Flute mode instability of rotating plasma

The influence of rotation on flute instability is studied in the frame of one-fluid magnetohydrodynamics. We consider the simplest model of gravitating cylindrical plasma in the straight nonuniform magnetic field to simulate plasma behavior in mirrors. Using linear stability analysis, we derive dispersion equation and integral expression for the increment of instability. In virtue of this expression, it is shown that rotation itself appears to be destabilizing factor due to centrifugal effect; we prove the corresponding theorem in general. Eigenmode structure and the dependence of the threshold on the frequency of rotation are calculated for linear radial profile of the angular velocity.В рамках одножидкостной магнитной гидродинамики исследуется влияние вращения на желобковую неустойчивость. Предполагается простейшая модель цилиндрической гравитирующей плазмы в прямом неоднородном магнитном поле для моделирования поведения плазмы в зеркальных ловушках. С помощью линейного анализа получено дисперсионное уравнение и интегральное выражение для инкремента неустойчивости. Показано, что в данной постановке задачи вращение из-за центробежного эффекта является сугубо дестабилизирующим фактором; в общем случае доказывается соответствующая теорема. Для линейного радиального профиля угловой скорости вращения рассчитана структура собственных мод и зависимость порога неустойивости от частоты вращения.В рамках однорідинної магнітної гідродинаміки досліджується вплив обертання на желобкову нестійкість. Припускається простіша модель циліндричної гравітуючої плазми в прямому неоднорідному магнітному полі для моделювання поведінки плазми в дзеркальних пастках. За допомогою лінійного аналізу отримано дисперсійне рівняння й інтегральний вираз для інкремента нестійкості. Показано, що в такій постановці задачі обертання завдяки центробіжного ефекту є сугубо дестабілізуючим фактором; в загальному випадку доводиться відповідна теорема. Для лінійного радіального профілю кутової швидкості обертання розраховано структуру власних мод та залежність порога нестійкості від частоти обертання

The hodograph method applicability in the problem of long-scale nonlinear dynamics of a thin vortex filament near a flat boundary

Hamiltonian dynamics of a thin vortex filament in ideal incompressible fluid near a flat fixed boundary is considered at the conditions that at any point of the curve determining shape of the filament the angle between tangent vector and the boundary plane is small, also the distance from a point on the curve to the plane is small in comparison with the curvature radius. The dynamics is shown to be effectively described by a nonlinear system of two (1+1)-dimensional partial differential equations. The hodograph transformation reduces that system to a single linear differential equation of the second order with separable variables. Simple solutions of the linear equation are investigated at real values of spectral parameter $\lambda$ when the filament projection on the boundary plane has shape of a two-branch spiral or a smoothed angle, depending on the sign of $\lambda$.Comment: 9 pages, revtex4, 6 eps-figure

Response to Comment on Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks' [Phys. Plasmas 19, 064701 (2012)]

The equations for the continuous spectra derived in our paper [V. P. Lakhin and V. I. Ilgisonis, Phys. Plasmas 18, 092103 (2011)] can be reduced to the matrix form used by Goedbloed [Phys. Plasmas 11, 28 (2004)]. It is shown that the assumptions made in our paper provide the elliptic flow regime and guarantee the existence of plasma equilibrium with nested magnetic surfaces of circular cross-section. The new results on magnetohydrodynamic instabilities of such tokamak equilibria obtained in our paper but absent in the paper by Goedbloed are emphasized. © 2012 American Institute of Physics

Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks

A theory for localized low-frequency ideal magnetohydrodynamical (MHD) modes in axisymmetric toroidal systems is generalized to take into account both toroidal and poloidal equilibrium plasma flows. The general set of equations describing the coupling of shear Alfvén and slow (sound) modes and defining the continuous spectrum of rotating plasmas in axisymmetric toroidal systems is derived. The equations are applied to study the continuous spectra in large aspect ratio tokamaks. The unstable continuous modes in the case of predominantly poloidal plasma rotation with the angular velocity exceeding the sound frequency are found. Their stabilization by the shear Alfvén coupling effect is studied. © 2011 American Institute of Physics

Response to Comment on Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks' [Phys. Plasmas 19, 064701 (2012)]

The equations for the continuous spectra derived in our paper [V. P. Lakhin and V. I. Ilgisonis, Phys. Plasmas 18, 092103 (2011)] can be reduced to the matrix form used by Goedbloed [Phys. Plasmas 11, 28 (2004)]. It is shown that the assumptions made in our paper provide the elliptic flow regime and guarantee the existence of plasma equilibrium with nested magnetic surfaces of circular cross-section. The new results on magnetohydrodynamic instabilities of such tokamak equilibria obtained in our paper but absent in the paper by Goedbloed are emphasized. © 2012 American Institute of Physics

Radial electric field and rotation of the ensemble of plasma particles in tokamak

The velocity of macroscopic rotation of an ensemble of charged particles in a tokamak in the presence of an electric field has been calculated in a collisionless approximation. It is shown that the velocity of toroidal rotation does not reduce to a local velocity of electric drift and has opposite directions on the inner and outer sides of the torus. This result is supplemented by an analysis of the trajectories of motion of individual particles in the ensemble, which shows that the passing and trapped particles of the ensemble acquire in the electric field, on the average, different toroidal velocities. For the trapped particles, this velocity is equal to that of electric drift in the poloidal magnetic field, while the velocity of passing particles is significantly different. It is shown that, although the electric-field-induced shift of the boundaries between trapped and passing particles in the phase space depends on the particle mass and charge and is, in the general case, asymmetric, this does not lead to current generation. © 2012 Pleiades Publishing, Ltd

Third adiabatic invariant and the collisionless distribution function of particles in a tokamak

It has been shown that the distribution function of an ensemble of particles with a given energy in a collisionless regime in a tokamak is formed as a function primarily of the third adiabatic invariant, particularly in the near-axis region. In the periphery of the plasma column, the contribution of the toroidal component of the canonical momentum/longitudinal adiabatic invariant to the distribution function becomes noticeable. The coordinate dependence of the ensemble distribution function in the velocity space is determined predominantly by the trajectories of charged particles. © 2011 Pleiades Publishing, Ltd

Radial electric field and rotation of the ensemble of plasma particles in tokamak

The velocity of macroscopic rotation of an ensemble of charged particles in a tokamak in the presence of an electric field has been calculated in a collisionless approximation. It is shown that the velocity of toroidal rotation does not reduce to a local velocity of electric drift and has opposite directions on the inner and outer sides of the torus. This result is supplemented by an analysis of the trajectories of motion of individual particles in the ensemble, which shows that the passing and trapped particles of the ensemble acquire in the electric field, on the average, different toroidal velocities. For the trapped particles, this velocity is equal to that of electric drift in the poloidal magnetic field, while the velocity of passing particles is significantly different. It is shown that, although the electric-field-induced shift of the boundaries between trapped and passing particles in the phase space depends on the particle mass and charge and is, in the general case, asymmetric, this does not lead to current generation. © 2012 Pleiades Publishing, Ltd

Continuum modes in rotating plasmas: General equations and continuous spectra for large aspect ratio tokamaks

A theory for localized low-frequency ideal magnetohydrodynamical (MHD) modes in axisymmetric toroidal systems is generalized to take into account both toroidal and poloidal equilibrium plasma flows. The general set of equations describing the coupling of shear Alfvén and slow (sound) modes and defining the continuous spectrum of rotating plasmas in axisymmetric toroidal systems is derived. The equations are applied to study the continuous spectra in large aspect ratio tokamaks. The unstable continuous modes in the case of predominantly poloidal plasma rotation with the angular velocity exceeding the sound frequency are found. Their stabilization by the shear Alfvén coupling effect is studied. © 2011 American Institute of Physics

Third adiabatic invariant and the collisionless distribution function of particles in a tokamak

It has been shown that the distribution function of an ensemble of particles with a given energy in a collisionless regime in a tokamak is formed as a function primarily of the third adiabatic invariant, particularly in the near-axis region. In the periphery of the plasma column, the contribution of the toroidal component of the canonical momentum/longitudinal adiabatic invariant to the distribution function becomes noticeable. The coordinate dependence of the ensemble distribution function in the velocity space is determined predominantly by the trajectories of charged particles. © 2011 Pleiades Publishing, Ltd