Collisional diffusion in toroidal plasmas with elongation and triangularity
Martin, P.; Castro, E.; Haines, M. G.
2007-05-15
Collisional diffusion is analyzed for plasma tokamaks with different ellipticities and triangularities. Improved nonlinear equations for the families of magnetic surfaces are used here. Dimensionless average velocities are calculated as a function of the inductive electric field, elongation, triangularity, and Shafranov shift. Confinement has been found to depend significantly on triangularity.
NASA Astrophysics Data System (ADS)
Sugama, H.; Nunami, M.; Nakata, M.; Watanabe, T.-H.
2017-02-01
A novel gyrokinetic formulation is presented by including collisional effects into the Lagrangian variational principle to yield the governing equations for background and turbulent electromagnetic fields and gyrocenter distribution functions, which can simultaneously describe classical, neoclassical, and turbulent transport processes in toroidal plasmas with large toroidal flows on the order of the ion thermal velocity. Noether's theorem modified for collisional systems and the collision operator given in terms of Poisson brackets are applied to derivation of the particle, energy, and toroidal momentum balance equations in the conservative forms, which are desirable properties for long-time global transport simulation.
Collisionality Scaling of Main-ion Toroidal and Poloidal Rotation in Low Torque DIII-D Plasmas
B A Grierson, et al
2013-05-10
In tokamak plasmas with low levels of toroidal rotation, the radial electric fi eld Er is a combination of pressure gradient and toroidal and poloidal rotation components, all having similar magnitudes. In order to assess the validity of neoclassical poloidal rotation theory for determining the poloidal rotation contribution to Er , Dα emission from neutral beam heated tokamak discharges in DIII-D [J.L. Luxon, Nucl. Fusion 42 , 614 (2002)] has been evaluated in a sequence of low torque (electron cyclotron resonance heating and balanced diagnostic neutral beam pulse) discharges to determine the local deuterium toroidal rotation velocity. By invoking the radial force balance relation the deuterium poloidal rotation can be inferred. It is found that the deuterium poloidal low exceeds the neoclassical value in plasmas with collisionality νi < 0: 1, being more ion diamagnetic, and with a stronger dependence on collisionality than neoclassical theory predicts. At low toroidal rotation, the poloidal rotation contribution to the radial electric fi eld and its shear is signi cant. The eff ect of anomalous levels of poloidal rotation on the radial electric fi eld and cross fi eld heat transport is investigated for ITER parameters.
Martin, Pablo; Castro, Enrique; Puerta, Julio
2009-07-26
Non-linear plasma diffusion effects due to hole currents in tokamaks is analyzed in this work. Since the recent discovery of hole currents in tokamaks, this matter has become very important in confinement and instabilities in tokamaks plasmas. The analysis here presented includes non-linear flows as well as hole currents. In the case of low vorticity plasmas our treatment is performed using MHD equations, an it is more suitable for plasmas with very low levels of turbulence, as in the H-mode. The present treatment follows the lines of previous works, and some of the equations and results look like those obtained on these papers. However, the form of the family of the magnetic surfaces is very different to previous treatment, since the hole current modifies those families in a very important way. Elliptic plasmas with triangularity are considered. Pfirsch-Schlueter type currents are obtained for these generalized cases. Diffusion with and without holes are calculated and compared for several values of ellipticity and triangularity. Negative and positive triangularities are considered. In most of the calculations triangularity improves confinement, but the results are different for the positive than for the negative case.
Low Collisionality Neoclassical Toroidal Viscosity in Tokamaks and Quasi-symmetric Stellarators
NASA Astrophysics Data System (ADS)
Cole, A. J.; Hegna, C. C.; Callen, J. D.
2008-11-01
Non-resonant magnetic perturbations can affect plasma rotation in toroidally confined plasmas through their modification to |B|. Variations along a field line induce nonambipolar radial transport and produce a global neoclassical toroidal viscous force [NTV]. In this work, previously calculated radial particle fluxes for the low-collisionality ``ν'' and ``1/ν'' regimes [1] are unified into a single particle flux (or toroidal viscous force). Provided pitch-angle scattering dominates over collisional energy exchange, the energy component of phase space can be decoupled into independent regions (E >Ec. for ν regime, E < Ec for 1/ν regime, with Ec determined by .νi(Ec) =ɛ,E) within which the perturbed distribution function can be calculated similar to [1]. Using a technique first employed in axisymmetric neoclassical theory [2], the smoothed particle flux is constructed by summing the partial contributions from ν and 1/ν banana drift effects respectively. The complete NTV force is expressed in terms of the equilibrium flows and a temperature-gradient-determined ``intrinsic'' flow. [1] K.C. Shaing, Phys. Plasmas, 10, 1443 (2003). [2] K.T. Tsang, and J.D. Callen, Phys. Fluids 19, 667 (1976).
Toroidal Flow in Tokamak Plasmas
NASA Astrophysics Data System (ADS)
Callen, J. D.; Cole, A. J.; Hegna, C. C.
2007-11-01
Many effects influence toroidal flow evolution in tokamak plasmas. Momentum sources and radial diffusion due to axisymmetric neoclassical, paleoclassical and anomalous transport are usually considered. In addition, the toroidal flow can be affected by field errors. Small, non-axisymmetric field errors arise from coil irregularities, active control coils and collective plasma magnetic distortions (e.g., NTMs, RWMs). Resonant field errors cause localized electromagnetic torques near rational surfaces in the plasma, which can lock the plasma to the wall leading to magnetic islands and reduced confinement or disruptions. Their penetration into the plasma is limited by flow-shielding effects; but they can be amplified by the plasma response at high beta. Non-resonant field errors cause magnetic pumping and radial banana drifts, and lead to toroidal flow damping over the entire plasma. Many of these processes can also produce momentum pinch and intrinsic flow effects. This poster will seek to present a coherent picture of all these effects and suggest ways they could be tested and distinguished experimentally.
Collisional processes in cometary plasmas
NASA Technical Reports Server (NTRS)
Cravens, T. E.
1991-01-01
The interaction of the solar wind with comets is initiated at large distances from the nucleus by the ionization of cometary neutrals. The resulting contamination of the solar wind with cometary ions mass-loads the solar wind flow, causing it to slow down. The plasma-comet interaction is largely collisionless at large cometocentric distances. However, collisional processes become important in the inner coma (within the cometopause). Collisional processes include charge-transfer between solar wind protons and neutrals, ion-neutral friction, electron and ion thermal cooling, and ion-neutral chemistry. For example, the magnetometer on the Giotto spacecraft observed a diamagnetic cavity near closest approach. This cavity is a consequence of the balance between an inward-directed magnetic pressure gradient force and an outward ion-netural frictional force. Thermalization of the cometary ion distribution function by Coulomb collisions is another important process in the inner coma of an active comet.
Edge ambipolar potential in toroidal fusion plasmas
Spizzo, G. Vianello, N.; Agostini, M.; Puiatti, M. E.; Scarin, P.; Spolaore, M.; Terranova, D.; White, R. B.; Abdullaev, S. S.; Schmitz, O.; Cavazzana, R.; Ciaccio, G.
2014-05-15
A series of issues with toroidally confined fusion plasmas are related to the generation of 3D flow patterns by means of edge magnetic islands, embedded in a chaotic field and interacting with the wall. These issues include the Greenwald limit in Tokamaks and reversed-field pinches, the collisionality window for ELM mitigation with the resonant magnetic perturbations (RMPs) in Tokamaks, and edge islands interacting with the bootstrap current in stellarators. Measurements of the 2D map of the edge electric field E{sup r}(r=a,θ,ϕ) in the RFX reversed-field pinch show that E{sup r} has the same helicity of the magnetic islands generated by a m/n perturbation: in fact, defining the helical angle u=mθ−nϕ+ωt, maps show a sinusoidal dependence as a function of u, E{sup r}=E{sup ~r}sin u. The associated E × B flow displays a huge convective cell with v(a)≠0 which, in RFX and near the Greenwald limit, determines a stagnation point for density and a reversal of the sign of E{sup r}. From a theoretical point of view, the question is how a perturbed toroidal flux of symmetry m/n gives rise to an ambipolar potential Φ=Φ{sup ~}sin u. On the basis of a model developed with the guiding center code ORBIT and applied to RFX and the TEXTOR tokamak, we will show that the presence of an m/n perturbation in any kind of device breaks the toroidal symmetry with a drift proportional to the gyroradius ρ, thus larger for ions (ρ{sub i} ≫ ρ{sub e}). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.
Steady state compact toroidal plasma production
Turner, William C.
1986-01-01
Apparatus and method for maintaining steady state compact toroidal plasmas. A compact toroidal plasma is formed by a magnetized coaxial plasma gun and held in close proximity to the gun electrodes by applied magnetic fields or magnetic fields produced by image currents in conducting walls. Voltage supply means maintains a constant potential across the electrodes producing an increasing magnetic helicity which drives the plasma away from a minimum energy state. The plasma globally relaxes to a new minimum energy state, conserving helicity according to Taylor's relaxation hypothesis, and injecting net helicity into the core of the compact toroidal plasma. Controlling the voltage so as to inject net helicity at a predetermined rate based on dissipative processes maintains or increases the compact toroidal plasma in a time averaged steady state mode.
Plasma transport coefficients for nonsymmetric toroidal confinement systems
Hirshman, S.P.; Shaing, K.C.; van Rij, W.I.; Beasley, C.O. Jr.; Crume, E.C. Jr.
1986-03-01
A variational principle is developed for computing accurate values of local plasma transport coefficients in nonsymmetric toroidal confinement configurations. Numerical solutions of the linearized drift Fokker-Planck equation are used to obtain the thermodynamic fluxes as functions of collision frequenty and the radial electric field. Effects resulting from the variation of the longitudinal adiabatic invariant J along an orbit (due to particle transitions from helically trapped to toroidally trapped orbits) are treated. The velocity-space distribution resulting from trapped, circulating, and transition particle orbits is well represented by a Legendre polynomial expansion in the pitch angle coordinate. The computational effort is significantly reduced from that required with Monte Carlo methods through use of an efficient treatment of the disparity between the time scales of collisionless and collisional particle dynamics. Numerical computations for a stellarator configuration are presented. 24 refs. 9 figs.
Effects of magnetic islands on bootstrap current in toroidal plasmas
NASA Astrophysics Data System (ADS)
Dong, G.; Lin, Z.
2017-03-01
The effects of magnetic islands on electron bootstrap current in toroidal plasmas are studied using gyrokinetic simulations. The magnetic islands cause little changes of the bootstrap current level in the banana regime because of trapped electron effects. In the plateau regime, the bootstrap current is completely suppressed at the island centers due to the destruction of trapped electron orbits by collisions and the flattening of pressure profiles by the islands. In the collisional regime, small but finite bootstrap current can exist inside the islands because of the pressure gradients created by large collisional transport across the islands. Finally, simulation results show that the bootstrap current level increases near the island separatrix due to steeper local density gradients.
Collisional damping rates for plasma waves
NASA Astrophysics Data System (ADS)
Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.
2016-06-01
The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.
Plasma Density Effects on Toroidal Flow Stabilization of Edge Localized Modes
NASA Astrophysics Data System (ADS)
Cheng, Shikui; Zhu, Ping; Banerjee, Debabrata
2016-10-01
Recent EAST experiments have demonstrated mitigation and suppression of edge localized modes (ELMs) with toroidal rotation flow in higher collisionality regime, suggesting potential roles of plasma density. In this work, the effects of plasma density on the toroidal flow stabilization of the high- n edge localized modes have been extensively studied in linear calculations for a circular-shaped limiter H-mode tokamak, using the initial-value extended MHD code NIMROD. In the single MHD model, toroidal flow has a weak stabilizing effects on the high- n modes. Such a stabilization, however, can be significantly enhanced with the increase in plasma density. Furthermore, our calculations show that the enhanced stabilization of high- n modes from toroidal flow with higher edge plasma density persists in the 2-fluid MHD model. These findings may explain the ELM mitigation and suppression by toroidal rotation in higher collisionality regime due to the enhancement of plasma density obtained in EAST experiment. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, the 100 Talent Program and the President International Fellowship Initiative of Chinese Academy of Sciences.
Microwave produced plasma in a Toroidal Device
NASA Astrophysics Data System (ADS)
Singh, A. K.; Edwards, W. F.; Held, E. D.
2010-11-01
A currentless toroidal plasma device exhibits a large range of interesting basic plasma physics phenomena. Such a device is not in equilibrium in a strict magneto hydrodynamic sense. There are many sources of free energy in the form of gradients in plasma density, temperature, the background magnetic field and the curvature of the magnetic field. These free energy sources excite waves and instabilities which have been the focus of studies in several devices in last two decades. A full understanding of these simple plasmas is far from complete. At Utah State University we have recently designed and installed a microwave plasma generation system on a small tokamak borrowed from the University of Saskatchewan, Saskatoon, Canada. Microwaves are generated at 2.45 GHz in a pulsed dc mode using a magnetron from a commercial kitchen microwave oven. The device is equipped with horizontal and vertical magnetic fields and a transformer to impose a toroidal electric field for current drive. Plasmas can be obtained over a wide range of pressure with and without magnetic fields. We present some preliminary measurements of plasma density and potential profiles. Measurements of plasma temperature at different operating conditions are also presented.
Neoclassical transport in enhanced confinement toroidal plasmas
Lin, Z.; Tang, W.M.; Lee, W.W.
1996-11-01
It has recently been reported that ion thermal transport levels in enhanced confinement tokamak plasmas have been observed to fall below the irreducible minimum level predicted by standard neoclassical theory. This apparent contradiction is resolved in the present analysis by relaxing the basic neoclassical assumption that the ions orbital excursions are much smaller than the local toroidal minor radius and the equilibrium scale lengths of the system.
Trapped ion mode in toroidally rotating plasmas
Artun, M.; Tang, W.M.; Rewoldt, G.
1995-04-01
The influence of radially sheared toroidal flows on the Trapped Ion Mode (TIM) is investigated using a two-dimensional eigenmode code. These radially extended toroidal microinstabilities could significantly influence the interpretation of confinement scaling trends and associated fluctuation properties observed in recent tokamak experiments. In the present analysis, the electrostatic drift kinetic equation is obtained from the general nonlinear gyrokinetic equation in rotating plasmas. In the long perpendicular wavelength limit k{sub {tau}}{rho}{sub bi} {much_lt} 1, where {rho}{sub bi} is the average trapped-ion banana width, the resulting eigenmode equation becomes a coupled system of second order differential equations nmo for the poloidal harmonics. These equations are solved using finite element methods. Numerical results from the analysis of low and medium toroidal mode number instabilities are presented using representative TFTR L-mode input parameters. To illustrate the effects of mode coupling, a case is presented where the poloidal mode coupling is suppressed. The influence of toroidal rotation on a TFTR L-mode shot is also analyzed by including a beam species with considerable larger temperature. A discussion of the numerical results is presented.
Hybrid simulations of weakly collisional plasmas
NASA Astrophysics Data System (ADS)
Xia, Qian; Reville, Brian; Tzoufras, Michail
2016-10-01
Laser produced plasma experiments can be exploited to investigate phenomena of astrophysical relevance. The high densities and velocities that can be generated in the laboratory provide ideal conditions to investigate weakly collisional or collisionless plasma shock physics. In addition, the high temperatures permit magnetic and kinetic Reynolds numbers that are difficult to achieve in other plasma experiments, opening the possibility to study plasma dynamo. Many of these experiments are based on a classic plasma physics problem, namely the interpenetration of two plasma flows. To investigate this phenomenon, we are constructing a novel multi-dimensional hybrid numerical scheme, that solves the ion distribution kinetically via a Vlasov-Fokker-Planck equation, with electrons providing a charge neutralizing fluid. This allows us to follow the evolution on hydrodynamic timescales, while permitting inclusion ofcollisionlesseffects on small scales. It also could be used to study the increasing collisional effects due to the stiff gradient and weakly anisotropic velocity distribution. We present some preliminary validation tests for the code, demonstrating its ability to accurately model key processes that are relevant to laboratory and astrophysical plasmas.
Heat flux viscosity in collisional magnetized plasmas
Liu, C.; Fox, W.; Bhattacharjee, A.
2015-05-15
Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.
Fine velocity structures collisional dissipation in plasmas
NASA Astrophysics Data System (ADS)
Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi
2016-04-01
In a weakly collisional plasma, such as the solar wind, collisions are usually considered far too weak to produce any significant effect on the plasma dynamics [1]. However, the estimation of collisionality is often based on the restrictive assumption that the particle velocity distribution function (VDF) shape is close to Maxwellian [2]. On the other hand, in situ spacecraft measurements in the solar wind [3], as well as kinetic numerical experiments [4], indicate that marked non-Maxwellian features develop in the three-dimensional VDFs, (temperature anisotropies, generation of particle beams, ring-like modulations etc.) as a result of the kinetic turbulent cascade of energy towards short spatial scales. Therefore, since collisional effects are proportional to the velocity gradients of the VDF, the collisionless hypothesis may fail locally in velocity space. Here, the existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can increase locally due to the velocity space deformation of the particle velocity distribution. In particular, by means of Eulerian simulations of collisional relaxation of a spatially homogeneous force-free plasma, in which collisions among particles of the same species are modeled through the complete Landau operator, we show that the system entropy growth occurs over several time scales, inversely proportional to the steepness of the velocity gradients in the VDF. We report clear evidences that fine velocity structures are dissipated by collisions in a time much shorter than global non-Maxwellian features, like, for example, temperature anisotropies. Moreover we indicate that, if small-scale structures
Toroidal plasma enhanced CVD of diamond films
Zvanya, John Cullen, Christopher Morris, Thomas Krchnavek, Robert R.; Holber, William Basnett, Andrew Basnett, Robert; Hettinger, Jeffrey
2014-09-01
An inductively coupled toroidal plasma source is used as an alternative to microwave plasmas for chemical vapor deposition of diamond films. The source, operating at a frequency of 400 kHz, synthesizes diamond films from a mixture of argon, methane, and hydrogen. The toroidal design has been adapted to create a highly efficient environment for diamond film deposition: high gas temperature and a short distance from the sample to the plasma core. Using a toroidal plasma geometry operating in the medium frequency band allows for efficient (≈90%) coupling of AC line power to the plasma and a scalable path to high-power and large-area operation. In test runs, the source generates a high flux of atomic hydrogen over a large area, which is favorable for diamond film growth. Using a deposition temperature of 900–1050 °C and a source to sample distance of 0.1–2.0 cm, diamond films are deposited onto silicon substrates. The results showed that the deposition rate of the diamond films could be controlled using the sample temperature and source to sample spacing. The results also show the films exhibit good-quality polycrystalline diamond as verified by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. The scanning electron microscopy and x-ray diffraction results show that the samples exhibit diamond (111) and diamond (022) crystallites. The Raman results show that the sp{sup 3} peak has a narrow spectral width (FWHM 12 ± 0.5 cm{sup −1}) and that negligible amounts of the sp{sup 2} band are present, indicating good-quality diamond films.
MHD edge instabilities in toroidal plasmas
NASA Astrophysics Data System (ADS)
Sugiyama, Linda
2015-11-01
Different types of MHD edge instabilities in different toroidal magnetically confined plasmas are compared. Large scale numerical simulations show that the nonlinear evolution of an unstable edge mode in a shaped plasma with a single X-point and a surrounding open field line region has a number of common features in the full resistive MHD model for strongly unstable and weaker instabilities. These include the relation of the nonlinear mode structure and dominant toroidal harmonics to the linear eigenmode spectrum, the effects of the mode on reducing the edge pressure or density gradient, the inward penetration of a ballooning-type perturbation into the plasma interior, and the potential to drive a coherent axisymmetric poloidal rotation of the outer part of the plasma, exhibited at different strengths. The results can be compared to experiment to estimate the usefulness and validity of the MHD model for predicting edge stability and instability properties. Work supported by the U.S. DOE OFES under Awards DE-SC-0007883, DE-FG02-04ER54802, and DE-SC-0008737. Some computation carried out at NERSC.
New regime of low ion collisionality in the neoclassical equilibrium of tokamak plasmas
Ramos, J. J.
2015-07-15
The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow, and the ion contribution to the bootstrap current.
Plasma-wall transition in weakly collisional plasmas
Manfredi, G.; Devaux, S.
2008-10-15
This paper reviews some theoretical and computational aspects of plasma-wall interactions, in particular the formation of sheaths. Some fundamental results are derived analytically using a simple fluid model, and are subsequently tested with kinetic simulations. The various regions composing the plasma-wall transition (Debye sheath, collisional and magnetic presheaths) are discussed in details.
Plasma current resonance in asymmetric toroidal systems
Hazeltine, R. D.; Catto, Peter J.
2015-09-15
The well-known singularity in the magnetic differential equation for plasma current in an asymmetric toroidal confinement system is resolved by including in the pressure tensor corrections stemming from finite Larmor radius. The result provides an estimate of the amplitude of spikes in the parallel current that occur on rational magnetic surfaces. Resolution of the singularity is shown to depend on both the ambipolarity condition—the requirement of zero surface-averaged radial current—and the form of the magnetic differential equation near the rational surface.
Collisional Drift Waves in Stellarator Plasmas
J.L.V. Lewandowski
2003-10-07
A computational study of resistive drift waves in the edge plasma of a stellarator with an helical magnetic axis is presented. Three coupled field equations, describing the collisional drift wave dynamics in the linear approximation, are solved as an initial-value problem along the magnetic field line. The magnetohydrodynamic equilibrium is obtained from a three-dimensional local equilibrium model. The use of a local magnetohydrodynamic equilibrium model allows for a computationally efficient systematic study of the impact of the magnetic field structure on drift wave stability.
Complexity Reduction of Collisional-Radiative Kinetics for Atomic Plasma
2013-12-23
or disclose the work. 14. ABSTRACT Thermal non- equilibrium processes in partially ionized plasmas can be most accurately modeled by collisional...prohibitively large, making multidimensional and unsteady simulations of non- equilibrium radiating plasma particularly challenging. In this paper, we...published online 23 December 2013) Thermal non- equilibrium processes in partially ionized plasmas can be most accurately modeled by collisional
NASA Astrophysics Data System (ADS)
Shaing, K. C.; Sabbagh, S. A.
2016-07-01
Theory for neoclassical toroidal plasma viscosity has been developed to model transport phenomena, especially, toroidal plasma rotation for tokamaks with broken symmetry. Theoretical predictions are in agreement with the results of the numerical codes in the large aspect ratio limit. The theory has since been extended to include effects of finite aspect ratio and finite plasma β. Here, β is the ratio of the plasma thermal pressure to the magnetic field pressure. However, there are cases where the radial wavelength of the self-consistent perturbed magnetic field strength B on the perturbed magnetic surface is comparable to the width of the trapped particles, i.e., bananas. To accommodate those cases, the theory for neoclassical toroidal plasma viscosity is further extended here to include the effects of the finite banana width. The extended theory is developed using the orbit averaged drift kinetic equation in the low collisionality regimes. The results of the theory can now be used to model plasma transport, including toroidal plasma rotation, in real finite aspect ratio, and finite plasma β tokamaks with the radial wavelength of the perturbed symmetry breaking magnetic field strength comparable to or longer than the banana width.
Perturbing macroscopic magnetohydrodynamic stability for toroidal plasmas
NASA Astrophysics Data System (ADS)
Comer, Kathryn J.
We have introduced a new perturbative technique to rapidly explore the dependence of long wavelength ideal magnetohydrodynamic (MHD) instabilities on equilibrium profiles, shaping properties, and wall parameters. Traditionally, these relations are studied with numerical parameter scans using computationally intensive stability codes. Our perturbative technique first finds the equilibrium and stability using traditional methods. Subsequent small changes in the original equilibrium parameters change the stability. We quickly find the new stability with an expansion of the energy principle, rather than with another run of the stability codes. We first semi-analytically apply the technique to the screw pinch after eliminating compressional Alfven wave effects. The screw pinch results validate the approach, but also indicate that allowable perturbations to equilibria with certain features may be restricted. Next, we extend the approach to toroidal geometry using experimental equilibria and a simple constructed equilibrium, with the ideal MHD stability code GATO. Stability properties are successfully predicted from perturbed toroidal equilibria when only the vacuum beyond the plasma is perturbed (through wall parameter variations), rather than the plasma itself. Small plasma equilibrium perturbations to both experimental and simple equilibria result in very large errors to the predicted stability, and valid results are found only over a narrow range of most perturbations. Despite the large errors produced when changing plasma parameters, the wall perturbations revealed two useful applications of this technique. Because the calculations are non-iterative matrix multiplications, the convergence issues that can disrupt a full MHD stability code are absent. Marginal stability, therefore, is much easier to find with the perturbative technique. Also, the perturbed results can be input as the initial guess for the eigenvalue for a full stability code, and improve subsequent
RF plasma heating in toroidal fusion devices
Golant, V.E.; Fedorov, V.I. )
1989-01-01
The purpose of the present book is to provide, in seven chapters, a unified overview of the methods for rf heating of plasmas in toroidal fusion experiments. In Chapter 1 the problem of plasma heating in tokamaks and stellarators is formulated and the requirements for auxiliary heating techniques are described. This chapter also contains a brief review of the results of research on tokamaks and stellarators. Chapter 2 is devoted to a theoretical description of the principal physical effects involved in the rf heating of plasmas, especially the characteristics of wave propagation, of the mechanisms by which waves are absorbed and plasma heating takes place, and of the nonlinear effects that accompany heating. The primary emphasis is on a qualitative physical picture of these effects. Chapters 3-6, in turn, deal with the major rf heating techniques currently under investigation, electron cyclotron (ECH), ion cyclotron (ICH), lower hybrid (LHH), and Alfven wave heating. In each of these chapters the main schemes for heating are described, the results of theoretical analyses and numerical simulations are discussed, the technology of the heating systems is briefly described, and experimental work published through the end of 1984 is reviewed. Finally, in Chapter 7 the different rf heating techniques are compared; they are contrasted with neutral beam injection, and the feasibility of adiabatic compression as a means of heating plasmas is examined. Separate abstracts were prepared for each chapter of this book. 246 refs.
Toroidal band limiter for a plasma containment device
Kelley, George G.
1978-01-01
This invention relates to a toroidal plasma confinement device having poloidal and toroidal magnetic fields for confining a toroidal plasma column with a plasma current induced therein along an endless, circular equilibrium axis in a torus vacuum cavity wherein the improvement comprises the use of a toroidal plasma band limiter mounted within the vacuum cavity in such a manner as to ensure that the plasma energy is distributed more uniformly over the limiter surface thereby avoiding intense local heating of the limiter while at the same time substantially preventing damage to the plasma containment wall of the cavity by the energetic particles diffusing out from the confined plasma. A plurality of poloidal plasma ring limiters are also utilized for containment wall protection during any disruptive instability that might occur during operation of the device.
Weak turbulence theory for collisional plasmas
NASA Astrophysics Data System (ADS)
Yoon, P. H.; Ziebell, L. F.; Kontar, E. P.; Schlickeiser, R.
2016-03-01
Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.
Weak turbulence theory for collisional plasmas.
Yoon, P H; Ziebell, L F; Kontar, E P; Schlickeiser, R
2016-03-01
Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.
High beta plasma operation in a toroidal plasma producing device
Clarke, John F.
1978-01-01
A high beta plasma is produced in a plasma producing device of toroidal configuration by ohmic heating and auxiliary heating. The plasma pressure is continuously monitored and used in a control system to program the current in the poloidal field windings. Throughout the heating process, magnetic flux is conserved inside the plasma and the distortion of the flux surfaces drives a current in the plasma. As a consequence, the total current increases and the poloidal field windings are driven with an equal and opposing increasing current. The spatial distribution of the current in the poloidal field windings is determined by the plasma pressure. Plasma equilibrium is maintained thereby, and high temperature, high beta operation results.
NASA Astrophysics Data System (ADS)
Shaing, K. C.; Lee, H.; Seol, J.; Aydemir, A. Y.
2015-08-01
Theory for neoclassical toroidal plasma viscosity in the low collisionality regime is extended to the vicinity of the magnetic axis in tokamaks with broken symmetry. The toroidal viscosity is induced by particles drifting off the perturbed magnetic surface under the influence of the symmetry breaking magnetic field. In the region away from the magnetic axis, the drift orbit dynamics is governed by the bounce averaged drift kinetic equation in the low collisionality regimes. In the vicinity of the magnetic axis, it is the drift kinetic equation, averaged over the trapped particle orbits, i.e., potato orbits, that governs the drift dynamics. The orbit averaged drift kinetic equation is derived when collision frequency is low enough for trapped particles to complete their potato trajectories. The resultant equation is solved in the 1 /ν regime to obtain transport fluxes and, thus, toroidal plasma viscosity through flux-force relation. Here, ν is the collision frequency. The viscosity does not vanish on the magnetic axis, and has the same scalings as that in the region away from magnetic axis, except that the fraction of bananas is replaced by the fraction of potatoes. It also has a weak radial dependence. Modeling of plasma flow velocity V for the case where the magnetic surfaces are broken is also discussed.
The effect of sheared toroidal rotation on pressure driven magnetic islands in toroidal plasmas
NASA Astrophysics Data System (ADS)
Hegna, C. C.
2016-05-01
The impact of sheared toroidal rotation on the evolution of pressure driven magnetic islands in tokamak plasmas is investigated using a resistive magnetohydrodynamics model augmented by a neoclassical Ohm's law. Particular attention is paid to the asymptotic matching data as the Mercier indices are altered in the presence of sheared flow. Analysis of the nonlinear island Grad-Shafranov equation shows that sheared flows tend to amplify the stabilizing pressure/curvature contribution to pressure driven islands in toroidal tokamaks relative to the island bootstrap current contribution. As such, sheared toroidal rotation tends to reduce saturated magnetic island widths.
Collisional Ionization Equilibrium for Optically Thin Plasmas
NASA Technical Reports Server (NTRS)
Bryans, P.; Mitthumsiri, W.; Savin, D. W.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.
2006-01-01
Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and their reliability are often highly suspect. We have utilized state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He to Zn. We have also utilized state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H to Zn. Using our data and the recommended electron impact ionization data of Mazzotta et al. (1998), we have calculated improved collisional ionization equilibrium calculations. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. (1998) for all elements from H to Ni, and with the fractional abundances derived from the modern DR and RR calculations of Gu (2003a,b, 2004) for Mg, Si, S, Ar, Ca, Fe, and Ni.
Confinement Time Exceeding One Second for a Toroidal Electron Plasma
Marler, J. P.; Stoneking, M. R.
2008-04-18
Nearly steady-state electron plasmas are trapped in a toroidal magnetic field for the first time. We report the first results from a new toroidal electron plasma experiment, the Lawrence Non-neutral Torus II, in which electron densities on the order of 10{sup 7} cm{sup -3} are trapped in a 270 deg. toroidal arc (670 G toroidal magnetic field) by application of trapping potentials to segments of a conducting shell. The total charge inferred from measurements of the frequency of the m=1 diocotron mode is observed to decay on a 3 s time scale, a time scale that approaches the predicted limit due to magnetic pumping transport. Three seconds represents {approx_equal}10{sup 5} periods of the lowest frequency plasma mode, indicating that nearly steady-state conditions are achieved.
Kinetic Stress and Intrinsic Flow in a Toroidal Plasma
NASA Astrophysics Data System (ADS)
Ding, W. X.; Lin, L.; Brower, D. L.; Almagri, A. F.; Chapman, B. E.; Fiksel, G.; Den Hartog, D. J.; Sarff, J. S.
2013-02-01
A new mechanism for intrinsic plasma flow has been experimentally identified in a toroidal plasma. For reversed field pinch plasmas with a few percent β (ratio of plasma pressure to magnetic pressure), measurements show that parallel pressure fluctuations correlated with magnetic fluctuations create a kinetic stress that can affect momentum balance and the evolution of intrinsic plasma flow. This implies kinetic effects are important for flow generation and sustainment.
Profiling compact toroid plasma density on CTIX with laser deflection
NASA Astrophysics Data System (ADS)
Brockington, Samuel Joseph Erwin
A laser deflectometer measures line-integrated plasma density gradient using laser diodes and amplified point detectors. A laser passing through an optically thin plasma is refracted by an amount proportional to the line-integrated electron density gradient. I have designed, installed, and operated a deflection diagnostic for the Compact Toroid Injection Experiment (CTIX), a plasma rail gun which can create compact toroid (CT) plasmas of controllable density and velocity. The diagnostic design and motivation are discussed, as well as three experiments performed with deflectometry. Thus, my thesis consists of the design of the deflectometer diagnostic, a comparison of its accuracy to interferometer density measurements, and finally a survey of compact toroid density profiles in two dimensions conducted with an array of detectors.
Toroidal midplane neutral beam armor and plasma limiter
Kugel, H.W.; Hand, S.W. Jr.; Ksayian, H.
1985-05-31
This invention contemplates an armor shield/plasma limiter positioned upon the inner wall of a toroidal vacuum chamber within which is magnetically confined an energetic plasma in a tokamak nuclear fusion reactor. The armor shield/plasma limiter is thus of a general semi-toroidal shape and is comprised of a plurality of adjacent graphite plates positioned immediately adjacent to each other so as to form a continuous ring upon and around the toroidal chamber's inner wall and the reactor's midplane coil. Each plate has a generally semi-circular outer circumference and a recessed inner portion and is comprised of upper and lower half sections positioned immediately adjacent to one another along the midplane of the plate. With the upper and lower half sections thus joined, a channel or duct is provided within the midplane of the plate in which a magnetic flux loop is positioned. The magnetic flux loop is thus positioned immediately adjacent to the fusing toroidal plasma and serves as a diagnostic sensor with the armor shield/plasma limiter minimizing the amount of power from the energetic plasma as well as from the neutral particle beams heating the plasma incident upon the flux loop.
Achieving Long Confinement in a Toroidal Electron Plasma
Marler, J. P.; Smoniewski, J.; Ha Bao; Stoneking, M. R.
2009-03-30
We observe the m = 1 diocotron mode in a partial toroidal trap, and use it as the primary diagnostic for observing the plasma confinement. The frequency of the m = 1 mode, which is approximately proportional to the trapped charge, decays on a three second timescale. The confinement time exceeds, by at least an order of magnitude, the confinement observed in all other toroidal traps for non-neutral plasmas and approaches the theoretical limit set by magnetic pumping transport. Numerical simulations that include toroidal effects are employed to accurately extract plasma charge, equilibrium position and m = 1 mode amplitude from the experimental data. Future work will include attempts to withdraw the electron source in order to study confinement in a full torus.
Effect of toroidal plasma rotation on double tearing modes in cylindrical geometry
NASA Astrophysics Data System (ADS)
Zhang, R. B.; Lu, X. Q.; Huang, Q. H.; Dong, J. Q.; Gong, X. Y.
2016-12-01
The effect of toroidal plasma rotation on q = 3 double tearing modes (DTMs) was studied numerically in cylindrical geometry using the method of reduced magnetohydrodynamic simulation. The results indicate that toroidal plasma rotation can reduce the growth rate of DTMs, but the magnitude of toroidal velocity has weak effect, especially without shear. When the shear of toroidal velocity exists, the suppression effect becomes better. Whether the velocity flow has shear or not, the growth rate of DTMs decreases as the magnitude of toroidal velocity increases. With the increase of velocity shear, the DTMs grow slowly. And the suppression effect of toroidal plasma rotation in early growth and transition stage is better, which means that the toroidal plasma rotation can suppress the linear growth of islands. Furthermore, the toroidal plasma rotation can suppress the evolution of poloidal stream. And the toroidal velocity shear on the q = 3 rational surface is more dominant than the magnitude of toroidal velocity in determining the DTM characteristics.
Stellarator approach to toroidal plasma confinement
Johnson, J.L.
1981-12-01
An overview is presented of the development and current status of the stellarator approach to controlled thermonuclear confinement. Recent experimental, theoretical, and systems developments have made this concept a viable option for the evolution of the toroidal confinement program. Some experimental study of specific problems associated with departure from two-dimensional symmetry must be undertaken before the full advantages and opportunities of steady-state, net-current-free operation can be realized.
Impact of plasma poloidal rotation on resistive wall mode instability in toroidally rotating plasmas
Aiba, N.; Shiraishi, J.; Tokuda, S.
2011-02-15
Stability of resistive wall mode (RWM) is investigated in a cylindrical plasma and an axisymmetric toroidal plasma by taking into account not only toroidal rotation but also poloidal rotation. Since the Doppler shifted frequency is responsible for the RWM stability, the modification of this Doppler shifted frequency by poloidal rotation affects the rotation effect on RWM. When a poloidal rotation frequency is not so large, the effect of poloidal rotation on the RWM stability can be approximately treated with the modified toroidal rotation frequency. In a toroidal plasma, this modified frequency is determined by subtracting a toroidal component of the rotation parallel to the magnetic field from the toroidal rotation frequency. The poloidal rotation that counteracts the effect of the Doppler shift strongly reduces the stabilizing effect of toroidal rotation, but by changing the rotational direction, the poloidal rotation enhances this stabilizing effect. This trend is confirmed in not only a cylindrical plasma but also a toroidal plasma. This result indicates that poloidal rotation produces the dependence of the critical toroidal rotation frequency for stabilizing RWM on the rotational direction of toroidal rotation in the same magnetic configuration.
Does the Bohm Criterion have meaning for collisional plasmas?
NASA Astrophysics Data System (ADS)
Severn, Greg; Yip, Chi-Shung; Nourgostar, Sirous; Hershkowitz, Noah
2014-10-01
Theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question of whether there exists a collisionally modified Bohm Criterion (CMBC) is often answered in the negative, and it is only a question of how the Bohm Criterion fails for the case of finite collisionality. The question is of importance considering that nearly all practical plasma processing applications involve plasmas of finite collisionality. There is, however, very little experimental work to help choose between competing models of how Bohm's Criterion fails. The question of critical importance is this: in plasmas of finite collisionality, do ions reach the Bohm speed at the location where the quasineutral plasma ends and where space charge appears? We have begun to examine the question experimentally in single ion species plasmas, and our goal is to vary the ion-neutral mean free path λ within the interval 1 < λ /λD <103 , where λD is the Debye length, and to present both plasma potential data and ion velocity distribution function profiles, measured by emissive probes and by LIF, respectively, to help us understand and assess the validity of theoretical claims. Work supported by NSF Grant No. PHY-1206421, CBET-0903783, and CBET-0903832, and U.S. Department of Energy (DOE) Grant Nos. DE-FG02- 97ER54437 and DE FG02- 03ER54728.
Antenna excitation of drift wave in a toroidal plasma
Diallo, A.; Ricci, P.; Fasoli, A.; Furno, I.; Labit, B.; Mueller, S. H.; Podesta, M.; Poli, F. M.; Skiff, F.
2007-10-15
In a magnetized toroidal plasma, an antenna tunable in vertical wave number is used to excite density perturbations. Coherent detection is performed by means of Langmuir probes to directly determine both the wave vector and the plasma response induced by the antenna. Comparison between the theoretical density response predicted by the generalized Hasegawa-Wakatani model, and the experimentally determined density response enables us the identification of one peak of the plasma response as a drift wave.
Control of impurities in toroidal plasma devices
Ohkawa, Tihiro
1980-01-01
A method and apparatus for plasma impurity control in closed flux plasma systems such as Tokamak reactors is disclosed. Local axisymmetrical injection of hydrogen gas is employed to reverse the normally inward flow of impurities into the plasma.
Toroidal modeling of plasma response to RMP fields in ITER
NASA Astrophysics Data System (ADS)
Li, L.; Liu, Y. Q.; Wang, N.; Kirk, A.; Koslowski, H. R.; Liang, Y.; Loarte, A.; Ryan, D.; Zhong, F. C.
2017-04-01
A systematic numerical study is carried out, computing the resistive plasma response to the resonant magnetic perturbation (RMP) fields for ITER plasmas, utilizing the toroidal code MARS-F (Liu et al 2000 Phys. Plasmas 7 3681). A number of factors are taken into account, including the variation of the plasma scenarios (from 15 MA Q = 10 inductive scenario to the 9 MA Q = 5 steady state scenario), the variation of the toroidal spectrum of the applied fields (n = 1, 2, 3, 4, with n being the toroidal mode number), the amplitude and phase variation of the currents in three rows of the RMP coils as designed for ITER, and finally a special case of mixed toroidal spectrum between the n = 3 and n = 4 RMP fields. Two-dimensional parameter scans, for the edge safety factor and the coil phasing between the upper and lower rows of coils, yield ‘optimal’ curves that maximize a set of figures of merit, that are defined in this work to measure the plasma response. Other two-dimensional scans of the relative coil current phasing among three rows of coils, at fixed coil currents amplitude, reveal a single optimum for each coil configuration with a given n number, for the 15 MA ITER inductive plasma. On the other hand, scanning of the coil current amplitude, at fixed coil phasing, shows either synergy or cancellation effect, for the field contributions between the off-middle rows and the middle row of the RMP coils. Finally, the mixed toroidal spectrum, by combining the n = 3 and the n = 4 RMP field, results in a substantial local reduction of the amplitude of the plasma surface displacement.
Experimental Realization of Nearly Steady-State Toroidal Electron Plasmas
NASA Astrophysics Data System (ADS)
Stoneking, M. R.
2008-11-01
Non-neutral plasmas are routinely confined in the uniform magnetic field of a Penning-Malmberg trap for arbitrarily long times and approach thermal equilibrium. Theory predicts that dynamically stable and therefore long-lived equilibria exist for non-neutral plasmas confined in the curved, non-uniform field of a toroidal trap, but that ultimately thermal equilibrium states do not exist. On long timescales, the poloidal ExB rotation through the non-uniform toroidal magnetic field leads to magnetic pumping transport. A new experiment has, for the first time, demonstrated the existence of a stable, long-lived (i.e. nearly steady-state) toroidal equilibrium for pure electron plasmas and is poised to observe the magnetic pumping transport mechanism. Electron plasmas with densities of order 10^6 cm-3 are trapped in the Lawrence Non-neutral Torus II for several seconds. LNT II is a high aspect ratio (Ro/a 10), partially toroidal trap (a 270^o arc with Bo=670 G). The m=1 diocotron mode is launched and detected using isolated segments of a fully-sectored conducting boundary and its frequency is used to determine the total trapped charge as a function of time. The observed confinement time ( 3 s) approaches the theoretical limit ( 6 s) set by the magnetic pumping transport mechanism of Crooks and O'Neil. We also present equilibrium modeling and numerical simulation of the toroidal m=1 mode constrained by experimental data. Future work includes the identification of the dominant transport mechanisms via confinement scaling experiments and measurement of the m=2 mode frequency, and development of a strategy for making a transition to fully toroidal confinement. J.P. Marler and M.R. Stoneking, Phys. Rev. Lett. 100, 155001 (2008). S.M. Crooks and T.M. O'Neil, Phys Plamas 3, 2533 (1996).
Magnetosonic wave in pair-ion electron collisional plasmas
NASA Astrophysics Data System (ADS)
Hussain, S.; Hasnain, H.
2017-03-01
Low frequency magnetosonic waves in positive and negative ions of equal mass and opposite charges in the presence of electrons in collisional plasmas are studied. The collisions of ions and electrons with neutrals are taken into account. The nonlinearities in the plasma system arise due to ion and electrons flux, Lorentz forces, and plasma current densities. The reductive perturbation method is applied to derive the Damped Korteweg de Vries (DKdV) equation. The time dependent solution of DKdV is presented. The effects of variations of different plasma parameters on propagation characteristics of magnetosonic waves in pair-ion electron plasma in the context of laboratory plasmas are discussed.
Toroidal Plasma Thruster for Interplanetary and Interstellar Space Flights
N.N. Gorelenkov; L.E. Zakharov; and M.V. Gorelenkova
2001-07-11
This work involves a conceptual assessment for using the toroidal fusion reactor for deep space interplanetary and interstellar missions. Toroidal thermonuclear fusion reactors, such as tokamaks and stellarators, are unique for space propulsion, allowing for a design with the magnetic configuration localized inside toroidal magnetic field coils. Plasma energetic ions, including charged fusion products, can escape such a closed configuration at certain conditions, a result of the vertical drift in toroidal rippled magnetic field. Escaping particles can be used for direct propulsion (since toroidal drift is directed one way vertically) or to create and heat externally confined plasma, so that the latter can be used for propulsion. Deuterium-tritium fusion neutrons with an energy of 14.1 MeV also can be used for direct propulsion. A special design allows neutrons to escape the shield and the blanket of the tokamak. This provides a direct (partial) conversion of the fusion energy into the directed motion of the propellant. In contrast to other fusion concepts proposed for space propulsion, this concept utilizes the natural drift motion of charged particles out of the closed magnetic field configuration.
Anomalous toroidal field penetration in Tormac V
Feinberg, B.; Vaucher, B. G.; Shaw, R. S.; Vella, M. C.
1981-07-01
We investigate magnetic field penetration into a cool, collisional, magnetized plasma in Tormac V. Magnetic probe and laser interferometer studies reveal anomalous penetration of the applied toroidal field into a plasma with an initial parallel bias toroidal field. The applied poloidal field, however, formed a well-defined magnetic front which was effective at sweeping up particles. Lastly, strong shear in the vacuum magnetic field does not inhibit the apparent decoupling of the applied toroidal field from the applied poloidal field.
Non-axisymmetric magnetic fields and toroidal plasma confinement
NASA Astrophysics Data System (ADS)
Boozer, Allen H.
2015-02-01
The physics of non-axisymmetry is a far more important topic in the theory of toroidal fusion plasmas than might be expected. (1) Even a small toroidal asymmetry in the magnetic field strength, δ ≡ ∂ln B/∂φ ˜ 10-4, can cause an unacceptable degradation in performance. (2) Nevertheless, asymmetries—even large asymmetries δ ˜ 1—can give beneficial plasma control and circumvent issues, such as magnetic-configuration maintenance and plasma disruptions, that make axisymmetric fusion devices problematic. Viewed from prospectives that are adequate for designing and studying axisymmetric plasmas, the physics of non-axisymmetric plasmas appears dauntingly difficult. Remarkably, Maxwell's equations provide such strong constraints on the physics of toroidal fusion plasmas that even a black-box model of a plasma answers many important questions. Kinetic theory and non-equilibrium thermodynamics provide further, but more nuanced, constraints. This paper is organized so these constraints can be used as a basis for the innovations and for the extrapolations that are required to go from existing experiments to fusion systems. Outlines are given of a number of calculations that would be of great importance to ITER and to the overall fusion program and that could be carried out now with limited resources.
Solitary perturbations in the steep boundary of magnetized toroidal plasma
NASA Astrophysics Data System (ADS)
Lee, J. E.; Yun, G. S.; Lee, W.; Kim, M. H.; Choi, M.; Lee, J.; Kim, M.; Park, H. K.; Bak, J. G.; Ko, W. H.; Park, Y. S.
2017-03-01
Solitary perturbations (SPs) localized both poloidally and radially are detected within ~100 μs before the partial collapse of the high pressure gradient boundary region (called pedestal) of magnetized toroidal plasma in the KSTAR tokamak device. The SP develops with a low toroidal mode number (typically unity) in the pedestal ingrained with quasi-stable edge-localized mode (QSM) which commonly appears during the inter-collapse period. The SPs have smaller mode pitch and different (often opposite) rotation velocity compared to the QSMs. Similar solitary perturbations are also frequently observed before the onset of complete pedestal collapse, suggesting a strong connection between the SP generation and the pedestal collapse.
NASA Astrophysics Data System (ADS)
Camporeale, E.; Pezzi, O.; Valentini, F.
2015-12-01
The longstanding problem of collisions in plasmas is a very fascinating and huge topic in plasma physics. The 'natural' operator that describes the Coulombian interactions between charged particles is the Landau (LAN) integral operator. The LAN operator is a nonlinear, integro-differential and Fokker-Planck type operator which satisfies the H theorem for the entropy growth. Due to its nonlinear nature and multi-dimensionality, any approach to the solution of the Landau integral is almost prohibitive. Therefore collisions are usually modeled by simplified collisional operators. Here collisional effects are modeled by i) the one-dimensional Lenard-Bernstein (LB) operator and ii) the three-dimensional Dougherty (DG) operator. In the first case i), by focusing on a 1D-1V phase space, we study recurrence effects in a weakly collisional plasma, being collisions modeled by the LB operator. By decomposing the linear Vlasov-Poisson system in the Fourier-Hermite space, the recurrence problem is investigated in the linear regime of the damping of a Langmuir wave and of the onset of the bump-on-tail instability. The analysis is then confirmed and extended to the nonlinear regime through a Eulerian collisional Vlasov-Poisson code. Despite being routinely used, an artificial collisionality is not in general a viable way of preventing recurrence in numerical simulations. Moreover, recursive phenomena affect both the linear exponential growth and the nonlinear saturation of a linear instability by producing a fake growth in the electric field, thus showing that, although the filamentation is usually associated with low amplitude fluctuations contexts, it can occur also in nonlinear phenomena. On the other hand ii), the effects of electron-electron collisions on the propagation of nonlinear electrostatic waves are shown by means of Eulerian simulations in a 1D-3V (one dimension in physical space, three dimensions in velocity space) phase space. The nonlinear regime of the symmetric
Collisional Radiative Models for non-Maxwellian plasmas
NASA Astrophysics Data System (ADS)
Hartgers, Bart; van Dijk, Jan; van der Mullen, Joost
1999-10-01
Collisional Radiative models are a useful tool for studying plasmas. In their simplest form, they are used to calculate an atomic state distribution function (ASDF) from given electron and neutral densities and an electron temperature. Additionally, global ionization and recombination coefficients can be calculated as a function of electron density and temperature. In turn, these coefficients are used as input for the general plasma model
Toroidal midplane neutral beam armor and plasma limiter
Kugel, Henry W.; Hand Jr, Samuel W.; Ksayian, Haig
1986-02-04
For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.
Toroidal midplane neutral beam armor and plasma limiter
Kugel, Henry W.; Hand, Jr, Samuel W.; Ksayian, Haig
1986-01-01
For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.
Bounce-Transit and Drift Resonance and Neoclassical Toroidal Plasma Viscosity in Tokamaks
NASA Astrophysics Data System (ADS)
Shaing, K. C.; Chu, M. S.; Sabbagh, S. A.
2009-05-01
The importance of the resonance between the bounce frequency of the trapped particles and precession drift frequency in tokamaks to the low frequency magnetohydroynamic instabilities has been recognized for a long time. The resonance is also important in the transport processes as demonstrated by Park, et al. in calculating the neoclassical toroidal plasma viscosity [1]. They found that the transport fluxes are independent of the collision frequency, i.e., a resonant plateau regime. Here, we develop a theory for neoclassical toroidal plasma viscosity to include not only the bounce and drift resonance of the trapped particles but also the transit and drift resonance the circulating particles [2]. In the resonant plateau regime, our results are similar to those obtained by Park, et al., except that bounce average over the trapped particle trajectories is not performed and that the contributions from the circulating particles are included. In the collisional limit, it is found that the resonant plateau regime is connected to the Pfirsch-Schluter regime. [1] PARK, J.-K.,et al., IAEA,Fusion Energy Conference, Geneva, October 2008, Paper EX/5-3Rb. [2] SHAING, K. C., CHU, M. S., and SABBAGH, S. A., (to be submitted to Plasma Phys. Control. Fusion)
Collisional Effects in Complex (Dusty) Plasmas
Khrapak, S. A.
2008-09-07
This is a short overview of recent results demonstrating the importance of ion-neutral collisions for different processes naturally occurring in complex (dusty) plasmas. Most important developments are briefly discussed and relevant references are provided.
A novel electron density reconstruction method for asymmetrical toroidal plasmas
Shi, N.; Ohshima, S.; Minami, T.; Nagasaki, K.; Yamamoto, S.; Mizuuchi, T.; Okada, H.; Kado, S.; Kobayashi, S.; Konoshima, S.; Sano, F.; Tanaka, K.; Ohtani, Y.; Zang, L.; Kenmochi, N.
2014-05-15
A novel reconstruction method is developed for acquiring the electron density profile from multi-channel interferometric measurements of strongly asymmetrical toroidal plasmas. It is based on a regularization technique, and a generalized cross-validation function is used to optimize the regularization parameter with the aid of singular value decomposition. The feasibility of method could be testified by simulated measurements based on a magnetic configuration of the flexible helical-axis heliotron device, Heliotron J, which has an asymmetrical poloidal cross section. And the successful reconstruction makes possible to construct a multi-channel Far-infrared laser interferometry on this device. The advantages of this method are demonstrated by comparison with a conventional method. The factors which may affect the accuracy of the results are investigated, and an error analysis is carried out. Based on the obtained results, the proposed method is highly promising for accurately reconstructing the electron density in the asymmetrical toroidal plasma.
Ion loss in weakly collisional three ion species plasmas
NASA Astrophysics Data System (ADS)
Hershkowitz, Noah; Yip, Chi-Shung; Severn, Greg
2016-10-01
Ion velocity distribution functions (ivdfs) at sheath-presheath boundaries are studied with laser-induced fluorescence in weakly collisional Xe-Kr-Ar and Xe-Ar-Ne plasmas using tunable diode lasers for Ar + and Xe + ions. The argon and xenon ivdfs are measured at the sheath-presheath boundary near a negatively biased boundary plate. The plasma potential profiles are measured by an emissive probe throughout the sheath and presheath. Relative ion concentrations resulting from the neutral gas mixtures are calculated using G-H. Kim's loss-production balance method. Ne + and Kr + ions are added to plasmas with approximately equal amounts of Ar + and Xr + ions, where Ar + and Xe + ions are previously observed to reach the sheath edge at nearly the system sound speed. In two ion species plasmas, instability enhanced collisional friction was demonstrated to dictate the escape velocities of the ions. When three ion species are present, it is demonstrated that as the concentration of the third ion species increases, Xe + and Ar + ion velocities at the sheath edge deviates from the common sound speed and approach their individual Bohm velocities. These observations are consistent with the predictions of the instability enhanced collisional friction theory This work was supported by NSF under Grant No. 1464741 and U.S. DOE under Grant No. DE-SC00114226.
Experimental realization of nearly steady-state toroidal electron plasmas
Stoneking, M. R.; Ha, B. N.; Smoniewski, J.; Marler, J. P.
2009-05-15
Electron plasmas with densities of 5x10{sup 6} cm{sup -3} are trapped in the Lawrence Non-neutral Torus II (LNT II) for times exceeding 1 s. LNT II is a high aspect ratio (R{sub 0}/a > or approx.10) partially toroidal trap (270 deg. arc, B{sub 0}=670 G). The m=1 diocotron mode is launched and detected using isolated segments of a fully sectored conducting boundary and its frequency is used to determine the total trapped charge as a function of time. The observed confinement time ({approx_equal}3 s) approaches the theoretical limit ({approx_equal}6 s) set by the magnetic pumping transport mechanism of Crooks and O'Neil [Phys. Plasmas 3, 2533 (1996)]. We also present equilibrium modeling and numerical simulations of the toroidal m=1 mode constrained by experimental data. Future work includes the identification of the dominant transport mechanisms via confinement scaling experiments and measurement of the m=2 mode frequency and development of a strategy for making a transition to fully toroidal confinement.
Solitary perturbations in the steep boundary of magnetized toroidal plasma
Lee, J. E.; Yun, G. S.; Lee, W.; Kim, M. H.; Choi, M.; Lee, J.; Kim, M.; Park, H. K.; Bak, J. G.; Ko, W. H.; Park, Y. S.
2017-01-01
Solitary perturbations (SPs) localized both poloidally and radially are detected within ~100 μs before the partial collapse of the high pressure gradient boundary region (called pedestal) of magnetized toroidal plasma in the KSTAR tokamak device. The SP develops with a low toroidal mode number (typically unity) in the pedestal ingrained with quasi-stable edge-localized mode (QSM) which commonly appears during the inter-collapse period. The SPs have smaller mode pitch and different (often opposite) rotation velocity compared to the QSMs. Similar solitary perturbations are also frequently observed before the onset of complete pedestal collapse, suggesting a strong connection between the SP generation and the pedestal collapse. PMID:28338046
Peeters, A G; Angioni, C; Strintzi, D
2007-06-29
In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.
Modeling collisional processes in plasmas using discontinuous numerical methods
NASA Astrophysics Data System (ADS)
Miller, Sean
Fluid-based plasma models are typically applied to parameter regimes where a local thermal equilibrium is assumed. The applicability of this regime is valid for many plasmas, however, it is limited to plasma dynamics dominated by collisional effects. This study attempts to extend the validity of the collisional fluid regime using an anisotropic 13-moment fluid model derived from the Pearson type-IV probability distribution. The model explicitly evolves the heat flux hyperbolically alongside the density, momentum, and energy in order to capture dynamics usually restricted to costly kinetic models. Each particle species is modeled individually and collectively coupled through electromagnetic and collision operators. To remove electromagnetic divergence errors inherent to numerical representations of Maxwell's equations, both hyperbolic and parabolic cleaning methods are presented. The plasma models are implemented using high-order finite volume and discontinuous Galerkin numerical methods designed for unstructured meshes. The unstructured code framework, numerical methods, and plasma models were developed in the University of Washington's WARPXM code for use on heterogeneous accelerated clusters.
Quasi-collisional Magneto-optic Effects in Collisionless Plasmas
NASA Astrophysics Data System (ADS)
Keenan, Brett; Ford, Alex; Medvedev, Mikhail
2016-03-01
High-amplitude, chaotic/turbulent electromagnetic fluctuations are ubiquitous in astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on ``sub-Larmor scales'' -- scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch-angles, thus establishing diffusive transport on long time-scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective ``collision'' frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma ``quasi-collisionality'', may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified magneto-optic effects in these plasmas provide an attractive, novel radiative diagnostic tool for the exploration and characterization of small-scale magnetic turbulence.
Harris, J.H.; Murakami, M.; Baylor, L.R.; Bell, J.D.; Bigelow, T.S.; Carreras, B.A.; Colchin, R.J.; Crume, E.C. Jr.; Dominguez, N.; Dory, R.A.; Dunlap, J.L.; Dyer, G.R.; England, A.C.; Glowienka, J.C.; Hillis, D.L.; Hiroe, S.; Howe, H.C.; Hutchinson, D.P.; Isler, R.C.; Jernigan, T.C.; Langley, R.A.; Leboeuf, J.N.; Lee, D.K.; Lyon, J.F.; Ma, C.H.; Rasmussen, D.A.; Simpkins, J.E.; Uckan, T.; Vander Sluis, K.L.; Wilgen, J.B.; Win
1991-01-01
In low-collisionality plasmas confined in tokamaks and stellarators, instabilities driven by particles trapped in inhomogeneities of the magnetic fields could be important in increasing plasma transport coefficients. In the Advanced Toroidal Facility (ATF), an {ell} = 2, M = 12 field-period stellarator device with major radius R = 2.1 m, average plasma minor radius a = 0.27 m, central and edge rotational transforms {chi}{sub 0} {approx} 0.3, {chi}{sub a} {approx} 1, the effects of electron trapping in the helical stellarator field are expected to be important in plasmas with {bar n}{sub e} {approx} 5 {times} 10{sup 12} cm{sup {minus}3}, T{sub e0} {approx} 1 keV. Such plasmas have already been sustained for long-pulses (20 s) using 150--400 kW of 53.2-GHz ECH power at B = 0.95 T. Transport analysis shows that for {rho} = r/a {le} 1/3, the electron anomalous transport is {le}10 times the neoclassical value, while at {rho} = 2/3 it is 10--100 times neoclassical; this is compatible with expectations for transport enhancement due to dissipative trapped-electron modes. 4 refs., 3 figs.
Transport scaling in interchange-driven toroidal plasmas
Ricci, Paolo; Rogers, B. N.
2009-06-15
Two-dimensional fluid simulations of a simple magnetized torus are presented, in which the vertical and toroidal components of the magnetic field create helicoidal field lines that terminate on the upper and lower walls of the plasma chamber. The simulations self-consistently evolve the full radial profiles of the electric potential, density, and electron temperature in the presence of three competing effects: the cross-field turbulent transport driven by the interchange instability, parallel losses to the upper and lower walls, and the input of particles and heat by external plasma sources. Considering parameter regimes in which equilibrium ExB shear flow effects are weak, we study the dependence of the plasma profiles--in particular the pressure profile scale length--on the parameters of the system. Analytical scalings are obtained that show remarkable agreement with the simulations.
Simulations of a molecular plasma in collisional-radiative nonequilibrium
NASA Technical Reports Server (NTRS)
Cambier, Jean-Luc; Moreau, Stephane
1993-01-01
A code for the simulation of nonequilibrium plasmas is being developed, with the capability to couple the plasma fluid-dynamics for a single fluid with a collisional-radiative model, where electronic states are treated as separate species. The model allows for non-Boltzmann distribution of the electronic states. Deviations from the Boltzmann distributions are expected to occur in the rapidly ionizing regime behind a strong shock or in the recombining regime during a fast expansion. This additional step in modeling complexity is expected to yield more accurate predictions of the nonequilibrium state and the radiation spectrum and intensity. An attempt at extending the code to molecular plasma flows is presented. The numerical techniques used, the thermochemical model, and the results of some numerical tests are described.
A model Monte Carlo collision operator for toroidal plasmas
NASA Astrophysics Data System (ADS)
Mukhtar, Q.; Hellsten, T.; Johnson, T.
2013-10-01
In order to simulate radio refquency (RF)-heating in toroidal plasmas in the banana regime a model collision operator has been developed, which relaxes the distribution function towards a prescribed local Maxwellian either determined by experiments or transport codes. The pitch angle scattering by Coulomb collisions gives rise to spatial diffusion in toroidal plasmas because of the coupling between spatial and velocity coordinates. The coupling between the spatial and velocity components results in drift terms in the Monte Carlo formulation of the Fokker-Planck equation due to spatial derivatives of the Jacobian, the fraction of the trapped particles, the density and the temperature profiles. A simple RF operator is used to test the collision operator in conjunction with RF heating. The formation of a high-energy tail on the distribution function during RF heating leads to reduction of the density of the thermal ions as the tail builds up. For central heating this reduction can lead to hollow density profiles of thermal ions. The spatial diffusion caused by the relaxation of the thermal ions towards a prescribed density profile then gives rise to an increase of the density of resonant ions in regions with strong heating where the thermal ions diffuse towards higher energies.
Nonlinear transport processes in tokamak plasmas. I. The collisional regimes
NASA Astrophysics Data System (ADS)
Sonnino, Giorgio; Peeters, Philippe
2008-06-01
An application of the thermodynamic field theory (TFT) to transport processes in L-mode tokamak plasmas is presented. The nonlinear corrections to the linear ("Onsager") transport coefficients in the collisional regimes are derived. A quite encouraging result is the appearance of an asymmetry between the Pfirsch-Schlüter (P-S) ion and electron transport coefficients: the latter presents a nonlinear correction, which is absent for the ions, and makes the radial electron coefficients much larger than the former. Explicit calculations and comparisons between the neoclassical results and the TFT predictions for Joint European Torus (JET) plasmas are also reported. It is found that the nonlinear electron P-S transport coefficients exceed the values provided by neoclassical theory by a factor that may be of the order 102. The nonlinear classical coefficients exceed the neoclassical ones by a factor that may be of order 2. For JET, the discrepancy between experimental and theoretical results for the electron losses is therefore significantly reduced by a factor 102 when the nonlinear contributions are duly taken into account but, there is still a factor of 102 to be explained. This is most likely due to turbulence. The expressions of the ion transport coefficients, determined by the neoclassical theory in these two regimes, remain unaltered. The low-collisional regimes, i.e., the plateau and the banana regimes, are analyzed in the second part of this work.
Electromagnetic drift waves dispersion for arbitrarily collisional plasmas
Lee, Wonjae Krasheninnikov, Sergei I.; Angus, J. R.
2015-07-15
The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvén wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionless and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvén wave instability with synergistic effects of high beta stabilization and Landau resonance.
An Extended Magnetohydrodynamics Model for Relativistic Weakly Collisional Plasmas
NASA Astrophysics Data System (ADS)
Chandra, Mani; Gammie, Charles F.; Foucart, Francois; Quataert, Eliot
2015-09-01
Black holes that accrete far below the Eddington limit are believed to accrete through a geometrically thick, optically thin, rotationally supported plasma that we will refer to as a radiatively inefficient accretion flow (RIAF). RIAFs are typically collisionless in the sense that the Coulomb mean free path is large compared to {GM}/{c}2, and relativistically hot near the event horizon. In this paper we develop a phenomenological model for the plasma in RIAFs, motivated by the application to sources such as Sgr A* and M87. The model is derived using Israel-Stewart theory, which considers deviations up to second order from thermal equilibrium, but modified for a magnetized plasma. This leads to thermal conduction along magnetic field lines and a difference in pressure, parallel and perpendicular to the field lines (which is equivalent to anisotropic viscosity). In the non-relativistic limit, our model reduces to the widely used Braginskii theory of magnetized, weakly collisional plasmas. We compare our model to the existing literature on dissipative relativistic fluids, describe the linear theory of the plasma, and elucidate the physical meaning of the free parameters in the model. We also describe limits of the model when the conduction is saturated and when the viscosity implies a large pressure anisotropy. In future work, the formalism developed in this paper will be used in numerical models of RIAFs to assess the importance of non-ideal processes for the dynamics and radiative properties of slowly accreting black holes.
Mechanism for blob generation in the TORPEX toroidal plasma
Furno, I.; Labit, B.; Fasoli, A.; Poli, F. M.; Ricci, P.; Theiler, C.; Brunner, S.; Diallo, A.; Graves, J. P.; Podesta, M.; Mueller, S. H.
2008-05-15
The mechanism for blob generation is detailed in the toroidal magnetized plasma of the TORPEX device [Fasoli et al., Phys. Plasmas 13, 055902 (2006)] using an experimental configuration, which features a plasma region dominated by a coherent wave and a region on the low field side characterized by the propagation of blobs. Predictions from linearized 2D drift-reduced Braginskii equations are compared with experimental data, revealing the interchange nature of the coherent wave. The dynamics of blob formation is investigated using time-resolved measurements of two-dimensional profiles of electron density, temperature, plasma potential and ExB velocity. Blobs form from radially elongated structures associated with the interchange wave. When a blob is generated, the following sequence of events is observed: 1) A decrease of local pressure gradient length provides an increase of the interchange mode drive; 2) in response, the interchange mode increases in amplitude and expands in the radial direction forming a radially elongated structure from the wave crest; 3) the elongated structure is convected by the ExB flow and is eventually sheared off, forming a blob on the low field side. The dependence of the blob amplitude upon the minimum pressure radial scale length before the blob ejection is also investigated.
Ion temperature and toroidal rotation in JET's low torque plasmas
NASA Astrophysics Data System (ADS)
Bernardo, J.; Nave, M. F. F.; Giroud, C.; Reyes Cortes, S.; Bizarro, João P. S.
2016-11-01
This paper reports on the procedure developed as the best method to provide an accurate and reliable estimation of the ion temperature Ti and the toroidal velocity vϕ from Charge-eXchange Recombination Spectroscopy (CXRS) data from intrinsic rotation experiments at the Joint European Torus with the carbon wall. The low impurity content observed in such plasmas, resulting in low active CXRS signal, alongside low Doppler shifts makes the determination of Ti and vϕ particularly difficult. The beam modulation method will be discussed along with the measures taken to increase photon statistics and minimise errors from the absolute calibration and magneto-hydro-dynamics effects that may impact the CXRS passive emission.
Toroidal modeling of interaction between resistive wall mode and plasma flow
Liu Yueqiang
2013-02-15
The non-linear interplay between the resistive wall mode (RWM) and the toroidal plasma flow is numerically investigated in a full toroidal geometry, by simultaneously solving the initial value problems for the n = 1 RWM and the n = 0 toroidal force balance equation. Here, n is the toroidal mode number. The neoclassical toroidal viscous torque is identified as the major momentum sink that brakes the toroidal plasma flow during the non-linear evolution of the RWM. This holds for a mode that is initially either unstable or stable. For an initially stable RWM, the braking of the flow, and hence the eventual growth of the mode, depends critically on the initial perturbation amplitude.
Self-focusing of electromagnetic pulsed beams in collisional plasmas
Faisal, Mohammad; Verma, M. P.; Sodha, Mahendra Singh
2008-10-15
In this paper, the self-focusing of an electromagnetic pulsed beam in a collisional plasma has been investigated in the paraxial approximation, following the formalism developed by Akhmanov. The energy balance equation for electrons, the equation expressing the equality of pressure gradient (of electrons and ions) to the force due to space charge field, and the equation for the beam width parameter f (obtained by following Akhmanov's approach) have been simultaneously solved for given initial (z=0) time profile of the pulse to obtain f as a function of {xi} (cz/{omega}r{sub 0}{sup 2}) and t{sup '}=t-z/V{sub g}, where V{sub g} is the group velocity. Both Gaussian and sine time profiles of the pulse have been investigated.
Collisional and radiative processes in high-pressure discharge plasmas
NASA Astrophysics Data System (ADS)
Becker, Kurt H.; Kurunczi, Peter F.; Schoenbach, Karl H.
2002-05-01
Discharge plasmas at high pressures (up to and exceeding atmospheric pressure), where single collision conditions no longer prevail, provide a fertile environment for the experimental study of collisions and radiative processes dominated by (i) step-wise processes, i.e., the excitation of an already excited atomic/molecular state and by (ii) three-body collisions leading, for instance, to the formation of excimers. The dominance of collisional and radiative processes beyond binary collisions involving ground-state atoms and molecules in such environments allows for many interesting applications of high-pressure plasmas such as high power lasers, opening switches, novel plasma processing applications and sputtering, absorbers and reflectors for electromagnetic waves, remediation of pollutants and waste streams, and excimer lamps and other noncoherent vacuum-ultraviolet light sources. Here recent progress is summarized in the use of hollow cathode discharge devices with hole dimensions in the range 0.1-0.5 mm for the generation of vacuum-ultraviolet light.
Transport, equilibrium, and stability of a toroidal edge plasma
McCarthy, D.R.
1992-01-01
The stability and transport of the drift resistive ballooning mode (DRBM) and its impact on the dynamics of a toroidal edge plasma is studied. The linear stability of the DRBM is calculated analytically and numerically, and is found to be unstable over a broad range of mode numbers. The nonlinear dynamics of the mode were studied using a fully linear, three dimensional finite difference code. It was found that the saturated turbulent transport was anomalously large and exhibited a large ballooning-like poloidal asymmetry. The growth and saturation of this mode occurred on the time scale t[sub B] = (c[sub s]/[radical]RL[sub n])[sup [minus]1]. Nonlinear two dimensional axisymmetric toroidal simulations of a tokamak edge and scrape off layer were performed to study the effect of this transport on the edge dynamics. Large parallel flows of order the local sound speed c[sub s] were generated on the longer time scale t[sub s] = (c[sub s]/qR)[sup [minus]1]. The stability of this [open quotes]equilibrium[close quotes] depends upon the parameter [alpha] = p[sub s]qR/aL[sub r]. For [alpha] [much lt] 1, the edge was unstable to the Stringer spin up instability. For weak magnetic pumping (H-mode), a poloidal rotation of order the poloidal sound speed ac[sub s]/qR was generated in the electron diamagnetic drift direction. For strong pumping (L-mode), the rotation opposed the ion diamagnetic drift. The impact of particle sources at various poloidal locations was also studied. For [alpha] > 1 the edge was unstable to the parallel velocity shear instability. The turbulence gave order unity fluctuation levels and was localized inside the last closed flux surface and on the inner side of the torus.
Collisional and Radiative Processes in High-Pressure Discharge Plasmas
NASA Astrophysics Data System (ADS)
Becker, Kurt
2001-10-01
High-pressure discharge plasmas (HPDPs) with operating pressures up to and exceeding atmospheric pressure have gained prominence in many areas of application such as EM absorbers and reflectors, remediation of waste streams, deposition and surface modification, surface cleaning and sterilization, and light source development. In particular, HPDPs are widely used as sources for the generation of non-coherent UV and VUV light such as excimer emissions in the spectral range from 50 nm to 300 nm using rare gases or rare gas admixed with other gases as the operating medium. In this talk we will discuss several common types of HPDPs (e.g. microhollow cathode discharge plasmas, dielectric barrier discharge plasmas, capillary dielectrode discharge plasmas) that are commonly used for the generation of non-coherent excimer emissions. The main focus of this talk will be on the elucidation of the underlying microscopic collisional and radiative processes in these plasmas that lead to the photon emission and that determine the efficiency and spectral characteristics of various sources. Processes of particular interest are the generation of intense, monochromatic atomic line emissions in the 90 - 130 nm range, in particular the H Lyman-alpha emission at 121.6 nm, from HPDPs in gas mixtures containing high-pressure He, Ne, or Ar with trace amounts (1which may have great potential in photolithography and related applications. The mechanism for the emission of these intense atomic VUV lines are near-resonant energy transfer processes from the excimer molecule to the diatomic gas (H2, O2, N2). This work was supported by the NSF and by DARPA/ARO and carried out in collaboration with P. Kurunczi, K.H. Schoenbach, M. Laroussi, M. Gupta, and N. Masoud. Helpful discussions with U. Kogelschatz and E. Kunhardt are gratefully acknowledged.
Labit, B.; Furno, I.; Fasoli, A.; Podesta, M.
2008-08-15
A new method for toroidal velocity measurements with Mach probes is presented. This technique is based on the conditional sampling technique, the triggering events being density blobs. A reconstruction of the time resolved two-dimensional profile of electron density, electron temperature, plasma potential, and toroidal velocity is possible with a single point measurement on a shot-to-shot basis.
NASA Astrophysics Data System (ADS)
Hsu, S. C.; Moser, A. L.; Merritt, E. C.; Adams, C. S.
2015-11-01
Over the past 4 years on the Plasma Liner Experiment (PLX) at LANL, we have studied obliquely and head-on-merging supersonic plasma jets of an argon/impurity or hydrogen/impurity mixture. The jets are formed/launched by pulsed-power-driven railguns. In successive experimental campaigns, we characterized the (a) evolution of plasma parameters of a single plasma jet as it propagated up to ~ 1 m away from the railgun nozzle, (b) density profiles and 2D morphology of the stagnation layer and oblique shocks that formed between obliquely merging jets, and (c) collisionless interpenetration transitioning to collisional stagnation between head-on-merging jets. Key plasma diagnostics included a fast-framing CCD camera, an 8-chord visible interferometer, a survey spectrometer, and a photodiode array. This talk summarizes the primary results mentioned above, and highlights analyses of inferred post-shock temperatures based on observations of density gradients that we attribute to shock-layer thickness. We also briefly describe more recent PLX experiments on Rayleigh-Taylor-instability evolution with magnetic and viscous effects, and potential future collisionless shock experiments enabled by low-impurity, higher-velocity plasma jets formed by contoured-gap coaxial guns. Supported by DOE Fusion Energy Sciences and LANL LDRD.
Potential around a dust grain in collisional plasma
Moulick, R. Goswami, K. S.
2015-04-15
The ion neutral collision can lead to interesting phenomena in dust charging, totally different from the expectations based on the traditional orbit motion limited theory. The potential around a dust grain is investigated for the collisional plasma considering the presence of ion neutral collisions. Fluid equations are solved for the one dimensional radial coordinate. It is observed that with the gradual increase in ion neutral collision, the potential structure around the dust grain changes its shape and is different from the usual Debye-Hückel potential. The shift however starts from a certain value of ion neutral collision and the electron-ion density varies accordingly. The potential variation is interesting and reconfirms the fact that there exists a region of attraction for negative charges. The collision modeling is done for the full range of plasma, i.e., considering the bulk and the sheath jointly. The potential variation with collision is also shown explicitly and the variation is found to cope up with the earlier observations.
On negative ion-drag force for dust in collisional plasmas
Patacchini, Leonardo; Hutchinson, Ian H.
2008-09-07
The ion-drag force on a dust particle in collisional plasmas is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionlality. It is shown that the ion-drag only reverses in the strongly collisional regime, where other forces are of much stronger magnitude than the ion-drag itself.
Formation of High-Beta Plasma and Stable Confinement of Toroidal Electron Plasma in RT-1
NASA Astrophysics Data System (ADS)
Saitoh, Haruhiko
2010-11-01
The Ring Trap 1 (RT-1) device is a laboratory magnetosphere generated by a levitated superconducting magnet. The goals of RT-1 are to realize stable formation of ultra high-beta plasma suitable for burning advanced fusion fuels, and confinement of toroidal non-neutral plasmas including antimatter particles. RT- 1 has produced high-beta plasma in the magnetospheric configuration. The effects of coil levitation and geomagnetic field compensation [Y. Yano et al., Plasma Fusion Res. 4, 039] resulted drastic improvements of the plasma properties, and a maximum local beta value exceeded 70%. Because plasma is generated by electron cyclotron resonance heating (ECH) in the present experiment, the plasma pressure is mainly due to hot electrons, whose bremsstrahlung was observed with an x-ray CCD camera. The pressure profiles have rather steep gradient near the superconducting coil in the strong field region. The decay rates of magnetic probe and interferometer signals have different time constants, suggesting multiple temperature components. The energy confinement time estimated from the input RF power and stored magnetic energy is on the order of 1s, which is comparable to the decay time constant of the density of hot electron component. Pure electron plasma experiments are also conducted in RT-1. Radial profiles of electrostatic potential and electron density showed that the plasma rigidly rotates in the toroidal direction in the stable confinement phase. Long time confinement of toroidal non- neutral plasma for more than 300s and inward particle diffusion to strong field regions, caused by the activation of the diocotron (Kelvin-Helmholtz) instability, have been realized [Z. Yoshida et al., Phys. Rev. Lett. 104, 235004].
Transport of parallel momentum induced by current-symmetry breaking in toroidal plasmas.
Camenen, Y; Peeters, A G; Angioni, C; Casson, F J; Hornsby, W A; Snodin, A P; Strintzi, D
2009-03-27
The symmetry of a physical system strongly impacts on its properties. In toroidal plasmas, the symmetry along a magnetic field line usually constrains the radial flux of parallel momentum to zero in the absence of background flows. By breaking the up-down symmetry of the toroidal currents, this constraint can be relaxed. The parallel asymmetry in the magnetic configuration then leads to an incomplete cancellation of the turbulent momentum flux across a flux surface. The magnitude of the subsequent toroidal rotation increases with the up-down asymmetry and its sign depends on the direction of the toroidal magnetic field and plasma current. Such a mechanism offers new insights in the interpretation and control of the intrinsic toroidal rotation in present day experiments.
Collisional relaxation of bi-Maxwellian plasma temperatures in magnetized plasmas
NASA Astrophysics Data System (ADS)
Yoon, Peter H.
2016-07-01
In the literature, collisional processes are customarily discussed within the context of the Boltzmann-Balescu-Lenard-Landau type of collision integral, but such an equation is strictly valid for unmagnetized plasmas. For plasmas immersed in the ambient magnetic field, the foundational equation that describes binary collisions must be generalized to include the effects of magnetic field. The present paper makes use of such an equation in order to describe the collisional relaxation of temperatures under the assumption of bi-Maxwellian velocity distribution function. The formalism derived in the present paper may be useful for studying the effects of binary collisions on the isotropization of temperatures in the solar wind plasma, among possible applications.
ATF (Advanced Toroidal Facility) flux surfaces and related plasma effects
Colchin, R.J.; England, A.C.; Harris, J.H.; Hillis, D.L.; Jernigan, T.C.; Murakami, M.; Neilson, G.H.; Rome, J.A.; Saltmarsh, M.J.; Anderson, F.S.B.
1989-01-01
Flux surfaces in the Advanced Toroidal Facility (ATF) were mapped using an electron beam which was incident on a fluorescent screen. Islands were found at r/a greater than or equal to 0.6, indicating the existence of field errors. Failure of the island size to scale with magnetic field indicated that the islands were intrinsic to the coils. The source of the field errors was found to be uncompensated dipoles in the helical coil feeds. The electron temperature was observed to be very low in the vicinity of the islands. Modifications were made to the helical field buswork to eliminate the field errors, and the flux surfaces were again checked using an electron beam. Islands at r/a greater than or equal to 0.6 were found to be greatly reduced in size, with the residual island at /tau/ = 1/2 scaling to 1 cm at B = 1 T. Initial experiments indicate that the plasma operating space has been extended since the buswork modifications. 4 refs., 3 figs.
Nonextensive statistics and the sheath criterion in collisional plasmas
Hatami, M. M.
2015-01-15
The Bohm criterion in an electropositive plasma containing nonextensively distributed electrons and warm ions is investigated by using a steady state two-fluid model. Taking into account the ion-neutral collisions and finite temperature of ions, a modified Bohm criterion is derived which limits both maximum and minimum allowable velocity of ions at the sheath edge (u{sub 0i}). It is found that the degree of nonextensivity of electrons (q) and temperature of positive ions (T{sub i}) affect only the lower limit of the entrance velocity of ions into the sheath while the degree of ion collisionality (α) influences both lower and upper limits of the ion velocities at the sheath edge. In addition, depending on the value of q, it is shown that the minimum velocity of positive ions at the sheath edge can be greater or smaller than its Maxwellian counterpart. Moreover, it is shown that, depending on the values of α and T{sub i}, the positive ions with subsonic velocity may enter the sheath for either q > 1 or −1 < q < 1. Finally, as a practical application, the density distribution of charged particles in the sheath region is studied for different values of u{sub 0i}, and it is shown that monotonical reduction of the positive ion density distribution occurs only when the velocity of positive ions at the sheath edge lies between two above mentioned limits.
The Dynamics of an Isolated Plasma Filament at the Edge of a Toroidal Device, Rev. 1
Ryutov, D D
2006-09-28
The dynamics of an isolated plasma filament (an isolated blob) in the far scrape-off layer (SOL) of a toroidal device is described, with a proper averaging of the geometrical parameters as well as plasma parameters along the filament. The analysis is limited to the magnetohydrodynamic description. The effects of the anchored ends and finite plasma resistivity are also discussed.
Role of Pressure Gradient on Intrinsic Toroidal Rotation in Tokamak Plasmas
Yoshida, M.; Kamada, Y.; Takenaga, H.; Sakamoto, Y.; Urano, H.; Oyama, N.; Matsunaga, G.
2008-03-14
The toroidal plasma rotation generated by the external momentum input and by the plasma itself (intrinsic rotation) has been separated through a novel momentum transport analysis in the JT-60U tokamak device. The toroidal rotation, which is not determined by the momentum transport coefficients and the external momentum input, has been observed. It is found that this intrinsic rotation is locally determined by the local pressure gradient and increases with increasing pressure gradient. This trend is almost the same for various plasmas: low and high confinement mode, co and counterrotating plasmas.
Modeling the effect of toroidal plasma rotation on drift-magnetohydrodynamic modes in tokamaks
NASA Astrophysics Data System (ADS)
Chapman, I. T.; Sharapov, S. E.; Huysmans, G. T. A.; Mikhailovskii, A. B.
2006-06-01
A new code, MISHKA-F (Flow), has been developed as an extension of the ideal magneto-hydrodynamic (MHD) code MISHKA-1 [Mikhailovskii et al., Plasma Phys. Rep. 23, 844 (1997)] in order to investigate the linear MHD stability of ideal and resistive eigenmodes with respect to the effects of toroidal rotation in tokamaks in general toroidal geometry with the ion diamagnetic drift effect taken into account. Benchmark test results of the MISHKA-F code show good agreement with analytic theory [A. B. Mikhailovskii and S. E. Sharapov, Plasma Phys. Controlled Fusion 42, 57 (2000)] for the stability limits of the ideal n /m=1/1 internal kink mode. The combined stabilizing effects of the ion diamagnetic drift frequency, ω*i, and the toroidal flow shear are also studied. The ω*i stabilization of the internal kink mode is found to be more effective at finite flow shear. Finite-n ballooning modes are studied in plasmas with the toroidal flow shear effect included. The stabilization of the ballooning modes by toroidal rotation is found to agree well with earlier predictions [Webster et al., Phys. Plasmas 11, 2135 (2004)]. The effect of high flow shear is analyzed for a sawtoothing discharge typical in the Mega Ampère Spherical Tokamak (MAST) [Sykes et al., Nucl. Fusion 41, 1423 (2001)]. It is found that the ideal n =1 internal kink mode can be stabilized by toroidal rotation at values observed experimentally.
Modeling the effect of toroidal plasma rotation on drift-magnetohydrodynamic modes in tokamaks
Chapman, I.T.; Sharapov, S.E.; Huysmans, G.T.A.; Mikhailovskii, A. B.
2006-06-15
A new code, MISHKA-F (Flow), has been developed as an extension of the ideal magneto-hydrodynamic (MHD) code MISHKA-1 [Mikhailovskii et al., Plasma Phys. Rep. 23, 844 (1997)] in order to investigate the linear MHD stability of ideal and resistive eigenmodes with respect to the effects of toroidal rotation in tokamaks in general toroidal geometry with the ion diamagnetic drift effect taken into account. Benchmark test results of the MISHKA-F code show good agreement with analytic theory [A. B. Mikhailovskii and S. E. Sharapov, Plasma Phys. Controlled Fusion 42, 57 (2000)] for the stability limits of the ideal n/m=1/1 internal kink mode. The combined stabilizing effects of the ion diamagnetic drift frequency, {omega}{sub *i}, and the toroidal flow shear are also studied. The {omega}{sub *i} stabilization of the internal kink mode is found to be more effective at finite flow shear. Finite-n ballooning modes are studied in plasmas with the toroidal flow shear effect included. The stabilization of the ballooning modes by toroidal rotation is found to agree well with earlier predictions [Webster et al., Phys. Plasmas 11, 2135 (2004)]. The effect of high flow shear is analyzed for a sawtoothing discharge typical in the Mega Ampere Spherical Tokamak (MAST) [Sykes et al., Nucl. Fusion 41, 1423 (2001)]. It is found that the ideal n=1 internal kink mode can be stabilized by toroidal rotation at values observed experimentally.
Transition in Electron Physics of Magnetic Reconnection in Weakly Collisional Plasma
NASA Astrophysics Data System (ADS)
Le, A.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.; Egedal, J.; Forest, C.
2013-12-01
Using self-consistent fully kinetic simulations with a Monte-Carlo treatment of the Coulomb collision operator, we explore the transition between collisional and kinetic regimes of magnetic reconnection in high-Lundquist-number current sheets. Recent research in collisionless reconnection has shown that electron kinetic physics plays a key role in the evolution. Large-scale electron current sheets may form, leading to secondary island formation and turbulent flux rope interactions in 3D. The new collisional simulations demonstrate how increasing collisionality modifies or eliminates these electron structures in the kinetic regimes. Additional basic questions that are addressed include how the reconnection rate and the release of magnetic energy into electrons and ions vary with collisionality. The numerical study provides insight into reconnection in dense regions of the solar corona, the solar wind, and upcoming laboratory experiments at MRX (Princeton) and MPDX (UW-Madison). The implications of these results for studies of turbulence dissipation in weakly collisional plasmas are discussed.
Terahertz generation by beating two Langmuir waves in a warm and collisional plasma
Zhang, Xiao-Bo; Qiao, Xin; Cheng, Li-Hong; Tang, Rong-An; Zhang, Ai-Xia; Xue, Ju-Kui
2015-09-15
Terahertz (THz) radiation generated by beating of two Langmuir waves in a warm and collisional plasma is discussed theoretically. The critical angle between the two Langmuir waves and the critical wave-length (wave vector) of Langmuir waves for generating THz radiation are obtained analytically. Furthermore, the maximum radiation energy is obtained. We find that the critical angle, the critical wave-length, and the generated radiation energy strongly depend on plasma temperature and wave-length of the Langmuir waves. That is, the THz radiation generated by beating of two Langmuir waves in a warm and collisional plasma can be controlled by adjusting the plasma temperature and the Langmuir wave-length.
Method to integrate full particle orbit in toroidal plasmas
NASA Astrophysics Data System (ADS)
Wei, X. S.; Xiao, Y.; Kuley, A.; Lin, Z.
2015-09-01
It is important to integrate full particle orbit accurately when studying charged particle dynamics in electromagnetic waves with frequency higher than cyclotron frequency. We have derived a form of the Boris scheme using magnetic coordinates, which can be used effectively to integrate the cyclotron orbit in toroidal geometry over a long period of time. The new method has been verified by a full particle orbit simulation in toroidal geometry without high frequency waves. The full particle orbit calculation recovers guiding center banana orbit. This method has better numeric properties than the conventional Runge-Kutta method for conserving particle energy and magnetic moment. The toroidal precession frequency is found to match that from guiding center simulation. Many other important phenomena in the presence of an electric field, such as E × B drift, Ware pinch effect and neoclassical polarization drift are also verified by the full orbit simulation.
NASA Astrophysics Data System (ADS)
Hong, Woo-Pyo; Jung, Young-Dae
2014-06-01
The influence of electron-exchange and quantum screening on the collisional entanglement fidelity for the elastic electron-ion collision is investigated in degenerate quantum plasmas. The effective Shukla-Eliasson potential and the partial wave method are used to obtain the collisional entanglement fidelity in quantum plasmas as a function of the electron-exchange parameter, Fermi energy, plasmon energy and collision energy. The results show that the quantum screening effect enhances the entanglement fidelity in quantum plasmas. However, it is found that the electron-exchange effect strongly suppresses the collisional entanglement fidelity. Hence, we have found that the influence of the electron-exchange reduces the transmission of quantum information in quantum plasmas. In addition, it is found that, although the entanglement fidelity decreases with an increase of the Fermi energy, it increases with increasing plasmon energy in degenerate quantum plasmas.
Quiet Monte Carlo Method for the Simulation of Semi-Collisional Plasmas
NASA Astrophysics Data System (ADS)
Albright, Brian J.
2001-10-01
The modeling of collisions among particles in a plasma poses a challenge for computer simulation. Traditional simulation methods are able to model well the extremes of highly collisional plasmas (MHD and Hall-MHD simulations) and collisionless plasmas (particle-in-cell simulations). However, the intermediate, semi-collisional regime is more problematic. In semi-collisional plasmas, the collision times are comparable to the dynamical time scales of interest in the system and the collisionality often varies as a function of time or position. Some examples include interpenetrating laser-produced plasmas, tokamak plasmas near edges and divertors, plasmas in the Earth's ionosphere, cometary exospheres, and the interstellar medium. Some PIC plasma simulations have been developed that can, in a limited way, model collisions. These include the early work of Shanny et al. [Phys. Fluids 10, 1281 (1967)], the binary collision model of Takizuka and Abe [J. Comput. Phys. 25 205 (1977)], and the collision field method of Jones et al. [J. Comput. Phys. 117, 194 (1996)]. In this talk, a new approach to particle simulation, called ``quiet direct simulation Monte Carlo'' (QDSMC), will be described that can, in principle, treat plasmas with arbitrary and arbitrarily varying collisionality. The essence of the QDSMC approach is the use of carefully chosen weights for the particles (e.g., Gauss-Hermite, for Maxwellian distributions), which are destroyed each time step after the particle information is deposited onto the grid and then reconstructed at the beginning of the next time step. The method overcomes the usual limitations of particle methods: limited dynamical range and excessive statistical noise. The QDSMC method will be discussed, as will its application as ``proof of principle'' to diffusion, hydrodynamics, and radiation transport. A QDSMC formulation of collisional, kinetic plasma simulation will be outlined, and preliminary results will be presented.
Degenerate four-wave mixing and phase conjugation in a collisional plasma
Federici, J.F.; Mansfield, D.K.
1986-06-01
Although degenerate four-wave mixing (DFWM) has many practical applications in the visible regime, no successful attempt has been made to study or demonstrate DFWM for wavelengths longer than 10..mu..m. Recently, Steel and Lam established plasma as a viable DFWM and phase conjugation (PC) medium for infrared, far-infrared, and microwaves. However, their analysis is incomplete since collisional effects were not included. Using a fluid description, our results demonstrate that when collisional absorption is small and the collisional mean-free path is shorter than the nonlinear density grating scale length, collisional heating generates a thermal force which substantially enhances the phase conjugate reflectivity. When the collisional attenuation length becomes comparable to the length of the plasma, the dominant effect is collisional absorption of the pump waves. Numerical estimates of the phase conjugate reflectivity indicate that for modest power levels, gains greater than or equal to1 are possible in the submillimeter to centimeter wavelength range. This suggests that a plasma is a viable PC medium at those long wavelengths. In addition, doubly DFWM is discussed.
Dawson, John M.; Furth, Harold P.; Tenney, Fred H.
1988-12-06
Method for producing fusion power wherein a neutral beam is injected into a toroidal bulk plasma to produce fusion reactions during the time permitted by the slowing down of the particles from the injected beam in the bulk plasma.
Air core poloidal magnetic field system for a toroidal plasma producing device
Marcus, Frederick B.
1978-01-01
A poloidal magnetics system for a plasma producing device of toroidal configuration is provided that reduces both the total volt-seconds requirement and the magnitude of the field change at the toroidal field coils. The system utilizes an air core transformer wound between the toroidal field (TF) coils and the major axis outside the TF coils. Electric current in the primary windings of this transformer is distributed and the magnetic flux returned by air core windings wrapped outside the toroidal field coils. A shield winding that is closely coupled to the plasma carries a current equal and opposite to the plasma current. This winding provides the shielding function and in addition serves in a fashion similar to a driven conducting shell to provide the equilibrium vertical field for the plasma. The shield winding is in series with a power supply and a decoupling coil located outside the TF coil at the primary winding locations. The present invention requires much less energy than the usual air core transformer and is capable of substantially shielding the toroidal field coils from poloidal field flux.
Dusty Plasma Modeling of the Fusion Reactor Sheath Including Collisional-Radiative Effects
Dezairi, Aouatif; Samir, Mhamed; Eddahby, Mohamed; Saifaoui, Dennoun; Katsonis, Konstantinos; Berenguer, Chloe
2008-09-07
The structure and the behavior of the sheath in Tokamak collisional plasmas has been studied. The sheath is modeled taking into account the presence of the dust{sup 2} and the effects of the charged particle collisions and radiative processes. The latter may allow for optical diagnostics of the plasma.
The quest to find the plasma edge and discover a collisionally modified Bohm criterion
NASA Astrophysics Data System (ADS)
Franklin, R. N.; Franklin
2013-10-01
The concepts of `plasma edge' and `collisionally modified Bohm criterion' have occupied attention for many years since the publication of work by Bohm that gave rise to the Bohm criterion. He acknowledged that his description of the plasma-sheath transition was incomplete. We summarize work that shows that neither concept has precision, at the same time giving a critique.
System and method for generating steady state confining current for a toroidal plasma fusion reactor
Bers, Abraham
1981-01-01
A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to estalish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated inthe plasma.
System and method for generating steady state confining current for a toroidal plasma fusion reactor
Fisch, Nathaniel J.
1981-01-01
A system for generating steady state confining current for a toroidal plasma fusion reactor providing steady-state generation of the thermonuclear power. A dense, hot toroidal plasma is initially prepared with a confining magnetic field with toroidal and poloidal components. Continuous wave RF energy is injected into said plasma to establish a spectrum of traveling waves in the plasma, where the traveling waves have momentum components substantially either all parallel, or all anti-parallel to the confining magnetic field. The injected RF energy is phased to couple to said traveling waves with both a phase velocity component and a wave momentum component in the direction of the plasma traveling wave components. The injected RF energy has a predetermined spectrum selected so that said traveling waves couple to plasma electrons having velocities in a predetermined range .DELTA.. The velocities in the range are substantially greater than the thermal electron velocity of the plasma. In addition, the range is sufficiently broad to produce a raised plateau having width .DELTA. in the plasma electron velocity distribution so that the plateau electrons provide steady-state current to generate a poloidal magnetic field component sufficient for confining the plasma. In steady state operation of the fusion reactor, the fusion power density in the plasma exceeds the power dissipated in the plasma.
Vlasov simulations of plasma-wall interactions in a magnetized and weakly collisional plasma
Devaux, S.; Manfredi, G.
2006-08-15
A Vlasov code is used to model the transition region between an equilibrium plasma and an absorbing wall in the presence of a tilted magnetic field, for the case of a weakly collisional plasma ({lambda}{sub mfp}>>{rho}{sub i}, where {lambda}{sub mfp} is the ion-neutral mean-free path and {rho}{sub i} is the ion Larmor radius). The phase space structure of the plasma-wall transition is analyzed in detail and theoretical estimates of the magnetic presheath width are tested numerically. It is shown that the distribution near the wall is far from Maxwellian, so that temperature measurements should be interpreted with care. Particular attention is devoted to the angular distribution of ions impinging on the wall, which is an important parameter to determine the level of wall erosion and sputtering.
Rodrigues, Paulo; Bizarro, João P S
2007-09-21
For the first time, tokamak equilibria with negative toroidal current flowing in the plasma core are computed consistently with available measurements from typical current-hole discharges. The equilibrium reconstruction, which leads to non-nested configurations where a system of axisymmetric magnetic islands unfolds, yields an overall good agreement between the computed and experimental plasma-pressure profiles, together with an excellent fit to motional-Stark-effect data. Therefore, considering the accuracy limits of present-day experimental results, care must be exercised when ruling out the existence of tokamak equilibria with central toroidal-current reversal, particularly if relying on reconstruction tools that cannot cope with non-nested configurations.
NASA Astrophysics Data System (ADS)
Kanno, Ryutaro; Nunami, Masanori; Satake, Shinsuke; Takamaru, Hisanori; Okamoto, Masao
2013-06-01
We investigate how the neoclassical thermal diffusivity of an axisymmetric toroidal plasma is modified by the effect of resonant magnetic perturbations (RMPs), using a drift-kinetic simulation code for calculating the radial thermal diffusivity of ion in the perturbed region under an assumption of zero electric field. Here, the perturbed region is assumed to be generated on and near the resonance surfaces, and is wedged in between the regular closed magnetic surfaces. We find that the dependence of the radial thermal diffusivity on parameters of the toroidal plasma is represented as \\chi_r=\\chi_r^{(0)} \\{1+ c_0\\,(\\omega_b/\
Yambe, Kiyoyuki; Koguchi, Haruhisa; Sakakita, Hajime; Hirano, Yoichi; Kiyama, Satoru
2011-06-15
The magnetic fluctuations and electrostatic probe potential have been measured in the Toroidal Pinch Experiment - RX (TPE-RX) reversed-field pinch plasma [Y. Yagi et al., Fusion Eng. Des. 45, 421 (1999)] (at the plasma surface r/a = 1.00). Fast electrons with energy comparable to or slightly higher than the core electron temperature are observed as many spikes in the electrostatic probe signal. These electrons are diffused by a fluctuating magnetic field from the core region. During the period of mild deepening of the reversal of the edge toroidal field, a significant reduction in the spike signal, increases in electron density and soft x-ray radiation, and a decrease in the D{alpha} line radiation are observed, even though the reduction in magnetic fluctuations is not significant during the same period, which indicates that the mild deepening of the reversal of the toroidal field can improve the confinement of fast electrons.
Observations of toroidicity-induced Alfvén eigenmodes in a reversed field pinch plasma
NASA Astrophysics Data System (ADS)
Regnoli, G.; Bergsâker, H.; Tennfors, E.; Zonca, F.; Martines, E.; Serianni, G.; Spolaore, M.; Vianello, N.; Cecconello, M.; Antoni, V.; Cavazzana, R.; Malmberg, J.-A.
2005-04-01
High frequency peaks in the spectra of magnetic field signals have been detected at the edge of Extrap-T2R [P. R. Brunsell, H. Bergsåker, M. Cecconello, J. R. Drake, R. M. Gravestijn, A. Hedqvist, and J.-A. Malmberg, Plasma Phys. Controlled Fusion, 43, 1457 (2001)]. The measured fluctuation is found to be mainly polarized along the toroidal direction, with high toroidal periodicity n and Alfvénic scaling (f∝B/√mini ). Calculations for a reversed field pinch plasma predict the existence of an edge resonant, high frequency, high-n number toroidicity-induced Alfvén eigenmode with the observed frequency scaling. In addition, gas puffing experiments show that edge density fluctuations are responsible for the rapid changes of mode frequency. Finally a coupling with the electron drift turbulence is proposed as drive mechanism for the eigenmode.
Goumiri, I. R.; Rowley, C. W.; Sabbagh, S. A.; Gates, D. A.; Gerhardt, S. P.; Boyer, M. D.; Andre, R.; Kolemen, E.; Taira, K.
2016-02-19
A model-based feedback system is presented to control plasma rotation in a magnetically confined toroidal fusion device, to maintain plasma stability for long-pulse operation. This research uses experimental measurements from the National Spherical Torus Experiment (NSTX) and is aimed at controlling plasma rotation using two different types of actuation: momentum from injected neutral beams and neoclassical toroidal viscosity generated by three-dimensional applied magnetic fields. Based on the data-driven model obtained, a feedback controller is designed, and predictive simulations using the TRANSP plasma transport code show that the controller is able to attain desired plasma rotation profiles given practical constraints on the actuators and the available measurements of rotation.
Computer simulation of the toroidal equilibrium and stability of a plasma in three dimensions.
Betancourt, O; Garabedian, P
1975-03-01
A computer program has been written to solve the equations for sharp boundary magnetohydrodynamic equilibrium of a toroidal plasma in three dimensions without restriction to axial symmetry. The numerical method is based on a variational principle that indicates whether the equilibria obtained are stable. Applications have been made to Tokamak, Stellarator, and Scyllac configurations.
Computer Simulation of the Toroidal Equilibrium and Stability of a Plasma in Three Dimensions
Betancourt, Octavio; Garabedian, Paul
1975-01-01
A computer program has been written to solve the equations for sharp boundary magnetohydrodynamic equilibrium of a toroidal plasma in three dimensions without restriction to axial symmetry. The numerical method is based on a variational principle that indicates whether the equilibria obtained are stable. Applications have been made to Tokamak, Stellarator, and Scyllac configurations. PMID:16592233
Inward transport of a toroidally confined plasma subject to strong radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.; Krawczonek, W. M.; Powers, E. J.; Hong, J.; Kim, Y. H.
1977-01-01
Digitally implemented spectral analysis techniques were used to investigate the frequency-dependent fluctuation-induced particle transport across a toroidal magnetic field. When the electric field pointed radially inward, the transport was inward and a significant enhancement of the plasma density and confinement time resulted.
Ha, B. N.; Stoneking, M. R.; Marler, J. P.
2009-03-15
Measurements of the image charge induced on electrodes provide the primary means of diagnosing plasmas in the Lawrence Non-neutral Torus II (LNT II) [Phys. Rev. Lett. 100, 155001 (2008)]. Therefore, it is necessary to develop techniques that determine characteristics of the electron plasma from features of the induced image charge signal. This paper presents a numerical study which finds that the frequency of the image charge signal due to the toroidal version of the m=1 diocotron mode is proportional to the total trapped charge and inversely proportional to magnetic field strength, as in the cylindrical case. In the toroidal case, additional information about the m=1 motion of the plasma can be obtained by analysis of the image charge signal amplitude and shape. Finally, results from the numerical simulations are compared to experimental data from the LNT II and plasma characteristics are reported.
The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity
Zhou, Deng
2014-08-15
Zonal flows, initially driven by ion-temperature-gradient turbulence, may evolve due to the neoclassic polarization in a collisionless tokamak plasma. In our previous work [D. Zhou, Nucl. Fusion 54, 042002 (2014)], the residual zonal flow in a tokamak plasma rotating toroidally at sonic speed is found to have the same form as that of a static plasma. In the present work, the form of the residual zonal flow is presented for tokamak plasmas rotating toroidally at arbitrary velocity. The gyro-kinetic equation is analytically solved for low speed rotation to give the expression of residual zonal flows, and the expression is then generalized for cases with arbitrary rotating velocity through interpolation. The zonal flow level decreases as the rotating velocity increases. The numerical evaluation is in good agreement with the former simulation result for high aspect ratio tokamaks.
Effects of Magnetic Shear on Toroidal Rotation in Tokamak Plasmas with Lower Hybrid Current Drive
NASA Astrophysics Data System (ADS)
Rice, J. E.; Podpaly, Y. A.; Reinke, M. L.; Mumgaard, R.; Scott, S. D.; Shiraiwa, S.; Wallace, G. M.; Chouli, B.; Fenzi-Bonizec, C.; Nave, M. F. F.; Diamond, P. H.; Gao, C.; Granetz, R. S.; Hughes, J. W.; Parker, R. R.; Bonoli, P. T.; Delgado-Aparicio, L.; Eriksson, L.-G.; Giroud, C.; Greenwald, M. J.; Hubbard, A. E.; Hutchinson, I. H.; Irby, J. H.; Kirov, K.; Mailloux, J.; Marmar, E. S.; Wolfe, S. M.
2013-09-01
Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core q profile. For discharges with q0<1, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase q0 above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear.
Flux tube train model for local turbulence simulation of toroidal plasmas
Watanabe, T.-H.; Sugama, H.; Ishizawa, A.; Nunami, M.
2015-02-15
A new simulation method for local turbulence in toroidal plasmas is developed by extending the conventional idea of the flux tube model. In the new approach, a train of flux tubes is employed, where flux tube simulation boxes are serially connected at each end along a field line so as to preserve a symmetry of the local gyrokinetic equations for image modes in an axisymmetric torus. Validity of the flux tube train model is confirmed against the toroidal ion temperature gradient turbulence for a case with a long parallel correlation of fluctuations, demonstrating numerical advantages over the conventional method in the time step size and the symmetry-preserving property.
Double layer field shaping systems for toroidal plasmas
Ohyabu, Nobuyoshi
1982-01-01
Methods and apparatus for plasma generation, confinement and control such as Tokamak plasma systems are described having a two layer field shaping coil system comprising an inner coil layer close to the plasma and an outer coil layer to minimize the current in the inner coil layer.
Advances in Steady Inductive Helicity Injection for Plasma Startup and Toroidal Current Drive
NASA Astrophysics Data System (ADS)
Victor, Brian S.; Jarboe, Thomas R.; Hossack, Aaron C.; Ennis, David A.; Nelson, Brian A.; Hansen, Chris J.; Wrobel, Jonathan S.
The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI) has achieved a breakthrough in the development of a new method of toroidal plasma startup and current drive. HIT-SI accomplishes helicity injection current drive on a spheromak of major radius 0.3 m with two injectors driven sinusoidally at 14.5 kHz. Results include the first sustainment of toroidal plasma current of over 50 kA at up to 3 times the injected currents added in quadrature. Separatrix toroidal currents—currents not linking the helicity injectors—are sustained at up to 40 kA. Toroidal currents persist for up to 0.65 ms after the injectors are turned off. Results are achieved after helium operations condition the alumina plasma-facing surface. The conditioned alumina walls then act to pump the deuterium, thereby reducing the spheromak density. High performance discharges (Itor/Iinj ≥ 2) are characterized by a decrease in the n = 1 mode activity measured by surface probes near the midplane of the confinement volume. Suppression of internal magnetic fields (measured by an internal probe) below the predicted Taylor equilibrium indicates that the magnetic fields in HIT-SI can no longer be described by a zero pressure, constant λ equilibrium.
Observation of the inward propagation of spontaneous toroidal flow from the plasma boundary in LHD
NASA Astrophysics Data System (ADS)
Kamiya, K.; Ida, K.; Itoh, K.; Itoh, S.-I.; Yoshinuma, M.; Yokoyama, M.; Kubo, S.; Tsuchiya, H.; Tamura, N.; Masuzaki, S.; Suzuki, C.; Akiyama, T.
2016-10-01
Spontaneous generation of toroidal flow from the separatrix and its inward radial propagation in association with the change in the electron temperature gradient have been observed near the plasma boundary in the modulated electron cyclotron heating (MECH) experiment in the Large Helical Device. The observations presented in this paper provide strongly the supports of the hypothesis for the conversion of the poloidal flow to the toroidal one at the plasma peripheral region, exhibiting a clear delay response on MECH in the time derivation of the toroidal flow ( V ˙ ϕ ≡ ∂ V ϕ / ∂ t ) to the poloidal one ( V ˙ θ ≡ ∂ V θ / ∂ t ) at a normalized radius of ρ ≈ 0.97. The ratio of order unity for | V ˙ ϕ / V ˙ θ | during a conversion phase from poloidal flow into toroidal one is consistent with that predicted by a quasi-stationary theoretical model based on the turbulent instability, regardless of its sign and spatial structure. The present work demonstrates a new dynamic response in the plasma momentum transport and represents a significant confirmation of its non-local nature.
Kinetic analysis of the ion temperature gradient modes in toroidally rotating plasmas
Zheng, L.; Tessarotto, M.
1996-12-01
With the two time scale feature revealed, an analytical method is developed to solve the combined eigenvalue and initial value problem describing the ion temperature gradient (ITG) modes in the toroidally rotating plasmas. With full gyrokinetics and toroidal geometry effects being taken into account in an ordering consistent manner, dispersion relations are obtained for ITG modes both of toroidal and slab-like branches. The results show that the sonic rotation can be harmful for the stability, while subsonic rotation with flow shear can be expected to be stabilizing. The existence of the flow shear leads the time evolution of the fluctuation signals to display two different time scales{emdash}a fast oscillating (either fast or slow growing) signal with its amplitude modulated by a slowly varying envelope, resembling fishbone-like fluctuations. {copyright} {ital 1996 American Institute of Physics.}
Chaudhuri, Manis; Khrapak, Sergei A.; Morfill, Gregor E.
2008-09-07
The ion drag force acting on a small absorbing spherical grain has been calculated analytically in highly collisional plasma with slowly drifting ions taking into account plasma production and loss mechanisms in the vicinity of the grain. It is shown that both the magnitude and direction of the ion drag force are strongly influenced by the plasma production and loss mechanisms. The parameter regimes for the 'positive' and 'negative' ion drag forces acting on an absorbing grain have been identified.
Turbulence and bias-induced flows in simple magnetized toroidal plasmas
Li, B.; Rogers, B. N.; Ricci, P.; Gentle, K. W.; Bhattacharjee, A.
2011-05-15
Turbulence and bias-induced flows in simple magnetized toroidal plasmas are explored with global three-dimensional fluid simulations, focusing on the parameters of the Helimak experiment. The simulations show that plasma turbulence and transport in the regime of interest are dominated by the ideal interchange instability. The application of a bias voltage alters the structure of the plasma potential, resulting in the equilibrium sheared flows.These bias-induced vertical flows located in the gradient region appear to reduce the radial extent of turbulent structures,and thereby lower the radial plasma transport on the low field side.
Dual-function magnetic structure for toroidal plasma devices
Brown, Robert L.
1978-01-01
This invention relates to a support system wherein the iron core and yoke of the plasma current system of a tokamak plasma containment device is redesigned to support the forces of the magnet coils. The containment rings, which occupy very valuable space around the magnet coils, are utilized to serve as yokes for the core such that the conventional yoke is eliminated. The overall result is an improved aspect ratio, reduction in structure, smaller overall size, and improved access to the plasma ring.
Effects of Equilibrium Toroidal Flow on Locked Mode and Plasma Response in a Tokamak
NASA Astrophysics Data System (ADS)
Zhu, Ping; Huang, Wenlong; Yan, Xingting
2016-10-01
It is widely believed that plasma flow plays significant roles in regulating the processes of mode locking and plasma response in a tokamak in presence of external resonant magnetic perturbations (RMPs). Recently a common analytic relation for both locked mode and plasma response has been developed based on the steady-state solution to the coupled dynamic system of magnetic island evolution and torque balance. The analytic relation predicts the size of the magnetic island of a locked mode or a static nonlinear plasma response for a given RMP amplitude, and rigorously proves a screening effect of the equilibrium toroidal flow. To test the theory, we solve for the locked mode and the nonlinear plasma response in presence of RMP for a circular-shaped limiter tokamak equilibrium with constant toroidal flow, using the initial-value, full MHD simulation code NIMROD. The comparison between the simulation results and the theory prediction, in terms of the quantitative screening effects of equilibrium toroidal flow, will be reported and discussed. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB101004, the 100 Talent Program of the Chinese Academy of Sciences, and U.S. Department of Energy Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.
NASA Astrophysics Data System (ADS)
Mikkelsen, D. R.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N.; Podpaly, Y.; Reinke, M.; Rice, J. E.; Hughes, J. W.; Ma, Y.; Candy, J.; Waltz, R. E.
2012-10-01
In nonlinear GYRO simulations of C-Mod plasmas, a turbulently driven pinch produces modest density peaking of all species. The ratio of density at r/a=0.44 and 0.74 is 1.2 for the majority and minority D & H (and electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.29 for neon, 1.36 for argon, 1.47 for molybdenum. Density peaking is only weakly affected when the ion temperature profile is varied to align the predicted heat flux to the experimental transport analysis. New simulations will extend the collisionality to the lower part of the experimentally accessible range in C-Mod to study the collisionality dependence of density peaking, and to establish whether much stronger peaking is predicted for lower collisionalities. Simulations based on measured I-mode ion and electron temperature profiles will also be presented.
Nonlinear evolution of an ion acoustic wave in two-species, moderately collisional plasma.
NASA Astrophysics Data System (ADS)
Valeo, E. J.; Berger, R. L.
2004-11-01
The dispersion properties of ion acoustic waves (IAW) in two-species plasma with disparate ion charges and masses has shown a sensitivity to inter-species collisions in the moderate-collisionality regime where the heavy, highly-charged ions are strongly collisional (fluid-like), but where light-ion Landau damping is competitive with light-heavy collisions.(R. Berger, E. Valeo and S. Brunner, Bull. Am. Phys. Soc., 47), QP1.98 (2002). The nonlinear evolution of a driven IAW is simulated using a low-noise hybrid simulation technique in which the electrons are a massless fluid, the heavy ions are a cold fluid, and the light ions are evolved using the δ f method with an evolving background distribution. The relative importance of several nonlinear effects in determining the mode amplitude, including (collisionally interrupted) trapping and nonlinear frequency shifts, is assessed.
Formation and evolution of vortices in a collisional strongly coupled dusty plasma
NASA Astrophysics Data System (ADS)
Jana, Sayanee; Banerjee, Debabrata; Chakrabarti, Nikhil
2016-07-01
Formation and evolution of vortices are studied in a collisional strongly coupled dusty plasma in the framework of a Generalized Hydrodynamic model (GH). Here we mainly present the nonlinear dynamical response of this strongly coupled system in presence of dust-neutral collisional drag. It is shown that the interplay between the nonlinear elastic stress and the dust-neutral collisional drag results in the generation of non-propagating monopole vortex for some duration before it starts to propagate like transverse shear wave. It is also found that the interaction between two unshielded monopole vortices having both same (co-rotating) and opposite (counter rotating) rotations result in the formation of two propagating dipole vortices of equal and unequal strength respectively. These results will provide some new understanding on the transport properties in such a strongly coupled system. The numerical simulation is carried out using a de-aliased doubly periodic pseudo-spectral code with Runge-Kutta-Gill time integrator.
Honda, M
2004-01-01
I theoretically found eigenmodes and growth rates of relativistic current filamentation instability in collisional regimes, deriving a generalized dispersion relation from self-consistent beam-Maxwell equations. For symmetrically counterstreaming, fully relativistic electron currents, the collisional coupling between electrons and ions creates the unstable modes of growing oscillation and wave, which stand out for long-wavelength perturbations. In the stronger collisional regime, the growing oscillatory mode tends to be dominant for all wavelengths. In the collisionless limit, those modes vanish, while maintaining another purely growing mode that exactly coincides with a standard relativistic Weibel mode. It is also shown that the effects of electron-electron collisions and thermal spread lower the growth rate of the relativistic Weibel instability. The present mechanisms of filamentation dynamics are essential for transport of homogeneous electron beam produced by the interaction of high power laser pulses with plasma.
Terahertz generation by two cross focused laser beams in collisional plasmas
Sharma, R. P. Singh, Ram Kishor
2014-07-15
The role of two cross-focused spatial-Gaussian laser beams has been studied for the high power and efficient terahertz (THz) radiation generation in the collisional plasma. The nonlinear current at THz frequency arises on account of temperature dependent collision frequency of electrons with ions in the plasma and the presence of a static electric field (applied externally in the plasma) and density ripple. Optimisation of laser-plasma parameters gives the radiated THz power of the order of 0.23 MW.
Reduction of collisional-radiative models for laser-produced argon plasmas
NASA Astrophysics Data System (ADS)
Abrantes, Richard June; Karagozian, Ann; Le, Hai
2016-10-01
The formation of a laser-induced plasma involves a variety of physical phenomena stemming from the laser-plasma interaction. A thorough understanding of these processes encourages improvement and innovation for many applications. In this work, we aim to computationally reduce a previously-developed collisional-radiative (CR) model constructed from the LANL database, which includes all of the relevant collisional and radiative processes for all the ionic stages of argon. The laser is coupled to the plasma via multiphoton ionization and inverse Bremsstrahlung, processes important for electron production and heating. The use of the CR model allows us to identify dominant mechanisms responsible for initial breakdown of the gas and thermal equilibriation processes. The results are compared with experimental data from laser-induced breakdown experiments. Research supported by the AFOSR.
Energetically consistent collisional gyrokinetics
Burby, J. W.; Brizard, A. J.; Qin, H.
2015-10-15
We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory.
Estimation of plasma flow and toroidal rotation on SSPX using a passive ion Doppler spectrometer
NASA Astrophysics Data System (ADS)
King, J. D.; McLean, H. S.; May, M. J.; Morse, E. C.
2008-11-01
We present results of ion Doppler spectrometer (IDS) measurements of helium ion velocity coupled with the MIST 1D impurity transport code calculations to estimate plasma flow and toroidal rotation in the SSPX spheromak. Helium discharges ensured sufficient light. Collection optics view a narrow, near-cylindrical volume with radius ˜ 1cm, and the intensity of collected light decreases as the inverse square of the distance from the plasma to the optic, or solid angle. Light was collected along a chord near the edge (red-shift) as well as a direct radial (null-shift) view through the center. By considering the helium charge state distribution calculated by MIST, and the solid angle of the collection optic to the plasma location, an estimate of the spatial resolution of the IDS was obtained. It was found that 70% of He-II 468.57 nm light collected by the IDS, was localized in a 6 cm radial region. The analysis of several shots indicate that plasma near the edge of the spheromak flows with a toroidal velocity of 5 to 45 km/s during spheromak formation. These flows correspond to a toroidal rotation frequency of 1.7 to 15.6 kHz. This work performed under the auspices of the U.S. DoE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma
NASA Astrophysics Data System (ADS)
Brower, D. L.; Ding, W. X.; Lin, L.; Almagri, A. F.; den Hartog, D. J.; Sarff, J. S.
2012-10-01
Magnetic fluctuations have been long observed in various magnetic confinement configurations. These perturbations may arise naturally from plasma instabilities such as tearing modes and energetic particle driven modes, but they can also be externally imposed by error fields or external magnetic coils. It is commonly observed that large MHD modes lead to plasma locking (no rotation) due to torque produced by eddy currents on the wall, and it is predicted that stochastic field induces flow damping where the radial electric field is reduced. Flow generation is of great importance to fusion plasma research, especially low-torque devices like ITER, as it can act to improve performance. Here we describe new measurements in the MST reversed field pinch (RFP) showing that the coherent interaction of magnetic and particle density fluctuations can produce a turbulent fluctuation-induced kinetic force, which acts to drive intrinsic plasma rotation. Key observations include; (1) the average kinetic force resulting from density fluctuations, ˜ 0.5 N/m^3, is comparable to the intrinsic flow acceleration, and (2) between sawtooth crashes, the spatial distribution of the kinetic force is directed to create a sheared parallel flow profile that is consistent with the measured flow profile in direction and amplitude, suggesting the kinetic force is responsible for intrinsic plasma rotation.
Ion acoustic shock wave in collisional equal mass plasma
Adak, Ashish; Ghosh, Samiran; Chakrabarti, Nikhil
2015-10-15
The effect of ion-ion collision on the dynamics of nonlinear ion acoustic wave in an unmagnetized pair-ion plasma has been investigated. The two-fluid model has been used to describe the dynamics of both positive and negative ions with equal masses. It is well known that in the dynamics of the weakly nonlinear wave, the viscosity mediates wave dissipation in presence of weak nonlinearity and dispersion. This dissipation is responsible for the shock structures in pair-ion plasma. Here, it has been shown that the ion-ion collision in presence of collective phenomena mediated by the plasma current is the source of dissipation that causes the Burgers' term which is responsible for the shock structures in equal mass pair-ion plasma. The dynamics of the weakly nonlinear wave is governed by the Korteweg-de Vries Burgers equation. The analytical and numerical investigations revealed that the ion acoustic wave exhibits both oscillatory and monotonic shock structures depending on the frequency of ion-ion collision parameter. The results have been discussed in the context of the fullerene pair-ion plasma experiments.
Electron Plasma Confinement in a Partially Toroidal Trap
2002-06-24
2002 American Institute of Physics 0-7354-0050-4/02/$19.00 671 plane superimposed on the cross - field drifts can close the drift orbits. In the tokamak...equipotential contours. Because the plasma is nonneutral, the drift results in a current, J, which when crossed into the magnetic field , B, balances the...equilibrium momentum equation is evident, J x B = Vp. In MHD theory the diamagnetic current crossed into the magnetic field balances the pressure gradient
Collisional-Radiative Recombination of Ar^+ Ions with Electrons in a Flowing Afterglow Plasma.
NASA Astrophysics Data System (ADS)
Skrzypkowski, Miroslaw P.; Golde, Michael F.; Johnsen, Rainer
1998-10-01
Langmuir probe measurements of electron densities, n_e, in an Ar^+/e^- plasma are quantitatively consistent with the semi-empirical rate coefficient for collisional-radiative recombination given by Stevefelt et al.(J. Stevefelt et al., Phys. Rev A 12, 1246 (1975)) : α_cr=1.55×10-10T-0.63 + 6.0×10-9T-2.18n_e^0.37+3.8×10- 9T-4.5ne over the initial electron density range 5×10^9-5×10^10cm-3 at T=300K. Optical emission spectroscopy data reveal transitions from highly-excited states of Ar to Ar(^3P). We believe that the collisional-radiative recombination of Ar^+ ions is responsible for the presence of Ar metastable atoms in flowing afterglow plasmas.
NASA Astrophysics Data System (ADS)
Abdoli-Arani, A.; Moghaddasi, M.
2016-07-01
Acceleration of an externally injected electron inside the collisional plasma-filled cylindrical waveguide during its motion in the fields of the ? mode excited by microwave radiation is studied. The effect of the electron collision frequency with background ions on the deflection angle and energy gain of electron, when it is injected along the direction of the mode propagation is investigated. The fields for the mode, the deflection angle of electron trajectory, due to these fields, and the electron energy gradient are obtained. The results for collisionless and collisional plasma are graphically presented. The numerical results illustrate that the presence of the electron collision term in the dielectric permittivity can reduce the electron's energy gain in the configuration.
NASA Astrophysics Data System (ADS)
Murakami, S.; Itoh, K.; Zheng, L. J.; Van Dam, J. W.; Bonoli, P.; Rice, J. E.; Fiore, C. L.; Gao, C.; Fukuyama, A.
2016-01-01
The averaged toroidal flow of energetic minority ions during ICRF (ion cyclotron range of frequencies) heating is investigated in the Alcator C-Mod plasma by applying the GNET code, which can solve the drift kinetic equation with complicated orbits of accelerated energetic particles. It is found that a co-directional toroidal flow of the minority ions is generated in the region outside of the resonance location, and that the toroidal velocity reaches more than 40% of the central ion thermal velocity (Vtor ˜ 300 km/s with PICRF ˜ 2 MW). When we shift the resonance location to the outside of |r /a |˜0.5 , the toroidal flow immediately inside of the resonance location is reduced to 0 or changes to the opposite direction, and the toroidal velocity shear is enhanced at r/a ˜ 0.5. A radial diffusion equation for toroidal flow is solved by assuming a torque profile for the minority ion mean flow, and good agreements with experimental radial toroidal flow profiles are obtained. This suggests that the ICRF driven minority ion flow is related to the experimentally observed toroidal rotation during ICRF heating in the Alcator C-Mod plasma.
The electromagnetic interchange mode in a partially ionized collisional plasma. [spread F region
NASA Technical Reports Server (NTRS)
Hudson, M. K.; Kennel, C. F.
1974-01-01
A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.
Wave enhancement of electron runaway rate in a collisional plasma
An, Z.; Liu, C.; Lee, Y.; Boyd, D.
1982-06-01
The effects of plasma waves on the electron runaway production rate is studied. For a wave packet with a one-dimensional spectrum directed along the electric field and with a phase velocity range containing the critical velocity v/sub c/ for runaway, the runaway production rate is found to be enhanced by many orders of magnitude. For an isotropic wave spectrum, however, the runaway production rate is reduced because of the wave-enhanced pitch angle scattering.
An experimentally constrained MHD model for a collisional, rotating plasma column
NASA Astrophysics Data System (ADS)
Wright, A. M.; Qu, Z. S.; Caneses, J. F.; Hole, M. J.
2017-02-01
A steady-state single fluid MHD model which describes the equilibrium of plasma parameters in a collisional, rotating plasma column with temperature gradients and a non-uniform externally applied magnetic field is developed. Two novel methods of simplifying the governing equations are introduced. Specifically, a ‘radial transport constraint’ and an ordering argument are applied. The reduced system is subsequently solved to yield the equilibrium of macroscopic plasma parameters in the bulk region of the plasma. The model is benchmarked by comparing these solutions to experimental measurements of axial velocity and density for a hydrogen plasma in the converging-field experiment MAGPIE and overall a good agreement is observed. The plasma equilibrium is determined by the interaction of a density gradient, due to a temperature gradient, with an electric field. The magnetic field and temperature gradient are identified as key parameters in determining the flow profile, which may be important considerations in other applications.
Simulation Study of an Extended Density DC Glow Toroidal Plasma Source
Granda-Gutierrez, E. E.; Piedad-Beneitez, A. de la; Lopez-Callejas, R.; Godoy-Cabrera, O. G.; Benitez-Read, J. S.; Pacheco-Sotelo, J. O.; Pena-Eguiluz, R.; Mercado-Cabrera, A.; Valencia A, R.; Barocio, S. R.
2006-12-04
Conventional wisdom assigns the DC glow discharge regime to plasma currents below {approx}500 mA values, beyond which the discharge falls into the anomalous glow and the turbulent arc regimes. However, we have found evidence that, during toroidal discharges, this barrier can be ostensibly extended up to 800 mA. Thus, a computer simulation has been applied to the evolution of the main electrical characteristics of such a glow discharge plasma in a toroidal vessel in order to design and construct a respective voltage/current controlled source. This should be able to generate a DC plasma in the glow regime with which currents in the range 10-3-100 A can be experimented and 109-1010 cm-3 plasma densities can be achieved to PIII optimization purposes. The plasma is modelled as a voltage-controlled current source able to be turned on whenever the breakdown voltage is reached across the gap between the anode and the vessel wall. The simulation outcome fits well our experimental measurements showing that the plasma current obeys power laws that are dependent on the power current and other control variables such as the gas pressure.
Modeling of Weakly Collisional Parallel Electron Transport for Edge Plasma Simulations
NASA Astrophysics Data System (ADS)
Umansky, M. V.; Dimits, A. M.; Joseph, I.; Omotani, J. T.; Rognlien, T. D.
2014-10-01
The parallel electron heat transport in a weakly collisional regime can be represented in the framework of the Landau-fluid (LF) model. Practical implementation of LF-based transport models has become possible due to the recent invention of an efficient non- spectral method for the non-local closure operators. Here the implementation of a LF based model for the parallel plasma transport is described, and the model is tested for different collisionality regimes against a Fokker-Plank code. The new method appears to represent weakly collisional parallel electron transport more accurately than the conventional flux-limiter based models; on the other hand it is computationally efficient enough to be used in tokamak edge plasma simulations. Implementation of an LF-based model for the parallel plasma transport in the UEDGE code is described, and applications to realistic divertor simulations are discussed. Work performed for U.S. DoE by LLNL under Contract DE-AC52-07NA27344.
Sheath energy transmission in a collisional plasma with collisionless sheath
Tang, Xian-Zhu Guo, Zehua
2015-10-15
Sheath energy transmission governs the plasma energy exhaust onto a material surface. The ion channel is dominated by convection, but the electron channel has a significant thermal conduction component, which is dominated by the Knudsen layer effect in the presence of an absorbing wall. First-principle kinetic simulations reveal a robustly supersonic sheath entry flow. The ion sheath energy transmission and the sheath potential are accurately predicted by a sheath model of truncated bi-Maxwellian electron distribution. The electron energy transmission is further enhanced by a parallel heat flux of the perpendicular degrees of freedom.
NASA Astrophysics Data System (ADS)
Ida, K.; Kobayashi, T.; Yoshinuma, M.; Suzuki, Y.; Narushima, Y.; Evans, T. E.; Ohdachi, S.; Tsuchiya, H.; Inagaki, S.; Itoh, K.
2016-09-01
Bifurcation physics of a magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in a large helical device (LHD) and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between the magnetic island with larger thermal diffusivity and that with smaller thermal diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.
NASA Astrophysics Data System (ADS)
Yan, Xingting; Zhu, Ping; Sun, Youwen
2016-10-01
The characteristic profile and magnitude are predicted in theory for the neoclassical toroidal viscosity (NTV) torque induced by the plasma response to the resonant magnetic perturbation (RMP) in a tokamak with an edge pedestal, using the newly developed module coupling the NIMROD and the NTVTOK codes. For a low β equilibrium, the NTV torque is mainly induced by the dominant toroidal mode of plasma response. The NTV torque profile is radially localized and peaked, which is determined by profiles of both the equilibrium temperature and the plasma response fields. In general, the peak of NTV torque profile is found to trace the pedestal location. The magnitude of NTV torque is extremely sensitive to the β of pedestal top; for a given plasma response, the peak value of NTV torque can increase by three orders of magnitude, when the pedestal β increases by only one order of magnitude. This suggests a more significant role of NTV torque in higher plasma β regimes. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, and the 100 Talent Program of the Chinese Academy of Sciences.
Measurement of toroidal vessel eddy current during plasma disruption on J-TEXT.
Liu, L J; Yu, K X; Zhang, M; Zhuang, G; Li, X; Yuan, T; Rao, B; Zhao, Q
2016-01-01
In this paper, we have employed a thin, printed circuit board eddy current array in order to determine the radial distribution of the azimuthal component of the eddy current density at the surface of a steel plate. The eddy current in the steel plate can be calculated by analytical methods under the simplifying assumptions that the steel plate is infinitely large and the exciting current is of uniform distribution. The measurement on the steel plate shows that this method has high spatial resolution. Then, we extended this methodology to a toroidal geometry with the objective of determining the poloidal distribution of the toroidal component of the eddy current density associated with plasma disruption in a fusion reactor called J-TEXT. The preliminary measured result is consistent with the analysis and calculation results on the J-TEXT vacuum vessel.
Measurement of toroidal vessel eddy current during plasma disruption on J-TEXT
NASA Astrophysics Data System (ADS)
Liu, L. J.; Yu, K. X.; Zhang, M.; Zhuang, G.; Li, X.; Yuan, T.; Rao, B.; Zhao, Q.
2016-01-01
In this paper, we have employed a thin, printed circuit board eddy current array in order to determine the radial distribution of the azimuthal component of the eddy current density at the surface of a steel plate. The eddy current in the steel plate can be calculated by analytical methods under the simplifying assumptions that the steel plate is infinitely large and the exciting current is of uniform distribution. The measurement on the steel plate shows that this method has high spatial resolution. Then, we extended this methodology to a toroidal geometry with the objective of determining the poloidal distribution of the toroidal component of the eddy current density associated with plasma disruption in a fusion reactor called J-TEXT. The preliminary measured result is consistent with the analysis and calculation results on the J-TEXT vacuum vessel.
Measurement of toroidal vessel eddy current during plasma disruption on J-TEXT
Liu, L. J.; Yu, K. X.; Zhang, M. Zhuang, G.; Li, X.; Yuan, T.; Rao, B.; Zhao, Q.
2016-01-15
In this paper, we have employed a thin, printed circuit board eddy current array in order to determine the radial distribution of the azimuthal component of the eddy current density at the surface of a steel plate. The eddy current in the steel plate can be calculated by analytical methods under the simplifying assumptions that the steel plate is infinitely large and the exciting current is of uniform distribution. The measurement on the steel plate shows that this method has high spatial resolution. Then, we extended this methodology to a toroidal geometry with the objective of determining the poloidal distribution of the toroidal component of the eddy current density associated with plasma disruption in a fusion reactor called J-TEXT. The preliminary measured result is consistent with the analysis and calculation results on the J-TEXT vacuum vessel.
Spontaneous three-dimensional magnetic reconnection in merging toroidal plasma experiment
Ii, Toru; Ono, Yasushi
2013-01-15
We investigated a new phenomenon of three-dimensional (3D) magnetic reconnection in TS-4 torus plasma merging experiments by directly measuring the 3D structures of the current sheet. Removal of all toroidal asymmetry of the device reveals that a strong external drive of reconnection inflow increases the toroidal asymmetry of the current sheet only during the reconnection. This spontaneous 3D deformation of the current sheet increases the reconnection outflow as well as the reconnection electric field, probably because local compression of the current sheet to a thickness less than the ion gyroradius triggers its strong dissipation of the current sheet, responsible for the onset of 3D reconnection. These mechanisms indicate that the 3D reconnection is a newly observed spontaneous process of fast reconnection.
NASA Astrophysics Data System (ADS)
Liu, Yueqiang
2016-10-01
The type-I edge localized mode (ELM), bursting at low frequency and with large amplitude, can channel a substantial amount of the plasma thermal energy into the surrounding plasma-facing components in tokamak devices operating at the high-confinement mode, potentially causing severe material damages. Learning effective ways of controlling this instability is thus an urgent issue in fusion research, in particular in view of the next generation large devices such as ITER and DEMO. Among other means, externally applied, three-dimensional resonant magnetic perturbation (RMP) fields have been experimentally demonstrated to be successful in mitigating or suppressing the type-I ELM, in multiple existing devices. In this work, we shall report results of a comparative study of ELM control using RMPs. Comparison is made between the modelled plasma response to the 3D external fields and the observed change of the ELM behaviour on multiple devices, including MAST, ASDEX Upgrade, EAST, DIII-D, JET, and KSTAR. We show that toroidal modelling of the plasma response, based on linear and quasi-linear magnetohydrodynamic (MHD) models, provides essential insights that are useful in interpreting and guiding the ELM control experiments. In particular, linear toroidal modelling results, using the MARS-F code, reveal the crucial role of the edge localized peeling-tearing mode response during ELM mitigation/suppression on all these devices. Such response often leads to strong peaking of the plasma surface displacement near the region of weak equilibrium poloidal field (e.g. the X-point), and this provides an alternative practical criterion for ELM control, as opposed to the vacuum field based Chirikov criteria. Quasi-linear modelling using MARS-Q provides quantitative interpretation of the side effects due to the ELM control coils, on the plasma toroidal momentum and particle confinements. The particular role of the momentum and particle fluxes, associated with the neoclassical toroidal
Collisional processes of interest in MFE plasma research
Olson, R.E.
1990-05-24
Research on this grant is devoted to the calculation of heavy particle collision cross sections needed for diagnostic studies of magnetic fusion plasmas. This work requires the development and testing of new theoretical methods, with the implementation of benchmarked techniques to collisions pertinent to fusion reactors. Within the last context, we have provided charge-exchange-recombination cross sections to specific n,1-levels for diagnostic studies on TFTR and for a major compilation for IAEA. We have also completed a cross section study related to the planned neutral beam current drive for ITER. In addition, calculations were completed to assess the use of He neutral atom angular scattering measurements for JT-60. Also, new theoretical methods have been developed to more accurately calculate cross sections involving either He or H{sub 2} targets and partially stripped multiply-charged ions.
Maitra, Sarit; Banerjee, Gadadhar
2014-11-15
The influence of dust size distribution on the dust ion acoustic solitary waves in a collisional dusty plasma is investigated. It is found that dust size distribution changes the amplitude and width of a solitary wave. A critical wave number is derived for the existence of purely damping mode. A deformed Korteweg-de Vries (dKdV) equation is obtained for the propagation of weakly nonlinear dust ion acoustic solitary waves and the effect of different plasma parameters on the solution of this equation is also presented.
Revealing an intermediate region between the collisional radiofrequency plasma bulk and its sheath
NASA Astrophysics Data System (ADS)
Beckers, J.; Trienekens, D. J. M.; Kroesen, G. M. W.
2015-03-01
Experimental evidence of the existence of an intermediate region between a capacitively coupled plasma and the collisional space-charge region at its borders is presented. This proof is generated by monitoring—in an airplane carrying out parabolic flights—the trajectory of plasma-confined microparticles. Based on only primary data and without the need for a sophisticated model, our analysis concludes a sharply marked transition from the sheath region into another region with a significantly lower—yet nonzero—space-charge density, i.e., a region which is often called the presheath.
Numerical study on the stability of weakly collisional plasma in E×B fields
Horký, M.
2015-02-15
Plasma stability in weakly collisional plasmas in the presence of E×B fields is studied with numerical simulations. Different types of ion-neutral collisions are considered in a fully magnetized regime. We study the influence of ion-neutral collisions and the role of collision types on the stability of plasma. It is found that the stability of plasma depends on the type of ion-neutral collisions, with the plasma being unstable for charge exchange collisions, and stable for the elastic scattering. The analysis focuses on the temporal evolution of the velocity phase space, RMS values of the potential fluctuations, and coherent structures in potential densities. For the unstable case, we observe growth and propagation of electrostatic waves. Simulations are performed with a three-dimensional electrostatic particle in cell code.
Fantz, U.; Wuenderlich, D.
2011-05-11
The quantitative analysis of spectroscopic data from low temperature plasmas is strongly supported from collisional radiative (CR) modeling. Low pressure plasmas for basic research in the lab and for industrial use have several aspects in common with the cold edge of magnetic fusion plasmas. On the basis of applications of CR modeling for atomic and molecular hydrogen, molecular nitrogen, and diatomic radicals such as CH and C{sub 2}, the relevance of individual processes for data interpretation is demonstrated for ionizing and recombining plasmas. Examples of such processes are opacity, dissociative excitation, dissociative recombination, mutual neutralization, and energy pooling. It is shown that the benchmark of CR modeling with experimental data can be used to identify problems in the ingoing data set of cross sections and rate coefficients. Using the flexible solver Yacora, the capability of CR modeling of low temperature plasmas is highlighted.
Borovsky, J.E.
1987-02-01
The propagation of ultralow-frequency (ulf) electromagnetic signals (Alfven and magnetosonic waves) in collisional, inhomogeneous, magnetized plasmas is analyzed by numerical simulation. The problem is formulated from a Maxwell-equation orbit-theory approach rather than from a magnetohydrodynamic point of view, and the problem is numerically treated in a fully time-dependent manner. Boundary-value-problem behavior is distinguished from initial-value-problem behavior. The propagation of two-dimensional small-amplitude electromagnetic disturbances in plasmas with spatially dependent densities and in plasmas with spatially dependent conductivities is numerically simulated, and when possible, the simulations are compared with theory. Changes in the plasma density lead to changes in the signal speed and to reflections; collisions lead to changes in the signal speed, to reflections, and to attenuations. Theoretical descriptions based upon discontinuities in the media are generally incorrect in predicting the amplitudes of signals reflected from plasma inhomogeneities. 19 refs., 16 figs.
Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Quataert, E.; Tatsuno, T.
2009-04-23
This paper presents a theoretical framework for understanding plasma turbulence in astrophysical plasmas. It is motivated by observations of electromagnetic and density fluctuations in the solar wind, interstellar medium and galaxy clusters, as well as by models of particle heating in accretion disks. All of these plasmas and many others have turbulentmotions at weakly collisional and collisionless scales. The paper focuses on turbulence in a strong mean magnetic field. The key assumptions are that the turbulent fluctuations are small compared to the mean field, spatially anisotropic with respect to it and that their frequency is low compared to the ion cyclotron frequency. The turbulence is assumed to be forced at some system-specific outer scale. The energy injected at this scale has to be dissipated into heat, which ultimately cannot be accomplished without collisions. A kinetic cascade develops that brings the energy to collisional scales both in space and velocity. The nature of the kinetic cascade in various scale ranges depends on the physics of plasma fluctuations that exist there. There are four special scales that separate physically distinct regimes: the electron and ion gyroscales, the mean free path and the electron diffusion scale. In each of the scale ranges separated by these scales, the fully kinetic problem is systematically reduced to a more physically transparent and computationally tractable system of equations, which are derived in a rigorous way. In the "inertial range" above the ion gyroscale, the kinetic cascade separates into two parts: a cascade of Alfvenic fluctuations and a passive cascade of density and magnetic-fieldstrength fluctuations. The former are governed by the Reduced Magnetohydrodynamic (RMHD) equations at both the collisional and collisionless scales; the latter obey a linear kinetic equation along the (moving) field lines associated with the Alfvenic component (in the collisional limit, these compressive fluctuations
The direct criterion of Newcomb for the ideal MHD stability of an axisymmetric toroidal plasma
NASA Astrophysics Data System (ADS)
Glasser, A. H.
2016-07-01
A method is presented for determining the ideal magnetohydrodynamic stability of an axisymmetric toroidal plasma, based on a toroidal generalization of the method developed by Newcomb for fixed-boundary modes in a cylindrical plasma. For toroidal mode number n ≠ 0 , the stability problem is reduced to the numerical integration of a high-order complex system of ordinary differential equations, the Euler-Lagrange equation for extremizing the potential energy, for the coupled amplitudes of poloidal harmonics m as a function of the radial coordinate ψ in a straight-fieldline flux coordinate system. Unlike the cylindrical case, different poloidal harmonics couple to each other, which introduces coupling between adjacent singular intervals. A boundary condition is used at each singular surface, where m = nq and q ( ψ ) is the safety factor, to cross the singular surface and continue the solutions beyond it. Fixed-boundary instability is indicated by the vanishing of a real determinant of a Hermitian complex matrix constructed from the fundamental matrix of solutions, the generalization of Newcomb's crossing criterion. In the absence of fixed-boundary instabilities, an M × M plasma response matrix W P , with M the number of poloidal harmonics used, is constructed from the Euler-Lagrange solutions at the plasma-vacuum boundary. This is added to a vacuum response matrix W V to form a total response matrix W T . The existence of negative eigenvalues of W T indicates the presence of free-boundary instabilities. The method is implemented in the fast and accurate DCON code.
Electron beam-plasma interaction experiments with the Versatile Toroidal Facility (VTF)
Murphy, S.M.; Lee, M.C.; Moriarty, D.T.; Riddolls, R.J.
1995-12-31
The laboratory investigation of electron beam-plasma interactions is motivated by the recent space shuttle experiments. Interesting but puzzling phenomena were observed in the shuttle experiments such as the bulk heating of background ionospheric plasmas by the injected electron beams and the excitation of plasma waves in the frequency range of ELF waves. The plasma machine, the Versatile Toroidal Facility (VTF) can generate a large magnetized plasma with the electron plasma frequency greater than the electron gyrofrequency by a factor of 3--5 similar to the plasma condition in the ionosphere. Short pulses of electron beams are injected into the VTF plasmas in order to simulate the beam injection from spacecrafts in the ionosphere. A Langmuir probe installed at a bottom port of VTF monitors the spatial variation of electron beams emitted from LaB6 filaments. An energy analyzer has been used to determine the particle energy distribution in the VTF plasmas. Several mechanisms will be tested as potential causes of the bulk heating of background plasmas by the injected electron beams as seen in the space shuttle experiments. It is speculated that the observed ELF emissions result from the excitation of purely growing modes detected by the space shuttle-borne detectors. Results of the laboratory experiments will be reported to corroborate this speculation.
NASA Astrophysics Data System (ADS)
Singh, Navpreet; Gupta, Naveen; Singh, Arvinder
2016-12-01
This paper investigates second harmonic generation (SHG) of an intense Cosh-Gaussian (ChG) laser beam propagating through a preformed underdense collisional plasma with nonlinear absorption. Nonuniform heating of plasma electrons takes place due to the nonuniform irradiance of intensity along the wavefront of laser beam. This nonuniform heating of plasma leads to the self-focusing of the laser beam and thus produces strong density gradients in the transverse direction. The density gradients so generated excite an electron plasma wave (EPW) at pump frequency that interacts with the pump beam to produce its second harmonics. To envision the propagation dynamics of the ChG laser beam, moment theory in Wentzel-Kramers-Brillouin (W.K.B) approximation has been invoked. The effects of nonlinear absorption on self-focusing of the laser beam as well as on the conversion efficiency of its second harmonics have been theoretically investigated.
Ogino, Yousuke; Ohnishi, Naofumi
2010-05-06
A thrust power of a gas-driven laser-propulsion system is obtained through interaction with a propellant gas heated by a laser energy. Therefore, understanding the nonequilibrium nature of laser-produced plasma is essential for increasing available thrust force and for improving energy conversion efficiency from a laser to a propellant gas. In this work, a time-dependent collisional-radiative model for air plasma has been developed to study the effects of nonequilibrium atomic and molecular processes on population densities for an air-driven type laser propulsion. Many elementary processes are considered in the number density range of 10{sup 12}/cm{sup 3}<=N<=10{sup 19}/cm{sup 3} and the temperature range of 300 K<=T<=40,000 K. We then compute the unsteady nature of pulsively heated air plasma. When the ionization relaxation time is the same order as the time scale of a heating pulse, the effects of unsteady ionization are important for estimating air plasma states. From parametric computations, we determine the appropriate conditions for the collisional-radiative steady state, local thermodynamic equilibrium, and corona equilibrium models in that density and temperature range.
Collisional damping of helicon waves in a high density hydrogen linear plasma device
NASA Astrophysics Data System (ADS)
Caneses, Juan F.; Blackwell, Boyd D.
2016-10-01
In this paper, we investigate the propagation and damping of helicon waves along the length (50 cm) of a helicon-produced 20 kW hydrogen plasma ({{n}\\text{e}}˜ 1-2 × 1019 m-3, {{T}\\text{e}}˜ 1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (4-8 G and {λz}˜ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40-50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based on experimental measurements. Theoretical calculations are consistent with experiment and indicate that for conditions where Coulomb collisions are dominant classical collisionality is sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in helicon based linear plasma devices.
Johns, H. M.; Kilcrease, D. P.; Colgan, J.; ...
2015-09-29
In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amendmore » by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of Ne ~1017 cm-3. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.« less
Johns, H. M.; Kilcrease, D. P.; Colgan, J.; Judge, E. J.; Barefield II, J. E.; Wiens, R. C.; Clegg, S. M.
2015-09-29
In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amend by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of N_{e} ~10^{17} cm^{-3}. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.
Pahari, Sambaran; Lachhvani, Lavkesh Bajpai, Manu; Rathod, Karan; Yeole, Yogesh; Chattopadhyay, P. K.
2015-08-15
A suitable charge-collector has been designed and developed to estimate charge-content of electron plasmas in a Small Aspect Ratio Toroidal Experiment in a C-shaped trap (SMARTEX-C). The electrons are periodically injected and held in the trap with the aid of electrostatic end-fields and a toroidal magnetic field. After a preset “hold” time, the trapped charges are dumped onto a grounded collector (by gating it). As the charges flow along the magnetic field lines onto the collector, the integrated current gives the charge-content of the plasma at the instant of dump. In designing such a charge collector, several challenges peculiar to the geometry of the trap and the nature of the plasma had to be addressed. Instantaneous charge measurements synchronised with the E × B drift of the plasma, along with fast transit times of electrons to the collector (few 100 ns or less) (due to the low aspect ratio of the trap) essentially require fast gating of the collector. The resulting large capacitive transients alongside low charge content (few nC) of such plasmas further lead to increasing demands on response and sensitivity of the collector. Complete cancellation of such transients is shown to be possible, in principle, by including the return path in our measurement circuit but the “non-neutrality” of the plasma acts as a further impediment. Ultimately, appropriate shielding and measurement circuits allow us to (re)distribute the capacitance and delineate the paths of these currents, leading to effective cancellation of transients and marked improvement in sensitivity. Improved charge-collector has thus been used to successfully estimate the time evolution of total charge of the confined electron plasma in SMARTEX-C.
Rosenberg, M. J.; Li, C. K.; Fox, W.; Zylstra, A. B.; Stoeckl, C.; Séguin, F. H.; Frenje, J. A.; Petrasso, R. D.
2015-05-20
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly-driven, β ≲ 20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely-directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (V_{jet}~ 20V_{A}) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. The absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly-driven regime.
Rosenberg, M. J.; Li, C. K.; Fox, W.; ...
2015-05-20
An evolution of magnetic reconnection behavior, from fast jets to the slowing of reconnection and the establishment of a stable current sheet, has been observed in strongly-driven, β ≲ 20 laser-produced plasma experiments. This process has been inferred to occur alongside a slowing of plasma inflows carrying the oppositely-directed magnetic fields as well as the evolution of plasma conditions from collisionless to collisional. High-resolution proton radiography has revealed unprecedented detail of the forced interaction of magnetic fields and super-Alfvénic electron jets (Vjet~ 20VA) ejected from the reconnection region, indicating that two-fluid or collisionless magnetic reconnection occurs early in time. Themore » absence of jets and the persistence of strong, stable magnetic fields at late times indicates that the reconnection process slows down, while plasma flows stagnate and plasma conditions evolve to a cooler, denser, more collisional state. These results demonstrate that powerful initial plasma flows are not sufficient to force a complete reconnection of magnetic fields, even in the strongly-driven regime.« less
Basic physics of Alfven instabilities driven by energetic particles in toroidally confined plasmas
Heidbrink, W. W.
2008-05-15
Superthermal energetic particles (EP) often drive shear Alfven waves unstable in magnetically confined plasmas. These instabilities constitute a fascinating nonlinear system where fluid and kinetic nonlinearities can appear on an equal footing. In addition to basic science, Alfven instabilities are of practical importance, as the expulsion of energetic particles can damage the walls of a confinement device. Because of rapid dispersion, shear Alfven waves that are part of the continuous spectrum are rarely destabilized. However, because the index of refraction is periodic in toroidally confined plasmas, gaps appear in the continuous spectrum. At spatial locations where the radial group velocity vanishes, weakly damped discrete modes appear in these gaps. These eigenmodes are of two types. One type is associated with frequency crossings of counterpropagating waves; the toroidal Alfven eigenmode is a prominent example. The second type is associated with an extremum of the continuous spectrum; the reversed shear Alfven eigenmode is an example of this type. In addition to these normal modes of the background plasma, when the energetic particle pressure is very large, energetic particle modes that adopt the frequency of the energetic particle population occur. Alfven instabilities of all three types occur in every toroidal magnetic confinement device with an intense energetic particle population. The energetic particles are most conveniently described by their constants of motion. Resonances occur between the orbital frequencies of the energetic particles and the wave phase velocity. If the wave resonance with the energetic particle population occurs where the gradient with respect to a constant of motion is inverted, the particles transfer energy to the wave, promoting instability. In a tokamak, the spatial gradient drive associated with inversion of the toroidal canonical angular momentum P{sub {zeta}} is most important. Once a mode is driven unstable, a wide variety
Preparation and magnetic properties of Co-Cr films by toroidal plasma (TP) type sputtering
Takahashi, T. ); Nao, M. )
1989-09-01
The authors describe a new type of sputtering apparatus which can form a stable toroidal plasma developed in order to deposit magnetic films with a homogeneous and dense structure and excellent properties under the conditions of low argon gas pressure, low applied voltage and low substrate temperature around 30 {sup 0}C. All Co-Cr films deposited by this apparatus were composed of hcp phase crystallites with c-axis orientation {Delta}{theta}/sub 50/ ranging from 8 to 13{sup 0}. The saturation magnetization Ms varied from 380 to 780 emu/cc and perpendicular coercivity Hc varied from 100 to 300 Oe.
Local 3-D Toroidal Plasma Tomography Using the Phillips-Tikhonov Regularization Method
NASA Astrophysics Data System (ADS)
Lee, Seung Hun; Kim, Junghee; Choe, Wonho
2008-11-01
Tomography is one of a powerful diagnostic method for obtaining the local information from the line-integrated plasma emission in fusion devices. The 3-D tomography is a complicated task compared to the 2-D tomography. Because of the limitation of the spatial distribution of the array detectors around a torus, the regularization algorithm such as the Phillips-Tikhonov method is advantageous to achieve more reliable reconstruction. In this work, we performed a feasibility study of 3-D tomography for toroidal plasmas. Four tangentially-viewing array detectors of each array consisting of 16x16 detector elements were assumed to be implemented. The reconstruction area is configured as 70 cm x 50 cm of poloidal cross-section and 40 toroidal layers, which has spatial resolution of 5 cm. We chose the phantoms which are KSTAR plasma-like profiles combined with the equilibrium flux surfaces with n = 0, 1, 2, 3 modes. The change of the emission peak in each layer in the reconstruction result agrees reasonably well with that of the phantom, with relative error of 5 - 10 %.
Electron runaway across a magnetic field in a collisional high-atomic-number plasma
Mosher, D.; Welch, D.R.
1995-12-31
Nonthermal x-ray spectra observed in high-atomic-number z-pinch plasmas indicate that electrons with energies greatly in excess of the plasma temperature are present. A favorite mechanism for the production of these nonthermal electrons is acceleration in inductive electric fields produced by localized collapse of plasma into pinch spots. One problem with this acceleration mechanism is the presence of intense azimuthal magnetic fields embedded in the plasma which impede the runaway of electrons along the electric field. In this work, a fluid model for nonthermal electron flow in dense, high-atomic-number plasmas is employed to determine how collisions affect their energy gain in crossed electric and magnetic fields. The simple scaling laws derived from this model are compared with IPRPO particle-in-cell simulations of the same plasma environment. Large cross-field energy gains are calculated by both models for high-atomic number plasmas where the electron scattering (momentum-transfer) frequency v{sub s} is of order Zv{sub e}, where v{sub e} is the rate associated with collisional energy loss and Z is the plasma ionization level. Once a threshold electric field is exceeded, a large number of scattering collisions across the magnetic field and along the electric field can occur in an energy-loss time and much larger energy gains are possible than in hydrogenic plasmas.
Study of micro-instabilities in toroidal plasmas with negative magnetic shear
Dong, J.Q.; Zhang, Y.Z.; Mahajan, S.M.; Guzdar, P.N.
1996-03-01
The micro-instabilities driven by a parallel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyro-kinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower, and the threshold temperature gradient {eta}{sub icr} is higher for plasmas with negative magnetic shear compared to plasmas with positive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insignificant, does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed.
Wall thickness effect on the resistive wall mode stability in toroidal plasmas
Zheng, L.-J.; Kotschenreuther, M.T.
2005-07-15
The effect of finite wall thickness on the stability of n=1 resistive wall modes in toroidal plasmas is investigated. A fusion reactor-relevant configuration is examined. The investigation employs a novel ideal-magnetohydrodynamics adaptive shooting code for axisymmetric plasmas, extended to take into account the wall thickness. Although finite wall thickness generally reduces the growth rate of the resistive wall modes, no contribution to stabilization is found to be made by the portion of the wall that is located beyond the critical position for perfectly conducting wall stabilization. Thus, when the inner side of the wall lies near the critical wall position, the scaling of the growth rate versus wall thickness in the realistic thick-wall calculation is significantly different from that of the usual thin-wall theory. The thin-wall estimate is relevant only when the wall is brought very close to the plasma and is not too thick.
Plasma blobs in a basic toroidal experiment: Origin, dynamics, and induced transport
Mueller, S. H.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Podesta, M.
2007-11-15
Detaching plasma blobs with very similar properties to tokamaks are observed in the basic toroidal plasma experiment TORPEX [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. The blobs originate from the breaking of wave crests of a drift-interchange wave, which span over regions characterized by strongly inhomogeneous background parameters. Once decoupled from the wave, the blobs follow a predominantly radial trajectory pattern. The blob-induced cross-field transport can instantaneously exceed the steady-state parallel fluxes by one order of magnitude, while accounting for only 10% of the time-average device losses. If the particles were confined in the parallel direction, as is the case in tokamaks, blobs would constitute the dominant loss mechanism in TORPEX. The presented results show that the presence of grad B is sufficient and neither a magnetic-topology change nor the presence of limiters, both absent in TORPEX, are necessary for the generation of blobs.
Development of electrostatic turbulence from drift-interchange instabilities in a toroidal plasma
Poli, F. M.; Podesta, M.; Fasoli, A.
2007-05-15
Electrostatic instabilities develop on TORPEX (TORoidal Plasma EXperiment) [A. Fasoli et al., Phys. of Plasmas, 13, 55902 (2006)] in the bad curvature region and propagate consistently with the drift wave dispersion relation. The wave number and frequency spectra are coherent at the location where the instabilities are generated, then broaden along the ExB convection. The phase coupling between spectral components at different frequencies, measured at different locations over the plasma cross section, indicates that the transition from a coherent to a turbulent spectrum is mainly due to three-wave interaction processes. Nonlinear interactions are measured between the linearly unstable mode and fluctuations with larger frequency, with transfer of energy away from the linearly unstable mode. The results are consistent with a nonlinearity induced by the convection of density fluctuations by the ExB fluctuating velocity.
Mikkelsen, D. R. Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.
2015-06-15
Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.
Moser, Auna L. Hsu, Scott C.
2015-05-15
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.
Collisional heating of a plasma column slowly forced across a squeeze potential
NASA Astrophysics Data System (ADS)
Dubin, D. H. E.
2016-10-01
When equilibrium plasmas have two or more locally-trapped particle populations, perturbations to the equilibrium can produce phase-space discontinuities in the distribution function that strongly enhance transport, plasma loss, and wave damping. This poster presents a simple version of this process, wherein a plasma is heated as it is slowly forced back and forth across a squeeze potential (at a frequency ω that is small compared to the particle bounce frequency) that traps particles on either side of the squeeze. Adiabatic theory is developed for the distribution function, showing that trapped and passing particles have different responses to the forcing that produces a collisional boundary layer at the separatrix. Expressions for both the adiabatic and non-adiabatic distribution functions are presented, and the heating rate caused by the collisional boundary layer at the separatrix is derived. The heating is proportional to √ (ν ω) , where ν is the collision rate. Supported by NSF Grant PHY-1414570, and DOE Grants DE-SC0002451 and DE-SC0008693.
On dust ion acoustic solitary waves in collisional dusty plasmas with ionization effect
NASA Astrophysics Data System (ADS)
Shalaby, M.; El-Labany, S. K.; El-Shamy, E. F.; Khaled, M. A.
2010-04-01
The propagation of solitary waves in an unmagnetized collisional dusty plasma consisting of a negatively charged dust fluid, positively charged ions, isothermal electrons, and background neutral particles is studied. The ionization, ion loss, ion-neutral, ion-dust, and dust-neutral collisions are considered. Applying a reductive perturbation theory, a damped Korteweg-de Vries (DKdV) equation is derived. On the other hand, at a critical phase velocity, the dynamics of solitary waves is governed by a damped modified Korteweg-de Vries (DMKdV) equation. The nonlinear properties of solitary waves in the two cases are discussed.
Merritt, Elizabeth C. Adams, Colin S.; Moser, Auna L.; Hsu, Scott C. Dunn, John P.; Miguel Holgado, A.; Gilmore, Mark A.
2014-05-15
We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼10{sup 14} cm{sup −3}, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].
Self-focusing of intense high frequency electromagnetic waves in a collisional magnetoactive plasma
Niknam, A. R.; Hashemzadeh, M.; Aliakbari, A.; Majedi, S.; Haji Mirzaei, F.
2011-11-15
The self-focusing of an intense electromagnetic beam in a collisional magnetoactive plasma has been investigated by the perturbation method. Considering the relativistic and ponderomotive nonlinearities and the first three terms of perturbation expansion for the electron density and velocity, the nonlinear wave equation is obtained. This wave equation is solved by applying the source dependent expansion method and the evolution of electromagnetic beam spot-size is discussed. It is shown that the laser spot-size decreases with increasing the collision frequency and external magnetic field strength.
Laser-pulse compression in a collisional plasma under weak-relativistic ponderomotive nonlinearity
NASA Astrophysics Data System (ADS)
Singh, Mamta; Gupta, D. N.
2016-05-01
We present theory and numerical analysis which demonstrate laser-pulse compression in a collisional plasma under the weak-relativistic ponderomotive nonlinearity. Plasma equilibrium density is modified due to the ohmic heating of electrons, the collisions, and the weak relativistic-ponderomotive force during the interaction of a laser pulse with plasmas. First, within one-dimensional analysis, the longitudinal self-compression mechanism is discussed. Three-dimensional analysis (spatiotemporal) of laser pulse propagation is also investigated by coupling the self-compression with the self-focusing. In the regime in which the laser becomes self-focused due to the weak relativistic-ponderomotive nonlinearity, we provide results for enhanced pulse compression. The results show that the matched interplay between self-focusing and self-compression can improve significantly the temporal profile of the compressed pulse. Enhanced pulse compression can be achieved by optimizing and selecting the parameters such as collision frequency, ion-temperature, and laser intensity.
Ponderomotive self-focusing of Gaussian laser beam in warm collisional plasma
Jafari Milani, M. R.; Niknam, A. R.; Farahbod, A. H.
2014-06-15
The propagation characteristics of a Gaussian laser beam through warm collisional plasma are investigated by considering the ponderomotive force nonlinearity and the complex eikonal function. By introducing the dielectric permittivity of warm unmagnetized plasma and using the WKB and paraxial ray approximations, the coupled differential equations defining the variations of laser beam parameters are obtained and solved numerically. Effects of laser and plasma parameters such as the collision frequency, the initial laser intensity and its spot size on the beam width parameter and the axis laser intensity distribution are analyzed. It is shown that, self-focusing of the laser beam takes place faster by increasing the collision frequency and initial laser spot size and then after some distance propagation the laser beam abruptly loses its initial diameter and vastly diverges. Furthermore, the modified electron density distribution is obtained and the collision frequency effect on this distribution is studied.
Experimental investigation of plasma flows in open trap with toroidal diverter under ECR discharge
NASA Astrophysics Data System (ADS)
Berezkin, A. V.; Bragin, E. Yu.; Zhil'tsov, V. A.; Kulygin, V. M.; Yanchenkov, S. V.
2015-12-01
The results of experimental investigations of plasma flows from an open trap with a toroidal diverter are presented. Cold plasma is generated when introducing microwave power under conditions of electron cyclotron resonance (ECR). The radiation is introduced by a waveguide through a vacuum-tight ceramic window across the axis of the device. By means of the Langmuir probes, the spatial distributions of plasma parameters are measured. The highest density is limited to a critical value n c (~1012 cm-3) for the generator frequency under use. It is found that the temperature and density of the plasma in the trap and in escaping flows are almost independent of the radius when the ECR zone is located near the open-trap confinement region and the density is close to n c. At the density n < n c, ring plasma structures, which collapse under the action of a low-frequency instability, are observed near the separatrix. The possible mechanisms of the occurrence of plasma structures and the nature of the plasma streams are discussed.
Experimental investigation of plasma flows in open trap with toroidal diverter under ECR discharge
Berezkin, A. V. Bragin, E. Yu. Zhil’tsov, V. A. Kulygin, V. M. Yanchenkov, S. V.
2015-12-15
The results of experimental investigations of plasma flows from an open trap with a toroidal diverter are presented. Cold plasma is generated when introducing microwave power under conditions of electron cyclotron resonance (ECR). The radiation is introduced by a waveguide through a vacuum-tight ceramic window across the axis of the device. By means of the Langmuir probes, the spatial distributions of plasma parameters are measured. The highest density is limited to a critical value n{sub c} (∼10{sup 12} cm{sup –3}) for the generator frequency under use. It is found that the temperature and density of the plasma in the trap and in escaping flows are almost independent of the radius when the ECR zone is located near the open-trap confinement region and the density is close to n{sub c}. At the density n < n{sub c}, ring plasma structures, which collapse under the action of a low-frequency instability, are observed near the separatrix. The possible mechanisms of the occurrence of plasma structures and the nature of the plasma streams are discussed.
Liang, G. Y.; Li, F.; Wang, F. L.; Zhong, J. Y.; Zhao, G.; Wu, Y.
2014-03-10
Several laboratory facilities were used to benchmark theoretical spectral models that are extensively used by astronomical communities. However, there are still many differences between astrophysical environments and laboratory miniatures that can be archived. Here we setup a spectral analysis system for astrophysical and laboratory plasmas to make a bridge between them, and we investigate the effects from non-thermal electrons and the contributions from a metastable level population on level populations and charge stage distribution for coronal-like, photoionized, and geocoronal plasmas. Test applications to laboratory measurement (i.e., electron beam ion trap plasma) and astrophysical observation (i.e., Comet, Cygnus X-3) are presented. A time evolution of the charge stage and level population are also explored for collisional and photoionized plasmas.
Grach, V. S. Garasev, M. A.
2015-07-15
We consider the interaction of a isolated conducting sphere with a collisional weakly ionized plasma in an external field. We assume that the plasma consists of two species of ions neglecting of electrons. We take into account charging of the sphere due to sedimentation of plasma ions on it, the field of the sphere charge and the space charge, as well as recombination and molecular diffusion. The nonstationary problem of interaction of the sphere with the surrounding plasma is solved numerically. The temporal dynamics of the sphere charge and plasma perturbations is analyzed, as well as the properties of the stationary state. It is shown that the duration of transient period is determined by the recombination time and by the reverse conductivity of ions. The temporal dynamics of the sphere charge and plasma perturbations is determined by the intensity of recombination processes relative to the influence of the space charge field and diffusion. The stationary absolute value of the sphere charge increases linearly with the external electric field, decreases with the relative intensity of recombination processes and increases in the presence of substantial diffusion. The scales of the perturbed region in the plasma are determined by the radius of the sphere, the external field, the effect of diffusion, and the relative intensity of recombination processes. In the limiting case of the absence of molecular diffusion and a strong external field, the properties of the stationary state coincide with those obtained earlier as a result of approximate solution.
NASA Astrophysics Data System (ADS)
Grach, V. S.; Garasev, M. A.
2015-07-01
We consider the interaction of a isolated conducting sphere with a collisional weakly ionized plasma in an external field. We assume that the plasma consists of two species of ions neglecting of electrons. We take into account charging of the sphere due to sedimentation of plasma ions on it, the field of the sphere charge and the space charge, as well as recombination and molecular diffusion. The nonstationary problem of interaction of the sphere with the surrounding plasma is solved numerically. The temporal dynamics of the sphere charge and plasma perturbations is analyzed, as well as the properties of the stationary state. It is shown that the duration of transient period is determined by the recombination time and by the reverse conductivity of ions. The temporal dynamics of the sphere charge and plasma perturbations is determined by the intensity of recombination processes relative to the influence of the space charge field and diffusion. The stationary absolute value of the sphere charge increases linearly with the external electric field, decreases with the relative intensity of recombination processes and increases in the presence of substantial diffusion. The scales of the perturbed region in the plasma are determined by the radius of the sphere, the external field, the effect of diffusion, and the relative intensity of recombination processes. In the limiting case of the absence of molecular diffusion and a strong external field, the properties of the stationary state coincide with those obtained earlier as a result of approximate solution.
How LIF has helped to understand ion loss at the boundaries of weakly collisional plasmas
NASA Astrophysics Data System (ADS)
Hershkowitz, N.; Ko, E.; Wang, X.; Oksuza, L.; Halab, A.; Servern, G.
2003-10-01
Recent experiments in weakly collisional multi-dipole plasmas with one and two positive ion species have provided a much better understanding of ion motion in presheaths near the boundaries of such plasmas. Plasma potential was determined with emissive probes, ion density with Langmuir probes and diode laser LIF, ion drift velocity with Mach probes calibrated with LIF, and directly with LIF, and from the phase velocity of ion acoustic waves. LIF provided measurements of the ion velocity distribution functions and showed that ion-neutral charge exchange results in ion "heating" near boundaries. LIF showed that Ar ions in Ar-He plasma exit the plasma at the plasma/sheath boundary with a velocity greater than the Ar ion Bohm velocity. In single species plasma, the same diagnostic shows Ar average ion exit velocity equals the Bohm velocity. ^A Suleyman Demirel University, Physics Dept., Isparta Turkey ^B KACST, Space Research Institute, Riyadh, Saudi Arabia *Work supported by US DOE grant DE-FG02-97ER 54437
Fully kinetic simulations of magnetic reconnction in semi-collisional plasmas
Daughton, William S; Roytershteyn, Vadim S; Albright, Brian J; Yin, Lin; Bowers, Kevin J; Karimabadi, Homa
2009-01-01
The influence of Coulomb collisions on the dynamics of magnetic reconnection is examined using fully kinetic simulations with a Monte-Carlo treatment of the Fokker-Planck collision operator. This powerful first-principles approach offers a bridge between kinetic and fluid regimes, which may prove useful for understanding the applicability of various fluid models. In order to lay the necessary groundwork, the collision algorithm is first carefully bench marked for a homogeneous plasma against theoretical predictions for beam-plasma interactions and electrical resistivity. Next, the collisional decay of a current layer is examined as a function of guide field, allowing direct comparisons with transport theory for the parallel and perpendicular resistivity as well as the thermoelectric force. Finally, the transition between collisional and collision less reconnection is examined in neutral sheet geometry. For modest Lundquist numbers S {approx}< 1000, a distinct transition is observed when the thickness of the Sweet-Parker layers falls below the ion inertia length {delta}{sub sp} {approx}< d,. At higher Lundquist number, deviations from the Sweet-Parker scaling are observed due to the growth of plasmoids (secondary-islands) within the elongated resistive layer. In certain cases, this instability leads to the onset of fast reconnection sooner than expected from {delta}{sub sp} {approx} d, condition. After the transition to fast reconnection, elongated electron current layers are formed which are unstable to the formation of new plasmoids. The structure and time-dependence of the electron diffusion region in these semi-collisional regimes is profoundly different than reported in two-fluid simulations.
Oz, E.; Myers, C. E.; Yamada, M.; Ji, H.; Kulsrud, R. M.; Xie, J.
2011-07-19
The stability properties of partial toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas, 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kink instability. Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., qa = 1).
Symmetry breaking in MAST plasma turbulence due to toroidal flow shear
NASA Astrophysics Data System (ADS)
Fox, M. F. J.; van Wyk, F.; Field, A. R.; Ghim, Y.-c.; Parra, F. I.; Schekochihin, A. A.; the MAST Team
2017-03-01
The flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up–down symmetry of the magnetic equilibrium. Using experimental beam-emission-spectroscopy measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating density field. The tilt is a statistical expression of the ‘shearing’ of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the nonlinear stability threshold. Away from the threshold, the symmetry is effectively restored.
Liu, Wei; Hsu, Scott; Li, Hui
2009-01-01
We present results from three-dimensional ideal magnetohydrodynamic simulations of low {beta} compact toroid (CT) injection into a hot strongly magnetized plasma, with the aim of providing insight into CT fueling of a tokamak with parameters relevant for ITER (International Thermonuclear Experimental Reactor). A regime is identified in terms of CT injection speed and CT-to-background magnetic field ratio that appears promising for precise core fueling. Shock-dominated regimes, which are probably unfavorable for tokamak fueling, are also identified. The CT penetration depth is proportional to the CT injection speed and density. The entire CT evolution can be divided into three stages: (1) initial penetration, (2) compression in the direction of propagation and reconnection, and (3) coming to rest and spreading in the direction perpendicular to injection. Tilting of the CT is not observed due to the fast transit time of the CT across the background plasma.
On the interplay between neoclassical tearing modes and nonlocal transport in toroidal plasmas
Ji, X. Q.; Xu, Y.; Hidalgo, C.; Diamond, P. H.; Liu, Yi; Pan, O.; Shi, Z. B.; Yu, D. L.
2016-01-01
This Letter presents the first observation on the interplay between nonlocal transport and neoclassical tearing modes (NTMs) during transient nonlocal heat transport events in the HL-2A tokamak. The nonlocality is triggered by edge cooling and large-scale, inward propagating avalanches. These lead to a locally enhanced pressure gradient at the q = 3/2 (or 2/1) rational surface and hence the onset of the NTM in relatively low β plasmas (βN < 1). The NTM, in return, regulates the nonlocal transport by truncation of avalanches by local sheared toroidal flows which develop near the magnetic island. These findings have direct implications for understanding the dynamic interaction between turbulence and large-scale mode structures in fusion plasmas. PMID:27595773
Ion confinement and transport in a toroidal plasma with externally imposed radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.; Krawczonek, W. M.; Powers, E. J.; Kim, Y. C.; Hong, H. Y.
1979-01-01
Strong electric fields were imposed along the minor radius of the toroidal plasma by biasing it with electrodes maintained at kilovolt potentials. Coherent, low-frequency disturbances characteristic of various magnetohydrodynamic instabilities were absent in the high-density, well-confined regime. High, direct-current radial electric fields with magnitudes up to 135 volts per centimeter penetrated inward to at least one-half the plasma radius. When the electric field pointed radially toward, the ion transport was inward against a strong local density gradient; and the plasma density and confinement time were significantly enhanced. The radial transport along the electric field appeared to be consistent with fluctuation-induced transport. With negative electrode polarity the particle confinement was consistent with a balance of two processes: a radial infusion of ions, in those sectors of the plasma not containing electrodes, that resulted from the radially inward fields; and ion losses to the electrodes, each of the which acted as a sink and drew ions out of the plasma. A simple model of particle confinement was proposed in which the particle confinement time is proportional to the plasma volume. The scaling predicted by this model was consistent with experimental measurements.
Collisional relaxation of a strongly magnetized two-species pure ion plasma
NASA Astrophysics Data System (ADS)
Chim, Chi Yung; O'Neil, Thomas M.; Dubin, Daniel H.
2014-04-01
The collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ω1,Ω2≫|Ω1-Ω2|≫v¯ij/b ¯ and v¯⊥j/Ωj≪b ¯, where Ω1 and Ω2 are two cyclotron frequencies, v¯ij=√T∥/μij is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b ¯=2 e2/T∥ is the classical distance of closest approach for such collisions, and v ¯⊥j/Ωj=√2T⊥j/mj /Ωj is the characteristic cyclotron radius for particles of species j. Here, μij is the reduced mass for the two particles, and T∥ and T⊥j are temperatures that characterize velocity components parallel and perpendicular to the magnetic field. For this ordering, the total cyclotron action for the two species, I1=∑i ∈1m1v⊥i2/(2Ω1) and I2=∑i∈2m2v⊥i2/(2Ω2) are adiabatic invariants that constrain the collisional dynamics. On the timescale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions I1 and I2, yielding a modified Gibbs distribution of the form exp[-H /T∥-α1I1-α2I2]. Here, the αj's are related to T∥ and T⊥j through T⊥j=(1/T∥+αj/Ωj)-1. Collisional relaxation to the usual Gibbs distribution, exp[-H /T∥], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b ¯2Ω12/v¯112)exp{5[3π(b¯|Ω1-Ω2|/v ¯12)]2/5/6}, the two species share action so that α1 and α2 relax to a common value α. On an even longer timescale, longer than the collisional timescale by a factor of the order exp {5[3π(v¯11)]2/5/6}, the total action ceases to be a good constant of the motion and α relaxes to zero.
Energetically consistent collisional gyrokinetics
Burby, J. W.; Brizard, A. J.; Qin, H.
2015-10-30
Here, we present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory. (C) 2015 AIP Publishing LLC.
NASA Astrophysics Data System (ADS)
Stults, Joshua
This research presents a numerical framework for diagnosing electron properties in collisional plasmas. Microwave diagnostics achieved a significant level of development during the middle part of the last century due to work in nuclear weapons and fusion plasma research. With the growing use of plasma-based devices in fields as diverse as space propulsion, materials processing and fluid flow control, there is a need for improved, flexible diagnostic techniques suitable for use under the practical constraints imposed by plasma fields generated in a wide variety of aerospace devices. Much of the current diagnostic methodology in the engineering literature is based on analytical diagnostic, or forward, models. The Appleton-Hartree formula is an oft-used analytical relation for the refractive index of a cold, collisional plasma. Most of the assumptions underlying the model are applicable to diagnostics for plasma fields such as those found in Hall Thrusters and dielectric barrier discharge (DBD) plasma actuators. Among the assumptions is uniform material properties, this assumption is relaxed in the present research by introducing a flexible, numerical model of diagnostic wave propagation that can capture the effects of spatial gradients in the plasma state. The numerical approach is chosen for its flexibility in handling future extensions such as multiple spatial dimensions to account for scattering effects when the spatial extent of the plasma is small relative to the probing beam's width, and velocity dependent collision frequency for situations where the constant collision frequency assumption is not justified. The numerical wave propagation model (forward model) is incorporated into a general tomographic reconstruction framework that enables the combination of multiple interferometry measurements. The combined measurements provide a quantitative picture of the spatial variation in the plasma properties. The benefit of combining multiple measurements in a coherent
Nonlinear coherent structures of Alfvén wave in a collisional plasma
NASA Astrophysics Data System (ADS)
Jana, Sayanee; Ghosh, Samiran; Chakrabarti, Nikhil
2016-07-01
The Alfvén wave dynamics is investigated in the framework of two-fluid approach in a compressible collisional magnetized plasma. In the finite amplitude limit, the dynamics of the nonlinear Alfvén wave is found to be governed by a modified Korteweg-de Vries Burgers equation (mKdVB). In this mKdVB equation, the electron inertia is found to act as a source of dispersion, and the electron-ion collision serves as a dissipation. The collisional dissipation is eventually responsible for the Burgers term in mKdVB equation. In the long wavelength limit, this weakly nonlinear Alfvén wave is shown to be governed by a damped nonlinear Schrödinger equation. Furthermore, these nonlinear equations are analyzed by means of analytical calculation and numerical simulation to elucidate the various aspects of the phase-space dynamics of the nonlinear wave. Results reveal that nonlinear Alfvén wave exhibits the dissipation mediated shock, envelope, and breather like structures. Numerical simulations also predict the formation of dissipative Alfvénic rogue wave, giant breathers, and rogue wave holes. These results are discussed in the context of the space plasma.
Nonlinear Coherent Structures of Alfvén Wave in a Collisional Plasma
NASA Astrophysics Data System (ADS)
Jana, Sayanee; Ghosh, Samiran; Chakrabarti, Nikhil
2016-10-01
The Alfvén wave dynamics is investigated in the framework of Lagrangian two-fluid model in a cold magnetized collisional plasma in presence of finite electron inertia. In the quasi-linear limit, the dynamics of the nonlinear Alfvén wave is shown to be governed by a modified Korteweg-de Vries Burgers (mKdVB) equation. In this mKdVB equation, the electron inertia is found to act as a source of dispersion and the electro-ion collision serves as a dissipation. In the long wavelength limit, we have also investigated wave modulation characteristics of the nonlinear Alfvén wave. The dynamics of this modulated wave is shown to be governed by a damped nonlinear Schrödinger equation (NLSE). These nonlinear equations are analysed by means of analytical and numerical simulation to elucidate the various aspects of the phase-space dynamics of the nonlinear wave. Results reveal that nonlinear Alfvén wave exhibits shock, envelope and breather like structures. Numerical simulations also predict the formation of Alfvénic rogue waves, rogue wave holes and giant breathers. These results could be useful for understanding the salient features of the Alfvénic magnetic field structures from observational data in very low- βmagnetized collisional plasmas in space and laboratory.
NASA Astrophysics Data System (ADS)
Cui, L.; Grierson, B.; Logan, N.; Nazikian, R.
2016-10-01
Application of RMPs to low collisionality (ν*e < 0.4) ITER shape plasmas on DIII-D leads to a rapid reduction in stored energy due to density pumpout that is sometimes followed by a gradual recovery in the plasma stored energy. Understanding this confinement recovery is essential to optimize the confinement of RMP plasmas in present and future devices such as ITER. Transport modeling using TRANSP+TGLF indicates that the core a/LTi is stiff in these plasmas while the ion temperature gradient is much less stiff in the pedestal region. The reduction in the edge density during pumpout leads to an increase in the core ion temperature predicted by TGLF based on experimental data. This is correlated to the increase in the normalized ion heat flux. Transport stiffness in the core combined with an increase in the edge a/LTi results in an increase of the plasma stored energy, consistent with experimental observations. For plasmas where the edge density is controlled using deuterium gas puffs, the effect of the RMP on ion thermal confinement is significantly reduced. Work supported by US DOE Grant DE-FC02-04ER54698 and DE-AC02-09CH11466.
The effect of radial inhomogeneity on the collisional power absorption in helicon plasma sources
NASA Astrophysics Data System (ADS)
Soltani, B.; Habibi, M.; Zakeri-khatir, H.
2016-02-01
The paper reports on the effects of plasma radial inhomogeneity on the power absorption in a helicon plasma source, which are computationally investigated by the CST Microwave Studio code. RF (13.56 MHz) power deposition was studied using three designs of antennas, namely, the Nagoya type-III, the fractional helix, and the single loop. Argon was used as the plasma working gas at the operating pressure of 15 mTorr. We have focused on the collisional power absorption utilizing WKB approximation to describe the plasma inhomogeneity. The obtained results show that the radial inhomogeneity has different effects on the power absorption at the low and the high magnetic fields. It is found that at low magnetic fields (i.e., B 0 = 0.01 T ) , there is a specific density ( n c ) ranging from 5 × 10 18 m - 3 to 1 × 10 19 m - 3 , before and after which the radial inhomogeneity decreases and increases the absorbed power, respectively. On the other hand, at high magnetic fields (i.e., B 0 = 0.1 T ), the inhomogeneity has no regular effect on the power absorption in various plasma densities. In addition, for a given plasma density (e.g., n = 10 18 m - 3 ), as the magnetic field increases, the radial inhomogeneity effect on the power absorption would decrease for the Nagoya type-III and the fractional helix designs. However, for the single loop antenna design, this effect is negligible.
NASA Astrophysics Data System (ADS)
Barni, R.; Caldirola, S.; Fattorini, L.; Riccardi, C.
2017-03-01
The analysis of the anomalous transport in magnetised plasmas has pointed out the substantial contribution of intermittent burst events corresponding to positive density fluctuations propagating outwards to the edges of the devices. Much less attention was paid to negative density fluctuation structures, which could be named depletions or voids, whose propagation could contribute to the global anomalous transport, in particular, when a non-negligible diffuse plasma background is present in magnetized plasma device edges. Here, we discuss the results of an experimental investigation aimed to study the spatio-temporal evolution of density depletion structures propagating inwards in a magnetized plasma column simply magnetized toroidal device. Evidence of this behavior was gathered by a conditional sampling analysis applied to time series of plasma fluctuations. We observe that a significant fraction of void structures, after being ejected outside the main plasma column, gets pulled inwards and disappears by merging at the column edge. On the other hand, a smaller fraction as well as most of the positive density structures, after ejection, ends up advected towards the edges of the device and gets lost from the main plasma column. These behaviors testify the richness and complexity of density structure evolution in magnetized plasma turbulence.
Theory of Collisional Two-Stream Plasma Instabilities in the Solar Chromosphere
NASA Astrophysics Data System (ADS)
Madsen, Chad Allen; Dimant, Yakov; Oppenheim, Meers; Fontenla, Juan
2014-06-01
The solar chromosphere experiences intense heating just above its temperature minimum. The heating increases the electron temperature in this region by over 2000 K. Furthermore, it exhibits little time variation and appears widespread across the solar disk. Although semi-empirical models, UV continuum observations, and line emission measurements confirm the existence of the heating, its source remains unexplained. Potential heating sources such as acoustic shocks, resistive dissipation, and magnetic reconnection via nanoflares fail to account for the intensity, persistence, and ubiquity of the heating. Fontenla (2005) suggested turbulence from a collisional two-stream plasma instability known as the Farley-Buneman instability (FBI) could contribute significantly to the heating. This instability is known to heat the plasma of the E-region ionosphere which bears many similarities to the chromospheric plasma. However, the ionospheric theory of the FBI does not account for the diverse ion species found in the solar chromosphere. This work develops a new collisional, two-stream instability theory appropriate for the chromospheric plasma environment using a linear fluid analysis to derive a new dispersion relationship and critical E x B drift velocity required to trigger the instability. Using a 1D, non-local thermodynamic equilibrium, radiative transfer model and careful estimates of collision rates and magnetic field strengths, we calculate the trigger velocities necessary to induce the instability throughout the chromosphere. Trigger velocities as low as 4 km s^-1 are found near the temperature minimum, well below the local neutral acoustic speed in that region. From this, we expect the instability to occur frequently, converting kinetic energy contained in neutral convective flows from the photosphere into thermal energy via turbulence. This could contribute significantly to chromospheric heating and explain its persistent and ubiquitous nature.
A model for particle confinement in a toroidal plasma subject to strong radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.
1977-01-01
A toroidal plasma is confined and heated by the simultaneous application of strong d.c. magnetic fields and electric fields. Strong radial electric fields (about 1 kilovolt per centimeter) are imposed by biasing the plasma with up to 12 negative electrode rings which surround its minor circumference. The plasma containment is consistent with a balance of two processes: a radial infusion of ions in those sectors not containing electrode rings, resulting from the radially inward electric fields; and ion losses to the electrode rings, each of which acts as a sink and draws ions out the plasma in the manner of a Langmuir probe in the ion saturation regime. The highest density on axis which has been observed so far in this steady-state plasma is 6.2 x 10 to the 12th power particles per cubic centimeter, for which the particle containment time is 2.5 milliseconds. The deuterium ion kinetic temperature for these conditions was in the range of 360 to 520 eV.
A model for particle confinement in a toroidal plasma subject to strong radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.
1977-01-01
The approach adopted in the NASA Lewis Bumpy Torus experiment is to confine and heat a toroidal plasma by the simultaneous application of strong dc magnetic fields and electric fields. Strong radial electric fields (about 1 kV/cm) are imposed by biasing the plasma with up to 12 negative electrode rings which surround its minor circumference. The plasma containment is consistent with a balance of two processes: a radial infusion of ions in those sectors not containing electrode rings, resulting from the radially inward electric fields; and ion losses to the electrode rings, each of which acts as a sink and draws ions out the plasma in the manner of a Langmuir probe in the ion saturation regime. The highest density on axis which has been observed so far in this steady-state plasma is 6.2 trillion particles per cu cm, for which the particle containment time is 2.5 msec. The deuterium ion kinetic temperature for these conditions was in the range of 360 to 520 eV.
H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment
NASA Astrophysics Data System (ADS)
Thome, K. E.; Bongard, M. W.; Barr, J. L.; Bodner, G. M.; Burke, M. G.; Fonck, R. J.; Kriete, D. M.; Perry, J. M.; Reusch, J. A.; Schlossberg, D. J.
2017-02-01
H-mode is obtained at A˜ 1.2 in the Pegasus Toroidal Experiment via Ohmic heating, high-field-side fueling, and low edge recycling in both limited and diverted magnetic topologies. These H-mode plasmas show the formation of edge current and pressure pedestals and a doubling of the energy confinement time to {{H}98y,2}˜ 1 . The L-H power threshold {{P}\\text{LH}} increases with density, and there is no {{P}\\text{LH}} minimum observed in the attainable density space. The power threshold is equivalent in limited and diverted plasmas, consistent with the FM3 model. However, the measured {{P}\\text{LH}} is ˜ 15 × higher than that predicted by conventional International Tokamak Physics Activity (ITPA) scalings, and {{P}\\text{LH}}/{{P}\\text{ITPA08}} increases as A\\to 1 . Small ELMs are present at low input power {{P}\\text{IN}}˜ {{P}\\text{LH}} , with toroidal mode number n≤slant 4 . At {{P}\\text{IN}}\\gg {{P}\\text{LH}} , they transition to large ELMs with intermediate 5. The dominant-n component of a large ELM grows exponentially, while other components evolve nonlinearly and can damp prior to the crash. Direct measurements of the current profile in the pedestal region show that both ELM types exhibit a generation of a current-hole, followed by a pedestal recovery. Large ELMs are shown to further expel a current-carrying filament. Small ELM suppression via injection of low levels of helical current into the edge plasma region is also indicated.
H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment
Thome, Kathleen E.; Bongard, Michael W.; Barr, Jayson L.; ...
2016-09-30
H-mode is obtained atmore » $$A\\sim 1.2$$ in the Pegasus Toroidal Experiment via Ohmic heating, high-field-side fueling, and low edge recycling in both limited and diverted magnetic topologies. These H-mode plasmas show the formation of edge current and pressure pedestals and a doubling of the energy confinement time to $${{H}_{98y,2}}\\sim 1$$ . The L–H power threshold $${{P}_{\\text{LH}}}$$ increases with density, and there is no $${{P}_{\\text{LH}}}$$ minimum observed in the attainable density space. The power threshold is equivalent in limited and diverted plasmas, consistent with the FM3 model. However, the measured $${{P}_{\\text{LH}}}$$ is $$\\sim 15\\,\\,\\times $$ higher than that predicted by conventional International Tokamak Physics Activity (ITPA) scalings, and $${{P}_{\\text{LH}}}/{{P}_{\\text{ITPA}08}}$$ increases as $$A\\to 1$$ . Small ELMs are present at low input power $${{P}_{\\text{IN}}}\\sim {{P}_{\\text{LH}}}$$ , with toroidal mode number $$n\\leqslant 4$$ . At $${{P}_{\\text{IN}}}\\gg {{P}_{\\text{LH}}}$$ , they transition to large ELMs with intermediate 5 < n < 15. The dominant-n component of a large ELM grows exponentially, while other components evolve nonlinearly and can damp prior to the crash. Direct measurements of the current profile in the pedestal region show that both ELM types exhibit a generation of a current-hole, followed by a pedestal recovery. Large ELMs are shown to further expel a current-carrying filament. Small ELM suppression via injection of low levels of helical current into the edge plasma region is also indicated.« less
H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment
Thome, Kathleen E.; Bongard, Michael W.; Barr, Jayson L.; Bodner, Grant M.; Burke, Marcus G.; Fonck, Raymonf J.; Kriete, David M.; Perry, Justin M.; Reusch, Joshua A.; Schlossberg, David J.
2016-09-30
H-mode is obtained at $A\\sim 1.2$ in the Pegasus Toroidal Experiment via Ohmic heating, high-field-side fueling, and low edge recycling in both limited and diverted magnetic topologies. These H-mode plasmas show the formation of edge current and pressure pedestals and a doubling of the energy confinement time to ${{H}_{98y,2}}\\sim 1$ . The L–H power threshold ${{P}_{\\text{LH}}}$ increases with density, and there is no ${{P}_{\\text{LH}}}$ minimum observed in the attainable density space. The power threshold is equivalent in limited and diverted plasmas, consistent with the FM3 model. However, the measured ${{P}_{\\text{LH}}}$ is $\\sim 15\\,\\,\\times $ higher than that predicted by conventional International Tokamak Physics Activity (ITPA) scalings, and ${{P}_{\\text{LH}}}/{{P}_{\\text{ITPA}08}}$ increases as $A\\to 1$ . Small ELMs are present at low input power ${{P}_{\\text{IN}}}\\sim {{P}_{\\text{LH}}}$ , with toroidal mode number $n\\leqslant 4$ . At ${{P}_{\\text{IN}}}\\gg {{P}_{\\text{LH}}}$ , they transition to large ELMs with intermediate 5 < n < 15. The dominant-n component of a large ELM grows exponentially, while other components evolve nonlinearly and can damp prior to the crash. Direct measurements of the current profile in the pedestal region show that both ELM types exhibit a generation of a current-hole, followed by a pedestal recovery. Large ELMs are shown to further expel a current-carrying filament. Small ELM suppression via injection of low levels of helical current into the edge plasma region is also indicated.
Experimental characterization of drift-interchange instabilities in a simple toroidal plasma
NASA Astrophysics Data System (ADS)
Poli, F. M.; Brunner, S.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Müller, S. H.; Plyushchev, G.; Podestà, M.
2006-10-01
Low frequency electrostatic instabilities are investigated on TORPEX [Fasoli, Labit, McGrath, Müller, Podestà, and Poli, Bull. Am. Phys. Soc. 48, 119 (2003)], a toroidal device for basic plasma physics experiments with a toroidal magnetic field 100mT and a small vertical magnetic field (⩽4mT). A two-dimensional (2D) profile of the frequency and amplitude of density and potential fluctuations is reconstructed using electrostatic probes with high space and time resolution. The measured phase velocity, corrected for the Doppler shift induced by the E×B drift, is consistent with the electron diamagnetic drift velocity. The local dispersion relation, measured along and across the magnetic field, is in agreement with the predictions of a linear kinetic slab model for drift waves. Unstable modes are generated in regions of unfavorable curvature, where the pressure gradient is colinear with the magnetic field gradient. It is demonstrated that the curvature of the magnetic field lines is essential for driving the observed instabilities, which are therefore identified as drift-interchange modes.
Experimental characterization of drift-interchange instabilities in a simple toroidal plasma
Poli, F. M.; Brunner, S.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Mueller, S. H.; Plyushchev, G.; Podesta, M.
2006-10-15
Low frequency electrostatic instabilities are investigated on TORPEX [Fasoli, Labit, McGrath, Mueller, Podesta, and Poli, Bull. Am. Phys. Soc. 48, 119 (2003)], a toroidal device for basic plasma physics experiments with a toroidal magnetic field 100 mT and a small vertical magnetic field ({<=}4 mT). A two-dimensional (2D) profile of the frequency and amplitude of density and potential fluctuations is reconstructed using electrostatic probes with high space and time resolution. The measured phase velocity, corrected for the Doppler shift induced by the ExB drift, is consistent with the electron diamagnetic drift velocity. The local dispersion relation, measured along and across the magnetic field, is in agreement with the predictions of a linear kinetic slab model for drift waves. Unstable modes are generated in regions of unfavorable curvature, where the pressure gradient is colinear with the magnetic field gradient. It is demonstrated that the curvature of the magnetic field lines is essential for driving the observed instabilities, which are therefore identified as drift-interchange modes.
An analytic model of toroidal half-wave oscillations: Implication on plasma density estimates
NASA Astrophysics Data System (ADS)
Bulusu, Jayashree; Sinha, A. K.; Vichare, Geeta
2015-06-01
The developed analytic model for toroidal oscillations under infinitely conducting ionosphere ("Rigid-end") has been extended to "Free-end" case when the conjugate ionospheres are infinitely resistive. The present direct analytic model (DAM) is the only analytic model that provides the field line structures of electric and magnetic field oscillations associated with the "Free-end" toroidal wave for generalized plasma distribution characterized by the power law ρ = ρo(ro/r)m, where m is the density index and r is the geocentric distance to the position of interest on the field line. This is important because different regions in the magnetosphere are characterized by different m. Significant improvement over standard WKB solution and an excellent agreement with the numerical exact solution (NES) affirms validity and advancement of DAM. In addition, we estimate the equatorial ion number density (assuming H+ atom as the only species) using DAM, NES, and standard WKB for Rigid-end as well as Free-end case and illustrate their respective implications in computing ion number density. It is seen that WKB method overestimates the equatorial ion density under Rigid-end condition and underestimates the same under Free-end condition. The density estimates through DAM are far more accurate than those computed through WKB. The earlier analytic estimates of ion number density were restricted to m = 6, whereas DAM can account for generalized m while reproducing the density for m = 6 as envisaged by earlier models.
Energetic particle driven geodesic acoustic mode in a toroidally rotating tokamak plasma
NASA Astrophysics Data System (ADS)
Ren, Haijun
2017-01-01
Energetic particle (EP) driven geodesic acoustic modes (EGAMs) in toroidally rotating tokamak plasmas are analytically investigated using the hybrid kinetic-fluid model and gyrokinetic equations. By ignoring high-order terms and ion Landau damping, the kinetic dispersion relation is reduced to the hybrid one in the large safety factor limit. There is one high-frequency branch with a frequency larger than {ωt0} , the transit frequency of EPs with initial energy, which is always stable. Two low-frequency solutions with a frequency smaller than {ωt0} are complex conjugates in the hybrid limit. In the presence of ion Landau damping, the growth rate of the unstable branch is decreased and the damping rate of the damped branch is increased. The toroidal Mach number is shown to increase {{ Ω }\\text{r}} , the normalized real frequency of both branches. Although not affecting the instability critical condition, the Mach number decreases the growth rate when {{ Ω }\\text{r}} is larger than a critical value Ω \\text{r}\\text{cri} and enlarges the growth rate when {{ Ω }\\text{r}}< Ω \\text{r}\\text{cri} . The ion Landau damping effect is negligible for large M. But the discrepancy between the kinetic dispersion relation and the hybrid one becomes ignorable only for q≳ 7 .
Magnetic topology and current channels in plasmas with toroidal current density inversions
Ciro, D.; Caldas, I. L.
2013-10-15
The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is considered. Previous works have shown that internal regions with negative current density lead to non-nested magnetic surfaces inside the plasma. Following these results, we derive a general expression relating the positive and negative currents inside the non-nested surfaces. This is done in terms of an anisotropy parameter that is model-independent and is based in very general properties of the magnetic field. We demonstrate that the positive currents in axisymmetric islands screen the negative one in the plasma center by reaching about twice its magnitude. Further, we illustrate these results by developing a family of analytical local solutions for the poloidal magnetic field in a region of interest that contains the inverted current. These local solutions exhibit non-nested magnetic surfaces with a combined current of at least twice the magnitude of the negative one, as prescribed from the topological arguments, and allow to study topological transitions driven by geometrical changes in the current profile. To conclude, we discuss the signatures of internal current density inversions in a confinement device and show that magnetic pitch measurements may be inappropriate to differentiate current reversals and small current holes in plasmas.
Evolution of plasma loops in a semi-toroidal pinch experiment
Mackel, F. Ridder, S.; Tenfelde, J.; Tacke, T.; Soltwisch, H.
2015-04-15
The FlareLab experiment is a pulsed-power discharge generating magnetized plasma loops similar to a pinch experiment in a semi-toroidal configuration. After gas breakdown along a circular magnetic guide field, the structure expands in its major radius as the plasma becomes highly conductive and the discharge current rises. Photographs, current and electron density measurements reveal a significant broadening in the lateral direction leading to an increasing departure from radial symmetry of plasma parameters in the cross section. It is shown that the luminosity is related to both high electron density and high current density. Simultaneous measurements of current density and electric field reveal a high parallel resistivity of the plasma leading to fast diffusion across the magnetic field. Indications for anomalous resistivity are found by comparison with the Spitzer formula. As the experiment differs from a z-pinch experiment only by the semi-circular shape of the current path, the observed evolution is unexpected and might be of more fundamental significance.
Optimization of confinement in a toroidal plasma subject to strong radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.
1977-01-01
The toroidal ring of plasma contained in the NASA Lewis Bumpy Torus facility may be biased to positive or negative potentials approaching 50 kV by applying dc voltages of the respective polarity to 12 or fewer midplane electrode rings. The radial electric fields, which are responsible for raising the ions to high energies by E x B/B-squared drift, then point out of or into the plasma. A preliminary report is given on the identification and optimization of independent variables which affect the ion density and confinement time in the Bumpy Torus plasma. The independent variables include the polarity, position, and number of the midplane electrode rings, the method of gas injection, and the polarity and strength of a weak vertical magnetic field. Some characteristic data taken under conditions where most of the independent variables were optimized are presented. The highest value of the electron number density on the plasma axis is 3.2 trillion per cu cm, the highest ion heating efficiency is 47%, and the longest particle containment time is 2.0 msec.
Public Data Set: H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment
Thome, Kathreen E.; Bongard, Michael W.; Barr, Jayson L.; Bodner, Grant M.; Burke, Marcus G.; Fonck, Raymond J.; Kriete, David M.; Perry, Justin M.; Reusch, Joshua A.; Schlossberg, David J.
2016-09-30
This data set contains openly-documented, machine readable digital research data corresponding to figures published in K.E. Thome et al., 'H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment,' Nucl. Fusion 57, 022018 (2017).
Self-regulated oscillation of transport and topology of magnetic islands in toroidal plasmas
Ida, K.; Kobayashi, T.; Evans, T. E.; Inagaki, S.; Austin, M. E.; Shafer, M. W.; Ohdachi, S.; Suzuki, Y.; Itoh, S.-I.; Itoh, K.
2015-01-01
The coupling between the transport and magnetic topology is an important issue because the structure of magnetic islands, embedded in a toroidal equilibrium field, depends on the nature of the transport at the edge of the islands. Measurements of modulated heat pulse propagation in the DIII-D tokamak have revealed the existence of self-regulated oscillations in the radial energy transport into magnetic islands that are indicative of bifurcations in the island structure and transport near the q = 2 surface. Large amplitude heat pulses are seen in one state followed by small amplitude pulses later in the discharge resulting in a repeating cycle of island states. These two states are interpreted as a bifurcation of magnetic island with high and low heat pulse accessibility. This report describes the discovery of a bifurcation in the coupled dynamics between the transport and topology of magnetic islands in tokamak plasmas. PMID:26530273
Self-regulated oscillation of transport and topology of magnetic islands in toroidal plasmas.
Ida, K; Kobayashi, T; Evans, T E; Inagaki, S; Austin, M E; Shafer, M W; Ohdachi, S; Suzuki, Y; Itoh, S-I; Itoh, K
2015-11-04
The coupling between the transport and magnetic topology is an important issue because the structure of magnetic islands, embedded in a toroidal equilibrium field, depends on the nature of the transport at the edge of the islands. Measurements of modulated heat pulse propagation in the DIII-D tokamak have revealed the existence of self-regulated oscillations in the radial energy transport into magnetic islands that are indicative of bifurcations in the island structure and transport near the q = 2 surface. Large amplitude heat pulses are seen in one state followed by small amplitude pulses later in the discharge resulting in a repeating cycle of island states. These two states are interpreted as a bifurcation of magnetic island with high and low heat pulse accessibility. This report describes the discovery of a bifurcation in the coupled dynamics between the transport and topology of magnetic islands in tokamak plasmas.
Self-regulated oscillation of transport and topology of magnetic islands in toroidal plasmas
Ida, K.; Kobayashi, T.; Evans, T. E.; Inagaki, S.; Austin, M. E.; Shafer, M. W.; Ohdachi, S.; Suzuki, Y.; Itoh, S. -I.; Itoh, K.
2015-11-04
The coupling between the transport and magnetic topology is an important issue because the structure of magnetic islands, embedded in a toroidal equilibrium field, depends on the nature of the transport at the edge of the islands. Measurements of modulated heat pulse propagation in the DIII-D tokamak have revealed the existence of self-regulated oscillations in the radial energy transport into magnetic islands that are indicative of bifurcations in the island structure and transport near the q = 2 surface. Furthermore, large amplitude heat pulses are seen in one state followed by small amplitude pulses later in the discharge resulting in a repeating cycle of island states. We interpret these two states as a bifurcation of magnetic island with high and low heat pulse accessibility. This report describes the discovery of a bifurcation in the coupled dynamics between the transport and topology of magnetic islands in tokamak plasmas.
Self-regulated oscillation of transport and topology of magnetic islands in toroidal plasmas
Ida, K.; Kobayashi, T.; Evans, T. E.; ...
2015-11-04
The coupling between the transport and magnetic topology is an important issue because the structure of magnetic islands, embedded in a toroidal equilibrium field, depends on the nature of the transport at the edge of the islands. Measurements of modulated heat pulse propagation in the DIII-D tokamak have revealed the existence of self-regulated oscillations in the radial energy transport into magnetic islands that are indicative of bifurcations in the island structure and transport near the q = 2 surface. Furthermore, large amplitude heat pulses are seen in one state followed by small amplitude pulses later in the discharge resulting inmore » a repeating cycle of island states. We interpret these two states as a bifurcation of magnetic island with high and low heat pulse accessibility. This report describes the discovery of a bifurcation in the coupled dynamics between the transport and topology of magnetic islands in tokamak plasmas.« less
Synchronization of Geodesic Acoustic Modes and Magnetic Fluctuations in Toroidal Plasmas
NASA Astrophysics Data System (ADS)
Zhao, K. J.; Nagashima, Y.; Diamond, P. H.; Dong, J. Q.; Itoh, K.; Itoh, S.-I.; Yan, L. W.; Cheng, J.; Fujisawa, A.; Inagaki, S.; Kosuga, Y.; Sasaki, M.; Wang, Z. X.; Wei, L.; Huang, Z. H.; Yu, D. L.; Hong, W. Y.; Li, Q.; Ji, X. Q.; Song, X. M.; Huang, Y.; Liu, Yi.; Yang, Q. W.; Ding, X. T.; Duan, X. R.
2016-09-01
The synchronization of geodesic acoustic modes (GAMs) and magnetic fluctuations is identified in the edge plasmas of the HL-2A tokamak. Mesoscale electric fluctuations (MSEFs) having components of a dominant GAM, and m /n =6 /2 potential fluctuations are found at the same frequency as that of the magnetic fluctuations of m /n =6 /2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m /n =6 /2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. Such nonlinear synchronization may also contribute to low-frequency zonal flow formation, reduction of turbulence level, and thus confinement regime transitions.
NASA Astrophysics Data System (ADS)
Itoh, K.; Itoh, S.-I.; Kamiya, K.; Kasuya, N.
2015-07-01
The solitary radial electric field in the edge of toroidal plasma is studied based on the electric field bifurcation model. Results are applied to tokamak and helical plasmas, and the dependence of the electric field structure on the plasma parameters and geometrical factors is analyzed. The order of magnitude estimate for tokamak plasma is not far from experimental observations. It is shown that, in helical plasmas, the height of electric field structure is reduced substantially owing to the ripple particle transport, while the width is influenced less. The implications of the results for the limit of achievable gradient in the H-mode pedestal are also discussed.
A collisional-radiative model for low-pressure weakly magnetized Ar plasmas
NASA Astrophysics Data System (ADS)
Zhu, Xi-Ming; Tsankov, Tsanko; Czarnetzki, Uwe; Marchuk, Oleksandr
2016-09-01
Collisional-radiative (CR) models are widely investigated in plasma physics for describing the kinetics of reactive species and for optical emission spectroscopy. This work reports a new Ar CR model used in low-pressure (0.01-10 Pa) weakly magnetized (<0.1 Tesla) plasmas, including ECR, helicon, and NLD discharges. In this model 108 realistic levels are individually studied, i.e. 51 lowest levels of the Ar atom and 57 lowest levels of the Ar ion. We abandon the concept of an ``effective level'' usually adopted in previous models for glow discharges. Only in this way the model can correctly predict the non-equilibrium population distribution of close energy levels. In addition to studying atomic metastable and radiative levels, this model describes the kinetic processes of ionic metastable and radiative levels in detail for the first time. This is important for investigation of plasma-surface interaction and for optical diagnostics using atomic and ionic line-ratios. This model could also be used for studying Ar impurities in tokamaks and astrophysical plasmas.
Energetic-Ion-Driven Toroidal Alfv{acute e}n Eigenmodes Observed in a Heliotron/Torsatron Plasma
Takechi, M.; Takagi, S.; Matsunaga, G.; Ohkuni, K.; Shimizu, M.; Toi, K.; Ohdachi, S.; Akiyama, R.; Fujisawa, A.; Gotoh, M.; Idei, H.; Iguchi, H.; Isobe, M.; Kojima, M.; Kubo, S.; Lee, S.; Minami, T.; Morita, S.; Matsuoka, K.; Nishimura, S.; Okamura, S.; Osakabe, M.; Sasao, M.; Takahashi, C.; Tanaka, K.; Yoshimura, Y.; Darrow, D.S.; Kondo, T.
1999-07-01
Toroidal Alfv{acute e}n eigenmodes (TAEs) of low toroidal mode number, n=1 and 2, are observed in neutral-beam-heated plasmas in the compact helical system heliotron/torsatron. The observed frequency is proportional to the computed TAE frequency and lies near the lower bound of the innermost TAE gap. The modes are excited only when the beam velocity exceeds about half the central Alfv{acute e}n velocity and when the net plasma current induced by coinjected neutral beams is in the required range. The modes are localized in the plasma core region, between 0.2 and 0.6 of the plasma minor radius. {copyright} {ital 1999} {ital The American Physical Society }
Khorashadizadeh, S. M. Taheri Boroujeni, S.; Niknam, A. R.
2015-11-15
In this paper, we have investigated the nonlinear interaction between high-frequency surface plasmons and low-frequency ion oscillations in a semi-bounded collisional quantum plasma. By coupling the nonlinear Schrodinger equation and quantum hydrodynamic model, and taking into account the ponderomotive force, the dispersion equation is obtained. By solving this equation, it is shown that there is a modulational instability in the system, and collisions and quantum forces play significant roles on this instability. The quantum tunneling increases the phase and group velocities of the modulated waves and collisions increase the growth rate of the modulational instability. It is also shown that the effect of quantum forces and collisions is more significant in high modulated wavenumber regions.
Application of a hybrid collisional radiative model to recombining argon plasmas
NASA Astrophysics Data System (ADS)
Benoy, D. A.; van der Mullen, J. A. M.; van de Sanden, M. C. M.; van der Sijde, B.; Schram, D. C.
1993-02-01
A collisional radiative model, in which a hybrid cut-off technique is used, is applied to recombining plasmas to study the atomic state distribution (ASDF) and the recombination coefficient. Computations of the ASDF using semi-empirical rate coefficients of Vriens and Smeets (V-S) and Drawin (D) are compared with experimental values measured at various positions in a free expanding argon arc jet. Apart from the shock position, where the calculated results are too low, the model calculations are higher than the experimental results. The volumetric recombination coefficient has a Te exp -4 and a Te exp -4.8 dependence when semiempirical rate coefficients of, respectively, V-S and D are used. The differences between the models based on the rate coefficients of V-S and D indicate that the recombination flow is sensitive to the low temperature behavior of the rate coefficients.
Bellemans, A.; Munafò, A.; Magin, T. E.; Degrez, G.; Parente, A.
2015-06-15
This article considers the development of reduced chemistry models for argon plasmas using Principal Component Analysis (PCA) based methods. Starting from an electronic specific Collisional-Radiative model, a reduction of the variable set (i.e., mass fractions and temperatures) is proposed by projecting the full set on a reduced basis made up of its principal components. Thus, the flow governing equations are only solved for the principal components. The proposed approach originates from the combustion community, where Manifold Generated Principal Component Analysis (MG-PCA) has been developed as a successful reduction technique. Applications consider ionizing shock waves in argon. The results obtained show that the use of the MG-PCA technique enables for a substantial reduction of the computational time.
Effects of edge dc biasing on plasma rotation and transport in a toroidal geometry
NASA Astrophysics Data System (ADS)
Fredriksen, Åshild; Riccardi, Claudia; Magni, Simone
2006-02-01
We report results from experiments performed to study how a change in boundary conditions affects the plasma state in the toroidal geometry of the Blaamann device in Tromso. The boundary condition was changed by applying a dc bias on a limiter extended around the entire poloidal circumference of the plasma column. Two distinctly different plasma potential states were found. One state was associated with a bias at or negative with respect to the floating potential of the limiter, and a small ion-saturation current. The other state was associated with a positive bias with respect to the floating potential, near or in the electron saturation regime of the limiter. In the latter case the potential minimum in the middle of the cross-section was significantly less negative than in the case of ion-saturation current to the limiter. On the other hand, the grounded limiter provided the best confinement properties, for which the density maximum was significantly higher than for both more positive and more negative biases. This state also had the lowest fluctuation levels, and near zero poloidal velocities close to the boundaries, as well as the smallest radial, anomalous particle transport.
Effects of Edge DC Biasing on Plasma Rotation and Transport in a Toroidal Geometry.
NASA Astrophysics Data System (ADS)
Fredriksen, Ashild; Riccardi, Claudia
2005-10-01
We report results from experiments performed to study how a change in boundary conditions is affecting the plasma states in the toroidal geometry of the Blaamann device in Tromso. The boundary condition was changed by applying a DC bias on a limiter extended around the entire poloidal circumference of the plasma column. Two distinctly different plasma potential states were found. One state was associated with a bias at or negative with respect to the floating potential of the limiter, and a small ion saturation current. The other state was associated with a positive bias with respect to the floating potential, near or in the electron saturation regime of the limiter. In the latter case the potential minimum in the middle of the cross-section was significantly less negative than in the case of ion-saturation current to the limiter. On the other hand, the grounded limiter provided the best confinement properties, for which the density maximum was significantly higher than for both more positive and more negative biases. This state also had the lowest fluctuation levels, and near zero poloidal velocities close to the boundaries, as well as the smallest radial, anomalous particle transport.
THE STABILITY OF WEAKLY COLLISIONAL PLASMAS WITH THERMAL AND COMPOSITION GRADIENTS
Pessah, Martin E.; Chakraborty, Sagar E-mail: sagarc@iitk.ac.in
2013-02-10
Over the last decade, substantial efforts have been devoted to understanding the stability properties, transport phenomena, and long-term evolution of weakly collisional, magnetized plasmas which are stratified in temperature. The insights gained via these studies have led to a significant improvement of our understanding of the processes that determine the physical evolution and observational properties of the intracluster medium (ICM) permeating galaxy clusters. These studies have been carried out under the assumption that the ICM is a homogeneous medium. This, however, might not be a good approximation if heavy elements are able to sediment in the inner region of the galaxy cluster. Motivated by the need to obtain a more complete picture of the dynamical properties of the ICM, we analyze the stability of a weakly collisional, magnetized plane-parallel atmosphere which is stratified in both temperature and composition. This allows us to discuss for the first time the dynamics of weakly collisional environments where heat conduction, momentum transport, and ion-diffusion are anisotropic with respect to the direction of the magnetic field. We show that depending on the relative signs and magnitudes of the gradients in the temperature and the mean molecular weight, the plasma can be subject to a wide variety of unstable modes which include modifications to the magnetothermal instability (MTI), the heat-flux-driven buoyancy instability (HBI), and overstable gravity modes previously studied in homogeneous media. We also find that there are new modes which are driven by heat conduction and particle diffusion. We discuss the astrophysical implications of our findings for a representative galaxy cluster where helium has sedimented. Our findings suggest that the core insulation that results from the magnetic field configurations that arise as a natural consequence of the HBI, which would be MTI stable in a homogeneous medium, could be alleviated if the mean molecular
Elements of Neoclassical Theory and Plasma Rotation in a Tokamak
NASA Astrophysics Data System (ADS)
Smolyakov, A.
2015-12-01
The following sections are included: * Introduction * Quasineutrality condition * Diffusion in fully ionized magnetized plasma and automatic ambipolarity * Toroidal geometry and neoclassical diffusion * Diffusion and ambipolarity in toroidal plasmas * Ambipolarity and equilibrium poloidal rotation * Ambipolarity paradox and damping of poloidal rotation * Neoclassical plasma inertia * Oscillatory modes of poloidal plasma rotation * Dynamics of the toroidal momentum * Momentum diffusion in strongly collisional, short mean free path regime * Diffusion of toroidal momentum in the weak collision (banana) regime * Toroidal momentum diffusion and momentum damping from drift-kinetic theory and fluid moment equations * Comments on non-axisymmetric effects * Summary * Acknowledgments * Appendix: Trapped (banana) particles and collisionality regimes in a tokamak * Appendix: Hierarchy of moment equations * Appendix: Plasma viscosity tensor in the magnetic field: parallel viscosity, gyroviscosity, and perpendicular viscosity * Appendix: Closure relations for the flux surface averaged parallel viscosity in neoclassical (banana and plateau) regimes * References
Collisional damping of helicon waves in a high density hydrogen linear plasma device
Caneses, Juan F.; Blackwell, Boyd D.
2016-09-28
In this paper, we investigate the propagation and damping of helicon waves along the length (~50 cm) of a helicon-produced 20 kW hydrogen plasma ( ~1-2 1019 m-3, ~1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (~10 G and ~ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40 to 50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based on experimental measurements. By comparing theory and experiment, we show that for the conditions associated with this paper classical collisions are sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in our device (MAGPIE).
SPEX (Plasma Code Spectral Fitting Tool). Collisional ionization for atoms and ions of H to Zn.
NASA Astrophysics Data System (ADS)
Urdampilleta, I.; Kaastra, J. S.
2017-03-01
Every observation of astrophysical objects involving a spectrum requires atomic data for the interpretation of line fluxes, ratios and ionization state of the emitting plasma. One of processes which determines it is collisional ionization. In this study an update of the direct ionization (DI) and excitation-autoionization (EA) processes is discussed for the H to Zn-like isoelectronic sequences. The previous assessments were performed by Dere (2007, A&A 466, 771) for H to Zn isoelectronc sequences, Arnaud & Raymond (1992, ApJ. 398, 394) for Fe and Arnaud & Rothenflug (1985, A&AS, 60, 425). However, in the last years new laboratory measurements and theoretical calculations of ionization cross sections have become accessible. We provide a review, extension and update of this previous work and fit the cross sections of all individuals shells of all ions from H to Zn. These data are described using an extension of Younger's formula, suitable for integration over a Maxwellian velocity distribution to derive the subshell ionization rate coefficients. These ionization rate coefficients are included together with the radiative recombination rates data (Mao et al. 2016, A&AS, 27568) and a change-exchange model (Gu et al. 2016, A&A 588, A52, 11) into the high-resolution plasma code and spectral fit tool SPEX V3.0 (Kaastra et al. 1996, UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas).
Collisional damping of helicon waves in a high density hydrogen linear plasma device
Caneses, Juan F.; Blackwell, Boyd D.
2016-09-28
In this paper, we investigate the propagation and damping of helicon waves along the length (~50 cm) of a helicon-produced 20 kW hydrogen plasma ( ~1-2 1019 m-3, ~1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (~10 G and ~ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40 to 50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based onmore » experimental measurements. By comparing theory and experiment, we show that for the conditions associated with this paper classical collisions are sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in our device (MAGPIE).« less
Electron and ion-molecule collisional data for the science of plasma processing
Garscadden, A.; Nagpal, R.; Haaland, P.D.; Clark, J.
1995-12-31
Plasma processing of materials has emerged as the enabling technology for many industrial applications ranging from the fabrication of microelectronic circuits to coatings for advanced combustion engines. After impressive, mainly empirical successes, further developments now require more precise control and understanding of the mechanisms for selective deposition, etching, or reaction. The electron temperature of a non-equilibrium plasma can easily be 20,000 K while the gas temperature is less than 500 K. The reactivity of the plasma-excited gases is often enhanced by many orders of magnitude. Electron and ion collisions, especially those causing dissociation of the initial gases, and reactions of the resulting radicals with gases and at surfaces are crucial. Extant collisional data and methods are reviewed in the context of emerging technological requirements. Examples are presented for (1) crossed-beam and swarm studies of electron-molecule collisions; (2) Fourier Transform Mass spectrometry probes of dissociative ionization, attachment, and charge-transfer collisions, and (3) Surface Desorption Spectroscopy examinations of surface reactions.
Matsunaga, G.; Kawada, S.; Kotani, J.; Toi, K.; Suzuki, C.; Matsuoka, K.
2005-06-10
A novel method of exciting shear Alfven waves using electrodes inserted in a plasma was developed for basic study of Alfven eigenmodes in a heliotron/torsatron plasma. The electrodes can induce excitation current along the confinement field line, and generate magnetic perturbations perpendicular to the confinement field. By sweeping the frequency of the current in a cold plasma, the toroidicity-induced Alfven eigenmode was resonantly excited at the predicted frequency and radial location. Plasma response to the applied magnetic perturbations indicates a fairly large damping rate caused by continuum damping.0.
Collisional relaxation of a strongly magnetized two-species pure ion plasma
Chim, Chi Yung; O’Neil, Thomas M.; Dubin, Daniel H.
2014-04-15
The collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ω{sub 1},Ω{sub 2}≫|Ω{sub 1}−Ω{sub 2}|≫v{sup ¯}{sub ij}/b{sup ¯} and v{sup ¯}{sub ⊥j}/Ω{sub j}≪b{sup ¯}, where Ω{sub 1} and Ω{sub 2} are two cyclotron frequencies, v{sup ¯}{sub ij}=√(T{sub ∥}/μ{sub ij}) is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b{sup ¯}=2e{sup 2}/T{sub ∥} is the classical distance of closest approach for such collisions, and v{sup ¯}{sub ⊥j}/Ω{sub j}=√(2T{sub ⊥j}/m{sub j})/Ω{sub j} is the characteristic cyclotron radius for particles of species j. Here, μ{sub ij} is the reduced mass for the two particles, and T{sub ∥} and T{sub ⊥j} are temperatures that characterize velocity components parallel and perpendicular to the magnetic field. For this ordering, the total cyclotron action for the two species, I{sub 1}=∑{sub i∈1}m{sub 1}v{sub ⊥i}{sup 2}/(2Ω{sub 1}) and I{sub 2}=∑{sub i∈2}m{sub 2}v{sub ⊥i}{sup 2}/(2Ω{sub 2}) are adiabatic invariants that constrain the collisional dynamics. On the timescale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions I{sub 1} and I{sub 2}, yielding a modified Gibbs distribution of the form exp[−H/T{sub ∥}−α{sub 1}I{sub 1}−α{sub 2}I{sub 2}]. Here, the α{sub j}’s are related to T{sub ∥} and T{sub ⊥j} through T{sub ⊥j}=(1/T{sub ∥}+α{sub j}/Ω{sub j}){sup −1}. Collisional relaxation to the usual Gibbs distribution, exp[−H/T{sub ∥}], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b{sup ¯2}Ω{sub 1}{sup 2}/v{sup ¯}{sub 11}{sup 2})exp(5[3π(b{sup ¯}|Ω{sub 1}−Ω{sub 2}|/v{sup ¯}{sub 12})]{sup 2/5}/6), the two
Advanced Power Conversion Efficiency in Inventive Plasma for Hybrid Toroidal Reactor
NASA Astrophysics Data System (ADS)
Hançerlioğullari, Aybaba; Cini, Mesut; Güdal, Murat
2013-08-01
Apex hybrid reactor has a good potential to utilize uranium and thorium fuels in the future. This toroidal reactor is a type of system that facilitates the occurrence of the nuclear fusion and fission events together. The most important feature of hybrid reactor is that the first wall surrounding the plasma is liquid. The advantages of utilizing a liquid wall are high power density capacity good power transformation productivity, the magnitude of the reactor's operational duration, low failure percentage, short maintenance time and the inclusion of the system's simple technology and material. The analysis has been made using the MCNP Monte Carlo code and ENDF/B-V-VI nuclear data. Around the fusion chamber, molten salts Flibe (LI2BeF4), lead-lithium (PbLi), Li-Sn, thin-lityum (Li20Sn80) have used as cooling materials. APEX reactor has modeled in the torus form by adding nuclear materials of low significance in the specified percentages between 0 and 12 % to the molten salts. In this study, the neutronic performance of the APEX fusion reactor using various molten salts has been investigated. The nuclear parameters of Apex reactor has been searched for Flibe (LI2BeF4) and Li-Sn, for blanket layers. In case of usage of the Flibe (LI2BeF4), PbLi, and thin-lityum (Li20Sn80) salt solutions at APEX toroidal reactors, fissile material production per source neutron, tritium production speed, total fission rate, energy reproduction factor has been calculated, the results obtained for both salt solutions are compared.
Camenen, Y; Bortolon, A; Duval, B P; Federspiel, L; Peeters, A G; Casson, F J; Hornsby, W A; Karpushov, A N; Piras, F; Sauter, O; Snodin, A P; Szepesi, G
2010-09-24
The first experimental evidence of parallel momentum transport generated by the up-down asymmetry of a toroidal plasma is reported. The experiments, conducted in the Tokamak à Configuration Variable, were motivated by the recent theoretical discovery of ion-scale turbulent momentum transport induced by an up-down asymmetry in the magnetic equilibrium. The toroidal rotation gradient is observed to depend on the asymmetry in the outer part of the plasma leading to a variation of the central rotation by a factor of 1.5-2. The direction of the effect and its magnitude are in agreement with theoretical predictions for the eight possible combinations of plasma asymmetry, current, and magnetic field.
NASA Astrophysics Data System (ADS)
Askinazi, L. G.; Bulanin, V. V.; Kornev, V. A.; Krikunov, S. V.; Lebedev, S. V.; Tukachinsky, A. S.; Vildjunas, M. I.; Zhubr, N. A.
2011-03-01
The results of the experimental study of confinement mode bifurcation performed on the TUMAN-3M tokamak are reported. As a trigger of confinement mode switching, plasma current ramp-up/-down or magnetic compression/decompression is used. It is found that the possibility and direction of confinement mode switching are correlated not with plasma current profile perturbation (peaking or broadening) but with the sign of toroidal electric field perturbation. A model connecting confinement bifurcation and toroidal electric field perturbation through the perturbation of the radial electric field is used to describe the phenomena observed in all eight scenarios investigated. This model ascribes the radial electric field generation to the non-compensated Ware drift of banana electrons at the TUMAN-3M peripheral plasma, where \
Tokamak with liquid metal toroidal field coil
Ohkawa, Tihiro; Schaffer, Michael J.
1981-01-01
Tokamak apparatus includes a pressure vessel for defining a reservoir and confining liquid therein. A toroidal liner disposed within the pressure vessel defines a toroidal space within the liner. Liquid metal fills the reservoir outside said liner. Electric current is passed through the liquid metal over a conductive path linking the toroidal space to produce a toroidal magnetic field within the toroidal space about the major axis thereof. Toroidal plasma is developed within the toroidal space about the major axis thereof.
Nonlinear interaction of fast particles with Alfven waves in toroidal plasmas
Candy, J.; Borba, D.; Huysmans, G.T.A.; Kerner, W.; Berk, H.L.
1996-12-17
A numerical algorithm to study the nonlinear, resonant interaction of fast particles with Alfven waves in tokamak geometry has been developed. The scope of the formalism is wide enough to describe the nonlinear evolution of fishbone modes, toroidicity-induced Alfven eigenmodes and ellipticity-induced Alfven eigenmodes, driven by both passing and trapped fast ions. When the instability is sufficiently weak, it is known that the wave-particle trapping nonlinearity will lead to mode saturation before wave-wave nonlinearities are appreciable. The spectrum of linear modes can thus be calculated using a magnetohydrodynamic normal-mode code, then nonlinearly evolved in time in an efficient way according to a two-time-scale Lagrangian dynamical wave model. The fast particle kinetic equation, including the effect of orbit nonlinearity arising from the mode perturbation, is simultaneously solved of the deviation, {delta}f = f {minus} f{sub 0}, from an initial analytic distribution f{sub 0}. High statistical resolution allows linear growth rates, frequency shifts, resonance broadening effects, and nonlinear saturation to be calculated quickly and precisely. The results have been applied to an ITER instability scenario. Results show that weakly-damped core-localized modes alone cause negligible alpha transport in ITER-like plasmas--even with growth rates one order of magnitude higher than expected values. However, the possibility of significant transport in reactor-type plasmas due to weakly unstable global modes remains an open question.
Linear global gyrokinetic simulations of toroidal Alfven eigenmodes in KSTAR plasmas
NASA Astrophysics Data System (ADS)
Shahzad, M.; Rizvi, H.; Ryu, C. M.
2016-12-01
Excitation of toroidal Alfven eigenmodes (TAEs) in KSTAR tokamak plasmas has been studied by using the GENE code. Verification and benchmark analysis are performed for Alfven eigenmodes (AEs) excited by the energetic particles (EPs) in comparison with the AEs from the GYGLES code, and excellent agreements are found. In addition, the threshold value of the EP density gradient to destabilize the TAE has been investigated. For the plasma equilibrium of KSTAR discharge (10574), TAEs of n = 2 are found to be excited by coupling of adjoining poloidal harmonics (5, 6), (6, 7), and (7, 8). The dependence of the growth rate and frequency of the TAE on the EP density gradient is examined. It is found that the threshold value of EP density gradient increases with the higher poloidal mode coupling, of which location moves outward in the radial direction. The growth rates of TAEs with higher poloidal mode numbers are smaller than those with lower poloidal mode numbers, indicating that perpendicular wavenumbers play an important role. The efficiency of the EP drive for the TAE decreases for a higher poloidal mode coupling. At a higher EP density gradient, TAEs with higher poloidal harmonics are less unstable due to the decrease in the radial extents of the modes.
NASA Astrophysics Data System (ADS)
Sonnino, Giorgio; Peeters, Philippe; Sonnino, Alberto; Nardone, Pasquale; Steinbrecher, György
2015-01-01
In previous works, we derived stationary density distribution functions (DDF) where the local equilibrium is determined by imposing the maximum entropy (MaxEnt) principle, under the scale invariance restrictions, and the minimum entropy production theorem. In this paper we demonstrate that it is possible to reobtain these DDF solely from the MaxEnt principle subject to suitable scale invariant restrictions in all the variables. For the sake of concreteness, we analyse the example of ohmic, fully ionized, tokamak-plasmas, in the weak-collisional transport regime. In this case we show that it is possible to reinterpret the stationary distribution function in terms of the Prigogine distribution function where the logarithm of the DDF is directly linked to the entropy production of the plasma. This leads to the suggestive idea that also the stationary neoclassical distribution functions, for magnetically confined plasmas in the collisional transport regimes, may be derived solely by the MaxEnt principle.
Moser, Auna L.; Hsu, Scott C.
2015-05-01
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease inmore » the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.« less
Simulation of laser-driven plasma beat-wave propagation in collisional weakly relativistic plasmas
NASA Astrophysics Data System (ADS)
Kaur, Maninder; Nandan Gupta, Devki
2016-11-01
The process of interaction of lasers beating in a plasma has been explored by virtue of particle-in-cell (PIC) simulations in the presence of electron-ion collisions. A plasma beat wave is resonantly excited by ponderomotive force by two relatively long laser pulses of different frequencies. The amplitude of the plasma wave become maximum, when the difference in the frequencies is equal to the plasma frequency. We propose to demonstrate the energy transfer between the laser beat wave and the plasma wave in the presence of electron-ion collision in nearly relativistic regime with 2D-PIC simulations. The relativistic effect and electron-ion collision both affect the energy transfer between the interacting waves. The finding of simulation results shows that there is a considerable decay in the plasma wave and the field energy over time in the presence of electron-ion collisions.
NASA Astrophysics Data System (ADS)
Rahman, M. T.; Hossain, M. Mofazzal
2017-01-01
The time-dependent model of ion motion is used to propose an analytical model for dual frequency (DF) capacitively coupled plasma (CCP) sheath driven by a pulsed source and a radio-frequency source. In this model, the sheath is considered to be collisional. In this model, the time dependent terms of ion fluid equations are ignored, but the electric field, ion motion and ion density remain time dependent. Electron profile is assumed to be step-like. Analytical expressions for electron sheath width and sheath potential have been developed. The calculated sheath width and potential are compared with the dual radio frequency driven time dependent models of capacitively coupled plasma sheath. From the temporal evaluation of sheath motion and potential, it has been found that pulse driven sheath has higher sheath potential and sheath width than that of conventional radio frequency driven DF CCP. Moreover, it is also found that ion energy spread can be reduced using pulsed power. From the temporal investigation of sheath motion and potential, it has been found that the duty cycle of the pulse power significantly affects sheath width and sheath potential.
NASA Astrophysics Data System (ADS)
Baalrud, S. D.; Hegna, C. C.; Callen, J. D.
2009-11-01
Ion-ion streaming instabilities are excited in the presheath region of plasmas with multiple ion species if the ions are much colder than the electrons. Streaming instabilities onset when the relative fluid flow between ion species exceeds a critical speed, δVc, of order the ion thermal speeds. Using a generalized Lenard-Balescu theory that accounts for instability-enhanced collective responses [1], one is able to show the instabilities rapidly enhance the collisional friction between ion species far beyond the contribution from Coulomb collisions alone. This strong frictional force determines the relative fluid speed between species. When this condition is combined with the Bohm criterion generalized for multiple ion species, the fluid speed of each ion species is determined at the sheath edge. For each species, this speed differs from the common ``system'' sound speed by a factor that depends on the species concentrations, masses and δVc.[4pt] [1] S.D. Baalrud, J.D. Callen, and C.C. Hegna, Phys. Plasmas 15, 092111 (2008).
Closure and transport theory for high-collisionality electron-ion plasmas
NASA Astrophysics Data System (ADS)
Ji, Jeong-Young; Held, Eric D.
2013-04-01
Systems of algebraic equations for a high-collisionality electron-ion plasma are constructed from the general moment equations with linearized collision operators [J.-Y. Ji and E. D. Held, Phys. Plasmas 13, 102103 (2006) and J.-Y. Ji and E. D. Held, Phys. Plasmas 15, 102101 (2008)]. A systematic geometric method is invented and applied to solve the system of equations to find closure and transport relations. It is known that some closure coefficients of Braginskii [S. I. Braginskii, Reviews of Plasma Physics (Consultants Bureau, New York, 1965), Vol. 1] are in error up to 65% for some finite values of x (cyclotron frequency × electron-ion collision time) and have significant error in the large-x limit [E. M. Epperlein and M. G. Haines, Phys. Fluids 29, 1029 (1986)]. In this work, fitting formulas for electron coefficients are obtained from the 160 moment (Laguerre polynomial) solution, which converges with increasing moments for x ≤100 and from the asymptotic solution for large x-values. The new fitting formulas are practically exact (less than 1% error) for arbitrary x and Z (the ion charge number, checked up to Z = 100). The ion coefficients for equal electron and ion temperatures are moderately modified by including the ion-electron collision operator. When the ion temperature is higher than the electron temperature, the ion-electron collision and the temperature change terms in the moment equations must be kept. The ion coefficient formulas from 3 moment (Laguerre polynomial) calculations, precise to less than 0.4% error from the convergent values, are explicitly written.
Intrinsic rotation driven by non-Maxwellian equilibria in Tokamak plasmas.
Barnes, M; Parra, F I; Lee, J P; Belli, E A; Nave, M F F; White, A E
2013-08-02
The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising from diamagnetic effects, introduce a strong dependence of the radial flux of cocurrent toroidal angular momentum on collisionality: As the plasma goes from nearly collisionless to weakly collisional, the flux reverses direction from radially inward to outward. This indicates a collisionality-dependent transition from peaked to hollow rotation profiles, consistent with experimental observations of intrinsic rotation.
Intrinsic Rotation Driven by Non-Maxwellian Equilibria in Tokamak Plasmas
NASA Astrophysics Data System (ADS)
Barnes, M.; Parra, F. I.; Lee, J. P.; Belli, E. A.; Nave, M. F. F.; White, A. E.
2013-08-01
The effect of small deviations from a Maxwellian equilibrium on turbulent momentum transport in tokamak plasmas is considered. These non-Maxwellian features, arising from diamagnetic effects, introduce a strong dependence of the radial flux of cocurrent toroidal angular momentum on collisionality: As the plasma goes from nearly collisionless to weakly collisional, the flux reverses direction from radially inward to outward. This indicates a collisionality-dependent transition from peaked to hollow rotation profiles, consistent with experimental observations of intrinsic rotation.
Resonant magnetic perturbations of edge-plasmas in toroidal confinement devices
Evans, T. E.
2015-11-13
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δ$b_⊥^{ext}$ ≈ $10^{-4}$ → $10^{-3}$ T). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes. At the same time the theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design [A. Loarte, et al., Nucl. Fusion 54 (2014) 033007]. This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.
Resonant magnetic perturbations of edge-plasmas in toroidal confinement devices
Evans, T. E.
2015-11-13
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δmore » $$b_⊥^{ext}$$ ≈ $$10^{-4}$$ → $$10^{-3}$$ T). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes. At the same time the theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design [A. Loarte, et al., Nucl. Fusion 54 (2014) 033007]. This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.« less
Resonant magnetic perturbations of edge-plasmas in toroidal confinement devices
NASA Astrophysics Data System (ADS)
Evans, T. E.
2015-12-01
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δ b\\bot\\text{ext}≈ {{10}-4}\\to {{10}-3}~\\text{T} ). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes (ELMs). At the same time, theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design (Loarte et al 2014 Nucl. Fusion 54 033007). This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.
Sheared velocity flows as a source of pressure anisotropy in low collisionality plasmas
NASA Astrophysics Data System (ADS)
Del Sarto, Daniele; Pegoraro, Francesco; Cerri, Silvio Sergio; Califano, Francesco; Tenerani, Anna
2015-04-01
Non-Maxwellian metaequilibrium states may exist in low-collisionality plasmas as evidenced by direct (particle distributions) and indirect (e.g., instabilities driven by pressure anisotropy) satellite and laboratory measurements. These are directly observed in the solar wind (e.g. [1]), in magnetospheric reconnection events [2], in magnetically confined plasmas [3] or in simulations of Vlasov turbulence [4]. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic. We discuss how the propagation of "magneto-elastic" waves can affect the pressure tensor anisotropization and the small scale formation that arise from the interplay between the gyrotropic terms due to the magnetic field and flow vorticity, and the non-gyropropic effect of the flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution. This anisotropization mechanism might provide a good candidate for the understanding of the observed correlation between the presence of a sheared velocity flow and the signature of pressure anisotropies which are not yet explained within the standard models based e.g. on the CGL paradigm (see also [5]). Examples of these signatures are provided by the threshold lowering of ion-Weibel instabilities in the geomagnetic tail, observed in concomitance to the presence of a velocity shear in the near-earth plasma profile [6], or by the relatively stronger anisotropization measured for core protons in the fast solar wind [4,7] or in "space simulation" laboratory plasma experiments [3]. 1] E. Marsch et al., Journ. Geophys. Res. 109, A04120 (2004); Yu. V. Khotyainstev at el., Phys. Rev. Lett. 106, 165001 (2011). [2] N. Aunai et al., Ann. Geophys. 29, 1571 (2011); N. Aunai et al., Journ. Geophys. Res. 116, A09232 (2011). [3] E.E. Scime et al., Phys. Plasmas 7, 2157
Anomalous collisional absorption of laser pulses in underdense plasma at low temperature
NASA Astrophysics Data System (ADS)
Kundu, M.
2015-04-01
In a previous paper [M. Kundu, Phys. Plasmas 21, 013302 (2014), 10.1063/1.4862038], fractional collisional absorption (α ) of laser light in underdense plasma was studied by using a classical scattering model of electron-ion collision frequency νei, where total velocity v =√{vth2+v02 } (with vth and v0 as the thermal and the ponderomotive velocity of an electron) dependent Coulomb logarithm lnΛ (v ) was shown to be responsible for the anomalous (unconventional) increase of νei and α (∝νei ) with the laser intensity I0 up to a maximum value about an intensity Ic in the low temperature (Te<15 eV ) regime and a conventional ≈I0-3 /2 decrease when I0≫Ic . One may object that the anomalous increase in νei and α were partly due to the artifact introduced in lnΛ through the maximum cutoff distance bmax∝v . In this work, we show similar anomalous increase in νei and α versus I0 (in the low temperature and underdense density regime) with more accurate quantum and classical kinetic models of νei without using lnΛ , but with a proper choice of the total velocity dependent inverse cutoff length kmax∝v2 (classical) or kmax∝v (quantum). For a given I0<5 ×1014Wcm -2 , νei versus Te also exhibits so far unnoticed identical anomalous increase as νei versus I0, even if the conventional kmax∝vth2 or kmax∝vth (without v0) is chosen. The total velocity dependent kmax in the kinetic models, as proposed here, is found to explain the anomalous increase of α with I0 measured in some earlier laser-plasma experiments.
Sheared velocity flows as a source of pressure anisotropy in low collisionality plasmas
NASA Astrophysics Data System (ADS)
Del Sarto, D.; Pegoraro, F.; Califano, F.
2014-12-01
Non-Maxwellian metaequilibrium states may exist in low-collisionality plasmas as evidenced by direct (particle distributions) and indirect (e.g., instabilities driven by pressure anisotropy) satellite and laboratory measurements. These are directly observed in the solar wind (e.g. [1]), in magnetospheric reconnection events [2], in magnetically confined plasmas [3] or in simulations of Vlasov turbulence [4]. By including the full pressure tensor dynamics in a fluid plasma model, we show that a sheared velocity field can provide an effective mechanism that makes an initial isotropic state anisotropic. We discuss how the propagation of magneto-elastic waves can affect the pressure tensor anisotropization and the small scale formation that arise from the interplay between the gyrotropic terms due to the magnetic field and the flow vorticity and the non-gyropropic effect of the flow strain tensor. We support this analysis by a numerical integration of the nonlinear equations describing the pressure tensor evolution. This anisotropization mechanism might provide a good candidate for the understanding of the observed correlation between the presence of a sheared velocity flow and the signature of pressure anisotropies which are not yet explained within the standard models based e.g. on the CGL paradigm. Examples of these signatures are provided e.g. by the threshold lowering of ion-Weibel instabilities in the geomagnetic tail, observed in concomitance to the presence of a velocity shear in the near-earth plasma profile [5], or by the relatively stronger anisotropization measured for core protons in the fast solar wind [4,6] or in "space simulation" laboratory plasma experiments [3]. [1] E. Marsch et al., Journ. Geophys. Res. 109, A04120 (2004); Yu. V. Khotyainstev at el., Phys. Rev. Lett. 106, 165001 (2011). [2] N. Aunai et al., Ann. Geophys. 29, 1571 (2011); N. Aunai et al., Journ. Geophys. Res. 116, A09232 (2011). [3] E.E. Scime et al., Phys. Plasmas 7, 2157 (2000). [4
Gupta, D. N.; Islam, M. R.; Jaroszynski, D. A.; Jang, D. G.; Suk, H.
2013-12-15
Self-focusing a laser beam in collisional plasma is investigated under the weak relativistic-ponderomotive nonlinearity. In this case, the plasma equilibrium density is modified and it causes generation of the nonlinearity due to the Ohmic heating of electrons, collisions, and the weak relativistic-ponderomotive force during the interaction of the laser beam with the plasma. Our theoretical and simulation results show that a significant nonlinearity in laser self-focusing can occur under the weak relativistic-ponderomotive regime for some appropriate simulation parameters.
MHD Stability Studies of Current-Carrying Plasmas in the Compact Toroidal Hybrid
NASA Astrophysics Data System (ADS)
Knowlton, S. F.; Hartwell, G. J.; Watts, C.; Hanson, J. D.
2000-10-01
A new stellarator experiment, the Compact Toroidal Hybrid (CTH), will be built to study MHD instability and disruptions in current-carrying stellarator plasmas. Current-driven MHD instabilities in stellarators are of interest because the bootstrap and Pfirsch-Schlüter currents may potentially destabilize external kink modes in high β stellarators such as LHD (J. L. Johnson et al, Phys. Plasmas 6, 2513 (1999)). On the other hand, helical coils could prove to provide a measure of passive disruption control in tokamaks. The CTH experiment at Auburn University will use ohmic current to investigate both ideal (vertical and kink) and resistive current-driven instabilities in a low aspect ratio (Ap \\underline> 4), low-β stellarator. The configuration of the CTH device is highly flexible, with the edge vacuum rotational transform variable from ι_V(a)= 0.2 to 0.75, and the current-generated transform ι_J(a) \\underline> 0.5. The rotational transform profile can be altered with several sets of vertical field coils. Stability will be investigated with ohmic currents Ip \\underline< 50 kA applied to RF-generated stellarator plasmas in which both peaked and hollow, bootstrap-like current profiles will be generated. The low-field (Bo \\underline< 0.5T) target plasmas in CTH will be generated by ICRF at ω=ω_ci using a Nagoya Type-III antenna. The expected RF power is P_RF \\underline˜ 250 kW at a frequency ω/2π=10 MHz. The susceptibility of the current-driven stellarator plasma to disruptions and their severity will experimentally determined. The CTH design is relatively simple, with a circular vacuum vessel (Ro =0.75m, a_v= 0.28 m) and a cast aluminum helical coil support to ensure coil placement accuracy. The winding of the CTH coils is scheduled to begin in summer of 2001 and ohmic operation is expected to begin in early 2003.
Collisional Transport in a Low Aspect Ratio Tokamak -- Beyond the Drift Kinetic Formalism
D.A. Gates; R.B. White
2004-01-28
Calculations of collisional thermal and particle diffusivities in toroidal magnetic plasma confinement devices order the toroidal gyroradius to be small relative to the poloidal gyroradius. This ordering is central to what is usually referred to as neoclassical transport theory. This ordering is incorrect at low aspect ratio, where it can often be the case that the toroidal gyroradius is larger than the poloidal gyroradius. We calculate the correction to the particle and thermal diffusivities at low aspect ratio by comparing the diffusivities as determined by a full orbit code (which we refer to as omni-classical diffusion) with those from a gyroaveraged orbit code (neoclassical diffusion). In typical low aspect ratio devices the omni-classical diffusion can be up to 2.5 times the calculated neoclassical value. We discuss the implications of this work on the analysis of collisional transport in low aspect ratio magnetic confinement experiments.
Kontar, Eduard P.; Jeffrey, Natasha L. S.; Bian, N. H.; Emslie, A. Gordon
2015-08-10
Extending previous studies of nonthermal electron transport in solar flares, which include the effects of collisional energy diffusion and thermalization of fast electrons, we present an analytic method to infer more accurate estimates of the accelerated electron spectrum in solar flares from observations of the hard X-ray spectrum. Unlike for the standard cold-target model, the spatial characteristics of the flaring region, especially the necessity to consider a finite volume of hot plasma in the source, need to be taken into account in order to correctly obtain the injected electron spectrum from the source-integrated electron flux spectrum (a quantity straightforwardly obtained from hard X-ray observations). We show that the effect of electron thermalization can be significant enough to nullify the need to introduce an ad hoc low-energy cutoff to the injected electron spectrum in order to keep the injected power in non-thermal electrons at a reasonable value. Rather, the suppression of the inferred low-energy end of the injected spectrum compared to that deduced from a cold-target analysis allows the inference from hard X-ray observations of a more realistic energy in injected non-thermal electrons in solar flares.
Collisional thermalization of hydrogen and helium in solar-wind plasma.
Maruca, B A; Bale, S D; Sorriso-Valvo, L; Kasper, J C; Stevens, M L
2013-12-13
In situ observations of the solar wind frequently show the temperature of α particles (fully ionized helium) Tα to significantly differ from that of protons (ionized hydrogen) Tp. Many heating processes in the plasma act preferentially on α particles, even as collisions among ions act to gradually establish thermal equilibrium. Measurements from the Wind spacecraft's Faraday cups reveal that, at r=1.0 AU from the Sun, the observed values of the α-proton temperature ratio, θαp≡Tα/Tp, has a complex, bimodal distribution. This study applied a simple model for the radial evolution of θαp to these data to compute expected values of θαp at r=0.1 AU. These inferred θαp values have no trace of the bimodality seen in the θαp values measured at r=1.0 AU but are instead consistent with the actions of the known mechanisms for α-particle preferential heating. This result underscores the importance of collisional processes in the dynamics of the solar wind and suggests that similar mechanisms may lead to preferential α-particle heating in both slow and fast wind.
Iordanova, Snejana Paunska, Tsvetelina
2016-02-15
A collisional radiative model of low-pressure hydrogen plasmas is elaborated and applied in optical emission spectroscopy diagnostics of a single element of a matrix source of negative hydrogen ions. The model accounts for the main processes determining both the population densities of the first ten states of the hydrogen atom and the densities of the positive hydrogen ions H{sup +}, H{sub 2}{sup +}, and H{sub 3}{sup +}. In the calculations, the electron density and electron temperature are varied whereas the atomic and molecular temperatures are included as experimentally obtained external parameters. The ratio of the H{sub α} to H{sub β} line intensities is calculated from the numerical results for the excited state population densities, obtained as a solution of the set of the steady-state rate balance equations. The comparison of measured and theoretically obtained ratios of line intensities yields the values of the electron density and temperature as well as of the degree of dissociation, i.e., of the parameters which have a crucial role for the volume production of the negative ions.
Particle transport in low-collisionality H-mode plasmas on DIII-D
Mordijck, Saskia; Wang, Xin; Doyle, Edward J.; Rhodes, Terry L.; Schmitz, Lothar; Zeng, Lei; Staebler, Gary M.; Petty, Clinton C.; Groebner, Richard J.; Ko, W. -H.; Grierson, Brian A.; Solomon, Wayne M.; Tala, Tuomas; Salmi, Antti; Chrystal, Colin; Diamond, P. H.; McKee, George R.
2015-10-05
In this article we show that changing from an ion temperature gradient (ITG) to trapped electron mode (TEM) dominant turbulence regime (based on linear gyrokinetic simulations) results experimentally in a strong density pump-out (defined as a reduction in line-averaged density) in low collisionality, low power H-mode plasmas. We vary the turbulence drive by changing the heating from pre-dominantly ion heatedusing neutral beam injection to electron heated using electron cyclotron heating, which changes the T_{e}/T_{i} ratio and the temperature gradients. Perturbed gas puff experiments show an increase in transport outside ρ = 0.6, through a strong increase in the perturbed diffusion coefficient and a decrease in the inward pinch. Linear gyrokinetic simulations with TGLF show an increase in the particle flux outside the mid-radius. In conjunction an increase in intermediate-scale length density fluctuations is observed, which indicates an increase in turbulence intensity at typical TEM wavelengths. However, although the experimental changes in particle transport agree with a change from ITG to TEM turbulence regimes, we do not observe a reduction in the core rotation at mid-radius, nor a rotation reversal.
Particle transport in low-collisionality H-mode plasmas on DIII-D
Mordijck, Saskia; Wang, Xin; Doyle, Edward J.; ...
2015-10-05
In this article we show that changing from an ion temperature gradient (ITG) to trapped electron mode (TEM) dominant turbulence regime (based on linear gyrokinetic simulations) results experimentally in a strong density pump-out (defined as a reduction in line-averaged density) in low collisionality, low power H-mode plasmas. We vary the turbulence drive by changing the heating from pre-dominantly ion heatedusing neutral beam injection to electron heated using electron cyclotron heating, which changes the Te/Ti ratio and the temperature gradients. Perturbed gas puff experiments show an increase in transport outside ρ = 0.6, through a strong increase in the perturbed diffusionmore » coefficient and a decrease in the inward pinch. Linear gyrokinetic simulations with TGLF show an increase in the particle flux outside the mid-radius. In conjunction an increase in intermediate-scale length density fluctuations is observed, which indicates an increase in turbulence intensity at typical TEM wavelengths. However, although the experimental changes in particle transport agree with a change from ITG to TEM turbulence regimes, we do not observe a reduction in the core rotation at mid-radius, nor a rotation reversal.« less
Formation of collisional sheath in electronegative plasma with two species of positive ions
Moulick, R. Goswami, K. S.
2015-03-15
Sheath formation is investigated for electronegative plasma in presence of two species of positive ions in collisional environment. The gas under consideration is a mixture of oxygen and argon. Argon is the considered as having fixed volume and impact of collision is studied with increasing pressure of oxygen. Fluid equations are solved for three species namely, the two positive ions and a negative ion. Electrons are considered to follow Boltzmann distribution. Collision is modeled by constant mean free path model and has been used as a parameter. It has been found that collision enhances the sheath formation. The negative ion core is nearly unaffected by the presence of collision and is governed by the electric potential. The negative flux field is, however, affected by the presence of collision and shows a steady behavior in front of the wall. The two positive ions are heavily affected by the presence of collision and the modeling is such that their equilibrium densities can be estimated by solving simultaneous cubic equations.
NASA Astrophysics Data System (ADS)
Kontar, Eduard P.; Jeffrey, Natasha L. S.; Emslie, A. Gordon; Bian, N. H.
2015-08-01
Extending previous studies of nonthermal electron transport in solar flares, which include the effects of collisional energy diffusion and thermalization of fast electrons, we present an analytic method to infer more accurate estimates of the accelerated electron spectrum in solar flares from observations of the hard X-ray spectrum. Unlike for the standard cold-target model, the spatial characteristics of the flaring region, especially the necessity to consider a finite volume of hot plasma in the source, need to be taken into account in order to correctly obtain the injected electron spectrum from the source-integrated electron flux spectrum (a quantity straightforwardly obtained from hard X-ray observations). We show that the effect of electron thermalization can be significant enough to nullify the need to introduce an ad hoc low-energy cutoff to the injected electron spectrum in order to keep the injected power in non-thermal electrons at a reasonable value. Rather, the suppression of the inferred low-energy end of the injected spectrum compared to that deduced from a cold-target analysis allows the inference from hard X-ray observations of a more realistic energy in injected non-thermal electrons in solar flares.
NASA Astrophysics Data System (ADS)
Sonnino, G.
2011-03-01
Fully ionized L-mode tokamak plasmas in the fully collisional (Pfirsch-Schlüter) and in the low-collisional (banana) nonlinear transport regimes are analyzed. We derive the expressions for particles and heat losses together with the steady-state particle distribution functions in the several collisional transport regimes. The validity of the nonlinear closure equations, previously derived, has been indirectly tested by checking that the obtained particle distribution functions are indeed solutions of the nonlinear, steady-state, Vlasov-Landau gyro-kinetic equations. A quite encouraging result is the fact that, for L-mode tokamak plasmas a dissymmetry appears between the ion and electron transport coefficients: the latter submits to a nonlinear correction, which makes the radial electron coefficients much larger than the former. In particular we show that when the L-mode JET plasma is out of the linear region, the Pfirsch-Schlüter electron transport coefficients are corrected by an amplification factor, which may reach values of order 102. Such a correction is absent for ions. On the contrary, in the banana regime, the ion transport coefficients are increased by a factor 2 and the nonlinear corrections for electrons are negligible. These results are in line with experiments.
Evans, T. E.
2016-03-01
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δmore » $$b_⊥^{ext}$$ ≈ $$10^{-4}$$ → $$10^{-3}$$ T). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes. At the same time the theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design [A. Loarte, et al., Nucl. Fusion 54 (2014) 033007]. This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.« less
NASA Astrophysics Data System (ADS)
Singh, Rameswar; Storelli, A.; Gürcan, Ö. D.; Hennequin, P.; Vermare, L.; Morel, P.; Singh, R.
2015-12-01
Starting from the Braginskii equations, relevant for the tokamak edge region, a complete set of nonlinear equations for the geodesic acoustic modes (GAM) has been derived which includes collisionality, plasma beta and external sources of particle, momentum and heat. Local linear analysis shows that the GAM frequency increases with collisionality at low radial wave number {{k}\\text{r}} and decreases at high {{k}\\text{r}} . GAM frequency also decreases with plasma beta. Radial profiles of GAM frequency for two Tore Supra shots, which were part of a collisionality scan, are compared with these calculations. A discrepancy between experiment and theory is observed, which seems to be explained by a finite {{k}\\text{r}} for the GAM when flux surface averaged density < n> and temperature < T> are assumed to vanish. It is shown that this agreement is incidental and self-consistent inclusion of < n> and < T> responses enhances the disagreement more with {{k}\\text{r}} at high {{k}\\text{r}} . So the discrepancy between the linear GAM calculation and experiment, (which also persist for more ‘complete’ linear models such as gyrokinetics) can probably not be resolved by simply adding a finite {{k}\\text{r}} .
NASA Astrophysics Data System (ADS)
Hershkowitz, N.; Yip, C.-S.; Severn, G. D.
2011-05-01
Recent experiments have shown that ions in weakly collisional plasmas containing two ion species of comparable densities approximately reach a common velocity at the sheath edge equal to the bulk plasma ion sound velocity. A recent theory [S. D. Baalrud, C. C. Hegna, and J. D. Callen, Phys. Rev. Lett. 103, 205002 (2009)] suggests that this is a consequence of collisional friction between the two ion species enhanced by the two stream instability. The theory finds that the difference in velocities at the sheath edge depends on the relative concentrations of the two ions. The difference in velocities is small, with both species approaching to the bulk sound velocity, when the concentrations are comparable, and is large, with each species reaching its own Bohm velocity, when the relative concentration differences are large. To test these findings, drift velocities of Ar and Xe ions were measured with laser-induced fluorescence in Ar-Xe and He-Xe plasmas and combined with ion acoustic wave and plasma potential data. In addition, electron temperature was varied by a Maxwell demon [K. R. MacKenzie et al., App. Phys. Lett. 18, 529 (1971)]. The predictions were found to be in excellent agreement with the experimental data. The generalized Bohm criterion in two ion species plasmas is also verified in a wider variety of relative ion concentrations.
NASA Astrophysics Data System (ADS)
Xinyi, Wang; Shali, Xiao; jian, Lu; Yufen, Wu; Jun, Shi; Jiayu, Qian; Shenye, Liu; Minxi, Wei; Bolun, Chen
2016-04-01
Based on the Bragg law and imaging principle of bent crystal, the imaging properties of the monochromic backlighting system with a toroidally bent crystal were studied via ray-tracing simulations and experiments. Comparison experiments with both toroidally and spherically bent crystals using a Cr line as the backlighter were performed, showing that using toroidally bent crystal, a 2D image with the same magnifications in meridional and sagittal directions can be obtained with higher spatial resolution. Experiments with laser-produced plasmas using Mica crystal were carried out on the Shenguang II laser facility. Five laser beams were focused onto a Ti planar target producing a line at 4.75 keV as the backlighter and an image of a metal grid with size of 200 μm × 200 μm was recorded with an x-ray image plate. A spatial resolution of 40 μm was demonstrated with a magnification of 3 due to the restriction of the target chamber size. 10 μm spatial resolution might be possible if the detector can be located outside the chamber to enlarge the magnification.
Using coherent population trapping in test atoms for magnetic field measurements in toroidal plasmas
Akhmedzhanov, R. A.; Gushchin, L. A.; Zelensky, I. V.; Litvak, A. G.; Tokman, M. D.
2007-09-15
A way to measure the profile of the safety factor in toroidal controlled-fusion setups has been developed. The method is based on measuring the ratio of the poloidal magnetic field and the toroidal one locally, based on a modification of the optical resonance-fluorescence signal. The effect of partial suppression of resonance fluorescence is used, which depends on the orientation of the magnetic field relative to the laser beam, and takes place in case of coherent population trapping in test atoms with the Zeeman split-level structure, as affected by double-frequency laser radiation.
NASA Astrophysics Data System (ADS)
Chim, Chi Yung
First in Chapter 2, we discuss the collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses, but both with singly-ionized atoms. In a limit of high cyclotron frequencies O j, the total cyclotron action Ij for the two species are adiabatic invariants. In a few collisions, maximizing entropy yields a modified Gibbs distribution of the form exp[-H/T ∥-alpha1 I 1-alpha2I2]. Here, H is the total Hamiltonian and alphaj's are related to parallel and perpendicular temperatures through T ⊥j=(1/T∥ +alphaj/Oj) -1. On a longer timescale, the two species share action so that alpha 1 and alpha2 relax to a common value alpha. On an even longer timescale, the total action ceases to be a constant of the motion and alpha relaxes to zero. Next, weak transport produces a low density halo of electrons moving radially outward from the pure electron plasma core, and the m = 1 mode begins to damp algebraically when the halo reaches the wall. The damping rate is proportional to the particle flux through the resonant layer at the wall. Chapter 3 explains analytically the new algebraic damping due to both mobility and diffusion transport. Electrons swept around the resonant "cat's eye" orbits form a dipole (m = 1) density distribution, setting up a field that produces ExB-drift of the core back to the axis, that is, damps the mode. Finally, Chapter 4 provides a simple mechanistic interpretation of the resonant wave-particle interaction of Landau. For the simple case of a Vlasov plasma oscillation, the non-resonant electrons are driven resonantly by the bare electric field from the resonant electrons, and this complex driver field is of a phase to reduce the oscillation amplitude. The wave-particle resonant interaction also occurs in 2D ExB-drift waves, such as a diocotron wave. In this case, the bare electric field from the resonant electrons causes ExB-drift motion back in the core plasma, thus damping the wave.
Theiler, C.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Ricci, P.; Podesta, M.; Poli, F. M.
2008-04-15
Intermittent cross-field particle transport events (ITEs) are studied in the basic toroidal device TORPEX [TORoidal Plasma EXperiment, A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)], with focus on the role of the density gradient. ITEs are due to the intermittent radial elongation of an interchange mode. The elongating positive wave crests can break apart and form blobs. This is not necessary, however, for plasma particles to be convected a considerable distance across the magnetic field lines. Conditionally sampled data reveal two different scenarios leading to ITEs. In the first case, the interchange mode grows radially from a slab-like density profile and leads to the ITE. A novel analysis technique reveals a monotonic dependence between the vertically averaged inverse radial density scale length and the probability for a subsequent ITE. In the second case, the mode is already observed before the start of the ITE. It does not elongate radially in a first stage, but at a later time. It is shown that this elongation is preceded by a steepening of the density profile as well.
Sedaghat, M.; Ettehadi-Abari, M.; Shokri, B. Ghorbanalilu, M.
2015-03-15
Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range Iλ{sup 2}≃10{sup 14}−10{sup 16}Wcm{sup −2}μm{sup 2}. The collisional effect is found to be significant when the incident laser intensity is less than 10{sup 16}Wcm{sup −2}μm{sup 2}. In the current work, the propagation of a high frequency electromagnetic wave, for underdense collisional plasma in the presence of an external magnetic field is investigated. It is shown that, by considering the effect of the ponderomotive force in collisional magnetized plasmas, the increase of laser pulse intensity leads to steepening of the electron density profile and the electron bunches of plasma makes narrower. Moreover, it is found that the wavelength of electric and magnetic fields oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison with the unmagnetized collisional plasma. Furthermore, the spatial damping rate of laser energy and the nonlinear bremsstrahlung absorption coefficient are obtained in the collisional regime of magnetized plasma. The other remarkable result is that by increasing the external magnetic field in this case, the absorption coefficient increases strongly.
Federspiel, L.; Labit, B.; Ricci, P.; Fasoli, A.; Furno, I.; Theiler, C.
2009-09-15
The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. This gradient is reached during a scan in the neutral gas pressure p{sub n}. Around a critical value for p{sub n}, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure profile is locally flattened, stabilizing the interchange mode observed at lower neutral gas densities. The measured value for the critical gradient is close to the linear theory estimate.
NASA Astrophysics Data System (ADS)
Christenson, Michael; Szott, Matthew; Kalathiparambil, Kishor; Sovinec, Carl; Ruzic, David
2016-10-01
The ThermoElectric-driven Liquid-metal plasma-facing Structures (TELS) device at the University of Illinois is a theta-pinched, plasma-material interaction test stand used to simulate extreme events in the edge and divertor regions of a tokamak plasma. Previous measurements of the electron and ion temperatures have shown that the isotropic heat load on target ranges between 0.1 and 0.2 MJ m-2 over a pulse lasting 0.2 ms. While this compares well to the heat loads from Type 1 ELMs in larger toroidal devices, it is still much less than the energy deposition from Type 1 ELMs expected in ITER, which are in excess of 1 MJ m-2. To this end, a compact toroid (CT) injector has been proposed as a modification to the existing TELS device. By using an externally applied bias field to force reconnection at the muzzle of the coaxial plasma accelerator source that drives ionization, NIMROD MHD simulations have shown a peak magnetic flux of 3.5 mWb is reached 0.025 ms into the pulse - more than sufficient to form a CT. Early calorimetry and magnetic field measurements indicate that a new plasma structure has been formed in the magnetized coaxial plasma source. This work presents the current results of CT generation with respect to the bias field strength as well as the coaxial source geometry. DOE OFES DE-SC0008587, DE-SC0008658, DE-FG02-99ER54515.
NASA Astrophysics Data System (ADS)
Kapper, Gernot; Kasilov, Sergei V.; Kernbichler, Winfried; Martitsch, Andreas F.; Heyn, Martin F.; Marushchenko, Nikolai B.; Turkin, Yuriy
2016-11-01
The Electron Cyclotron Current Drive (ECCD) efficiency is usually modeled in the collisionless limit. While such models are sufficient for plasmas with rather low collisionality, they might underestimate the current drive in plasmas at low temperatures likely to occur at the initial phase of high density device operation. In this paper, the impact of finite collisionality effects on the wave-induced current drive is studied for a high-mirror configuration of Wendelstein 7-X using a combination of the drift kinetic equation solver NEO-2 and the ray-tracing code TRAVIS for a realistic set of plasma parameter profiles. The generalized Spitzer function, which describes the ECCD efficiency in phase space, is modeled with help of NEO-2, which uses the full linearized Coulomb collision operator, including energy and momentum conservation. Within this approach, the linearized drift kinetic equation is solved by means of the field line integration technique without any simplifications on device geometry. The results of the ray-tracing code TRAVIS using the ECCD efficiency from NEO-2 within the adjoint approach show a significant difference for the driven current when compared to commonly used collisionless models for the ordinary as well as the extraordinary second harmonic mode.
Héron, A.; Adam, J. C.
2015-07-15
We present a set of 2D collisional particle-in-cell simulations of the interaction of ultra-intense laser pulses with over-dense cold collisional plasmas. The size of these simulations is about 100 times as large as those previously published. This allows studying the transport of energetic particles on time scale of the order of 400 fs without perturbations due to the influence of boundary effects and performing a very detailed analysis of the physics of the transport. We confirm the existence of a threshold in intensity close to the relativistic threshold above which the beam of energetic particles diverges when it penetrates the cold plasma. We also study the applicability of Ohm's law to compute the electric field, which is the method commonly used in hybrid codes. The heating of the cold plasma is then studied and we show that half of the heating is anomalous, i.e., not given by standard Joule effect. We discuss the previously published results in the light of these new simulations.
NASA Astrophysics Data System (ADS)
Sciamma, Ella Marion
A spectroscopic diagnostic tool has been developed to determine the electron temperature and the neutral density in helium, hydrogen and argon plasmas from absolutely calibrated spectroscopic measurements. For each gas, a method of analysis which uses models specific to each species present in the plasma (neutral atom or singly ionized atom) has been defined. The experimental electron density is used as an input parameter to the models, and the absolutely calibrated spectroscopic data are processed beforehand to obtain the populations of the upper excited levels corresponding to the observed spectral lines. For helium plasmas, the electron temperature is inferred from the experimental helium ion excited level p = 4 population using a corona model, and then the neutral density is determined from the experimental helium neutral excited level populations using a collisional-radiative model for helium neutrals. For hydrogen plasmas, combinations of the electron temperature and the neutral density are determined from the experimental hydrogen neutral excited level populations using a collisional-radiative model specific to hydrogen atoms. For argon plasmas, the electron temperature is inferred from the experimental argon ion excited level populations using a collisional-radiative model for argon ions, and then the neutral density is determined from the experimental argon neutral excited level populations using a collisional-radiative model for argon neutrals. This diagnostic tool was applied to three experiments with different geometries and plasma conditions to test the validity of each data analysis method. The helium and hydrogen data analysis methods were tested and validated on helium and hydrogen plasmas produced in the VASIMR experiment, a plasma propulsion system concept. They gave electron temperatures and neutral densities that were consistent with other diagnostics and theory. The argon diagnostic tool was tested on argon plasmas produced in the VASIMR
NASA Astrophysics Data System (ADS)
Zhao, K. J.; Shi, Yuejiang; Liu, H.; Diamond, P. H.; Li, F. M.; Cheng, J.; Chen, Z. P.; Nie, L.; Ding, Y. H.; Wu, Y. F.; Chen, Z. Y.; Rao, B.; Cheng, Z. F.; Gao, L.; Zhang, X. Q.; Yang, Z. J.; Wang, N. C.; Wang, L.; Jin, W.; Xu, J. Q.; Yan, L. W.; Dong, J. Q.; Zhuang, G.; J-TEXT Team
2016-07-01
The acceleration of the co-current toroidal rotations around resonant surfaces by resonant magnetic perturbations (RMPs) through turbulence is presented. These experiments were performed using a Langmuir probe array in the edge plasmas of the J-TEXT tokamak. This study aims at understanding the RMP effects on edge toroidal rotations and exploring its control method. With RMPs, the flat electron temperature T e profile, due to magnetic islands, appears around resonant surfaces (Zhao et al 2015 Nucl. Fusion 55 073022). When the resonant surface is closer to the last closed flux surface, the flat T e profile vanishes with RMPs. In both cases, the toroidal rotations significantly increase in the direction of the plasma current around the resonant surfaces with RMPs. The characteristics of turbulence are significantly affected by RMPs around the resonant surfaces. The turbulence intensity profile changes and the poloidal wave vector k θ increases with RMPs. The power fraction of the turbulence components in the ion diamagnetic drift direction increases with RMPs. The measurements of turbulent Reynolds stresses are consistent with the toroidal flows that can be driven by turbulence. The estimations of the energy transfer between the turbulence and toroidal flows suggest that turbulence energy transfers into toroidal flows. The result has the implication of the intrinsic rotation being driven by RMPs via turbulence.
Properties of toroidal Alfvén eigenmode in DIII-D plasma
Wang, Zhixuan; Lin, Zhihong Holod, Ihor; Heidbrink, W. W.; Deng, Wenjun; Xiao, Y.; Zhang, H.; Zhang, W.; Van Zeeland, M.
2015-02-15
Linear properties of the toroidal Alfvén eigenmode (TAE) excited by energetic particles (EP) in a DIII-D tokamak experiment have been studied in global gyrokinetic particle simulations treating self-consistently kinetic effects of EP, thermal ions, and electrons. Simulation results of the TAE frequency and mode structure agree very well with the experimental measurements. The non-perturbative EP contribution induces a radial localization of the TAE mode structure, a break-down of mode radial symmetry, as well as a frequency dependence on the toroidal mode number. The simulations further demonstrate the dependence of the growth rate and mode structure on EP pressure gradients. The in-out asymmetry of the mode structure and the experimental identification of the poloidal harmonics have also been clarified.
NASA Astrophysics Data System (ADS)
Bortolon, A.; Camenen, Y.; Karpushov, A. N.; Duval, B. P.; Andrebe, Y.; Federspiel, L.; Sauter, O.; the TCV Team
2013-02-01
An alternative experimental spectroscopic measurement of poloidal plasma rotation in toroidally confined plasmas is proven effective in the TCV tokamak. Charge exchange recombination measurements of the toroidal rotation profile over the full mid-plane plasma diameter are used to infer the complete bi-dimensional flow structure of the intrinsic C6+ impurity, which includes its poloidal component. For divergence free flows, the difference between the toroidal rotation frequency ft = ut/R at the inboard and outboard locations on the same flux surface is proportional to the poloidal rotation. This indirect measurement provides increased accuracy as the measured quantity ft,in - ft,out≈4qup/Raxis(q is the local safety factor) is larger than the intrinsic uncertainties of a direct spectroscopic measurement of poloidal velocity. The method is applied in a variety of TCV ohmic and electron cyclotron heated L-mode plasmas in the banana-plateau collisionality regime (0.2<\
Oz, E.; Myers, C. E.; Yamada, M.; Ji, H.; Kulsrud, R. M.; Xie, J.
2011-10-15
The stability properties of partial-toroidal flux ropes are studied in detail in the laboratory, motivated by ubiquitous arched magnetic structures found on the solar surface. The flux ropes studied here are magnetized arc discharges formed between two electrodes in the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936 (1997)]. The three dimensional evolution of these flux ropes is monitored by a fast visible light framing camera, while their magnetic structure is measured by a variety of internal magnetic probes. The flux ropes are consistently observed to undergo large-scale oscillations as a result of an external kink instability. Using detailed scans of the plasma current, the guide field strength, and the length of the flux rope, we show that the threshold for kink stability is governed by the Kruskal-Shafranov limit for a flux rope that is held fixed at both ends (i.e., q{sub a} = 1).
Plyushchev, G.; Diallo, A.; Fasoli, A.; Furno, I.; Labit, B.; Mueller, S. H.; Podesta, M.; Poli, F. M.; Boehmer, H.; Heidbrink, W. W.; Zhang, Y.
2006-10-15
A specific experimental apparatus consisting of an ion source and a detector for the investigation of the interaction between suprathermal ions and drift-wave turbulence is developed on the toroidal plasma experiment. Due to the low plasma temperature ({approx}5 eV), a spatially localized, small-size ion source ({approx}4 cm) mounted inside the vacuum vessel with relatively low ion energy ({approx}100 eV-1 keV) can be used. The source consists of an aluminosilicate Li-6 ion emitter (6 mm diameter, 10-30 {mu}A current) installed on a two-dimensional (2D) poloidally moving system. The location, energy, and current density profile of the ion beam will be measured using a 2D movable gridded energy analyzer.
Effects of Toroidal Forces in Current Loops Embedded in a Background Plasma.
1987-12-29
loop in stable MHD equilibrium described by c’V x B - Vp = 0 where the major radial forces as well as the minor e radial forces arc explicitly...dimensional semi-toroidal equilibria previously identified. ’’It is found that somec equilibrium loops are u~nstable jo such perturbations. resulting in...pressure gradient and drag force due to the ambient gas. For the equilibrium loops studied, the motion is found to be subsonic. Time evolution of the
Qiu, Hui-Bin; Song, Hai-Ying; Liu, Shi-Bing
2015-09-15
Nonlinear Raman forward scattering of an intense short laser pulse with a duration shorter than the plasma period propagating through a homogenous collisional nonextensive distributed plasma in the presence of a uniform magnetic field perpendicular to both the direction of propagation and electric vector of the radiation field is investigated theoretically when ponderomotive, relativistic, and collisional nonlinearities are taken into account. The governing equations for nonlinear wave in the context of nonextensive statistics are given, the nonextensive coupled equations describing the nonlinear Raman forward scattering instability are solved by the Fourier transformation method, and the growth rate of the nonlinear Raman forward scattering instability is obtained. The results in the case q → 1 are consistent with those in the framework of the Maxwellian distribution. It is found that the instability growth rate first decreases on increasing electron thermal velocity, minimizes at a critical thermal velocity, and then increases steeply; the critical temperature dependents on the nonextensive parameter, and the greater nonextensive parameter, correspond to the greater critical temperature; when the thermal velocity of electron is less than the critical speed, the instability growth rate is found to be enhanced as the nonextensive parameter increases; but when the thermal velocity is greater than the critical speed, the instability growth rate decreases on increasing the nonextensive parameter.
NASA Astrophysics Data System (ADS)
Kuroda, Kengoh; Wada, Manato; Uchida, Masaki; Tanaka, Hitoshi; Maekawa, Takashi
2016-02-01
In toroidal electron cyclotron resonance (ECR) plasmas under a weak external vertical field {{B}\\text{V}} a part of the pressure driven vertical charge separation current returns along the helical field lines, generating a toroidal current. The rest circulates via the conducting vacuum vessel. Only the toroidal current contributes to the production of a closed flux surface. Both the toroidal and vertical currents are an equilibrium current that provides a radial force by the interaction with the vertical field and the toroidal field, respectively, to counter-balance the outward pressure ballooning force. We have done experiments using 2.45 GHz microwaves in the low aspect ratio torus experiment (LATE) device to investigate in what way and how much the toroidal current is generated towards the initiation of a closed flux surface. In steady discharges by {{P}\\text{inj}}=1.5 kW under various {{B}\\text{V}} both the pressure and the toroidal current become large with {{B}\\text{V}} . When {{B}\\text{V}}=6.8 G, a toroidal current of 290 A is generated and the vertical field is reduced to 1.2 G inside the current channel, being close to the initiation of a closed flux surface. In this plasma the return current does not obey Ohm’s law. Instead, the return current flows so that the electric force on the electron fluid is balanced with the pressure gradient along the field lines. Near the top and bottom boundaries superthermal electrons flow beyond the potential barrier onto the walls along the field lines. In another discharge by the low power of {{P}\\text{inj}}=1.0 kW under {{B}\\text{V}}=8.3 G, both the toroidal current and the pressure steadily increase for an initial duration of 1.1 s and then abruptly jump, generating an initial closed flux surface. While the counter force from the vertical current is initially dominant, that from the toroidal current gradually increases and becomes four times larger than that from the vertical current just before the initiation
NASA Astrophysics Data System (ADS)
Frassinetti, L.; Beurskens, M. N. A.; Saarelma, S.; Boom, J. E.; Delabie, E.; Flanagan, J.; Kempenaars, M.; Giroud, C.; Lomas, P.; Meneses, L.; Maggi, C. S.; Menmuir, S.; Nunes, I.; Rimini, F.; Stefanikova, E.; Urano, H.; Verdoolaege, G.; Contributors, JET
2017-01-01
A dimensionless collisionality scan in low-triangularity plasmas in the Joint European Torus with the ITER-like wall (JET-ILW) has been performed. The increase of the normalized energy confinement (defined as the ratio between thermal energy confinement and Bohm confinement time) with decreasing collisionality is observed. Moreover, at low collisionality, a confinement factor H98, comparable to JET-C, is achieved. At high collisionality, the low normalized confinement is related to a degraded pedestal stability and a reduction in the density-profile peaking. The increase of normalized energy confinement is due to both an increase in the pedestal and in the core regions. The improvement in the pedestal is related to the increase of the stability. The improvement in the core is driven by (i) the core temperature increase via the temperature-profile stiffness and by (ii) the density-peaking increase driven by the low collisionality. Pedestal stability analysis performed with the ELITE (edge-localized instabilities in tokamak equilibria) code has a reasonable qualitative agreement with the experimental results. An improvement of the pedestal stability with decreasing collisionality is observed. The improvement is ascribed to the reduction of the pedestal width, the increase of the bootstrap current and the reduction of the relative shift between the positions of the pedestal density and pedestal temperature. The EPED1 model predictions for the pedestal pressure height are qualitatively well correlated with the experimental results. Quantitatively, EPED1 overestimates the experimental pressure by 15-35%. In terms of the pedestal width, a correct agreement (within 10-15%) between the EPED1 and the experimental width is found at low collisionality. The experimental pedestal width increases with collisionality. Nonetheless, an extrapolation to low-collisionality values suggests that the width predictions from the KBM constraint are reasonable for ITER.
NASA Astrophysics Data System (ADS)
Guo, Shimin; Mei, Liquan; He, Yaling; Li, Ying
2016-02-01
The nonlinear propagation of ion-acoustic waves is theoretically reported in a collisional plasma containing strongly coupled ions and nonthermal electrons featuring Tsallis distribution. For this purpose, the nonlinear integro-differential form of the generalized hydrodynamic model is used to investigate the strong-coupling effect. The modified complex Ginzburg-Landau equation with a linear dissipative term is derived for the potential wave amplitude in the hydrodynamic regime, and the modulation instability of ion-acoustic waves is examined. When the dissipative effect is neglected, the modified complex Ginzburg-Landau equation reduces to the nonlinear Schrödinger equation. Within the unstable region, two different types of second-order ion-acoustic rogue waves including single peak type and rogue wave triplets are discussed. The effect of the plasma parameters on the rogue waves is also presented.
A Kilogauss-scale, High-vacuum Toroidal Electron Plasma Experiment
Marler, J. P.; Stoneking, M. R.
2006-10-18
We describe in detail the newly constructed Lawrence Non-Neutral Torus (LNT) II apparatus. The LNT II features an improved toroidal magnetic field magnitude ({approx} 1 kG) and base vacuum pressure (<10-9 Torr). A segmented Au-plated Al electrode shell contributes to the reduction in field asymmetries and enables enhanced diagnostic capabilities. Additionally, the electron source is located on a retractable bellows for study of confinement dynamics in a complete torus. Conservative estimates suggest confinement times on the order of 1 second are achievable which would represent almost two orders of magnitude improvement over measurements made with the previous apparatus.
Current density and poloidal magnetic field for toroidal elliptic plasmas with triangularity
Martin, P.; Haines, M.G.; Castro, E.
2005-08-15
Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift.
Complete fluid equations for low-n singular modes in axisymmetric toroidal plasmas
Glasser, A.H.
1990-01-01
The goal of this work is to develop a complete linear theory of the singular region, including all important dynamical effects. The present phase of the work treats the more collision fluid regime. A later phase will treat the less collisional gyrokinetic regime. This paper concerns the derivation and form of the fluid equations for the singular region of low-n modes. Later work will treat high-n ballooning modes. In addition, the ordering in the present work must be amended before it is applicable to the neighborhood of the field reversal surface of the RFP.
Tracy, Mark David
1993-01-08
Collective Thomson scattering from ion-acoustic waves at 266nm is used to obtain spatially resolved, two-dimensional electron density, sound speed, and radial drift profiles of a collisional laser plasma. An ultraviolet diagnostic wavelength minimizes the complicating effects of inverse bremsstrahlung and refractive turning in the coronal region of interest, where the electron densities approach n_{c}/10. Laser plasmas of this type are important because they model some of the aspects of the plasmas found in high-gain laser-fusion pellets irradiated by long pulse widths where the laser light is absorbed mostly in the corona. The experimental results and LASNEX simulations agree within a percent standard deviation of 40% for the electron density and 50% for the sound speed and radial drift velocity. Thus it is shown that the hydrodynamics equations with classical coefficients and the numerical approximations in LASNEX are valid models of laser-heated, highly collisional plasmas. The versatility of Thomson scattering is expanded upon by extending existing theory with a Fokker-Planck based model to include plasmas that are characterized by (0 ≤ k_{ia}λ_{ii} ≤ ∞) and ZT_{e}/T_{i}, where k_{ia} is the ion- acoustic wave number, λ_{ii} is the ion-ion mean free path, Z is the ionization state of the plasma, and T_{e}. T_{i} are the electron and ion temperatures in electron volts respectively. The model is valid for plasmas in which the electrons are approximately collisionless, (k_{ia}λ_{ei}, k_{ia}λ_{ee} ≥ 1), and quasineutrality holds, (α ≥1), where α = 1/kλ_{DE} and λ_{De} is the electron Debye length. This newly developed model predicts the lineshape of the ion-acoustic Thomson spectra and when fit to experimental data provides a direct measurement of the relative thermal flow velocity between the electrons and ions.
Matsumoto, T; Sekiguchi, J; Asai, T; Gota, H; Garate, E; Allfrey, I; Valentine, T; Morehouse, M; Roche, T; Kinley, J; Aefsky, S; Cordero, M; Waggoner, W; Binderbauer, M; Tajima, T
2016-05-01
A compact toroid (CT) injector was developed for the C-2 device, primarily for refueling of field-reversed configurations. The CTs are formed by a magnetized coaxial plasma gun (MCPG), which consists of coaxial cylindrical electrodes and a bias coil for creating a magnetic field. First, a plasma ring is generated by a discharge between the electrodes and is accelerated by Lorenz self-force. Then, the plasma ring is captured by an interlinkage flux (poloidal flux). Finally, the fully formed CT is ejected from the MCPG. The MCPG described herein has two gas injection ports that are arranged tangentially on the outer electrode. A tungsten-coated inner electrode has a head which can be replaced with a longer one to extend the length of the acceleration region for the CT. The developed MCPG has achieved supersonic CT velocities of ∼100 km/s. Plasma parameters for electron density, electron temperature, and the number of particles are ∼5 × 10(21) m(-3), ∼40 eV, and 0.5-1.0 × 10(19), respectively.
Gupta, Naveen Singh, Arvinder; Singh, Navpreet
2015-11-15
This paper presents a scheme for second harmonic generation of an intense q-Gaussian laser beam in a preformed parabolic plasma channel, where collisional nonlinearity is operative with nonlinear absorption. Due to nonuniform irradiance of intensity along the wavefront of the laser beam, nonuniform Ohmic heating of plasma electrons takes place. Due to this nonuniform heating of plasma, the laser beam gets self-focused and produces strong density gradients in the transverse direction. The generated density gradients excite an electron plasma wave at pump frequency that interacts with the pump beam to produce its second harmonics. The formulation is based on a numerical solution of the nonlinear Schrodinger wave equation in WKB approximation followed by moment theory approach. A second order nonlinear differential equation governing the propagation dynamics of the laser beam with distance of propagation has been obtained and is solved numerically by Runge Kutta fourth order technique. The effect of nonlinear absorption on self-focusing of the laser beam and conversion efficiency of its second harmonics has been investigated.
NASA Astrophysics Data System (ADS)
Hou, Lujing; Wang, Younian; Z, L. Miskvic
2004-08-01
The characteristics of collisional radio-frequency (rf) sheath dynamics over an electrode with a cylindrical hole is simulated by means of a self-consistent model which consists of two-dimensional time-dependent fluid equations coupled with Poisson equation. In addition, an equivalent-circuit model is coupled to the fluid equations in order to self-consistently determine relationship between the instantaneous potential at the rf-biased electrode and the sheath thickness. Two-dimensional profiles of the potential, the ion fluid velocity, and the distributions of the ion and electron densities within the sheath are computed under various discharge conditions, such as the discharge powers and the gas pressures. The results show that the existence of the cylindrical hole on the electrode significantly affects the sheath structure and generates a potential trap in the horizontal direction, which is particularly strong when the sheath thickness is comparable to the depth of the hole. Moreover, it is found that the collisional effects have a significant influence on the sheath characteristics.
Toroidal rotation studies in KSTAR
NASA Astrophysics Data System (ADS)
Lee, S. G.; Lee, H. H.; Yoo, J. W.; Kim, Y. S.; Ko, W. H.; Terzolo, L.; Bitter, M.; Hill, K.; KSTAR Team
2014-10-01
Investigation of the toroidal rotation is one of the most important topics for the magnetically confined fusion plasma researches since it is essential for the stabilization of resistive wall modes and its shear plays an important role to improve plasma confinement by suppressing turbulent transport. The most advantage of KSTAR tokamak for toroidal rotation studies is that it equips two main diagnostics including the high-resolution X-ray imaging crystal spectrometer (XICS) and charge exchange spectroscopy (CES). Simultaneous core toroidal rotation and ion temperature measurements of different impurity species from the XICS and CES have shown in reasonable agreement with various plasma discharges in KSTAR. It has been observed that the toroidal rotation in KSTAR is faster than that of other tokamak devices with similar machine size and momentum input. This may due to an intrinsically low toroidal field ripple and error field of the KSTAR device. A strong braking of the toroidal rotation by the n = 1 non-resonant magnetic perturbations (NRMPs) also indicates these low toroidal field ripple and error field. Recently, it has been found that n = 2 NRMPs can also damp the toroidal rotation in KSTAR. The detail toroidal rotation studies will be presented. Work supported by the Korea Ministry of Science, ICT and Future Planning under the KSTAR project.
Futatani, Shimpei; Bos, Wouter J. T.; Morales, Jorge A.
2015-05-15
It can be shown that in the presence of a toroidal magnetic field induced by poloidal coils, combined with the electromagnetic field induced by a central solenoid, no static equilibrium is possible within the MHD description, as soon as non-zero resistivity is assumed. The resulting dynamic equilibrium was previously discussed for the case of spatially homogeneous resisitivity. In the present work, it is shown how a spatial inhomogeneity of the viscosity and resisitivity coefficients influences this equilibrium. Parameters in both the stable, tokamak-like regime and unstable, reversed field pinch-like regime are considered. It is shown that, whereas the magnitudes of the velocity and magnetic field fluctuations are strongly modified by the spatial variation of the transport coefficients, the qualitative flow behaviour remains largely unaffected.
Stability of the toroidicity-induced Alfven eigenmode in axisymmetric toroidal equilibria
Fu, G.Y.; Cheng, C.Z.; Wong, K.L.
1993-09-01
The stability of toroidicity-induced Alfven eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values of v{sub h}/v{sub A} (> 1) and destabilizing for smaller values of v{sub h}/v{sub A} (< 1), where v{sub h} is the hot particle speed and v{sub A} is the Alfven speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measurements.
NASA Astrophysics Data System (ADS)
Alvarez Laguna, A.; Lani, A.; Deconinck, H.; Mansour, N. N.; Poedts, S.
2016-08-01
We present a Finite Volume scheme for solving Maxwell's equations coupled to magnetized multi-fluid plasma equations for reactive and collisional partially ionized flows on unstructured meshes. The inclusion of the displacement current allows for studying electromagnetic wave propagation in a plasma as well as charge separation effects beyond the standard magnetohydrodynamics (MHD) description, however, it leads to a very stiff system with characteristic velocities ranging from the speed of sound of the fluids up to the speed of light. In order to control the fulfillment of the elliptical constraints of the Maxwell's equations, we use the hyperbolic divergence cleaning method. In this paper, we extend the latter method applying the CIR scheme with scaled numerical diffusion in order to balance those terms with the Maxwell flux vectors. For the fluids, we generalize the AUSM+-up to multiple fluids of different species within the plasma. The fully implicit second-order method is first verified on the Hartmann flow (including comparison with its analytical solution), two ideal MHD cases with strong shocks, namely, Orszag-Tang and the MHD rotor, then validated on a much more challenging case, representing a two-fluid magnetic reconnection under solar chromospheric conditions. For the latter case, a comparison with pioneering results available in literature is provided.
Ohkawa, Tihiro; Baker, Charles C.
1981-01-01
In a plasma device having a toroidal plasma containment vessel, a toroidal field-generating coil system includes fixed linking coils each formed of first and second sections with the first section passing through a central opening through the containment vessel and the second section completing the linking coil to link the containment vessel. A plurality of removable unlinked coils are each formed of first and second C-shaped sections joined to each other at their open ends with their bights spaced apart. The second C-shaped section of each movable coil is removably mounted adjacent the second section of a linking coil, with the containment vessel disposed between the open ends of the first and second C-shaped sections. Electric current is passed through the linking and removable coils in opposite sense in the respective adjacent second sections to produce a net toroidal field.
Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence
NASA Astrophysics Data System (ADS)
Schmid, B.; Manz, P.; Ramisch, M.; Stroth, U.
2017-02-01
The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.
Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence.
Schmid, B; Manz, P; Ramisch, M; Stroth, U
2017-02-03
The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.
Wakefields generated by collisional neutrinos in neutral-electron-positron-ion plasma
Tinakiche, Nouara
2015-12-15
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron-ion plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in presence of a fraction of ions in a neutral-electron-positron plasma. The results obtained in the present work are interpreted and compared with previous studies.
NASA Astrophysics Data System (ADS)
Sabbagh, S. A.; Berkery, J. W.; Park, Y. S.; Bell, R. E.; Gates, D. A.; Gerhardt, S. P.; Goumiri, I.; Evans, T. E.; Ferraro, N.; Jeon, Y. M.; Ko, W.; Shaing, K. C.; Sun, Y.
2014-10-01
Three-dimensional magnetic fields producing non-resonant magnetic braking allow control of the plasma rotation profile, ωφ, in tokamaks. Experimental angular momentum alteration created by 3D field configurations with dominant n = 2 and n = 3 components in NSTX is compared to theoretical neoclassical toroidal viscosity (NTV) torque density profiles, TNTV. Large radial variations of TNTV are typically found when flux surface displacements are computed using ideal MHD assumptions. In contrast, experimentally measured TNTV does not show strong torque localization. This may be explained by ion banana width orbit-averaging effects. A favorable characteristic for ωφ control clearly illustrated by KSTAR experiments is the lack of hysteresis of ωφ when altered by non-resonant NTV. Results from a model-based rotation controller designed using NBI and NTV from the applied 3D field as actuators are shown. The dependence of TNTV on δB2 significantly constrains the allowable field amplification in plasma response models when compared to experiment. Initial analysis shows that the single fluid model in the M3D-C1 resistive MHD code produces a flux surface-averaged δB consistent with the experimentally measured TNTV. Supported by US DOE Contracts DE-FG02-99ER54524 and DE-AC02-09CH11466.
Transport equations in tokamak plasmas
Callen, J. D.; Hegna, C. C.; Cole, A. J.
2010-05-15
Tokamak plasma transport equations are usually obtained by flux surface averaging the collisional Braginskii equations. However, tokamak plasmas are not in collisional regimes. Also, ad hoc terms are added for neoclassical effects on the parallel Ohm's law, fluctuation-induced transport, heating, current-drive and flow sources and sinks, small magnetic field nonaxisymmetries, magnetic field transients, etc. A set of self-consistent second order in gyroradius fluid-moment-based transport equations for nearly axisymmetric tokamak plasmas has been developed using a kinetic-based approach. The derivation uses neoclassical-based parallel viscous force closures, and includes all the effects noted above. Plasma processes on successive time scales and constraints they impose are considered sequentially: compressional Alfven waves (Grad-Shafranov equilibrium, ion radial force balance), sound waves (pressure constant along field lines, incompressible flows within a flux surface), and collisions (electrons, parallel Ohm's law; ions, damping of poloidal flow). Radial particle fluxes are driven by the many second order in gyroradius toroidal angular torques on a plasma species: seven ambipolar collision-based ones (classical, neoclassical, etc.) and eight nonambipolar ones (fluctuation-induced, polarization flows from toroidal rotation transients, etc.). The plasma toroidal rotation equation results from setting to zero the net radial current induced by the nonambipolar fluxes. The radial particle flux consists of the collision-based intrinsically ambipolar fluxes plus the nonambipolar fluxes evaluated at the ambipolarity-enforcing toroidal plasma rotation (radial electric field). The energy transport equations do not involve an ambipolar constraint and hence are more directly obtained. The 'mean field' effects of microturbulence on the parallel Ohm's law, poloidal ion flow, particle fluxes, and toroidal momentum and energy transport are all included self-consistently. The
Superfluid-like Motion of a Small Absorbing Body in a Collisional Plasma
Khrapak, S. A.; Chaudhuri, M.; Morfill, G. E.; Vladimirov, S. V.
2008-09-07
It is shown that the total frictional (drag) force acting on a slowly moving absorbing grain in a stationary weakly ionized high pressure plasma can be directed along its motion, causing the grain acceleration. At some velocity the forces associated with different plasma components balance each other, allowing free undamped superfluid motion of the grain.
Ion-acoustic instability of a two-temperature, collisional, fully-ionized plasma.
NASA Technical Reports Server (NTRS)
Rognlien, T. D.; Self, S. A.
1971-01-01
From a perturbation analysis of the fluid equations for a homogeneous unmagnetized plasma, it is shown that long wavelength ion waves are unstable when the electron temperature exceeds the ion temperature. Thus, the temperature difference can drive a resistive-type ion wave instability in a plasma which on a collisionless basis is stable. The additional destabilizing effect of a current is also investigated.
Modeling the Compression of Merged Compact Toroids by Multiple Plasma Jets
NASA Technical Reports Server (NTRS)
Thio, Y. C. Francis; Knapp, Charles E.; Kirkpatrick, Ron; Rodgers, Stephen L. (Technical Monitor)
2000-01-01
A fusion propulsion scheme has been proposed that makes use of the merging of a spherical distribution of plasma jets to dynamically form a gaseous liner. The gaseous liner is used to implode a magnetized target to produce the fusion reaction in a standoff manner. In this paper, the merging of the plasma jets to form the gaseous liner is investigated numerically. The Los Alamos SPHINX code, based on the smoothed particle hydrodynamics method is used to model the interaction of the jets. 2-D and 3-D simulations have been performed to study the characteristics of the resulting flow when these jets collide. The results show that the jets merge to form a plasma liner that converge radially which may be used to compress the central plasma to fusion conditions. Details of the computational model and the SPH numerical methods will be presented together with the numerical results.
Song, Mi-Young; Yoon, Jung-Sik; Jung, Young-Dae
2015-03-15
The electron-neutral collision effects on the Compton scattering process are investigated in warm collisional plasmas. The Compton scattering cross section in warm collisional plasmas is obtained by the Salpeter structure factor with the fluctuation-dissipation theorem and the plasma dielectric function as a function of the electron-neutral collision frequency, Debye length, and wave number. It is shown that the influence of electron-neutral collision strongly suppresses the Compton scattering cross section in warm collisional plasmas. It is also found that the electron-neutral collision effect on the differential Compton scattering cross section is more significant in forward scattering directions. We show that the differential Compton scattering cross section has a maximum at the scattering angle φ=π/2. In addition, we find that the electron-neutral collision effect on the total Compton scattering cross section increases with increasing Debye length and wave number. The variation of the Compton scattering cross section due to the change of collision frequency and plasma parameters is also discussed.
Moser, Auna L.; Hsu, Scott C.
2015-05-01
We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.
Collisional-Radiative Modeling of Free-Burning Arc Plasma in Argon
2013-06-01
chemistry used in non-equilibrium modelling of free-burning arc in argon. A simple chemistry model based on the approximation of prompt ionization, a...highlight of the model was the unified description of the whole plasma domain avoiding the division into sub-domains in which different models were used ...description. Therefore, the present work is aimed at the analysis of the plasma chemistry in a way that the model enables a deeper look into the polulations
NASA Astrophysics Data System (ADS)
Albert, Christopher G.; Heyn, Martin F.; Kapper, Gernot; Kasilov, Sergei V.; Kernbichler, Winfried; Martitsch, Andreas F.
2016-08-01
Toroidal torque generated by neoclassical viscosity caused by external non-resonant, non-axisymmetric perturbations has a significant influence on toroidal plasma rotation in tokamaks. In this article, a derivation for the expressions of toroidal torque and radial transport in resonant regimes is provided within quasilinear theory in canonical action-angle variables. The proposed approach treats all low-collisional quasilinear resonant neoclassical toroidal viscosity regimes including superbanana-plateau and drift-orbit resonances in a unified way and allows for magnetic drift in all regimes. It is valid for perturbations on toroidally symmetric flux surfaces of the unperturbed equilibrium without specific assumptions on geometry or aspect ratio. The resulting expressions are shown to match the existing analytical results in the large aspect ratio limit. Numerical results from the newly developed code NEO-RT are compared to calculations by the quasilinear version of the code NEO-2 at low collisionalities. The importance of the magnetic shear term in the magnetic drift frequency and a significant effect of the magnetic drift on drift-orbit resonances are demonstrated.
Shinozaki, Keisuke; Hoshino, Akio; Ishisaki, Yoshitaka; Morita, Umeyo; Ohashi, Takaya; Mihara, Tatehiro; Mitsuda, Kazuhisa; Tanaka, Keiichi; Yagi, Yasuyuki; Koguchi, Haruhisa; Hirano, Yoichi; Sakakita, Hajime
2006-04-15
A superconductive transition edge sensor (TES) calorimeter is for the first time applied for the diagnostics of the reversed field pinch plasma produced in the toroidal pinch experiment RX (TPE-RX), and the instrumental system is fully described. The first result from the soft x-ray spectroscopy in 0.2-3 keV with an energy resolution {approx}50 eV are also presented. The TES calorimeter is made of a thin bilayer film of titanium and gold with a transition temperature of 151 mK and its best energy resolution at our laboratory is 6.4 eV, while it was significantly degraded by about a factor of eight during the plasma operation. The TES microcalorimeter was installed in a portable adiabatic demagnetization refrigerator (ADR), which is originally designed for a rocket experiment. The detector box is carefully designed to shield the strong magnetic field produced by the ADR and TPE-RX. The ADR was directly connected to TPE-RX with a vacuum duct in the sideway configuration, and cooled down to 125 mK stabilized with an accuracy of 10 {mu}K rms using an improved proportional, integral, and derivative (PID) control method. Thin aluminized Toray Lumirror or Parylene-N films were used for the IR to UV blocking filters of the incident x-ray window to allow soft x-rays coming into the detector with good efficiency. TPE-RX was operated with the plasma current of I{sub p}=220 kA, and the wave forms of the TES output for every plasma shot lasting {approx}80 ms were obtained with a digital oscilloscope. The wave forms were analyzed with the optimal filtering method, and x-ray signals were extracted. A total of 3472 counts of x-ray signals were detected for 210 plasma shots during the flat-top phase of t=35-70 ms. Combined with the data measured with a lithium drifted silicon detector in the 1.3-8 keV range, spectral features are investigated using a spectral fitting package XSPEC. The obtained spectrum is well explained by thermal plasma emission, although an impurity iron-L line
NASA Astrophysics Data System (ADS)
Shinozaki, Keisuke; Hoshino, Akio; Ishisaki, Yoshitaka; Morita, Umeyo; Ohashi, Takaya; Mihara, Tatehiro; Mitsuda, Kazuhisa; Tanaka, Keiichi; Yagi, Yasuyuki; Koguchi, Haruhisa; Hirano, Yoichi; Sakakita, Hajime
2006-04-01
A superconductive transition edge sensor (TES) calorimeter is for the first time applied for the diagnostics of the reversed field pinch plasma produced in the toroidal pinch experiment RX (TPE-RX), and the instrumental system is fully described. The first result from the soft x-ray spectroscopy in 0.2-3keV with an energy resolution ˜50eV are also presented. The TES calorimeter is made of a thin bilayer film of titanium and gold with a transition temperature of 151mK and its best energy resolution at our laboratory is 6.4eV, while it was significantly degraded by about a factor of eight during the plasma operation. The TES microcalorimeter was installed in a portable adiabatic demagnetization refrigerator (ADR), which is originally designed for a rocket experiment. The detector box is carefully designed to shield the strong magnetic field produced by the ADR and TPE-RX. The ADR was directly connected to TPE-RX with a vacuum duct in the sideway configuration, and cooled down to 125mK stabilized with an accuracy of 10μK rms using an improved proportional, integral, and derivative (PID) control method. Thin aluminized Toray Lumirror or Parylene-N films were used for the IR to UV blocking filters of the incident x-ray window to allow soft x-rays coming into the detector with good efficiency. TPE-RX was operated with the plasma current of Ip=220kA, and the wave forms of the TES output for every plasma shot lasting ˜80ms were obtained with a digital oscilloscope. The wave forms were analyzed with the optimal filtering method, and x-ray signals were extracted. A total of 3472 counts of x-ray signals were detected for 210 plasma shots during the flat-top phase of t =35-70ms. Combined with the data measured with a lithium drifted silicon detector in the 1.3-8keV range, spectral features are investigated using a spectral fitting package XSPEC. The obtained spectrum is well explained by thermal plasma emission, although an impurity iron-L line emissions at variously
Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas.
Stevenson, B A; Knowlton, S F; Hartwell, G J; Hanson, J D; Maurer, D A
2014-09-01
A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.
Transport analysis in toroidal helical plasmas using the integrated code: TASK3D
NASA Astrophysics Data System (ADS)
Wakasa, A.; Fukuyama, A.; Murakami, S.; Beidler, C. D.; Maassberg, H.; Yokoyama, M.; Sato, M.
2009-11-01
The integrated simulation code in helical plasmas, TASK3D, is being developed on the basis of an integrated modeling code for tokamak plasma, TASK. In helical systems, the neoclassical transport is one of the important issues in addition to the anomalous transport, because of strong temperature dependence of heat conductivity and an important role in determining the radial electric field. We have already constructed the neoclassical transport database in LHD, DGN/LHD. The mono-energetic diffusion coefficients are evaluated based on the Monte Carlo method by DCOM code and the mono-energetic diffusion coefficients database is constructed using a neural network technique. Also we apply GSRAKE code, which solves the ripple-averaged drift kinetic equation, to obtain transport coefficients in highly collisionless regime. We have newly incorporated the DGN/LHD module into TASK3D. We will present several results of transport simulation in typical LHD plasmas.
Hall probe measurements of the poloidal magnetic field in Compact Toroidal Hybrid plasmas
Stevenson, B. A.; Knowlton, S. F.; Hartwell, G. J. Hanson, J. D.; Maurer, D. A.
2014-09-15
A linear array of 16 Hall effect sensors has been developed to directly measure the poloidal magnetic field inside the boundary of a non-axisymmetric hybrid torsatron/tokamak plasma. The array consists of miniature gallium arsenide Hall sensor elements mounted 8 mm apart on a narrow, rotatable printed circuit board inserted into a re-entrant stainless steel tube sheathed in boron nitride. The sensors are calibrated on the bench and in situ to provide accurate local measurements of the magnetic field to aid in reconstructing the equilibrium plasma current density profiles in fully three-dimensional plasmas. Calibrations show that the sensor sensitivities agree with the nominal manufacturers specifications of 1.46 V/T. Poloidal fields measured with the Hall sensor array are found to be within 5% of poloidal fields modeled with a Biot-Savart code.
On RF heating of inhomogeneous collisional plasma under ion-cyclotron resonance conditions
Timofeev, A. V.
2015-11-15
During ion-cyclotron resonance (ICR) heating of plasma by the magnetic beach method, as well as in some other versions of ICR heating, it is necessary to excite Alfvén oscillations. In this case, it is difficult to avoid the phenomenon of the Alfvén resonance, in which Alfvén oscillations transform into lower hybrid oscillations. The latter efficiently interact with electrons, due to which most of the deposited RF energy is spent on electron (rather than ion) heating. The Alfvén resonance takes place due to plasma inhomogeneity across the external magnetic field. Therefore, it could be expected that variations in the plasma density profile would substantially affect the efficiency of the interaction of RF fields with charged particles. However, the results obtained for different plasma density profiles proved to be nearly the same. In the present work, a plasma is considered the parameters of which correspond to those planned in future ICR plasma heating experiments on the PS-1 facility at the Kurchatov Institute. When analyzing the interaction of RF fields with charged particles, both the collisionless resonance interaction and the interaction caused by Coulomb collisions are taken into account, because, in those experiments, the Coulomb collision frequency will be comparable with the frequency of the heating field. Antennas used for ICR heating excite RF oscillations with a wide spectrum of wavenumbers along the magnetic field. After averaging over the spectrum, the absorbed RF energy calculated with allowance for collisions turns out to be close to that absorbed in collisionless plasma, the energy fraction absorbed by electrons being substantially larger than that absorbed by ions.
On RF heating of inhomogeneous collisional plasma under ion-cyclotron resonance conditions
NASA Astrophysics Data System (ADS)
Timofeev, A. V.
2015-11-01
During ion-cyclotron resonance (ICR) heating of plasma by the magnetic beach method, as well as in some other versions of ICR heating, it is necessary to excite Alfvén oscillations. In this case, it is difficult to avoid the phenomenon of the Alfvén resonance, in which Alfvén oscillations transform into lower hybrid oscillations. The latter efficiently interact with electrons, due to which most of the deposited RF energy is spent on electron (rather than ion) heating. The Alfvén resonance takes place due to plasma inhomogeneity across the external magnetic field. Therefore, it could be expected that variations in the plasma density profile would substantially affect the efficiency of the interaction of RF fields with charged particles. However, the results obtained for different plasma density profiles proved to be nearly the same. In the present work, a plasma is considered the parameters of which correspond to those planned in future ICR plasma heating experiments on the PS-1 facility at the Kurchatov Institute. When analyzing the interaction of RF fields with charged particles, both the collisionless resonance interaction and the interaction caused by Coulomb collisions are taken into account, because, in those experiments, the Coulomb collision frequency will be comparable with the frequency of the heating field. Antennas used for ICR heating excite RF oscillations with a wide spectrum of wavenumbers along the magnetic field. After averaging over the spectrum, the absorbed RF energy calculated with allowance for collisions turns out to be close to that absorbed in collisionless plasma, the energy fraction absorbed by electrons being substantially larger than that absorbed by ions.
May, M J; Schneider, M B; Hansen, S B; Chung, H; Hinkel, D E; Baldis, H A; Constantin, C
2008-02-20
M-Band and L-Band Gold spectra between 3 to 5 keV and 8 to 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the plasma in the laser deposition region of a 'hot hohlraum'. This is a reduced-scale hohlraum heated with {approx} 9 kJ of 351 nm light in a 1 ns square pulse at the Omega laser. The space- and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s {yields} 2p, 3d{sub 5/2} {yields} 2p{sub 3/2} and 3d{sub 3/2} {yields} 2p{sub 1/2} transitions at {approx}9 keV, {approx}10 keV and {approx}13 keV, respectively. M-Band 5f {yields} 3d, 4d {yields} 3p, and 4p {yields} 3s transition features from Fe-like to P-like gold were also recorded between 3 to 5 keV. Modeling from the radiation-hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be {approx} 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.
May, M J; Schneider, M B; Hansen, S B; Chung, H; Hinkel, D E; Baldis, H A; Constantin, C
2008-07-02
M-Band and L-Band Gold spectra between 3 to 5 keV and 8 to 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the plasma in the laser deposition region of a 'hot hohlraum'. This is a reduced-scale hohlraum heated with {approx} 9 kJ of 351 nm light in a 1 ns square pulse at the OMEGA laser. The space- and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s {yields} 2p, 3d{sub 5/2} {yields} 2p{sub 3/2} and 3d{sub 3/2} {yields} 2p{sub 1/2} transitions at {approx}9 keV, {approx}10 keV and {approx}13 keV, respectively. M-Band 5f {yields} 3d, 4d {yields} 3p, and 4p {yields} 3s transition features from Fe-like to P-like gold were also recorded between 3 to 5 keV. Modeling from the radiation-hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be between 6.0 and 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.
NASA Astrophysics Data System (ADS)
Hematizadeh, Ayoob; Bakhtiari, Farhad; Jazayeri, Seyed Masud; Ghafary, Bijan
2016-05-01
A scheme of terahertz (THz) radiation generation is proposed by beating of two spatial-triangular laser beams in plasma with a spatially periodic density when electron-neutral collisions have taken into account. In this process, the laser beams exert a ponderomotive force on the electrons of the plasma and impart the oscillatory velocity at the difference frequency in the presence of a static magnetic field which is applied parallel to the direction of the lasers. We show that higher efficiency and stronger THz radiation are achieved when the parallel magnetic field is used to compare the perpendicular magnetic field. The effects of beam width of lasers, collision frequency, periodicity of density ripples, and magnetic field strength are analyzed for strong THz radiation generation. The THz field of the emitted radiations is found to be highly sensitive to collision frequency and magnetic field strength. In this scheme with the optimization of plasma parameters, the efficiency of order 21% is achieved.
Lakhin, V. P.; Sorokina, E. A. E-mail: vilkiae@gmail.com; Ilgisonis, V. I.; Konovaltseva, L. V.
2015-12-15
A set of reduced linear equations for the description of low-frequency perturbations in toroidally rotating plasma in axisymmetric tokamak is derived in the framework of ideal magnetohydrodynamics. The model suitable for the study of global geodesic acoustic modes (GGAMs) is designed. An example of the use of the developed model for derivation of the integral conditions for GGAM existence and of the corresponding dispersion relation is presented. The paper is dedicated to the memory of academician V.D. Shafranov.
Advanced Multifluid and Collisional-Radiative Models for Laser-Plasma Interaction (Briefing Charts)
2014-12-01
1-d propagation: Maxwell tensor Poynting vector 17Distribution A – Approved for public release; Distribution Unlimited. PA# XXXXX Laser-Plasma...Shape Preservation Inhibits Thermalization Mass/Momentum/Energy Conserving Merge for Both Energy Conserved ‐But‐ Entropy Unequal 21Distribution A
Tokamak with mechanical compression of toroidal magnetic field
Ohkawa, Tihiro
1981-01-01
A tokamak apparatus includes a pressure vessel for defining a reservoir and confining liquid therein. A collapsible toroidal liner disposed within the pressure vessel defines a toroidal space within the liner. Liquid metal fills the reservoir outside said liner. A toroidal magnetic field is developed within the toroidal space about the major axis thereof. A toroidal plasma is developed within the toroidal space about the major axis thereof. Pressure is applied to the liquid metal to collapse the liner and reduce the volume of the toroidal space, thereby increasing the toroidal magnetic flux density therein.
Optimization of confinement in a toroidal plasma subject to strong radial electric fields
NASA Technical Reports Server (NTRS)
Roth, J. R.
1977-01-01
A preliminary report on the identification and optimization of independent variables which affect the ion density and confinement time in a bumpy torus plasma is presented. The independent variables include the polarity, position, and number of the midplane electrode rings, the method of gas injection, and the polarity and strength of a weak vertical magnetic field. Some characteristic data taken under condition when most of the independent variables were optimized are presented. The highest value of the electron number density on the plasma axis is 3.2 x 10 to the 12th power/cc, the highest ion heating efficiency is 47 percent, and the longest particle containment time is 2.0 milliseconds.
Measurement of the current sheet during magnetic reconnection in a toroidal plasma.
Crocker, N A; Fiksel, G; Prager, S C; Sarff, J S
2003-01-24
The current and magnetic-field fluctuations associated with magnetic-field-line reconnection have been measured in the reversed field pinch plasma configuration. The current sheet resulting from this reconnection has been measured. The current layer is radially broad, comparable to a magnetic-island width, as may be expected from current transport along magnetic-field lines. It is much larger than that predicted by resistive MHD for linear tearing modes and larger than prediction from two-fluid linear theory.
Extended MHD Studies of Flow-Driven and Reconnecting Instabilities in Toroidal Plasmas
Ebrahimi, Fatima
2014-04-30
For steady-state reactor scenarios, inductive ohmic current drive alone is not sufficient. If helicity (a topological property which quantifies the knottedness of the magnetic field lines) is created and injected into a plasma configuration, the additional linkage of the magnetic fluxes can sustain the configuration indefinitely against resistive decay. Injection of magnetic helicity into the plasma is closely related to current drive. Various techniques such as DC and AC helicity injection can be used for steady-state current drive, which both rely on relaxation process for core current penetration. However, helicity injection has also been used for edge current drive and non-inductive startup current drive. A solenoid-free plasma startup method called coaxial helicity injection (CHI) has been investigated in the NSTX, and has shown to generate a closedflux equilibrium and produce a CHI-driven current well-coupled to the induction. We propose to perform nonlinear CHI simulations in NSTX, which will provide further insight into the viability of CHI as a startup current drive technique and its role in ultimate steady-state operation of fusion reactors. The goals of our proposed simulations are to understand the physics of current relaxation by CHI in relation to transport and mode dynamics, and to perform long term simulations when CHI is coupled to the induction.
Spontaneous healing and growth of locked magnetic island chains in toroidal plasmas
Fitzpatrick, R.; Waelbroeck, F. L.
2012-11-15
Recent experiments have demonstrated that locked magnetic island chains in stellarator plasmas spontaneously heal under certain conditions, and spontaneously grow under others. A formalism initially developed to study magnetic island dynamics in tokamak plasmas is employed to investigate this phenomenon. It is found that island healing/growth transitions can be caused either by a breakdown in torque balance in the vicinity of the island chain, or by an imbalance between the various terms in the island width evolution equation. The scaling of the healing/growth thresholds with the standard dimensionless plasma parameters {beta}, {nu}{sub *}, and {rho}{sub *} is determined. In accordance with the experimental data, it is found that island healing generally occurs at high {beta} and low {nu}{sub *}, and island growth at low {beta} and high {nu}{sub *}. In further agreement, it is found that island healing is accompanied an ion poloidal velocity shift in the electron diamagnetic direction, and island growth by a velocity shift in the ion diamagnetic direction. Finally, it is found that there is considerable hysteresis in the healing/growth cycle, as is also seen experimentally.
NASA Astrophysics Data System (ADS)
Jiang, Bing-feng; Hou, De-fu; Li, Jia-rong
2016-10-01
We derive the electric permittivity ɛ and magnetic permeability μM of the quark-gluon plasma (QGP) with the kinetic theory associated with a Bhatnagar-Gross-Krook (BGK) collisional kernel. Based on them, we study the effect of collisions on the refractive index of QGP. Compared to the collisionless case, collisions change the ω -behavior of ɛ and μM dramatically, which is responsible for the fact that the real and imaginary parts of n2 and the Depine-Lakhtakia index nDL are smooth functions of ω . For a small collision rate ν , the Depine-Lakhtakia index nDL is negative in some frequency range. When the collision rate increases, the frequency range for nDL<0 becomes narrower. Numerical results show a critical collision rate ν ˜0.2 mD, above which the Depine-Lakhtakia index nDL is positive for all frequency regions, which indicates a normal refractive index. In contrast to the collisionless case, there exists some frequency range in which nDL<0 and the propagating mode may satisfy the dispersion relation n2ω2=k2 simultaneously, which implies the existence of a negative refractive index.
The collisional drift mode in a partially ionized plasma. [in the F region
NASA Technical Reports Server (NTRS)
Hudson, M. K.; Kennel, C. F.
1974-01-01
The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.
Terahertz generation by mixing of two super-Gaussian laser beams in collisional plasma
Singh, Divya; Malik, Hitendra K. E-mail: hkmalik@physics.iitd.ac.in
2014-08-15
Considering a realistic situation, where electron-neutral collisions persist in plasma, analytical calculations are carried out for the Terahertz (THz) radiation generation by beating of two Super-Gaussian (SG) lasers of index p. The competency of these lasers over Gaussian lasers is discussed in detail with respect to the effects of collision and beam width on the THz field amplitude and efficiency of the mechanism. A critical transverse distance of the peak of the THz field is defined that shows a dependence on the index of SG lasers. Although electron-neutral collisions and larger beam width lead to the drastic reduction in the THz field when the SG lasers are used in the plasma, the efficiency of the mechanism remains much larger than the case of Gaussian lasers. Moreover, the higher index SG lasers produce stronger and focused THz radiation.
Khorashadizadeh, S. M. Rastbood, E.; Niknam, A. R.
2015-07-15
The evolution of filamentation instability in a weakly ionized current-carrying plasma with nonextensive distribution was studied in the diffusion frequency region, taking into account the effects of electron-neutral collisions. Using the kinetic theory, Lorentz transformation formulas, and Bhatnagar-Gross-Krook collision model, the generalized dielectric permittivity functions of this plasma system were achieved. By obtaining the dispersion relation of low-frequency waves, the possibility of filamentation instability and its growth rate were investigated. It was shown that collisions can increase the maximum growth rate of instability. The analysis of temporal evolution of filamentation instability revealed that the growth rate of instability increased by increasing the q-parameter and electron drift velocity. Finally, the results of Maxwellian and q-nonextensive velocity distributions were compared and discussed.
Filamentation instability of current-driven dust ion-acoustic waves in a collisional dusty plasma
Niknam, A. R.; Haghtalab, T.; Khorashadizadeh, S. M.
2011-11-15
A theoretical investigation has been made of the dust ion-acoustic filamentation instability in an unmagnetized current-driven dusty plasma by using the Lorentz transformation formulas. The effect of collision between the charged particles with neutrals and their thermal motion on this instability is considered. Developing the filamentation instability of the current-driven dust ion-acoustic wave allows us to determine the period and the establishment time of the filamentation structure and threshold for instability development.
Nonlinear penetration of whistler pulses into collisional plasmas via conductivity modifications
NASA Technical Reports Server (NTRS)
Urrutia, J. M.; Stenzel, R. L.
1991-01-01
A strong electromagnetic impulse (about 0.2 microsec) with central frequency in the whistler-wave regime is applied to a large laboratory plasma dominated by Coulomb collisions. Local electron heating at the antenna and transport along B0 create a channel of high conductivity along which the whistler pulse penetrates with little damping. Because of its rapid temporal evolution, this new form of modulational instability does not involve ducting by density gradients which require ion time scales to develop.
Formation of high-{beta} plasma and stable confinement of toroidal electron plasma in Ring Trap 1
Saitoh, H.; Yoshida, Z.; Morikawa, J.; Furukawa, M.; Yano, Y.; Kawai, Y.; Kobayashi, M.; Vogel, G.; Mikami, H.
2011-05-15
Formation of high-{beta} electron cyclotron resonance heating plasma and stable confinement of pure electron plasma have been realized in the Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet. The effects of coil levitation resulted in drastic improvements of the confinement properties, and the maximum local {beta} value has exceeded 70%. Hot electrons are major component of electron populations, and its particle confinement time is 0.5 s. Plasma has a peaked density profile in strong field region [H. Saitoh et al., 23rd IAEA Fusion Energy Conference EXC/9-4Rb (2010)]. In pure electron plasma experiment, inward particle diffusion is realized, and electrons are stably trapped for more than 300 s. When the plasma is in turbulent state during beam injection, plasma flow has a shear, which activates the diocotron (Kelvin-Helmholtz) instability. The canonical angular momentum of the particle is not conserved in this phase, realizing the radial diffusion of charged particles across closed magnetic surfaces. [Z. Yoshida et al., Phys Rev. Lett. 104, 235004 (2010); H. Saitoh et al., Phys. Plasmas 17, 112111 (2010).].
NASA Astrophysics Data System (ADS)
Chung, Sang-Young; Kwon, Deuk-Chul; Song, Mi-Young; Yoon, Jung-Sik
2014-10-01
For reliable plasma simulation an accurate full-set data of collision cross sections between each species participated in the plasma is required. However, the full-set of the reaction data is hard to achieve and estimated data have been used for the missing. To achieve reliable reaction data researchers have tuned the estimated reaction data so that the simulation results with the data agree with experimental results. However, as the number of data to be tuned is increased it becomes very hard work for researchers. In this study, we developed a code to optimize the data numerically based on the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm and adopted with a 0-dimensional global simulator for semiconductor processing plasma. BFGS algorithm is a type of a quasi-Newton method. The second derivatives are used for a next estimation like Newton method but are calculated by iterations from first derivatives and previous second derivatives. So the function is called (i.e. the simulator is executed) much smaller times than Newton method. Parallel algorithm was applied to the code to save time. In the serial code the calculation time for each iteration were proportional to the number of unknown variables but it became independent of the number of the variables in the parallel code.
Stimulated Scattering of Light from Ion Acoustic Waves in Collisional Multi-species Plasma.
NASA Astrophysics Data System (ADS)
Berger, Richard; Valeo, Ernest
2003-10-01
The dispersion properties of ion acoustic waves (IAW) are sensitive to the strength of ion-ion collisions,especially in multi-species plasma in which the different species have differing charge-to-mass ratios(Bychenkov et al., PRE 51, 1400 (1995)). Here, we consider the modification of the frequency and damping of the fast and slow acoustic modes in a plasma composed of light (low Z) and heavy (high Z) ions. In the fluid limit, kλ_lh <<1, the friction between the two species causes the damping whereas, in the collisionless limit, Landau damping of the light ions provides the dissipation. Collisions between light and heavy ions also affect the nonlinear response(P. W. Rambo, S. C. Wilks, and W. L. Kruer, Phys. Rev. Lett. 79), 83 (1997).. We examine the effects of collisions on the linear evolution of ion waves driven by the ponderomotive force of two light waves within the context of linear parametric instability theory. The simulation of the nonlinear evolution is done with a δ f model that evolves the background(E. J. Valeo and S. Brunner, Bull. Am. Phys. Soc. 46), QP1.137 (2001)., and includes the effects of collisions of light on heavy ions within the Lorentz model. The calculated effect of a small number of high Z ions on SBS in low Z plasmas will be compared with recent experimental results(Suter et al.,private communication). l
NASA Astrophysics Data System (ADS)
Schlossberg, D. J.; Bodner, G. M.; Bongard, M. W.; Fonck, R. J.; Winz, G. R.
2014-10-01
A multipoint Thomson scattering diagnostic has recently been installed on the Pegasus ST. The system utilizes a frequency-doubled Nd:YAG laser (λ0 ~ 532 nm), spectrometers with volume phase holographic gratings, and a gated, intensified CCD camera. It provides measurements of Te and ne at 8 spatial locations for each spectrometer once per discharge. A new multiple aperture and beam dump system has been implemented to mitigate interference from stray light. This system has provided initial measurements in the core region of plasmas initiated by local helicity injection (LHI), as well as conventional Ohmic L- and H-mode discharges. Multi-shot averages of low-density (ne ~ 3 ×1018 m-3) , Ip ~ 0 . 1 MA LHI discharges show central Te ~ 75 eV at the end of the helicity injection phase. Ip ~ 0 . 13 MA Ohmic plasmas at moderate densities (ne ~ 2 ×1019 m-3) have core Te ~ 150 eV in L-mode. Generally, these plasmas do not reach transport equilibrium in the short 25 ms pulse length available. After an L-H transition, strong spectral broadening indicates increasing Te, to values above the range of the present spectrometer system with a high-dispersion VPH grating. Near-term system upgrades will focus on deploying a second spectrometer, with a lower-dispersion grating capable of measuring the 0.1-1.0 keV range. The second spectrometer system will also increase the available number of spatial channels, enabling study of H-mode pedestal structure. Work supported by US DOE Grant DE-FG02-96ER54375.
Quasi-steady multiple flux tubes induced by localized current perturbation in toroidal plasma
NASA Astrophysics Data System (ADS)
Yun, Gunsu
2015-11-01
Quasi-steady helical modes with dual, triple, or more flux tubes are easily produced by localized current drive in the core of sawtoothing plasma on the KSTAR tokamak. Individual flux tubes have m / n = 1 / 1 helicity, co-rotate around the magnetic axis, and later merge into a single m = 1 mode. The merged mode eventually crashes with rapid collapse of the core pressure and the next cycle repeats the same pattern, exhibiting sawtooth-like oscillations in the core pressure. The generation mechanism of multiple flux tubes (MFTs) has been studied in two different approaches to understand the observed trend that the number of flux tubes increases as the current drive location moves away from the magnetic axis up to about the magnetic surface of the safety factor q = 1 at the mode collapse: (1) nonlinear reduced MHD simulation with a localized current source modeling the time-varying interaction between the current source and flux tubes and (2) linear MHD simulation with a prescribed q profile with a radially localized current blip. Both studies show that MFTs can be produced only in plasmas with nearly flat q profile close to unity, suggesting the collapse of the m = 1 mode (i.e., sawtooth crash) is complete. Recent observation of long-lived MFTs induced by localized current drive in non-sawtoothing plasma suggests that q profile evolution toward lower- m instability is required for the merging and crash of MFTs. Work supported by the National Research Foundation of Korea, US D.O.E., and Japan Society for the Promotion of Science.
Alfv'en instabilities and energetic particle physics in toroidal plasmas
NASA Astrophysics Data System (ADS)
Spong, Donald
2012-03-01
Modeling capabilities and experimental diagnostics for energetic particle-driven Alfv'en instabilities have advanced significantly in recent years. Simulation tools now range from rapidly applied reduced-dimensionality models and hybrid fluid particle models to more comprehensive gyrokinetic approaches. Alfv'en mode theory has been applied not only to tokamaks, but also to stellarators and reversed field pinches. Current diagnostic techniques allow direct imaging of the mode structure, fast ion density and loss patterns at the plasma edge, allowing theory/experiment comparisons in greater depth than previously possible. Examples from a variety of tokamak, stellarator and reversed field pinch experiments and the associated theory will be described. These activities are preparing the way for future ignited devices, such as ITER, where energetic alpha particles will provide the dominant plasma heating mechanism. High fidelity models of alpha behavior will be required for predicting their effects on the alpha heating profile, non-diffusive transport, nonlinear feedback loops and localized wall heat loads; in addition, understanding Alfv'en spectral emissions can provide diagnostic opportunities. Projections of the current models to ITER and future physics needs will be discussed.
Simulations of SBS in a Multi-Ion-Species Collisional Plasma.
NASA Astrophysics Data System (ADS)
Valeo, Ernest; Berger, Richard
2002-11-01
Collisions between light and heavy ions can affect both the linear damping of acoustic waves in a multi-ion species plasma(R. Berger, etal.) adjacent poster and the saturated state of driven waves(P. W. Rambo, S. C. Wilks, and W. L. Kruer, Phys. Rev. Lett. 79), 83 (1997).. We examine the effects of collisions on the nonlinear evolution of SBS in two-dimensional simulations, using a δ f model with evolving background(E. J. Valeo and S. Brunner, Bull. Am. Phys. Soc. 46), QP1.137 (2001)., including the effects of collisions of light on heavy ions within the Lorentz model.
Fedila, D. Ali; Djebli, M.
2010-10-15
The effect of collision on small amplitude dust-acoustic waves is investigated for a plasma with positively charged dust grains. Taking into account the presence of different electron populations in thermal equilibrium, a modified Korteweg-de Vries equation is established. The existence conditions and nature of the waves, i.e., rarefactive or compressive, are found to be mainly dependent on the temperature and the density of the cold electrons. The present model is used to understand the salient features of the fully nonlinear dust-acoustic waves in the lower region of the Earth's ionosphere, at an altitude of {approx}85 km with the presence of an external heating source.
Spolaore, M. Vianello, N.; Agostini, M.; Cavazzana, R.; De Masi, G.; Martines, E.; Momo, B.; Scaggion, A.; Scarin, P.; Spagnolo, S.; Spizzo, G.; Zuin, M.; Furno, I.; Avino, F.; Fasoli, A.; Theiler, C.; Carralero, D.; Alonso, J. A.; Hidalgo, C.
2015-01-15
Electromagnetic features of turbulent filaments, emerging from a turbulent plasma background, have been studied in four different magnetic configurations: the stellarator TJ-II, the Reversed Field Pinch RFX-mod, a device that can be operated also as a ohmic tokamak, and the Simple Magnetized Torus, TORPEX. By applying an analogous diagnostic concept in all cases, direct measurements of both field-aligned current density and vorticity were performed inside the filament. The inter-machine comparison reveals a clear dependence of the filament vorticity upon the local time-averaged E × B flow shear. Furthermore, a wide range of local beta was explored allowing concluding that this parameter plays a fundamental role in the appearance of filament electromagnetic features.
Electron Landau damping in toroidal plasma with Solov’ev equilibrium
Grishanov, N. I. Azarenkov, N. A.
2013-12-15
The contribution of untrapped and two groups of trapped particles to the longitudinal (with respect to the magnetic field) elements of the dielectric susceptibility is determined by solving the drift-kinetic equations for such particles in axisymmetric tokamaks with Solov’ev equilibrium. The obtained dielectric characteristics are applicable for studying linear wave processes in the frequency range of Alfvén and fast magnetosonic waves in small- and large-aspect-ratio tokamaks with circular, elliptical, and D-shaped cross sections of magnetic surfaces. The high-frequency power absorbed in plasma via electron Landau damping is estimated by summing up terms containing the imaginary parts of both diagonal and non-diagonal elements of the longitudinal susceptibility. The imaginary part of the longitudinal susceptibility is calculated numerically for spherical tokamaks in a wide range of wave frequencies and magnetic surface radii.
NASA Astrophysics Data System (ADS)
Lin, L.; Ding, W. X.; Brower, D. L.
2016-12-01
Magnetic fluctuation-induced particle transport is explored in the high-temperature, high-beta interior of the Madison symmetric torus (MST) reversed-field pinch by performing a multifield measurement of the correlated product of magnetic and density fluctuations associated with global resistive tearing modes. Local density fluctuations are obtained by inverting the line-integrated interferometry data after resolving the mode helicity through correlation techniques. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of Faraday-effect polarimetry measurements. Reconstructed 2D images of density and current density perturbations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particle transport flux and its spatial distribution are resolved. The convective magnetic fluctuation-induced particle flux profile is measured for both standard and high-performance plasmas in MST with tokamak-like confinement, showing large reduction in the flux during improved confinement.
Hamza, A.M.; Sudan, R.N.
1995-03-01
The equations governing the nonlinear evolution of density fluctuations in a low-pressure weakly ionized plasma driven unstable by the ExB or gradient-drift instability were derived by Sudan and Keskinen for addressing the electrostatic turbulence in the E and F regions of the Earth`s ionosphere. The authors have developed a subgrid model suitable for the numerical simulation of these equations which is closely related to renormalized diffusion caused by small-scale fluctuation spectrum. {open_quotes}Dynamical Renormalization Group{close_quotes} (RNG) methods are employed to obtain the renormalized diffusion. This procedure computes the long-wavelength, long-time behavior of density correlations generated by the evolution equation for the plasma stirred by a Gaussian random force characterized by a correlation function {proportional_to} k{sup m} where k is the wavenumber of the forcing function. The effect of small scales on the large-scale dynamics in the limit k{yields}0 and infinite Reynolds number can be expressed in the form of renormalized coefficients; in this case, renormalized diffusion. If one assumes the power spectra to be given by the Kolmogorov argument of cascading of energy through k space then one can derive a subgrid model based on the results of RNG. 27 refs.
NASA Astrophysics Data System (ADS)
Dimant, Y. S.; Oppenheim, M. M.; Fletcher, A. C.
2016-08-01
In weakly ionized plasmas neutral flows drag plasma across magnetic field lines generating intense electric fields and currents. An example occurs in the Earth's ionosphere near the geomagnetic equator. Similar processes take place in the Solar chromosphere and magnetohydrodynamic generators. This paper argues that not all convective neutral flows generate electric fields and currents and it introduces the corresponding universal criterion for their formation, ∇×(U ×B )≠∂B /∂t , where U is the neutral flow velocity, B is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ ̂ . For many systems, the displacement current, ∂B /∂t , is negligible making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates E-fields and currents plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law.
Generation of Currents in Weakly Ionized Plasmas through a Collisional Dynamo
NASA Astrophysics Data System (ADS)
Dimant, Yakov; Oppenheim, Meers; Fletcher, Alex
2016-10-01
Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. We argue that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for the current formation, ∇ × (U-> × B->) ≠ ∂ B-> / ∂ t , where U-> is the neutral flow velocity, B-> is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ̂ . For many systems, the displacement current, ∂ B-> / ∂ t , is negligible, making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates electrojets plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law. Work supported by NSF/DOE Grant PHY-1500439.
Full orbit simulation of collisional transport of impurity ions in the MAST spherical tokamak
NASA Astrophysics Data System (ADS)
Romanelli, M.; McClements, K. G.; Cross, J.; Knight, P. J.; Thyagaraja, A.; Callaghan, J.
2011-05-01
Transport analysis of MAST discharges indicates that collisions are an important loss mechanism in the core of a tight aspect ratio tokamak. In the strongly varying equilibrium fields of MAST many of the assumptions of drift kinetic and neoclassical theory (e.g. small plasma inverse aspect ratio and low ratio of toroidal Larmor radius to poloidal Larmor radius) are not met by all particle species and it becomes appropriate to use full orbit analysis to evaluate heat and particle fluxes. Collisional transport of impurity ions (C6+ and W20+) has been studied using a full orbit solver, CUEBIT, to integrate the test-particle dynamics. Electromagnetic fields in MAST plasma have been modelled using the cylindrical and toroidal two-fluid codes CUTIE and CENTORI. A detailed study of the scaling of the test-particle diffusivity with collisionality in the equilibrium field reveals deviations from the standard neoclassical theory, in both the Pfirsch-Schlüter and banana regimes, and difficulties in defining a local diffusivity at low collisionalities. The effect of electric and magnetic fluctuations is also briefly addressed. It is found that field fluctuations enhance the non-diffusive nature of transport. The full orbit analysis presented here predicts levels of transport and confinement times for the examined species broadly consistent with the experimental observations.
Instability of a current-carrying finite-beta collisional plasma.
Choueiri, E Y
2001-12-01
The microinstability of a cross-field current-carrying plasma in which the electron collisions are important on the time scale of the oscillations and can be modeled with a Bhatnagar-Gross-Krook operator is studied using linearized kinetic theory under conditions of finite electron beta. The finiteness of beta allows for coupling between electrostatic and electromagnetic modes and necessitates dealing with the entire dispersion tensor. Fundamental features of the resulting instability are identified and contrasted with those found in previous studies of the lower hybrid current-driven instability in which either collisions or finite-beta effects were neglected. As beta increases, collisions play a more important role in destabilization, alter the character and extent of electromagnetic coupling, shift the instability to more perpendicular modes, and lead to a recapturing of some of the fluidlike properties the modes have in the electrostatic limit in contrast with their highly kinetic character in the collisionless limit.
Olson, R. E.
1980-09-24
Research is divided into two general topics: (1) H/sup -/ formation collision processes and (2) the determination of scattering cross sections used to diagnose plasma properties. On topic (1) we investigated the effect on the H/sup +/ electron capture cross section when an alkali atom is optically pumped to its resonance state, the angular scattering in H/sup 0/ + Cs ..-->.. H/sup -/ + Cs/sup +/ collisions, and electron detachment processes in H/sup -/ and alkali and alkaline earth atom collisions. On topic (2) we completed work on the determination of the electron capture cross sections down to 10 eV for C/sup +5/, N/sup +5/, O/sup +6/ + H collisions and developed a model for the calculation of multi-ionization cross sections in energetic, highly charged ion-atom collisions.
NASA Astrophysics Data System (ADS)
Sasaki, Akira; Sunahara, Atsushi; Nishihara, Katsunobu; Nishikawa, Takeshi
2016-10-01
The ionization balance of the bismuth-to-tin plasmas is systematically investigated on the basis of a collisional radiative model, which has been generated using a computer algorithm to analyze the level structure of multiple charged ions to construct the model. The atomic energy levels and rate coefficients corresponding to the model are calculated using the HULLAC code. With this method, we investigate the plasma temperature, which is required to obtain emission in the extreme ultraviolet wavelength range from 13.5 nm to the water window.
Evans, T. E.
2016-03-01
Controlling the boundary layer in fusion-grade, high-performance, plasma discharges is essential for the successful development of toroidal magnetic confinement power generating systems. A promising approach for controlling the boundary plasma is based on the use of small, externally applied, edge resonant magnetic perturbation (RMP) fields (δ$b_⊥^{ext}$ ≈ $10^{-4}$ → $10^{-3}$ T). A long-term focus area in tokamak fusion research has been to find methods, involving the use of non-axisymmetric magnetic perturbations to reduce the intense particle and heat fluxes to the wall. Experimental RMP research has progressed from the early pioneering work on tokamaks with material limiters in the 1970s, to present day research in separatrix-limited tokamaks operated in high-confinement mode, which is primarily aimed at the mitigation of the intermittent fluxes due edge localized modes. At the same time the theoretical research has evolved from analytical models to numerical simulations, including the full 3D complexities of the problem. Following the first demonstration of ELM suppression in the DIII-D tokamak during 2003, there has been a rapid worldwide growth in theoretical, numerical and experimental edge RMP research resulting in the addition of ELM control coils to the ITER baseline design [A. Loarte, et al., Nucl. Fusion 54 (2014) 033007]. This review provides an overview of edge RMP research including a summary of the early theoretical and numerical background along with recent experimental results on improved particle and energy confinement in tokamaks triggered by edge RMP fields. The topics covered make up the basic elements needed for developing a better understanding of 3D magnetic perturbation physics, which is required in order to utilize the full potential of edge RMP fields in fusion relevant high performance, H-mode, plasmas.
NASA Astrophysics Data System (ADS)
Truong, D. D.; Fonck, R. J.; McKee, G. R.; Yan, Z.; Grierson, B. A.
2016-10-01
The UF-CHERS (Ultra Fast CHarge Exchange Recombination Spectroscopy) diagnostic at DIII-D measures local, long-wavelength ion temperature and toroidal velocity fluctuations at turbulence-relevant spatiotemporal scales from emission of the CVI n=8 ->7 transition. During Quiescent H-mode (QH-mode) plasmas, which offer ELM-free improved confinement, UF-CHERS measurements observed coherent, low frequency (fo 10kHz) pedestal oscillations in Ti and vtor at the Edge Harmonic Oscillation (EHO) frequency while several modes between 35-75 kHz are suppressed when the EHO appears. Although broadband ion temperature and density fluctuations were reduced by the EHO, the toroidal rotation showed increased fluctuation amplitude. Investigating ion temperature and toroidal fluctuations associated with the EHO may provide insights into the saturated instability driving the EHO. Supported by DOE Grants DE-FG02-08ER54999, DE-FC02-04ER54698, and NSF GRFP Grant DGE-1256259.
Tokamak with in situ magnetohydrodynamic generation of toroidal magnetic field
Schaffer, Michael J.
1986-01-01
A tokamak apparatus includes an electrically conductive metal pressure vessel for defining a chamber and confining liquid therein. A liner disposed within said chamber defines a toroidal space within the liner and confines gas therein. The metal vessel provides an electrically conductive path linking the toroidal space. Liquid metal is forced outwardly through the chamber outside of the toroidal space to generate electric current in the conductive path and thereby generate a toroidal magnetic field within the toroidal space. Toroidal plasma is developed within the toroidal space about the major axis thereof.
NASA Astrophysics Data System (ADS)
Barton, Justin E.; Boyer, Mark D.; Shi, Wenyu; Schuster, Eugenio; Luce, Tim C.; Ferron, John R.; Walker, Michael L.; Humphreys, David A.; Penaflor, Ben G.; Johnson, Robert D.
2012-12-01
In order for ITER to be capable of operating in advanced tokamak operating regimes, characterized by a high fusion gain, good plasma confinement, magnetohydrodynamic stability and a non-inductively driven plasma current, for extended periods of time, several challenging plasma control problems still need to be solved. Setting up a suitable toroidal current density profile in the tokamak is key for one possible advanced operating scenario characterized by non-inductive sustainment of the plasma current. At the DIII-D tokamak, the goal is to create the desired current profile during the ramp-up and early flat-top phases of the plasma discharge and then actively maintain this target profile for the remainder of the discharge. The evolution in time of the toroidal current profile in tokamaks is related to the evolution of the poloidal magnetic flux profile, which is modelled in normalized cylindrical coordinates using a first-principles, nonlinear, dynamic partial differential equation (PDE) referred to as the magnetic diffusion equation. The magnetic diffusion equation is combined with empirical correlations developed from physical observations and experimental data from DIII-D for the electron temperature, the plasma resistivity and the non-inductive current drive to develop a simplified, control-oriented, nonlinear, dynamic PDE model of the poloidal flux profile evolution valid for low confinement mode discharges. In this work, we synthesize a robust feedback controller to reject disturbances and track a desired reference trajectory of the poloidal magnetic flux gradient profile by employing the control-oriented model of the system. A singular value decomposition of the static gain matrix of the plant model is utilized to identify the most relevant control channels and is combined with the dynamic response of system around a given operating trajectory to design the feedback controller. A general framework for real-time feedforward + feedback control of magnetic and
Transport and Dynamics in Toroidal Fusion Systems
Schnack, Dalton D
2006-05-16
This document reports the successful completion of the OFES Theory Milestone for FY2005, namely, Perform parametric studies to better understand the edge physics regimes of laboratory experiments. Simulate at increased resolution (up to 20 toroidal modes), with density evolution, late into the nonlinear phase and compare results from different types of edge modes. Simulate a single case including a study of heat deposition on nearby material walls. The linear stability properties and nonlinear evolution of Edge Localized Modes (ELMs) in tokamak plasmas are investigated through numerical computation. Data from the DIII-D device at General Atomics (http://fusion.gat.com/diii-d/) is used for the magnetohydrodynamic (MHD) equilibria, but edge parameters are varied to reveal important physical effects. The equilibrium with very low magnetic shear produces an unstable spectrum that is somewhat insensitive to dissipation coefficient values. Here, linear growth rates from the non-ideal NIMROD code (http://nimrodteam.org) agree reasonably well with ideal, i.e. non-dissipative, results from the GATO global linear stability code at low toroidal mode number (n) and with ideal results from the ELITE edge linear stability code at moderate to high toroidal mode number. Linear studies with a more realistic sequence of MHD equilibria (based on DIII-D discharge 86166) produce more significant discrepancies between the ideal and non-ideal calculations. The maximum growth rate for the ideal computations occurs at toroidal mode index n=10, whereas growth rates in the non-ideal computations continue to increase with n unless strong anisotropic thermal conduction is included. Recent modeling advances allow drift effects associated with the Hall electric field and gyroviscosity to be considered. A stabilizing effect can be observed in the preliminary results, but while the distortion in mode structure is readily apparent at n=40, the growth rate is only 13% less than the non-ideal MHD
Kanki, T.; Nagata, M.
2006-07-15
Two-fluid flowing equilibrium configurations of a helicity-driven spherical torus (HD-ST) in the realistic confinement region, including a flux conserver and a coaxial helicity source, are numerically determined by means of the combination of the finite difference and the boundary element methods. It is found from the numerical results that electron fluid near the central conductor is tied to a vacuum toroidal field and ion fluid is not. The magnetic configurations change from the high-q HD-ST (safety factor, q>1) with a paramagnetic toroidal field and low-{beta} (volume average {beta} value, <{beta}>{approx_equal}2%) through the helicity-driven spheromak and reversed-field pinch to the ultra-low-q HD-ST (0toroidal field and high-{beta} (<{beta}>{approx_equal}18%) as the vacuum toroidal field at the inner edge regions decreases and reverses the sign. The two-fluid effects are more significant in this equilibrium transition when the ion diamagnetic drift has the same direction as the ExB one.
Toroidal modeling of penetration of the resonant magnetic perturbation field
Liu Yueqiang; Kirk, A.
2013-04-15
A toroidal, quasi-linear model is proposed to study the penetration dynamics of the resonant magnetic perturbation (RMP) field into the plasma. The model couples the linear, fluid plasma response to a toroidal momentum balance equation, which includes torques induced by both fluid electromagnetic force and by (kinetic) neoclassical toroidal viscous (NTV) force. The numerical results for a test toroidal equilibrium quantify the effects of various physical parameters on the field penetration and on the plasma rotation braking. The neoclassical toroidal viscous torque plays a dominant role in certain region of the plasma, for the RMP penetration problem considered in this work.
Toroidal modeling of penetration of the resonant magnetic perturbation field
NASA Astrophysics Data System (ADS)
Liu, Yueqiang; Kirk, A.; Sun, Y.
2013-04-01
A toroidal, quasi-linear model is proposed to study the penetration dynamics of the resonant magnetic perturbation (RMP) field into the plasma. The model couples the linear, fluid plasma response to a toroidal momentum balance equation, which includes torques induced by both fluid electromagnetic force and by (kinetic) neoclassical toroidal viscous (NTV) force. The numerical results for a test toroidal equilibrium quantify the effects of various physical parameters on the field penetration and on the plasma rotation braking. The neoclassical toroidal viscous torque plays a dominant role in certain region of the plasma, for the RMP penetration problem considered in this work.
Transport Equations In Tokamak Plasmas
NASA Astrophysics Data System (ADS)
Callen, J. D.
2009-11-01
Tokamak plasma transport equations are usually obtained by flux surface averaging the collisional Braginskii equations. However, tokamak plasmas are not in collisional regimes. Also, ad hoc terms are added for: neoclassical effects on the parallel Ohm's law (trapped particle effects on resistivity, bootstrap current); fluctuation-induced transport; heating, current-drive and flow sources and sinks; small B field non-axisymmetries; magnetic field transients etc. A set of self-consistent second order in gyroradius fluid-moment-based transport equations for nearly axisymmetric tokamak plasmas has been developed recently using a kinetic-based framework. The derivation uses neoclassical-based parallel viscous force closures, and includes all the effects noted above. Plasma processes on successive time scales (and constraints they impose) are considered sequentially: compressional Alfv'en waves (Grad-Shafranov equilibrium, ion radial force balance); sound waves (pressure constant along field lines, incompressible flows within a flux surface); and ion collisions (damping of poloidal flow). Radial particle fluxes are driven by the many second order in gyroradius toroidal angular torques on the plasma fluid: 7 ambipolar collision-based ones (classical, neoclassical, etc.) and 8 non-ambipolar ones (fluctuation-induced, polarization flows from toroidal rotation transients etc.). The plasma toroidal rotation equation [1] results from setting to zero the net radial current induced by the non-ambipolar fluxes. The radial particle flux consists of the collision-based intrinsically ambipolar fluxes plus the non-ambipolar fluxes evaluated at the ambipolarity-enforcing toroidal plasma rotation (radial electric field). The energy transport equations do not involve an ambipolar constraint and hence are more directly obtained. The resultant transport equations will be presented and contrasted with the usual ones. [4pt] [1] J.D. Callen, A.J. Cole, C.C. Hegna, ``Toroidal Rotation In
Chen, Yang
2012-03-07
At Colorado University-Boulder the primary task is to extend our gyrokinetic Particle-in-Cell simulation of tokamak micro-turbulence and transport to the area of energetic particle physics. We have implemented a gyrokinetic ion/massless fluid electron hybrid model in the global {delta} f-PIC code GEM, and benchmarked the code with analytic results on the thermal ion radiative damping rate of Toroidal Alfven Eigenmodes (TAE) and with mode frequency and spatial structure from eigenmode analysis. We also performed nonlinear simulations of both a single-n mode (n is the toroidal mode number) and multiple-n modes, and in the case of single-n, benchmarked the code on the saturation amplitude vs. particle collision rate with analytical theory. Most simulations use the f method for both ions species, but we have explored the full-f method for energetic particles in cases where the burst amplitude of the excited instabilities is large as to cause significant re-distribution or loss of the energetic particles. We used the hybrid model to study the stability of high-n TAEs in ITER. Our simulations show that the most unstable modes in ITER lie in the rage of 10 < n < 20. Thermal ion pressure effect and alpha particles non-perturbative effect are important in determining the mode radial location and stability threshold. The thermal ion Landau damping rate and radiative damping rate from the simulations are compared with analytical estimates. The thermal ion Landau damping is the dominant damping mechanism. Plasma elongation has a strong stabilizing effect on the alpha driven TAEs. The central alpha particle pressure threshold for the most unstable n=15 mode is about {beta}{sub {alpha}}(0) = 0.7% for the fully shaped ITER equilibrium. We also carried nonlinear simulations of the most unstable n = 15 mode and found that the saturation amplitude for the nominal ITER discharge is too low to cause large redistribution or loss of alpha particles. To include kinetic electron effects
NASA Astrophysics Data System (ADS)
Lee, H. H.; Seol, J.; Ko, W. H.; Terzolo, L.; Aydemir, A. Y.; In, Y.; Ghim, Y.-c.; Lee, S. G.
2016-08-01
Effects of neoclassical toroidal viscosity (NTV) induced by intrinsic error fields and toroidal field ripple on cocurrent toroidal rotation in H-mode tokamak plasmas are investigated. It is expected that large NTV torque can be localized at the edge region through the 1/ν-regime in the vicinity of E r ˜ 0 in the cocurrent rotating H-mode plasma. Numerical simulation on toroidal rotation demonstrates that the edge localized NTV torque determined by the intrinsic error fields and toroidal field ripples in the level of most tokamaks can damp the toroidal rotation velocity over the whole region while reducing the toroidal rotation pedestal which is clearly observed in Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak. It is found that the NTV torque changes the toroidal rotation gradient in the pedestal region dramatically, but the toroidal rotation profile in the core region responds rigidly without a change in the gradient. On the other hand, it shows that the NTV torque induced by the intrinsic error fields and toroidal field ripple in the level of the KSTAR tokamak, which are expected to be smaller than most tokamaks by at least one order of magnitude, is negligible in determining the toroidal rotation velocity profile. Experimental observation on the toroidal rotation change by the externally applied nonaxisymmetric magnetic fields on KSTAR also suggests that NTV torque arising from nonaxisymmetric magnetic fields can damp the toroidal rotation over the whole region while diminishing the toroidal rotation pedestal.
Ettehadi Abari, Mehdi; Sedaghat, Mahsa; Shokri, Babak
2015-10-15
The propagation characteristics of a Gaussian laser beam in collisional magnetized plasma are investigated by considering the ponderomotive and ohmic heating nonlinearities. Here, by taking into account the effect of the external magnetic field, the second order differential equation of the dimensionless beam width parameter is solved numerically. Furthermore, the nonlinear dielectric permittivity of the mentioned plasma medium in the paraxial approximation and its dependence on the propagation characteristics of the Gaussian laser pulse is obtained, and its variation in terms of the dimensionless plasma length is analyzed at different initial normalized plasma and cyclotron frequencies. The results show that the dimensionless beam width parameter is strongly affected by the initial plasma frequency, magnetic strength, and laser pulse intensity. Furthermore, it is found that there exists a certain intensity value below which the laser pulse tends to self focus, while the beam diverges above of this value. In addition, the results confirm that, by increasing the plasma and cyclotron frequencies (plasma density and magnetic strength), the self-focusing effect can occur intensively.
NASA Astrophysics Data System (ADS)
Fitzgerald, M.; Appel, L. C.; Hole, M. J.
2013-11-01
A new force balance model for the EFIT magnetohydrodynamic equilibrium technique for tokamaks is presented which includes the full toroidal flow and anisotropy changes to the Grad-Shafranov equation. The free functions are poloidal flux functions and all non-linear contributions to the toroidal current density are treated iteratively. The parallel heat flow approximation chosen for the model is that parallel temperature is a flux function and that both parallel and perpendicular pressures may be described using parallel and perpendicular temperatures. This choice for the fluid thermodynamics has been shown elsewhere to be the same as a guiding-centre kinetic solution of the same problem under the same assumptions. The model reduces identically to the static and isotropic Grad-Shafranov equation in the appropriate limit as different flux functions are set to zero. An analytical solution based on a modified Soloviev solution for non-zero toroidal flow and anisotropy is also presented. The force balance model has been demonstrated in the code EFIT TENSOR, a branch of the existing code EFIT++. Benchmark results for EFIT TENSOR are presented and the more complicated force balance model is found to converge to force balance similarly to the usual EFIT model and with comparable speed.
LETTER: Toroidally asymmetric ELM precursors in TCV
NASA Astrophysics Data System (ADS)
Reimerdes, H.; Pochelon, A.; Suttrop, W.
1998-03-01
Coherent magnetic oscillations precede edge localized modes (ELMs) in TCV. The precursor has been detected prior to ELMs considered to be of type III and others previously referred to as TCV large ELMs. This permits the identification of both as type III ELMs according to the usual classification scheme. The strong localization of these precursors on the bad curvature side of the plasma and their medium toroidal mode numbers indicate their ballooning character. Unlike conventional MHD modes, these modes start toroidally localized and grow in amplitude and toroidal extent. When the precursor encompasses the whole toroidal circumference, the increased transport phase, as indicated by the characteristic Dα spike, begins.
Tokamak with liquid metal for inducing toroidal electrical field
Ohkawa, Tihiro
1981-01-01
A tokamak apparatus includes a vessel for defining a reservoir and confining liquid therein. A toroidal liner disposed within said vessel defines a toroidal space within the liner confines gas therein. Liquid metal fills the reservoir outside the liner. A magnetic field is established in the liquid metal to develop magnetic flux linking the toroidal space. The gas is ionized. The liquid metal and the toroidal space are moved relative to one another transversely of the space to generate electric current in the ionized gas in the toroidal space about its major axis and thereby heat plasma developed in the toroidal space.
Toroidal current asymmetry in tokamak disruptions
Strauss, H. R.
2014-10-15
It was discovered on JET that disruptions were accompanied by toroidal asymmetry of the toroidal plasma current I{sub ϕ}. It was found that the toroidal current asymmetry was proportional to the vertical current moment asymmetry with positive sign for an upward vertical displacement event (VDE) and negative sign for a downward VDE. It was observed that greater displacement leads to greater measured I{sub ϕ} asymmetry. Here, it is shown that this is essentially a kinematic effect produced by a VDE interacting with three dimensional MHD perturbations. The relation of toroidal current asymmetry and vertical current moment is calculated analytically and is verified by numerical simulations. It is shown analytically that the toroidal variation of the toroidal plasma current is accompanied by an equal and opposite variation of the toroidal current flowing in a thin wall surrounding the plasma. These currents are connected by 3D halo current, which is π/2 radians out of phase with the n = 1 toroidal current variations.
Theory comparison and numerical benchmarking on neoclassical toroidal viscosity torque
Wang, Zhirui; Park, Jong-Kyu; Logan, Nikolas; Kim, Kimin; Menard, Jonathan E.; Liu, Yueqiang
2014-04-15
Systematic comparison and numerical benchmarking have been successfully carried out among three different approaches of neoclassical toroidal viscosity (NTV) theory and the corresponding codes: IPEC-PENT is developed based on the combined NTV theory but without geometric simplifications [Park et al., Phys. Rev. Lett. 102, 065002 (2009)]; MARS-Q includes smoothly connected NTV formula [Shaing et al., Nucl. Fusion 50, 025022 (2010)] based on Shaing's analytic formulation in various collisionality regimes; MARS-K, originally computing the drift kinetic energy, is upgraded to compute the NTV torque based on the equivalence between drift kinetic energy and NTV torque [J.-K. Park, Phys. Plasma 18, 110702 (2011)]. The derivation and numerical results both indicate that the imaginary part of drift kinetic energy computed by MARS-K is equivalent to the NTV torque in IPEC-PENT. In the benchmark of precession resonance between MARS-Q and MARS-K/IPEC-PENT, the agreement and correlation between the connected NTV formula and the combined NTV theory in different collisionality regimes are shown for the first time. Additionally, both IPEC-PENT and MARS-K indicate the importance of the bounce harmonic resonance which can greatly enhance the NTV torque when E×B drift frequency reaches the bounce resonance condition.
Smith, R F; Dunn, J; Filevich, J; Moon, S; Nilsen, J; Keenan, R; Shlyaptsev, V N; Rocca, J J; Hunter, J R; Marconi, M C
2004-10-04
We have directly probed the plasma conditions in which the Ni-like Pd transient collisional x-ray laser is generated and propagates by measuring the near-field image and by utilizing picosecond resolution soft x-ray laser interferometry of the preformed Pd plasma gain medium. The electron density and gain region of the plasma have been determined experimentally and are found to be in good agreement with simulations. We observe a strong dependence of the laser pump-gain medium coupling on the laser pump parameters. The most efficient coupling of laser pump energy into the gain region occurs with the formation of lower density gradients in the pre-formed plasma and when the duration of the main heating pulse is comparable to the gain lifetime ({approx}10ps for mid-Z Ni-like schemes). This increases the output intensity by more than an order of magnitude relative to the commonly utilized case where the same pumping energy is delivered within a shorter heating pulse duration (< 3ps). In contrast, the higher intensity heating pulses are observed to be absorbed at higher electron densities and in regions where steep density gradients limit the effective length of the gain medium.
Fokker-Planck model for collisional loss of fast ions in tokamaks
NASA Astrophysics Data System (ADS)
Yavorskij, V.; Goloborod'ko, V.; Schoepf, K.
2016-11-01
Modelling of the collisional loss of fast ions from tokamak plasmas is important from the point of view of the impact of fusion alphas and neutral beam injection ions on plasma facing components as well as for the development of diagnostics of fast ion losses [1-3]. This paper develops a Fokker-Planck (FP) method for the assessment of distributions of collisional loss of fast ions as depending on the coordinates of the first wall surface and on the velocities of lost ions. It is shown that the complete 4D drift FP approach for description of fast ions in axisymmetric tokamak plasmas can be reduced to a 2D FP problem for lost ions with a boundary condition delivered by the solution of a 3D boundary value problem for confined ions. Based on this newly developed FP approach the poloidal distribution of neoclassical loss, depending on pitch-angle and energy, of fast ions from tokamak plasma may be examined as well as the contribution of this loss to the signal detected by the scintillator probe may be evaluated. It is pointed out that the loss distributions obtained with the novel FP treatment may serve as an alternative approach with respect to Monte-Carlo models [4, 5] commonly used for simulating fast ion loss from toroidal plasmas.
NASA Astrophysics Data System (ADS)
Jeffrey, N. L. S.; Kontar, E. P.; Emslie, A. G.; Bian, N. H.
2015-09-01
X-ray observations are a direct diagnostic of fast electrons produced in solar flares, energized during the energy release process and directed towards the Sun. Since the properties of accelerated electrons can be substantially changed during their transport and interaction with the background plasma, a model must ultimately be applied to X-ray observations in order to understand the mechanism responsible for their acceleration. A cold thick target model is ubiquitously used for this task, since it provides a simple analytic relationship between the accelerated electron spectrum and the emitting electron spectrum in the X-ray source, with the latter quantity readily obtained from X-ray observations. However, such a model is inappropriate for the majority of solar flares in which the electrons propagate in a hot megaKelvin plasma, because it does not take into account the physics of thermalization of fast electrons. The use of a more realistic model, properly accounting for the properties of the background plasma, and the collisional diffusion and thermalization of electrons, can alleviate or even remove many of the traditional problems associated with the cold thick target model and the deduction of the accelerated electron spectrum from X-ray spectroscopy, such as the number problem and the need to impose an ad hoc low energy cut-off.
Pacella; Fournier; Zerbini; Finkenthal; Mattioli; May; Goldstein
2000-05-01
This work presents and interprets, by means of detailed atomic calculations, observations of L-shell (n = 3-->n = 2) transitions in highly ionized molybdenum, the main intrinsic heavy impurity in the Frascati tokamak upgrade plasmas. These hot plasmas were obtained by additional electron cyclotron resonance heating (ECRH), at the frequency of 140 Ghz, during the current ramp-up phase of the discharge. Injecting 400 kW on axis and 800 kW slightly off axis, the peak central electron temperature reached 8.0 and 7.0 keV, respectively, for a time much longer than the ionization equilibrium time of the molybdenum ions. X-ray emissions from rarely observed high charge states, Mo30+ to Mo39+, have been studied with moderate spectral resolution (lambda/delta lambda approximately 150) and a time resolution of 5 ms. A sophisticated collisional-radiative model for the study of molybdenum ions in plasmas with electron temperature in the range 4-20 keV is presented. The sensitivity of the x-ray emission to the temperature and to impurity transport processes is discussed. This model has been then used to investigate two different plasma scenarios. In the first regime the ECRH heating occurs on axis during the current ramp up phase, when the magnetic shear is evolving from negative to zero up to the half radius. The spectrum is well reproduced with the molybdenum ions in coronal equilibrium and with a central impurity peaking. In the second regime, at the beginning of the current flat top when magnetic shear is monotonic and sawtoothing activity is appearing, the lowest charge states (Mo33+ to Mo30+), populated off axis, are affected by anomalous transport and the total molybdenum profile is found to be flat up to the half radius. We conclude with the presentation of "synthetic spectra" computed for even higher temperature plasmas that are expected in future experiments with higher ECRH power input.
Seol, J; Lee, S G; Park, B H; Lee, H H; Terzolo, L; Shaing, K C; You, K I; Yun, G S; Kim, C C; Lee, K D; Ko, W H; Kwak, J G; Kim, W C; Oh, Y K; Kim, J Y; Kim, S S; Ida, K
2012-11-09
It is observed that the magnitude of the toroidal rotation speed is reduced by the central electron cyclotron resonance heating (ECRH) regardless of the direction of the toroidal rotation. The magnetohydrodynamics activities generally appear with the rotation change due to ECRH. It is shown that the internal kink mode is induced by the central ECRH and breaks the toroidal symmetry. When the magnetohydrodynamics activities are present, the toroidal plasma viscosity is not negligible. The observed effects of ECRH on the toroidal plasma rotation are explained by the neoclassical toroidal viscosity in this Letter. It is found that the neoclassical toroidal viscosity torque caused by the internal kink mode damps the toroidal rotation.
Collisional Excitation and De-Excitation of N2 and N2+ in High-Pressure Discharge Plasmas
NASA Astrophysics Data System (ADS)
Kurunczi, P.; Abramzon, N.; Figus, M.; Becker, K.
2003-05-01
Emission spectroscopy using the 2nd positive system of N2 and the 1st negative system of N2+ can be used to determine important plasma parameters such the translational, vibrational, and rotational temperatures of the plasma species. The rotational temperature is perhaps the most frequently determined quantity as its determination may reflect the gas temperature in the plasma and/or provide insight into the reaction kinetics of important plasma species. If the emitting species are in equilibrium with the bulk gas in the plasma, then this temperature can be interpreted as the gas kinetic temperature in the plasma. We determined rotational temperatures for N2 and N2+ in high-pressure (400 Torr) discharges in mixtures in Ne with a trace admixture of N2. Significantly different values were obtained for respectively N2 and N2+. The relation of these rotational temperatures to the gas kinetic temperature and to the reaction kinetics leading to the formation and the decay of the emitting species will be discussed. We also carried out a rotational analysis of the unresolved N2 second positive system emitted by an atmospheric-pressure capillary plasma electrode (CPE) discharge in ambient air. Work supported by the US National Science Foundation.
NASA Astrophysics Data System (ADS)
Goto, M.; Sawada, K.
2014-04-01
Spectra of neutral helium in the visible wavelength range are measured for a discharge in the Large Helical Device (LHD). The electron temperature (Te) and density (ne) are derived from the intensity distribution of helium emission lines. For that purpose, a collisional-radiative model developed by Sawada et al. [Plasma and Fusion Res. 2010;5:001] which takes the reabsorption effect into account is used. It is found that incorporation of the reabsorption effect is necessary to obtain a set of Te and ne giving consistent line intensity distribution with the measurement, and that those parameters obtained vary as the line-averaged ne changes in the course of time. The position where the helium line emission dominantly takes place is located with the help of Te and ne profiles measured by the Thomson scattering system. The result indicates that the emission position is almost fixed at the place where the connection length of the magnetic field lines to the divertor plate leaps beyond 10 m. Because intense neutral atom line emission suggests the vigorous ionization of neutral atoms, the helium line emission location determined here can be regarded as the effective boundary of the plasma.
NASA Astrophysics Data System (ADS)
Raybould, T. A.; Fedotov, V. A.; Papasimakis, N.; Kuprov, I.; Youngs, I. J.; Chen, W. T.; Tsai, D. P.; Zheludev, N. I.
2016-07-01
We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism will be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics.
Experimental studies of compact toroids
Not Available
1991-01-01
The Berkeley Compact Toroid Experiment (BCTX) device is a plasma device with a Marshall-gun generated, low aspect ratio toroidal plasma. The device is capable of producing spheromak-type discharges and may, with some modification, produce low-aspect ratio tokamak configurations. A unique aspect of this experimenal devie is its large lower hybrid (LH) heating system, which consists of two 450MHz klystron tubes generating 20 megawatts each into a brambilla-type launching structure. Successful operation with one klystron at virtually full power (18 MW) has been accomplished with 110 {mu}s pulse length. A second klystron is currently installed in its socket and magnet but has not been added to the RF drive system. This report describes current activities and accomplishments and describes the anticipated results of next year's activity.
Lindenmeyer, Carl W.
1981-01-01
A lower support receives a toroid at a winding station with the axis of the toroid aligned with a slot in the support. An upper guide member applies an axial force to hold the toroid against the lower support. A pair of movable jaws carried by an indexing mechanism engage the outer surface of the toroid to apply a radial holding force. While the toroid is thus held, a wire is placed axially through the toroid, assisted by a funnel-shaped surface in the upper guide member, and is drawn tight about the toroid by a pair of cooperating draw rollers. When operated in the "full cycle" mode, the operator then actuates a switch which energizes a power drive to release the axial clamp and to drive the indexing mechanism and the jaws to rotate the toroid about its axis. At the same time, the wire is ejected from the draw rollers beneath the toroid so that the operator may grasp it to form another loop. When the toroid is fully indexed, the jaws release it, and the upper guide member is returned to clamp the toroid axially while the indexing mechanism is returned to its starting position. The apparatus may also be operated in a "momentary contact" mode in which the mechanism is driven only for the time a switch is actuated.
Sensing with toroidal metamaterial
NASA Astrophysics Data System (ADS)
Gupta, Manoj; Srivastava, Yogesh Kumar; Manjappa, Manukumara; Singh, Ranjan
2017-03-01
Localized electromagnetic excitation in the form of toroidal dipoles has recently been observed in metamaterial systems. The origin of the toroidal dipole lies in the currents flowing on the surface of a torus. Thus, the exotic toroidal excitations play an important role in determining the optical properties of a system. Toroidal dipoles also contribute towards enabling high quality factor subwavelength resonances in metamaterial systems which could be an excellent platform for probing the light matter interaction. Here, we demonstrate sensing with toroidal resonance in a two-dimensional terahertz metamaterial in which a pair of mirrored asymmetric Fano resonators possesses anti-aligned magnetic moments at an electromagnetic resonance that gives rise to a toroidal dipole. Our proof of concept demonstration opens up an avenue to explore the interaction of matter with toroidal multipoles that could have strong applications in the sensing of dielectrics and biomolecules.
NASA Astrophysics Data System (ADS)
HL-2A Team; Chen, W.; Ding, X. T.; Yu, L. M.; Ji, X. Q.; Dong, J. Q.; Yang, Q. W.; Liu, Yi.; Yan, L. W.; Zhou, Y.; Li, W.; Song, X. M.; Chen, S. Y.; Shi, Z. B.; Duan, X. R.
2013-01-01
In this Letter, it is reported that the first experimental results are associated with the GAM induced by energetic electrons (EGAM) in HL-2A Ohmic plasma. The energetic electrons are jointly generated by Ohmic electric fields and parallel electric fields during magnetic reconnection associated with tearing mode (TM). The EGAM localizes in the core plasma, i.e. in the vicinity of q=2 surface, and is very different from one excited by the drift-wave turbulence in the edge plasma. The analysis indicated that the EGAM is provided with the magnetic components, whose intensities depend on the poloidal angles, and its mode numbers are |m/n|=2/0. Further, there exist intense nonlinear interactions among EGAM, BAEs and strong tearing modes (TMs). These new findings shed light on the underlying physics mechanism for the excitation of the low frequency (LF) Alfvénic and acoustic fluctuations.
Barnes, D.C.; Fernandez, J.C.; Rej, D.J.
1990-05-01
The US-Japan Workshop on Field-Reversed Configurations with Steady-State High-Temperature Fusion Plasma and the 11th US-Japan Workshop on Compact Toroids were held at Los Alamos National Laboratory, Los Alamos, New Mexico on November 7--9, 1989. These proceedings contain the papers presented at the workshops as submitted by the authors. These papers have been indexed separately.
Auluck, S. K. H.
2014-10-15
Direct measurement of axial magnetic field in the PF-1000 dense plasma focus (DPF), and its reported correlation with neutron emission, call for a fresh look at previous reports of existence of axial magnetic field component in the DPF from other laboratories, and associated data suggesting toroidal directionality of fast ions participating in fusion reactions, with a view to understand the underlying physics. In this context, recent work dealing with application of the hyperbolic conservation law formalism to the DPF is extended in this paper to a curvilinear coordinate system, which reflects the shape of the DPF current sheath. Locally unidirectional shock propagation in this coordinate system enables construction of a system of 7 one-dimensional hyperbolic conservation law equations with geometric source terms, taking into account all the components of magnetic field and flow velocity. Rankine-Hugoniot jump conditions for this system lead to expressions for the axial magnetic field and three components of fluid velocity having high ion kinetic energy.
Motie, Iman; Bokaeeyan, Mahyar
2015-02-15
A close analysis of dust charging process in the presence of radio frequency (RF) discharge on low pressure and fully ionized plasma for both weak and strong discharge's electric field is considered. When the electromagnetic waves pass throughout fully ionized plasma, the collision frequency of the plasma is derived. Moreover, the disturbed distribution function of plasma particles in the presence of the RF discharge is obtained. In this article, by using the Krook model, we separate the distribution function in two parts, the Maxwellian part and the perturbed part. The perturbed part of distribution can make an extra current, so-called the accretion rate of electron (or ion) current, towards a dust particle as a function of the average electron-ion collision frequency. It is proven that when the potential of dust grains increases, the accretion rate of electron current experiences an exponential reduction. Furthermore, the accretion rate of electron current for a strong electric field is relatively smaller than that for a weak electric field. The reasons are elaborated.
NASA Astrophysics Data System (ADS)
Li, Yan; Sung, Yung-Ta; Scharer, John
2015-11-01
Ion acceleration through plasma double layer and non-Maxwellian two temperature electron distributions have been observed in Madison Helicon Experiment (MadHeX) operated in high RF power (>1000 W) and low Ar pressure (0.17 mtorr) inductive mode. By applying Optical Emission Spectroscopy (OES) cross-checked with an RF-compensated Langmuir probe (at 13.56 MHz and its second and third harmonics), the fast (>80 eV), untrapped electrons downstream of the double layer have a higher temperature of 13 eV than the trapped bulk electrons upstream with a temperature of 4 eV. The reduction of plasma potential and density observed in the double layer region require an upstream temperature ten times the measured 4 eV if occurring via Boltzmann ambipolar expansion. The hot tail electrons of the non-Maxwellian electron distribution affect the formation and the potential drop of the double layer region. The mechanism behind this has been explored via several non-invasive plasma diagnostics tools. The OES measured electron temperatures and densities are also cross-checked with Atomic Data and Analysis Structure (ADAS) and a millimeter wave interferometer respectively. The IEDF is measured by a four-grid RPA and also cross-checked with argon 668 nm Laser Induced Fluorescence (LIF). An emissive probe has been used to measure the plasma potential.
Samus Toroid Installation Fixture
Stredde, H.; /Fermilab
1990-06-27
The SAMUS (Small Angle Muon System) toroids have been designed and fabricated in the USSR and delivered to D0 ready for installation into the D0 detector. These toroids will be installed into the aperture of the EF's (End Toroids). The aperture in the EF's is 72-inch vertically and 66-inch horizontally. The Samus toroid is 70-inch vertically by 64-inch horizontally by 66-inch long and weighs approximately 38 tons. The Samus toroid has a 20-inch by 20-inch aperture in the center and it is through this aperture that the lift fixture must fit. The toroid must be 'threaded' through the EF aperture. Further, the Samus toroid coils are wound about the vertical portion of the aperture and thus limit the area where a lift fixture can make contact and not damage the coils. The fixture is designed to lift along a surface adjacent to the coils, but with clearance to the coil and with contact to the upper steel block of the toroid. The lift and installation will be done with the 50 ton crane at DO. The fixture was tested by lifting the Samus Toroid 2-inch off the floor and holding the weight for 10 minutes. Deflection was as predicted by the design calculations. Enclosed are sketches of the fixture and it relation to both Toroids (Samus and EF), along with hand calculations and an Finite Element Analysis. The PEA work was done by Kay Weber of the Accelerator Engineering Department.
Thorson, T.; Fonck, R.; Lewicki, B.
1999-01-01
An optical neutral beam spectroscopy system is being designed to provide equilibrium and stability measurements for the PEGASUS toroidal experiment. Spatially localized measurements of the electron temperature and plasma density are possible by observing the intensity of the collisionally induced neutral beam fluorescence. In a helium beam, the population of the singlet levels are relatively independent of the plasma temperature compared to the triplet levels. Therefore, the ratio of intensities of a triplet transition (e.g., 3{sup 3}S{r_arrow}2{sup 3}P, {lambda}=706.5 nm) to a singlet transition (e.g., 3{sup 1}P{r_arrow}2{sup 1}S, {lambda}=501.6 nm) provides a measure of the local plasma temperature for the range 10 eV{lt}T{sub e}{lt}1.0 keV. The plasma density profile can be inferred from the attenuation of the beam fluorescence signal as the beam passes through the plasma. Additionally in a deuterium beam, the local plasma density can be directly inferred from the local radial gradient in the observed beam fluorescence signal. Plasma stability will be studied with localized magnetohydrodynamics measurements via beam emission spectroscopy, which otherwise is problematic for low-field spherical plasmas. {copyright} {ital 1999 American Institute of Physics.}
Kaur, Manjit Bose, Sayak; Chattopadhyay, P. K.; Sharma, D.; Ghosh, J.; Saxena, Y. C.; Thomas, Edward
2015-09-15
Observation of two well-separated dust vortices in an unmagnetized parallel plate DC glow discharge plasma is reported in this paper. A non-monotonic radial density profile, achieved by an especially designed cathode structure using a concentric metallic disk and ring of different radii, is observed to produce double dust tori between cathode and anode. PIV analysis of the still images of the double tori shows oppositely rotating dust structures between the central disk and the ring. Langmuir probe measurements of background plasma shows a non-uniform plasma density profile between the disk and the ring. Location and sense of rotation of the dust vortices coincides with the location and direction of the radial gradient in the ion drag force caused by the radial density gradient. The experimentally observed dust vorticity matches well with the calculated one using hydrodynamic formulations with shear in ion drag dominating over the dust charge gradient. These results corroborate that a radial gradient in the ion drag force directed towards cathode is the principal cause of dust rotation.
NASA Astrophysics Data System (ADS)
Schlossberg, D. J.; Bodner, G. M.; Fonck, R. J.; Reusch, J. A.; Winz, G. R.
2015-11-01
Extrapolation of non-solenoidal startup via local helicity injection (LHI) to larger devices depends critically on confinement during the injection process. To begin quantifying confinement regimes, the Thomson scattering diagnostic on the Pegasus ST was upgraded to include 12 radial positions and high temperature (0.1
NASA Astrophysics Data System (ADS)
Choe, Wonho; Kim, Jayhyun; Ono, Masayuki
2005-12-01
Eventual elimination of the in-board Ohmic heating solenoid is required for the spherical torus (ST) to function as a compact component test facility and as an attractive fusion power plant. An in-board Ohmic solenoid, along with the shielding needed for its insulation, can dramatically increase the size and, hence, the cost of the plant. Advanced tokamak reactor designs also assume no or a small in-board solenoid to reduce the size and cost of the plant. In addition, elimination of the in-board solenoid greatly reduces the coil stresses and simplifies the coil design. Here, we investigate using static as well as dynamic codes in ST geometries with two complementary solenoid-free plasma start-up approaches: one utilizes only the outer poloidal field coils to create a relatively high quality field null region while retaining significant poloidal flux, and the other takes advantage of the poloidal flux stored in the conducting centre-post to create a start-up condition similar to that of the conventional Ohmic solenoid method. We find that it is therefore possible to come up with a promising configuration, which produces a quality multi-pole field-null and sufficient loop-voltage needed for plasma initiation and significant poloidal flux for subsequent current ramp-up. The present solenoid-free start-up concept, if proved feasible, can be readily extended to higher field devices due to relatively simple physics principles and favourable scaling with the device size and toroidal field.
Jeans stability in collisional quantum dusty magnetoplasmas
Jamil, M.; Asif, M.; Mir, Zahid; Salimullah, M.
2014-09-15
Jeans instability is examined in detail in uniform dusty magnetoplasmas taking care of collisional and non-zero finite thermal effects in addition to the quantum characteristics arising through the Bohm potential and the Fermi degenerate pressure using the quantum hydrodynamic model of plasmas. It is found that the presence of the dust-lower-hybrid wave, collisional effects of plasma species, thermal effects of electrons, and the quantum mechanical effects of electrons have significance over the Jeans instability. Here, we have pointed out a new class of dissipative instability in quantum plasma regime.
NASA Astrophysics Data System (ADS)
Morel, V.; Bultel, A.; Chéron, B. G.
2010-09-01
A 0D numerical approach including a Collisional-Radiative model is elaborated in the purpose of describing the behavior of the nascent plasma resulting from the interaction between a 4 ns/65 mJ/532 nm Q-switched Nd:YAG laser pulse and an aluminum sample in vacuum. The heavy species considered are Al, Al +, Al 2+ and Al 3+ on their different excited states and free electrons. The translation temperatures of free electrons and heavy species are assumed different ( T e and TA respectively). Numerous elementary processes are accounted for as electron impact induced excitation and ionization, elastic collisions, multiphoton ionization and inverse Bremsstrahlung. Atoms passing from the sample to gas phase are described by using classical vaporization theory so that the surface temperature is arbitrarily limited to values less than the critical point one at 6700 K. The laser flux density considered in the study is therefore moderate with a fluence lower than 7 J cm - 2 . This model puts forward the major influence of multiphoton ionization in the plasma formation, whereas inverse Bremsstrahlung turns out to be quasi negligible. The increase of electron temperature is mainly due to multiphoton ionization and Te does not exceed 10,000 K. The electron induced collisions play an important role during the subsequent phase which corresponds to the relaxation of the excited states toward Boltzmann equilibrium. The electron density reaches its maximum during the laser pulse with a value ≈ 10 22, 10 23 m - 3 depending highly on the sample temperature. The ionization degree is of some percents in our conditions.
Phelps, A. V.
1990-01-01
The interpretation of measurements of the properties of weakly ionized plasmas in terms of diffusion of electrons and ions is reviewed both critically and tutorially. A particular effort is made to tie together various aspects of charged particle diffusion phenomena in quiescent, partially ionized plasmas. The concepts of diffusion length and effective diffusion coefficient and the treatment of partially reflecting boundaries are developed in the limit of the space-charge-free motion of the electrons or ions. A simplified derivation of the screening length for space charge electric fields is followed by a review of the conventional derivation of diffusion in the ambipolar limit. A discussion of the scaling parameters of the ratio of the diffusion length to the screening length and the ratio of the diffusion length to the ion mean-free-path leads to a map used to correlate published models covering the complete range of these parameters. The models of measurements of the diffusion of electrons, several types of positive ions, and negative ions are reviewed. The role of diffusion in the decay of charged particle densities and wall currents during the afterglow of a discharge is then considered. The effects of collapse of the space charge field and of diffusion cooling are reviewed. Finally, the application of the diffusion models to a number of different discharges is discussed. PMID:28179784
Landau damping of geodesic acoustic mode in toroidally rotating tokamaks
Ren, Haijun; Cao, Jintao
2015-06-15
Geodesic acoustic mode (GAM) is analyzed by using modified gyro-kinetic (MGK) equation applicable to low-frequency microinstabilities in a rotating axisymmetric plasma. Dispersion relation of GAM in the presence of arbitrary toroidal Mach number is analytically derived. The effects of toroidal rotation on the GAM frequency and damping rate do not depend on the orientation of equilibrium flow. It is shown that the toroidal Mach number M increases the GAM frequency and dramatically decreases the Landau damping rate.
NASA Astrophysics Data System (ADS)
Lee, Jaehyun; Yun, Gunsu S.; Choi, Minjun J.; Kwon, Jae-Min; Jeon, Young-Mu; Lee, Woochang; Luhmann, Neville C.; Park, Hyeon K.
2016-08-01
The effect of static n =1 resonant magnetic perturbation (RMP) on the spatial structure and temporal dynamics of edge-localized modes (ELMs) and edge turbulence in tokamak plasma has been investigated. Two-dimensional images measured by a millimeter-wave camera on the KSTAR tokamak revealed that the coherent filamentary modes (i.e., ELMs) are still present in the edge region when the usual large scale collapse of the edge confinement, i.e., the ELM crash, is completely suppressed by n =1 RMP. Cross-correlation analyses on the 2D images show that (1) the RMP enhances turbulent fluctuations in the edge toward the ELM-crash-suppression phase, (2) the induced turbulence has a clear dispersion relation for wide ranges of wave number and frequency, and (3) the turbulence involves a net radially outward energy transport. Nonlinear interactions of the turbulent eddies with the coexisting ELMs are clearly observed by bispectral analysis, which implies that the exchange of energy between them may be the key to the prevention of large scale crashes.
Ono, Masayuki; Furth, Harold
1993-01-01
An electron injection scheme for controlling transport in a tokamak plasma. Electrons with predominantly perpendicular energy are injected into a ripple field region created by a group of localized poloidal field bending magnets. The trapped electrons then grad-B drift vertically toward the plasma interior until they are detrapped, charging the plasma negative. Calculations indicate that the highly perpendicular velocity electrons can remain stable against kinetic instabilities in the regime of interest for tokamak experiments. The penetration distance can be controlled by controlling the "ripple mirror ratio", the energy of the injected electrons, and their v.sub..perp. /v.sub.51 ratio. In this scheme, the poloidal torque due to the injected radial current is taken by the magnets and not by the plasma. Injection is accomplished by the flat cathode containing an ECH cavity to pump electrons to high v.sub..perp..
The linear tearing instability in three dimensional, toroidal gyro-kinetic simulations
Hornsby, W. A. Migliano, P.; Buchholz, R.; Kroenert, L.; Weikl, A.; Peeters, A. G.; Zarzoso, D.; Poli, E.; Casson, F. J.
2015-02-15
Linear gyro-kinetic simulations of the classical tearing mode in three-dimensional toroidal geometry were performed using the global gyro-kinetic turbulence code, GKW. The results were benchmarked against a cylindrical ideal MHD and analytical theory calculations. The stability, growth rate, and frequency of the mode were investigated by varying the current profile, collisionality, and the pressure gradients. Both collisionless and semi-collisional tearing modes were found with a smooth transition between the two. A residual, finite, rotation frequency of the mode even in the absence of a pressure gradient is observed, which is attributed to toroidal finite Larmor-radius effects. When a pressure gradient is present at low collisionality, the mode rotates at the expected electron diamagnetic frequency. However, the island rotation reverses direction at high collisionality. The growth rate is found to follow a η{sup 1∕7} scaling with collisional resistivity in the semi-collisional regime, closely following the semi-collisional scaling found by Fitzpatrick. The stability of the mode closely follows the stability analysis as performed by Hastie et al. using the same current and safety factor profiles but for cylindrical geometry, however, here a modification due to toroidal coupling and pressure effects is seen.
Kamiya, K.; Honda, M.; Urano, H.; Yoshida, M.; Kamada, Y.; Itoh, K.
2014-12-15
Modulation charge eXchange recombination spectroscopy measurements with high spatial and temporal resolution have made the evaluation of the toroidal plasma flow of fully stripped carbon impurity ions (V{sub ϕ}{sup C6+}) in the JT-60U tokamak peripheral region (including, in particular, the separatrix) possible with a better signal-to-noise ratio. By comparing co- and counter-neutral beam injection discharges experimentally, we have identified the boundary condition of V{sub ϕ}{sup C6+} and radial electric field shear (∇E{sub r}) imposed at the separatrix in high confinement (H-mode) plasmas with edge localized modes (ELMs). The V{sub ϕ}{sup C6+} value at the separatrix is not fixed at zero but varies with the momentum input direction. On the other hand, the ∇E{sub r} value is nearly zero (or very weakly positive) at the separatrix. Furthermore, the edge localized mode perturbation does not appear to affect both V{sub ϕ}{sup C6+} and ∇E{sub r} values at the separatrix as strongly as that in the pedestal region. The above experimental findings based on the precise edge measurements have been used to validate a theoretical model and develop a new empirical model. A better understanding of the physical process in the edge transport barrier (ETB) formation due to the sheared E{sub r} formation is also discussed.
NCSX Toroidal Field Coil Design
Kalish, M.; Rushinski, J.; Myatt, L.; Brooks, A.; Dahlgren, F.; Chrzanowski, J.; Reiersen, W.; Freudenberg, K.
2005-10-07
The National Compact Stellarator Experiment (NCSX) is an experimental device whose design and construction is underway at the Department of Energy's Princeton Plasma Physics Laboratory (PPPL). The primary coil systems for the NCSX device consist of the twisted plasma-shaping Modular Coils, the Poloidal Field Coils, and the Toroidal Field (TF) Coils. The TF Coils are D-shaped coils wound from hollow copper conductor, and vacuum impregnated with a glass-epoxy resin system. There are 18 identical, equally spaced TF coils providing 1/R field at the plasma. They operate within a cryostat, and are cooled by LN2, nominally, to 80K. Wedge shaped castings are assembled to the inboard face of these coils, so that inward radial loads are reacted via the nesting of each of the coils against their adjacent partners. This paper outlines the TF Coil design methodology, reviews the analysis results, and summarizes how the design and analysis support the design requirements.
Potthoff, Clifford M.
1978-01-01
The disclosure is directed to an apparatus for placing wire windings on a toroidal body, such as a transformer core, having an orifice in its center. The apparatus comprises a wire storage spool, a wire loop holding continuous belt maintained in a C-shaped loop by a belt supporting structure and provision for turning the belt to place and tighten loops of wire on a toroidal body, which is disposed within the gap of the C-shaped belt loop.
Spontaneous toroidal flow generation due to negative effective momentum diffusivity
McMillan, Ben F.
2015-02-15
Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.
Spontaneous toroidal flow generation due to negative effective momentum diffusivity
NASA Astrophysics Data System (ADS)
McMillan, Ben F.
2015-02-01
Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.
Living Toroids - Cells on Toroidal Surfaces
NASA Astrophysics Data System (ADS)
Chang, Ya-Wen; Angelini, Thomas; Marquez, Samantha; Kim, Harold; Fernandez-Nieves, Alberto
2014-03-01
Cellular environment influences a multitude of cellular functions by providing chemical and physical signals that modulate cell behavior, dynamics, development, and eventually survival. Substrate mechanics has been recognized as one of the important physical cues that governs cell behavior at single cell level as well as in collective cell motion. Past research has suggested several contact-guided behaviors to be the result of surface curvature. However, studies on the effect of curvature are relatively scarce likely due to the difficulty in generating substrates with well-defined curvature. Here we describe the generation of toroidal droplets, which unlike spherical droplets, have regions of both positive and negative Gaussian curvature. Additionally, the range of curvatures can be controlled by varying the size and aspect ratio of the torus. Cells are either encapsulated inside toroidal droplets or located on toroidal hydrogel surfaces. Preliminary studies use B. Subtilis to study the organization of bacteria biofilms. When confined in droplets surrounded by yield-stress fluid, bacteria self-organize into heterogeneous biofilm at fluid- substrate interface. It is found that the surface curvature in the sub-millimeter scale has little effect on biofilm architecture.
System and method of operating toroidal magnetic confinement devices
Chance, M.S.; Jardin, S.C.; Stix, T.H.; Grimm, R.C.; Manickam, J.; Okabayashi, M.
1984-08-30
This invention pertains to methods and arrangements for attaining high beta values in plasma confinement devices. More specifically, this invention pertains to methods for accessing the second stability region of operation in toroidal magnetic confinement devices.
Influence of toroidal rotation on resistive tearing modes in tokamaks
NASA Astrophysics Data System (ADS)
Wang, S.; Ma, Z. W.
2015-12-01
Influence of toroidal equilibrium plasma rotation on m/n = 2/1 resistive tearing modes is studied numerically using a 3D toroidal MHD code (CLT). It is found that the toroidal rotation with or without shear can suppress the tearing instability and the Coriolis effect in the toroidal geometry plays a dominant role on the rotation induced stabilization. For a high viscosity plasma (τR/τV ≫ 1, where τR and τV represent resistive and viscous diffusion time, respectively), the effect of the rotation shear combined with the viscosity appears to be stabilizing. For a low viscosity plasmas (τR/τV ≪ 1), the rotation shear shows a destabilizing effect when the rotation is large.
Influence of toroidal rotation on resistive tearing modes in tokamaks
Wang, S.; Ma, Z. W.
2015-12-15
Influence of toroidal equilibrium plasma rotation on m/n = 2/1 resistive tearing modes is studied numerically using a 3D toroidal MHD code (CLT). It is found that the toroidal rotation with or without shear can suppress the tearing instability and the Coriolis effect in the toroidal geometry plays a dominant role on the rotation induced stabilization. For a high viscosity plasma (τ{sub R}/τ{sub V} ≫ 1, where τ{sub R} and τ{sub V} represent resistive and viscous diffusion time, respectively), the effect of the rotation shear combined with the viscosity appears to be stabilizing. For a low viscosity plasmas (τ{sub R}/τ{sub V} ≪ 1), the rotation shear shows a destabilizing effect when the rotation is large.
Gerald, II, Rex E.; Sanchez, Jairo; Rathke, Jerome W.
2004-08-10
A video toroid cavity imager for in situ measurement of electrochemical properties of an electrolytic material sample includes a cylindrical toroid cavity resonator containing the sample and employs NMR and video imaging for providing high-resolution spectral and visual information of molecular characteristics of the sample on a real-time basis. A large magnetic field is applied to the sample under controlled temperature and pressure conditions to simultaneously provide NMR spectroscopy and video imaging capabilities for investigating electrochemical transformations of materials or the evolution of long-range molecular aggregation during cooling of hydrocarbon melts. The video toroid cavity imager includes a miniature commercial video camera with an adjustable lens, a modified compression coin cell imager with a fiat circular principal detector element, and a sample mounted on a transparent circular glass disk, and provides NMR information as well as a video image of a sample, such as a polymer film, with micrometer resolution.
NASA Astrophysics Data System (ADS)
Suttrop, Wolfgang; Nazikian, Raffi; Kirk, Andrew; ASDEX Upgrade Team; Diii-D Team; Eurofusion Mst1 Team
2016-10-01
Controlled plasma shape scans at low pedestal collisionality νped* < 0.4 in DIII-D reveal that the threshold of magnetic perturbation field strength for suppression of edge-localized modes (ELMs) depends on both upper and lower plasma triangularity. Similar plasmas with matching shape and matching plasma parameters have been performed in DIII-D and ASDEX Upgrade. In these discharges, stationary ELM suppression by magnetic perturbations is observed for the first time in ASDEX Upgrade.Despite different divertor geometry and different first wall materials in the two machines, these plasmas show many similarities: Complete ELM suppression occurs in a narrow windows around q95 3.7 with transitions to phases with ``fuzzy'' ELMs outside these windows, electron density and temperature profiles as well as the total pedestal pressure are well matched, while there are variations of other quantities such as impurity concentrations and impurity rotation frequencies. A first experiment with injection of tungsten shows that the tungsten impurity content in the plasma decays on the time scale of energy confinement. see http://www.euro-fusionscipub.org/mst1.
NASA Astrophysics Data System (ADS)
Kuroda, Kengoh; Wada, Manato; Uchida, Masaki; Tanaka, Hitoshi; Maekawa, Takashi
2015-07-01
We have investigated the electron and ion flows in toroidal electron cyclotron resonance (ECR) plasmas maintained by a 2.45 GHz microwave power around 1 kW under a simple toroidal field in the low aspect ratio torus experiment (LATE) device. We have found that a vertically uniform ridge of electron pressure that also constitutes the source belt of electron impact ionization is formed along just lower field side of the ECR layer and a cross-field potential hill ({{V}S}\\cong 30 V while {{T}e}\\cong 10 eV), eccentrically shifted toward the corner formed by the top panel and the ECR layer, arises. Combination of the hill-driven E× B drift and the vertical drift due to the field gradient and curvature, being referred to as vacuum toroidal field (VTF) drift, realizes steady flows of electrons and ions from the source to the boundary. In particular, the ions, of which VTF drift velocity is much slower than the electron VTF drift velocity near the source belt, are carried by the E× B drift around the hill to the vicinity of the top panel, where the ion VTF drift is enhanced on the steep down slope of potential toward the top panel. On the other hand the electron temperature strongly decreases in this area. Thus the carrier of VTF drift current is replaced from the electrons to the ions before the top panel, enabling the current circulation through the top and bottom panels and the vessel (electrons mainly to the bottom and ions mainly to the top) that keeps the charge neutrality very high. A few percent of electrons from the source turn around the hill by 360 degree and reentry the source belt from the high field side as seed electrons for the impact ionization, keeping the discharge stable.
Tearing Mode Stability with Sheared Toroidal Flows
NASA Astrophysics Data System (ADS)
White, Ryan; Coppi, Bruno
2016-10-01
Toroidal plasma flow induced by neutral beam heating has been found to increase the stability of tearing modes in tokamak plasmas. The need to extrapolate current (experimentally-based) knowledge of tearing mode onset to future machines, requiresa better understanding of the essential physics. We consider the physics of flow near the rational surfaces. For realistic flow profiles, the velocity shear near the rational surface can be treated as a perturbation, and is found to amplify the dominant stabilizing effect of magnetic curvature. This effect can be seen using a cylindrical model if large-aspect-ratio corrections to the magnetic curvature are incorporated. On the other hand, the physical effects of toroidal rotation are completely absent in a cylinder, and require a fully-toroidal calculation to study. The toroidal rotation near the rational surface is found to couple to a geometrical parameter which vanishes for up-down symmetric profiles. Physically, the dominant effects of rotation arise from a Coriolis force, leading to flow directional dependence. This work is supported by the US DOE.
Collisional Evolution of Planetesimals
NASA Astrophysics Data System (ADS)
Leinhardt, Zoë Malka
2010-05-01
Over 400 extrasolar planets have been discovered. These planetary systems are very different from our solar system and surprisingly diverse. The large number of planets detected suggests that planet formation is common around main sequence stars. The major problem facing the scientific community with regards to these discoveries is that observations cannot trace the history of planet formation. Observations provide snapshots of the early stages of a protoplanetary gas disk orbiting a young star and the late stages after planetary systems have formed. But the evolution from a young star to a planetary system has not been observed. Thus, the challenge is to connect the early and late stages of planet formation. Planets form from the collisional growth of planetary building blocks, planetesimals. In recent numerical work we found that the resistance of planetesimals to collisional erosion changes dramatically during planet formation. Young planetesimals are weak aggregates that are easily disrupted due to efficient momentum coupling during low-velocity collisions in early phases of collisional evolution. However, as impact speeds increase the same weak planetesimals become dramatically stronger because the shock from a supersonic impact loses energy to deformation and phase changes. Our work identifies a paradox for the early stages of planet formation. Objects in the km-size range are weak and susceptible to collisional disruption. However, this disruption may actually produce large amounts of debris that can be accreted by remaining undisrupted planetesimals allowing growth. As we work to disentangle these sorts of conundrums we can expect to put forward hypotheses for collisional remnants in our solar system - for example, the dwarf planet Haumea and its collisional family. In this talk I will review the current understanding of planetesimal evolution and discuss how future numerical simulations may connect observational snapshots to provide a complete history of
Proposal to produce large compact toroids
Phillips, J.A.
1981-03-01
Relatively large, hot compact toroids might be produced in the annular space between two concentric one-turn coils. With currents in the two coils flowing in the same direction, the magnetic fields on each side of the plasma are in opposite directions. As the fields are raised, the plasma ring is heated and compressed radially towards the center of the annular space. By the addition of two sets of auxiliary coils, the plasma ring can be ejected out one end of the two-coil system into a long axial magnetic field.
Future Directions for the PEGASUS Toroidal Experiment
NASA Astrophysics Data System (ADS)
Fonck, R.; Pegasus Team
1999-11-01
The PEGASUS Toroidal Experiment is uniquely poised to explore the tokamak/spheromak transition regime in the near future. To this end, a new low-inductance toroidal field coil set will allow transient exploration of the Ip/ITF > 3 regime and associated plasma relaxation phenomena. The addition of a transformer and inline inductor to the ohmic power supply will increase the pulse length to 0.03-0.05 s and will couple 5-10x the present power to the plasma. The High Harmonic Fast Wave (HHFW) antenna is complete and installation is planned for Fall 1999. The power supplies for the HHFW system have been tested up to 0.7 MW into dummy loads with future upgrades to 2 MW. Poloidal current injection via plasma guns is being tested for generating non-inductive target plasmas, thus reducing startup volt second consumption. If successful, a coaxial array of plasma guns will be used to initiate and drive the startup plasma, achieving non-inductive plasma currents 0.1-0.2 MA. Investigation of the viability of Electron Bernstein Wave heating in overdense ST plasmas is also planned, and may lead to an alternative method of non-inductive current ramp and sustainment.
Collisional effects on nonlinear ion drag force for small grains
Hutchinson, I. H.; Haakonsen, C. B.
2013-08-15
The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.
Collisional Effects in Simulations of High Altitude Nuclear Explosions
NASA Astrophysics Data System (ADS)
Islam, Tanim
2013-10-01
The simulation of the later-time (> 1 second) debris dynamics of a high altitude nuclear explosion (HANE) require, at a minimum, an understanding of the interaction of the ionized blast material with the relatively collisional upper ionosphere and lower exosphere (<= 200 km). At these altitudes, the collisional mean free path of ionized atmospheric particles may become smaller than the length scale of the diamagnetic bubble. Here we report on the local dynamics about the debris/air interface for Starfish Prime like, and lower energy, HANEs at altitudes in which collisionality becomes important. We model the debris dynamics with the hybrid plasma simulation code KIM3D, and use a standard Miller-Combi particle pairing algorithm to model particle collisions. We demonstrate new dynamics associated with finite collisionality in mildly collisional HANEs.
Equilibrium analysis of tokamak discharges with toroidal variation
Zwingmann, W.; Becoulet, M.; Moreau, Ph.; Nardon, E.
2006-11-30
Tokamaks provide a field structure that is almost axisymmetric around the torus axis. There are however always small toroidal variations due to the limited number of toroidal field coils, the magnetic field ripple. On the other hand, non-axisymmetric external fields are applied on purpose to ergodise the field structure close to the separatrix, to control the heat and particle transport across the plasma boundary. We present a perturbation method to calculate the magnetic field of tokamak discharges with with weak toroidal variation. The method is applied for the equilibrium reconstruction of Tore Supra discharges with toroidal ripple. The perturbation method does not rely on a flux surface representation and can therefore be applied to structures with magnetic islands. We obtain the plasma response to the field of ergodising external coils, as proposed for the ITER device.
Neoclassical Poloidal and Toroidal Velocities of Impurity Ions
NASA Astrophysics Data System (ADS)
Wong, S. K.; Chan, V. S.; Solomon, W. M.
2008-11-01
The poloidal and toroidal velocities of impurity ions in a two-ion species plasma for large aspect ratio circular flux surfaces are calculated in the banana and Pfirsch-Schulter regimes of neoclassical theory. The toroidal velocity is allowed to be comparable to the thermal speed of the impurity ions. Closed form expressions are obtained for these velocities in terms of the radial electric field as well as density and temperature gradients. The standard kinetic derivation adopted is compared with the moment approach to the same problems in the case of small toroidal velocities. Comparisons of the calculated poloidal velocity with experimental observations in DIII-D [1] show improved agreement due to the allowance of larger toroidal flows. 6pt [1] W.M. Solomon, Phys. Plasmas 13, 056116 (2006).
Experiments on the Propagation of Plasma Filaments
Katz, Noam; Egedal, Jan; Fox, Will; Le, Ari; Porkolab, Miklos
2008-07-04
We investigate experimentally the motion and structure of isolated plasma filaments propagating through neutral gas. Plasma filaments, or 'blobs,' arise from turbulent fluctuations in a range of plasmas. Our experimental geometry is toroidally symmetric, and the blobs expand to a larger major radius under the influence of a vertical electric field. The electric field, which is caused by {nabla}B and curvature drifts in a 1/R magnetic field, is limited by collisional damping on the neutral gas. The blob's electrostatic potential structure and the resulting ExB flow field give rise to a vortex pair and a mushroom shape, which are consistent with nonlinear plasma simulations. We observe experimentally this characteristic mushroom shape for the first time. We also find that the blob propagation velocity is inversely proportional to the neutral density and decreases with time as the blob cools.
SOLAR WIND COLLISIONAL AGE FROM A GLOBAL MAGNETOHYDRODYNAMICS SIMULATION
Chhiber, R; Usmanov, AV; Matthaeus, WH; Goldstein, ML
2016-04-10
Simple estimates of the number of Coulomb collisions experienced by the interplanetary plasma to the point of observation, i.e., the “collisional age”, can be usefully employed in the study of non-thermal features of the solar wind. Usually these estimates are based on local plasma properties at the point of observation. Here we improve the method of estimation of the collisional age by employing solutions obtained from global three-dimensional magnetohydrodynamics simulations. This enables evaluation of the complete analytical expression for the collisional age without using approximations. The improved estimation of the collisional timescale is compared with turbulence and expansion timescales to assess the relative importance of collisions. The collisional age computed using the approximate formula employed in previous work is compared with the improved simulation-based calculations to examine the validity of the simplified formula. We also develop an analytical expression for the evaluation of the collisional age and we find good agreement between the numerical and analytical results. Finally, we briefly discuss the implications for an improved estimation of collisionality along spacecraft trajectories, including Solar Probe Plus.
Inflatable nested toroid structure
NASA Technical Reports Server (NTRS)
Johnson, Christopher J. (Inventor); Raboin, Jasen L. (Inventor); Spexarth, Gary R. (Inventor)
2011-01-01
An inflatable structure comprises at least two generally toroidal, inflatable modules. When in a deployed mode, the first, inner module has a major diameter less than that of a second, outer module and is positioned within the inner circumference of the outer module such that the first module is nested circumferentially alongside the second module. The inflatable structure, in a non-deployed, non-inflated mode, is of compact configuration and adapted to be transported to a site of deployment. When deployed, the inflatable structure is of substantially increased interior volume. In one embodiment, access between the interior of the first module and the second module is provided by at least one port or structural pass-through. In another embodiment, the inflatable structure includes at least one additional generally toroidal module external of and circumferentially surrounding the second module.
Simulation study of toroidal flow generation by ICRF heating using GNET code
NASA Astrophysics Data System (ADS)
Murakami, S.; Itoh, K.; Zheng, L. J.; van Dam, J. W.; Fukuyama, A.
2010-11-01
The toroidal flow generation by the ICRF heating is investigated in the tokamak plasma applying GNET code, in which the drift kinetic equation is solved in 5D phase-space. We assume a tokamak plasma similar to the Alcator C-mod plasma as a first step. We obtain a steady state distribution of energetic minority ions and the flux surface averaged toroidal flow is evaluated. It is found that a co-directional toroidal flow is generated outside of the RF wave power absorption region. The dominant part of toroidal flow does not depend on the sign of k. When we change the sign of the toroidal current we obtain a reversal of the toroidal flow velocity, which is consistent with the experimental observations. We consider the toroidal precession motion of energetic tail ions accelerated by the ICRF heating. The magnetic shear and the poloidal magnetic drift increases a net toroidal drift motion during one bounce of banana motion. We estimate the toroidal flow by these toroidal precession motion and the results are compared with the simulation ones.
Physics models in the toroidal transport code PROCTR
Howe, H.C.
1990-08-01
The physics models that are contained in the toroidal transport code PROCTR are described in detail. Time- and space-dependent models are included for the plasma hydrogenic-ion, helium, and impurity densities, the electron and ion temperatures, the toroidal rotation velocity, and the toroidal current profile. Time- and depth-dependent models for the trapped and mobile hydrogenic particle concentrations in the wall and a time-dependent point model for the number of particles in the limiter are also included. Time-dependent models for neutral particle transport, neutral beam deposition and thermalization, fusion heating, impurity radiation, pellet injection, and the radial electric potential are included and recalculated periodically as the time-dependent models evolve. The plasma solution is obtained either in simple flux coordinates, where the radial shift of each elliptical, toroidal flux surface is included to maintain an approximate pressure equilibrium, or in general three-dimensional torsatron coordinates represented by series of helical harmonics. The detailed coupling of the plasma, scrape-off layer, limiter, and wall models through the neutral transport model makes PROCTR especially suited for modeling of recycling and particle control in toroidal plasmas. The model may also be used in a steady-state profile analysis mode for studying energy and particle balances starting with measured plasma profiles.
Yamamoto, T; Shibata, T; Ohta, M; Yasumoto, M; Nishida, K; Hatayama, A; Mattei, S; Lettry, J; Sawada, K; Fantz, U
2014-02-01
To control the H(0) atom production profile in the H(-) ion sources is one of the important issues for the efficient and uniform surface H(-) production. The purpose of this study is to construct a collisional radiative (CR) model to calculate the effective production rate of H(0) atoms from H2 molecules in the model geometry of the radio-frequency (RF) H(-) ion source for Linac4 accelerator. In order to validate the CR model by comparison with the experimental results from the optical emission spectroscopy, it is also necessary for the model to calculate Balmer photon emission rate in the source. As a basic test of the model, the time evolutions of H(0) production and the Balmer Hα photon emission rate are calculated for given electron energy distribution functions in the Linac4 RF H(-) ion source. Reasonable test results are obtained and basis for the detailed comparisons with experimental results have been established.
Plasma rotation from momentum transport by neutrals in tokamaks
NASA Astrophysics Data System (ADS)
Omotani, J.; Pusztai, I.; Newton, S.; Fülöp, T.
2016-12-01
Neutral atoms can strongly influence the intrinsic rotation and radial electric field at the tokamak edge. Here, we present a framework to investigate these effects when the neutrals dominate the momentum transport. We explore the parameter space numerically, using highly flexible model geometries and a state of the art kinetic solver. We find that the most important parameters controlling the toroidal rotation and electric field are the major radius where the neutrals are localized and the plasma collisionality. This offers a means to influence the rotation and electric field by, for example, varying the radial position of the X-point to change the major radius of the neutral peak.
Free-boundary toroidal Alfven eigenmodes
Chen, Eugene Y.; Berk, H. L.; Breizman, B.; Zheng, L. J.
2011-05-15
A numerical study is presented for the n = 1 free-boundary toroidal Alfven eigenmodes (TAE) in tokamaks, which shows that there is considerable sensitivity of n = 1 modes to the position of the conducting wall. An additional branch of the TAE is shown to emerge from the upper continuum as the ratio of conducting wall radius to plasma radius increases. Such phenomena arise in plasma equilibria with both circular and shaped cross sections, where the shaped profile studied here is similar to that found in Alcator C-Mod.
Nonideal magnetohydrodynamic instabilities and toroidal magnetic confinement
Furth, H.P.
1985-05-01
The marked divergence of experimentally observed plasma instability phenomena from the predictions of ideal magnetohydrodynamics led in the early 1960s to the formulations of finite-resistivity stability theory. Beginning in the 1970s, advanced plasma diagnostics have served to establish a detailed correspondence between the predictions of the finite-resistivity theory and experimental plasma behavior - particularly in the case of the resistive kink mode and the tokamak plasma. Nonlinear resistive-kink phenomena have been found to govern the transport of magnetic flux and plasma energy in the reversed-field pinch. The other predicted finite-resistivity instability modes have been more difficult to identify directly and their implications for toroidal magnetic confinement are still unresolved.
Numerical Study of Tokamak Equilibrium with Toroidal Flow on EAST
NASA Astrophysics Data System (ADS)
Ren, Qilong; Zhang, Cheng
2006-09-01
The effect of the toroidal flow on the equilibrium of tokamak plasmas is a sensitive point for high performance plasma and its precise control. In this paper the effect is studied numerically using the EFIT (Equilibrium Fitting) code on EAST (Experimental Advanced Superconducting Tokamak). Firstly, the numerical calculation exhibits a clear outward shift of pressure contour from the magnetic surfaces in the plasma core and the shift grows with the increase of the toroidal velocity. The peak shift of 8% is observed when the ratio between the plasma velocity and the Alfvén speed equals to 0.15. Secondly, it is shown that the magnetic surfaces shift outwards from those without flow. With a certain plasma current the safety factor on the magnetic axis decreases as the plasma flow velocity increases. The magnetic shear increases about 10% on the plasma boundary compared with the case without flow.
Toroidal Alfven Waves in Advanced Tokamaks
NASA Astrophysics Data System (ADS)
Berk, Herbert L.
2003-10-01
In burning plasma experiments, alpha particles have speeds that readily resonate with shear Alfven waves. It is essential to understand this Alfven wave spectrum for toroidal plasma confinement. Most interest has focused on the Toroidal Alfven Eigenmode (TAE), and a method of analysis has been developed to understand the structure of this mode at a flux surface with a given magnetic shear. However, this model fails when the shear is too low or reversed. In this case a new method of analysis is required, which must incorporate novel fluid-like effects from the energetic particles [1] and also include effects that are second order in the inverse toroidal aspect ratio. With this new method [2] we can obtain spectral features that agree with experimental results. In particular, this theory gives an explanation for the so-called Cascade modes that have been observed in JT-60 [3], JET [4], and TFTR [5]. For these Cascade modes, slow upward frequency sweeping is observed, beginning from frequencies below the TAE range but then often blending into the TAE range of frequencies. The theoretical understanding of the Cascades modes has evolved to the point where these modes can be used as a diagnostic "signature" [6] to experimentally optimize the formation of thermal barriers in reversed-shear operation when the minimum q value is an integer. [1] H. L. Berk et al., Phys. Rev. Lett. 87, 185 (2002). [2] B. N. Breizman et al., submitted to Phys. Plasmas (2003). [3] H. Kimura et al., Nucl. Fusion 38, 1303 (1998). [4] S. Sharapov et al., Phys. Lett. A 289, 127 (2001); S. Sharapov, Phys. Plasmas 9, 2027 (2002). [5] R. Nazikian, H. L. Berk, et al., Bull. Am. Phys. Soc. 47, 327 (2002). [6] E. Joffrin et al., Plasma Phys. Contr. Fusion 44, 1739 (2002); E. Joffrin et al., in Proc. 2002 IAEA Fusion Energy Conference, submitted to Nucl. Fusion.
Compact Toroid Propagation in a Magnetized Drift Tube
NASA Astrophysics Data System (ADS)
Horton, Robert D.; Baker, Kevin L.; Hwang, David Q.; Evans, Russell W.
2000-10-01
Injection of a spheromak-like compact toroid (SCT) plasma into a toroidal plasma confinement device may require the SCT to propagate through a drift tube region occupied by a pre-existing magnetic field. This field is expected to extert a retarding force on the SCT, but may also result in a beneficial compression. The effects of transverse and longitudinal magnetic fields will be measured using the CTIX compact-toroid injector, together with a fast framing camera with an axial view of the formation, coaxial, and drift-tube regions. In the case of longitudinal magnetic field, comparisons will be made with the predictions of two-dimensional numerical simulation. The use of localized magnetic field to reduce plasma bridging of the insulating gap will also be investigated.
Bonanos, Peter
1983-01-01
A toroidal magnet for confining a high magnetic field for use in fusion reactor research and nuclear particle detection. The magnet includes a series of conductor elements arranged about and fixed at its small major radius portion to the outer surface of a central cylindrical support each conductor element having a geometry such as to maintain the conductor elements in pure tension when a high current flows therein, and a support assembly which redistributes all or part of the tension which would otherwise arise in the small major radius portion of each coil element to the large major radius portion thereof.
Transition from Collisionless to Collisional MRI
Prateek Sharma; Gregory W. Hammett; Eliot Quataert
2003-07-24
Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.
Collisional lifetimes of meteoroids
NASA Astrophysics Data System (ADS)
Soja, R. H.; Schwarzkopf, G. J.; Sommer, M.; Vaubaillon, J.; Albin, T.; Rodmann, J.; Grün, E.; Srama, R.
2016-01-01
Collisions of meteoroids with interplanetary dust grain fragments particles, dispersing larger particles amongst lower mass intervals. Here we use the method of Grün et al. (1985) and the IMEM interplanetary dust model to calculate the collisional lifetimes for different orbits, and for particles in different meteor showers. The timescales are usually long - of order 10^4 years for 1mm grains on Jupiter-family and Hally-type comet orbits. However, near-sun orbits particles suffer more frequent collisions and therefore have much shorter lifetimes. We discuss factors that affect the accuracy of these calculations.
The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX
Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.
2012-11-28
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
The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX
Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.
2012-11-27
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.
NASA Astrophysics Data System (ADS)
Biersack, Jochen P.
The collisional mixing of thin metal markers in silicon is investigated with the computer program TRIM-DYNAMIC (T-DYN). This code assumes that at high dose irradiation, the substrate Si or Ge, will get fully amorphized, and the recoil atom can stop in any position after slowing down below a certain final energy Ef (taken here as 3 eV). In order to avoid chemical effects, the system Au marker in a silicon matrix was chosen for the TRIM simulation. The results are in good agreement with the experimental findings, as compiled in the review article by Paine and Averback. Similar collisional mixing effects occur in the process of SIMS or Auger electron depth profiling, and cannot be avoided. An example is given here for a thin layer of arsenic vapor deposited on Si and covered by amorphous silicon. The analysing ion beam in this case was 14.5 keV Cs+ incident at 37° towards the surface normal. In comparison with the SIMS measurements by modern depth profiling equipment, again good agreement was found between the T-DYN results and the experiment.
Collisional-Radiative Kinetics in Monatomic Gases
NASA Astrophysics Data System (ADS)
Le, Hai; Karagozian, Ann
2012-11-01
A detailed model of electronic excited states is essential in capturing all the nonequilibrium processes of a partially ionized plasma by means of collisional and radiative interactions. This collisional-radiative (CR) model allows us to consider deviations from equilibrium distribution of the internal states, and is now more commonly used in the study of plasma discharges. Prior studies by Kapper and Cambier and Panesi et al. suggest that this level of detail is needed for an accurate prediction of the flow field, and it is particularly relevant to plasma-combustion interactions. The required number of excited states needed to be included in the CR model is often prohibitively large due to the nonequilibrium condition of the plasma. The consequence is a large system of ODE's which needs to be solved at each time step. A reduced mechanism for the CR model can be attained by grouping the upper states of the atomic state distribution (ASDF) into a pseudo-level in which the population is characterized either by a uniform distribution or a Boltzmann distribution. This talk presents both detailed and reduced models for an ionizing shock in Argon. Supported by the US Air Force/ERC, Inc. under subcontract RS111738.
Analytical solutions for Tokamak equilibria with reversed toroidal current
Martins, Caroline G. L.; Roberto, M.; Braga, F. L.; Caldas, I. L.
2011-08-15
In tokamaks, an advanced plasma confinement regime has been investigated with a central hollow electric current with negative density which gives rise to non-nested magnetic surfaces. We present analytical solutions for the magnetohydrodynamic equilibria of this regime in terms of non-orthogonal toroidal polar coordinates. These solutions are obtained for large aspect ratio tokamaks and they are valid for any kind of reversed hollow current density profiles. The zero order solution of the poloidal magnetic flux function describes nested toroidal magnetic surfaces with a magnetic axis displaced due to the toroidal geometry. The first order correction introduces a poloidal field asymmetry and, consequently, magnetic islands arise around the zero order surface with null poloidal magnetic flux gradient. An analytic expression for the magnetic island width is deduced in terms of the equilibrium parameters. We give examples of the equilibrium plasma profiles and islands obtained for a class of current density profile.
Shrinking instability of toroidal droplets.
Fragkopoulos, Alexandros A; Pairam, Ekapop; Berger, Eric; Segre, Phil N; Fernández-Nieves, Alberto
2017-03-14
Toroidal droplets are inherently unstable due to surface tension. They can break up, similar to cylindrical jets, but also exhibit a shrinking instability, which is inherent to the toroidal shape. We investigate the evolution of shrinking toroidal droplets using particle image velocimetry. We obtain the flow field inside the droplets and show that as the torus evolves, its cross-section significantly deviates from circular. We then use the experimentally obtained velocities at the torus interface to theoretically reconstruct the internal flow field. Our calculation correctly describes the experimental results and elucidates the role of those modes that, among the many possible ones, are required to capture all of the relevant experimental features.
Ribe, F.L.
1986-12-31
Progress over the past year has enabled us to complete the comprehensive experimental investigation of the equilibrium and stability of the linear heliac and the linear l = 1 stellarator configration. In the case of the heliac work, we discoverd axisymmetric hot plasma near the axial conductor (''hardcore'') in amounts which are comparable to the helically symmetric hot plasma centered on the magnetic axis. From this result came the motivation for an extended investigation which concentrates on the details of high-beta heliac formation. Important first results of the formation study have been obtained. In the case of the stellarator work, we have observed the flute-like m = 1 instability foe a specific set of experimental parameters and, for a different set, we have observed the mode stabilized by the combined effects of a finite ion Larmor radius and a nearby conducting wall. The single-discharge CV ion-temperature diagnostic system has been debugged and has yielded a heliac temperature measurement of (90 +- 10)eV. The plasma density diagnostic system based on cross-tube interferometry has been modified from its previous design for use with the somewhat wrinkly helical discharge tube.
Ryutov, D. D.
2015-12-01
Laser-generated interpenetrating plasma jets are widely used in the studies of collisionless interaction of counter-streaming plasmas in conjunction with possible formation of collisionless shocks. In a number of experiments of this type the plasma is formed on plastic targets made of CH or CD. The study of the DD neutron production from the interaction between two CD jets on the one hand and between a CD jet and a CH jet could serve as a qualitative indicator of the collisionless shock formation. The purpose of this memo is a discussion of the effect of collisions on the neutron generation in the interpenetrating CH and CD jets. First, the kinematics of the large-deflection collisions of the deuterons and carbon are discussed. Then the scattering angles are related with the corresponding Rutherford cross-section. After that expression for the number of the backscattered deuterons is provided, and their contribution to the neutron yield is evaluated. The results may be of some significance to the kinetic codes benchmarking and developing the neutron diagnostic.
Ion closure theory for high collisionality revisited
Ji, Jeong-Young Held, Eric D.
2015-06-15
According to analytical calculations of the ion collision operator, the ion-electron collision terms could be larger than the ion-ion collision terms. In the previous work [J.-Y. Ji and E. D. Held, Phys. Plasmas 20, 042114 (2013)], the ion-electron collision effects are diminished by the ion temperature change terms introduced from unlikely assumptions. In this work, the high-collisionality closures for ions are calculated without the temperature change terms. The ion-electron collision terms significantly modify existing closure coefficients.
Forced Magnetic Reconnection In A Tokamak Plasma
NASA Astrophysics Data System (ADS)
Callen, J. D.; Hegna, C. C.
2015-11-01
The theory of forced magnetic field reconnection induced by an externally imposed resonant magnetic perturbation usually uses a sheared slab or cylindrical magnetic field model and often focuses on the potential time-asymptotic induced magnetic island state. However, tokamak plasmas have significant magnetic geometry and dynamical plasma toroidal rotation screening effects. Also, finite ion Larmor radius (FLR) and banana width (FBW) effects can damp and thus limit the width of a nascent magnetic island. A theory that is more applicable for tokamak plasmas is being developed. This new model of the dynamics of forced magnetic reconnection considers a single helicity magnetic perturbation in the tokamak magnetic field geometry, uses a kinetically-derived collisional parallel electron flow response, and employs a comprehensive dynamical equation for the plasma toroidal rotation frequency. It is being used to explore the dynamics of bifurcation into a magnetically reconnected state in the thin singular layer around the rational surface, evolution into a generalized Rutherford regime where the island width exceeds the singular layer width, and assess the island width limiting effects of FLR and FBW polarization currents. Support by DoE grants DE-FG02-86ER53218, DE-FG02-92ER54139.
Simulation Study of Toroidal Flow Generation of Minority Ions by Local ICRF Heating
NASA Astrophysics Data System (ADS)
Murakami, Sadayoshi; Itoh, Kimitaka; Zheng, Linjin; Van Dam, James W.; Fukuyama, Atsushi
2015-12-01
The toroidal flow generation of minority ions by the local ion cyclotron range of frequencies (ICRF) heating is investigated in a tokamak plasma by applying the GNET code, which can solve the drift kinetic equation in the 5-D phase space. An asymmetry of velocity distribution function in the parallel direction is found and two types of toroidal averaged flow of minority ions are observed. One is the sheared flow near the RF power absorption region depending on the sign of k||, and the other is the toroidal flow, which is larger than the previous one, independent of the sign of k||. It is found that the k||-sign-independent toroidal flow is generated by the net toroidal motion of energetic tail ions and that the k||-sign-dependent flow is related to the mechanism proposed by Ohkawa [http://dx.doi.org/10.1063/1.2047629, Phys. Plasmas 12, 094506 (2005)].
Grinding Inside A Toroidal Cavity
NASA Technical Reports Server (NTRS)
Mayer, Walter; Adams, James F.; Burley, Richard K.
1987-01-01
Weld lines ground smooth within about 0.001 in. Grinding tool for smoothing longitudinal weld lines inside toroidal cavity includes curved tunnel jig to guide grinding "mouse" along weld line. Curvature of tunnel jig matched to shape of toroid so grinding ball in mouse follows circular arc of correct radius as mouse is pushed along tunnel. Tool enables precise control of grindout shape, yet easy to use.
Bott-Suzuki, Simon
2014-11-05
We have developed a new experimental platform to study bow-shock formation in plasma flows generated using an inverse wire array z-pinch. We have made significant progress on the analysis of both hydrodynamic and magnetized shocks using this system. The hydrodynamic experiments show formation of a well-defined Mach cone, and highly localized shock strong associated with radiative losses and rapidly cooling over the shock. Magnetized shocks show that the balance of magnetic and ram pressures dominate the evolution of the shock region, generating a low plasma beta void around the target. Manuscripts are in preparation for publication on both these topics. We have also published the development of a novel diagnostic method which allow recovery of interferometry and self-emission data along the same line of sight. Finally, we have carried out work to integrate a kinetic routine with the 3D MHD code Gorgon, however it remains to complete this process. Both undergraduate and graduate students have been involved in both the experimental work and publications.
FLYCHK Collisional-Radiative Code
National Institute of Standards and Technology Data Gateway
SRD 160 FLYCHK Collisional-Radiative Code (Web, free access) FLYCHK provides a capability to generate atomic level populations and charge state distributions for low-Z to mid-Z elements under NLTE conditions.
Inclined, collisional sediment transport
NASA Astrophysics Data System (ADS)
Berzi, Diego; Fraccarollo, Luigi
2013-10-01
We apply the constitutive relations of kinetic theory of granular gases to the transport of cohesionless sediments driven by a gravitational liquid turbulent stream in steady uniform conditions. The sediment-laden flow forms self-equilibrated mechanisms of resistance at the bed surface, below which the sediments are at rest. This geo-physical process takes place quite often in streams at moderate slope and may be interpreted through tools common to fluid mechanics and particle physics. Taking into account the viscous dissipation of the fluctuation energy of the particles, and using approximate methods of integration of the governing differential equations, permit to obtain a set of simple formulas for predicting how depths and flow rates adjust to the angle of inclination of the bed, without requiring additional tuning parameters besides the particle and fluid properties. The agreement with laboratory experiments performed with either plastic cylinders or gravel in water is remarkable. We also provide quantitative criteria to determine the range of validity of the theory, i.e., the values of the Shields number and the angle of inclination of the bed for which the particle stresses can be mostly ascribed to collisional exchange of momentum.
Investigation of the Electron-Ion Hybrid Instability in a Collisional Environment
NASA Astrophysics Data System (ADS)
Tejero, E. M.; Enloe, L.; Sotnikov, V. I.; Amatucci, B.; Ganguli, G.
2013-12-01
The Electron-Ion Hybrid (EIH) instability, a transverse velocity shear-driven instability with frequency near the lower hybrid frequency, was previously predicted theoretically to explain the observation of lower hybrid waves in applications from the plasma sheet boundary layer to laser produced plasmas. The EIH instability has also been observed in the laboratory in scaled magnetospheric plasma conditions and in laser produced plasma expansion experiments across magnetic fields. In the work presented, we have expanded the theoretical framework to highly collisional plasmas for applications to the plasma region surrounding a hypersonic vehicle. In this collisional plasma layer, strongly sheared transverse flows can exist that can give rise to the EIH instability. We wish to study whether the resulting lower hybrid turbulence can impede communication to and from the hypersonic vehicle. Results from theory and a comparison from laboratory experiments on the generation of the EIH instability in a collisional plasma environment will be presented.
Investigation of rotation at the plasma edge in TCABR
NASA Astrophysics Data System (ADS)
Severo, J. H. F.; Ronchi, G.; Galvao, R. M. O.; Nascimento, I. C.; Guimaraes-Filho, Z. O.; Kuznetsov, Yu. K.; Nave, M. F. F.; Oliveira, A. M.; do Nascimento, F.; Tendler, M.
2015-09-01
This paper summarizes experimental results from recent studies on intrinsic rotation at the plasma edge of the TCABR tokamak. These results were obtained after upgrading the number of channels of the rotation diagnostic to three. The measurements were carried out in the collisional (Pfirsch-Schluter) regime and the rotation profiles of the ions were obtained from the Doppler shifts of the impurity carbon lines, CIII (464.74 nm), and CVI (529.06 nm). Results on the correlation between toroidal rotation at the plasma edge and direction of gas injection are also presented. They indicate that the direction of gas injection has a small effect on rotation; the velocity of the background neutral hydrogen is affected by direct momentum transfer from the injected gas (also hydrogen), while the carbon ions' velocity is affected by inward radial friction force between the injected gas atoms and ions, increasing their velocity in the opposite sense of the plasma current.
Plasma resistivity measurements in the Wisconsin levitated octupole
Brouchous, D. A.
1980-11-01
Resistivity measurements parallel to the magnetic field were made on gun injected plasmas ranging in density from 10/sup 9/cm/sup -3/ to 10/sup 1/parallelcm/sup -3/ in the Wisconsin levitated octupole with toroidal and poloidal magnetic fields. The 10/sup 9/cm/sup -3/ plasma was collisionless with lambda/sub mfp/ > 100 mirror lengths, had T/sub e/ = 10 eV, T/sub i/ = 30 eV and was found to have anomalous resistivity scaling like eta = ..sqrt..T/sub e//n/sub e/ when E/sub parallel/ > E/su c/ is the Dreicer critical field. The 10/sup 12/cm/sup -3/ plasma was collisional with lambda/sub mfp/ < mirror length, had T/sub e/ = T/sub i/ approx. = .2 eV and was found to have Spitzer resistivity when E/sub parallel/ < E/sub c/.
Control of toroidal-like asymmetries in a heliac
Spanjers, G.G.; Nelson, B.A.; Ribe, F.L.; Jarboe, T.R. ); Barnes, D.C. )
1993-05-01
A simple modification to the heliac coil configuration [A. H. Boozer [ital et] [ital al]., [ital Plasma] [ital Physics] [ital and] [ital Controlled] [ital Nuclear] [ital Fusion] (International Atomic Energy Agency, Vienna, 1966), Vol. 1, p. 103] is described that reduces the toroidal perturbation to the magnetic field structure and significantly restores the helical symmetry. This is accomplished by shifting the internal current-carrying conductor (hardcore) of the heliac radially inward from its normal position at the geometric center of the external [ital l]=1 coils. It is shown by computations that a large-aspect-ratio toroidal heliac is similar to a helically symmetric linear heliac in which the hardcore has been shifted. This similarity is seen in the analytic form of the magnetic potential, the flux surface shape, and in the harmonic spectra of the field lines. It is then shown that the toroidicity perturbations can be reduced in a toroidal heliac by combining these effects---using a radially inward hardcore shift in the toroidal configuration. In the experiments reported here the toroidal-like effects are created in the linear High Beta Q Machine (HBQM) heliac [C. M. Greenfield [ital et] [ital al]., Phys. Fluids B [bold 2], 133 (1990)] by shifting the hardcore off the geometric center of the [ital l]=1 coils. The induced toroidal-like effects are seen from an asymmetry in the axial excluded flux; however, no decrease in global beta is seen as compared to the unshifted symmetric case (G. G. Spanjers, Ph.D. dissertation, University of Washington, 1992) indicating the absence of large-scale magnetohydrodynamic instabilities at high beta.
Progress in toroidal confinement and fusion research
Furth, H.P.
1987-10-01
During the past 30 years, the characteristic T/sub i/n tau/sub E/-value of toroidal-confinement experiments has advanced by more than seven orders of magnitude. Part of this advance has been due to an increase of gross machine parameters. Most of this advance has been due to an increase of gross machine parameters. Most of the advance is associated with improvements in the ''quality of plasma confinement.'' The combined evidence of spherator and tokamak research clarifies the role of magnetic-field geometry in determining confinement and points to the importance of shielding out plasma edge effects. A true physical understanding of anomalous transport remains to be achieved. 39 refs., 11 figs., 1 tab.
Vlasov tokamak equilibria with sheared toroidal flow and anisotropic pressure
Kuiroukidis, Ap; Throumoulopoulos, G. N.; Tasso, H.
2015-08-15
By choosing appropriate deformed Maxwellian ion and electron distribution functions depending on the two particle constants of motion, i.e., the energy and toroidal angular momentum, we reduce the Vlasov axisymmetric equilibrium problem for quasineutral plasmas to a transcendental Grad-Shafranov-like equation. This equation is then solved numerically under the Dirichlet boundary condition for an analytically prescribed boundary possessing a lower X-point to construct tokamak equilibria with toroidal sheared ion flow and anisotropic pressure. Depending on the deformation of the distribution functions, these steady states can have toroidal current densities either peaked on the magnetic axis or hollow. These two kinds of equilibria may be regarded as a bifurcation in connection with symmetry properties of the distribution functions on the magnetic axis.
Ryutov, D. D.
2015-12-08
Part 1 of this note considered the kinematics of large-angle scattering (LAS) of the deuterons on the counter-streaming carbon ions, with both flows having the same velocity V. Due to a large mass ratio m_{C}/m_{D}, the backscattered deuterons have high velocity of up to (24/7)V. This significantly increases the cross-section for the neutron production in the collisions between the back-scattered and incoming deuterons and may provide significant contribution to the total neutron yield, despite the smallness of a large-angle Coulomb cross-section. This effect becomes particularly important when only one of the colliding streams is made of CD, whereas the other stream is made of CH. Part 1 evaluated the neutron yield produced by this mechanism and have found that its relative role increases for higher plasma densities and lower velocities. Part 2 discusses signatures of this effect which can be used to identify it experimentally and also discusses in some more detail its spatio-temporal characteristics. It goes without saying that a complete quantitative assessment should be based on numerical simulations accounting for the large-angle scattering.
Podesta, M; Fredrickson, E D; Gorelenkov, N N; LeBlanc, B P; Heidbrink, W W; Crocker, N A; Kubota, S
2010-08-19
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Podesta, M.; Bell, R. E.; Fredrickson, E. D.; Gorelenkov, N. N.; LeBlanc, B. P.; Heidbrink, W. W.; Crocker, N. A.; Kubota, S.; Yuh, H.
2010-12-15
The effects of a sheared toroidal rotation on the dynamics of bursting toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of decorrelation of the modes by the sheared rotation is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes on NSTX.
3D toroidal physics: Testing the boundaries of symmetry breaking
Spong, Donald A.
2015-05-15
Toroidal symmetry is an important concept for plasma confinement; it allows the existence of nested flux surface MHD equilibria and conserved invariants for particle motion. However, perfect symmetry is unachievable in realistic toroidal plasma devices. For example, tokamaks have toroidal ripple due to discrete field coils, optimized stellarators do not achieve exact quasi-symmetry, the plasma itself continually seeks lower energy states through helical 3D deformations, and reactors will likely have non-uniform distributions of ferritic steel near the plasma. Also, some level of designed-in 3D magnetic field structure is now anticipated for most concepts in order to provide the plasma control needed for a stable, steady-state fusion reactor. Such planned 3D field structures can take many forms, ranging from tokamaks with weak 3D edge localized mode suppression fields to stellarators with more dominant 3D field structures. This motivates the development of physics models that are applicable across the full range of 3D devices. Ultimately, the questions of how much symmetry breaking can be tolerated and how to optimize its design must be addressed for all fusion concepts. A closely coupled program of simulation, experimental validation, and design optimization is required to determine what forms and amplitudes of 3D shaping and symmetry breaking will be compatible with the requirements of future fusion reactors.
3D toroidal physics: Testing the boundaries of symmetry breakinga)
NASA Astrophysics Data System (ADS)
Spong, Donald A.
2015-05-01
Toroidal symmetry is an important concept for plasma confinement; it allows the existence of nested flux surface MHD equilibria and conserved invariants for particle motion. However, perfect symmetry is unachievable in realistic toroidal plasma devices. For example, tokamaks have toroidal ripple due to discrete field coils, optimized stellarators do not achieve exact quasi-symmetry, the plasma itself continually seeks lower energy states through helical 3D deformations, and reactors will likely have non-uniform distributions of ferritic steel near the plasma. Also, some level of designed-in 3D magnetic field structure is now anticipated for most concepts in order to provide the plasma control needed for a stable, steady-state fusion reactor. Such planned 3D field structures can take many forms, ranging from tokamaks with weak 3D edge localized mode suppression fields to stellarators with more dominant 3D field structures. This motivates the development of physics models that are applicable across the full range of 3D devices. Ultimately, the questions of how much symmetry breaking can be tolerated and how to optimize its design must be addressed for all fusion concepts. A closely coupled program of simulation, experimental validation, and design optimization is required to determine what forms and amplitudes of 3D shaping and symmetry breaking will be compatible with the requirements of future fusion reactors.
Coaxial helicity injection in open-flux low-aspect-ratio toroidal discharges
Redd, A. J.; Jarboe, T. R.; Nelson, B. A.; O'Neill, R. G.; Smith, R. J.
2007-11-15
Open-flux low-aspect-ratio toroidal discharges generated and sustained by coaxial helicity injection (CHI) in the Helicity Injected Torus device (HIT-II) are described. The discharges in this study are flux tubes directly connected to the CHI electrodes, with poloidal flux less than or equal to the CHI injector flux, and no possibility of a significant closed-flux plasma core. Theoretically derived scalings for the dependence of CHI injector current on the toroidal field current and magnitude of the injector flux are experimentally confirmed, and empirical models are developed for the poloidal magnetic field and toroidal plasma current in open-flux discharges. In particular, the toroidal plasma current is independent of the toroidal magnetic field, both theoretically and empirically. Variations in injector flux geometry demonstrate that the CHI injector current leaves the electrode surfaces at the flux strike points, and that the relative width of the CHI injector determines whether the dominant observed relaxation mechanism is a harmonic mode at the plasma edge or reconnection near the CHI electrodes. In the case of an effective interelectrode distance approximately equal to the device minor radius, the ratio of toroidal plasma current to CHI injector current is maximized. Global magnetic equilibrium quantities and local magnetic measurements are consistent with modelling these open-flux discharges as thin current sheets connected to the CHI electrodes.
Concentric Nested Toroidal Inflatable Structures
NASA Technical Reports Server (NTRS)
Johnson, Christopher J.; Raboin, Jasen L.; Spexarth, Gary R.
2010-01-01
Assemblies comprising multiple limited- height toroidal inflatable structures nested in a concentric arrangement have been invented to obtain more design flexibility than can be obtained in single taller, wider toroidal inflatable structures (see figure). Originally intended for use as containers for habitats for humans in outer space or on remote planets, these and related prior inflatable structures could also be useful on Earth as lightweight, compactly stowable, portable special-purpose buildings that could be transported to remote locations and there inflated to full size and shape. In the case of a single inflatable toroidal structure, one important source of lack of design flexibility is the fact that an increase in outer diameter (which is sometimes desired) is necessarily accompanied by an increase in height (which is sometimes undesired). Increases in diameter and height can also cause difficulty in utilization of the resulting larger volume, in that it can become necessary to partition the volume by means of walls and floors, and features (e.g., stairs or ladders) must be added to enable vertical movement between floors. Moreover, ascending and descending between floors in a gravitational environment could pose unacceptable difficulty for the inhabitants under some circumstances. Another source of lack of design flexibility in a single toroidal inflatable structure is that for a given inflation pressure, an increase in the outer diameter of the structure necessarily entails an increase in the maximum stress in the structure. Because it is necessary to keep the maximum stress within the load-bearing capability of the structural materials, consistent with other aspects of the design, this may translate to a limit on the outer diameter. In an assembly comprising concentric nested toroidal structures, an increase in outer diameter does not necessarily entail an increase in height or a maximum stress in excess of the load-bearing capability of the structural
NASA Astrophysics Data System (ADS)
Liu, Yueqiang; Ryan, D.; Kirk, A.; Li, Li; Suttrop, W.; Dunne, M.; Fischer, R.; Fuchs, J. C.; Kurzan, B.; Piovesan, P.; Willensdorfer, M.; the ASDEX Upgrade Team; the EUROfusion MST1 Team
2016-05-01
The plasma response to the vacuum resonant magnetic perturbation (RMP) fields, produced by the ELM control coils in ASDEX Upgrade experiments, is computationally modelled using the MARS-F/K codes (Liu et al 2000 Phys. Plasmas 7 3681, Liu et al 2008 Phys. Plasmas 15 112503). A systematic investigation is carried out, considering various plasma and coil configurations as in the ELM control experiments. The low q plasmas, with {{q}95}˜ 3.8 (q 95 is the safety factor q value at 95% of the equilibrium poloidal flux), responding to low n (n is the toroidal mode number) field perturbations from each single row of the ELM coils, generates a core kink amplification effect. Combining two rows, with different toroidal phasing, thus leads to either cancellation or reinforcement of the core kink response, which in turn determines the poloidal location of the peak plasma surface displacement. The core kink response is typically weak for the n = 4 coil configuration at low q, and for the n = 2 configuration but only at high q ({{q}95}˜ 5.5 ). A phase shift of around 60 degrees for low q plasmas, and around 90 degrees for high q plasmas, is found in the coil phasing, between the plasma response field and the vacuum RMP field, that maximizes the edge resonant field component. This leads to an optimal coil phasing of about 100 (-100) degrees for low (high) q plasmas, that maximizes both the edge resonant field component and the plasma surface displacement near the X-point of the separatrix. This optimal phasing closely corresponds to the best ELM mitigation observed in experiments. A strong parallel sound wave damping moderately reduces the core kink response but has minor effect on the edge peeling response. For low q plasmas, modelling shows that both the resonant electromagnetic torque and the neoclassical toroidal viscous (NTV) torque (due to the presence of 3D magnetic field perturbations) contribute to the toroidal flow damping, in particular near the
Turbulence-driven bootstrap current in low-collisionality tokamaks.
McDevitt, C J; Tang, Xian-Zhu; Guo, Zehua
2013-11-15
Neoclassical bootstrap current is expected to provide a significant fraction of the equilibrium plasma current in tokamak reactors. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons and thus driving a bootstrap current. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.
Material equations for electromagnetism with toroidal polarizations.
Dubovik, V M; Martsenyuk, M A; Saha, B
2000-06-01
With regard to the toroid contributions, a modified system of equations of electrodynamics moving continuous media has been obtained. Alternative formalisms to introduce the toroid moment contributions in the equations of electromagnetism has been worked out. The two four-potential formalism has been developed. Lorentz transformation laws for the toroid polarizations has been given. Covariant form of equations of electrodynamics of continuous media with toroid polarizations has been written.
Toroidal Tank Development for Upper-stages
NASA Technical Reports Server (NTRS)
DeLay, Tom; Roberts, Keith
2003-01-01
The advantages, development, and fabrication of toroidal propellant tanks are profiled in this viewgraph presentation. Several images are included of independent research and development (IR&D) of toroidal propellant tanks at Marshall Space Flight Center (MSFC). Other images in the presentation give a brief overview of Thiokol conformal tank technology development. The presentation describes Thiokol's approach to continuous composite toroidal tank fabrication in detail. Images are shown of continuous and segmented toroidal tanks fabricated by Thiokol.
Observation of Central Toroidal Rotation Induced by ICRF on EAST
NASA Astrophysics Data System (ADS)
Pan, Xiayun; Wang, Fudi; Zhang, Xinjun; Lyu, Bo; Chen, Jun; Li, Yingying; Fu, Jia; Shi, Yuejiang; Yu, Yi; Ye, Minyou; Wan, Baonian
2016-02-01
Core plasma rotation of both L-mode and H-mode discharges with ion cyclotron range of frequency (ICRF) minority heating (MH) scheme was measured with a tangential X-ray imaging crystal spectrometer on EAST (Experimental Advanced Superconducting Tokamak). Co-current central impurity toroidal rotation change was observed in ICRF-heated L- and H-mode plasmas. Rotation increment as high as 30 km/s was generated at ∼1.7 MW ICRF power. Scaling results showed similar trend as the Rice scaling but with significant scattering, especially in L-mode plasmas. We varied the plasma current, toroidal field and magnetic configuration individually to study their effect on L-mode plasma rotation, while keeping the other major plasma parameters and heating unchanged during the scanning. It was found that larger plasma current could induce plasma rotation more efficiently. A scan of the toroidal magnetic field indicated that the largest rotation was obtained for on-axis ICRF heating. A comparison between lower-single-null (LSN) and double-null (DN) configurations showed that LSN discharges rendered a larger rotation change for the same power input and plasma parameters. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB112004 and 2015GB103002), National Natural Science Foundation of China (Nos. 11175208, 11305212, 11375235, 11405212 and 11261140328), the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology (2014FXCX003) and Brain Korea 21 Program for Leading Universities & Students (BK21 PLUS)
Neoclassical offset toroidal velocity and auxiliary ion heating in tokamaks
NASA Astrophysics Data System (ADS)
Lazzaro, E.
2016-05-01
In conditions of ideal axisymmetry, for a magnetized plasma in a generic bounded domain, necessarily toroidal, the uniform absorption of external energy (e.g., RF or any isotropic auxiliary heating) cannot give rise to net forces or torques. Experimental evidence on contemporary tokamaks shows that the near central absorption of RF heating power (ICH and ECH) and current drive in presence of MHD activity drives a bulk plasma rotation in the co- I p direction, opposite to the initial one. Also the appearance of classical or neoclassical tearing modes provides a nonlinear magnetic braking that tends to clamp the rotation profile at the q-rational surfaces. The physical origin of the torque associated with P RF absorption could be due the effects of asymmetry in the equilibrium configuration or in power deposition, but here we point out also an effect of the response of the so-called neoclassical offset velocity to the power dependent heat flow increment. The neoclassical toroidal viscosity due to internal magnetic kink or tearing modes tends to relax the plasma rotation to this asymptotic speed, which in absence of auxiliary heating is of the order of the ion diamagnetic velocity. It can be shown by kinetic and fluid calculations, that the absorption of auxiliary power by ions modifies this offset proportionally to the injected power thereby forcing the plasma rotation in a direction opposite to the initial, to large values. The problem is discussed in the frame of the theoretical models of neoclassical toroidal viscosity.
Observations of Intrinsic Rotation Reversal Hysteresis in Alcator C-Mod Plasmas
NASA Astrophysics Data System (ADS)
Cao, Norman; Rice, John; White, Anne; Baek, Seung; Chilenski, Mark; Creely, Alexander; Ennever, Paul; Hubbard, Amanda; Hughes, Jerry; Irby, Jim; Rodriguez-Fernandez, Pablo; Reinke, Matthew; Diamond, Patrick; Alcator C-Mod Team
2016-10-01
Intrinsic core toroidal rotation in Alcator C-Mod L-mode plasmas has been observed to spontaneously reverse direction when the normalized collisionality ν*, evaluated at the profile minimum, passes through a critical value around 0.4. In Ohmic plasmas, the low density linear Ohmic confinement regime exhibits co-current toroidal rotation, and the higher density saturated Ohmic confinement regime exhibits counter-current rotation. The reversal manifests a hysteresis loop in ν*, where the critical collisionalities for the forward and reverse transitions differ by 10-15%. There appears to be memory associated with the rotation state, since reversals which do not begin from fully saturated rotation states do not manifest this hysteresis. In addition, high-k PCI fluctuation ``wings'' (kθρs up to 1) at low density and high current appear only in the co-current rotation state, while density peaking and ``non-local'' heat transport behavior do not appear to change significantly with the rotation state. Results from fluctuation measurements and preliminary transport and stability analyses will also be presented. This work is supported by the US DOE under Grant DE-FC02-99ER54512 (C-Mod).
Toroidal momentum transport in a tokamak due to profile shearing
Buchholz, R.; Grosshauser, S. R.; Hornsby, W. A.; Migliano, P.; Peeters, A. G.; Camenen, Y.; Casson, F. J.
2014-06-15
The effect of profile shearing on toroidal momentum transport is studied in linear and non-linear gyro-kinetic simulations. Retaining the radial dependence of both plasma and geometry parameters leads to a momentum flux that has contributions both linear in the logarithmic gradients of density and temperature, as well as contributions linear in the derivatives of the logarithmic gradients. The effect of the turbulence intensity gradient on momentum transport is found to be small for the studied parameters. Linear simulations at fixed normalized toroidal wave number predict a weak dependence of the momentum flux on the normalized Larmor radius ρ{sub *}=ρ/R. Non-linear simulations, however, at sufficiently small ρ{sub *} show a linear scaling of the momentum flux with ρ{sub *}. The obtained stationary rotation gradients are in the range of, although perhaps smaller than, current experiments. For a reactor plasma, however, a rather small rotation gradient should result from profile shearing.
Experimental studies of compact toroids. Progress report, 1990--1991
Not Available
1991-12-01
The Berkeley Compact Toroid Experiment (BCTX) device is a plasma device with a Marshall-gun generated, low aspect ratio toroidal plasma. The device is capable of producing spheromak-type discharges and may, with some modification, produce low-aspect ratio tokamak configurations. A unique aspect of this experimenal devie is its large lower hybrid (LH) heating system, which consists of two 450MHz klystron tubes generating 20 megawatts each into a brambilla-type launching structure. Successful operation with one klystron at virtually full power (18 MW) has been accomplished with 110 {mu}s pulse length. A second klystron is currently installed in its socket and magnet but has not been added to the RF drive system. This report describes current activities and accomplishments and describes the anticipated results of next year`s activity.
Nonlinear stability of field-reversed configurations with self-generated toroidal field
Omelchenko, Y. A.; Schaffer, M. J.; Parks, P. B.
2001-10-01
The field-reversed configuration (FRC) is a high-beta compact toroidal plasma confinement scheme in which the external poloidal field is reversed on the geometric axis by azimuthal (toroidal) plasma current. A quasineutral, hybrid, particle-in-cell (PIC) approach [Y. A. Omelchenko and R. N. Sudan, Phys. Plasmas 2, 2773 (1995)] is applied to study long-term nonlinear stability of computational FRC equilibria to a number of toroidal modes, including the most disruptive tilt mode. In particular, a self-generated toroidal magnetic field is found to be an important factor in mitigating the instability and preventing the confinement disruption. This is shown to be a unique FRC property resulting from the Hall effect in the regions of vanishing poloidal magnetic field. The instability-driven toroidal field stabilizes kink formation by increasing the magnetic field energy without destabilizing curvature-driven plasma motion. Finally, the tilt instability saturates due to nonlinear, finite Larmor radius (FLR) effects and plasma relaxation to a quasisteady kinetic state. During this transition the FRC is shown to dissipate a substantial amount of initially trapped flux and plasma energy. These effects are demonstrated for kinetic and fluid-like, spherical and prolate FRCs.
Resonant-magnetic-perturbation-induced plasma transport in H-mode pedestals
Callen, J. D.; Hegna, C. C.; Cole, A. J.
2012-11-15
Plasma toroidal rotation reduces reconnection of externally applied resonant magnetic perturbation (RMP) fields {delta}B on rational (q = m/n) magnetic flux surfaces. Hence, it causes radial perturbations {delta}B{sub {rho}m/n} to be small there, and thus inhibits magnetic island formation and stochasticity in the edge of high (H-) mode confinement tokamak plasmas. However, electron collisional damping combined with the spatial magnetic flutter {delta}B{sub {rho}m/n} induced by RMPs in the vicinity of rational surfaces causes a radial electron heat diffusivity in which {chi}{sub e Parallel-To }{sup eff}{approx}(v{sub Te}{sup 2}/{nu}{sub e})/(1+x{sup 2}/{delta}{sub Parallel-To }{sup 2}) is an effective parallel electron thermal diffusivity. These effects are reduced by magnetic shear effects at a distance x from rational surfaces for |x|>{delta}{sub Parallel-To} but amplified for {delta}B-caret{sub {rho}m/n}(x)>{delta}B-caret{sub {rho}m/n}(0). A kinetic, toroidal model of these RMP-flutter-induced plasma transport effects is developed and compared to a previously developed cylindrical model. The RMP-induced increases in plasma transport can be large enough to reduce plasma gradients in H-mode pedestals. Thus, they may contribute to suppressing edge localized modes in tokamak plasmas.
Finite Larmor Radius and Collisional Effects on the Electron-Ion Hybrid Instability
2013-11-18
Particle Physics Branch Plasma Physics Division V. SoTnikoV Air Force Research Laboratory Dayton, Ohio C.l. EnloE Air Force Academy Colorado Springs...applying this theory to the plasma region surrounding hypersonic vehicles. In this plasma layer, these sorts of transverse sheared flows can exist in...a collisional plasma . While this dense layer of plasma can itself impede communications, the density structures created by the lower hybrid
Toroidal universal drift instability: A global gyrokinetic study
Chowdhury, J.; Ganesh, R.; Brunner, S.; Vaclavik, J.; Villard, L.
2010-10-15
An electron density gradient driven instability identified as the toroidal branch of the universal drift instability is studied using a global gyrokinetic model treating both electrons and ions fully nonadiabatically and valid at all orders in the ratio of the Larmor radius to the wavelength. The physics of the magnetic drift resonance, Landau resonance and transit resonance, which are considered to be important for the toroidal universal mode, are kept for both species. A systematic parametric study is carried out for the mode. The toroidal universal drift mode is observed to sustain finite temperature gradient and can thus coexist with the temperature gradient driven modes and may contribute to the observed particle transport along with other drift modes. Especially at intermediate scales between the ion temperature gradient driven mode and electron temperature gradient driven mode, this branch of the drift instability can also be a plausible candidate for the observed particle loss. The effect of magnetic fluctuations on the mode is also investigated. In contrast to the slab mode, the toroidal branch of the universal drift mode is found to be strongly stabilized by electromagnetic effects at finite plasma {beta}. Finally, the effect of trapped electrons on the universal mode is studied and compared with the other possible modes in the same parameter regime, namely, ion temperature gradient mode in the presence of trapped electrons and pure trapped electron modes.
Sawtooth Instability in the Compact Toroidal Hybrid
NASA Astrophysics Data System (ADS)
Herfindal, J. L.; Maurer, D. A.; Hartwell, G. J.; Ennis, D. A.; Knowlton, S. F.
2015-11-01
Sawtooth instabilities have been observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator/tokamak hybrid device. The sawtooth instability is driven by ohmic heating of the core plasma until the safety factor drops below unity resulting in the growth of an m = 1 kink-tearing mode. Experiments varying the vacuum rotational transform from 0.02 to 0.13 are being conducted to study sawtooth property dependance on vacuum flux surface structure. The frequency of the sawtooth oscillations increase from 2 kHz to 2.8 kHz solely due the decrease in rise time of the oscillation, the crash time is unchanged. CTH has three two-color SXR cameras, a three-channel 1mm interferometer, and a new bolometer system capable of detecting the signatures of sawtooth instabilities. The new bolometer system consists of two cameras, each containing a pair of diode arrays viewing the plasma directly or through a beryllium filter. Electron temperature measurements are found with the two-color SXR cameras through a ratio of the SXR intensities. Impurity radiation can drastically affect the electron temperature measurement, therefore new filters consisting of aluminum and carbon were selected to avoid problematic line radiation while maximizing the signal for a 100 eV plasma. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.
Prospects for toroidal fusion reactors
Sheffield, J.; Galambos, J.D.
1994-06-01
Work on the International Thermonuclear Experimental Reactor (ITER) tokamak has refined understanding of the realities of a deuterium-tritium (D-T) burning magnetic fusion reactor. An ITER-like tokamak reactor using ITER costs and performance would lead to a cost of electricity (COE) of about 130 mills/kWh. Advanced tokamak physics to be tested in the Toroidal Physics Experiment (TPX), coupled with moderate components in engineering, technology, and unit costs, should lead to a COE comparable with best existing fission systems around 60 mills/kWh. However, a larger unit size, {approximately}2000 MW(e), is favored for the fusion system. Alternative toroidal configurations to the conventional tokamak, such as the stellarator, reversed-field pinch, and field-reversed configuration, offer some potential advantage, but are less well developed, and have their own challenges.
Hollow nanotubular toroidal polymer microrings.
Lee, Jiyeong; Baek, Kangkyun; Kim, Myungjin; Yun, Gyeongwon; Ko, Young Ho; Lee, Nam-Suk; Hwang, Ilha; Kim, Jeehong; Natarajan, Ramalingam; Park, Chan Gyung; Sung, Wokyung; Kim, Kimoon
2014-02-01
Despite the remarkable progress made in the self-assembly of nano- and microscale architectures with well-defined sizes and shapes, a self-organization-based synthesis of hollow toroids has, so far, proved to be elusive. Here, we report the synthesis of polymer microrings made from rectangular, flat and rigid-core monomers with anisotropically predisposed alkene groups, which are crosslinked with each other by dithiol linkers using thiol-ene photopolymerization. The resulting hollow toroidal structures are shape-persistent and mechanically robust in solution. In addition, their size can be tuned by controlling the initial monomer concentrations, an observation that is supported by a theoretical analysis. These hollow microrings can encapsulate guest molecules in the intratoroidal nanospace, and their peripheries can act as templates for circular arrays of metal nanoparticles.
Investigation of compact toroid physics. Annual report, period ending September 30, 1980
Vlases, G C; Pietrzyk, Z A
1980-01-01
In the past year the major emphases have been on: (a) initiation of a small high density compact toroid experiment of the FRC configuration, characterized by no toroidal field and high ..beta..; (b) construction and testing of an imploding shell device for plasma heating; and (c) two-dimensional modeling of CT-FRC plasmas for our own use, as well as for interpretation and predictions for experiments at LASL and MSNW. In addition, we have nearly completed our work on material end plugging of dense linear open field plasma columns.
Uniform derivation of Coulomb collisional transport thanks to Debye shielding
NASA Astrophysics Data System (ADS)
Escande, Dominique; Elskens, Yves; Doveil, Fabrice
2016-10-01
The effective potential acting on particles in plasmas being essentially the Debye-shielded Coulomb potential, the particles collisional transport in thermal equilibrium is calculated for all impact parameters b, with a convergent expression reducing to Rutherford scattering for small b, in agreement with both usual expressions holding for large b and small b. No cutoff at the Debye length scale is needed, and the Coulomb logarithm is only slightly modified.
Magnetic Properties of 3D Printed Toroids
NASA Astrophysics Data System (ADS)
Bollig, Lindsey; Otto, Austin; Hilpisch, Peter; Mowry, Greg; Nelson-Cheeseman, Brittany; Renewable Energy; Alternatives Lab (REAL) Team
Transformers are ubiquitous in electronics today. Although toroidal geometries perform most efficiently, transformers are traditionally made with rectangular cross-sections due to the lower manufacturing costs. Additive manufacturing techniques (3D printing) can easily achieve toroidal geometries by building up a part through a series of 2D layers. To get strong magnetic properties in a 3D printed transformer, a composite filament is used containing Fe dispersed in a polymer matrix. How the resulting 3D printed toroid responds to a magnetic field depends on two structural factors of the printed 2D layers: fill factor (planar density) and fill pattern. In this work, we investigate how the fill factor and fill pattern affect the magnetic properties of 3D printed toroids. The magnetic properties of the printed toroids are measured by a custom circuit that produces a hysteresis loop for each toroid. Toroids with various fill factors and fill patterns are compared to determine how these two factors can affect the magnetic field the toroid can produce. These 3D printed toroids can be used for numerous applications in order to increase the efficiency of transformers by making it possible for manufacturers to make a toroidal geometry.
Lemons, D.S.; Feldman, W.C.
1983-09-01
A theoretical model of suprathermal halo or strahl solar wind electrons, including both binary collisions and conservative force fields, is proposed. From this model we derive the collisionally modified electron pitch angle distribution and compare it with relevant measurements made in the solar wind at 1 AU by using the Los Alamos IMP 8 plasma analyzer. Although the collisionally modified distribution is more isotropic than that predicted by simple exospheric theory, it is not isotropic enough to describe the measurements.
Neoclassical toroidal viscosity and error-field penetration in tokamaks
NASA Astrophysics Data System (ADS)
Cole, Andrew
2007-11-01
A model for field error penetration is developed that includes both resonant and non-resonant perturbed 3-D magnetic fields [1]. The non-resonant components give rise to a global neoclassical toroidal viscous [NTV] torque while a single resonant component produces a localized electromagnetic braking torque on its respective resonant surface. The NTV torque tries to keep the plasma flowing at a rate comparable to the ion diamagnetic flow. A phenomenological cross-field viscosity is included which resists the resonant electromagnetic torque in the vicinity of the resonant surface. Steady-state toroidal momentum balance across the resonant layer gives a solubility condition determining the ``critical'' resonant error-field strength---termed the penetration threshold---above which rotational shielding is lost and the resonant surface locks to the lab frame. Such locking occurs in low-density start-up tokamak plasmas [2], leading to plasma disruptions or confinement degradation and is a key issue for ITER. The toroidal momentum balance equation admits a WKB-type solution which implies that NTV acts to enhance cross-field viscosity in the vicinity of the resonant surface. This enhancement makes the plasma less sensitive to error-field penetration than previously predicted [3]. In particular, if τEne (neo-Alcator-like) and the perpendicular momentum confinement time has no density dependence, we find the penetration threshold scales linearly with electron density---a result giving quantitative agreement for the first time between theory and experiment [2]. [1] A.J. Cole, C.C. Hegna, and J.D. Callen, to be published in PRL (2007). [2] S.M. Wolfe, I.R. Hutchinson, et al., Phys. Plasmas 12, 056110 (2005) and refs. cited therein. [3] A.J. Cole and R. Fitzpatrick, Phys. Plasmas 13, 032503 (2006) and refs. cited therein.
System and method of operating toroidal magnetic confinement devices
Chance, Morrell S.; Jardin, Stephen C.; Stix, Thomas H.; Grimm, deceased, Ray C.; Manickam, Janardhan; Okabayashi, Michio
1987-01-01
For toroidal magnetic confinement devices the second region of stability against ballooning modes can be accessed with controlled operation. Under certain modes of operation, the first and second stability regions may be joined together. Accessing the second region of stability is accomplished by forming a bean-shaped plasma and increasing the indentation until a critical value of indentation is reached. A pusher coil, located at the inner-major-radius side of the device, is engaged to form a bean-shaped poloidal cross-section in the plasma.
Effect of alpha particles on Toroidal Alfven Eigenmodes
Berk, H.L.
1992-11-01
An overview is given of the analytic structure for the linear theory of the Toroidal Alfven Eigenmode (TAE), where multiple gap structures occur. A discussion is given of the alpha particle drive and the various dissipation mechanisms that can stabilize the system. A self-consistent calculation of the TAE mode, for a low-beta high-aspect-ratio plasma, indicates that though the alpha particle drive is comparable to the dissipation mechanisms, overall stability is still achieved for ignited ITER-like plasma. A brief discussion is given of the nonlinear theory for the TAE mode and how nonlinear alpha particle dynamics can be treated by mapping methods.
Compact toroid injection into C-2U
NASA Astrophysics Data System (ADS)
Roche, Thomas; Gota, H.; Garate, E.; Asai, T.; Matsumoto, T.; Sekiguchi, J.; Putvinski, S.; Allfrey, I.; Beall, M.; Cordero, M.; Granstedt, E.; Kinley, J.; Morehouse, M.; Sheftman, D.; Valentine, T.; Waggoner, W.; the TAE Team
2015-11-01
Sustainment of an advanced neutral beam-driven FRC for a period in excess of 5 ms is the primary goal of the C-2U machine at Tri Alpha Energy. In addition, a criteria for long-term global sustainment of any magnetically confined fusion reactor is particle refueling. To this end, a magnetized coaxial plasma-gun has been developed. Compact toroids (CT) are to be injected perpendicular to the axial magnetic field of C-2U. To simulate this environment, an experimental test-stand has been constructed. A transverse magnetic field of B ~ 1 kG is established (comparable to the C-2U axial field) and CTs are fired across it. As a minimal requirement, the CT must have energy density greater than that of the magnetic field it is to penetrate, i.e., 1/2 ρv2 >=B2 / 2μ0 . This criteria is easily met and indeed the CTs traverse the test-stand field. A preliminary experiment on C-2U shows the CT also capable of penetrating into FRC plasmas and refueling is observed resulting in a 20 - 30% increase in total particle number per single-pulsed CT injection. Results from test-stand and C-2U experiments will be presented.
Mathematical Foundations for Fields of Toroidal Current Loops
NASA Astrophysics Data System (ADS)
Sharma, Stephen
2016-10-01
Motivating the functions that define electromagnetic fields for a toroidal shaped current loop are centered around three main isomorphisms: fundamental additions to solutions of differential equations, solving for the geodesics of thermonuclear magnetic reactors, and constructing accurate computational combinatoric models for fusion plasmas. Thermonuclear plasmas in tokamaks are essentially loops of current where the ions and electrons create two current densities which contribute to the magnetic field of the electricity generating current loop. The toroidal shaped current loop necessitates, however, new calculus. In the Biot Savart circular loop, off axis solutions are generated from an integral of a line segment. The non circular shape's differing eccentricity is in corner regions and the linear section and requires new integration and coordinates. The solution of the incremental loop elements in the toroidal shaped coil case are now loops considered parts of semicircles and step functions. When constructing a field, new elliptic functions are going to be generated and a new polynomial function-called an elliptic function of the first and second kind-must be uncovered.
Modeling of Divertor Plates in the Compact Toroidal Hybrid
NASA Astrophysics Data System (ADS)
Hartwell, G. J.; Small, C. M.; Ennis, D. A.; Hanson, J. D.; Knowlton, S. F.; Maurer, D. A.
2014-10-01
In long pulse length stellarator experiments, edge island divertors can be used as a method of plasma particle and heat exhaust. Knowledge of the detailed power loading on these structures and its relationship to the long connection length scrape off layer physics is a new Compact Toroidal Hybrid research thrust. We report the results of connection length studies for divertor plates to be installed in the Compact Toroidal Hybrid (CTH), a five field period torsatron with R0 = 0 . 75 m, ap ~ 0 . 2 m, and B <= 0 . 7 T. For these studies, CTH will be operated as a pure stellarator with no ohmically generated plasma current. The CTH edge rotational transform can be varied from tvac (a) = 0.02-0.35 by adjusting the ratio of currents in the helical and toroidal field coils. A poloidal field coil is used to adjust the shear of the rotational transform profile, and hence the size of edge islands, while the phase of the island is rotated with a set of five error coils producing an n = 1 perturbation. For the studies conducted, a magnetic configuration with a large n = 1, m = 3 magnetic island at the edge is generated. Results from multiple possible divertor plate locations relative to the island structure will be presented. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.
Predictive Simulations of ITER Including Neutral Beam Driven Toroidal Rotation
Halpern, Federico D.; Kritz, Arnold H.; Bateman, Glenn; Pankin, Alexei Y.; Budny, Robert V.; McCune, Douglas C.
2008-06-16
Predictive simulations of ITER [R. Aymar et al., Plasma Phys. Control. Fusion 44, 519 2002] discharges are carried out for the 15 MA high confinement mode (H-mode) scenario using PTRANSP, the predictive version of the TRANSP code. The thermal and toroidal momentum transport equations are evolved using turbulent and neoclassical transport models. A predictive model is used to compute the temperature and width of the H-mode pedestal. The ITER simulations are carried out for neutral beam injection (NBI) heated plasmas, for ion cyclotron resonant frequency (ICRF) heated plasmas, and for plasmas heated with a mix of NBI and ICRF. It is shown that neutral beam injection drives toroidal rotation that improves the confinement and fusion power production in ITER. The scaling of fusion power with respect to the input power and to the pedestal temperature is studied. It is observed that, in simulations carried out using the momentum transport diffusivity computed using the GLF23 model [R.Waltz et al., Phys. Plasmas 4, 2482 (1997)], the fusion power increases with increasing injected beam power and central rotation frequency. It is found that the ITER target fusion power of 500 MW is produced with 20 MW of NBI power when the pedesta temperature is 3.5 keV. 2008 American Institute of Physics. [DOI: 10.1063/1.2931037
Nonlinear particle simulation of ion cyclotron waves in toroidal geometry
Kuley, A. Lin, Z.; Bao, J.; Wei, X. S.; Xiao, Y.
2015-12-10
Global particle simulation model has been developed in this work to provide a first-principles tool for studying the nonlinear interactions of radio frequency (RF) waves with plasmas in tokamak. In this model, ions are considered as fully kinetic particles using the Vlasov equation and electrons are treated as guiding centers using the drift kinetic equation with realistic electron-to-ion mass ratio. Boris push scheme for the ion motion has been developed in the toroidal geometry using magnetic coordinates and successfully verified for the ion cyclotron and ion Bernstein waves in global gyrokinetic toroidal code (GTC). The nonlinear simulation capability is applied to study the parametric decay instability of a pump wave into an ion Bernstein wave side band and a low frequency ion cyclotron quasi mode.
Nonlinear particle simulation of ion cyclotron waves in toroidal geometry
NASA Astrophysics Data System (ADS)
Kuley, A.; Bao, J.; Lin, Z.; Wei, X. S.; Xiao, Y.
2015-12-01
Global particle simulation model has been developed in this work to provide a first-principles tool for studying the nonlinear interactions of radio frequency (RF) waves with plasmas in tokamak. In this model, ions are considered as fully kinetic particles using the Vlasov equation and electrons are treated as guiding centers using the drift kinetic equation with realistic electron-to-ion mass ratio. Boris push scheme for the ion motion has been developed in the toroidal geometry using magnetic coordinates and successfully verified for the ion cyclotron and ion Bernstein waves in global gyrokinetic toroidal code (GTC). The nonlinear simulation capability is applied to study the parametric decay instability of a pump wave into an ion Bernstein wave side band and a low frequency ion cyclotron quasi mode.
Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows
Lin, Z.; Hahm, T.S.; Lee, W.W.; Tang, W.M.; White, R.B.
2000-02-15
A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion-ion collision frequency even in regimes where the instabilities are collisionless.
Suttrop, Wolfgang; Kirk, A.; Nazikian, R.; Leuthold, N.; Strumberger, E.; Willensdorfer, M.; Cavedon, M.; Dunne, M.; Fischer, R.; Fietz, S.; Fuchs, J. C.; Liu, Y. Q.; McDermott, R. M.; Orain, F.; Ryan, D. A.; Viezzer, E.
2016-11-22
Here, the interaction of externally applied small non-axisymmetric magnetic perturbations (MP) with tokamak high-confinement mode (H-mode) plasmas is reviewed and illustrated by recent experiments in ASDEX Upgrade. The plasma response to the vacuum MP field is amplified by stable ideal kink modes with low toroidal mode number n driven by the H-mode edge pressure gradient (and associated bootstrap current) which is experimentally evidenced by an observable shift of the poloidal mode number m away from field alignment (m = qn, with q being the safety factor) at the response maximum. A torque scan experiment demonstrates the importance of the perpendicular electron flow for shielding of the resonant magnetic perturbation, as expected from a two-fluid MHD picture. Two significant effects of MP occur in H-mode plasmas at low pedestal collisionality, $\