at the ATF, as well as initial physics experiments on coherent synchrotron radiation emission (and associated emittance growth) at 70 MeV, and expected performance enhancement of the VISA SASE FEL experiment, are discussed.

A method to obtain uniform magnetic-field energy density gradient distribution using discrete pole pieces for a microelectromechanical-system-based magnetic cell separator

J. Appl. Phys. 99, 08R905 (2006)

Pulak Nath, Biomedical Engineering, The Cleveland Clinic Foundation, Cleveland, Ohio 44195 and Department of Chemical and Biomedical Engineering, Cleveland State University, Cleveland, Ohio 44115

Lee R. Moore, Maciej Zborowski, Shuvo Roy, and Aaron Fleischman, Biomedical Engineering, The Cleveland Clinic Foundation, Cleveland, Ohio 44195

A spatially uniform magnetic energy density gradient (delB²) distribution offers a controlled environment to separate magnetically tagged cells or biomolecules based on their magnetophoretic mobility [L. R. Moore et al., J. Biochem. Biophys. Methods 37, 11 (1998)]. A design to obtain a uniform delB² distribution for a microelectromechanical-systems-based magnetic cell separator was developed. The design consists of an external magnetic circuit and a microfabricated channel (biochip) with embedded discrete pole pieces on the channel walls. The two-dimensional and three-dimensional magnetostatic simulation softwares utilizing boundary element methods were used to optimize the positions and the dimensions of the discrete pole pieces, as well as the external magnetic circuit—the combination of which would generate a uniform delB² profile over the channel cross section. It was found that the discrete pole pieces required specific magnetic properties (saturation magnetization constant >1.55 T) to affect the overall delB2 distribution. Investigating different positions of the discrete pole pieces inside the external magnetic field indicated that the proposed design could generate uniform delB² distribution with ±100 µm displacements along the height/width and ±1° inclination from the optimum position.

Design studies for a H^⎯ ion extraction system

Review of Scientific Instruments -- May 2004 -- Volume 75, Issue 5, pp. 1783-1785

A. Ushakov, K. Volk, H. Klein, and U. Ratzinger, Institut für Angewandte Physik, Universität Frankfurt, Robert-Mayer-Strasse 2-4, 60054 Frankfurt, Germany

At the University of Frankfurt, a high current H^- ion source was developed and tested. A H^- beam current of 120 mA with an energy of 35 keV was extracted using an emission opening radius of 5 mm. This source was equipped with a diode extraction system. Thus, the extraction voltage determines the beam energy, depending on the plasma density. In order to adjust the extraction voltage independently from the beam energy, a 65 kV extractor is being designed. It consists of a compact four electrode (tetrode) system. The electron dumping will be performed after the tetrode system. For computing three dimensional magnetic field distributions the code AMPERES has been used. The influence of magnetic fields on the beam path has been taken into account. The article presents the layout of a compact 65 kV extractor for 120 mA H^-.

Magnetic cross-talk compensation for an optical current transducer

IEEE Transactions on Instrumentation and Measurement, Vol.50, No.5, pp.1071-1075, 2001.

P. Niewczas, W.I. Madden, W.C. Michie, A. Cruden and J.R McDonald

In this paper, we analyze the errors associated with magnetic crosstalk within point type, or unlinked, optical current transducers (OCTs) working in a three-phase electric current transmission systems. For many practical conductor arrangements, the magnetic crosstaIk may introduce errors unacceptable for the accuracy requirements demanded from the OCT. A solution to this problem is devised around a unique compensation method which solves, in real time, a set of linear equations, each representing the instantaneous output signal from one phase current sensor.

Faraday shielding in coaxial winding transformer

International Journal of Applied Electromagnetics and Mechanics, Volume 11, Number 4 / 2000, 261-267

Junwei Lu and Fu Wong, School of Microelectronic Engineering, Faculty of Engineering, Griffith University, Queensland Australia

This paper presents the configuration of a high frequency (HF) coaxial winding transformer with Faraday shield and discusses the shielding effect of the transformer in the high frequency range. The experimental results show the voltage ratio, coupling coefficient and load characteristic of the HF coaxial transformer in the range up to 2 MHz. The numerical result illustrates the eddy current distribution in the windings and shielding coil, and the magnetic flux distribution in the shielded HF coaxial transformer.

Studies on Geometries for Inducing Homogeneous Magnetic Fields in the Application of Real Time Imaging of Steel Reinforcing Bars Embedded Within Pre-Stressed and Reinforced Concrete

AIP Conference Proceedings -- March 6, 2006 -- Volume 820, pp. 1298-1304, QUANTITATIVE NONDESTRUCTIVE EVALUATION

S. Quek, D. Benitez, P. Gaydecki, and V. Torres, School of Electrical and Electronic Engineering, The University of Manchester, PO Box 88, Manchester, M60 1QD, United Kingdom

This paper addresses fundamental issues associated with the development of a real time inductive scanning system for non-destructive testing of pre-stressed and reinforced concrete. Simulated results has indicated that given a coil dimension of 300mm×300mm×2.5mm, 10mm rebars can be imaged down to a depth of 100 mm. Studies also indicate that the vertical component of the induced magnetic field is most favourable as it can be readily reconstructed to yield geometryand dimensional information pertaining to the rebar structure.

The Application of Magneto Inductive Sensors for Non-Destructive Testing of Steel Reinforcing Bars Embedded Within Pre-Stressed and Reinforced Concrete

AIP Conference Proceedings -- March 6, 2006 -- Volume 820, pp. 1298-1304, QUANTITATIVE NONDESTRUCTIVE EVALUATION

SD. S. Benitez, S. Quek, P. Gaydecki, V. Torres, and B. Fernandes, School of Electrical and Electronic Engineering, The University of Manchester, PO Box 88, Manchester, M60 1QD, United Kingdom

This paper addresses fundamental issues associated with the development of a real time inductive scanning system for non-destructive testing of pre-stressed and reinforced concrete. Simulated results has indicated that given a coil dimension of 300mm×300mm×2.5mm, 10mm rebars can be imaged down to a depth of 100 mm. Studies also indicate that the vertical component of the induced magnetic field is most favourable as it can be readily reconstructed to yield geometryand dimensional information pertaining to the rebar structure.

Forming of High Current Density Sheet Electron Beams for a sub-THz TWT Vacuum Amplifier

Nikolai A. Bushuev, *Yuri A. Grigoriev, Anton A. Burtsev, Igor A. Navrotsky, Georgy V. Sahajee.; Institute of Radio Engineering and Electronic of RAS, Saratov, Russia

In this paper we present the computer analysis of magnetic focusing sheet electron beam with low perveance in the electron-optical systems with an electron gun based on thermionic cathode with a current density of 100 A/cm2 at the distance of tunnel 25 mm.The results of experimental study in the diode mode of impregnated thermionic cathode with linear dimensions 0,1 × 0,7 mm have shown the possibility of using this cathode in sub-THz vacuum amplifier..

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

Plasma Science, IEEE Transactions, Jan. 2011, Volume: 39 Issue:1, 555 - 561, Sponsored by: IEEE Nuclear and Plasma Sciences Society

Lester, C.; Browning, J.; Matthews, L.; Department of Electrical and Computer Engineering, Boise State University, Boise, ID, USA

Electron hop funnels have been fabricated using a low-temperature cofired ceramic. The 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.

Electron Optics Simulation Software at NUS

H. Q. Hoang, M. Osterberg, and A. Khursheed, Department of Electrical and Computer Engineering, National University of Singapore,

LORENTZ is demonstrated as a simulation tool by NUS at the Eighth International Conference on Charged Particle Optics, July 2010. Please see page 221 of the conference handbook for the Electron Optics Simulation Software at NUS article.

Phase-contrast x-ray imaging with a liquid-metal-jet-anode microfocus source

Appl. Phys. Lett. 91, 074104 (2007)

T. Tuohimaa, M. Otendal, and H. M. Hertz

Phase-contrast methods increase contrast, detail, and selectivity in x-ray imaging. Present compact x-ray sources do not provide the necessary spatial coherence with sufficient power to allow the laboratory-scale high-resolution phase-contrast imaging with adequate exposure times. In this letter, the authors demonstrate phase-contrast imaging with few-micron detail employing a compact ~6.5 µm spot liquid-metal-jet-anode high-brightness microfocus source. The 40 W source is operated at more than ten times higher electron-beam power density than present microfocus sources and is shown to provide sufficient spatial coherence as well as scalability to high power, thereby enabling the application of phase-contrast x-ray imaging with short exposure times in clinics and laboratories.

High-intensity electron beam for liquid-metal-jet anode hard x-ray generation

Proceedings of SPIE, Laser-Generated, Synchrotron, and Other Laboratory X-Ray and EUV Sources, Optics, and Applications II, Volume 5918 (Sep. 10, 2005)

T. Tuohimaa, M. Otendal, and H. M. Hertz

We report on our progress towards the experimental realization of a liquid-metal-jet-anode x-ray source with high brightness. We have previously shown that this electron-impact source has potential for very high x-ray brightness by combining small-spot high-flux operation of the electron beam with high-speed operation of the regenerative liquid-metal-jet anode. In the present paper we review the system and describe theoretical calculations for improving the 50 kV, 600 W electron-beam focussing to ~30 µm spot size. With such a system the power density on the liquid-metal-jet would be ~400 kW/mm2, i.e., more than an order of magnitude higher than the power density on a state-of-the-art rotating anode.

Modeling of a High Current H^- LEBT with the Lorentz-EM 3D Ion Optics Code

AIP Conf. Proc. - August 10, 2007 - Volume 925, pp. 318-323, 11th International Symposium on the Production and Neutralization of Negative Ions and Beams

S. K. Hahto, D. G. Bilbrough, R. Keller

High current electrostatic Low-Energy Beam Transport (LEBT) systems are currently being developed for several applications ranging from H^- cyclotrons to high intensity linear accelerators. A new design building on the experiences gained from the Spallation Neutron Source (SNS) LEBT system was modeled recently in 2D with PBGUNS. In this paper a 3D treatment is given for this new LEBT design for a 60 mA, 65 kV H^- beam. For this type of LEBT 3D modeling is essential to accurately model the deflection of the co-extracted electrons from the beam. The beam chopping and steering for RFQ injection also presents a 3D problem for the otherwise cylindrically symmetric geometry. The modeled LEBT can transport a 60 mA H^- beam with 0.2 mm mrad 1-rms emittance and Twiss parameters that are in accordance with established SNS LEBT specifications.

Towards coherent control of supersonic beams: a new approach to atom optics

New Journal of Physics 8 (2006), 77

A Libson, M Riedel, G Bronshtein, E Narevicius, U Even and M G Raizen

A supersonic beam of noble gas atoms is a source of unprecedented brightness. A novel short pulse supersonic nozzle is developed with beam intensity that is higher by at least an order of magnitude than other available sources. We show how this beam can be coherently slowed and focused using elastic reflection from single crystals. Simulations show beam fluxes of 1011 atoms s-1 at velocities of 50ms-1 and temperatures of less than 20 µK in the longitudinal direction. Possible applications of this slow beam to the study of atom–surface interactions and atom interferometry are discussed.

∗although LORENTZ isn't mentioned by name, reference 11 states that Integrated Engineering Software was used for simulations

Gas delivery and virtual process chamber concept for gas-assisted material processing in a focused ion beam system

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures -- November 2004 -- Volume 22, Issue 6, pp. 3008-3011

Valery Ray, Particle Beam Systems & Technology, 290 Broadway Street, Suite 298, Methuen, Massaschusetts 01844

Gas-assisted etching and material deposition using gaseous precursors have become a critical part of integrated circuit modification and other applications of focused ion beam (FIB) systems. Widely used methods of gas injection in FIB systems are either needle-type or shroud-type gas delivery nozzles. Each of these methods of gas delivery has significant drawbacks. Release of the gas from the needle-type nozzles is detrimental for the vacuum level in the main chamber of the system, as the gas quickly dissipates from the process area. Insertion of shroud concentrators into the primary ion beam path and the path of secondary electrons leads to a significant decline in the signal-to-noise ratio of the FIB image. Proposed "CUPOLA" geometry of the gas delivery nozzle could allow one to effectively concentrate process gas in the area of interest, as is currently done by shroud concentrators, and, according to secondary-electron trajectory simulations, would significantly improve the signal level of the secondary-electron image, as compared to the shroud concentrators.

Vertically aligned carbon nanofiber-based field emission electron sources with an integrated focusing electrode

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures -- January 2004 -- Volume 22, Issue 1, pp. 35-39

M. A. Guillorn, X. Yang, A. V. Melechko, D. K. Hensley, M. D. Hale, V. I. Merkulov, and M. L. Simpson, L. R. Baylor and W. L. Gardner, D. H. Lowndes

We report on the design, fabrication, and initial characterization of vertically aligned carbon nanofiber-based microfabricated field emission devices with an integrated out-of-plane electrostatic focusing electrode. The potential placed on this electrode was found to have a profound impact on the diameter of the beam emitted from the device as observed on a phosphor screen. Aspects of the device fabrication process and device operation are discussed. The experimental results obtained are compared to a numerical simulation of device performance and found to be within good agreement.