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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

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

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

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

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

L-H Threshold Studies in NSTX

Description: Recent experiments in the low aspect ratio National Spherical Torus Experiment (NSTX) have been run in support of the high priority ITER and ITPA issue of access to the H-mode. Specifically, a series of experiments showed reduced power threshold values for deuterium vs helium plasmas, and for plasmas with lower current, lower triangularity and with lithium conditioning. Application of n=3 fields at the plasma edge resulted in higher power thresholds. To within the constraints of temporal and spatial resolutions, no systematic difference in T{sub e}, n{sub e}, p{sub e}, T{sub i}, v or their derivatives was found in discharges that transitioned into the H-mode versus those at slightly lower power that did not. Finally, H{sub 98y,2} {approx} 1 confinement quality could be achieved for powers just above the threshold power in ELM-free conditions.
Date: September 6, 2011
Creator: Kaye, S. M.; Battaglia, D.; Bell, R. E.; Chang, C. S.; Hosea, J.; Kugel, H. et al.
Partner: UNT Libraries Government Documents Department

The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX

Description: Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.
Date: November 27, 2012
Creator: S.M.. Kaye, S. Gerhardt, W. Guttenfelder, R. Maingi, R.E. Bell, A. Diallo, B.P. LeBlanc and M. Podesta
Partner: UNT Libraries Government Documents Department

On the Dynamics of Edge-core Coupling

Description: One of the nagging, unresolved questions in fusion theory is concerned with the extent of the edge. Gyrokinetic particle simulations of toroidal ion temperature gradient (ITG) turbulence spreading using the Gyrokinetic Toroidal Code (GTC) [Z. Lin et al., Science 281, 1835 (1998)] and its related dynamical model have been extended to a system with radially varying ion temperature gradient, in order to study the inward spreading of edge turbulence toward the core plasma. Due to such spreading, the turbulence intensity in the core region is significantly enhanced over the value obtained from simulations of the core region only, and the precise boundary of the edge region is blurred. Even when the core gradient is within the Dimits shift regime (i.e., dominated by self-generated zonal flows which reduce the transport to a negligible value), a significant level of turbulence can penetrate to the core due to spreading from the edge. The scaling of the turbulent front propagation speed is closer to the prediction from a nonlinear diffusion model than from one based on linear toroidal coupling.
Date: August 26, 2005
Creator: Hahm,T.S.; Diamond, P.H.; Lin, Z.; Rewoldt, G.; Gurcan, O. & Ethier, S.
Partner: UNT Libraries Government Documents Department

The Center for Multiscale Plasma Dynamics, Final Report

Description: The University of Michigan participated in the joint UCLA/Maryland fusion science center focused on plasma physics problems for which the traditional separation of the dynamics into microscale and macroscale processes breaks down. These processes involve large scale flows and magnetic fields tightly coupled to the small scale, kinetic dynamics of turbulence, particle acceleration and energy cascade. The interaction between these vastly disparate scales controls the evolution of the system. The enormous range of temporal and spatial scales associated with these problems renders direct simulation intractable even in computations that use the largest existing parallel computers. Our efforts focused on two main problems: the development of Hall MHD solvers on solution adaptive grids and the development of solution adaptive grids using generalized coordinates so that the proper geometry of inertial confinement can be taken into account and efficient refinement strategies can be obtained.
Date: October 13, 2008
Creator: Gombosi, Tamas I.
Partner: UNT Libraries Government Documents Department

Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX

Description: This paper describes the first observations in NSTX of ‘quiet periods’ in the edge turbulence preceding the L-H transition, as diagnosed by the GPI diagnostic near the outer midplane separatrix. During these quiet periods the GPI Dα light emission pattern was transiently similar to that seen during Hmode, i.e. with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ~3 kHz for at least 30 msec before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also analyzed to obtain an estimate for the dimensionless poloidal shearing S =(dVp/dr)(Lr/Lp)τ. The values of S were strongly modulated by the quiet periods, but not otherwise varying for at least 30 msec preceding the L-H transition. Since neither the quiet periods nor the shear flow increased significantly immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX.
Date: April 26, 2010
Creator: Zweben, S.; Hager, R.; Hallatschek, K.; Kaye, S. M.; Munsat, T.; Poli, F. M. et al.
Partner: UNT Libraries Government Documents Department

Plasma containment in a toroidal bicusp (tormac)

Description: The stable confinement of a fully ionized, high-beta plasma in a toroidal bicusp (Tormac) is discussed. The bicusp geometry is described along with ''shaker'' heating by magnetoacoustic waves propagating orthogonal to the internal toroidal magnetic field. (MOW)
Date: August 1, 1975
Creator: Levine, M.A.; Brown, I.G. & Gallagher, C.C.
Partner: UNT Libraries Government Documents Department