Showing papers by "John R. Cary published in 2001"
TL;DR: In this article, the authors present 2D simulations of beam-driven and laser-driven wakefield accelerators, using the object-oriented particle-in-cell code XOOPIC, which is time explicit, fully electromagnetic, and capable of running on massively parallel supercomputers.
Abstract: We present 2D simulations of both beam-driven and laser-driven plasma wakefield accelerators, using the object-oriented particle-in-cell code XOOPIC, which is time explicit, fully electromagnetic, and capable of running on massively parallel supercomputers. Simulations of laser-driven wakefields with low $\(\ensuremath{\sim}{10}^{16}\mathrm{W}/{\mathrm{cm}}^{2}\)$ and high $\(\ensuremath{\sim}{10}^{18}\mathrm{W}/{\mathrm{cm}}^{2}\)$ peak intensity laser pulses are conducted in slab geometry, showing agreement with theory and fluid simulations. Simulations of the E-157 beam wakefield experiment at the Stanford Linear Accelerator Center, in which a 30 GeV electron beam passes through 1 m of preionized lithium plasma, are conducted in cylindrical geometry, obtaining good agreement with previous work. We briefly describe some of the more significant modifications to XOOPIC required by this work, and summarize the issues relevant to modeling relativistic electron-neutral collisions in a particle-in-cell code.
85 citations
Oak Ridge National Laboratory1, University of Wisconsin-Madison2, Lehigh University3, University of California, San Diego4, University of Colorado Boulder5, Lawrence Livermore National Laboratory6, University of California, Los Angeles7, Princeton Plasma Physics Laboratory8, Georgia Institute of Technology9, University of Texas at Austin10, Massachusetts Institute of Technology11, University of Alberta12
TL;DR: In this paper, external impurity injection into L mode edge discharges in DIII-D has produced clear confinement improvement (a factor of 2 in energy confinement and neutron emission), reduction in all transport channels (particularly ion thermal diffusivity to the neoclassical level), and simultaneous reduction of long wavelength turbulence.
Abstract: External impurity injection into L mode edge discharges in DIII-D has produced clear confinement improvement (a factor of 2 in energy confinement and neutron emission), reduction in all transport channels (particularly ion thermal diffusivity to the neoclassical level), and simultaneous reduction of long wavelength turbulence. Suppression of the long wavelength turbulence and transport reduction are attributed to synergistic effects of impurity induced enhancement of E × B shearing rate and reduction of toroidal drift wave turbulence growth rate. A prompt reduction of density fluctuations and local transport at the beginning of impurity injection appears to result from an increased gradient of toroidal rotation enhancing the E × B shearing. Transport simulations carried out using the National Transport Code Collaboration demonstration code with a gyro-Landau fluid model, GLF23, indicate that E × B shearing suppression is the dominant transport suppression mechanism.
52 citations
TL;DR: In this paper, a method for finding four-dimensional symplectic maps with an enlarged nearly integrable region is described, which relies on solving for parameter values at which the linear stability factors of the fixed points (periodic orbits) of the map have the values corresponding to integer island tunes.
Abstract: A method for finding four-dimensional symplectic maps with an enlarged nearly integrable region is described. The method relies on solving for parameter values at which the linear stability factors of the fixed points (periodic orbits) of the map have the values corresponding to integer island tunes. This method is applied to accelerator lattices in order to increase dynamic aperture. The result shows a significant increase of the dynamic aperture after correction.
11 citations
TL;DR: In this article, a method for distinguishing between data from a strange attractor and data from colored random noise is presented, based on the variance growth test, which measures the increase in the variance, as measured by the average squared deviation, of a subset of data as the length of that subset is increased.
Abstract: A method for distinguishing between data from a strange attractor and data from colored random noise is presented. For both types of data the apparent dimension, as measured by the scaling of the correlation function with length, is finite and noninteger for certain length scales. This would seem to indicate that such measurements by themselves are insufficient for concluding that the dynamics of the underlying system are low-dimensional. To distinguish these two types of data, we have developed the variance growth test. The test looks for the increase in the variance, as measured by the average squared deviation, of a subset of data as the length of that subset is increased. For strange attractor data the variance saturates once the length of the subset exceeds the characteristic first return time. In contrast, the variance of colored random noise continues to increase with increasing subset length indefinitely, with a scaling law that is related to the apparent correlation dimension. Application of the method to the Bargatze data set shows that the AL index behaves like a deterministic dynamical system.
10 citations
18 Jun 2001
TL;DR: In this article, self-consistent particle-in-cell simulations of electron injection into a plasma wake field by colliding laser pulses are presented, which can be used to study electron injection as it varies with amplitude, wavelength and phases of the pulses.
Abstract: First time, self-consistent particle-in-cell simulations of electron injection into a plasma wake field by colliding laser pulses are presented. This method for injecting electrons in a laser wake field has been proposed recently by Esarey et al. (1997). An intense pump pulse generates a fast wake field. Forward going and backward going injection pulses collide at some distance behind the pump pulse generating a slow ponderomotive beat wave which can be used to inject plasma electrons into the fast wake field for acceleration to high energies. We have modified XOOPIC to run numerical simulations of the colliding pulses scheme. We have analyzed the influence of plasma and pulse parameters, so that we are able to study electron injection as it varies with amplitude, wavelength, and phases of the pulses. We will present preliminary results.
1 citations
18 Jun 2001
TL;DR: In this paper, a microwave bath was introduced to transfer energy from the poorly cooled parallel degree of freedom to the well cooled (by synchrotron radiation) perpendicular degree of free energy.
Abstract: Crystallization of beams and non neutral plasmas is a fundamental process. A factor limiting the cooling of beams and non neutral plasmas is the energy exchange between the different degrees of freedom. To understand this problem, we study the crystallization of a strongly magnetized, non neutral plasma, where the exchange between perpendicular and parallel energy is small (in the limit of gyroradius small compared to Debye length). We introduce a microwave bath to transfer energy from the poorly cooled parallel degree of freedom to the well cooled (by synchrotron radiation) perpendicular degree of freedom. Results for the cooling of the parallel degree of freedom will be presented.
01 Oct 2001
TL;DR: In this paper, a microwave bath was introduced to transfer energy from the poorly cooled parallel degree of freedom to the well cooled (by synchrotron radiation) perpendicular degree of free energy.
Abstract: Crystallization of beams and non neutral plasmas is a fundamental process. A factor limiting the cooling of beams and non neutral plasmas is the energy exchange between the different degrees of freedom. To understand this problem, we study the crystallization of a strongly magnetized, non neutral plasma, where the exchange between perpendicular and parallel energy is small (in the limit of gyroradius small compared to Debye length). We introduce a microwave bath to transfer energy from the poorly cooled parallel degree of freedom to the well cooled (by synchrotron radiation) perpendicular degree of freedom. Results for the cooling of the parallel degree of freedom will be presented.
17 Jun 2001
TL;DR: In this paper, the authors report on 2D PIC studies using the XOOPIC code and compare the results with theory and 1D simulations, and make comparisons with the results of 1D theory and fluid simulations.
Abstract: Summary form only given. It has been suggested that colliding a short laser pulse with a long laser pulse in a plasma can, under appropriate circumstances, greatly amplify the short pulse by drawing energy from the long pulse. The coupling between laser pulses occurs through a three-wave interaction with a resonant plasma wave, and is sensitive to the shape of the laser pulse. Previous studies of this concept have been based primarily on 1D theory and fluid simulations. Here, we report on 2D PIC studies using the XOOPIC code. Energy transfer between pulses is studied for a range of system parameters and comparisons are made with theory and 1D simulations.