Papers by Douglas Kirkpatrick
Thr temporal evolution of the beam emlttance from a multi-&~~trodz field rnli&a drctron gun (1.3 ... more Thr temporal evolution of the beam emlttance from a multi-&~~trodz field rnli&a drctron gun (1.3 MV, 0 5 kA, 30 ns) has hem measurrd n tth nanosecond time resolution, using a novel Cerenkov-dectrooptic dlag"ost,c In addition, WC report experimental studies of the cathod? plasma umiformlt,y from a field rmission dmdr (250 kV, 2 kA. 100 ns) The obwrvatic~r~s from both systems show that diodes provided with wlvethackrd cathodes behavr differzntfy, and are superior to, the more conven-t~c~nal graphite cathodes.
Physical Review A, 1985
Off-axis electron orbits in free-electron laser (FEL) beams of finite thickness, subjected to com... more Off-axis electron orbits in free-electron laser (FEL) beams of finite thickness, subjected to combined helical wiggler and axial guide fields, have been studied analytically. A semi-empirical equation for the electron velocity components, averaged over the electron's oscillatory (betatron) motion, has been derived as a function of the radial displacement of the electron guiding center. The predictions from the equation are compared with single particle numerical simulations, and with free-electron laser experiments. Good agreement is found.
SPIE Proceedings, 1988
We report high power emission (18 MW) at a wavelength of λ = 640 μm and a bandwidth ΔAλ/λ< 0.0... more We report high power emission (18 MW) at a wavelength of λ = 640 μm and a bandwidth ΔAλ/λ< 0.04 from a superradiant free electron laser (FEL) excited by a 2MeV, 1 kA electron beam. Comparison of the experiment with a nonlinear simulation yields good agreement. Theoretical extrapolation to a tapered wiggler experiment shows that power levels of 140 MW could be achieved with an efficiency of 7%.
Physics of Fluids B: Plasma Physics, 1990
A Ka-band gyrotron oscillator experiment using a 1–1.35 MeV, multikiloampere beam from a pulse li... more A Ka-band gyrotron oscillator experiment using a 1–1.35 MeV, multikiloampere beam from a pulse line accelerator has produced approximately 250 MW at 35 GHz in a circular TE62 mode with a peak efficiency exceeding 10&amp;amp;amp;amp;amp;amp;amp;percnt;. Time-dependent simulation studies have been used to predict the behavior of a high-peak-power, short-pulse gyrotron in this parameter range. The simulations demonstrate the occurrence of
21st European Photovoltaic Solar …, 2006
Very high efficiency is an important characteristic of the value proposition for solar to electri... more Very high efficiency is an important characteristic of the value proposition for solar to electric conversion. High efficiency is the shortest path to cost-effective commercial applications and leads to new high value applications such as portable battery charging. The Defense Advanced Research Projects Agency has initiated the Very High Efficiency Solar Cell (VHESC) program to address the critical need of the soldier for power in the field. Very High Efficiency Solar Cells for portable applications 1,2 that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being developed. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new architecture paradigm. An integrated team effort is now underway that requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC Program.
Thin Solid Films, 1997
Solar thermal electric power systems use large solar reflectors to concentrate sunlight to genera... more Solar thermal electric power systems use large solar reflectors to concentrate sunlight to generate electricity. The economic viability of these systems depends on developing a durable, low-cost reflector. The goals for such a reflector are specular reflectance above 90% for at least 10 years under outdoor service conditions and a large-volume manufacturing cost of less than $10.8/m2 ($1.00/ft 2). Currently, the best candidate materials for solar reflectors are silver-coated, low-iron glass and silvered polymer films. Polymer reflectors are lighter in weight, offer greater system design flexibility, and have the potential for lower cost than glass reflectors. A promising lowcost reflector consists of a silvered polymer protected by an optically transparent alumina coating. The coating is deposited by an ion-beam-assisted physical vapor deposition (IBAD) technique. Samples of this reflector have maintained high optical performance in accelerated testing at the National Renewable Energy Laboratory for more than 3000 hours. Solar reflectors produced using this technique may represent an opportunity to bring solar power generation to reality.
Journal of Applied Physics, 1987
The temporal evolution of the beam emittance and beam brightness from a field emission electron g... more The temporal evolution of the beam emittance and beam brightness from a field emission electron gun (1.3 MV, 0.5 kA, 30 ns) has been measured with nanosecond time resolution, using a novel Oerenkov-electrooptic diagnostic. Observations show that guns provided with velvet-backed cathodes behave differently, and are superior to, the more conventional graphite cathodes.
The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system - PV ... more The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system - PV modules for portable applications that operate at greater than 50 percent efficiency. We are integrating the optical design with the solar cell design, and have entered previously ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1989
Approved for public release, distribution unlimited UNCLASSIFIED Approved for public release; dis... more Approved for public release, distribution unlimited UNCLASSIFIED Approved for public release; distribution 2 0 DECASS C a-n' '.O RAD %C SC E D unlimited. 4 P-P-ORM, NO ORCA% Z.A ON% PEPO5T N _jMBER S 5 MO0N OR "(7 uF ZA-G'N Pf) NRL Memorandum Report 6388 6a NAME OF PI-RFOPV NO OPGA% ZAT ON 6b OFF CE SYMBOL 7a NAVE OF V-). 'o N: 1 (if applicable) Naval Research Laboratory Code 4740 Ec ADDRESS CTay State and ZIP Code) 11, ADDRES Ci ty State and 1P Co,1e) Washington, DC 20375-5000 8a NAME OF FND NOC SPONSOR NO 8bo OFF CE SYMBOL 9 PPOC PEVEN'Nr~.N F CaA % %-3c OP(3ANFZA' ON (if 'Phcable) ONR I_______ Sc ADDRESS (Coty State, and ZIP Code) '0 SO.ACE OF KNDI(NO N.,MEPS
SPIE Proceedings, 2004
In this contribution we consider the problem of designing coupling optics to optimally transfer l... more In this contribution we consider the problem of designing coupling optics to optimally transfer light from a metal-halide arc lamp to a large core polymethyl methacrylate (PMMA) fiber optic cable. We investigate a refractive optical coupling concept comprising a non-axisymmetric bifurcated refractive glass TIR lens (TIRL) set. The design goal is to maximize the photometric flux incident onto two 19-mm-diameter apertures within an acceptance half angle of 38º. The light source is an 80-Watt metal halide arc lamp, characterized by means of photometric data measured by Radiant Imaging. The lenses each comprise a central refractive section combined with an annular TIR section. The exit pupil of each TIR lens is separated from the entrance aperture of the target by a short air gap. The refractive section of the TIR lens utilizes two aspheric surfaces to collect source flux over a central solid-angular region and redirect it into the target. The TIR section utilizes a total of three aspheric surfaces, two of which are refractive and one of which is a TIR surface. To account for right-left asymmetries in the optical source, the TIR lenses were independently globally optimized for both sides. Our TIRL design has the advantage of being able to collect and control radiation emanating at both large and small angles from the source, with little overall loss. The TIRL, with an ideal AR coating, has a predicted coupling efficiency of 89.6%. This was accomplished even though the target to source étendue ratio is only 63.7%. This is possible due to the ability of this design to preferentially transfer radiation from the higher radiance portions of the source phase space to the target. The work described above was funded by the Defense Advanced Research Projects Agency's High Efficiency Distributed Lighting Program known as HEDLight.
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
Nonimaging Optics and Efficient Illumination Systems III, 2006
The Defense Advanced Research Projects Agency has initiated the Very High Efficiency Solar Cell (... more The Defense Advanced Research Projects Agency has initiated the Very High Efficiency Solar Cell (VHESC) program to address the critical need of the soldier for power in the field. Very High Efficiency Solar Cells for portable applications that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being developed. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new architecture paradigm. An integrated team effort is now underway that requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC Program.
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
Very High Efficiency Solar Cells (VHESC) for portable applications [1] that operate at greater th... more Very High Efficiency Solar Cells (VHESC) for portable applications [1] that operate at greater than 55 percent efficiency in the laboratory and 50 percent in production are being created. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space that leads to a new paradigm. This project requires us to invent, develop and transfer to production these new solar cells. Our approach is driven by proven quantitative models for the solar cell design, the optical design and the integration of these designs. We start with a very high performance crystalline silicon solar cell platform. Examples will be presented. Initial solar cell device results are shown for devices fabricated in geometries designed for this VHESC Program.
SPIE Proceedings, 2001
Fusion Lighting, Inc. has been developing an RF-powered electrodeless light source known as the B... more Fusion Lighting, Inc. has been developing an RF-powered electrodeless light source known as the ByteLightTM. This source is spectrally stable, has a high luminous efficiency and exceptional spatial and angular uniformity. In this paper we describe a nonimaging projection lens designed to efficiently collect and transfer flux from the circular aperture of a ByteLightTM lamp into a rectangular aperture of an optical train of an InFocus Model #LP0335-V single-panel DMDbased front projector. The source was experimentally characterized by Radiant Imaging, Inc. using a technique that captures its full four-dimensional phase space behaviour. The lens was then designed by implementing a global optimization procedure over a parametrization search space with variables that determine the positional and aspheric geometrical properties of the lens. The optimization was performed subject to constraints arising from packaging and fabrication considerations. The resulting lens employs a combination of refraction and total-internal reflection (TIR) mechanisms to achieve a total flux-transfer efficiency of 75.6%, which compares favourably to a baseline design that employs a UHP arc lamp.
Progress in Photovoltaics: Research and Applications, 2009
The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system-PV mo... more The Very High Efficiency Solar Cell (VHESC) program is developing integrated optical system-PV modules for portable applications that operate at greater than 50% efficiency. We are integrating the optical design with the solar cell design, and have entered previously unoccupied design space. Our approach is driven by proven quantitative models for the solar cell design, the optical design, and the integration of these designs. Optical systems efficiency with an optical efficiency of 93% and solar cell device results under ideal dichroic splitting optics summing to 42Á7 W 2Á5% are described.
MILCOM 2015 - 2015 IEEE Military Communications Conference, 2015
Minimizing size, weight, and power consumption (SWaP) in any communication system requires that t... more Minimizing size, weight, and power consumption (SWaP) in any communication system requires that the transmitter power amplifier operate at peak possible efficiency at all times and at all frequencies. Here a GaN watt-level transmitter is presented that operates across 0.2 to 3 GHz, with no matching network reconfiguration, and broadband efficiency exceeding 50%. Besides minimizing power consumption, this design provides the required power simultaneously with having the smallest possible transistor size, power supply, and heat sink. Frequency agility is across the entire PA bandwidth, and no circulator is required to operate in phased-array applications. Signal modulation compatibility is also discussed.
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Papers by Douglas Kirkpatrick