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ECRH (electron-cyclotron resonance heating)-heated distributions in thermal-barrier tandem mirrors

Description: The distribution function is calculated for electrons subjected to strong electron-cyclotron resonance heating (ECRH) at the plug and barrier in a tandem-mirror thermal-barrier cell. When ECRH diffusion locally dominates over collisions and a boundary condition (associated with electrons passing to the center cell) imposes variations on the distribution function rapid compared to the variation of the ECRH and collisional diffusion coefficients, the kinetic equation can be reduced approximately … more
Date: September 1, 1987
Creator: Cohen, R. H. & LoDestro, L. L.
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Partner: UNT Libraries Government Documents Department
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Theory and Fluid Simulations of Boundary Plasma Fluctuations

Description: Theoretical and computational investigations are presented of boundary plasma microturbulence that take into account important effects of the geometry of diverted tokamaks--in particular, the effect of x-point magnetic shear and the termination of field lines on divertor plates. We first generalize our previous 'heuristic boundary condition' which describes, in a lumped model, the closure of currents in the vicinity of the x-point region to encompass three current-closure mechanisms. We then us… more
Date: January 9, 2007
Creator: Cohen, R. H.; LaBombard, B.; LoDestro, L. L.; Rognlien, T. D.; Ryutov, D. D.; Terry, J. L. et al.
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Partner: UNT Libraries Government Documents Department
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The Search for Reconnection and Helicity During Formation of a Bounded Spheromak

Description: Recent results from investigations using insertable magnetic probes at the Sustained Spheromak Physics Experiment (SSPX) [E. B. Hooper et al., Nucl. Fusion 39, 863 (1999)] are presented. Experiments were carried out during pre-programmed, constant amplitude coaxial gun current pulses, where magnetic field increases stepwise with every pulse, but eventually saturates. Magnetic traces from the probe, which is electrically isolated from the plasma and spans the flux conserver radius, indicate ther… more
Date: April 30, 2007
Creator: Romero-Talamas, C. A.; McLean, H. S.; Hooper, E. B.; Wood, R. D.; LoDestro, L. L. & Moller, J. M.
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Partner: UNT Libraries Government Documents Department
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Exact solution of the envelope equations for a matched quadrupole-focused beam in the low space-charged limit

Description: The Kapchinskij-Vladimirskij equations are widely used to study the evolution of the beam envelopes in a periodic system of quadrupole focusing cells. In this paper, we analyze the case of a matched beam. Our model is analogous to that used by Courant and Snyder [E.D. Courant and H.S. Snyder, Ann. Phys. 3, 1 (1958)]in obtaining a first-order approximate solution for a synchrotron. Here, we treat a linear machine and obtain an exact solution. The model uses a full occupancy, piecewise-constant f… more
Date: September 23, 2008
Creator: Anderson, O. A. & LoDestro, L. L.
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Partner: UNT Libraries Government Documents Department
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Exact solution of the envelope equations for a matchedquadrupole-focused beam in the zero space-charge limit

Description: The Kapchinskij-Vladimirskij equations are widely used to study the evolution of the beam envelopes in a periodic system of quadrupole focusing cells. In this paper, we analyze the case of a matched beam. Our model is analogous to that used by Courant and Snyder [E.D. Courant and H.S. Snyder, Ann. Phys. 3, 1 (1958)] in obtaining a first-order approximate solution for a synchrotron. Here, we treat a linear machine and obtain an exact solution. The model uses a full occupancy, piecewise-constant … more
Date: November 7, 2008
Creator: Anderson, Oscar A. & LoDestro, L. L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Comment on "Paleoclassical Transport in Low-Collisionality Toroidal Plasmas"

Description: Paleoclassical transport [1] is a recently proposed fundamental process that is claimed to occur in resistive plasmas and to be missing in the collisional drift-kinetic equations (DKE) in standard use. In this Comment we raise three puzzles presented by paleoclassical transport as developed in [1], one to do with conservation and two concerning uniqueness.
Date: October 13, 2006
Creator: LoDestro, L. L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Spheromak formation studies in SSPX

Description: We present results from the Sustained Spheromak Physics Experiment (SSPX) at LLNL, which has been built to study energy confinement in spheromak plasmas sustained for up to 2 ms by coaxial DC helicity injection. Peak toroidal currents as high as 600kA have been obtained in the 1m dia. (0.23m minor radius) device using injection currents between 200-400kA; these currents generate edge poloidal fields in the range of 0.2-0.4T. The internal field and current profiles are inferred from edge field m… more
Date: September 29, 2000
Creator: Hill, D. N.; Bulmer, R. H.; Cohen, B. L.; Hooper, E. B.; LoDestro, L. L.; Mattor, N. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Electron Cyclotron Heating and Current Drive for Maintaining Minimum q in Negative Central Shear Discharges

Description: Toroidal plasmas created with negative magnetic shear in the core region offer advantages in terms of MHD stability properties. These plasmas, transiently created in several tokamaks, have exhibited high performance as measured by normalized stored energy and neutron production rates. A critical issue with extending the duration of these plasmas is the need to maintain the off-axis-peaked current distribution required to support the minimum in the safety factor q at large radii. We present equi… more
Date: April 24, 2003
Creator: Casper, T. A.; Kaiser, T. B.; Jong, R. A.; LoDestro, L. L.; Moller, J.; Pearlstein, L. D. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Exact matched-beam envelopes for undepressed transport in a quadrupole lattice with unequal drift lengths and arbitrary field strength

Description: In 1958, Courant and Snyder analyzed the problem of alternating-gradient beam transport and treated a model without focusing gaps or space charge. Recently we revisited their work and found the exactsolution for matched-beam envelopes in a linear quadrupole lattice [O.A. Anderson and L.L. LoDestro, Phys. Rev. ST Accel. Beams, 2009]. We extend that work here to include the effect of gaps. We derive the exact envelopes and show results for various field strengths, occupancies eta,and gap-length r… more
Date: April 29, 2009
Creator: Anderson, O. A. & LoDestro, L. L.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Analytic Solution of the Envelope Equations for an Undepressed Matched Beam in a FODO Quadrupole Channel

Description: In 1958, Courant and Snyder analyzed the problem of alternating-gradient beam transport and treated a model without focusing gaps or space charge. Recently we revisited their work and found the exact solution for matchedbeam envelopes in a linear quadrupole lattice [O.A. Anderson and L.L. LoDestro, Phys. Rev. ST Accel. Beams, 2009]. We extend that work here to include the effect of asymmetric drift spaces. We derive the solution and show exact envelopes for the first two solution bands and the … more
Date: April 29, 2009
Creator: Anderson, Oscar & LoDestro, L. L.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Calculation of Neutral Beam Injection into SSPX

Description: The SSPX spheromak experiment has achieved electron temperatures of 350eV and confinement consistent with closed magnetic surfaces. In addition, there is evidence that the experiment may be up against an operational beta limit for Ohmic heating. To test this barrier, there are firm plans to add two 0.9MW Neutral Beam (NB) sources to the experiment. A question is whether the limit is due to instability. Since the deposited Ohmic power in the core is relatively small the additional power from the… more
Date: June 13, 2006
Creator: Pearlstein, L. D.; Casper, T. A.; Hill, D. N.; LoDestro, L. L. & McLean, H. S.
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Partner: UNT Libraries Government Documents Department
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Magnetic Reconnection in the Spheromak: Physics and Consequences

Description: Magnetic reconnection in the spheromak changes magnetic topology by conversion of injected toroidal flux into poloidal flux and by magnetic surface closure (or opening) in a slowly decaying spheromak. Results from the Sustained Spheromak Physics Experiment, SSPX, are compared with resistive MHD simulations using the NIMROD code. Voltage spikes on the SSPX gun during spheromak formation are interpreted as reconnection across a negative-current layer close to the mean-field x-point. Field lines a… more
Date: February 28, 2006
Creator: Hooper, E. B.; Cohen, B. I.; Hill, D. N.; LoDestro, L. L.; McLean, H. S.; Romero-Talamas, C. A. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Transport simulations for tokamak edge-plasmas

Description: The edge plasma plays key roles in tokamak devices: generates the edge transport-barrier yielding the L-H core confinement transition, distributes the core charged-particle energy to surrounding material surfaces, shields the core from impurities, and removes helium ash in fusion plasmas. The transport of density, momentum, and energy in the near-separatrix edge region, and the corresponding self-consistent electrostatic potential, require a two-dimensional description, here incorporated into t… more
Date: September 27, 2000
Creator: Rognlien, T. D.; Cohen, R. H.; LoDestro, L. L.; Porter, G. D.; Rensink, M. E.; Ryutov, D. D. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Hyper-resistivity Theory in a Cylindrical Plasma

Description: A model is presented for determining the hyper-resistivity coefficient that arises due to the presence of magnetic structures that appear in plasma configurations such as the reversed field pinch and spheromak. Emphasis is placed on modeling cases where magnetic islands pass from non-overlap to overlap regimes. Earlier works have shown that a diffusion-based model can give realistic transport scalings when magnetic islands are isolated, and this formalism is extended to apply to the hyper-resis… more
Date: February 27, 2001
Creator: Berk, H. L.; Fowler, T. K.; LoDestro, L. L. & Pearlstein, L. D.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Confinement Studies in High Temperature Spheromak Plasmas

Description: Recent results from the SSPX spheromak experiment demonstrate the potential for obtaining good energy confinement (Te > 350eV and radial electron thermal diffusivity comparable to tokamak L-mode values) in a completely self-organized toroidal plasma. A strong decrease in thermal conductivity with temperature is observed and at the highest temperatures, transport is well below that expected from the Rechester-Rosenbluth model. Addition of a new capacitor bank has produced 60% higher magnetic … more
Date: October 23, 2006
Creator: Hill, D. N.; Mclean, H. S.; Wood, R. D.; Casper, T. A.; Cohen, B. I.; Hooper, E. B. et al.
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Partner: UNT Libraries Government Documents Department
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Integrated simulation and modeling capability for alternate magnetic fusion concepts

Description: This document summarizes a strategic study addressing the development of a comprehensive modeling and simulation capability for magnetic fusion experiments with particular emphasis on devices that are alternatives to the mainline tokamak device. A code development project in this area supports two defined strategic thrust areas in the Magnetic Fusion Energy Program: (1) comprehensive simulation and modeling of magnetic fusion experiments and (2) development, operation, and modeling of magnetic … more
Date: November 3, 1998
Creator: Cohen, B. I.; Hooper, E.B.; Jarboe, T. R.; LoDestro, L. L.; Pearlstein, L. D.; Prager, S. C. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Edge and coupled core/edge transport modeling in tokamak

Description: Recent advances in the theory and modelling of tokamak edge, scrape-off-layer and divertor plasmas are described. The effects of the poloidal <i>E</i>x<i>B</i> drift on inner/outer divertor-plate asymmetries within a 1D analysis are shown to be in good agreement with experimental observations; above a critical <i>v</i><sub> <i>E</i>x<i>B</i></sub>, the model predicts transitions to supersonic SOL flow at the inboard midplane. Two-dimensional simulations show the importance of <i>E</i>x<i>B</i> … more
Date: October 14, 1998
Creator: Pearlstein, L. D.; Casper, T. A.; Cohen, R. H.; LoDestro, L. L.; Mattor, N.; Porter, G. D. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Energy confinement and magnetic field generation in the SSPX spheromak

Description: The Sustained Spheromak Physics Experiment (SSPX) [E.B. Hooper, et. al., Nuclear Fusion, Vol. 39, No. 7] explores the physics of efficient magnetic field buildup and energy confinement, both essential parts of advancing the spheromak concept. Extending the spheromak formation phase increases the efficiency of magnetic field generation with the maximum edge magnetic field for a given injector current (B/I) from 0.65 T/MA previously to 0.9 T/MA. We have achieved the highest electron temperatures … more
Date: February 11, 2008
Creator: Hudson, B.; McLean, H. S.; Wood, R. D.; Hooper, E. B.; Hill, D. N.; Jayakumar, J. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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