1,156 Matching Results

Search Results

Advanced search parameters have been applied.

A Theory of Mutual Impedances and Multiple Reflections in an N-Element Array Environment

Description: Abstract: A general theoretical approach is formulated to describe the complex electromagnetic environment of an N-element array. The theory reveals the element-to-element interactions and multiple reflections within the array. From the formulation, it is found that the interaction between an excited element and an open-circuited element can be viewed as the sum of terms describing all possible signal paths within the array environment which start from the radiating element and terminate on the element under observation. Within all paths except the most direct one, multiple reflections between subgroups of elements take place. The resulting solution is highly structured and recursive and is discussed in detail in the text. Illustrative examples are provided to facilitate understanding of these ideas.
Date: February 1985
Creator: Muth, Lorant A.
Partner: UNT Libraries Government Documents Department

LONGITUDINAL RESISTIVE INSTABILITIES OF INTENSE COASTING BEAMS IN PARTICLE ACCELERATORS

Description: The longitudinal electromagnetic interaction of an intense coasting beam with itself, including the effect of a resistive vacuum tank, is investigated theoretically. It is shown that even in the range where the particle frequency is an increasing function of particle energy, the beam can be longitudinally unstable due to the resistivity of the vacuum tank walls. In the absence of frequency spread in the unperturbed beam the beam is shown to be always unstable against longitudinal bunching with a growth rate which depends upon (N/{sigma}){sup 1/2}, where N is the number of particles in the beam and {sigma} is the conductivity of the surface material. By means of the Vlasov equation, a criterion for stability of the beam is obtained; and shown in the limit of high-conductivity walls to involve the frequency spread in the unperturbed beam, the number of particles N, the beam energy, geometrical properties of the accelerator, but not the conductivity {sigma}. A numerical example is presented which indicates that certain observations of beam behavior in the MURA 40 MeV electron accelerator may be related to the phenomena investigated here.
Date: October 23, 1963
Creator: Neil, V. Kelvin & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

COHERENT ELECTROMAGNETIC EFFECTS IN HIGH-CURRENT PARTICLE ACCELERATORS; III ELECTROMAGNETIC-COUPLING INSTABILITIES IN A COASTING BEAM

Description: The electromagnetic interaction of an intense relativistic coasting beam with itself, including the effect of a confining nonperfect vacuum tank, or a quiescent rf cavity, is investigated theoretically. It is shown that the resonances that may occur between harmonics of the particle circulation frequencies and the electromagnetic modes of the cavities can lead to a longitudinal instability of the beam. A criterion for stability of the beam against such longitudinal bunching is obtained as a restriction on the shunt impedance of the rf cavity, or the Q of the vacuum tank. This criterion contains the energy spread and intensity of the coasting beam, as well as the parameters of the accelerator. Numerical examples are given which indicate that in general the resonances with the vacuum tank will not cause instabilities, while those with an rf cavity can be prevented from causing instabilities by choosing the shunt impedance at a sufficiently low but still convenient value.
Date: August 4, 1960
Creator: Laslett, L. J.; Neil, V. Kelvin & Sessler, A. M.
Partner: UNT Libraries Government Documents Department

Current conservation and electromagnetic interaction currents for non-relativistic systems

Description: It is shown how to construct non-relativistic interaction currents which satisfy current conservation. The construction permits the use of different electromagnetic form factors for the pion, nucleon, and contact contributions, and therefore also permits the use of either G{sub E} of F{sub 1}. The numerical importance of this freedom for calculations of the electromagnetic form factors of {sup 3}He is studied, and found to be significant in some cases.
Date: May 1, 1991
Creator: Gross, Franz & Gross, Franz
Partner: UNT Libraries Government Documents Department

Development of 3D beam-beam simulation for the Tevatron

Description: We present status of development of a 3D Beam-Beam simulation code for simulating the Fermilab Tevatron collider. The essential features of the code are 3D particle-in-cell Poisson solver for calculating the Beam-Beam electromagnetic interactions with additional modules for linear optics, machine impedance and chromaticity, and multiple bunch tracking. The simulations match synchrobetatron oscillations measured at the VEPP-2M collider. The impedance calculations show beam instability development consistent with analytic expressions.
Date: June 1, 2007
Creator: Stern, E.; Amundson, J.; Spentzouris, P.; Valishev, A.; /Fermilab; Qiang, J. et al.
Partner: UNT Libraries Government Documents Department

Polarization Phenomena in Electromagnetic Interactions at Intermediate Energies

Description: Recent results of polarization measurements in electromagnetic interactions at intermediate energies are discussed. Prospects of polarization experiments at the new CW electron accelerators, as well as on upgraded older machines are outlined. It is concluded that polarization experiments will play a very important role in the study of the structure of the nucleon and of light nuclei.
Date: July 1, 1990
Creator: Burkert, Volker
Partner: UNT Libraries Government Documents Department

Electron and Photon Interactions in the Regime of Strong LPM Suppression

Description: Most searches for ultra-high energy (UHE) astrophysical neutrinos look for radio emission from the electromagnetic and hadronic showers produced in their interactions. The radio frequency spectrum and angular distribution depend on the shower development, so are sensitive to the interaction cross sections. At energies above about 1016 eV (in ice), the Landau-Pomeranchuk-Migdal (LPM) effect significantly reduces the cross sections for the two dominant electromagnetic interactions: bremsstrahlung and pair production. At higher energies, above about 1020 eV, the photonuclear cross section becomes larger than that for pair production, and direct pair production and electronuclear interactions become dominant over bremsstrahlung. The electron interaction length reaches a maximum around 1021 eV, and then decreases slowly as the electron energy increases further. In this regime, the growth in the photon cross section and electron energy loss moderates the rise in nu e shower length, which rises from ~;;5 m at 1016 eV to ~;;40 m at 1019 eV and ~;;100 m at 1020 eV, but only to ~;;300 m at 1024 eV. In contrast, without photonuclear and electronuclear interactions, the shower length would be over 10 km at 1024 eV.
Date: June 10, 2010
Creator: Gerhardt, L. & Klein, S.
Partner: UNT Libraries Government Documents Department

Measurements of the electromagnetic form factor of the Proton at Jlab

Description: The ratio of the proton's elastic electromagnetic form factors G{sub E{sub p}}/G{sub M{sub p}} was obtained by measuring P{sub t} and P{sub {ell}}, the transverse and longitudinal recoil proton polarization, respectively. For the elastic reaction {rvec e}p {yields} e{rvec p}, G{sub E{sub p}}/G{sub M{sub p}} is proportional to P{sub t}/P{sub {ell}}. The simultaneous measurement of P{sub t} and P{sub {ell}} in a polarimeter reduces systematic uncertainties. The results for the ratio G{sub E{sub p}}/G{sub M{sub p}} measured in Hall A so far show a systematic decrease with increasing Q{sup 2}, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. Together these experiments cover the Q{sub 2}- range of 0.5 to 5.6 GeV{sup 2}. A new experiment is currently being prepared, to extend the Q{sup 2}-range to 9 GeV{sup 2} in Hall C.
Date: April 1, 2003
Creator: Punjabi, Vina & Perdrisat, Charles
Partner: UNT Libraries Government Documents Department

Investigations of the dynamics and electromagnetic interactions of few-body systems. Progress report, June 30, 1994--September 30, 1995

Description: This progress report summarizes the work of The George Washington University (GW) nuclear theory group during the period 1 July 1994 - 30 September 1995 under DOE Grant No. DE-FG02-95-ER40907 mainly dealing with photonuclear reactions and few-body problems of nuclei. This report contains: papers published or in press, submitted for publication, and in preparation; invited talks at conferences and meetings; invited talks at universities and laboratories; contributed papers or abstracts at conferences; visitors to the group; and research progress by topic.
Date: October 1, 1995
Creator: Lehman, D.R.
Partner: UNT Libraries Government Documents Department

Probing the structure of nucleons in electromagnetic interactions

Description: The author discusses open problems in nucleon structure studies using electromagnetic probes. The focus is on the regime of strong interaction QCD. Significant progress in their understanding of the nucleon structure in the region of strong QCD may be expected in the first decade of the new millennium due to major experimental and theoretical efforts currently underway in this field.
Date: June 1, 1999
Creator: Burkert, V.D.
Partner: UNT Libraries Government Documents Department

Leptonic production of baryon resonances

Description: In these lectures, the author focuses on the electromagnetic transition between non-strange baryon states. This sector received much attention in the early 1970's after the development of the first dynamical quark models. However, experimental progress was slow, partly because of the low rates associated with electromagnetic interactions, and partly because of the lack of guidance by theoretical models that went beyond the simplest quark models. It was also difficult for experiments to achieve the precision needed for a detailed analysis of the entire resonance region in terms of the fundamental photocoupling amplitudes over a large range in momentum transfer.
Date: March 1, 1994
Creator: Burkert, V.
Partner: UNT Libraries Government Documents Department

The electroweak theory

Description: After a short essay on the current state of particle physics, the author reviews the antecedents of the modern picture of the weak and electromagnetic interactions and then undertakes a brief survey of the SU(2){sub L} {circle_times} U(1){sub Y} electroweak theory. The authors reviews the features of electroweak phenomenology at tree level and beyond, presents an introduction to the Higgs boson and the 1-TeV scale, and examines arguments for enlarging the electroweak theory. The author concludes with a brief look at low-scale gravity.
Date: August 10, 2001
Creator: Quigg, Chris
Partner: UNT Libraries Government Documents Department

Beyond the standard model in many directions

Description: These four lectures constitute a gentle introduction to what may lie beyond the standard model of quarks and leptons interacting through SU(3){sub c} {direct_product} SU(2){sub L} {direct_product} U(1){sub Y} gauge bosons, prepared for an audience of graduate students in experimental particle physics. In the first lecture, I introduce a novel graphical representation of the particles and interactions, the double simplex, to elicit questions that motivate our interest in physics beyond the standard model, without recourse to equations and formalism. Lecture 2 is devoted to a short review of the current status of the standard model, especially the electroweak theory, which serves as the point of departure for our explorations. The third lecture is concerned with unified theories of the strong, weak, and electromagnetic interactions. In the fourth lecture, I survey some attempts to extend and complete the electroweak theory, emphasizing some of the promise and challenges of supersymmetry. A short concluding section looks forward.
Date: April 28, 2004
Creator: Quigg, Chris
Partner: UNT Libraries Government Documents Department

Recent enhancements to the MARS15 code

Description: The MARS code is under continuous development and has recently undergone substantial improvements that further increase its reliability and predictive power in numerous shielding, accelerator, detector and space applications. The major developments and new features of the MARS15 (2004) version described in this paper concern an extended list of elementary particles and arbitrary heavy ions and their interaction cross-sections, inclusive and exclusive nuclear event generators, module for modeling particle electromagnetic interactions, enhanced geometry and histograming options, improved MAD-MARS Beam Line Builder, enhanced Graphical-User Interface, and an MPI-based parallelization of the code.
Date: May 12, 2004
Creator: al., Nikolai V. Mokhov et
Partner: UNT Libraries Government Documents Department

Beam losses from ultra-peripheral nuclear collisions between 208Pb82+ ions in the Large Hadron Collider and their alleviation

Description: Electromagnetic interactions between colliding heavy ions at the Large Hadron Collider (LHC) at CERN will give rise to localized beam losses that may quench superconducting magnets, apart from contributing significantly to the luminosity decay. To quantify their impact on the operation of the collider, we have used a three-step simulation approach, which consists of optical tracking, a Monte-Carlo shower simulation and a thermal network model of the heat flow inside a magnet. We present simulation results for the case of {sup 208}Pb{sup 82+} ion operation in the LHC, with focus on the ALICE interaction region, and show that the expected heat load during nominal {sup 208}Pb{sup 82+} operation is 40% above the quench level. This limits the maximum achievable luminosity. Furthermore, we discuss methods of monitoring the losses and possible ways to alleviate their effect.
Date: July 1, 2009
Creator: Bruce, R.; Gildardoni, S.; Jowett, J.M.; /CERN; Bocian, D. & /Fermilab
Partner: UNT Libraries Government Documents Department

Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation

Description: Electromagnetic interactions between colliding heavy ions at the Large Hadron Collider (LHC) at CERN will give rise to localized beam losses that may quench superconducting magnets, apart from contributing significantly to the luminosity decay. To quantify their impact on the operation of the collider, we have used a three-step simulation approach, which consists of optical tracking, a Monte-Carlo shower simulation and a thermal network model of the heat flow inside a magnet. We present simulation results for the case of {sup 208}Pb{sup 82+} ion operation in the LHC, with focus on the alice interaction region, and show that the expected heat load during nominal {sup 208}Pb{sup 82+} operation is 40% above the quench level. This limits the maximum achievable luminosity. Furthermore, we discuss methods of monitoring the losses and possible ways to alleviate their effect.
Date: August 1, 2009
Creator: Bruce, R.; Bocian, D.; Gilardoni, S. & Jowett, J. M.
Partner: UNT Libraries Government Documents Department