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Studies of Global Stability of Fluid-reversed Configuration Plasmas using a Rigid Body Model

Description: Global stability of field-reversed configuration (FRC) plasmas has been studied using a simple rigid body model in the parameter space ofs (ratio of separatrix radius to average ion gyroradius) and plasma elongation E (ratio of separatrix length to separatrix diameter). Tilt stability is predicted, independent of s, for FRC`s with low E(oblate), while the tilt stability of FRC`s with large E (prolate)depends on s/E. It is found that plasma rotation due to ion diamagnetic drift can stabilize the… more
Date: April 1998
Creator: Ji, H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Conservation of magnetic helicity during plasma relaxation

Description: Decay of the total magnetic helicity during the sawtooth relaxation in the MST Reversed-Field Pinch is much larger than the MHD prediction. However, the helicity decay (3--4%) is smaller than the magnetic energy decay (7--9%), modestly supportive of the helicity conservation hypothesis in Taylor`s relaxation theory. Enhanced fluctuation-induced helicity transport during the relaxation is observed.
Date: July 1, 1994
Creator: Ji, H.; Prager, S. C. & Sarff, J. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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An Analytic Study of the Perpendicularly Propagating Electromagnetic Drift Instabilities in the Magnetic Reconnection Experiment

Description: A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients and modest collisions as in the Magnetic Reconnection Experiment (MRX) [10]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of… more
Date: December 3, 2008
Creator: Wang, Y.; Kulsrud, R. & Ji, H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Time-resolved observation of discrete and continuous MHD dynamo in the reversed-field pinch edge

Description: We report the first experimental verification of the MHD dynamo in the RFP. A burst of magnetohydrodynamic (MHD) dynamo electric field is observed during the sawtooth crash, followed by an increase in the local parallel current in the MST RFP edge. By measuring each term, the parallel MHD mean-field Ohm`s law is observed to hold within experimental error bars both between and during sawtooth crashes.
Date: January 6, 1994
Creator: Ji, H.; Almagri, A. F.; Prager, S. C. & Sarff, J. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Nonlinear and Non-ideal Effects on FRC Stability

Description: New computational results are presented which advance the understanding of the stability properties of the Field-Reversed Configuration (FRC). We present results of hybrid and two-fluid (Hall-MHD) simulations of prolate FRCs in strongly kinetic and small-gyroradius, MHD-like regimes. The n = 1 tilt instability mechanism and stabilizing factors are investigated in detail including nonlinear and resonant particle effects, particle losses along the open field lines, and Hall stabilization. It is s… more
Date: October 21, 2002
Creator: Belova, E. V.; Davidson, R. C.; Ji, H. & Yamada, M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Kinetic Stability of the Field Reversed Configuration

Description: New computational results are presented which advance the understanding of the stability properties of the Field-Reversed Configuration (FRC). The FRC is an innovative confinement approach that offers a unique fusion reactor potential because of its compact and simple geometry, translation properties, and high plasma beta. One of the most important issues is FRC stability with respect to low-n (toroidal mode number) MHD modes. There is a clear discrepancy between the predictions of standard MHD… more
Date: July 9, 2002
Creator: Belova, E. V.; Davidson, R. C.; Ji, H. & Yamada, M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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A Liquid Metal Flume for Free Surface Magnetohydrodynamic Experiments

Description: We present an experiment designed to study magnetohydrodynamic effects in free-surface channel flow. The wide aspect ratio channel (the width to height ratio is about 15) is completely enclosed in an inert atmosphere to prevent oxidization of the liquid metal. A custom-designed pump reduces entrainment of oxygen, which was found to be a problem with standard centrifugal and gear pumps. Laser Doppler Velocimetry experiments characterize velocity profiles of the flow. Various flow constraints mit… more
Date: August 27, 2008
Creator: Nornberg, M. D.; Ji, H.; Peterson, J. L. & Rhoads, J. R.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Fluctuation and transport reduction in a reversed field pinch by inductive poloidal current drive

Description: An auxilliay poloidal inductive electric field applied to a reversed field pinch plasma reduces the current density gradient, slows the growth of m=1 tearing fluctations, suppresses their associated sawteeth, and doubles the energy confinement time. Small sawteeth occur in the improved state but with m=0 precursors. By requiring a change of toroidal flux embedding the plasma, inductive poloidal current profile drive is transient, but the improvement encourages the program of RFP transport suppr… more
Date: December 1, 1993
Creator: Sarff, J. S.; Hokin, S. A.; Ji, H.; Prager, S. C. & Sovinec, C. R.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Measurement of the Transverse Spitzer Resistivity during Collisional Magnetic Reconnection

Description: Measurement of the transverse resistivity was carried out in a reconnecting current sheet where the mean free path for the Coulomb collision is smaller than the thickness of the sheet. In a collisional neutral sheet without a guide field, the transverse resistivity is directly related to the reconnection rate. A remarkable agreement is found between the measured resistivity and the classical value derived by L. Spitzer. In his calculation the transverse resistivity for the electrons is higher t… more
Date: September 18, 2000
Creator: Trintchouk, F.; Yamada, M.; Ji, H.; Kulsrud, R.M. & Carter, T.A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Free MHD Shear Layers In The Presence Of Rotation And Magnetic Field

Description: We present an experimental and numerical study of hydrodynamic and magnetohydrodynamic free shear layers and their stability. We first examine the experimental measurement of globally unstable hydrodynamic shear layers in the presence of rotation, and their range of instability. These are compared to numerical simulations, which are used to explain the modification of the shear layer and thus the critical Rossby number for stability. Magnetic fields are then applied to these scenarios, and glob… more
Date: March 20, 2012
Creator: Spence, E. J.; Roach, A. H.; Edlund, E. M.; Sloboda, P. & Ji, H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Magnetic Reconnection with Sweet-Parker Characteristics in Two-dimensional Laboratory Plasmas

Description: Magnetic reconnection has been experimentally studied in a well-controlled, two-dimensional laboratory magnetohydrodynamic plasma. The observations are found to be both qualitatively and quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the collisionless limit. This generalized Sweet-Parker model also applies to the case in which… more
Date: January 1, 1999
Creator: Carter, T.; Hsu, S.; Ji, H.; Kulsrud, R.; Yamada, M. & al, et
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Measurement of Lower-hybrid Drift Turbulence in a Reconnecting Current Sheet

Description: We present a detailed study of fluctuations in a laboratory current sheet undergoing magnetic reconnection. The measurements reveal the presence of lower-hybrid-frequency range fluctuations on the edge of current sheets produced in the Magnetic Reconnection Experiment (MRX). The measured fluctuation characteristics are consistent with theoretical predictions for the lower-hybrid drift instability (LHDI). Our observations suggest that the LHDI does not provide any significant turbulent resistivi… more
Date: June 20, 2001
Creator: Carter, T.A.; Ji, H.; Trintchouk, F.; Yamada, M. & Kulsrud, R.M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Numerical Study of Global Stability of Oblate Field-Reversed Configurations

Description: Global stability of the oblate (small elongation, E < 1) Field-Reversed Configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic (MHD) and hybrid (fluid electrons and kinetic ions) simulations. For every non-zero value of the toroidal mode number n, there are three MHD modes that must be stabilized. For n = 1, these are the interchange, the tilt and the radial shift; while for n > 1 these are the interchange and two co-interchange modes with d… more
Date: October 27, 2000
Creator: Belova, E. V.; Jardin, S. C.; Ji, H.; Yamada, M. & Kulsrud, R.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Measurement of the Dynamo Effect in a Plasma

Description: A series of the detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line (the {alpha} effect) arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E x B drift and electron diamagnetic drift. The three major findings are (1) the {alpha} effect accounts for the dynamo current generation, even i… more
Date: November 1, 1995
Creator: Ji, H.; Prager, S. C.; Almagri, A. F.; Sarff, J. S.; Hirano, Y. & Toyama, H.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Experimental Investigation of the Neutral sheet Profile During Magnetic Reconnection

Description: During magnetic reconnection, a ''neutral sheet'' current is induced, heating the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic fields. The reconnection layer profile holds significant clues about the physical mechanisms which control reconnection. On the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet profile has been measured precisely using a magnet… more
Date: November 1, 1999
Creator: Trintchouk, F.; Ji, H.; Yamada, M.; Kulsrud, R.; Hsu, S. & Carter, T.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Experimental Verification of the Kruskal-Shafranov Stability Limit in Line-Tied Partial Toroidal Plasmas

Description: The stability properties of partial toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas, 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is me… more
Date: July 19, 2011
Creator: Oz, E.; Myers, C. E.; Yamada, M.; Ji, H.; Kulsrud, R. M. & Xie, J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Particle transport due to magnetic fluctuations

Description: Electron current fluctuations are measured with an electrostatic energy analyzer at the edge of the MST reversed-field pinch plasma. The radial flux of fast electrons (E>T{sub e}) due to parallel streaming along a fluctuating magnetic field is determined locally by measuring the correlated product <{tilde J}{sub e}{tilde B}{sub r}>. Particle transport is small just inside the last closed flux surface ({Gamma}{sub e,mag} < 0.1 {Gamma}{sub e,total}), but can account for all observed particle loss… more
Date: January 1, 1994
Creator: Stoneking, M. R.; Hokin, S. A.; Prager, S. C.; Fiksel, G.; Ji, H. & Den Hartog, D. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Quantitative Study Of Guide Field Effects on Hall Reconnection In A Laboratory Plasma

Description: The effect of guide field on magnetic reconnection is quantitatively studied by systematically varying an applied guide field in the Magnetic Reconnection Experiment (MRX). The quadrupole field, a signature of two-fluid reconnection at zero guide field, is significantly altered by a finite guide field. It is shown that the reconnection rate is significantly reduced with increasing guide field, and this dependence is explained by a combination of local and global physics: locally, the in-plane H… more
Date: April 17, 2012
Creator: Tharp, T. D.; Yamada, M.; Ji, H.; Lawrence, E.; Dorfman, S. & Myers, C.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Center for Momentum Transport and Flow Organization (CMTFO). Final technical report

Description: The Center for Momentum Transport and Flow Organization (CMTFO) is a DOE Plasma Science Center formed in late 2009 to focus on the general principles underlying momentum transport in magnetic fusion and astrophysical systems. It is composed of funded researchers from UCSD, UW Madison, U. Colorado, PPPL. As of 2011, UCSD supported postdocs are collaborating at MIT/Columbia and UC Santa Cruz and beginning in 2012, will also be based at PPPL. In the initial startup period, the Center supported the… more
Date: July 29, 2013
Creator: Tynan, George R.; Diamond, P. H.; Ji, H.; Forest, C. B.; Terry, P. W.; Munsat, T. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Experimental Study of Ion Heating and Acceleration During Magnetic Reconnection

Description: Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma out flow is sub-Alfvonic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that the … more
Date: October 24, 2000
Creator: Hsu, S.C.; Carter, T.A.; Fiksel, G.; Ji, H.; Kulsrud, R.M. & Yamada, M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Global Stability of the Field Reversed Configuration

Description: New computational results are presented which provide a theoretical basis for the stability of the Field Reversed Configuration (FRC). The FRC is a compact toroid with negligible toroidal field in which the plasma is confined by a poloidal magnetic field associated with toroidal diamagnetic current. Although many MHD modes are predicted to be unstable, FRCs have been produced successfully by several formation techniques and show surprising macroscopic resilience. In order to understand this dis… more
Date: November 15, 2000
Creator: Belova, E. V.; Jardin, S. C.; Ji, H.; Kulsrud, R. M.; Park, W. & Yamada, M.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Local Measurement of Non-Classical Ion Heating During Magnetic Reconnection

Description: Local ion temperature is measured directly in the well-characterized reconnection layer of a laboratory plasma. These measurements demonstrate definitively that ions are heated due to reconnection and that more than half of the reconnected field energy is converted to ion kinetic energy. Neither classical Ohmic dissipation nor thermalization of energetic flows is sufficient to account for the energy converted, suggesting the importance of non-classical dissipation mechanisms such as wave-partic… more
Date: November 1, 1999
Creator: Fiskel, G.; Ji, H.; Yamada, M.; Kulsrud, R.M.; Hsu, S.C. & Carter, T.A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Numerical Study of the Formation, Ion Spin-up and Nonlinear Stability Properties of Field-reversed Configurations

Description: Results of three-dimensional numerical simulations of field-reversed configurations (FRCs) are presented. Emphasis of this work is on the nonlinear evolution of magnetohydrodynamic (MHD) instabilities in kinetic FRCs and the new FRC formation method by the counter-helicity spheromak merging. Kinetic simulations show nonlinear saturation of the n = 1 tilt mode, where n is the toroidal mode number. The n = 2 and n = 3 rotational modes are observed to grow during the nonlinear phase of the tilt in… more
Date: November 12, 2004
Creator: Belova, E. V.; Davidson, R. C.; Ji, H.; Yamada, M.; Cothran, C. D.; Brown, M. R. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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