88 Matching Results

Search Results

Advanced search parameters have been applied.

Time Evolution of Beam in the Recycler Ring

Description: We study the time evolution of the beam current in the Fermilab Recycler Ring due to abrupt physical processes (single coulomb scattering, nuclear scattering) that cause sudden loss of beam, and diffusive processes (multiple coulomb scattering, lattice dependence, etc.) which cause emittance growth. This emittance growth combined with finite aperture of the beam pipe will lead to eventual loss of most beam. We develop a fitting technique to the time evolution of beam current to estimate emittance growth. Finally we compare the directly measured growth with the fitted value.
Date: May 7, 2003
Creator: Krish Gounder, John Marriner and Shekhar Mishra
Partner: UNT Libraries Government Documents Department

The recycler ring beam life time

Description: We study the Fermilab Recycler Ring beam life time due to various physical processes associated with beam-gas interactions. This includes single coulomb scattering, electronic excitations, nuclear and multiple scattering processes. We compare the measured life time with those obtained from theoretical estimations. The results indicate additional processes are also contributing to the actual beam life time.
Date: July 20, 2001
Creator: al., Krishnaswamy Gounder et
Partner: UNT Libraries Government Documents Department

Formation of pre-sheath boundary layers in electronegative plasmas

Description: In electronegative plasmas Coulomb scattering between positive and negative ions can lead to the formation of a pre-sheath boundary layer containing the bulk of the negative ions. The negative ion boundary layer forms when momentum transfer from positive to negative ions dominates the negative ion acceleration from the electric field. This condition is met in Inductively Coupled Plasma reactors that operate at low pressure and high plasma density. Simulations of the GEC reactor for Chlorine and Oxygen chemistries using the INDUCT95 2D model are presented showing the pre-sheath boundary layer structure as a function of applied power and neutral pressure.
Date: May 1, 1998
Creator: Vitello, P., LLNL
Partner: UNT Libraries Government Documents Department

Proton radiography as a means of material characterization

Description: The authors describe how protons with energies of 800 MeV or greater can be used as radiographic probes for material characterization. A feature which distinguishes protons from x-rays is their charge, which results in multiple Coulomb scattering effects in proton radiographs. Magnetic lensing can ameliorate these effects and even allow mixed substances to be disentangled. They illustrate some of these effects using 800 MeV protons radiographs of a composite step wedge composed of Aluminum, Foam, and Graphite. They discuss how proton radiographs must be manipulated in order to use standard tomographic reconstruction algorithms. They conclude with a brief description of an upcoming experiment, which is performed at Brookhaven National Laboratory at 25 GeV.
Date: June 23, 1999
Creator: Aufderheide, M B; Barnes, P D; Bionta, R M; Hartouni, E P; Morris, C L; Park, H S et al.
Partner: UNT Libraries Government Documents Department

Numerical Study of Coulomb Scattering Effects on Electron Beamfrom a Nano-Tip

Description: Nano-tips with high acceleration gradient around the emission surface have been proposed to generate high brightness beams. However, due to the small size of the tip, the charge density near the tip is very high even for a small number of electrons. The stochastic Coulomb scattering near the tip can degrade the beam quality and cause extra emittance growth and energy spread. In the paper, we present a numerical study of these effects using a direct relativistic N-body model. We found that emittance growth and energy spread, due to Coulomb scattering, can be significantly enhanced with respect to mean-field space-charge calculations.
Date: June 25, 2007
Creator: Qiang, Ji; Corlett, John N.; Lidia, Steven M.; Padmore, HowardA.; Wan, Weishi; Zholent, Andrew A. et al.
Partner: UNT Libraries Government Documents Department

Emittance Growth from Multiple Coulomb Scattering in a Plasma Wakefield Accelerator

Description: Emittance growth is an important issue for plasma wakefield accelerators (PWFAs). Multiple Coulomb scattering (MCS) is one factor that contributes to this growth. Here, the MCS emittance growth of an electron beam traveling through a PWFA in the blow out regime is calculated. The calculation uses well established formulas for angular scatter in a neutral vapor and then extends the range of Coulomb interaction to include the effects of traveling through an ion column. Emittance growth is negligible for low Z materials; however, becomes important for high Z materials.
Date: June 27, 2007
Creator: Kirby, N.; Berry, M.; Blumenfeld, I.; Hogan, M.J.; Ischebeck, R.; Siemann, R. et al.
Partner: UNT Libraries Government Documents Department

Beam Losses and Background Loads on Collider Detectors Due to Beam-Gas Interactions in the LHC

Description: With a fully-operational high-efficient collimation system in the LHC, nuclear interactions of circulating protons with residual gas in the machine beam pipe can be a major source of beam losses in the vicinity of the collider detectors, responsible for the machine-induced backgrounds. Realistic modeling of Coulomb scattering, elastic and inelastic interactions of 7-TeV protons with nuclei in the vacuum chamber of the cold and warm sections of the LHC ring--with an appropriate pressure profile--is performed with the STRUCT and MARS15 codes. Multi-turn tracking of the primary beams, propagation of secondaries through the lattice, their interception by the tertiary collimators TCT as well as properties of corresponding particle distributions at the CMS and ATLAS detectors are studied in great detail and results presented in this paper.
Date: April 1, 2009
Creator: Drozhdin, A.I.; Mokhov, N.V.; Striganov, S.I. & /Fermilab
Partner: UNT Libraries Government Documents Department

Nonthermal effects in two component DT fusion reactors

Description: Net energy generation rates and f-factors are calculated for a variety of two component DT reactor configurations using a computer code that follows the energy distributions of the reactants and products explicitly, utilizing the Fokker--Planck approximation for low-angle Coulomb scattering and a transfer matrix for high-angle Coulomb, nuclear, and radiative processes. The relative importance of such non-thermal effects as alpha particle deposition, non- Maxwellian energy distributions for the target tritons and electrons, and the influence of high-angle Coulomb and nuclear scattering on the energy loss rate of the injected deuterons is explicitly assessed. (auth)
Date: November 1, 1975
Creator: Weaver, T.A. & Chu, T.C.
Partner: UNT Libraries Government Documents Department

Particle Diffusion Due to Coulomb Scattering

Description: Conventionally, the multiple and single particle scattering in a storage ring are considered to be independent. Such an approach is simple and often yields sufficiently accurate results. Nevertheless, there is a class of problems where such an approach is not adequate and the single and multiple scattering need to be considered together. This can be achieved by solving an integro-differential equation for the particle distribution function, which correctly treats particle Coulomb scattering in the presence of betatron motion. A derivation of the equation is presented in the article. A numerical solution for one practical case is also considered.
Date: June 3, 2002
Creator: Nagaitsev, V. Lebedev and S.
Partner: UNT Libraries Government Documents Department

Effects of non-equilibrium particle distributions in deuterium-tritium burning

Description: We investigate the effects of non-equilibrium particle distributions resulting from rapid deuterium-tritium burning in plasmas using a Fokker-Planck code that incorporates small-angle Coulomb scattering, Brehmsstrahlung, Compton scattering, and thermal-nuclear burning. We find that in inertial confinement fusion environments, deviations away from Maxwellian distributions for either deuterium or tritium ions are small and result in 1% changes in the energy production rates. The deuterium and tritium effective temperatures are not equal, but differ by only about 2.5% near the time of peak burn rate. Simulations with high Z (Xe) dopants show that the dopant temperature closely tracks that of the fuel. On the other hand, fusion product ion distributions are highly non-Maxwellian, and careful treatments of energy-exchange between these ions and other particles is important for determining burn rates.
Date: August 18, 2009
Creator: Michta, D; Graziani, F; Pruet, J & Luu, T
Partner: UNT Libraries Government Documents Department

Conceptual study of moderately coupled plasmas and experimental comparison of laboratory x-ray sources

Description: In this thesis the fundamental concepts of moderately coupled plasmas, for which 2{approx_lt}ln{Lambda}{sub b}{approx_lt}10, are, for the first time, presented. This investigation is motivated because neither the conventional Fokker-Planck approximation [for weakly coupled plasmas (ln{Lambda}{sub b}{approx_lt}10)] nor the theory of dielectric response with correlations for strongly coupled plasmas (ln{Lambda}{sub b}{approx_lt}1) has satisfactorily addressed this regime. Specifically, herein the standard Fokker-Planck operator for Coulomb collisions has been modified to include hitherto neglected terms that are directly associated with large-angle scattering. In addition a reduced electron-ion collision operator has been calculated that, for the first time, manifests 1/ln{Lambda}{sub b} corrections. Precise calculations of some relaxation rates and crude calculations of electron transport coefficients have been made. As one of major applications of the modified Fokker-Planck equation, the stopping powers and {rho}R have been calculated for charged fusion products ({alpha}`s, {sup 3}H, {sup 3}He) and hot electrons interacting with plasmas relevant to inertial confinement fusion. In the second major topic of this thesis, advances made in the area of laboratory x-ray sources are presented. First, and most importantly, through the use a Cockcroft-Walton linear accelerator, a charged particle induced x-ray emission (PIXE) source has been developed. Intense line x radiation (including K-, L-, M-, and N-lines) with wavelengths from 0.5 {angstrom} to 111 {angstrom} have been successfully produced. Second, a new high intensity electron-beam x-ray generator has also been developed, and it has been used with advantage in the soft x-ray region ( < 3 keV). Finally, a direct comparisons of both sources (PIXE and electron-beam x-ray sources) to a commercially available radioactive {alpha} fluorescent x-ray source has been made.
Date: December 1993
Creator: Li, C.
Partner: UNT Libraries Government Documents Department

Design and operation of a proton microscope for radiography at 800 MEV

Description: A high-magnification high-resolution option is desirable for the study of small-scale dynamic experiments at the LANSCE 800-MeV Proton Radiography Facility. Magnification is achievable by either repowering the existing imaging-lens quadrupoles, using new high-gradient quadrupoles, or some hybrid combination of the two. The large and complex parameter space of magnetic optics solutions was studied extensively with the 3rd order optics code MARYLIE. Some of the hybrid solutions achieve magnifications up to 150, but at the price of high chromatic aberrations. In the end, a design using only new high-gradient permanent-magnet quadrupoles was selected and built at the design parameters that minimized chromatic aberration per unit magnification. The design has a moderate magnification of 7.1 and 15.8 at the two existing image stations. First-beam commissioning results exceeded expectations. Image contrast is produced by multiple Coulomb scattering in the thin objects. Early experimental objectives are to optimize this contrast by collimator design and by adjusting the correlation in the illuminating beam, as well as to characterize the (quite high) resolution limits of the system.
Date: January 1, 2003
Creator: Mottershead, C. T.; Barlow, D. B. (David B.); Blind, B. (Barbara); Hogan, G. E. (Gary E.); Jason, A. J. (Andrew J.); Merrill, F. E. (Frank E.) et al.
Partner: UNT Libraries Government Documents Department

CNI polarimetry and the hadronic spin dependence of pp scattering

Description: Methods for limiting the size of hadronic spin-flip in the Coulomb- Nuclear Interference. region are critically assessed. This work was presented at the High Energy Polarimetry Workshop in Amsterdam, Sept. 9, 1996 and the RHIC Spin Collaboration meeting in Marseille, Sept. 17, 1996.
Date: November 22, 1996
Creator: Trueman, T.L.
Partner: UNT Libraries Government Documents Department

Deterministic proton transport solving a one dimensional Fokker-Planck equation

Description: The transport of protons through matter is characterized by many interactions which cause small deflections and slight energy losses. The few which are catastrophic or cause large angle scattering can be viewed as extinction for many applications. The transport of protons at this level of approximation can be described by a Fokker Planck Equation. This equation is solved using a deterministic multigroup differencing scheme with a highly resolved set of discrete ordinates centered around the beam direction which is adequate to properly account for deflections and energy losses due to multiple Coulomb scattering. Comparisons with LAHET for a large variety of problems ranging from 800 MeV protons on a copper step wedge to 10 GeV protons on a sandwich of material are presented. The good agreement with the Monte Carlo code shows that the solution method is robust and useful for approximate solutions of selected proton transport problems.
Date: October 1, 1997
Creator: Marr, D.; Prael, R.; Adams, K. & Alcouffe, R.
Partner: UNT Libraries Government Documents Department


Description: Integral part of the primary collimator of the SNS accumulator ring is a halo intercept assembly in the form of movable scraper blades that allow interception of the halo protons in four planes. In order to achieve large coulomb scattering of the halo protons and energy losses of less than 1%, platinum was chosen as the material of choice while its thickness was optimized to satisfy the energy loss requirements. This paper outlines the adopted design of the scraper assembly and presents the thermal response of the system that intercepts the beam halo as well as the subsequent thermal stress analysis and the issues associated with the performance of the scraper. Specifically, the current design incorporates a highly conducting material (copper) in the blade structure interfacing with the platinum scraper and is responsible for conducting the deposited energy away from the beam interception region. The mechanical performance and durability of such system, especially of the special bonding between the dissimilar materials, is the primary focus of this effort.
Date: June 18, 2001
Partner: UNT Libraries Government Documents Department

Simulation of nucleon elastic scattering in the MARS14 code system

Description: Correct modeling of nucleon elastic scattering is of special importance in many applications at high energy accelerators, such as deep penetration, beam loss and collimation studies. In present paper, the work performed to update the MARS elastic scattering model at E &lt; 5 GeV is described. Modern evaluated nuclear data as well as fitting formulae are used in the new model. For protons as projectiles, Coulomb scattering and Coulomb-nuclear interference are taken into account in addition to nuclear elastic scattering. Comparisons with experimental angular distributions and calculations by means of other codes are presented.
Date: November 26, 2001
Creator: Rakhno, Igor L.; Mohkov, N.; Sukhovitski, E. & Chiba, S.
Partner: UNT Libraries Government Documents Department


Description: The authors summarize the methods used for simulation of polarization effects in the front end of a possible neutrino factory. They first discuss the helicity of muons in the pion decay process. They find that, neglecting acceptance considerations, the average helicity asymptotically approaches a magnitude of 0.185 at large pion momenta. Next they describe the methods used for tracking the spin through the complicated electromagnetic field configurations in the front end of the neutrino factory, including rf phase rotation and ionization cooling channels. Various depolarizing effects in matter are then considered, including multiple Coulomb scattering and elastic scattering from atomic electrons. Finally, they include all these effects in a simulation of a 480 m long, double phase rotation front end scenario.
Date: June 12, 2000
Partner: UNT Libraries Government Documents Department

On the theory and simulation of multiple Coulomb scattering of heavy charged particles

Description: The Moliere theory of multiple Coulomb scattering is modified to take into account difference between scattering off atomic nuclei and electron. A simple analytical expression for angular distribution of charged particles passing through a thick absorber is found. It does not assume any special form for a differential scattering cross section and has wider range of applicability than a Gaussian approximation. A well-known method to simulate multiple Coulomb scattering is based on the different treatment of ''soft'' and ''hard'' collisions. An angular deflection in a large number of ''soft'' collisions is sampled using the proposed distribution function, a small number of ''hard'' collision are simulated directly. A boundary between ''hard'' and ''soft'' collisions is defined providing a precise sampling of a scattering angle (1% level) and a small number of ''hard'' collisions. A corresponding simulating module takes into account projectile and nucleus charged distributions and exact kinematics of a projectile-electron interactions.
Date: May 12, 2004
Creator: Striganov, Sergei I.
Partner: UNT Libraries Government Documents Department

Physics considerations for laser-plasma linear colliders

Description: Physics considerations for a next-generation linear collider based on laser-plasma accelerators are discussed. The ultra-high accelerating gradient of a laser-plasma accelerator and short laser coupling distance between accelerator stages allows for a compact linac. Two regimes of laser-plasma acceleration are discussed. The highly nonlinear regime has the advantages of higher accelerating fields and uniform focusing forces, whereas the quasi-linear regime has the advantage of symmetric accelerating properties for electrons and positrons. Scaling of various accelerator and collider parameters with respect to plasma density and laser wavelength are derived. Reduction of beamstrahlung effects implies the use of ultra-short bunches of moderate charge. The total linac length scales inversely with the square root of the plasma density, whereas the total power scales proportional to the square root of the density. A 1 TeV center-of-mass collider based on stages using a plasma density of 10{sup 17} cm{sup -3} requires tens of J of laser energy per stage (using 1 {micro}m wavelength lasers) with tens of kHz repetition rate. Coulomb scattering and synchrotron radiation are examined and found not to significantly degrade beam quality. A photon collider based on laser-plasma accelerated beams is also considered. The requirements for the scattering laser energy are comparable to those of a single laser-plasma accelerator stage.
Date: June 11, 2010
Creator: Schroeder, Carl; Esarey, Eric; Geddes, Cameron; Benedetti, Carlo & Leemans, Wim
Partner: UNT Libraries Government Documents Department

Simulation of PEP-II Accelerator Backgrounds Using TURTLE

Description: We present studies of accelerator-induced backgrounds in the BaBar detector at the SLAC B-Factory, carried out using LPTURTLE, a modified version of the DECAY TURTLE simulation package. Lost-particle backgrounds in PEP-II are dominated by a combination of beam-gas bremstrahlung, beam-gas Coulomb scattering, radiative-Bhabha events and beam-beam blow-up. The radiation damage and detector occupancy caused by the associated electromagnetic shower debris can limit the usable luminosity. In order to understand and mitigate such backgrounds, we have performed a full program of beam-gas and luminosity-background simulations, that include the effects of the detector solenoidal field, detailed modeling of limiting apertures in both collider rings, and optimization of the betatron collimation scheme in the presence of large transverse tails.
Date: February 15, 2006
Creator: Barlow, R. J.; Fieguth, T.; Kozanecki, W.; Majewski, S. A.; Roudeau, P. & Stocchi, A.
Partner: UNT Libraries Government Documents Department

Intra-beam scattering and its application to ERL

Description: Treatment of Coulomb collisions within the beam requires consideration of both large and small angle scattering. Such collisions lead to the Touschek effect and Intrabeam Scattering (IBS). The Touschek effect refers to particle loss as a result of a single collision, where only transfer from the transverse direction into longitudinal plays a role. It is important to consider this effect for ERL design to have an appropriate choice of collimation system. The IBS is a diffusion process which leads to changes of beam distribution but does not necessarily result in a beam loss. Evaluation of IBS in ERLs, where beam distribution is non-Gaussian, requires special treatment. Here we describe the IBS and Touschek effects with application to ERLs. In circular accelerators both the Touschek effect and IBS were found important. The generalized formulas for Touschek calculations are available and are already being used in advanced tracking simulations of several ERL-based projects. The IBS (which is diffusion due to multiple Coulomb scattering) is not expected to cause any significant effect on beam distribution in ERLs, unless one considers very long transport of high-brightness beams at low energies. Both large and small-angle Coulomb scattering can contribute to halo formation in future ERLs with high-brightness beams, as follows from simple order-of-magnitude estimates. In this report, a test comparison between 'local' and 'sliced' IBS models within the BET ACOOL code was presented for an illustrative ERL distribution. We also presented accumulated current loss distribution due to Touschek scattering for design parameters of ERL proposed for the eRHIC project, as well as scaling for multi-pass ERLs.
Date: October 16, 2011
Creator: Fedotov, A.
Partner: UNT Libraries Government Documents Department

Transverse Emittance Reduction with Tapered Foil

Description: The idea of reducing transverse emittance with tapered energy-loss foil is proposed by J.M. Peterson in 1980s and recently by B. Carlsten. In this paper, we present the physical model of tapered energy-loss foil and analyze the emittance reduction using the concept of eigen emittance. The study shows that, to reduce transverse emittance, one should collimate at least 4% of particles which has either much low energy or large transverse divergence. The multiple coulomb scattering is not trivial, leading to a limited emittance reduction ratio. Small transverse emittances are of essential importance for the accelerator facilities generating free electron lasers, especially in hard X-ray region. The idea of reducing transverse emittance with tapered energy-loss foil is recently proposed by B. Carlsten [1], and can be traced back to J.M. Peterson's work in 1980s [2]. Peterson illustrated that a transverse energy gradient can be produced with a tapered energy-loss foil which in turn leads to transverse emittance reduction, and also analyzed the emittance growth from the associated multiple coulomb scattering. However, what Peterson proposed was rather a conceptual than a practical design. In this paper, we build a more complete physical model of the tapered foil based on Ref. [2], including the analysis of the transverse emittance reduction using the concept of eigen emittance and confirming the results by various numerical simulations. The eigen emittance equals to the projected emittance when there is no cross correlation in beam's second order moments matrix [3]. To calculate the eigen emittances, it requires only to know the beam distribution at the foil exit. Thus, the analysis of emittance reduction and the optics design of the subsequent beam line section can be separated. In addition, we can combine the effects of multiple coulomb scattering and transverse energy gradient together in the beam matrix and analyze ...
Date: December 9, 2011
Creator: Jiao, Yi; Chao, Alex; Cai, Yunhai & /SLAC
Partner: UNT Libraries Government Documents Department

Comparison of Carbon and Hi-Z Primary Collimators for the LHC Phase II Collimation System

Description: A current issue with the LHC collimation system is single-diffractive, off-energy protons from the primary collimators that pass completely through the secondary collimation system and are absorbed immediately downbeam in the cold magnets of the dispersion suppressor section. Simulations suggest that the high impact rate could result in quenching of these magnets. We have studied replacing the 60 cm primary graphite collimators, which remove halo mainly by inelastic strong interactions, with 5.25 mm tungsten, which remove halo mainly by multiple coulomb scattering and thereby reduce the rate of single-diffractive interactions that cause losses in the dispersion suppressor.
Date: October 31, 2011
Creator: Keller, Lewis; /SLAC; Markiewicz, Thomas; /SLAC; Smith, Jeffrey; /SLAC et al.
Partner: UNT Libraries Government Documents Department