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Search Results: 1 - 10 of 149819 matches for " H. Tasso "
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Mathematical genesis ? Big Bang and Cantor set
H. Tasso
Physics , 2007,
Abstract: A mathematical framework is proposed for the "big bang". It starts with some Cantor set and assumes the existence of a transformation from that set to the continuum set used in conventional physical theories like general relativity and quantum mechanics.
On MHD stability of gravitating plasmas with field aligned flows
H. Tasso,G. N. Throumoulopoulos
Physics , 2009,
Abstract: A previous stability condition (see Throumoulopoulos and Tasso, Physics of Plasmas 14, 122104 (2007)) for incompressible plasmas with field aligned flows is extended to gravitating plasmas including self-gravitation. It turns out that the stability condition is affected by gravitation through the equilibrium values only.
On Vlasov approach to tokamaks near magnetic axis
H. Tasso,G. N. Throumoulopoulos
Physics , 2007,
Abstract: A previous proof of non existence of tokamak equilibria with purely poloidal flow within macroscopic theory [Throumoulopoulos, Weitzner, Tasso, Physics of Plasmas Vol. 13, 122501 (2006)] motivated this microscopic analysis near magnetic axis for toroidal and "straight" tokamak plasmas. Despite the new exact solutions of Vlasov's equation found here, the structure of macroscopic flows remains elusive.
Elliptic and hyperelliptic magnetohydrodynamic equilibria
H. Tasso,G. N. Throumoulopoulos
Physics , 2004, DOI: 10.1393/ncb/i2004-10130-x
Abstract: The present study is a continuation of a previous one on "hyperelliptic" axisymmetric equilibria started in [Tasso and Throumoulopoulos, Phys. Plasmas 5, 2378 (1998)]. Specifically, some equilibria with incompressible flow nonaligned with the magnetic field and restricted by appropriate side conditions like "isothermal" magnetic surfaces, "isodynamicity" or P + B^2/2 constant on magnetic surfaces are found to be reducible to elliptic integrals. The third class recovers recent equilibria found in [Schief, Phys. Plasmas 10, 2677 (2003)]. In contrast to field aligned flows, all solutions found here have nonzero toroidal magnetic field on and elliptic surfaces near the magnetic axis.
Tokamak-like Vlasov equilibria
H. Tasso,G. N. Throumoulopoulos
Physics , 2014, DOI: 10.1140/epjd/e2014-50007-9
Abstract: Vlasov equilibria of axisymmetric plasmas with vacuum toroidal magnetic field can be reduced, up to a selection of ions and electrons distributions functions, to a Grad-Shafranov-like equation. Quasineutrality narrow the choice of the distributions functions. In contrast to two-dimensional translationally symmetric equilibria whose electron distribution function consists of a displaced Maxwellian, the toroidal equilibria need deformed Maxwellians. In order to be able to carry through the calculations, this deformation is produced by means of either a Heaviside step function or an exponential function. The resulting Grad-Shafranov-like equations are established explicitly.
Ideal magnetohydrodynamic equilibria with helical symmetry and incompressible flows
G. N. Throumoulopoulos,H. Tasso
Physics , 1999, DOI: 10.1017/S0022377899008041
Abstract: A recent study on axisymmetric ideal magnetohydrodynamic equilibria with incompressible flows [H. Tasso and G. N. Throumoulopoulos, Phys. Plasmas {\bf 5}, 2378 (1998)] is extended to the generic case of helically symmetric equilibria with incompressible flows. It is shown that the equilibrium states of the system under consideration are governed by an elliptic partial differential equation for the helical magnetic flux function $\psi$ containing five surface quantities along with a relation for the pressure. The above mentioned equation can be transformed to one possessing differential part identical in form to the corresponding static equilibrium equation, which is amenable to several classes of analytic solutions. In particular, equilibria with electric fields perpendicular to the magnetic surfaces and non-constant-Mach-number flows are constructed. Unlike the case in axisymmetric equilibria with isothermal magnetic surfaces, helically symmetric $T=T(\psi)$ equilibria are over-determined, i.e., in this case the equilibrium equations reduce to a set of eight ordinary differential equations with seven surface quantities. In addition, it is proved the non-existence of incompressible helically symmetric equilibria with (a) purely helical flows (b) non-parallel flows with isothermal magnetic surfaces and the magnetic field modulus being a surface quantity (omnigenous equilibria).
Cylindrical ideal magnetohydrodynamic equilibria with incompressible flows
G. N. Throumoulopoulos,H. Tasso
Physics , 1997, DOI: 10.1063/1.872322
Abstract: It is proved that (a) the solutions of the ideal magnetohydrodynamic equation, which describe the equlibrium states of a cylindrical plasma with purely poloidal flow and arbitrary cross sectional shape [G. N. Throumoulopoulos and G. Pantis, Plasma Phys. and Contr. Fusion 38, 1817 (1996)] are also valid for incompressible equlibrium flows with the axial velocity component being a free surface quantity and (b) for the case of isothermal incompressible equilibria the magnetic surfaces have necessarily circular cross section.
On resistive magnetohydrodynamic equilibria of an axisymmetric toroidal plasma with flow
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.
A sufficient condition for the linear stability of magnetohydrodynamic equilibria with field aligned incompressible flows
G. N. Throumoulopoulos,H. Tasso
Physics , 2007, DOI: 10.1063/1.2817957
Abstract: A sufficient condition for the linear stability of three dimensional equilibria with incompressible flows parallel to the magnetic field is derived. The condition involves physically interpretable terms related to the magnetic shear and the flow shear.
Analytic, quasineutral, two-dimensional Maxwell-Vlasov equilibria
G. N. Throumoulopoulos,H. Tasso
Physics , 2009,
Abstract: Two-dimensional Maxwell-Vlasov equilibria with finite electric fields, axial ("toroidal") plasma flow and isotropic pressure are constructed in plane geometry by using the quasineutrality condition to express the electrostatic potential in terms of the vector potential. Then for Harris-type distribution functions, Ampere's equation becomes of Liouville type and can be solved analytically. As an example, a periodic "cat-eyes" steady state consisting of a row of magnetic islands is presented. The method can be extended to (toroidal) axisymmetric equilibria.
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