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Transverse Two-Stream Instability in the Presence of Strong Species-Species and Image Forces

Description: The theory of coherent transverse oscillations of two particle species is extended to include strong species-species and image forces. It is shown that in general the species-species force can considerably alter the instability threshold. Conversely, it is shown that the limit on the performance of an electron ring accelerator imposed by the requirement of stable ion electron oscillations, is not significantly improved by the inclusion of images.
Date: September 1972
Creator: Laslett, L. J.; Sessler, A. M. & Mohl, D.
Partner: UNT Libraries Government Documents Department

Oscillating two stream instability at the resonance of obliquely incident radiation in inhomogeneous plasmas

Description: The growth rate and the threshold value were calculated for the oscillating two-stream instability for an electromagnetic wave obliquely incident on an inhomogeneous plasma. The localization of the instability is found to be in the overdense region near the threshold and to shift toward the local plasma resonance when the pump intensity increases. (auth)
Date: October 1, 1975
Creator: Kuo, Y.Y.; Oberman, C.; Liu, C.S. & Troyon, F.
Partner: UNT Libraries Government Documents Department

TRANSVERSE ELECTRON-PROTON TWO-STREAM INSTABILITY IN A BUNCHED BEAM

Description: This paper is an analytical investigation of the trans-verse electron-proton (e-p) two-stream instability in a pro-ton bunch propagating through a stationary electron back-ground. The equations of motion, including the effect of damping, are derived for the centroids of the proton beam and the electron cloud. An approach is developed to solve the coupled linear centroid equations in the time domain describing the e-p instability in proton bunches with non-uniform line densities. Examples are presented for proton line densities corresponding to uniform and parabolic profiles.
Date: June 1, 2001
Creator: WANG, T.F.; CHANNELL, P.J.; MACEK, R.J. & DAVIDSON, R.C.
Partner: UNT Libraries Government Documents Department

Electron proton two-stream instability at the PSR.

Description: A strong, fast, transverse instability has long been observed at the Los Alamos Proton Storage Ring (PSR) where it is a limiting factor on peak intensity. Most of the available evidence, based on measurements of the unstable proton beam motion, is consistent with an electron-proton two-stream instability. The need for higher beam intensity at PSR [1] and for future high-intensity, proton drivers has motivated a multi-lab collaboration (LANL, ANL, FNAL, LBNL, BNL, ORNL, and PPPL) to coordinate research on the causes, dynamics and cures for this instability. Important characteristics of the electron cloud were recently measured with retarding field electron analyzers and various collection electrodes. Suppression of the electron cloud formation by TiN coatings has confirmed the importance of secondary emission processes in its generation. New tests of potential controls included dual harmonic rf, damping by higher order multipoles, damping by X,Y coupling and the use of inductive inserts to compensate longitudinal space charge forces. With these controls and higher rf voltage the PSR has accumulated stable beam intensity up to 9.7 {micro}C/pulse (6 x 10{sup 13} protons), which is a 60% increase over the previous maximum.
Date: February 19, 2002
Creator: Macek, R. J.; Browman, A.; Fitzgerald, D.; McCrady, R.; Merrill, F.; Plum, M. et al.
Partner: UNT Libraries Government Documents Department

Decay of Magnetic Helicity Producing Polarized Alfven Waves

Description: When a super-Alfvenic electron beam propagates along an ambient magnetic field, the left-hand circularly polarized Alfven wave is Cherenkov-emitted (two stream instability). This instability results in a spontaneous conversion of the background plasma helicity to the wave helicity. The background helicity induces a frequency (energy) shift in the eigenmodes, which changes the critical velocity for Cherenkov emission, and it becomes possible for a sub-Alfvenic electron beam to excite a nonsingular Alfven mode.
Date: February 1, 1994
Creator: Yoshida, Z. & Mahajan, S. M.
Partner: UNT Libraries Government Documents Department

Algorithm for Wave-Particle Resonances in Fluid Codes - Final Report

Description: We review the work performed under LDRD ER grant 98-ERD-099. The goal of this work is to write a subroutine for a fluid turbulence code that allows it to incorporate wave-particle resonances (WPR). WPR historically have required a kinetic code, with extra dimensions needed to evolve the phase space distribution function, f(x, v, t). The main results accomplished under this grant have been: (1) Derivation of a nonlinear closure term for 1D electrostatic collisionless fluid; (2) Writing of a 1D electrostatic fluid code, ''es1f,'' with a subroutine to calculate the aforementioned closure term; (3) derivation of several methods to calculate the closure term, including Eulerian, Euler-local, fully local, linearized, and linearized zero-phase-velocity, and implementation of these in es1f; (4) Successful modeling of the Landau damping of an arbitrary Langmuir wave; (5) Successful description of a kinetic two-stream instability up to the point of the first bounce; and (6) a spin-off project which uses a mathematical technique developed for the closure, known as the Phase Velocity Transform (PVT) to decompose turbulent fluctuations.
Date: March 3, 2000
Creator: Mattor, N.
Partner: UNT Libraries Government Documents Department

Effects on axial momentum spread on the electron-ion two-stream instability in high-intensity ion beams

Description: Use is made of the Vlasov-Maxwell equations to describe the electron-ion two-stream instability driven by the directed axial motion of a high-intensity ion beam propagating through a stationary population of (unwanted) background electrons. The ion beam is treated as continuous in the z-direction, and the electrons are electrostatically confined in the transverse direction by the space-charge potential produced by the excession charge. The analysis is carried out for arbitrary beam intensity, consistent with transverse confinement of the beam particles, and arbitrary fractional charge neutralization by the background electrons. For the case of overlapping step-function ion and electron density profiles, corresponding to monoenergetic electrons and ions in the transverse direction, detailed stability properties are calculated, including the important effects of an axial momentum spread, over a wide range of system parameters for dipole perturbations with azimuthal mode number l=1. The two-stream instability growth rate is found to increase with increasing beam intensity, increasing fractional charge neutralization, and decreasing proximity of the conducting wall. It is shown that Landau damping associated with a modest axial momentum spread of the beam ions and background electrons has a strong stabilizing influence on the instability.
Date: June 15, 2000
Creator: Davidso, R. & Qin, H.
Partner: UNT Libraries Government Documents Department

Simulating Electron Clouds in Heavy-Ion Accelerators

Description: Contaminating clouds of electrons are a concern for most accelerators of positive-charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly-, weakly-, and un-magnetized. They describe their approach to such self-consistency, and in particular a scheme for interpolating between full-orbit (Boris) and drift-kinetic particle pushes that enables electron time steps long compared to the typical gyro period in the magnets. They present tests and applications: simulation of electron clouds produced by three different kinds of sources indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the High-Current Experiment (HCX) at Lawrence Berkeley National Laboratory, in which the machine can be flooded with electrons released by impact of the ion beam and an end plate, demonstrate the ability to reproduce key features of the ion-beam phase space; and simulation of a two-stream instability of thin beams in a magnetic field demonstrates the ability of the large-timestep mover to accurately calculate the instability.
Date: April 7, 2005
Creator: Cohen, R.H.; Friedman, A.; Kireeff Covo, M.; Lund, S.M.; Molvik,A.W.; Bieniosek, F.M. et al.
Partner: UNT Libraries Government Documents Department

LINEAR ELECTROSTATIC INSTABILITY OF THE ELECTRON BEAM ION SOURCE

Description: Linear plasma fluid theory is used to study the stability of a cold electron beam in Brillouin equilibrium which passes through a stationary cold ion background, with particular interest in stability for parameters relevant to EBIS devices. Dispersion is studied both analytically and numerically. For {ell}=0, the usual infinite medium two stream instability condition is shown to correspond to a requirement that beam perveance exceed a minimum value, P>33 {micro}pervs; hence, this mode is stable for EBIS (P {approx} l{micro}perv). The Brillouin equilibrium rotation is shown to cause an electron-ion rotating stream instability, which is convectively unstable. The {ell}=1 mode is also found to be unstable. Higher modes numbers, {ell}>1, are unstable, but have reduced growth. Instability is only weakly affected by finite beam radius and boundary conditions.
Date: December 1, 1981
Creator: Litwin, C.; Vella, M.C. & Sessler, A.
Partner: UNT Libraries Government Documents Department

High frequency parametric wave phenomena and plasma heating: a review

Description: A survey of parametric instabilities in plasma, and associated particle heating, is presented. A brief summary of linear theory is given. The physical mechanism of decay instability, the purely growing mode (oscillating two-stream instability) and soliton and density cavity formation is presented. Effects of density gradients are discussed. Possible nonlinear saturation mechanisms are pointed out. Experimental evidence for the existence of parametric instabilities in both unmagnetized and magnetized plasmas is reviewed in some detail. Experimental observation of plasma heating associated with the presence of parametric instabilities is demonstrated by a number of examples. Possible application of these phenomena to heating of pellets by lasers and heating of magnetically confined fusion plasmas by high power microwave sources is discussed. (auth)
Date: November 1, 1975
Creator: Porkolab, M.
Partner: UNT Libraries Government Documents Department

Comparison of Electron Cloud Simulation and Experiments in the High-Current Experiment

Description: Contaminating clouds of electrons are a common concern for accelerators of positive-charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly, weakly, and un-magnetized. We describe our approach to such self-consistency, and in particular a scheme for interpolating between full-orbit (Boris) and drift-kinetic particle pushes that enables electron time steps long compared to the typical gyro period in the magnets. We present tests and applications: simulation of electron clouds produced by three different kinds of sources indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the High-Current Experiment (HCX) at LBNL, in which the machine can be flooded with electrons released by impact of the ion beam on an end plate, demonstrate the ability to reproduce key features of the ion-beam phase space; and simulation of a two-stream instability of thin beams in a magnetic field demonstrate the ability of the large-timestep mover to accurately calculate the instability.
Date: November 11, 2004
Creator: Cohen, R H; Friedman, A; Covo, M K; Lund, S M; Molvik, A W; Bieniosek, F M et al.
Partner: UNT Libraries Government Documents Department

Anomalous thermalization of fast ions in magnetized plasma

Description: A novel anomalous process causing the perpendicular energy of fast ions to be thermalized and lost on average to bulk ion heating, instead of classical slowing down and bulk electron heating, is investigated with PIC simulations. More than half of the fast ions are slowed down to the thermal ion level, although some are heated to twice their birth energy. The fast ion density perturbation is large. This process is excited by a new two-gyro-stream instability and may continually occur in a burning plasma. The implications for fusion ignition and fast ion confinement are assessed.
Date: November 1, 1993
Creator: Chen, K. R.
Partner: UNT Libraries Government Documents Department

Ion cyclotron emission due to the newly-born fusion products induced fast Alfven wave radiative instabilities in tokamaks

Description: The velocity distribution functions of the newly born (t = 0) charged fusion products of tokamak discharges can be approximated by a monoenergetic ring distribution with a finite v{sub {parallel}} such that v{sub {perpendicular}} {approx} v{sub {parallel}} {approx} v{sub j} where (M{sub j}V{sub j}{sup 2}/2) = E{sub j}, the directed birth energy of the charged fusion product species j of mass M{sub j}. As the time t progresses these distribution functions will evolve into a Gaussian in velocity with thermal spreadings given by the perpendicular and parallel temperatures T{sub {perpendicular}j}(t) = T{sub {parallel}j}(t) with T{sub j}(t) increasing as t increases and finally reaches an isotropic saturation value of T{sub {perpendicular}j}(t {approx} {tau}{sub j}) = T{sub {parallel}j}(t {approx} {tau}{sub j}) = T{sub j}(t {approx} {tau}{sub j}) {approx} [M{sub j}T{sub d}E{sub j}/(M{sub j} + M)]{sup 1/2}, where T{sub d} is the temperature of the background deuterium plasma ions, M is the mass of a triton or a neutron for j = protons and alpha particles, respectively, and {tau}{sub j} {approx} {tau}{sub sj}/4 is the thermalization time of the fusion product species j in the background deuterium plasma and {tau}{sub sj} is the slowing-down time. For times t of the order of {tau}{sub j} their distributions can be approximated by a Gaussian in their total energy. Then for times t {ge} {tau}{sub sj} the velocity distributions of these fusion products will relax towards their appropriate slowing-down distributions. Here the authors will examine the radiative stability of all these distributions. The ion cyclotron emission from energetic ion produced by fusion reactions or neutral beam injection promises to be a useful diagnostic tool.
Date: August 1, 1995
Creator: Arunasalam, V.
Partner: UNT Libraries Government Documents Department

Nonlinear delta(f) Simulations of Collective Effects in Intense Charged Particle Beams

Description: A nonlinear delta(f) particle simulation method based on the Vlasov-Maxwell equations has been recently developed to study collective processes in high-intensity beams, where space-charge and magnetic self-field effects play a critical role in determining the nonlinear beam dynamics. Implemented in the Beam Equilibrium, Stability and Transport (BEST) code [H. Qin, R.C. Davidson, and W.W. Lee, Physical Review -- Special Topics on Accelerator and Beams 3 (2000) 084401; 3 (2000) 109901.], the nonlinear delta(f) method provides a low-noise and self-consistent tool for simulating collective interactions and nonlinear dynamics of high-intensity beams in modern and next-generation accelerators and storage rings, such as the Spallation Neutron Source and heavy ion fusion drivers. A wide range of linear eigenmodes of high-intensity charged-particle beams can be systematically studied using the BEST code. Simulation results for the electron-proton two-stream instability in the Proton Storage Ring experiment [R. Macek, et al., in Proc. of the Particle Accelerator Conference, Chicago, 2001 (IEEE, Piscataway, NJ, 2001), Vol. 1, p. 688.] at the Los Alamos National Laboratory agree well with experimental observations. Large-scale parallel simulations have also been carried out for the ion-electron two-stream instability in the very-high-intensity heavy ion beams envisioned for heavy ion fusion applications. In both cases, the simulation results indicate that the dominant two-stream instability has a dipole-mode (hose-like) structure and can be stabilized by a modest axial momentum spread of the beam particles.
Date: January 21, 2003
Creator: Qin, Hong
Partner: UNT Libraries Government Documents Department

Electron-cloud build-up in hadron machines

Description: The first observations of electron-proton coupling effect for coasting beams and for long-bunch beams were made at the earliest proton storage rings at the Budker Institute of Nuclear Physics (BINP) in the mid-60's [1]. The effect was mainly a form of the two-stream instability. This phenomenon reappeared at the CERN ISR in the early 70's, where it was accompanied by an intense vacuum pressure rise. When the ISR was operated in bunched-beam mode while testing aluminum vacuum chambers, a resonant effect was observed in which the electron traversal time across the chamber was comparable to the bunch spacing [2]. This effect (''beam-induced multipacting''), being resonant in nature, is a dramatic manifestation of an electron cloud sharing the vacuum chamber with a positively-charged beam. An electron-cloud-induced instability has been observed since the mid-80's at the PSR (LANL) [3]; in this case, there is a strong transverse instability accompanied by fast beam losses when the beam current exceeds a certain threshold. The effect was observed for the first time for a positron beam in the early 90's at the Photon Factory (PF) at KEK, where the most prominent manifestation was a coupled-bunch instability that was absent when the machine was operated with an electron beam under otherwise identical conditions [4]. Since then, with the advent of ever more intense positron and hadron beams, and the development and deployment of specialized electron detectors [5-9], the effect has been observed directly or indirectly, and sometimes studied systematically, at most lepton and hadron machines when operated with sufficiently intense beams. The effect is expected in various forms and to various degrees in accelerators under design or construction. The electron-cloud effect (ECE) has been the subject of various meetings [10-15]. Two excellent reviews, covering the phenomenology, measurements, simulations and historical development, have been recently given by ...
Date: August 9, 2004
Creator: Furman, M.A.
Partner: UNT Libraries Government Documents Department

Weibel and Two-Stream Instabilities for Intense Charged Particle Beam Propagation through Neutralizing Background Plasma

Description: Properties of the multi-species electromagnetic Weibel and electrostatic two-stream instabilities are investigated for an intense ion beam propagating through background plasma. Assuming that the background plasma electrons provide complete charge and current neutralization, detailed linear stability properties are calculated within the framework of a macroscopic cold-fluid model for a wide range of system parameters.
Date: April 9, 2004
Creator: Davidson, Ronald C.; Kaganovich, Igor & Startsev, Edward A.
Partner: UNT Libraries Government Documents Department

Relativistic electron beam propagation: two-stream theory, January 1978-January 1979

Description: Progress achieved in the theoretical understanding of the two-stream instability as it pertains to the propagation of relativistic electron beams through low pressure neutral gases is presented. Research has been performed on both aspects of the stability issue: linear stabilization of the two-stream mode and the nonlinear state of an unstable system.
Date: July 1, 1979
Creator: Newberger, B.S.
Partner: UNT Libraries Government Documents Department

Space-time evolution of the nonlinear two-stream instability

Description: A cold electron beam penetrating a cold plasma is electrostatically unstable. The instability produces a growing electric field that saturates when the beam electrons are suddenly trapped by a single wave. During trapping a significant amount of energy is transferred from the beam to the field and ultimately to the plasma. At Los Alamos experiments are being performed that demonstrate this anomalous beam-driven plasma heating. The heating efficiency is a function of the phase velocity of the trapping wave. According to our generalization of a previous calculation, the instability is absolute and its wave form evolves in both space and time. Modifying trapping theory to account for the space and time evolution of the two-stream instability, we find that the heating efficiency should change in time. This prediction is in agreement with results from one-dimensional PIC simulations.
Date: January 1, 1983
Creator: Lemons, D.S.; Jones, M.E. & Lee, H.
Partner: UNT Libraries Government Documents Department

Relativistic fluid equations of motion, equilibrium and stability of beams

Description: A general relativistic fluid formulation has been obtained by Siambis. The set of relativistic fluid equations includes a general equation of state. The use of these equations, however, is hampered by the presence of additional fluid variables resulting from relativistic corrections. The systematic expansion and associated nice variables introduced by Newcomb, have been utilized in the formulation of Siambis to yield a compact set of relativistic fluid equations which is the relativistic generalization of the well-known non-relativistic set of fluid equations. Specifically a general relativistic equation of state is obtained, which can be reduced to much simpler forms for specific cases. Equilibrium constraints are obtained and discussed. A stability analysis has been carried out for the two-stream instability including relativistic thermal corrections. A new mode of beam oscillation has been found, the thermal-relativistic mode. This mode is a fast-wave mode and it interacts resonantly, under certain conditions, with the well-known positive energy beam fast wave. 5 refs., 2 figs.
Date: January 1, 1983
Creator: Siambis, J.G.
Partner: UNT Libraries Government Documents Department

Nonlinear two-stream interaction between a cold, relativistic electron beam and a collisional plasma-Astron experiment

Description: Experiments on the two-stream instability of a relativistic electron beam propagating through a neutral gas, carried out with the Lawrence Livermore Laboratory Astron beam, have been analyzed using a nonlinear saturation model for a cold beam. The behavior of the observed microwave emission due to the instability is in good agreement with that of the beam energy loss. Collisions on the plasma electrons weaken the nonlinear state of the instability but do not stabilize the mode. The beam essentially acts as if it were cold, a result substantiated by linear theory for waves propagating along the beam. In order to predict the effect of both beam momentum scatter and plasma electron collisions on the stability of the mode in future experiments a full two-dimensional linear theory must be developed.
Date: May 1, 1979
Creator: Newberger, B. S. & Thode, L. E.
Partner: UNT Libraries Government Documents Department