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Retuning the APS storage ring for better chromaticity correction.

Description: When the APS storage ring was retuned to provide smaller {beta}{sub y} values in the insertion straight sections, it was necessary to increase the vertical tune by at least two units. Since the design values for the horizontal and vertical tunes are 35.22 and 16.30, respectively, this put the tunes dangerously close to the sextupole 2v{sub y}-v{sub x} coupling resonance. The large injection horizontal oscillations could couple to the vertical plane and exceed the 5-mm vertical apertures that exist in some of the insertion straight sections. To avoid this resonance, the vertical tune was raised beyond the resonance to 19.30. The result was a reduction in the ability of the chromaticity sextuples to correct the chromaticity. Recent investigation has shown that the chromaticity correction capability of the sextuples can be greatly increased by a modest increase in the horizontal tune. Increasing the horizontal tune by one unit and reducing the vertical tune by three units produces a lattice with better chromaticity control while maintaining an acceptable dynamic aperture.
Date: September 11, 1999
Creator: Chae, Y.-C. & Crosbie, E.A.
Partner: UNT Libraries Government Documents Department

Comparison of Tevatron C0 and F0 Lambertson beam impedance

Description: Both the longitudinal and transverse beam impedance measurements for the Tevatron C0 and F0 lambertsons are presented. The C0 lambertsons were designed for circulating beam to travel through the 1 inch high by 6 inch wide field region. In the F0 lambertsons, circulating beam passes through the 2.5 inch high by 4 in ch wide field free region. The more recently designed F0 lambertsons have significantly less impedance than the older C0 lambertsons. Transverse impedance scales as one over the diameter of the aperture cubed. The three C0 style lambertsons were recently removed from the Tevatron. Four of the F0 lambertsons remain. Nine of the F0 style lambertsons are in the Main Injector and three more are required for Numi.
Date: April 11, 2003
Creator: Fellenz, James L Crisp and Brian
Partner: UNT Libraries Government Documents Department

Initial Operation of the NSTX Fast Tangential Soft X-Ray Camera

Description: Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of MHD instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the National Spherical Torus Experiment. It is based on a recently developed 64 x 64 pixel CCD camera capable of capturing 300 frames at up to 500,000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2-10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.
Date: May 11, 2004
Creator: Stratton, B.C.; Feder, R.; Goeler, S. von; Renda, G.F.; Lowrance, J.L. & Mastrocola, V.J.
Partner: UNT Libraries Government Documents Department

Frequency map analysis of nonlinear dynamics in the NLC main damping rings

Description: To avoid radiation damage, the acceptance of linear collider damping rings must be large enough that injection efficiency close to 100 percent can be achieved. Survival plots based on tracking particles in the NLC Main Damping Ring lattice suggest a dynamic aperture with some margin over the specified injected beam size and energy spread. Here, we apply Frequency Map Analysis to give a more detailed picture of the dynamical stability of particle trajectories in the presence of lattice nonlinearities arising from the sextupoles and the damping wiggler. The techniques that we use are of general applicability to nonlinear elements in beamlines, and in particular will be used for analysis of wiggler effects in future damping ring designs.
Date: October 11, 2004
Creator: Wolski, Andrzej; Venturini, Marco; Wan, Weishi & Marks, Steve
Partner: UNT Libraries Government Documents Department

Performance results for Beamlet: A large aperture multipass Nd glass laser

Description: The Beamlet laser is a large aperture, flashlamp pumped Nd: glass laser that is a scientific prototype of an advanced Inertial Fusion laser. Beamlet has achieved third harmonic, conversion efficiency of near 80% with its nominal 35cm {times} 35cm square beam at mean 3{omega} fluences in excess of 8 J/cm{sup 2}(3-ns). Beamlet uses an adaptive optics system to correct for aberrations and achieve less than 2 {times} diffraction limited far field spot size.
Date: April 11, 1995
Creator: Campbell, J.H.; Barker, C.E.; VanWonterghem, B.M.; Speck, D.R.; Behrendt, W.C.; Murray, J.R. et al.
Partner: UNT Libraries Government Documents Department

Measurement and simulation of the UMERbeam in the sourceregion

Description: As the beam propagates in the University of Maryland Electron Ring (UMER) complex transverse density structure including halos has been observed. A primary objective of the experiment is to understand the evolution of a space-charge-dominated beam as it propagates over a substantial distance. It is therefore important to understand which details of the beam structure result from propagation of the beam in the ring and which characteristics result from the specific details of the initial distribution. Detailed measurements of the initial beam characteristics have therefore been performed. These include direct measurement of the density using a phosphor screen, as well as pepper pot measurements of the initial transverse distribution function. Detailed measurements of the distribution function have also been obtained by scanning a pinhole aperture across a beam diameter, and recording phosphor screen pictures of the beam downstream of the pinhole. Simulations of the beam characteristics in the gun region have also been performed using the WARP P.I.C. code. From these simulations, the observed behavior has been attributed to a combination of perturbations to the transverse distribution by a cathode grid that is used to modulate the beam current, as well as the complex transverse dynamics that results from the combination of the nonlinear external focusing fields of the gun structure and the nonlinear space charge forces.
Date: June 11, 2004
Creator: Haber, I.; Bernal, S.; Kishek, R.A.; O'Shea, P.G.; Quinn, B.; Reiser, M. et al.
Partner: UNT Libraries Government Documents Department

FODO-Supercell Based Compact Ring Design with Tunable Momentum Compaction and Optimized Dynamic Aperture

Description: A storage ring with tunable momentum compaction has the advantage in achieving different RMS bunch length with similar RF capacity, which is potentially useful for many applications, such as linear collider damping ring and pre-damping ring where injected beam has a large energy spread and a large transverse emittance. A tunable bunch length also makes the commissioning and fine tuning easier in manipulating the single bunch instabilities. In this paper, a compact ring design based on a supercell is presented, which achieves a tunable momentum compaction while maintaining a large dynamic aperture.
Date: May 11, 2012
Creator: Sun, Yipeng
Partner: UNT Libraries Government Documents Department

Design and Fabrication of Racetrack Coil Accelerator Magnets

Description: Most accelerator magnets for applications in the field range up to 9 T utilize NbTi superconductor and a cosine theta coil design. For fields above 9 T, it is necessary to use Nb{sub 3}Sn or other strain sensitive materials, and other coil geometries that are more compatible with these materials must be considered. This paper describes their recent efforts to design a series of racetrack coil magnets that will provide experimental verification of this alternative magnet design for a dual aperture dipole magnet with the goal of reaching a field level of 15 T, will be described. The experimental program, which consists of a series of steps leading to a high field accelerator quality magnet, will be presented. Fabrication of a racetrack dipole magnet utilizing Nb{sub 3}Sn superconductor and a wind and react approach will be presented.
Date: November 11, 1998
Creator: Chow, K.; Dietderich, D.R.; Gourlay, S.A.; Gupta, R.; Harnden, W.; Lietzke, A. et al.
Partner: UNT Libraries Government Documents Department

Searching for optimal mitigation geometries for laser resistant multilayer high reflector coatings

Description: Growing laser damage sites on multilayer high reflector coatings can limit mirror performance. One of the strategies to improve laser damage resistance is to replace the growing damage sites with pre-designed benign mitigation structures. By mitigating the weakest site on the optic, the large aperture mirror will have a laser resistance comparable to the intrinsic value of the multilayer coating. To determine the optimal mitigation geometry, the finite difference time domain method (FDTD) was used to quantify the electric-field intensification within the multilayer, at the presence of different conical pits. We find that the field intensification induced by the mitigation pit is strongly dependent on the polarization and the angle of incidence (AOI) of the incoming wave. Therefore the optimal mitigation conical pit geometry is application specific. Furthermore, our simulation also illustrates an alternative means to achieve an optimal mitigation structure by matching the cone angle of the structure with the AOI of the incoming wave, except for the p-polarization wave at a range of incident angles between 30{sup o} and 45{sup o}.
Date: February 11, 2011
Creator: Qiu, S R; Wolfe, J E; Monterrosa, A M; Feit, M D; Pistor, T V & STolz, C J
Partner: UNT Libraries Government Documents Department

Studies to Increase the Anti-Proton Transmission from the Targetto the Debuncher Ring

Description: The AP2 beamline at Fermilab transports anti-protons from the production target to the Debuncher ring. The measured admittance of the Debuncher ring and the theoretical aperture of the line are larger than the size of the transmitted beam. Extensive tracking studies were done using the Accelerator Toolbox (AT) to understand the sources of the difference. As simulations pointed to chromatic effects being a source of problems, measurements were done to study this. Several possible remedies were studied including adding sextupoles to the line to reduce the chromatic effects.
Date: May 11, 2005
Creator: Reichel, Ina; Zisman, Michael S.; Gollwitzer, Keith & Werkema, Steve
Partner: UNT Libraries Government Documents Department

The Storage Ring Magnets of the Australian Synchrotron

Description: A 3 GeV Synchrotron Radiation Source is being built in Melbourne, Australia. Commissioning is foreseen in 2006. The Storage ring has a circumference of 216 m and has a 14 fold DBA structure. For the storage ring the following magnets will be installed: 28 dipoles with a field of 1.3 T, and a gradient of 3.35 T/m; 56 quadrupoles with a gradient of 18 T/m and 28 with a gradient of 10 T/m; 56 sextupoles with a strength of B'' = 350 T/m and 42 with 150 T/m. The sextupoles are equipped with additional coils for horizontal and vertical steering and for a skew quadrupole. The pole profile was determined by scaling the pole profile of the SPEAR magnets [1] to the aperture of the ASP magnets. The magnets are to be supplied by Buckley Systems Ltd in Auckland, New Zealand.
Date: May 11, 2005
Creator: Barg, B.; Jackson, A.; LeBlanc, G.; U., /Melbourne; Huttel, E.; /Karlsruhe, Forschungszentrum et al.
Partner: UNT Libraries Government Documents Department

Comparison of Non-Redundant Array and Double Pinhole Coherence Measurements with Soft X-rays

Description: Experiments on the future Linac Coherent Light Source (LCLS) and other Free Electron Lasers will need to be performed on a single-shot basis. The double pinhole method of measuring spatial coherence requires a separate measurement, with a different pinhole separation distance, for each length scale sampled. This limits its utility for LCLS. A potential alternative uses a Non-Redundant Array (NRA) of apertures designed to probe the coherence over the range of length scales defined by their physical extent, in a single measurement. This approach was tested by comparing diffraction patterns from soft x-rays incident on double pinhole and NRA absorption mask structures. The double pinhole fringe visibility data serve as discrete reference points that verify the continuous spectrum of the NRA coherence data. The results present a quantitative analysis of the double pinhole coherence measurements and a qualitative comparison to the NRA images.
Date: September 11, 2006
Creator: Weil, Gabriel & /SLAC, /Northwestern U.
Partner: UNT Libraries Government Documents Department

Summary of Radionuclide Reactive Transport Experiments in Fractured Tuff and Carbonate Rocks from Yucca Flat, Nevada Test Site

Description: In the Yucca Flat basin of the Nevada Test Site (NTS), 747 shaft and tunnel nuclear detonations were conducted primarily within the tuff confining unit (TCU) or the overlying alluvium. The TCU in the Yucca Flat basin is hypothesized to inhibit radionuclide migration to the highly transmissive and regionally extensive lower carbonate aquifer (LCA) due to its wide-spread aerial extent, low permeability, and chemical reactivity. However, fast transport pathways through the TCU by way of fractures may provide a migration path for radionuclides to the LCA. Radionuclide transport in both TCU and the LCA fractures is likely to determine the location of the contaminant boundary for the Yucca Flat/Climax Mine Corrective Action Unit (CAU). Radionuclide transport through the TCU may involve both matrix and fracture flow. However, radionuclide migration over significant distances is likely to be dominated by fracture transport. Transport through the LCA will almost certainly be dominated by fracture flow, as the LCA has a very dense, low porosity matrix with very low permeability. Because of the complex nature of reactive transport in fractures, a stepwise approach to identifying mechanisms controlling radionuclide transport was used. The simplest LLNL experiments included radionuclide transport through synthetic parallel-plate fractured tuff and carbonate cores. These simplified fracture transport experiments isolated matrix diffusion and sorption effects from all other fracture transport processes (fracture lining mineral sorption, heterogeneous flow, etc.). Additional fracture transport complexity was added by performing induced fractured LCA flowthrough experiments (effect of aperture heterogeneity) or iron oxide coated parallel plate TCU flowthrough experiments (effect of fracture lining minerals). Finally naturally fractured tuff and carbonate cores were examined at LLNL and LANL. All tuff and carbonate core used in the experiments was obtained from the USGS Core Library, Mercury, Nevada. Readers are referred to the original reports ''Radionuclide Transport in Tuff and ...
Date: October 11, 2006
Creator: Zavarin, M; Roberts, S; Reimus, P & Johnson, M
Partner: UNT Libraries Government Documents Department

Measurement of Emittance of Beam in the Debuncher During Stacking

Description: The emittance of antiprotons in the debuncher was measured using two methods during normal stacking conditions. With 2.3 seconds of cooling the vertical emittance was found to be 3.6 {pi} mm-mr using scraper D:TJ308, and 2.9 {pi} mm-mr using the profile on SEM806. With 6.9 seconds of cooling time time the measured horizontal emittance was 2.1 {pi} mm-mr using D:RJ306 v.s. 1.9 {pi} mm-mr using SEM806; but with 2.3 seconds of cooling the measured emittance in the debuncher was larger than in the DTOA line, 4.5 {pi} mm-mr v.s. 2.8 {pi} mm-mr. This suggests that some beam is being scraped on a horizontal aperture restriction someplace in the extraction process.
Date: December 11, 1991
Creator: Halling, Mike
Partner: UNT Libraries Government Documents Department

A Simple Apparatus for the Injection of Lithium Aerosol into the Scrape-Off Layer of Fusion Research Devices

Description: A simple device has been developed to deposit elemental lithium onto plasma facing components in the National Spherical Torus Experiment. Deposition is accomplished by dropping lithium powder into the plasma column. Once introduced, lithium particles quickly become entrained in scrape-off layer flow as an evaporating aerosol. Particles are delivered through a small central aperture in a computer-controlled resonating piezoelectric disk on which the powder is supported. The device has been used to deposit lithium both during discharges as well as prior to plasma breakdown. Clear improvements to plasma performance have been demonstrated. The use of this apparatus provides flexibility in the amount and timing of lithium deposition and, therefore, may benefit future fusion research devices.
Date: October 11, 2010
Creator: D. K. Mansfield, A.L Roquemore, H. Schneider, J. Timberlake, H. Kugel, M.G. Bell and the NSTX Research Team
Partner: UNT Libraries Government Documents Department

Dipole aperture and superconductor requirements

Description: The cost of an accelerator is not proportional to the aperture. A change in aperture by a certain percentage results in an overall accelerator cost change by only a fraction of that percentage; the fraction may be between 0.1 and 0.5 and is almost independent of the bending field. This estimate is obtained by analyzing the superconductor requirements as a function of aperture and by making rough estimates of the largest cost items of the accelerator such as magnets and ring tunnel.
Date: December 11, 1983
Creator: Wipf, S.L.
Partner: UNT Libraries Government Documents Department

Methods for Mitigating Growth of Laser-Initiated Surface Damage on DKDP Optics at 351nm

Description: We report an experimental investigation of mitigating surface damage growth at 351nm for machine-finished DKDP optics. The objective was to determine which methods could be applied to pre-initiated or retrieved-from-service optics, in order to stop further damage growth for large aperture DKDP optics used in high-peak-power laser applications. The test results, and the evaluation thereof, are presented for several mitigation methods applied to DKDP surface damage. The mitigation methods tested were CW-CO{sub 2} laser processing, aqueous wet-etching, short-pulse laser ablation, and micro-machining. We found that micro-machining, using a single crystal diamond tool to completely remove the damage pit, produces the most consistent results to halt the growth of surface damage on DKDP. We obtained the successful mitigation of laser-initiated surface damage sites as large as 0.14mm diameter, for up to 1000 shots at 351nm and fluences in the range of 2 to 13J/cm{sup 2}, {approx} 11ns pulse length. Data obtained to-date indicates that micro-machining is the preferred method to process large-aperture optics.
Date: October 11, 2002
Creator: Hrubesh, L W; Brusasco, R B; Grundler, W; Norton, M A; Donohue, E E; Molander, W A et al.
Partner: UNT Libraries Government Documents Department

Satiated Relative Permeability of Variable-Aperture Fractures

Description: The relative permeability of a variable-aperture fracture under satiated conditions (wetting phase spans the fracture, non-wetting phase is completely entrapped) is controlled by the distribution of the entrapped phase within the fracture plane. We use simulations to investigate the combined influence of capillary forces and aperture variability on satiated relative permeability and demonstrate the effectiveness of a dimensionless perturbation curvature number (C') for predicting entrapped-phase structure. C' combines the relative influence of in-plane and out-of-plane interface curvature and the aperture coefficient of variation ({sigma}{sub a}/<a>) on local capillary forces. Results suggest that C' provides a single parameter that can be used to estimate satiated relative permeability.
Date: December 11, 2001
Creator: Detwiler, R L; Glass, R J; Rajaram, H & Nicholl, M J
Partner: UNT Libraries Government Documents Department

Progress in Long Scale Length Laser-Plasma Interactions

Description: The first experiments on the National Ignition Facility (NIF) have employed the first four beams to measure propagation and laser backscattering losses in large ignition-size plasmas. Gas-filled targets between 2 mm and 7 mm length have been heated from one side by overlapping the focal spots of the four beams from one quad operated at 351 nm (3{omega}) with a total intensity of 2 x 10{sup 15} W cm{sup -2}. The targets were filled with 1 atm of CO{sub 2} producing of up to 7 mm long homogeneously heated plasmas with densities of n{sub e} = 6 x 10{sup 20} cm{sup -3} and temperatures of T{sub e} = 2 keV. The high energy in a NIF quad of beams of 16kJ, illuminating the target from one direction, creates unique conditions for the study of laser plasma interactions at scale lengths not previously accessible. The propagation through the large-scale plasma was measured with a gated x-ray imager that was filtered for 3.5 keV x rays. These data indicate that the beams interact with the full length of this ignition-scale plasma during the last {approx}1 ns of the experiment. During that time, the full aperture measurements of the stimulated Brillouin scattering and stimulated Raman scattering show scattering into the four focusing lenses of 6% for the smallest length ({approx}2 mm). increasing to 12% for {approx}7 mm. These results demonstrate the NIF experimental capabilities and further provide a benchmark for three-dimensional modeling of the laser-plasma interactions at ignition-size scale lengths.
Date: November 11, 2003
Creator: Glenzer, S. H.; Arnold, P.; Bardsley, G.; Berger, R. L.; Bonanno, G.; Borger, T. et al.
Partner: UNT Libraries Government Documents Department

Large Diffractive Optics for GEo-Based Earth Surveillance

Description: The natural vantage point for performing Earth-centric operations from space is geosynchronous orbit (GEO); a platform there moves at the same rate as the Earth's surface, so appears to continually ''hover'' over a fixed site on the Earth. Unlike spacecraft in other orbits, which rapidly fly-over targets, a GEO-based platform remains in-position all the time. In order to insure continual access to sites using low earth orbit (LEO) platforms, one needs a large enough constellation ({approx} 50) of spacecraft so that one is always overhead; in contrast, a single GEO platform provides continuous coverage over sites throughout Euro-Asia. This permanent coverage comes, unfortunately, with a stiff price-tag; geosynchronous orbit is 36,000 km high, so space platforms there must operate at ranges roughly 100 times greater than ones located in LEO. For optical-based applications, this extreme range is difficult to deal with; for surveillance the price is a 100-fold loss of resolution, for laser weapons it is a 10,000-fold loss in flux-on-target. These huge performance penalties are almost always unacceptable, preventing us from successfully using GEO-based platforms. In practice, we are forced to either settle for brief, infrequent access to targets, or, if we demand continuous coverage, to invest in large, many-satellite, constellations. There is, fortunately, a way to use GEO-based optical platforms without incurring the huge, range-dependent, performance penalties; one must simply use bigger optics. As long as the aperture of a platform's optics increases as much as its operating range, then its performance (resolution and/or flux) does not suffer; the price for operating from GEO is simply 100-fold larger optics. This is, of course, a very stiff price; while meter-class optics may suffice for many low-earth-orbit applications, 100 meter apertures are needed in order to achieve similar performance from GEO. Since even the largest Earth-based telescope is only 10 ...
Date: September 11, 2003
Creator: Hyde, R A
Partner: UNT Libraries Government Documents Department

Results of Pulse-Scaling Experiments on Rapid-Growth DKDP Triplers Using the Optical Sciences Laser at 351 nm

Description: Results are reported from recently performed bulk-damage, pulse-scaling experiments on DKDP tripler samples taken from NIF-size, rapid-growth boule BD7. The tests were performed on LLNL's Optical Sciences Laser. A matrix of samples was exposed to single shots at 351 mn (3 {omega}) with average fluences from 4 to 8 J/cm{sup 2} for pulse durations of 1, 3 and 10 ns. The damage sites were scatter-mapped after testing to determine the damage evolution as a function of local beam fluence. The average bulk damage microcavity (pinpoint) density varied nearly linearly with fluence with peak values of approximately 16,000 pp/mm{sup 3} at 1 ns, 10,000 pp/mm{sup 3} at 3 ns and 400 pp/mm{sup 3} at 10 ns for fluences in the 8-10 J/cm{sup 2} range. The average size of a pinpoint was 10(+14,-9) {micro}m at 1 ns, 37 {+-} 20 {micro}m at 3 ns and {approx} 110 {micro}m at 10 ns, although all pulse durations produced pinpoints with a wide distribution of sizes. Analysis of the pinpoint density data yielded pulse-scaling behavior of t{sup 0.35}. Significant planar cracking around the pinpoint as was observed for the 10 ns case but not for the 1 and 3 ns pulses. Crack formation around pinpoints has also been observed frequently for Zeus ADT tests at {approx}8 ns. The high pinpoint densities also lead to significant eruption of near-surface bulk damage. Measurements of the damage site area for surface and bulk gave ratios (A{sub surf}/A{sub bulk}) of 2:1 at 1 ns, 7:1 at 3 ns and 110:1 at 10 ns. Maximum aperture averaged transmission losses on the order 15 percent have been measured by photometry for the worst damage at 1 and 3 ns for beam fluences in the 8-10 J/cm{sup 2} range. Analysis of this data yielded a pulse-scaling behavior of t{sup 0.25} for the ...
Date: December 11, 2000
Creator: Runkel, M; Burnham, A K; Milam, D; Sell, W; Feit, M & Rubenchik, A
Partner: UNT Libraries Government Documents Department