805 Matching Results

Search Results

Advanced search parameters have been applied.

Effects of Pulse Duration on Bulk Laser Damage in 350-nm Raster-Scanned DKDP

Description: In this paper we present the results of bulk damage experiments done on Type-I1 DKDP triple harmonic generator crystals that were raster conditioned with 351-355 nm wavelengths and pulse durations of 4 and 23.2 ns. In the first phase of experiments 20 different scan protocols were rastered into a sample of rapid growth DKDP. The sample was then rastered at damage-causing fluences to determine the three most effective protocols. These three protocols were scanned into a 15-cm sample of conventional-growth DKDP and then exposed to single shots of a I-cm beam from LLNL's Optical Sciences Laser at fluences ranging from 0.5 - 1.5X of the 10% damage probability fluence and nominal pulse durations of 0.1,0.3,0.8,3.2,7.0 and 20 ns. The experiment showed that pulse durations in the 1-3 ns range were much more effective at conditioning than pulses in the 16.3 ns range and that the multiple pass 'peak fluence' scan was more effective than the single pass 'leading edge' scan for 23.2 ns XeF scans.
Date: October 30, 2002
Creator: Runkel, M; Bruere, J; Sell, W; Weiland, T; Milam, D; Hahn, D E et al.
Partner: UNT Libraries Government Documents Department

Higher order modes of a 3rd harmonic cavity with an increased end-cup iris

Description: The cavity design for a 3rd harmonic cavity for the TTF 2 photoinjector has been revised to increase the coupling between the main coupler and the cavity cells. The iris radius of the end cup of the cavity has been increased to accomplish a better coupling. The basic rf-parameters and the higher order modes of the modified design are summarized in this report.
Date: May 19, 2003
Creator: Khabibouline, T.; Solyak, N. & Wanzenberg, R.
Partner: UNT Libraries Government Documents Department

Beehive and Hornet : Reactor Codes for Spherical Geometry

Description: Abstract: Beehive is a five energy group, two region, time independent spherical reactor code. It considers the problem of reactor system in which the core material is assumed to be at a higher energy (temperature) than the reflector material. The code obtains a closed solution for the critical reactor assembly by a procedure which is a logical extension of normal two group theory. The companion code, Hornet, computes the neutron fluxes for the critical assembly determined by the Beehive calculation. Both codes have been programmed for the IBM Magnetic Drum Data-Processing Machine, Type 650. The codes, together with the flow diagrams, are included with this report.
Date: February 8, 1957
Creator: Stone, Stuart P.
Partner: UNT Libraries Government Documents Department

Measuring Spherical Harmonic Coefficients on a Sphere

Description: The eigenfunctions of Rayleigh-Taylor modes on a spherical capsule are the spherical harmonics Y{sub l,m} These can be measured by measuring the surface perturbations along great circles and fitting them to the first few modes by a procedure described in this article. For higher mode numbers, it is more convenient to average the Fourier power spectra along the great circles, and then transform them to spherical harmonic modes by an algorithm derived here.
Date: May 16, 2003
Creator: Pollaine, S & Haan, S W
Partner: UNT Libraries Government Documents Department

Analysis and algorithms for a regularized Cauchy problem arising from a non-linear elliptic PDE for seismic velocity estimation

Description: In the present work we derive and study a nonlinear elliptic PDE coming from the problem of estimation of sound speed inside the Earth. The physical setting of the PDE allows us to pose only a Cauchy problem, and hence is ill-posed. However we are still able to solve it numerically on a long enough time interval to be of practical use. We used two approaches. The first approach is a finite difference time-marching numerical scheme inspired by the Lax-Friedrichs method. The key features of this scheme is the Lax-Friedrichs averaging and the wide stencil in space. The second approach is a spectral Chebyshev method with truncated series. We show that our schemes work because of (1) the special input corresponding to a positive finite seismic velocity, (2) special initial conditions corresponding to the image rays, (3) the fact that our finite-difference scheme contains small error terms which damp the high harmonics; truncation of the Chebyshev series, and (4) the need to compute the solution only for a short interval of time. We test our numerical scheme on a collection of analytic examples and demonstrate a dramatic improvement in accuracy in the estimation of the sound speed inside the Earth in comparison with the conventional Dix inversion. Our test on the Marmousi example confirms the effectiveness of the proposed approach.
Date: January 1, 2009
Creator: Cameron, M.K.; Fomel, S.B. & Sethian, J.A.
Partner: UNT Libraries Government Documents Department

METHODS FOR ADDRESSING THE PROBLEM OF THE DEPENDENCE OF THE TIME OF FLIGHT ON TRANSVERSE AMPLITUTE IN LINEAR NON-SCALING FFAGs

Description: Because the time of flight in a linear non-scaling FFAG depends on the transverse amplitude, motion in the longitudinal plane will be different for different transverse particle amplitudes. This effect, if not considered, will lead the failure of a substantial portion of the beam to be accelerated. I will first briefly review this effect. Then I will outline some techniques for addressing the problems created by the effect. In particular, I will discuss partially correcting the chromaticity and increasing the energy gain per cell. I will discuss potential problems with another technique, namely the introduction of higher harmonic cavities.
Date: November 6, 2006
Creator: Berg, J. S.
Partner: UNT Libraries Government Documents Department

Simulations of RF capture with barrier bucket in booster at injection

Description: As part of the effort to increase the number of ions per bunch in RHIC, a new scheme for RF capture of EBIS ions in Booster at injection has been developed. The scheme was proposed by M. Blaskiewicz and J.M. Brennan. It employs a barrier bucket to hold a half turn of beam in place during capture into two adjacent harmonic 4 buckets. After acceleration, this allows for 8 transfers of 2 bunches from Booster into 16 buckets on the AGS injection porch. During the Fall of 2011 the necessary hardware was developed and implemented by the RF and Controls groups. The scheme is presently being commissioned by K.L. Zeno with Au32+ ions from EBIS. In this note we carry out simulations of the RF capture. These are meant to serve as benchmarks for what can be achieved in practice. They also allow for an estimate of the longitudinal emittance of the bunches on the AGS injection porch.
Date: January 23, 2012
Creator: Gardner, C.J.
Partner: UNT Libraries Government Documents Department

Anisotropic scattering in the variational nodal simplified spherical harmonics formulation

Description: Under the assumption of isotropic scattering, the simplified spherical harmonics method (SP{sub N}) was recently formulated in variational nodal form and implemented successfully as an option of the VARIANT code. The authors here remove the isotopic scattering restriction. The variational nodal form of the SPN approximation is formulated and implemented with both within-group and group-to-group anisotropic scattering. Results are presented for a model problem previously utilized with the standard P{sub N} variational nodal method.
Date: May 1, 1996
Creator: Lewis, E.E. & Palmiotti, G.
Partner: UNT Libraries Government Documents Department

AGS slow extracted beam improvement

Description: The Brookhaven AGS is a strong focusing accelerator which is used to accelerate protons and various heavy ion species to an equivalent proton energy of 29 GeV. Since the late 1960`s it has been serving high energy physics (HEP - proton beam) users of both slow and fast extracted beams. The AGS fixed target program presently uses primary proton and heavy ion beams (HIP) in slowly extracted fashion over spill lengths of 1.5 to 4.0 seconds. Extraction is accomplished by flattoping the main and extraction magnets and exciting a third integer resonance in the AGS. Over the long spill times, control of the subharmonic amplitude components up to a frequency of 1 kilohertz is very crucial. One of the most critical contributions to spill modulation is due to the AGS MMPS. An active filter was developed to reduce these frequencies and it`s operation is described in a previous paper. However there are still frequency components in the 60-720 Hz sub-harmonic ripple range, modulating the spill structure due to extraction power supplies and any remaining structures on the AGS MMPS. A recent scheme is being developed to use the existing tune-trim control horizontal quadrupole magnets and power supply to further reduce these troublesome noise sources. Feedback from an external beam sensor and overcoming the limitations of the quadrupole system by lead/lag compensation techniques will be described.
Date: July 1, 1997
Creator: Marneris, I.; Danowski, G.; Sandberg, J. & Soukas, A.
Partner: UNT Libraries Government Documents Department

NEW NONLINEAR ACOUSTIC TECHNIQUES FOR NDE

Description: Acoustic nonlinearity in a medium may occur as a result of a variety of mechanisms. Some of the more common nonlinear effects may come from: (1) one or several cracks, volumetrically distributed due to age or fatigue or single disbonds or delamination; (2) imperfect grain-to-grain contacts, e.g., materials like concretes that are cemented together and have less than perfect bonds; (3) hard parts in a soft matrix, e.g., extreme duty materials like tungsten/copper alloys; or (4) atomic-scale nonlinearities. Nonlinear effects that arise from the first two mechanisms are considerably larger than the last two; thus, we have focused considerable attention on these. The most pervasive nonlinear measure of damage today is a second harmonic measurement. We show that for many cases of interest to NDE, a second harmonic measurement may not be the best choice. We examine the manifestations of nonlinearity in (nonlinear) materials with cracks and/or imperfect bonds and illustrate their applicability to NDE. For example, nonlinear resonance frequency shifts measured at increasing drive levels correlate strongly with the amount of ASR (alkali-silica reaction) damage of concrete cores. Memory effects (slow dynamics) also seem to correlate with the amount of damage.
Date: September 1, 2000
Creator: TENCATE, J. A.
Partner: UNT Libraries Government Documents Department

A hydrologic view on Biot's theory of poroelasticity

Description: The main objective of this work is to obtain a simplified asymptotic representation of the reflection of seismic signal from a fluid-saturated porous medium in the low-frequency domain. In the first part, we derive the equations of low-frequency harmonic waves in a fluid-saturated elastic porous medium from the basic concepts of filtration theory. We demonstrate that the obtained equations can be related to the poroelasticity model of Frenkel-Gassmann-Biot, and to pressure diffusion model routinely used in well test analysis as well. We thus try to put the poroelastic and filtration theories on the same ground. We study the reflection of a low-frequency signal from a plane interface between elastic and elastic fluid-saturated porous media. We obtain an asymptotic scaling of the frequency-dependent component of the reflection coefficient with respect to a dimensionless parameter depending on the frequency of the signal and the reservoir fluid mobility. We also investigate the impact of the relaxation time and tortuosity on this scaling.
Date: January 13, 2004
Creator: Silin, D.B.; Korneev, V.A.; Goloshubin, G.M. & Patzek, T.W.
Partner: UNT Libraries Government Documents Department

Coherent parasitic energy loss of the recycler beam

Description: Parasitic energy loss of the particle beam in the Recycler Ring is discussed. The long beam confined between two barrier waves has a spectrum that falls off rapidly with frequency. Discrete summation over the revolution harmonics must be made to obtain the correct energy loss per particle per turn, because only a few lower revolution harmonics of real part of the longitudinal impedance contribute to the parasitic energy loss. The longitudinal impedances of the broadband rf cavities, the broadband resistive-wall monitors, and the resistive wall of the vacuum chamber are discussed. They are the main sources of the parasitic energy loss.
Date: July 14, 2004
Creator: Ng, K.Y.
Partner: UNT Libraries Government Documents Department

Compensation of dogleg effect in Fermilab Booster

Description: The edge focusing of dogleg magnets in Fermilab Booster has been causing severe distortion to the horizontal linear optics. The doglegs are vertical rectangular bends, therefore the vertical edge focusing is canceled by body focusing and the overall effect is focusing in the horizontal plane. The maximum horizontal beta function is changed from 33.7m to 46.9m and maximum dispersion from 3.19m to 6.14m. Beam size increases accordingly. This is believed to be one of the major reasons of beam loss. In this technote we demonstrate that this effect can be effectively corrected with Booster's quadrupole correctors in short straight sections (QS). There are 24 QS correctors which can alter horizontal linear optics with negligible perturbation to the vertical plane. The currents of correctors are determined by harmonic compensation, i.e., cancellation of dogleg's harmonics that are responsible for the distortion with that of QS correctors. By considering a few leading harmonics, the ideal lattice can be partly restored. For the current dogleg layout, maximum {beta}{sub x} is reduced to 40.6m and maximum D{sub x} is reduced to 4.19m. This scheme can be useful after the dogleg in section No.3 is repositioned. In this case it can bring {beta}{sub x} from 40.9m down to 37.7m, D{sub x} from 4.57m to 4.01m.
Date: October 6, 2003
Creator: Huang, Xiaobiao & Ohnuma, Sho
Partner: UNT Libraries Government Documents Department

Computer Programs Using Zonal Harmonics for Magnetic Properties of Current Systems with Special Reference to the IBM 7090

Description: Report that "discusses the magnetic vector and scalar potentials, magnetic field components and their derivatives, and flux linkage for single current systems, and the mutual inductance, forces and torques between two such systems, whose axes are coplanar but not necessarily coincident" (p. 1).
Date: December 4, 1962
Creator: Garrett, M. W.
Partner: UNT Libraries Government Documents Department

Pressure Balance in a Toroidal Pinch

Description: Abstract: In the study of a linear pinch, use of the equation of pressure balance has proven to be a powerful method of analyzing data taken with a magnetic probe. The toroidal pinch, however, is a geometrically more complicated object, and the use of the pressure balance equations is not so clean cut. It is the object of this note to analyze the pressure balance equations for a torus to the point where they might prove useful in interpreting probe data.
Date: December 1958
Creator: Suydam, Bergen R.
Partner: UNT Libraries Government Documents Department

Field Quality Optimization in a Common Coil Magnet Design

Description: This paper presents the results of initial field quality optimization of body and end harmonics in a 'common coil magnet design'. It is shown that a good field quality, as required in accelerator magnets, can be obtained by distributing conductor blocks in such a way that they simulate an elliptical coil geometry. This strategy assures that the amount of conductor used in this block design is similar to that is used in a conventional cosine theta design. An optimized yoke that keeps all harmonics small over the entire range of operation using a single power supply is also presented. The field harmonics are primarily optimized with the computer program ROXIE.
Date: September 1, 1999
Creator: Gupta, Ramesh & Ramberger, Suitbert
Partner: UNT Libraries Government Documents Department

HARMONIC NUMBER JUMP IN A RING WITH CAVITIES DISTRIBUTED EVERYWHERE.

Description: One of the primary motivations for using fixed field alternating gradient accelerators (FFAGs) is their ability to accelerate rapidly, since the magnetic fields do not need to be varied. However, one must then face the difficulty that the time of flight in an FFAG depends strongly on the particle energy. Traditionally, this is dealt with by varying the RF frequency. The rate at which one can vary the RF frequency is limited, and a cavity and power source which have a rapidly varying RF frequency are costly. One solution to this is harmonic number jump acceleration, where the RF frequency is fixed. The RF frequency is chosen so that each turn has an integer number of RF periods, but that integer number is different on each turn. When accelerating rapidly, a large number of cavities is often required. This paper will show that in general, the time of flight can only be an integer number of RF periods for all turns at one position in the ring. It will then compute how well one can do when cavities are distributed everywhere in the ring. The paper will show some examples, and will discuss possible applications for this technique.
Date: November 6, 2006
Creator: BERG,J.S.
Partner: UNT Libraries Government Documents Department

PRELIMINARY IMPEDANCE BUDGET FOR NSLS-II STORAGE RING.

Description: The wakefield and impedance produced by the components of the NSLS-II storage ring have been computed for an electron bunch length of 3mm rms. The results are summarized in a table giving for each component, the loss factor ({kappa}{sub {parallel}}), the imaginary part of the longitudinal impedance at low frequency divided by the revolution harmonic (ImZ{sub {parallel}}/n), and the transverse kick factors ({kappa}{sub x}, {kappa}{sub y}).
Date: June 25, 2007
Creator: BLEDNYKH,A. & KRINSKY, S.
Partner: UNT Libraries Government Documents Department

Field Quality Optimization in a Common Coil Magnet Design

Description: This paper presents the results of initial field quality optimization of body and end harmonics in a 'common coil magnet design'. It is shown that a good field quality, as required in accelerator magnets, can be obtained by distributing conductor blocks in such a way that they simulate an elliptical coil geometry. This strategy assures that the amount of conductor used in this block design is similar to that is used in a conventional cosine theta design. An optimized yoke that keeps all harmonics small over the entire range of operation using a single power supply is also presented. The field harmonics are primarily optimized with the computer program ROXIE.
Date: September 1, 1999
Creator: Gupta, R. & Ramberger, S.
Partner: UNT Libraries Government Documents Department