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Plasma Confinement at Uniform Temperature

Description: Report discussing the properties of a plasma held in a steady state by a magnetic field. Properties such as "electric and magnetic fields, current density, particle density, and macroscopic velocity" are determined analytically by assuming uniform temperature throughout the plasma.
Date: October 24, 1956
Creator: Woods, Cornelius H.
Partner: UNT Libraries Government Documents Department

Injection of Electrons into the Astron Reactor

Description: "The injection of the E-layer electrons into the Astron reactor is described by following the electrons as they emerge from the anode of the 1-Mev electron gun through the various steps up to their injection in the reactor volume. Several problems are imposed by this injection process and their solutions are discussed briefly. The detailed mathematical theory and calculations will be presented in a separate paper now in preparation."
Date: January 27, 1958
Creator: Christofilos, Nicholas C.
Partner: UNT Libraries Government Documents Department

Plasma Containment Configuration

Description: Report discussing a plasma containment configuration which appears to have no escape cone. From abstract: "Arguments are given to show how the containment process works, including experimental evidence deduced from published reports on "electromagnetic levitation."
Date: October 11, 1956
Creator: Linlor, William I.
Partner: UNT Libraries Government Documents Department

Pyrotron Plasma-Heating Experiments

Description: Report discussing experiments on particle density, plasma compression, electron heating, and electron energy distribution of plasma in a pyrotron. Past experiments that led to this investigation are discussed as well.
Date: May 6, 1958
Creator: Coensgen, F. H.; Ford, F. C. & Ellis, R.E.
Partner: UNT Libraries Government Documents Department

Pyrotron High-Energy Experiments

Description: "In these studies ions of several-kilovolts energy were extracted from an ion source located inside one of the peaks of the mirror field...The extraction slot of the source is located near the field injection plane, about midway between the mirror peak and the center, and ions are injected perpendicularly to magnetic field lines. In their traversal of the distance between the mirrors, the ions are in an inhomogeneous magnetic field and have a component of velocity along curved field lines. This gives rise to a to a 'guiding center' drift in the azimuthal direction and prevents the particle trajectory from intersecting the ion source after the first reflection. The magnetic field is increased during the injection period by an amount sufficient to move the reflection surface inside the ion source region by the time the ions have precessed completely about the symmetry axis."
Date: April 11, 1958
Creator: Damm, Charles C. & Eby, F. S.
Partner: UNT Libraries Government Documents Department

Overview of H-mode studies in DIII-D

Description: A major portion of the DIII-D program includes studies of the L-H transition, of the VH-mode, of particle transport and control and of the power-handling capability of a diverter. Significant progress has been made in all of these areas and the purpose of this paper is to summarize the major results obtained during the last two years. An increased understanding of the origin of improved confinement in H-mode and in VH-mode discharges has been obtained, good impurity control has been achieved in several operating scenarios, studies of helium transport provide encouraging results from the point of view of reactor design, an actively pumped diverter chamber has controlled the density in H-mode discharges and a radiative diverter is a promising technique for controlling the heat flux from the main plasma.
Date: January 1, 1994
Creator: Groebner, R. J.; Baker, D. R, & Allen, S. L.
Partner: UNT Libraries Government Documents Department

Sustained spheromak physics experiment

Description: The Sustained Spheromak Physics Experiment, SSPX, will study spheromak physics with particular attention to energy confinement and magnetic fluctuations in a spheromak sustained by electrostatic helicity injection. In order to operate in a low collisionality mode, requiring <i>T<sub>e</sub></i>> 100 eV, vacuum techniques developed for tokamaks will be applied, and a divertor will be used for the first time in a spberomak. The discharge will operate for pulse lengths of several milliseconds, long compared to the time to establish a steady-state equilibrium but short compared to the L/R time of the flux conserver. The spheromak and helicity injector ("gun") are closely coupled, as shown by an ideal MHD model with force-free injector and edge plasmas. The current from the gun passes along the symmetry axis of the spheromak, and the resulting toroidal magnetic field causes the safety factor, <i>q</i>, to diverge on the separatrix. The <i>q</i>-profile depends on the ratio of the injector current to spheromak current and on the. magnetic flux coupling the injector to the spheromak. New diagnostics include magnetic field measurements by a reflectometer operating in combined 0- and X-modes and by a transient internal probe (TIP).
Date: September 29, 1998
Creator: Hooper, E B
Partner: UNT Libraries Government Documents Department

Summary of UCRL Pyrotron (Mirror Machine) Program

Description: "This report presents some of the theory of operation of the Mirror Machine, and summarizes the experimental work which has been carried out...The modus operandi of the Mirror Machine is to create, heat and control a high temperature plasma by means of externally generating magnetic fields."
Date: June 27, 1958
Creator: Post, Richard F.
Partner: UNT Libraries Government Documents Department

Dynamics of the L {yields} H transition, VH-mode evolution, edge localized modes and R.F. driven confinement control in tokamaks

Description: Several novel theoretical results related to L {yields} H transition physics, VH-mode evolution, Edge Localized Modes and active confinement control are presented. Critical issues are identified, results are discussed and important unresolved questions are listed. The basic physics is discussed in the contexts of current experiments and of ITER.
Date: February 1, 1995
Creator: Diamond, P. H.; Lebedev, V. B.; Liang, Y. M.; Gruzinov, A. V.; Gruzinov, I.; Medvedev, M. et al.
Partner: UNT Libraries Government Documents Department

L-H transition in tokamaks and stellarators

Description: It is shown that the bifurcation dynamics in the H-mode theory based on the ion orbit loss and nonlinear viscosity is not sensitive to the radial pressure and temperature gradients after bifurcation. This allows the poloidal flow velocity to be opposite to that of the poloidal E x B velocity in the H-mode phase if the pressure gradient is steep. Here, E(B) is the electric (magnetic) field. The theory is also extended to stellarator configurations to demonstrate that the tokamak H-mode theory can be tested in a controlled manner in those devices. A set of poloidal and toroidal momentum evolution equations is derived in which the radial current density outside the last closed flux surface is expressed in terms of the radial integral of the poloidal current density into the diverter plates. This facilitates the calculation of the radial electric field profile across the separatrix.
Date: December 31, 1993
Creator: Shaing, K. C.; Hsu, C. T. & Christenson, P. J.
Partner: UNT Libraries Government Documents Department

Physics of the L-mode to H-mode transition in tokamaks

Description: Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E {times} B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabilization of turbulence have been seen in several tokamaks. The purpose of this paper is to discuss the most recent data in the light of the basic paradigm of electric field shear stabilization and to critically compare the experimental results with various theories.
Date: July 1, 1992
Creator: Burrell, K. H.; Carlstrom, T. N.; Gohil, P.; Groebner, R. J.; Kim, J.; Osborne, T. H. et al.
Partner: UNT Libraries Government Documents Department

The effect of current profile changes on confinement in the DIII-D tokamak

Description: Experiments in the DIII-D tokamak have demonstrated that the effect of changes in the current profile on plasma confinement varies with the discharge shape. The results are similar in many respects to those from other tokamaks. In all cases, a rapid change in the plasma current in an L-mode, circular or moderately elongated, discharge has been used to produce a transient change in the current density profile. Although the detailed results vary among tokamaks, it is generally observed that during and immediately following a negative plasma current ramp, the stored energy does not follow the L-mode scaling that predicts that confinement should be proportional to the total plasma current. The stored energy changes on the time scale of the relaxation of the current density profile rather than the shorter time scales of the energy confinement time or the change in the total current. Because of the discharge having capability of the DIII-K tokamak it has been possible to extend these current ramp experiments beyond the L-mode, moderate elongation case to highly elongated double-null divertor discharges in H-mode. In separate experiments, a rapid change in the discharge elongation has also been used to vary the current density profile. This paper shows that the dependence of the plasma confinement on the current profile changes when the discharge shape is changed. This variation with discharge shape provides evidence for a model that predicts that changes in the local magnetic shear resulting from the changes in the current profile can result in decreased local transport.
Date: May 1, 1992
Creator: Ferron, J. R.; Lao, L. L. & Taylor, T. S.
Partner: UNT Libraries Government Documents Department

ELM-related fluctuations in PBX-M H-modes

Description: Edge Localized Modes, or ELMs, are at the same time both disadvantageous and advantageous features of H-modes. ELMs can cause energy and particle losses from the plasma, with instantaneous energy losses reaching 40% of the total stored energy in the case of large-amplitude ELMs. The energy loss from these ELMs, or closely spaced smaller ELMs, may result in what is known as a beta-collapse, an event in which energy is lost over a substantial duration of the discharge. On the other hand, if controlled, the ELM related energy and, especially, impurity losses can lead to near steady-state discharge conditions with relatively low radiative power losses. The importance of ELMs in the development of the H-phase has led to numerous studies which attempt to uncover their nature. The purpose of the present work is to present additional observations of, most notably, high frequency magnetic fluctuations associated with ELMS. There are some observations here that are consistent with previously reported ones, namely the appearance of high frequency ({ge}250 kHz) activity prior to the D{sub {alpha}} increase, suggesting again that the rise in D{sub {alpha}} is some delayed response to an instability occurring farther inside the plasma edge. While this high frequency activity is global, with high coherence for all coil pairs both on the inside and outside midplane, there is no identifiable mode structure. Reported here for the first time are observations of a very intense outward ballooning feature that appears simultaneously with the D{sub {alpha}} increase and lasts for about 5 msec. The toroidal mode structure of this feature is clearly identifiable, consisting of a series of toroidal harmonics from n=3 to 8, at frequencies given by f{sub n}=f{sub 0}+n{Delta}f, with f{sub 0}=30 to 50 kHz and A{Delta}=20 to 30 kHz.
Date: April 1, 1994
Creator: Kaye, S. M.; Hahm, T. S.; Sesnic, S.; Tang, W.; Roney, P.; Davis, W. et al.
Partner: UNT Libraries Government Documents Department

Modeling of Effects of Neutrals on the L-H Transition Power Threshold in DIII-D

Description: In order to study possible effects of neutrals on the power threshold for transition from L mode to the H mode confinement in DIII-D, the problem of reconstructing neutral particle distributions inside the separatrix from available edge, scrape-off layer, and divertor plasma diagnostic data is addressed.
Date: December 31, 1997
Creator: Owen, L.W.; Carreras, B.A.; Maingi, R.; Mioduszewski, P.K.; Carlstrom, T.N. & Groebner, R.J.
Partner: UNT Libraries Government Documents Department

Theory and application of maximum magnetic energy in toroidal plasmas

Description: The magnetic energy in an inductively driven steady-state toroidal plasma is a maximum for a given rate of dissipation of energy (Poynting flux). A purely resistive steady state of the piecewise force-free configuration, however, cannot exist, as the periodic removal of the excess poloidal flux and pressure, due to heating, ruptures the static equilibrium of the partitioning rational surfaces intermittently. The rupture necessitates a plasma with a negative q{prime}/q (as in reverse field pinches and spheromaks) to have the same {alpha} in all its force-free regions and with a positive q{prime}/q (as in tokamaks) to have centrally peaked {alpha}'s.
Date: February 1, 1992
Creator: Chu, T.K.
Partner: UNT Libraries Government Documents Department

Confinement and stability of VH-mode discharges in the DIII-D tokamak

Description: A regime of very high confinement (VH-mode) has been observed in neutral beam-heated deuterium discharges in the DIII-D tokamak with thermal energy confinement times up to [approx]3.6 times that predicted by the ITER-89P L-mode scaling and 2 times that predicted by ELM-free H-mode thermal confinement scalings. This high confinement has led to increased plasma performance, n[sub D] (0)T[sub i](0)[tau][sub E] = 2 [times] 10[sup 20] m[sup [minus]3] keV sec with I[sub p] = 1.6 MA, B[sub T] = 2.1 T, Z[sub eff] [le] 2. Detailed transport analysis shows a correspondence between the large decrease in thermal diffusivity in the region 0.75 [le] [rho] [le] 0.9 and the development of a strong shear in the radial electric field in the same region. This suggests that stabilization of turbulence by sheared E [times] B flow is responsible for the improved confinement in VH-mode. A substantial fraction of the edge plasma entering the second regime of stability may also contribute to the increase in confinement. The duration of the VH-mode phase has been lengthened by feedback controlling the input power to limit plasma beta.
Date: October 1, 1992
Creator: Taylor, T.S.; Osborne, T.H.; Burrell, K.H.; Carlstrom, T.N.; Chan, V.S.; Chu, M.S. et al.
Partner: UNT Libraries Government Documents Department

Regimes of improved confinement and stability in DIII-D obtained through current profile modifications

Description: Several regimes of improved confinement and stability have been obtained in recent experiments in the DIII-D tokamak by dynamically varying the toroidal current density profile to transiently produce a poloidal magnetic field profile with more favorable confinement and stability properties. A very peaked current density profile with high plasma internal inductance, [ell][sub i], is produced either by a rapid change in the plasma poloidal cross section or by a rapid change in the total plasma current. Values of thermal energy confinement times nearly 1.8 times the JET/DIII-D ELM-free H-mode thermal confinement scaling are obtained. The confinement enhancement factor over the ITER89-P L-mode confinement scaling, H, is as high as 3. Normalized toroidal beta, [beta][sub N], greater than 6%-m-T/MA and values of the product [beta][sub N]H greater than 15 have also been obtained. Both the confinement and the maximum achievable [beta] vary with [ell][sub i] and decrease as the current profile relaxes. For strongly shaped H-mode discharges, in addition to the current density profile peakedness, as measured by [ell][sub i] other current profile parameters, such as its distribution near the edge region, may also affect the confinement enhancement.
Date: September 1, 1992
Creator: Lao, L.L.; Ferron, J.R.; Taylor, T.S.; Chan, V.S.; Osborne, T.H.; Burrell, K.H. et al.
Partner: UNT Libraries Government Documents Department