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Long Pulse High Performance Plasma Scenario Development for the National Spherical Torus Experiment

Description: The National Spherical Torus Experiment [Ono et al., Nucl. Fusion, 44, 452 (2004)] is targeting long pulse high performance, noninductive sustained operations at low aspect ratio, and the demonstration of nonsolenoidal startup and current rampup. The modeling of these plasmas provides a framework for experimental planning and identifies the tools to access these regimes. Simulations based on neutral beam injection (NBI)-heated plasmas are made to understand the impact of various modifications and identify the requirements for (1) high elongation and triangularity, (2) density control to optimize the current drive, (3) plasma rotation and/or feedback stabilization to operate above the no-wall limit, and (4) electron Bernstein waves (EBW) for off-axis heating/current drive (H/CD). Integrated scenarios are constructed to provide the transport evolution and H/CD source modeling, supported by rf and stability analyses. Important factors include the energy confinement, Zeff, early heating/H mode, broadening of the NBI-driven current profile, and maintaining q(0) and qmin>1.0. Simulations show that noninductive sustained plasmas can be reached at IP=800 kA, BT=0.5 T, 2.5, N5, 15%, fNI=92%, and q(0)>1.0 with NBI H/CD, density control, and similar global energy confinement to experiments. The noninductive sustained high plasmas can be reached at IP=1.0 MA, BT=0.35 T, 2.5, N9, 43%, fNI=100%, and q(0)>1.5 with NBI H/CD and 3.0 MW of EBW H/CD, density control, and 25% higher global energy confinement than experiments. A scenario for nonsolenoidal plasma current rampup is developed using high harmonic fast wave H/CD in the early low IP and low Te phase, followed by NBI H/CD to continue the current ramp, reaching a maximum of 480 kA after 3.4 s.
Date: January 1, 2006
Creator: Kessel, C.E.; Bell, R.E.; Bell, M.G.; Gates, D.A. & Harvey, R.W.
Partner: UNT Libraries Government Documents Department
open access

Gyrokinetic Simulation of Global Turbulent Transport Properties in Tokamak Experiments

Description: A general geometry gyro-kinetic model for particle simulation of plasma turbulence in tokamak experiments is described. It incorporates the comprehensive influence of noncircular cross section, realistic plasma profiles, plasma rotation, neoclassical (equilibrium) electric fields, and Coulomb collisions. An interesting result of global turbulence development in a shaped tokamak plasma is presented with regard to nonlinear turbulence spreading into the linearly stable region. The mutual interaction between turbulence and zonal flows in collisionless plasmas is studied with a focus on identifying possible nonlinear saturation mechanisms for zonal flows. A bursting temporal behavior with a period longer than the geodesic acoustic oscillation period is observed even in a collisionless system. Our simulation results suggest that the zonal flows can drive turbulence. However, this process is too weak to be an effective zonal flow saturation mechanism.
Date: January 1, 2006
Creator: Wang, W. X.; Lin, Z.; Tang, W. M.; Lee, W. W.; Ethier, S.; Lewandowski, J. L. V. et al.
Partner: UNT Libraries Government Documents Department
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Double Gap Alfvén Eigenmodes: Revisiting Eigenmodes Interaction with the Alfvén Continuum

Description: A new type of global shear Alfvén Eigenmode is found in tokamak plasmas where the mode localization is in the region intersecting the Alfvén continuum. The eigenmode is formed by the coupling of two solutions from two adjacent gaps (akin to potential wells) in the shear Alfvén continuum. For tokamak plasmas with reversed magnetic shear it is shown that the toroidiciy-induced solution tunnels through the continuum to match the ellipticity-induced Alfvén eigenmode (TAE and EAE, respectively) so that the resulting solution is continuous at the point of resonance with the continuum. The existence of these Double Gap Alfvén Eigenmodes (DGAEs) allows for potentially new ways of coupling edge fields to the plasma core in conditions where the core region is conventionally considered inaccessible. Implications include new approaches to heating and current drive in fusion plasmas as well as its possible use as core diagnostic in burning plasmas.
Date: December 1, 2005
Creator: Gorelenkov, N. N.
Partner: UNT Libraries Government Documents Department
open access

Final Report for Grant No. DE-FG02-03ER54706 "Support for the 7th Workshop on The Interrelationship between Plasma Experiment in Laboratory and Space"

Description: We describe the support given to support the 7th IPELS meeting which brings together space and laboratory based physicists. The meeting was a great success with more than 80 attendees and a significant number of young scientists. The major topics of discussion were magnetic reconnection, plasma turbulence, and waves in plasmas.
Date: September 13, 2005
Creator: Kletzing, C.
Partner: UNT Libraries Government Documents Department
open access

Mode-conversion induced tearing effects in a plasma neutral sheet

Description: A new collisionless dissipation mechanism which can drive tearing modes in a plasma neutral sheet is described. The new mechanism relies on the presence of a background cold plasma which leads to mode conversion into a continuous spectrum of cold plasma waves.
Date: January 1, 1981
Creator: Kaw, P.K. & Sudan, R.N.
Partner: UNT Libraries Government Documents Department
open access

Final Report of MBX experiment

Description: The MBX experiment was built during the grant period. Details can be found in publications about MBX experiment. We created a low density plasma in a mirror configuration and rotated it at supersonic speeds in the theta direction. Under these conditions the plasma presents a high asymmetry in the current, plasma potential and consequently rotation with the voltage applied. We developed a two fluid model to describe the measurements based on a magnetofluid states ansatz. We also observed bistable and multiple states predicted by the two fluid model.
Date: April 2, 2007
Creator: Bengtson, Roger D & Valanju, Prashant
Partner: UNT Libraries Government Documents Department
open access

Measurements of Secondary Electron Emission Effects in the Hall Thruster Discharge

Description: The dependence of the maximum electron temperature on the discharge voltage is studied for two Hall thruster configurations, in which a collisionless plasma is bounded by channel walls made of materials with different secondary electron emission (SEE) properties. The linear growth of the temperature with the discharge voltage, observed in the channel with a low SEE yield, suggests that SEE is responsible for the electron temperature saturation in the thruster configuration with the channel walls having a higher SEE yield. The fact that the values of the electron temperature at saturation are rather high may indirectly support the recently predicted kinetic regime of the space charge saturation of the near-wall sheath in the thruster discharge. A correlation between the effects of the channel wall material on the electron temperature and the electron cross-field current was also observed.
Date: December 1, 2005
Creator: Raitses, Y.; Smirnov, A.; Staack, D. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department
open access

Final Report - Investigation of Intermittent Turbulence and Turbulent Structures in the Presence of Controlled Sheared Flows

Description: Final Report for grant DE-FG02-06ER54898. The dynamics and generation of intermittent plasma turbulent structures, widely known as "blobs" have been studied in the presence of sheared plasma flows in a controlled laboratory experiment.
Date: June 27, 2013
Creator: Gilmore, Mark A.
Partner: UNT Libraries Government Documents Department
open access

Studies of Flows in Plasmas

Description: Note a pdf document "DOE-flow-final-report' should be attached. If it somehow is not please notify Walter Gekelman (gekelman@physics.ucla.edu) who will e mail it directly
Date: March 7, 2009
Creator: Gekelman, Walter; Morales, George & Maggs, James
Partner: UNT Libraries Government Documents Department
open access

Self-organized T(sub)e Redistribution during Driven Reconnection Processes in High Temperature Plasmas

Description: Two-dimensional (2-D) images of electron temperature fluctuations with a high temporal and spatial resolution were employed to study the sawtooth oscillation in TEXTOR tokamak plasmas. The new findings are: 1) 2-D images revealed that the reconnection is localized and permitted the determination of the physical dimensions of the reconnection zone in the poloidal and toroidal planes. 2) The combination of a pressure driven mode and a kink instability leads to an "X-point" reconnection process. 3) Reconnection can take place anywhere along the q~1 rational magnetic surface (both high and low field sides). 4) Heat flow from the core to the outside of the inversion radius during the reconnection time is highly asymmetric and the behavior is collective. These new findings are compared with the characteristics of various theoretical models and experimental results for the study of the sawtooth oscillation in tokamak plasmas.
Date: December 1, 2005
Creator: Park, H. K.; Mazzucato, E.; Luhmann, N. C. Jr.; Domier, C. W.; Xia, Z.; Munsat, T. et al.
Partner: UNT Libraries Government Documents Department
open access

Theory and numerical simulations on collisionless drift instabilities in three dimensions

Description: Nonlinear behavior of the collisionless drift instabilities and the resultant anomalous plasma diffusion have been studied by means of computer simulations and analytic theory. The simulation model used is a full three dimensional electrostatic model in a cylindrical geometry in an external magnetic field. Full dynamics is employed for the ion motion while the guiding center approximations are used for the motion of electrons which allows us to use rather realistic plasma parameters in the simulations. The results of simulations indicate that a strong turbulence develops through the nonlinear interaction of the drift instabilities which results in the formation of convective cells and anomalous particle diffusion. The broad frequency spectrum resembles to those observed recently in toroidal confinement devices. Analytic theory is developed based on the mode-coupling process to explain the generation of convective cells and strong plasma turbulence along with the estimate of the resultant particle diffusion.
Date: November 1, 1977
Creator: Cheng, C. Z. & Okuda, H.
Partner: UNT Libraries Government Documents Department
open access

Dust-Plasma Interactions

Description: The objective of our theoretical research under this grant over the past 3 years was to develop new understanding in a range of topics in the physics of dust-plasma interactions, with application to space and the laboratory. We conducted studies related to the physical properties of dust, waves and instabilities in both weakly coupled and strongly coupled dusty plasmas, and innovative possible applications. A major consideration in our choice of topics was to compare theory with experiments or observations, and to motivate new experiments, which we believe is important for developing this relatively new field. Our research is summarized, with reference to our list of journal publications.
Date: January 5, 2010
Creator: Rosenberg, M.
Partner: UNT Libraries Government Documents Department
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The Absence of Plasma in"Spark Plasma Sintering"

Description: Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (<100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions.
Date: April 10, 2008
Creator: Hulbert, Dustin M.; Anders, Andre; Dudina, Dina V.; Andersson, Joakim; Jiang, Dongtao; Unuvar, Cosan et al.
Partner: UNT Libraries Government Documents Department
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Modelling multi-ion plasma gun simulations of Tokamak disruptions

Description: The effect of impurity ions in plasma gun ablation tests of various targets is considered. Inclusion of reasonable amounts of impurity ({approximately}10%) is adequate to explain observed energy transmission and erosion measurements. The gun tests and the computer code calculations are relevant to the parameter range expected for major disruptions on large tokamaks.
Date: August 1, 1995
Creator: Ehst, D.A.
Partner: UNT Libraries Government Documents Department
open access

Final technical report on studies of plasma transport

Description: This document gives an overview of the scientific results obtained under the DOE grant, and references the journal articles which give more complete descriptions of the various topics. Recently, the research has been focused on 2-dimensional vortices and turbulence: experiments using a new camera-diagnosed electron plasma apparatus have given surprising results which both clarify and challenge theories. Here, the crossfield E x B flow of the electron plasma is directly analogous to the 2-d flow of an ideal fluid such as water, and may also give insight into more complicated poloidal flows exhibited in toroidal plasmas. The shear-flow instabilities, turbulence, and vortices can be accurately observed, and the free relaxation of this turbulence has been characterized. The physical processes underlying the complicated turbulent evolution can also be studied in more controlled near-linear regimes. The original experimental focus of this program was on radial particle transport from applied external field asymmetries. Here, this research program clearly identified the importance of the collective response of the plasma, giving smaller fields from shielding, or enhanced fields from resonant modes. Experiments and theory work have also elucidated the flow of a plasma along the magnetic field. Finally, some theory was pursued for direct application to fusion plasmas, and to gravitating gas clouds in astrophysics. This program was highly successful in clarifying basic plasma transport processes.
Date: April 1, 1997
Creator: O`Neil, T.M.; Driscoll, C.F. & Malmberg, J.H.
Partner: UNT Libraries Government Documents Department
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Tapered plasma channels to phase-lock accelerating and focusing forces in laser-plasma accelerators

Description: Tapered plasma channels are considered for controlling dephasing of a beam with respect to a plasma wave driven by a weakly-relativistic, short-pulse laser. Tapering allows for enhanced energy gain in a single laser plasma accelerator stage. Expressions are derived for the taper, or longitudinal plasma density variation, required to maintain a beam at a constant phase in the longitudinal and/or transverse fields of the plasma wave. In a plasma channel, the phase velocities of the longitudinal and transverse fields differ, and, hence, the required tapering differs. The length over which the tapered plasma density becomes singular is calculated. Linear plasma tapering as well as discontinuous plasma tapering, which moves beams to adjacent plasma wave buckets, are also considered. The energy gain of an accelerated electron in a tapered laser-plasma accelerator is calculated and the laser pulse length to optimize the energy gain is determined.
Date: May 17, 2010
Creator: Rittershofer, W.; Schroeder, C. B.; Esarey, E.; Gruner, F. J. & Leemans, W. P.
Partner: UNT Libraries Government Documents Department
open access

Gyrokinetic Theory for Arbitrary Wavelength Electromagnetic Modes in Tokamaks

Description: A linear gyrokinetic system for arbitrary wavelength electromagnetic modes is developed. A wide range of modes in inhomogeneous plasmas, such as the internal kink modes, the toroidal Alfvén eigenmode (TAE) modes, and the drift modes, can be recovered from this system. The inclusion of most of the interesting physical factors into a single framework enables us to look at many familiar modes simultaneously and thus to study the modifications of and the interactions between them in a systematic way. Especially, we are able to investigate self-consistently the kinetic MHD phenomena entirely from the kinetic side. Phase space Lagrangian Lie perturbation methods and a newly developed computer algebra package for vector analysis in general coordinate system are utilized in the analytical derivation. In tokamak geometries, a 2D finite element code has been developed and tested. In this paper, we present the basic theoretical formalism and some of the preliminary results.
Date: October 1, 1997
Creator: Qin, H.; Rewoldt, G. & Tang, W.M.
Partner: UNT Libraries Government Documents Department
open access

High beta tokamaks. [MHD equilibrium, stability, and transport calculations]

Description: MHD equilibrium, stability, and transport calculations are made to study the accessibility and behavior of ''high beta'' tokamak plasmas in the range ..beta.. approximately 5 to 15 percent. For next generation devices, beta values of at least 8 percent appear to be accessible and stable if there is a conducting surface nearby.
Date: January 1, 1978
Creator: Dory, R. A.; Berger, D. P.; Charlton, L. A.; Hogan, J. T.; Munro, J. K.; Nelson, D. B. et al.
Partner: UNT Libraries Government Documents Department
open access

Experimental Investigation of Active Feedback Control of Turbulent Transport in a Magnetized Plasma

Description: A new and unique basic plasma science laboratory device - the HelCat device (HELicon-CAThode) - has been constructed and is operating at the University of New Mexico. HelCat is a 4 m long, 0.5 m diameter device, with magnetic field up to 2.2 kG, that has two independent plasmas sources - an RF helicon source, and a thermionic cathode. These two sources, which can operate independently or simultaneously, are capable of producing plasmas with a wide range of parameters and turbulence characteristics, well suited to a variety of basic plasma physics experiments. An extensive set of plasma diagnostics is also operating. Experiments investigating the active feedback control of turbulent transport of particles and heat via electrode biasing to affect plasma ExB flows are underway, and ongoing.
Date: July 7, 2013
Creator: Gilmore, Mark Allen
Partner: UNT Libraries Government Documents Department
open access

Stability and magnetic tearing of finite-. beta. modified drift waves

Description: A new simplified approach to the analysis of radial eigenmodes of finite-..beta.. modified drift waves in a sheared magnetic field is described. Applying this approach to the universal drift mode, one recovers, for the lowest (n = 0) radial eigenmode, the previous result that finite-..beta.. effects are stabilizing. For the next (n = 1) radial eigenmode, however, one finds that finite-..beta.. effects further destabilize the mode. Moreover, the corresponding mode structure exhibits nonzero radial (tearing) magnetic perturbations around the mode-rational surface. The consequences of a structure of microscopic magnetic islands, created in this way, for plasma transport are also briefly discussed.
Date: October 1, 1977
Creator: Chen, L.; Hsu, J.; Kaw, P. K. & Rutherford, P. H.
Partner: UNT Libraries Government Documents Department
open access

Unstable universal drift eigenmodes in toroidal plasmas

Description: The eigenmode equation describing ballooning collisionless drift instabilities is analyzed both analytically and numerically. A new branch of eigenmodes, which corresponds to quasi-bound states due to the finite toroidicity, is shown to be destabilized by electron Landau damping for typical Tokamak parameters. This branch cannot be understood by the strong coupling approximation. However, the slab-like (Pearlstein-Berk type) branch is found to remain stable and experience enhanced shear damping due to finite toroidicity.
Date: August 1, 1979
Creator: Cheng, C. Z. & Chen, L.
Partner: UNT Libraries Government Documents Department
open access

Studies of impurity mode and ITG mode in toroidal plasmas

Description: The impurity mode and {eta}{sub i} mode driven by impurity ions with outwardly peaked density profiles, just as it is at the boundary of tokamak plasmas, and the ion temperature gradient, respectively, are studied in high temperature toroidal plasmas. The gyrokinetic theory is applied and finite Larmor radius effects of both hydrogenic and impurity ions are included. It is found that the impurity mode is enhanced by the ion temperature gradient. In addition, the impurity ions with outwardly peaked density profiles are demonstrated to have destabilizing effects on the {eta}{sub i} mode. These two modes are strongly coupled to each other so that it is impossible to distinguish between them when both the driving mechanisms axe strong enough to drive the corresponding mode unstable independently. The correlation of the results with nonlinear simulations and the experimental observations are discussed.
Date: April 1, 1995
Creator: Dong, J.Q. & Horton, W.
Partner: UNT Libraries Government Documents Department
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