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Soft x-ray camera for internal shape and current density measurements on a noncircular tokamak

Description: Soft x-ray measurements of the internal plasma flux surface shaped in principle allow a determination of the plasma current density distribution, and provide a necessary monitor of the degree of internal elongation of tokamak plasmas with a noncircular cross section. A two-dimensional, tangentially viewing, soft x-ray pinhole camera has been fabricated to provide internal shape measurements on the PBX-M tokamak. It consists of a scintillator at the focal plane of a foil-filtered pinhole camera,… more
Date: May 1, 1988
Creator: Fonck, R. J.; Jaehnig, K. P.; Powell, E. T.; Reusch, M.; Roney, P. & Simon, M. P.
Partner: UNT Libraries Government Documents Department
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Superthermal electron distribution measurements from polarized electron cyclotron emission

Description: Measurements of the superthermal electron distribution can be made by observing the polarized electron cyclotron emission. The emission is viewed along a constant magnetic field surface. This simplifies the resonance condition and gives a direct correlation between emission frequency and kinetic energy of the emitting electron. A transformation technique is formulated which determines the anisotropy of the distribution and number density of superthermals at each energy measured. The steady-stat… more
Date: June 1, 1988
Creator: Luce, T. C.; Efthimion, P. C. & Fisch, N. J.
Partner: UNT Libraries Government Documents Department
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Diagnostic applications of transient synchrotron radiation in tokamak plasmas

Description: Transient radiation, resulting from a brief, deliberate perturbation of the velocity distribution of superthermal tokamak electrons, can be more informative than the steady background radiation that is present in the absence of the perturbation. It is possible to define a number of interesting inverse problems, which exploit the two-dimensional frequency-time data of the transient radiation signal. 17 refs.
Date: February 1, 1990
Creator: Fisch, N. J. (Princeton Univ., NJ (USA). Plasma Physics Lab.) & Kritz, A. H. (Hunter Coll., New York, NY (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department
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The ANU (Australian National University) Heliac Program

Description: The history and current status of experimental and theoretical work on heliacs at the Australian National University are reviewed. 18 refs., 1 fig., 1 tab.
Date: January 1, 1989
Creator: Dewar, R. L.; Gardner, H. J.; Cooper, G. J.; Hamberger, S. M.; Sharp, L. E.; Blackwell, B. D. et al.
Partner: UNT Libraries Government Documents Department
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Simulation of Spheromak Evolution and Energy Confinement

Description: Simulation results are presented that illustrate the formation and decay of a spheromak plasma driven by a coaxial electrostatic plasma gun, and that model the energy confinement of the plasma. The physics of magnetic reconnection during spheromak formation is also illuminated. The simulations are performed with the three-dimensional, time-dependent, resistive magnetohydrodynamic NIMROD code. The dimensional, simulation results are compared to data from the SSPX spheromak experiment at the Lawr… more
Date: November 12, 2004
Creator: Cohen, B; Hooper, E; Cohen, R; Hill, D; McLean, H; Wood, R et al.
Partner: UNT Libraries Government Documents Department
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Effects of an External Perturbation on a Cylindrical Spheromak

Description: In experiments like the spheromak, it becomes interesting to investigate the quality o f the magnetic flux surfaces in the device. One method of doing so is to impose an external perturbation. If the magnetic field without perturbation is tangled and no flux surfaces exist, then the perturbation will have little effect. However, if the field has well defined flux surfaces, the field should react strongly to a perturbation. Magnetic islands should form and potentially cause a degradation of the … more
Date: May 13, 2002
Creator: Terry, M R
Partner: UNT Libraries Government Documents Department
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Progress in the SSPX Spheromak

Description: The spheromak, with its simply connected geometry, holds promise as a less expensive fusion reactor. It has reasonably good plasma beta and can be formed and sustained in steady state with a magnetized coaxial plasma gun. The Sustained Spheromak Physics Experiment (SSPX) shown in Fig. 1 was constructed to investigate the key issues of magnetic field generation and energy confinement. In addition to the coaxial gun, nine magnetic field coils are utilized to shape the vacuum magnetic flux. This f… more
Date: July 7, 2003
Creator: McLean, H. S.; Woodruff, S.; Hill, D. N.; Bulmer, R. H.; Cohen, B. I.; Hooper, E. B. et al.
Partner: UNT Libraries Government Documents Department
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Circuit Model for Gun Driven Spheromaks

Description: In this note we derive circuit equations for sustained spheromaks, in the phase after a spheromak is detached from the gun and sustained in a flux conserver. The impedance of the spheromak during the formation and ''bubble burst'' phase has been discussed by Barnes et. al. We assume here that the spheromak is formed and helicity is being delivered to it from the gun, currents are above the threshold current, and the {lambda}-gradients are outward ({lambda} decreasing inward). We follow an open … more
Date: July 14, 2000
Creator: Thomassen, K I
Partner: UNT Libraries Government Documents Department
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Turbulence in the Divertor Region of Tokamak Edge Plasma

Description: Results of recent modeling of tokamak edge plasma with the turbulence code BOUT are presented. In previous studies with BOUT the background profiles of plasma density and temperature were set as flux surface functions. However in the divertor region of a tokamak the temperature is typically lower and density is higher than those at the mid-plane. To account for this in the present study a poloidal variation of background plasma density and temperature is included to provide a more realistic mod… more
Date: September 3, 2003
Creator: Umansky, M V; Rognlien, T D; Xu, X Q; Cohen, R H & Nevins, W M
Partner: UNT Libraries Government Documents Department
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Suppression of Large Edge Localized Modes with a Stochastic Magnetic Boundary in High Confinement DIII-D Plasmas

Description: Large sub-millisecond heat pulses due to Type-I ELMs have been reproducibly eliminated in DIII-D for periods approaching 7 energy confinement times with small dc currents driven in a simple magnetic perturbation coil. The current required to eliminate all but a few isolated Type-I ELM impulses during a perturbation coil pulse lasting several seconds is less than 0.4% of plasma current. Based on vacuum magnetic field line modeling, perturbation fields from the coil resonate strongly with plasma … more
Date: October 18, 2004
Creator: Evans, T. E.; Moyer, R. A.; Watkins, J. G.; Osborne, T. H.; Thomas, P. R.; Becoulet, M. et al.
Partner: UNT Libraries Government Documents Department
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Investigation of Main-Chamber and Divertor Recycling in DIII-D Using Tangentially Viewing CID Cameras

Description: Measurements of the D{sub {alpha}} emission profiles from the divertor and main chamber region in DIII-D, performed in low-density L-mode, and low and high-density ELMy H-mode plasmas imply that core plasma fueling occurs through the divertor channel. Emission profiles of carbon, combined with UEDGE modeling of the L-mode plasmas, also suggests that chemical sputtering of carbon from the flux surface adjacent to the inner divertor walls, and temperature gradient forces in the scrape-off layer, … more
Date: June 16, 2003
Creator: Groth, M.; Porter, G. D.; Petrie, T. W.; Fenstermacher, M. E. & Brooks, N. H.
Partner: UNT Libraries Government Documents Department
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Simulation of Spheromak Evolution and Energy Confinement

Description: Simulation results are presented that illustrate the formation and decay of a spheromak plasma driven by a coaxial electrostatic plasma gun, and that model the energy confinement of the plasma. The physics of magnetic reconnection during spheromak formation is also illuminated. The simulations are performed with the three-dimensional, time-dependent, resistive magnetohydrodynamic NIMROD code. The simulation results are compared to data from the SSPX spheromak experiment at the Lawrence Livermor… more
Date: November 9, 2004
Creator: Cohen, B; Hooper, E; Cohen, R; Hill, D; McLean, H; Wood, R et al.
Partner: UNT Libraries Government Documents Department
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Long wavelength magnetic fluctuations in toroidal plasmas

Description: Fluctuating bootstrap currents provide a mechanism for long wavelength electromagnetic fluctuations in tokamak plasmas. The existence of micro-magnetic islands may be responsible for the experimental observations of core density fluctuations. A fluctuation model is introduced for the tokamak that describes the magnetic topology as a time-varying mix of magnetic islands, stochastic zones and ``good`` magnetic surfaces.
Date: October 1, 1992
Creator: Hegna, C. C. & Callen, J. D.
Partner: UNT Libraries Government Documents Department
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Turbulent transport across invariant canonical flux surfaces

Description: Net transport due to a combination of Coulomb collisions and turbulence effects in a plasma is investigated using a fluid moment description that allows for kinetic and nonlinear effects via closure relations. The model considered allows for ``ideal`` turbulent fluctuations that distort but preserve the topology of species-dependent canonical flux surfaces {psi}{sub {number_sign},s} {triple_bond} {integral} dF {center_dot} B{sub {number_sign},s} {triple_bond} {gradient} {times} [A + (m{sub s}/q… more
Date: July 1, 1994
Creator: Hollenberg, J. B. & Callen, J. D.
Partner: UNT Libraries Government Documents Department
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Studies of plasma confinement in linear and RACETRACK mirror configurations. Progress report, January 1--October 31, 1986

Description: This report discusses research on the following magnetic mirror configurations: Racetrack; ECRH generated plasmas; RF generated plasmas; potential structures; surface multipole fields, and lamex; hot electron physics; axial loss processes; and RF induced effects.
Date: June 30, 1986
Creator: Kuthi, A. & Wong, A. Y.
Partner: UNT Libraries Government Documents Department
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Particle balance in a TFTR supershot

Description: Particle balance has been studied self-consistently for a TFTR supershot during a relatively steady-state phase of the neutral beam injection. The TRANSP analysis code was used to model plasma parameters within the last closed flux surface, deriving time-dependent plasma profiles from measurements. The poloidal flux surfaces were obtained from TRANSP and an equivalent-filament analysis code. The edge plasma and recycling were modeled using the combined B2/DEGAS code with boundary conditions fro… more
Date: November 1, 1992
Creator: Budny, R. V.; Coster, D.; Stotler, D.; Bell, M. G.; Janos, A. C. & Owens, D. K.
Partner: UNT Libraries Government Documents Department
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Theoretical Investigation of Field-Line Quality in a Driven Spheromak

Description: Theoretical studies aimed at predicting and diagnosing field-line quality in a spheromak are described. These include nonlinear 3-D MHD simulations, stability studies, analyses of confinement in spheromaks dominated by either open (stochastic) field lines or approximate flux surfaces, and a theory of fast electrons as a probe of field-line length.
Date: October 7, 2002
Creator: Cohen, R. H.; Berj, H.; Cohen, B. I.; Fowler, T. K.; Glasser, A. H.; Hooper, E. B. et al.
Partner: UNT Libraries Government Documents Department
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A method for neutral spectral analysis taking ripple-trapped particle losses into account

Description: An analysis technique of charge exchange neutral spectra is proposed tested to obtain ion temperatures of a tokamak plasma. The technique models the deviation of the ``ion distribution from Maxwellian because of ripple trapped particles and introduces a hot ion effective temperature as a fitting parameter. The analysis code has been used to analyze active charge exchange data from TEXT discharges in which a significant up-down asymmetry in the neutral spectra was noted. An analysis considering … more
Date: June 24, 1994
Creator: Dnestrovskij, A. Yu; Bengtson, R. D.; Karzhavin, Y. & Ouroua, A.
Partner: UNT Libraries Government Documents Department
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Stochastic broadening of the scrapeoff layer of a single-null divertor tokamak

Description: Magnetic perturbations cause the region near the separatrix of a magnetic divertor to become stochastic. The last magnetic surface to provide magnetic confinement passes inside the X-point a distance that is proportional to the square root of the applied perturbation. Particles that diffuse across the last confining surface can follow open magnetic lines to the divertor plates. The strike points of these field lines on the divertor plates lie in helical discrete stripes. The properties of these… more
Date: December 31, 1992
Creator: Punjabi, A.; Verma, A. & Boozer, A.
Partner: UNT Libraries Government Documents Department
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Filamentation, current profiles and transport in a tokamak

Description: A Tokamak with slightly imperfect magnetic surfaces should have a microscopically filamented current structure. If so, its equilibrium has an exact analog in the dynamics of interacting charged rods. Then there will be a natural current-profile, analogous to thermal equilibrium of the rods (and the natural profile can be calculated by conventional statistical mechanics). This would account for the phenomenon of profile consistency or resilience in Tokamaks. In addition to the natural profiles, … more
Date: June 1, 1993
Creator: Taylor, J. B.
Partner: UNT Libraries Government Documents Department
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Evaluation of potential runaway generation in large-tokamak disruptions

Description: A detailed evaluation of various potential mechanisms for the generation of strong runaway beams during disruptions of largetokamak devices, including TFTR, JET, DIIID and ITER, is performed based on typical operating parameters of these devices and the presently accepted disruption model. The main results include: (1) In the existing devices, the evaporative ``preicer`` process by itself can lead to sizable runaway beams in disruptions of high-current-medium-to-low-ne discharges. In ITER, such… more
Date: June 1, 1993
Creator: Fleischmann, H. H. & Zweben, S. J.
Partner: UNT Libraries Government Documents Department
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TSC simulation of ohmic discharges in TFTR

Description: The Tokamak Simulation Code (TSC) has been used to model the time dependence of several ohmic discharges in the TFTR experiment. We have refined the semi-empirical thermal conductivity model and the sawtooth model in TSC so that good agreement is obtained between the simulation and the experiment in electron and ion temperature profiles, and in the current profiles for the entire duration of the discharges. Neoclassical resistivity gives good agreement with the measured surface voltages and rat… more
Date: April 1, 1992
Creator: Jardin, S. C.; Bell, M. G. & Pomphrey, N.
Partner: UNT Libraries Government Documents Department
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A Fokker-Planck Operator for the Emission and Absorption of Electron Plasma Waves in a Magnetized Plasma

Description: For slab geometry the perturbation of the electrostatic wake of a superthermal test electron in a magnetized plasma ({omega}{sub ce} {much_gt} {omega}{sub pe}) due to moderate magnetic shear is determined. Allowing for the spherical symmetry of the surfaces of constant phase to the rear of the test electron, the ``resonant`` field electrons causing the damping of the wave in a magnetic surface at a distance x from the test electron are those with parallel velocity {upsilon}{prime}{parallel} = {… more
Date: March 1, 1993
Creator: Ware, A. A.
Partner: UNT Libraries Government Documents Department
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Pressure profiles, resonant Pfirsch-Schlueter currents, thermal instabilities and magnetic island formation

Description: A prescription for constructing the plasma pressure profile in the vicinity of an equilibrium magnetic island is derived by solving a sourced pressure diffusion equation near the island region. For pressure sources and sinks that are relatively constant in space, it is found that the plasma pressure profile is insensitive to pressure sources; thus the pressure profile can be constructed by assuming that the net pressure flux across any topologically toroidal magnetic surface is constant. This c… more
Date: June 1, 1992
Creator: Hegna, C. C. & Callen, J. D.
Partner: UNT Libraries Government Documents Department
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