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The origin of transport barriers in toroidal plasmas  [PDF]
Fedor V. Prigara
Physics , 2005,
Abstract: A transport barrier in a toroidal plasma is treated as the boundary region between the hot and cold phases of the plasma. These two phases possess essentially different collisional and transport properties, so the boundary region between them corresponds to the minimum values of specific resistivity and transport coefficients of the plasma. The behavior of magnetic shear in the region of a transport barrier and some other specific properties of transport barriers are the consequences of the minimum plasma resistivity in this region. The origin of sawtooth oscillations in toroidal plasmas is shown to have a similar nature.
Investigation of toroidal acceleration and potential acceleration forces in EAST and J-TEXT plasmas  [PDF]
Fudi Wang,Bo Lyu,Xiayun Pan,Zhifeng Cheng,Jun Chen,Guangming Cao,Yuming Wang,Xiang Han,Hao Li,Bin Wu,Zhongyong Chen,Manfred Bitter,Kenneth Hill,John Rice,Shigeru Morita,Yadong Li,Ge Zhuang,Minyou Ye,Baonian Wan,Yuejiang Shi,EAST team
Physics , 2014,
Abstract: In order to produce intrinsic rotation, bulk plasmas must be collectively accelerated by the net force exerted on them, which results from both driving and damping forces. So, to study the possible mechanisms of intrinsic rotation generation, it is only needed to understand characteristics of driving and damping terms because the toroidal driving and damping forces induce net acceleration which generates intrinsic rotation. Experiments were performed on EAST and J-TEXT for ohmic plasmas with net counter- and co-current toroidal acceleration generated by density ramping up and ramping down. Additionally on EAST, net co-current toroidal acceleration was also formed by LHCD or ICRF. For the current experimental results, toroidal acceleration was between - 50 km/s^2 in counter-current direction and 70 km/s^2 in co-current direction. According to toroidal momentum equation, toroidal electric field (E\-(\g(f))), electron-ion toroidal friction, and toroidal viscous force etc. may play roles in the evolution of toroidal rotation. To evaluate contribution of each term, we first analyze characteristics of E\-(\g(f)). E\-(\g(f)) is one of the co-current toroidal forces that acts on the plasma as a whole and persists for the entire discharge period. It was shown to drive the co-current toroidal acceleration at a magnitude of 10^3 km/s^2, which was much larger than the experimental toroidal acceleration observed on EAST and J-TEXT. So E\-(\g(f)) is one of co-current forces producing cocurrent intrinsic toroidal acceleration and rotation. Meanwhile, it indicates that there must be a strong counter-current toroidal acceleration resulting from counter-current toroidal forces. Electron-ion toroidal friction is one of the counter-current toroidal forces because global electrons move in the counter-current direction in order to produce a toroidal plasma current.
Magnetohydrodynamic equations for toroidal plasmas  [PDF]
M. Asif
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.22015
Abstract: A set of reduced MHD equations is derived us-ing the standard energy balance equation. By applying assumption of internal energy, i.e. , a set of reduced magnetohydro-dynamic equations are obtained for large aspect ratio, high tokamaks. These equations in-clude all terms of the same or der as the toroidal effect and only involve three variables, namely the ?ux, stream function and internal energy.
Nondiffusive suprathermal ion transport in simple magnetized toroidal plasmas  [PDF]
K. Gustafson,P. Ricci,I. Furno,A. Fasoli
Physics , 2011, DOI: 10.1103/PhysRevLett.108.035006
Abstract: We investigate suprathermal ion dynamics in simple magnetized toroidal plasmas in the pres- ence of electrostatic turbulence driven by the ideal interchange instability. Turbulent fields from fluid simulations are used in the non-relativistic equation of ion motion to compute suprathermal tracer ion trajectories. Suprathermal ion dispersion starts with a brief ballistic phase, during which particles do not interact with the plasma, followed by a turbulence interaction phase. In this one simple system, we observe the entire spectrum of suprathermal ion dynamics, from subdiffusion to superdiffusion, depending on beam energy and turbulence amplitude. We estimate the duration of the ballistic phase and identify basic mechanisms during the interaction phase that determine the character of suprathermal ion dispersion upon the beam energy and turbulence fluctuation amplitude.
On resistive magnetohydrodynamic equilibria of an axisymmetric toroidal plasma with flow  [PDF]
G. N. Throumoulopoulos,H. Tasso
Physics , 2000, DOI: 10.1017/S0022377800008849
Abstract: It is shown that the magnetohydrodynamic equilibrium states of an axisymmetric toroidal plasma with finite resistivity and flows parallel to the magnetic field are governed by a second-order partial differential equation for the poloidal magnetic flux function $\psi$ coupled with a Bernoulli type equation for the plasma density (which are identical in form to the corresponding ideal MHD equilibrium equations) along with the relation $\Delta^\star \psi=V_c \sigma$. (Here, $\Delta^\star$ is the Grad-Schl\"{u}ter-Shafranov operator, $\sigma$ is the conductivity and $V_c$ is the constant toroidal-loop voltage divided by $2 \pi $). In particular, for incompressible flows the above mentioned partial differential equation becomes elliptic and decouples from the Bernoulli equation [H. Tasso and G. N. Throumoulopoulos, Phys. Plasmas {\bf 5}, 2378 (1998)]. For a conductivity of the form $\sigma=\sigma(R, \psi)$ ($R$ is the distance from the axis of symmetry) several classes of analytic equilibria with incompressible flows can be constructed having qualitatively plausible $\sigma$ profiles, i.e. profiles with $\sigma$ taking a maximum value close to the magnetic axis and a minimum value on the plasma surface. For $\sigma=\sigma(\psi)$ consideration of the relation $\Delta^\star\psi = V_c \sigma(\psi)$ in the vicinity of the magnetic axis leads therein to a proof of the non-existence of either compressible or incompressible equilibria. This result can be extended to the more general case of non-parallel flows lying within the magnetic surfaces.
Influence of shear viscosity on the correlation between the triangular flow and initial spatial triangularity  [PDF]
A. K. Chaudhuri
Physics , 2011, DOI: 10.1016/j.physletb.2012.05.041
Abstract: In a hydrodynamic model, with fluctuating initial conditions, the correlation between triangular flow and initial spatial triangularity is studied. The triangular flow, even in ideal fluid, is only weakly correlated with the initial triangularity. The correlation is largely reduced in viscous fluid. Elliptic flow on the other hand appears to be strongly correlated with initial eccentricity. Weak correlation between triangular flow and initial triangularity indicate that a part of triangular flow is unrelated to initial triangularity. Triangularity acquired during the fluid evolution also contributes to the triangular flow.
Exact axisymmetric Taylor states for shaped plasmas  [PDF]
Antoine J. Cerfon,Michael O'Neil
Physics , 2014, DOI: 10.1063/1.4881466
Abstract: We present a general construction for exact analytic Taylor states in axisymmetric toroidal geometries. In this construction, the Taylor equilibria are fully determined by specifying the aspect ratio, elongation, and triangularity of the desired plasma geometry. For equilibria with a magnetic X-point, the location of the X-point must also be specified. The flexibility and simplicity of these solutions make them useful for verifying the accuracy of numerical solvers and for theoretical studies of Taylor states in laboratory experiments.
Effect of plasma subsonic toroidal flows induced by Alfvén waves on transport processes in the edge of elongated tokamaks
Tsypin, V. S.;Severo, J. H. F.;Nascimento, I. C.;Galv?o, R. M. O.;Kuznetsov, Yu. K.;
Brazilian Journal of Physics , 2001, DOI: 10.1590/S0103-97332001000100006
Abstract: there is a renewed interest in using alfvén waves (aw) in tokamak plasmas. previously, aw were actively explored mostly for current drive and plasma heating in tokamaks. presently, the possibility of the anomalous and neoclassical transport suppression by aw in tokamak plasmas is being vividly discussed. aw can also induce poloidal and toroidal plasma rotation. toroidal plasma rotation can reach the subsonic level. these flows can substantially affect neoclassical transport both in collisional and weakly collisional plasmas. in this paper, the effect of plasma subsonic toroidal flows induced by alfvén waves on transport processes in the edge of elongated tokamak is investigated. the dependence of poloidal plasma rotation and ion heat conductivity on the elongation parameter and the ratio of induced toroidal velocity to the sonic speed are analytically obtained.
Effect of plasma subsonic toroidal flows induced by Alfvén waves on transport processes in the edge of elongated tokamaks  [cached]
Tsypin V. S.,Severo J. H. F.,Nascimento I. C.,Galv?o R. M. O.
Brazilian Journal of Physics , 2001,
Abstract: There is a renewed interest in using Alfvén waves (AW) in tokamak plasmas. Previously, AW were actively explored mostly for current drive and plasma heating in tokamaks. Presently, the possibility of the anomalous and neoclassical transport suppression by AW in tokamak plasmas is being vividly discussed. AW can also induce poloidal and toroidal plasma rotation. Toroidal plasma rotation can reach the subsonic level. These flows can substantially affect neoclassical transport both in collisional and weakly collisional plasmas. In this paper, the effect of plasma subsonic toroidal flows induced by Alfvén waves on transport processes in the edge of elongated tokamak is investigated. The dependence of poloidal plasma rotation and ion heat conductivity on the elongation parameter and the ratio of induced toroidal velocity to the sonic speed are analytically obtained.
Study of electron temperature gradient instability in toroidal plasmas with negative magnetic shear
Jian Guang-De,Dong Jia-Qi,
简广德
,董家齐

中国物理 B , 2004,
Abstract: Electron temperature gradient driven instability in toroidal plasmas with negative magnetic shear is studied. Full electron kinetics is considered, and the behaviours of the modes and corresponding turbulent transport in the parameter regimes close to the instability threshold are emphasized. Growing and damped modes are both investigated. The singular points of the integrand are disposed of, and the fitting formulae for the critical gradient are given. The theoretical results are shown to be close to the experimental observations.
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