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Pinhole closure measurements

Description: Spatial-filter pinholes and knife-edge samples were irradiated in vacuum by 1053-nm, 5-20 ns pulses at intensities to 500 GW/cm<sup2</sup>. The knife-edge samples were fabricated of plastic, carbon, ahnuinum, stainless steel, molybdenum, tantalum, gold and an absorbing glass. Time-resolved two-beam interferometry with a 40-ns probe pulse was used to observe phase shifts in the expanding laser-induced plasma. For all of these materials, at any time during square-pulse irradiation, the phase shift fell exponentially with distance from the edge of the sample. The expansion was characterized by the propagation velocity V<sub>2x</sub> of the contour for a 2(pi) phase shift. To within experimental error, V<sub>2x</sub>, was constant during irradiation at a particular intensity, and it increased linearly with intensity for intensities <300 GW/cn<sup>2</sup>. For metal samples, V, exhibited an approximate M<sup>-0.5</sup> dependence where M is the atomic mass. Plasmas of plastic, carbon and absorbing glass produced larger phase shifts, and expanded more rapidly, than plasmas of the heavy metals. The probe beam and interferometer were also used to observe the closing of pinholes. With planar pinholes, accumulation of on-axis plasma was observed along with the advance of plasma away from the edge of the hole. On-axis closure was not observed in square, 4-leaf pinholes.
Date: July 20, 1998
Creator: Afeyan, B. B.; Boley, C. D.; Estabrook, K. G.; Kirkwood, R. K.; Milam, D.; Murray, J. E. et al.
Partner: UNT Libraries Government Documents Department

The Adiabatic Matching Section Solution for the Source Injector

Description: Typical designs for a Heavy Ion Fusion Power Plant require the source injector to deliver 100 beams, packed into an array with a spacing of 7 cm. When designing source injectors using a single large aperture source for each beam, the emitter surfaces are packed into an array with a spacing of 30 cm. Thus, the matching section of the source injector must not only prepare the beam for transport in a FODO lattice, but also funnel the beams together. This can be accomplished by an ESQ matching section in which each beam travels on average at a slight angle to the axis of the quadrupoles and uses the focusing effect of the FODO lattice to maintain the angle. At the end of the matching section, doublet steering is used to bring the beams parallel to each other for injection into the main accelerator. A specific solution of this type for an 84-beam source injector is presented.
Date: March 1, 2000
Creator: Ahle, L.; Grote, D.P.; Halaza, E.; Henestroza, E.; Kwan, J.W. & MaClaren, S.A.
Partner: UNT Libraries Government Documents Department

Initial experiments of RF gas plasma source for heavy ionfusion

Description: The Source Injector Program for the US Heavy Ion Fusion Virtual National Laboratory is currently exploring the feasibility of using RF gas plasma sources for a HIF driver. This source technology is presently the leading candidate for the multiple aperture concept, in which bright millimeter size beamlets are extracted and accelerated electrostatically up to 1 MeV before the beamlets are allowed to merge and form 1 A beams. Initial experiments have successfully demonstrated simultaneously high current density, {approx} 100 mA/cm{sup 2} and fast turn on, {approx} 1 {micro}s. These experiments were also used to explore operating ranges for pressure and RF power. Results from these experiments are presented as well as progress and plans for the next set of experiments for these sources.
Date: May 22, 2002
Creator: Ahle, L.; Hall, R.; Molvik, A.W.; Chacon-Golcher, E.; Kwan, J.W.; Leung, K.N. et al.
Partner: UNT Libraries Government Documents Department

RF gas plasma source development for heavy ion fusion

Description: Presently the Heavy Ion Fusion Virtual National Laboratory is researching ion sources and injector concepts to understand how to optimize beam brightness over a range of currents (50-2000 mA argon equivalent). One concept initially accelerates millimeter size, milliamp beamlets to 1 MeV before merging them into centimeter size, ampere beams. Computer simulations have shown the final brightness of the merged beams is dominated by the emittance growth of the merging process, as long as the beamlets ion temperature is below a few eV. Thus, a RF multicusp source capable of high current density can produce beams with better brightness compared to ones extracted from a colder source with a large aperture and lower current density. As such, experiments have begun to develop a RF multicusp source capable of delivering one amp of extracted beam current. It is expected that it will require 10 kW of 13 MHz RF power delivered via a quartz shielded, one and half turn, four inch diameter antenna. Important considerations in the development of the source include the dependence of current density and beam ion temperature on consumed RF power and gas pressure. A fast rise time ({approx}100 ns) for the extracted beam pulse must also be achieved. Progress on these experiments will be presented.
Date: February 22, 2002
Creator: Ahle, L.E.; Hall, R.P. & Molvik, A.W.
Partner: UNT Libraries Government Documents Department

RF Gas Plasma Source Development for Heavy Ion Fusion

Description: Presently the Heavy Ion Fusion Virtual National Laboratory is researching ion sources and injector concepts to understand how to optimize beam brightness over a range of currents (50-2000 mA argon equivalent). One concept initially accelerates millimeter size, milliamp beamlets to 1 MeV before merging them into centimeter size, ampere beams. Computer simulations have shown the final brightness of the merged beams is dominated by the emittance growth of the merging process, as long as the beamlets ion temperature is below a few eV. Thus, a RF multicusp source capable of high current density can produce beams with better brightness compared to ones extracted from a colder source with a large aperture and lower current density. As such, experiments have begun to develop a RF multicusp source capable of delivering one amp of extracted beam current. It is expected that it will require 10 kW of 13 MHz RF power delivered via a quartz shielded, one and half turn, four inch diameter antenna. Important considerations in the development of the source include the dependence of current density and beam ion temperature on consumed RF power and gas pressure. A fast rise time ({approx} 100 ns) for the extracted beam pulse must also be achieved. Progress on these experiments will be presented.
Date: September 4, 2001
Creator: Ahle, L; Hall, R P; Molvik, A W; Kwan, J W & Leung, K N
Partner: UNT Libraries Government Documents Department

Surface figure and roughness tolerances for NIF optics and the interpretation of the gradient, P-V wavefront and RMS specifications

Description: In a high energy laser system such as the National Ignition Facility (NIF), the ability to focus light into as small a spot as possible at the highest possible fluence is highly dependent on the quality of the optics used in the system. Typically, surface form errors and transmitted and reflected wavefront errors are specified in terms of a peak-to-valley wavefront error (P-V), or occasionally in terms of an RMS wavefront error (RMS) 1 . It has been shown, however, that the parameter that most closely correlates with beam focusability is neither of these, but the RMS of the gradients of the wavefront error (RMS Gradient). Further, the spatial frequency of the wavefront error plays a significant role in the way that a given error effects the performance of the laser system, so careful attention must be paid to how the spatial filtering is both specified and accomplished. Since ISO 10110 has no specific provisions for a gradient specification, LLNL has developed its own notation and procedures for these critical specifications. In evaluating surface figure errors as specified by the NIF drawings, modern phase modulating interferometers (PMI) will be used. In addition to performing QA testing of the optics, LLNL intends to utilize the software capabilities of the instruments to obtain the information to model the wavefront of the 131 passes through various optical elements comprising the NIF front end. Tests will be performed and documented after coating and as installed in the specified mechanical mounts. This paper describes the evaluation of the wavefront error for NIF small optics including specifications over a given spatial period callout, the proper low pass filtering of the data and the allowable filtering and settings that can be applied to obtain proper wavefront data. This paper also describes the origin and evolution of other ...
Date: July 1, 1999
Creator: Aikens, D M; English, R E; House, W; Lawson, J K; Nichols, M A & Whistler, W T
Partner: UNT Libraries Government Documents Department

BNL Volume H{sup {minus}} Sources

Description: An H{sup -} current of up 30 mA has been extracted from a 1 cm{sup 2} aperture in a 20 cm diameter volume source with a conical filter field. From a 9.7 cm diameter version of this source, an H{sup -} current of up to 35 mA was extracted from a 0.5 cm{sup 2} aperture.In both sources, the electron-to-H{sup -} ratio is typically < 10, and often < 5.
Date: December 31, 1992
Creator: Alessi, J. G.; Prelec, K. & McCafferty, D.
Partner: UNT Libraries Government Documents Department

A circular aperture magnetron for injection into an RFQ

Description: A magnetron with a circular anode aperture and a spherical dimple in the cathode has been operated. With this configuration, a normalized emittance (90%) of 0.1..pi..cm-mrad has been measured in both planes for an H/sup -/ current of >50 mA. Other than this symmetric emittance, the source performance is the same as with the typical anode slit and grooved cathode.
Date: January 1, 1986
Creator: Alessi, J.G.
Partner: UNT Libraries Government Documents Department

The BNL toroidal volume H sup minus source

Description: The BNL toroidal volume H{sup {minus}} ion source, in pulsed operation is now producing up to 35 mA with an electron to H{sup {minus}} ratio of less than 5, and a ratio of less than 3 for currents up to 20 mA. This improvement came about by increasing the strength of the conical filter field. The source has also been operated steady state at low arc currents, where up to 6 mA of H{sup {minus}} was extracted. The electron to H{sup {minus}} ratio is 2--3 times larger for dc operation. For dc currents up to 5 mA, the arc power efficiency was 5 mA/kW. Pulsed performance with Ta and W filaments were very similar, except for the large gas pumping observed with the Ta filament. In dc operation, the Ta filament performed somewhat better than W. Extraction from 7 apertures having a total area of 1 cm{sup 2} produced the same results as a single 1 cm{sup 2} aperture. 5 refs., 4 figs.
Date: January 1, 1991
Creator: Alessi, J.G. & Prelec, K.
Partner: UNT Libraries Government Documents Department

A 3 TeV Muon Collider Lattice Design

Description: A new lattice for 3 TeV c.o.m. energy with {beta}* = 5mm was developed which follows the basic concept of the earlier 1.5 TeV design but uses quad triplets for the final focus in order to keep the maximum magnet strength and aperture close to those in 1.5 TeV case. Another difference is employment of combined-function magnets with the goal to lower heat deposition in magnet cold mass and to eliminate bending field free regions which produce 'hot spots' of neutrino radiation that can be an issue at higher energy. The proposed lattice is shown to satisfy the requirements on luminosity, dynamic aperture and momentum acceptance.
Date: May 1, 2012
Creator: Alexahin, Y. & Gianfelice-Wendt, E.
Partner: UNT Libraries Government Documents Department

Chromaticity correction for a muon collider optics

Description: Muon Collider (MC) is a promising candidate for the next energy frontier machine. However, in order to obtain peak luminosity in the 10{sup 34} cm{sup 2}s{sup -1} range the collider lattice designmust satisfy a number of stringent requirements. In particular the expected large momentum spread of the muon beam and the very small {beta}* call for a careful correction of the chromatic effects. Here we present a particular solution for the interaction region (IR) optics whose distinctive feature is a three-sextupole local chromatic correction scheme. The scheme may be applied to other future machines where chromatic effects are expected to be large. The expected large muon energy spread requires the optics to be stable over a wide range of momenta whereas the required luminosity calls for {beta}* in the mm range. To avoid luminosity degradation due to hour-glass effect, the bunch length must be comparatively small. To keep the needed RF voltage within feasible limits the momentum compaction factor must be small over the wide range of momenta. A low {beta}* means high sensitivity to alignment and field errors of the Interaction Region (IR) quadrupoles and large chromatic effects which limit the momentum range of optics stability and require strong correction sextupoles, which eventually limit the Dynamic Aperture (DA). Finally, the ring circumference should be as small as possible, luminosity being inversely proportional to the collider length. A promising solution for a 1.5 TeV center of mass energy MC with {beta}* = 1 m in both planes has been proposed. This {beta}* value has been chosen as a compromise between luminosity and feasibility based on the magnet design and energy deposition considerations. The proposed solution for the IR optics together with a new flexible momentum compaction arc cell design allows to satisfy all requirements and is relatively insensitive to the ...
Date: March 1, 2011
Creator: Alexahin, Y.; Gianfelice-Wendt, E.; Kapin, V. & /Fermilab
Partner: UNT Libraries Government Documents Department

Effect of Field Errors in Muon Collider IR Magnets on Beam Dynamics

Description: In order to achieve peak luminosity of a Muon Collider (MC) in the 10{sup 35} cm{sup -2}s{sup -1} range very small values of beta-function at the interaction point (IP) are necessary ({beta}* {le} 1 cm) while the distance from IP to the first quadrupole can not be made shorter than {approx}6 m as dictated by the necessity of detector protection from backgrounds. In the result the beta-function at the final focus quadrupoles can reach 100 km making beam dynamics very sensitive to all kind of errors. In the present report we consider the effects on momentum acceptance and dynamic aperture of multipole field errors in the body of IR dipoles as well as of fringe-fields in both dipoles and quadrupoles in the ase of 1.5 TeV (c.o.m.) MC. Analysis shows these effects to be strong but correctable with dedicated multipole correctors.
Date: May 1, 2012
Creator: Alexahin, Y.; Gianfelice-Wendt, E.; Kapin, V.V. & /Fermilab
Partner: UNT Libraries Government Documents Department

Conceptual design of the muon collider ring lattice

Description: Muon collider is a promising candidate for the next energy frontier machine. However, in order to obtain peak luminosity in the 10{sup 35}/cm{sup 2}/s range the collider lattice design must satisfy a number of stringent requirements, such as low beta at IP ({beta}* &lt; 1 cm), large momentum acceptance and dynamic aperture and small value of the momentum compaction factor. Here we present a particular solution for the interaction region optics whose distinctive feature is a three-sextupole local chromatic correction scheme. Together with a new flexible momentum compaction arc cell design this scheme allows to satisfy all the above-mentioned requirements and is relatively insensitive to the beam-beam effect.
Date: May 1, 2010
Creator: Alexahin, Y.; Gianfelice-Wendt, E.; Netepenko, A. & /Fermilab
Partner: UNT Libraries Government Documents Department

Beam loss and collimation in the Fermilab 16 GeV proton driver

Description: A high beam power of 1.15 MW in the proposed 16-GeV Proton Driver [1] implies serious constraints on beam losses in the machine. The main concerns are the hands-on maintenance and ground-water activation. Only with a very efficient beam collimation system can one reduce uncontrolled beam losses to an allowable level. The results on tolerable beam loss and on a proposed beam collimation system are summarized in this paper. A multi-turn particle tracking in the accelerator defined by all lattice components with their realistic strengths and aperture restrictions, and halo interactions with the collimators is done with the STRUCT code [2]. Full-scale Monte Carlo hadronic and electromagnetic shower simulations in the lattice elements, shielding, tunnel and surrounding dirt with realistic geometry, materials and magnetic field are done with the MARS14 code [3]. It is shown that the proposed 3-stage collimation system, allows localization of more than 99% of beamloss in a special straight section. Beam loss in the rest of the accelerator is 0.2 W/m on average.
Date: July 20, 2001
Creator: Alexandr I. Drozhdin, Oleg E. Krivosheev and Nikolai V. Mokhov
Partner: UNT Libraries Government Documents Department

Aperture calculation of the Pierre Auger Observatory surface detector

Description: We determine the instantaneous aperture and integrated exposure of the surface detector of the Pierre Auger Observatory, taking into account the trigger efficiency as a function of the energy, arrival direction (with zenith angle lower than 60 degrees) and nature of the primary cosmic-ray. We make use of the so-called Lateral Trigger Probability function (or LTP) associated with an extensive air shower, which summarizes all the relevant information about the physics of the shower, the water tank Cherenkov detector, and the triggers.
Date: August 1, 2005
Creator: Allard, D.; Allekotte, I.; Armengaud, E.; Aublin, J.; Bertou, Xavier; Chou, A. et al.
Partner: UNT Libraries Government Documents Department

Highly-Efficient Laser with Self-Aligned Waveguide and Current Confinement by Selective Oxidation

Description: We report highly efficient, low-threshold-current edge-emitting lasers where both the optical waveguide and lateral current confinement are achieved by lateral selective oxidation of AlGaAs. External differential quantum efficiency in excess of 95% and 40% wall-plug efficiency are demonstrated in 600 {micro}m-long devices without facet coatings. Shorter, 300-{micro}m-long, uncoated devices have &lt;6 mA threshold currents. This high-performance is a combined result of placement of the oxide layers so as to achieve the minimum optical mode volume and bi-parabolic grading of the Al{sub x}Ga{sub 1{minus}x}As heteroepitaxy for minimum height/potential barriers, less than 15 meV, created by the wide-energy-gap layers required for selective wet oxidation. Since the initial development of wet AlGaAs oxidation methods, a number of oxidized edge-emitting laser concepts have been tried. The most successful of these have used lateral selective oxidation of AlGaAs layers between 100 and 300 nm thickness. These layers have been used as current restricting apertures or for both current restriction and lateral waveguiding. Use of an oxide layer above and below the laser active region offers the ability to create a self-aligned waveguide with current apertures on both sides of the pn-junction in a process requiring only one epitaxial growth step. Previous use apertures for these dual purposes resulted multi-moded lasers with reduced efficiency and elevated threshold current density due to non-ideal formation of the waveguide and possibly excess stress caused by the thick (300 nm) oxide layer.
Date: July 27, 1999
Creator: Allerman, A.; Blum, O.; Gao, Y. & Vawter, G.A.
Partner: UNT Libraries Government Documents Department

Development and coil fabrication for the LARP 3.7-m long Nb3Sn quadruple

Description: The U.S. LHC Accelerator Research Program (LARP) has started the fabrication of 3.7-m long Nb{sub 3}Sn quadrupole models. The Long Quadrupoles (LQ) are 'Proof-of-Principle' magnets which are to demonstrate that Nb3Sn technology is mature for use in high energy particle accelerators. Their design is based on the LARP Technological Quadrupole (TQ) models, developed at FNAL and LBNL, which have design gradients higher than 200 T/m and an aperture of 90 mm. The plans for the LQ R&amp;D and a design update are presented and discussed in this paper. The challenges of fabricating long accelerator-quality Nb{sub 3}Sn coils are presented together with the solutions adopted for the LQ coils (based on the TQ experience). During the fabrication and inspection of practice coils some problems were found and corrected. The fabrication at BNL and FNAL of the set of coils for the first Long Quadrupole is in progress.
Date: February 1, 2009
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S. et al.
Partner: UNT Libraries Government Documents Department

Development and Coil Fabrication for the LARP 3.7-m Long Nb3Sn Quadrupole

Description: The U.S. LHC Accelerator Research Program (LARP) has started the fabrication of 3.7-m long Nb{sub 3}Sn quadrupole models. The Long Quadrupoles (LQ) are 'Proof-of-Principle' magnets which are to demonstrate that Nb{sub 3}Sn technology is mature for use in high energy particle accelerators. Their design is based on the LARP Technological Quadrupole (TQ) models, developed at FNAL and LBNL, which have design gradients higher than 200 T/m and an aperture of 90 mm. The plans for the LQ R&amp;D and a design update are presented and discussed in this paper. The challenges of fabricating long accelerator-quality Nb{sub 3}Sn coils are presented together with the solutions adopted for the LQ coils (based on the TQ experience). During the fabrication and inspection of practice coils some problems were found and corrected. The fabrication at BNL and FNAL of the set of coils for the first Long Quadrupole is in progress.
Date: August 17, 2008
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S. et al.
Partner: UNT Libraries Government Documents Department

LARP Long Nb3Sn Quadrupole Design

Description: A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb3Sn conductor. The goal of these magnets is to be a proof of principle that Nb3Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.
Date: August 1, 2007
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S. et al.
Partner: UNT Libraries Government Documents Department

LARP Long Nb3Sn Quadrupole Design.

Description: A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb{sub 3}Sn conductor. The goal of these magnets is to be a proof of principle that Nb{sub 3}Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.
Date: August 27, 2007
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S. et al.
Partner: UNT Libraries Government Documents Department

LARP Long Nb3Sn Quadrupole Design

Description: A major milestone for the LHC Accelerator Research Program (LARP) is the test, by the end of 2009, of two 4m-long quadrupole magnets (LQ) wound with Nb{sub 3}Sn conductor. The goal of these magnets is to be a proof of principle that Nb{sub 3}Sn is a viable technology for a possible LHC luminosity upgrade. The design of the LQ is based on the design of the LARP Technological Quadrupoles, presently under development at FNAL and LBNL, with 90-mm aperture and gradient higher than 200 T/m. The design of the first LQ model will be completed by the end of 2007 with the selection of a mechanical design. In this paper we present the coil design addressing some fabrication technology issues, the quench protection study, and three designs of the support structure.
Date: June 1, 2008
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Caspi, S. et al.
Partner: UNT Libraries Government Documents Department

Design of Nb3Sn coils for LARP long magnets

Description: The LHC Accelerator Research Program (LARP) has a primary goal to develop, assemble, and test full size Nb{sub 3}Sn quadrupole magnet models for a luminosity upgrade of the Large Hadron Collider (LHC). A major milestone in this development is to assemble and test, by the end of 2009, two 4m-long quadrupole cold masses, which will be the first Nb3Sn accelerator magnet models approaching the length of real accelerator magnets. The design is based on the LARP Technological Quadrupoles (TQ), under development at FNAL and LBNL, with gradient higher than 200 T/m and aperture of 90 mm. The mechanical design will be chosen between two designs presently explored for the TQs: traditional collars and Al-shell based design (preloaded by bladders and keys). The fabrication of the first long quadrupole model is expected to start in the last quarter of 2007. Meanwhile the fabrication of 4m-long racetrack coils started this year at BNL. These coils will be tested in an Al-shell based supporting structure developed at LBNL. Several challenges have to be addressed for the successful fabrication of long Nb{sub 3}Sn coils. This paper presents these challenges with comments and solutions adopted or under study for these magnets. The coil design of these magnets, including conductor and insulation features, and quench protection studies are also presented.
Date: August 1, 2006
Creator: Ambrosio, G.; Andreev, N.; Anerella, M.; Barzi, E.; Bossert, R.; Dietderich, D. et al.
Partner: UNT Libraries Government Documents Department

Microarcsecond relative astrometry from the ground with a diffractive pupil

Description: The practical use of astrometry to detect exoplanets via the reflex motion of the parent star depends critically on the elimination of systematic floors in imaging systems. In the diffractive pupil technique proposed for space-based detection of exo-earths, extended diffraction spikes generated by a dotted primary mirror are referenced against a wide-field grid of background stars to calibrate changing optical distortion and achieve microarcsecond astrometric precision on bright targets (Guyon et al. 2010). We describe applications of this concept to ground-based uncrowded astrometry using a diffractive, monopupil telescope and a wide-field camera to image as many as {approx}4000 background reference stars. Final relative astrometric precision is limited by differential tip/tilt jitter caused by high altitude layers of turbulence. A diffractive 3-meter telescope is capable of reaching {approx}35 {micro}as relative astrometric error per coordinate perpendicular to the zenith vector in three hours on a bright target star (I &lt; 10) in fields of moderate stellar density ({approx}40 stars arcmin{sup -2} with I &lt; 23). Smaller diffractive apertures (D &lt; 1 m) can achieve 100-200 {micro}as performance with the same stellar density and exposure time and a large telescope (6.5-10 m) could achieve as low as 10 {micro}as, nearly an order of magnitude better than current space-based facilities. The diffractive pupil enables the use of larger fields of view through calibration of changing optical distortion as well as brighter target stars (V &lt; 6) by preventing star saturation. Permitting the sky to naturally roll to average signals over many thousands of pixels can mitigate the effects of detector imperfections.
Date: September 8, 2011
Creator: Ammons, S M; Bendek, E & Guyon, O
Partner: UNT Libraries Government Documents Department

Wideband beam patterns from sparse arrays

Description: Transient radiated fields due to impulsively excited apertures and aperture response due to incident impulsive waves has been the subject of considerable research in acoustics over the last decade. This research is also of importance to wideband radar. Medical ultrasound steered phased arrays use transmitted pulses consisting of from 1 to 3 cycles of a damped sinusoid, which is similar to certain radar systems. As will be shown, planar arrays using ultra-wide band pulses may be formed with very sparsely spaced elements. This makes feasible very high resolution, economical, and relatively simple, steered beam phased arrays. The resolution may be increased simply by moving the array elements further apart. Grating lobes due to aliasing are not formed when the elements are sparsely spaced. In a very sparse wide band array, element spacing effects the form, or signal shape in time, rather than the peak amplitude of the sidelobe structure. The number of elements in the aperture determines the peak sidelobe level which, in theory, may be decreased without limit. 13 refs., 7 figs.
Date: January 12, 1990
Creator: Anderson, F. (Anderson (Forrest), Bernalillo, NM (USA)); Fullerton, L. (Time Domain Systems, Huntsville, AL (USA)); Christensen, W. & Kortegaard, B. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department