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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

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

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

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

Common Coil Magnet System for VLHC

Description: This paper introduces the common coil magnet system for the proposed very large hadron collider (VLHC). In this system, the high energy booster (HEB), the injector to VLHC, is integrated as the iron dominated low field aperture within the coldmass of the common coil magnet design introduced earlier. This 4-in-1 magnet concept for a 2-in-1 machine should provide a major cost reduction in building and operating VLHC. Moreover, the proposed design reduces the field quality problems associated with the large persistent currents in Nb{sub 3}Sn magnets. The paper also shows that the geometric field harmonics can be made small. In this preliminary magnetic design. the current dependence in harmonics is significant but not umnanageable.
Date: February 12, 1999
Creator: Gupta, R.
Partner: UNT Libraries Government Documents Department

3Q120 Low Gradient Behaviour-Companion Report

Description: Three 3Q120 magnets--representative of those in the AP 1 line--have been measured with a harmonics probe at MDTF at both low (0-48 A) and high (to >= 400 A). The intent of the measurements was to learn their behavior at the low gradients necessary to transport 8 Gev antiprotons back through the AP 1 line for injection into the Main Ring. This paper describes some aspects of the measurements that were not included in the main paper, in order to keep the size of the main report reasonably small. It includes as Appendix I a chronology of the measurements made and significant changes made to the measurement apparatus and analysis programs.
Date: October 1, 1985
Creator: Wehmann, A.
Partner: UNT Libraries Government Documents Department

A General Method for Calculating the External Magnetic Field from a Cylindrical Magnetic Source using Toroidal Functions

Description: An alternative method is developed to compute the magnetic field from a circular cylindrical magnetic source. Specifically, a Fourier series expansion whose coefficients are toroidal functions is introduced which yields an alternative to the more familiar spherical harmonic solution or the Elliptic integral solution. This alternate formulation coupled with a method called charge simulation allows one to compute the external magnetic field from an arbitrary magnetic source in terms of a toroidal expansion. This expansion is valid on any finite hypothetical external observation cylinder. In other words, the magnetic scalar potential or the magnetic field intensity is computed on a exterior cylinder which encloses the magnetic source. This method can be used to accurately compute the far field where a finite element formulation is known to be inaccurate.
Date: February 14, 2006
Creator: Selvaggi, J; Salon, S & Chari, O Kwon CVK
Partner: UNT Libraries Government Documents Department

Design of HD2: a 15 T Nb3Sn dipole with a 35 mm bore

Description: The Nb{sub 3}Sn dipole HD1, recently fabricated and tested at LBNL, pushes the limits of accelerator magnet technology into the 16 T field range, and opens the way to a new generation of HEP colliders. HD1 is based on a flat racetrack coil configuration and has a 10 mm bore. These features are consistent with the HD1 goals: exploring the Nb{sub 3}Sn conductor performance limits at the maximum fields and under high stress. However, in order to further develop the block-coil geometry for future high-field accelerators, the bore size has to be increased to 30-50 mm. With respect to HD1, the main R&D challenges are: (a) design of the coil ends, to allow a magnetically efficient cross-section without obstructing the beam path; (b) design of the bore, to support the coil against the pre-load force; (c) correction of the geometric field errors. HD2 represents a first step in addressing these issues, with a central dipole field above 15 T, a 35 mm bore, and nominal field harmonics within a fraction of one unit. This paper describes the HD2 magnet design concept and its main features, as well as further steps required to develop a cost-effective block-coil design for future high-field, accelerator-quality dipoles.
Date: June 1, 2005
Creator: Sabbi, G.; Bartlett, S. E.; Caspi, S.; Dietderich, D. R.; Ferracin, P.; Gourlay, S. A. et al.
Partner: UNT Libraries Government Documents Department

High Power Picosecond Laser Pulse Recirculation

Description: We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.
Date: April 12, 2010
Creator: Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J et al.
Partner: UNT Libraries Government Documents Department

Computing the correlation and other things directly from the raw pairs

Description: We want a faster and more robust way to compute the correlation, expanded in Spherical (or Cartesian) Harmonics. We also want to include the cross-{ell},m data covariance that are there, but currently ignored. We don't want to get bogged down in fancy binning in x-y-z or r-{theta}-{phi}, just r. Want to just look at C{sub {ell}m} to decide how many terms to keep--or better yet the pair distributions directly.
Date: August 16, 2007
Creator: Brown, D A
Partner: UNT Libraries Government Documents Department

MEASUREMENT OF THE ANISOTROPY OF COSMIC RAY ARRIVAL DIRECTIONS WITH ICECUBE

Description: We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi TeV region in the Southern sky using data from the IceCube detector. Between June 2007 and March 2008, the partially-deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over 22 strings at depths between 1450 and 2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic ray muons. Therefore, the background data are suitable for high-statistics studies of cosmic rays in the Southern sky. The data include 4.3 billion muons produced by downgoing cosmic ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3 degrees and a median energy of ~;; 20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first harmonic amplitude of (6.4 +- 0.2 stat. +- 0.8 syst.) x 10-4.
Date: May 17, 2010
Creator: Collaboration, IceCube & Abbasi, 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

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

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