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Description: The response of an intense beam of interacting particles to a deflecting rf-signal is computed theoretically and shown to be closely related to transverse coherent beam stability. It is shown that the beam response to sinusoidal excitation provides a direct measure of the stability of beam modes for given machine conditions (beam intensity, octupole current, sextupole current, momentum spread, etc.). This measurement includes the properties of the beam surroundings as well as the frequency spread effective for Landau damping. Since it is generally difficult to evaluate theoretically the wall and beam properties that enter into stability calculations, the information which can be obtained from rf excitation experiments should be very valuable; especially in devising practical procedures for reducing the severity of coherent transverse instabilities.
Date: August 1, 1971
Creator: Muhl, Dieter & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Optimization Of Chromaticity Compensation And Dynamic Aperture In MEIC Collider Rings

Description: The conceptual design of the Medium-energy Electron-Ion Collider (MEIC) at Jefferson Lab relies on an ultra-small beta-star to achieve high luminosities of up to 10{sup 34} cm{sup -2} s{sup -1}. A low-beta insertion for interaction regions unavoidably induces large chromatic effects that demand a proper compensation. The present approach of chromatic compensation in the MEIC collider rings is based on a local correction scheme using two symmetric chromatic compensation blocks that includes families of sextupoles, and are placed in a beam extension area on both sides of a collision point. It can simultaneously compensate the first order chromaticity and chromatic beam smear at the IP without inducing significant second order aberrations. In this paper, we investigate both the momentum acceptance and dynamic aperture in the MEIC ion collider ring by considering the aberration effects up to the third order, such as amplitude dependent tune shift. We also explore the compensation of the third order effects by introducing families of octupoles in the extended beam area.
Date: July 1, 2012
Creator: Fanglei Lin, Yaroslav Derbenev, Vasiliy Morozov, Yuhong Zhang, Kevin Beard
Partner: UNT Libraries Government Documents Department

Effect of Wiggler insertions on the single-particle dynamics of the NLC main damping rings

Description: As they are expected to occupy a large portion of the lattice, wiggler insert ions will introduce significant linear and nonlinear perturbations to the single-particle dynamics in the NLC Main Damping Rings (MDR). The nonlinearities are of particular concern as a sufficiently large Dynamic Aperture (DA) is required for high injection efficiency. The main content of this report is a study of the wigglers impact on the DA of the NLC-MDR latest lattice design. The particle dynamics is modeled by transfer maps calculated by integration through the wiggler fields. For field representation we employed a 3D multipole expansion derived from the field data that were obtained with the aid of a magnet design code. Additional contents of this paper include an investigation of a simplified model of wiggler consisting of a sequence of standard magnet elements (where thin octupoles are used to represent the dominant nonlinearities) and the suggestion of a possible correction scheme to compensate the wiggler nonlinearities.
Date: July 30, 2003
Creator: Venturini, Marco
Partner: UNT Libraries Government Documents Department

Muon Acceleration with RLA and Non-scaling FFAG Arcs

Description: Recirculating Linear Accelerators (RLA) are the most likely means to achieve the rapid acceleration of shortlived muons to multi-GeV energies required for Neutrino Factories and TeV energies required for Muon Colliders. In this paper, we present a novel return-arc optics design based on a Non Scaling Fixed Field Alternating Gradient (NS-FFAG) lattice that allows 5 and 9 GeV/c muons of both charges to be transported in the same string of magnets. The return arcs are made up of super cells with each super cell consisting of three triplets. By employing combined function magnets with dipole, quadrupole, sextupole and octupole magnetic field components, each super cell is designed to be achromatic and to have zero initial and final periodic orbit offsets for both 5 and 9 GeV/c muon momenta. This solution would reduce the number of arcs by a factor of 2, simplifying the overall design.
Date: May 1, 2010
Creator: Vasiliy Morozov,Alex Bogacz,Dejan Trbojevic
Partner: UNT Libraries Government Documents Department

Observation of hyperfine mixing in measurements of a magnetic octupole decay in isotopically pure nickel-like 129Xe and 132Xe ions

Description: We present measurements of high statistical significance of the rate of the magnetic octupole (M3) decay in nickel-like ions of isotopically pure {sup 129}Xe and {sup 132}Xe. On {sup 132}Xe, an isotope with zero nuclear spin and therefore without hyperfine structure, the lifetime of the metastable level was established as (15.06 {+-} 0.24) ms. On {sup 129}Xe, an additional fast (2.7 {+-} 0.1 ms) decay component was established that represents hyperfine mixing with a level that decays by electric quadrupole (E2) radiation.
Date: December 21, 2006
Creator: Trabert, E; Beiersdorfer, P & Brown, G V
Partner: UNT Libraries Government Documents Department

Octupole and hexadecapole bands in 152Sm

Description: The nucleus {sup 152}Sm is characterized by a variety of low-energy collective modes, conventionally described as rotations, {beta} vibrations, and {gamma} vibrations. Recently, it has been suggested that {sup 152}Sm is at a critical point between spherical and deformed collective phases. Consequently, {sup 152}Sm is being studied by a variety of techniques, including radioactive decay, multi-step Coulomb excitation, in-beam ({alpha},2n{gamma}) {gamma}-ray spectroscopy, and (n,n'{gamma}) spectroscopy. The present work focuses on the latter two reactions; these have been used to investigate the low-lying bands associated with the octupole degree of freedom, including one built on the first excited 0{sup +} band. In addition, the K{sup {pi}} = 4{sup +} hexadecapole vibrational band has been identified.
Date: May 13, 2005
Creator: Garrett, P E; Kulp, W D; Wood, J L; Bandyopadhyay, D; Christen, S; Choudry, S et al.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics studies in the Fermilab tevatron using an AC dipole

Description: An AC dipole magnet produces a sinusoidally oscillating dipole field with frequency close to betatron frequency and excites large sustained oscillations of beam particles circulating in a synchrotron. Observation of such oscillations with beam position monitors allows direct measurements of a synchrotron's nonlinear parameters. This paper presents experimental studies to measure perturbative effects of sextupole and octupole fields, performed in the Fermilab Tevatron using an ACdipole.
Date: May 4, 2009
Creator: Miyamoto,R.; Jansson, A.; Syphers, M. J. & Kopp, S. E.
Partner: UNT Libraries Government Documents Department

Effect of a large Oth harmonic octupole on stable betatron oscillations

Description: S>The effect of a 0th harmonic octupole (that is, constant in dependence on azimuth) on stable betatron oscillations is treated in smooth approximation. In this approximation, an exact invariant is obtained. Bounded motion results, except when the octupole component is very large. A condition for stability- is obtained and, in the case of bounded motion, an expression for the amplitude variation is given. Some comments are made regarding the method of phase averaging. (auth)
Date: September 20, 1973
Creator: Month, M.
Partner: UNT Libraries Government Documents Department

Particle beams with uniform transverse distribution

Description: A successfully tested method is described which achieves a more uniform illumination of an extended flat target by the charged particle beam from an accelerator, by proper use of a combination of quadrupole and octupole magneto-optical elements.
Date: October 1, 1996
Creator: Tsoupas, N.; Zucker, M.S.; Snead, C.L. & Ward, T.E.
Partner: UNT Libraries Government Documents Department

Quadrupole-octupole coupled states in 112Cd

Description: Negative-parity excitations in the 2.5 MeV region in {sup 112}Cd have been investigated with the (n,n`{gamma}) reaction. Several of these states exhibit enhanced B(E2) values for L decay to the 3{sub 1}{sup -} octupole state, indicative of quadrupole-octupole coupled (2{sup +} {circle_times} 3{sup -}) structures. The B(E1) values observed are typically in the range of 1-5 x 1O{sup -4} W u , irrespective of the final state.
Date: May 5, 1998
Creator: Garrett, P. E.
Partner: UNT Libraries Government Documents Department

Octupole fragmentation and the structure of the O(6)-like Ba nuclei

Description: The low energy octupole states in {sup 134}Ba were examined using proton inelastic scattering. The data show that there is no significant octupole strength in addition to that corresponding to the lowest 3{sup -} state. Consequently, the strong fragmentation of the low energy octupole state expected for a {gamma} soft nucleus does not occur in {sup 134}Ba. The apparent contradiction that the positive parity states in this nucleus present an O(6) type structure and the negative parity ones do not follow the selection rules of the E3 operator for the O(6) symmetry might be explained by noticing that the wave function of an O(6) nucleus has a significant overlap with the wave function of an U(5) - SU(3) transitional nucleus. 9 refs., 3 figs., 2 tabs.
Date: October 1, 1996
Creator: Zamfir, N.V.; Casten, R.F. & Cottle, P.D.
Partner: UNT Libraries Government Documents Department

Simulations of octupole compensation of head-tail instability at the Tevatron

Description: The proton lifetime in the Tevatron depends sensitively on chromaticities. Too low chromaticities can make the beam unstable due to the weak head-tail instability. One way to compensate this effect is to introduce octupoles to create a larger amplitude dependent betatron tune spread. However, the use of octupoles will also introduce additional side effects such as second order chromaticity, differential tune shifts and chromaticities on both proton and anti-proton helices. The non-linear effects may also reduce the dynamic aperture. There are 67 octupoles in 4 different circuits in the Tevatron which may be used for this purpose. We report on a simulation study to find the best combinations of polarities and strengths of the octupoles.
Date: May 28, 2003
Creator: Xiao, Meiqin; Sen, Tanaji & Schmidts, Frank
Partner: UNT Libraries Government Documents Department


Description: The last nms in both gold-gold and polarized proton-proton required necessary corrections in the ramp as the intensities in the two rings were rising towards design values. Corrections were made with respect to the beam-beam effects, transverse and longitudinal instabilities, transition crossing (for the gold-gold ramps), transverse tune resonances, local and global coupliug problems, aperture restrictions, chromatic effects. Along the ramps we had to use the beam separation, ''Landau'' cavities, chromatic and tune control, orbit correction, special gamma-t quadrupole system for the transition crossing in the gold run, correction octupole circuits, beam position monitor system decoupling etc.
Date: June 2, 2002
Partner: UNT Libraries Government Documents Department

Dual AC Dipole Excitation for the Measurement of Magnetic Multipole Strength from Beam Position Monitor Data

Description: An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a technique for characterizing the nonlinear fields of the beam transport system. Two air-core dipole magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the electron beam. Fourier decomposition of beam position monitor data was then used to measure the amplitude of these frequencies at different positions along the beamline. For a purely linear transport system one expects to find solely the frequencies that were applied to the dipoles with amplitudes that depend on the phase advance of the lattice. In the presence of nonlinear fields one expects to also find harmonics of the driving frequencies that depend on the order of the nonlinearity. The technique was calibrated using one of the sextupole magnets in a CEBAF beamline and then applied to a dipole to measure the sextupole and octupole strength of the magnet. A comparison is made between the beam-based measurements, results from TOSCA and data from our Magnet Measurement Facility.
Date: September 1, 2011
Creator: M. Spata, G.A. Krafft
Partner: UNT Libraries Government Documents Department

Construction and Operational Experience with a Superconducting Octupole Used to Trap Antihydrogen

Description: A superconducting octupole magnet has seen extensive service as part of the ALPHA experiment at CERN. ALPHA has trapped antihydrogen, a crucial step towards performing precision measurements of anti-atoms. The octupole was made at the Direct Wind facility by the Superconducting Magnet Division at Brookhaven National Laboratory. The magnet was wound with a six-around-one NbTi cable about 1 mm in diameter. It is about 300 mm long, with a radius of 25 mm and a peak field at the conductor of 4.04 T. Specific features of the magnet, including a minimal amount of material in the coil and coil ends with low multipole content, were advantageous to its use in ALPHA. The magnet was operated for six months a year for five years. During this time it underwent about 900 thermal cycles (between 4K and 100K). A novel operational feature is that during the course of data-taking the magnet was repeatedly shut off from its 950 A operating current. The magnet quenches during the shutoff, with a decay constant of 9 ms. Over the course of the five years, the magnet was deliberately quenched many thousands of times. It still performs well.
Date: September 6, 2011
Creator: P., Wanderer; Escallier, J.; Marone, A. & Parker, B.
Partner: UNT Libraries Government Documents Department

Diagnostics of the Fermilab Tevatron using an AC dipole

Description: The Fermilab Tevatron is currently the world's highest energy colliding beam facility. Its counter-rotating proton and antiproton beams collide at 2 TeV center-of-mass. Delivery of such intense beam fluxes to experiments has required improved knowledge of the Tevatron's beam optical lattice. An oscillating dipole magnet, referred to as an AC dipole, is one of such a tool to non-destructively assess the optical properties of the synchrotron. We discusses development of an AC dipole system for the Tevatron, a fast-oscillating (f {approx} 20 kHz) dipole magnet which can be adiabatically turned on and off to establish sustained coherent oscillations of the beam particles without affecting the transverse emittance. By utilizing an existing magnet and a higher power audio amplifier, the cost of the Tevatron AC dipole system became relatively inexpensive. We discuss corrections which must be applied to the driven oscillation measurements to obtain the proper interpretation of beam optical parameters from AC dipole studies. After successful operations of the Tevatron AC dipole system, AC dipole systems, similar to that in the Tevatron, will be build for the CERN LHC. We present several measurements of linear optical parameters (beta function and phase advance) for the Tevatron, as well as studies of non-linear perturbations from sextupole and octupole elements.
Date: August 1, 2008
Creator: Miyamoto, Ryoichi & U., /Texas
Partner: UNT Libraries Government Documents Department

Time-resolved soft-x-ray spectroscopy of a magnetic octupole transition in nickel-like xenon, cesium, and barium ions

Description: A microcalorimeter with event mode capability for time-resolved soft-x-ray spectroscopy, and a high-resolution flat-field EUV spectrometer have been employed at the Livermore EBIT-I electron beam ion trap for observations and wavelength measurements of M1, E2, and M3 decays of long-lived levels in the Ni-like ions Xe{sup 26+}, Cs{sup 27+}, and Ba{sup 28+}. Of particular interest is the lowest excited level, 3d{sup 9}4s {sup 3}D{sub 3}, which can only decay via a magnetic octupole (M3) transition. For this level in Xe an excitation energy of (590.40 {+-} 0.03eV) and a level lifetime of (11.5 {+-} 0.5 ms) have been determined.
Date: November 11, 2005
Creator: Trabert, E; Beiersdorfer, P; Brown, G V; Boyce, K; Kelley, R L; Kilbourne, C A et al.
Partner: UNT Libraries Government Documents Department

The Superconducting Magnets of the ILC Beam Delivery System

Description: The ILC Beam Delivery System (BDS) uses a variety of superconducting magnets to maximize luminosity and minimize background. Compact final focus quadrupoles with multifunction correction coils focus incoming beams to few nanometer spot sizes while focusing outgoing disrupted beams into a separate extraction beam line. Anti-solenoids mitigate effects from overlapping focusing and the detector solenoid field. Far from the interaction point (IP) strong octupoles help minimize IP backgrounds. A low-field but very large aperture dipole is integrated with the detector solenoid to reduce backgrounds from beamstrahlung pairs generated at the IP. Physics requirements and magnetic design solutions for the BDS superconducting magnets are reviewed in this paper.
Date: September 28, 2007
Creator: Parker, B.; Anerella, M.; Escallier, J.; He, P.; Jain, A.; Marone, A. et al.
Partner: UNT Libraries Government Documents Department

A simple crunching of the AGS 'bare' machine ORM data - February 2007 - to extract some aspects of AGS transverse coupling at injection and extraction

Description: The objective of this note is to (once again) explore the AGS 'ORM' (orbit response matrix) data taken (by Operations) early during the 2007 run with an AGS bare machine and gold beam. Indeed the present motivation is to extract as much information about the AGS inherent transverse coupling as possible - from general arguments and the copious ORM data. And taking this one step further, (though not accomplished yet) the goal really should be to tell the model how to describe this coupling. 'Bare' as used here means the AGS with no quadrupole, sextupole or octupole magnets powered. Only the main (combined-function) magnet string and dipole bumps necessary to optimize beam survival are powered. 'ORM data' means the systematic recording of the equilibrium orbit beam position monitor response to powering individual dipole corrector magnets. The 'matrix' results from looking at the effect of each of the (12 superperiods X 4 dipoles per superperiod) 'kicks' on each of the (12 X 6) pick up electrodes (pues) in each transverse plane. So then we have two (48 X 72) matrices of numbers from the ORM data. (Though 'pue' usually refers to the hardware in the vacuum chamber and 'bpm' to the beam position monitoring system, the two labels will be used casually here.) The exercise is carried out at two magnet rigidities, injection (AGS field {approx}434 Gauss) and extraction to RHIC ({approx}9730 Gauss), - a ratio of rigidities of about 22.4. Since we stick with a bare machine, we are also stuck with the bare tunes which means the tunes are rather close together and near 8.75. Injection: (h,v) {approx} (8.73, 8.76).
Date: November 1, 2010
Creator: Ahrens, L.
Partner: UNT Libraries Government Documents Department

Preliminaries toward studying resonant extraction from the Debuncher

Description: A recent proposal to detect {mu} {yields} e direct conversion at Fermilab asks for slow extraction of protons from the antiproton source, specifically from the Debuncher. [1] A third-integer resonance originally was considered for this, partly because of the Debuncher's three-fold symmetry and partly because its operational horizontal tune, {nu}{sub x} {approx} 9.765, is already within 0.1 of {nu}{sub x} = 29/3. Using a half integer resonance, {nu}{sub x} = 19/2, though not part of the original proposal, has been suggested more recently because (a) Fermilab has had a good deal of experience with half-integer extraction from the Tevatron, the Main Injector and the erstwhile Main Ring, and (b) for reasons we shall examine later, it depopulates the entire bunch without an abort at the end. This memo presents considerations preliminary to studying both possibilities. It is meant only as a starting point for investigations to be carried out in the future. The working constraints and assumptions have oscillated between two extremes: (1) making minimal changes in the antiproton source to minimize cost and (2) building another machine in the same tunnel. In this memo we adopt an attitude aligned more toward the first. The assumed parameters are listed in Table 1. A few are not (easily) subject to change, such as those related to the beam's momentum and revolution frequency and the acceptance of the debuncher. Two resonance exemplars are presented in the next section, with an explanation of the analytic and semi-analytic calculations that can be done for each. Section 3 contains preliminary numerical work that was done to validate the exemplars within the context of extraction from the Debuncher. A final section contains a summary. Following the bibliography, appendices contain (a) a qualitative, conceptual discussion of extraction for the novice, (b) a telegraphic review of the perturbative ...
Date: June 1, 2009
Creator: Michelotti, Leo & Johnstone, John
Partner: UNT Libraries Government Documents Department

Transverse Instabilities of Coasting Beams with Space Charge

Description: Transverse beam stability is strongly affected by the beam space charge. Usually it is analyzed with the rigid-beam model. However this model is only valid when a bare (not affected by the space charge) tune spread is small compared to the space charge tune shift. This condition specifies a relatively small area of parameters which, however, is the most interesting for practical applications. The Landau damping rate and the beam Schottky spectra are computed assuming that validity condition is satisfied. The results are applied to a round Gaussian beam. The stability thresholds are described by simple fits for the cases of chromatic and octupole tune spreads.
Date: December 1, 2008
Creator: Burov, Alexey & Lebedev, Valeri
Partner: UNT Libraries Government Documents Department

Analytic second- and third-order achromat designs

Description: An achromat is a transport system that carries a beam without distorting its transverse phase space distribution. In this study, we apply the Lie algebraic technique to a repetitive FODO array to make it either a second-order or a third-order achromat. (Achromats based on reflection symmetries are not studied here.) We consider third-order achromats whose unit FODO cell layout is shown. The second-order achromat layout is the same, except the octupoles are absent. For the second-order achromats, correction terms (due to the finite bending of the dipoles) to the well-known formulae for the sextupole strengths are derived. For the third-order achromats, analytic expressions for the five octupole strengths are given. The quadrupole, sextupole and octupole magnets are assumed to be thin-lens elements. The dipoles are assumed to be sector magnets filling the drift spaces. More details of the analysis have been reported elsewhere.
Date: July 1, 1995
Creator: Wang, Chunxi & Chao, Alex
Partner: UNT Libraries Government Documents Department

Considerations in using third order focusing of proton beams for uniform irradiation of extended targets

Description: The latest target designs for the National Spallation Neutron Source (NSNS) and Accelerator Production of Tritium (APT), require that the geometrical target cross-section (normal to the proton beam direction) be of rectangular shape with dimensions (10 cm x 30 cm) and (16 cm x 160 cm) for the NSNS and APT targets, respectively. These targets are to be irradiated with high-intensity proton beams. At present, plans are to use beam-expanded uniform intensities for the APT target, with possibly a small horizontal and vertical jitter superimposed. Although current plans for the NSNS target call for non expanded gaussian distributions, the authors nevertheless investigate the application of a beam expander to provide beam on that target. The high aspect ratios, 3:1 and 1:10, currently proposed for the NSNS and APT targets prompt a feasibility study for the creation of uniform beams over such targets. This paper presents a beam-optics design of two proposed beam expanders which will generate a beam to irradiate uniformly the NSNS and APT targets. Both beam optics designs are representative only, and independent of any other official designs that may exist within the design groups of the APT or NSNS project. Recent experimental work on uniform beam profiles on the target of the Brookhaven Isotope Resource Center (BIRC) of the BNL-200 MeV-LINAC will also be presented.
Date: December 1, 1997
Creator: Tsoupas, N.; Kponou, A. & Snead, C.L. Jr.
Partner: UNT Libraries Government Documents Department