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Kinetic Ballooning Instability for Substorm Onset and Current Disruption Observed by AMPTE/CCE

Description: A new scenario of AMPTE/CCE observation of substorm onset and current disruption and the corresponding physical processes is presented. Toward the end of late growth phase plasma beta increases to greater than or equal to 50 and a low-frequency instability with a wave period of 50-75 seconds is excited and grows exponentially to a large amplitude at the onset of current disruption. At the current disruption onset, higher-frequency instabilities are excited so that the plasma and electromagnetic magnetic field form a turbulent state. Plasma transport takes place to modify the ambient plasma pressure and velocity profiles so that the ambient magnetic field recovers from a tail-like geometry to a more dipole-like geometry. To understand the excitation of the low-frequency global instability, a new theory of kinetic ballooning instability (KBI) is proposed to explain the high critical beta threshold (the high critical beta threshold is greater than or equal to 50) of the low-frequency global instability observed by the AMPTE/CCE. The stabilization is mainly due to kinetic effects of trapped electrons and finite ion Larmor radii which give rise to a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension to the ballooning mode. As a result, the high critical beta threshold for excitation of KBI is greatly increased over the ideal-MHD ballooning instability threshold by greater than or equal to O(10 exp 2). The wave-ion magnetic drift resonance effect produces a perturbed resonant ion velocity distribution with a duskward velocity roughly equal to the average ion magnetic (gradient B and curvature) drift velocity. Higher-frequency instabilities such as cross-field current instability (CCI) can be excited by the additional velocity space free energy associated with the positive slope in the perturbed resonant ion velocity distribution in the current disruption phase.
Date: May 1, 1998
Creator: Cheng, C.Z. & Lui, A.T.Y., PPPL
Partner: UNT Libraries Government Documents Department

Physical Processes of Substorm Onset and Current Disruption Observed by AMPTE/CCE

Description: A new scenario of AMPTE/CCE observation of substorm onset and current disruption and the corresponding physical processes is presented. Toward the end of the late growth phase, plasma beta increases to greater than or equal to 50 and a low-frequency instability with a wave period of 50-75 seconds is excited and grows exponentially to a large amplitude at the onset of current disruption. At the current disruption onset, higher-frequency instabilities are excited so that the plasma and electromagnetic field form a turbulent state. Plasma transport and heating take place to reduce plasma beta and modify the ambient plasma pressure and velocity profiles so that the ambient magnetic field recovers from a tail-like geometry to a more dipole- like geometry. To understand the excitation of the low-frequency global instability, a new theory of kinetic ballooning instability (KBI) is proposed to explain the high critical beta threshold (greater than or equal to 50) of the low-frequency global instability observed by the AMPTE/CCE. The stabilization kinetic effects of trapped electron and finite ion Larmor radii give rise to a large parallel electric field and hence a parallel current that greatly enhances the stabilizing effect of field line tension to the ballooning mode. As a result, the high critical beta threshold for excitation of KBI is greatly increased over the ideal MHD ballooning instability threshold by greater than O(10 squared). The wave-ion magnetic drift resonance effect typically reduces the high critical beta threshold by up to 20% and produces a perturbed resonant ion velocity distribution with a duskward velocity roughly equal to the average ion magnetic drift velocity as the KBI grows to a large amplitude. Higher-frequency instabilities, such as the cross-field current instability (CCI), can be excited by the additional velocity space free energy associated with the positive slope in the perturbed resonant ...
Date: March 1998
Creator: Cheng, C. Z. & Lui, A. T. Y.
Partner: UNT Libraries Government Documents Department

Stabilization of ballooning modes with sheared toroidal rotation

Description: A new code demonstrates the stabilization of MHD ballooning modes by sheared toroidal rotation. A shifted-circle model is used to elucidate the physics and numerically reconstructed equilibria are used to analyze DIII-D discharges. In the ballooning representation, the modes shift periodically along the field line to the next point of unfavorable curvature. The shift frequency (d{Omega}/dq where {Omega} is the angular toroidal velocity and q is the safety factor) is proportional to the rotation shear and inversely proportional to the magnetic shear. Stability improves with increasing shift frequency and, in the shifted circle model, direct stable access to the second stability regime occurs when this frequency is a fraction of the Alfven frequency {omega}{sub A} = V{sub A}/qR. Shear stabilization is also demonstrated for an equilibrium reconstruction of a DIII-D VH-mode.
Date: November 1, 1994
Creator: Miller, R.L.; Waelbroeck, F.W.; Lao, L.L. & Taylor, T.S.
Partner: UNT Libraries Government Documents Department

Alpha-driven magnetohydrodynamics (MHD) and MHD-induced alpha loss in the Tokamak Fusion Test Reactor

Description: Alpha-driven toroidal Alfven eigenmodes (TAEs) are observed as predicted by theory in the post neutral beam phase in high central q (safety factor) deuterium-tritium (D-T) plasmas in the Tokamak Fusion Test Reactor (TFTR). The mode location, poloidal structure and the importance of q profile for TAE instability are discussed. So far no alpha particle loss due to these modes was detected due to the small mode amplitude. However, alpha loss induced by kinetic ballooning modes (KBMs) was observed in high confinement D-T discharges. Particle orbit simulation demonstrates that the wave-particle resonant interaction can explain the observed correlation between the increase in alpha loss and appearance of multiple high-n (n {ge} 6, n is the toroidal mode number) modes.
Date: February 1, 1997
Creator: Chang, Z.; Nazikian, R. & Fu, G.Y.
Partner: UNT Libraries Government Documents Department

Pseudo-MHD ballooning modes in tokamak plasmas

Description: The MHD description of a plasma is extended to allow electrons to have both fluid-like and adiabatic-regime responses within an instability eigenmode. In the resultant {open_quotes}pseudo-MHD{close_quotes} model, magnetic field line bending is reduced in the adiabatic electron regime. This makes possible a new class of ballooning-type, long parallel extent, MHD-like instabilities in tokamak plasmas for {alpha} > s{sup 2}(2 {sup 7/3}/9) (r{sub p}/R{sub 0}) or-d{radical}{Beta}/dr > (2{sup 1/6} /3)(s/ R{sub 0q}), which is well below the ideal-MHD stability boundary. The marginally stable pressure profile is similar in both magnitude and shape to that observed in ohmically heated tokamak plasmas.
Date: August 1, 1996
Creator: Callen, J.D. & Hegna, C.C.
Partner: UNT Libraries Government Documents Department

Spectrum of the ballooning Schroedinger equation

Description: The ballooning Schroedinger equation (BSE) is a model equation for investigating global modes that can, when approximated by a Wentzel-Kramers-Brillouin (WKB) ansatz, be described by a ballooning formalism locally to a field line. This second order differential equation with coefficients periodic in the independent variable {theta}{sub k} is assumed to apply even in cases where simple WKB quantization conditions break down, thus providing an alternative to semiclassical quantization. Also, it provides a test bed for developing more advanced WKB methods: e.g. the apparent discontinuity between quantization formulae for {open_quotes}trapped{close_quotes} and {open_quotes}passing{close_quotes} modes, whose ray paths have different topologies, is removed by extending the WKB method to include the phenomena of tunnelling and reflection. The BSE is applied to instabilities with shear in the real part of the local frequency, so that the dispersion relation is inherently complex. As the frequency shear is increased, it is found that trapped modes go over to passing modes, reducing the maximum growth rate by averaging over {theta}{sub k}.
Date: January 1, 1997
Creator: Dewar, R.L.
Partner: UNT Libraries Government Documents Department

Shear flow effects on resistive ballooning turbulence

Description: Resistive ballooning modes could be responsible for the turbulence and induced transport observed at the edge of present tokamaks. Due to the mode structure, the geometry of the calculation is fully toroidal. The increase in computer capabilities allows now high resolution turbulence calculations. This is very important in the case of ballooning modes since the spectrum is very flat. Two main issues are addressed in this paper: (1) The validity of the mixing length approach for toroidal modes. It is especially important to identify the characteristic spatial and temporal scales in this approach, since these scales would be determinant of the induced transport. (2) The role and characterization of the Reynolds stress in toroidal geometry. Because of the intrinsic poloidal asymmetry of the ballooning modes, flows with m {ne} 0 are generated. The effect of these flows will be analyzed.
Date: December 31, 1997
Creator: Garcia, L.; Carreras, B.A. & Lynch, V.E.
Partner: UNT Libraries Government Documents Department

Ballooning mode stability for self-consistent pressure and current profiles at the H-mode edge

Description: The edge pressure gradient (H-mode pedestal) for computed equilibria in which the current density profile is consistent with the bootstrap current may not be limited by the first regime ballooning limit. The transition to second stability is easier for: higher elongation, intermediate triangularity, larger ratio, pedestal at larger radius, narrower pedestal width, higher q{sub 95}, and lower collisionality.
Date: November 1, 1997
Creator: Miller, R.L.; Lin-Liu, Y.R.; Osborne, T.H. & Taylor, T.S.
Partner: UNT Libraries Government Documents Department

Anderson Localization of Ballooning Modes, Quantum Chaos and the Stability of Compact Quasiaxially Symmetric Stellarators

Description: The radially local magnetohydrodynamic (MHD) ballooning stability of a compact, quasiaxially symmetric stellarator (QAS), is examined just above the ballooning beta limit with a method that can lead to estimates of global stability. Here MHD stability is analyzed through the calculation and examination of the ballooning mode eigenvalue isosurfaces in the 3-space [s, alpha, theta(subscript ''k'')]; s is the edge normalized toroidal flux, alpha is the field line variable, and q(subscript ''k'') is the perpendicular wave vector or ballooning parameter. Broken symmetry, i.e., deviations from axisymmetry, in the stellarator magnetic field geometry causes localization of the ballooning mode eigenfunction, and gives rise to new types of nonsymmetric eigenvalue isosurfaces in both the stable and unstable spectrum. For eigenvalues far above the marginal point, isosurfaces are topologically spherical, indicative of strong ''quantum chaos.'' The complexity of QAS marginal isosurfaces suggests that finite Larmor radius stabilization estimates will be difficult and that fully three-dimensional, high-n MHD computations are required to predict the beta limit.
Date: October 31, 2001
Creator: Redi, M.H.; Johnson, J.L.; Klasky, S.; Canik, J.; Dewar, R.L. & Cooper, W.A.
Partner: UNT Libraries Government Documents Department

High-{beta} disruption in tokamaks

Description: Three dimensional MHD simulations of high-{beta} plasmas show that toroidally localized high-n ballooning modes can be driven unstable by the local pressure steepening which arises from the evolution of low-n modes. Nonlinearly, the high-n mode becomes even more localized and produces a strong local pressure bulge which destroys the flux surfaces resulting in a thermal quench. The flux surfaces then recover temporarily but now contain large magnetic islands. This scenario is supported by experimental data.
Date: July 1, 1995
Creator: Park, W.; Fredrickson, E.D. & Janos, A.
Partner: UNT Libraries Government Documents Department

Ballooning instability precursors to high {beta} disruptions

Description: Strongly ballooning modes have been found as precursors to high {beta} disruptions on TFTR. The modes are typically localized to a region spanning about 60{degree} in the toroidal direction. The toroidal localization is associated with lower frequency, global Magneto-Hydro-Dynamic (MHD) activity, typically an ideal n = 1 kink mode. They have moderate to high frequency (f = 10--20 f{sub rot}), implying toroidal mode numbers in the range n = 10--20. The growth rates for the modes are large, of order 10{sup 4}/sec.
Date: December 1, 1995
Creator: Fredrickson, E.D.; McGuire, K.M. & Chang, Z.Y.
Partner: UNT Libraries Government Documents Department

Effects of plasma shape and profiles on edge stability in DIII-D

Description: The results of recent experimental and theoretical studies concerning the effects of plasma shape and current and pressure profiles on edge instabilities in DIII-D are presented. Magnetic oscillations with toroidal mode number n {approx} 2--9 and a fast growth time {gamma}{sup {minus}1} = 20--150 {micro}s are often observed prior to the first giant type 1 ELM in discharges with moderate squareness. High n ideal ballooning second stability access encourages edge instabilities by facilitating the buildup of the edge pressure gradient and bootstrap current density which destabilize the intermediate to low n modes. Analysis suggests that discharges with large edge pressure gradient and bootstrap current density are more unstable to n > 1 modes. Calculations and experimental results show that ELM amplitude and frequency can be varied by controlling access to the second ballooning stability regime at the edge through variation of the squareness of the discharge shape. A new method is proposed to control edge instabilities by reducing access to the second ballooning stability regime at the edge using high order local perturbation of the plasma shape in the outboard bad curvature region.
Date: December 1, 1998
Creator: Lao, L.L.; Chan, V.S. & Chen, L.
Partner: UNT Libraries Government Documents Department

Advances in the simulation of toroidal gyro Landau fluid model turbulence

Description: The gyro-Landau fluid (GLF) model equations for toroidal geometry have been recently applied to the study ion temperature gradient (ITG) mode turbulence using the 3D nonlinear ballooning mode representation (BMR). The present paper extends this work by treating some unresolved issues conceming ITG turbulence with adiabatic electrons. Although eddies are highly elongated in the radial direction long time radial correlation lengths are short and comparable to poloidal lengths. Although transport at vanishing shear is not particularly large, transport at reverse global shear, is significantly less. Electrostatic transport at moderate shear is not much effected by inclusion of local shear and average favorable curvature. Transport is suppressed when critical E{times}B rotational shear is comparable to the maximum linear growth rate with only a weak dependence on magnetic shear. Self consistent turbulent transport of toroidal momentum can result in a transport bifurcation at suffciently large r/(Rq). However the main thrust of the new formulation in the paper deals with advances in the development of finite beta GLF models with trapped electron and BMR numerical methods for treating the fast parallel field motion of the untrapped electrons.
Date: December 1994
Creator: Waltz, R. E.; Kerbel, G. D.; Milovich, J. & Hammett, G. W.
Partner: UNT Libraries Government Documents Department

Ballooning Stability of the Compact Quasiaxially Symmetric Stellarator

Description: The magnetohydrodynamic (MHD) ballooning stability of a compact, quasiaxially symmetric stellarator (QAS), expected to achieve good stability and particle confinement is examined with a method that can lead to estimates of global stability. Making use of fully 3D, ideal-MHD stability codes, the QAS beta is predicted to be limited above 4% by ballooning and high-n kink modes. Here MHD stability is analyzed through the calculation and examination of the ballooning mode eigenvalue isosurfaces in the 3-space [s, alpha, theta(subscript ''k'')]; s is the edge normalized toroidal flux, alpha is the field line variable, and theta(subscript ''k'') is the perpendicular wave vector or ballooning parameter. Broken symmetry, i.e., deviations from axisymmetry, in the stellarator magnetic field geometry causes localization of the ballooning mode eigenfunction, with new types of nonsymmetric, eigenvalue isosurfaces in both the stable and unstable spectrum. The isosurfaces around the most unstable points i n parameter space (well above marginal) are topologically spherical. In such cases, attempts to use ray tracing to construct global ballooning modes lead to a k-space runaway. Introduction of a reflecting cutoff in k(perpendicular) to model numerical truncation or finite Larmor radius (FLR) yields chaotic ray paths ergodically filling the allowed phase space, indicating that the global spectrum must be described using the language of quantum chaos theory. However, the isosurface for marginal stability in the cases studied are found to have a more complex topology, making estimation of FLR stabilization more difficult.
Date: September 19, 2001
Creator: Redi, M. H.; Canik, J.; Dewar, R.L.; Johnson, J. L.; Klasky, S.; Cooper, W. A. et al.
Partner: UNT Libraries Government Documents Department

Drift waves in stellarator geometry

Description: Drift waves are investigated in a real three-dimensional stellarator geometry. A linear system, based on the cold ion fluid model and a ballooning mode formalism, is solved numerically in the geometry of the stellarator H1-NF. The spectra of stable and unstable modes, as well as localization, are discussed. The dependence of the spectrum of the unstable modes on the wavevector, plasma density variation, and the location in the plasma is presented.
Date: February 7, 2000
Creator: Persson, M.; Nadeem, M.; Lewandowski, J.L.V. & Gardner, H.J.
Partner: UNT Libraries Government Documents Department

Stability of short wavelength tearing and twisting modes

Description: The stability and mutual interaction of tearing and twisting modes in a torus is governed by matrices that generalize the well-known {Delta}{prime} stability index. The diagonal elements of these matrices determine the intrinsic stability of modes that reconnect the magnetic field at a single resonant surface. The off-diagonal elements indicate the strength of the coupling between the different modes. The author shows how the elements of these matrices can be evaluated, in the limit of short wavelength, from the free energy driving radially extended ballooning modes. The author applies the results by calculating the tearing and twisting {Delta}{prime} for a model high-beta equilibrium with circular flux surfaces.
Date: September 22, 1998
Creator: Waelbroeck, F.L.
Partner: UNT Libraries Government Documents Department

Properties of High Beta, Quasi-Axisymmetric NCSX Stellarator Configurations

Description: Quasi-axisymmetry, external kinks and ballooning stability are studied with respect to the plasma shaping and variation in the pressure and current profiles for NCSX. We show that while the kink stability may require a delicate boundary shaping, most quasi-axisymmetry may be achieved using a few low order modes that eliminate the large mirror fields arising partly from boundary shaping for the kink stability. In addition, we demonstrate that the kink and ballooning instability may be improved in the NCSX configurations by a more peaked pressure profile or a broader current profile. Finally, we show numerically that it is possible to construct a quasi-axisymmetric configuration that is stable to the external kink at all current levels for which the edge rotational transform is less than 0.5.
Date: September 28, 1999
Creator: Boozer, A.; Fu, G.Y.; Ku, L.P.; Monticello, D. & Reiman, A.
Partner: UNT Libraries Government Documents Department

High frequency core localized modes in neutral beam heated plasmas on TFTR

Description: A band of high frequency modes in the range 50--150 kHz with intermediate toroidal mode numbers 4 < n < 10 are commonly observed in the core of supershot plasmas on TFTR. Two distinct varieties of MHD modes are identified corresponding to a flute-like mode predominantly appearing around the q = 1 surface and an outward ballooning mode for q > 1. The flute-like modes have nearly equal amplitude on the high field and low field side of the magnetic axis and are mostly observed in moderate performance supershot plasmas with {tau}{sub E} < 2{tau}{sub L} while the ballooning-like modes have enhanced amplitude on the low field side of the magnetic axis and tend to appear in higher performance supershot plasmas with {tau}{sub E} > 2{tau}{sub L}, where {tau}{sub L} is the equivalent L-mode confinement time. The modes propagate in the ion diamagnetic drift direction and are highly localized with radial widths {Delta}r {approximately} 5--10 cm, fluctuation levels {tilde n}/n, {tilde T}{sub e}/T{sub e} < 0.01, and radial displacements {zeta}{sub r} {approximately} 0.1 cm. Unlike the toroidally localized high-n activity observed just prior to major and minor disruptions on TFTR, these modes are typically much weaker, more benign, and may be indicative of kinetic ballooning modes destabilized by resonant circulating neutral beam ions.
Date: November 1, 1995
Creator: Nazikian, R.; Chang, Z. & Fredrickson, E.D.
Partner: UNT Libraries Government Documents Department

Search for alpha-driven BAE modes in TFTR

Description: A search for alpha-driven beta-induced Alfven eigenmodes (BAE modes) was conducted in low current (1.0--1.6 MA) TFTR supershots. Stable high-beta deuterium-tritium (DT) discharges were obtained with B{rho} = 2.4 and central alpha beta of 0.1%. Instabilities between 75--200 kHz were observed by magnetic probes in many DT discharges, but the activity was also present in deuterium-deuterium (DD) comparison discharges, indicating that these modes are not destabilized (principally) by the alpha-particle population. Losses of fusion products are also similar in the two sets of discharges.
Date: May 1, 1996
Creator: Heidbrink, W.W.; Batha, S. & Bell, R.
Partner: UNT Libraries Government Documents Department

Properties of High Beta, Quasi-Axisymmetric NCSX Stellarator Configurations

Description: Quasi-axisymmetry, external kinks and ballooning stability are studied with respect to the plasma shaping and the variation in the pressure and current profiles for NCSX. We show that while the kink stability may require a delicate boundary shaping, most quasi-axisymmetry may be achieved using a few low order modes that eliminate the large mirror fields arising partly from boundary shaping for the kink stability. In addition, we demonstrate that the kink and ballooning instability may be improved in the NCSX configurations by a more peaked pressure profile or a broader current profile. Finally, we show numerically that it is possible to construct a quasi-axisymmetric configuration that is stable to the external kink at all current levels for which the edge rotational transform is less than 0.5.
Date: November 1, 1999
Creator: Boozer, A.; Reiman, A.; Monticello, D.; Fu, G.Y. & Ku, L.P.
Partner: UNT Libraries Government Documents Department

Ballooning-mirror instability and internally driven Pc 4--5 wave events

Description: A kinetic-MHD field-aligned eigenmode stability analysis of low frequency ballooning-mirror instabilities has been performed for anisotropic pressure plasma sin the magnetosphere. The ballooning mode is mainly a transverse wave driven unstable by pressure gradient in the bad curvature region. The mirror mode with a dominant compressional magnetic field perturbation is excited when the product of plasma beta and pressure anisotropy (P{sub {perpendicular}}/P{sub {parallel}} > 1) is large. From the AMPTE/CCE particle and magnetic field data observed during Pc 4--5 wave events the authors compute the ballooning-mirror instability parameters and perform a correlation study with the theoretical instability threshold. They find that compressional Pc 5 waves approximately satisfy the ballooning-mirror instability condition, and transverse Pc 4--5 waves are probably related to resonant ballooning instabilities with small pressure anisotropy.
Date: March 1, 1994
Creator: Cheng, C.Z.; Qian, Q.; Takahashi, K. & Lui, A.T.Y.
Partner: UNT Libraries Government Documents Department

PROGRESS IN THE PEELING-BALLOONING MODEL OF ELMS: NUMERICAL STUDIES OF 3D NONLINEAR ELM DYNAMICS

Description: Nonlinear simulations with the 3D electromagnetic two-fluid BOUT code are employed to study the dynamics of edge localized modes (ELMs) driven by intermediate wavelength peeling-ballooning modes. It is found that the early behavior of the modes is similar to expectations from linear, ideal peeling-ballooning mode theory, with the modes growing linearly at a fraction of the Alfven frequency. In the nonlinear phase, the modes grow explosively, forming a number of extended filaments which propagate rapidly from the outer closed flux region into the open flux region toward the outboard wall. Similarities to non-linear ballooning theory, as well as additional complexities are observed. Comparison to observations reveals a number of similarities. Implications of the simulations and proposals for the dynamics of the full ELM crash are discussed.
Date: November 1, 2004
Creator: SNYDER,P.B; WILSON,H.R & XU,X.Q
Partner: UNT Libraries Government Documents Department

Global structures of Alfven-ballooning modes in magnetospheric plasmas

Description: The authors show that a steep plasma pressure gradient can lead to radially localized Alfven modes, which are damped through coupling to filed line resonances. These have been called drift Alfven balloning modes (DABM) and are the prime candidates to explain Pc4-Pc5 geomagnetic pulsations observed during storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. The authors find that higher m DABMs are better localized, which is consistent with high-m observations.
Date: March 1, 1994
Creator: Vetoulis, G. & Chen, Liu
Partner: UNT Libraries Government Documents Department

Fast particle destabilization of TAE modes

Description: High-n TAE modes are studied based on a kinetic model that includes full thermal ion finite Larmor radius effects, trapped electron collisions and fast particle instability drive. Lower KTAE modes are shown to be non-existent. Like TAE modes, upper KTAE modes are shown to exist due to thermal ion FLR effects in the dissipationless limit. Dissipation effects on the stability of both TAE and upper KTAE modes can be treated perturbatively. However, due to their extended mode structure in the ballooning space, upper KTAE modes usually remain stable or weakly unstable even with large fast particle free energy. On the other hand, TAE modes can be strongly destabilized. A new resonant TAE mode (RTAE) can be excited when the fast particle drive is significantly large. The RTAE mode is a beam-like mode with its frequency determined mainly by the wave-particle resonance condition. The frequency of the RTAE mode can be much less than the TAE gap frequency and may be interpreted as the BAE observed in DIII-D experiments. As plasma {beta} increases, the TAE, RTAE and kinetic ballooning modes strongly couple; the TAE mode changes into the RTAE mode and eventually connects to the kinetic ballooning mode. Numerical results and analytical analysis on the stability of the RTAE and KTAE modes will be presented and compared with the TAE mode stability.
Date: September 1, 1995
Creator: Cheng, C.Z.; Gorelenkov, N.N. & Hsu, C.T.
Partner: UNT Libraries Government Documents Department