جستجوی مقالات مرتبط با کلیدواژه "instability" در نشریات گروه "فیزیک"

In this article, a one-dimensional kinetic model is used to obtain space charge solitary waves in a beam of hot charged particles into a transmission channel with a resistance wall of radius rw. The axial electric field is obtained as , where  and are geometric constants. In addition, due to the resistance of the wall, an electric field  appears. The moments of the Vlasov equation for the water bag distribution function are converted into fluid equations and these fluid equations are reduced to the kdv equation using the reduced perturbation method. The shape of the fast and slow space charge solitary waves caused by the beam of hot charged particles in the presence of wall resistance is obtained by numerically examining the KdV equation at different times. Finally, it is revealed that with the increase of the wall resistance, the growth(attenuation) rate of the relative amplitude of the slow (fast) space charge soliton waves caused by the beams of charged particles increases.

We study the extended scalar-tensor Gauss-Bonnet. First, we review a model in which there is a coupling between the Gauss-Bonnet scalar and the scalar field. Then we extend the model to a hybrid model with two scalar fields. We study the conditions under which the solutions are unstable and spontaneous scalarization occurs. We show that the coupling coefficients in the hybrid state and in the presence of a scalar field are asymptotically the same but the sufficient condition of instability is different between these two models.

Short and intense laser pulses in laser-plasma interaction stimulate various local structures like solitary waves in the plasma. Relative salitons should be given special attention because the amplitude of the electromagnetic field is intense enough to set plasma electrons in relativistic motions. In the interaction of intense laser with plasma, collisions can play an important role in the physical phenomena. In this paper, the effect of the collision on the emission of solitons is investigated by considering the interaction of an intense laser with plasma. Then, the NLS equation is numerically solved and the different results are compared with each other. Also, the stability conditions of individual waves and the effect of the collision on these waves are investigated.

In this study, waves instability in free electron laser with background plasma, under the influence of self-electric and self-magnetic fields, are analyzed. A dispersion relation in the Raman regime for free electron laser with a helical wiggler magnetic field and an axial magnetic field derived in which all possible wave modes can have unstable couplings with each other. This dispersion relation is solved numerically to investigate the influence of self-fields on unstable couplings. It was found that self-fields reduce the growth rate of the group I orbits and increase it in the group II orbits

Ideal magnetohydrodynamic (MHD) equilibrium is vulnerable to numerous unstabilizing mechanisms. Instabilities introduce distortions to the plasma magnetic surfaces and their boundaries, their driving force being the radial gradient of plasma toroidal current density. For certain modal numbers, internal kink modes may develop, and their study is feasible according to the energy principle, in which the change in total potential energy is evaluated due to the disturbance. In this paper, we present a new analysis of MHD equilibrium and stability, and apply it to Damavand Tokamak which has a large aspect ratio. For this purpose, we combine the perturbation and Green's function methods to solve the equilibrium configuration problem. At this stage, plasma profiles are found explicitly in terms of Bessel functions, and we present a simple expression for estimation of total toroidal plasma current. Then the rest of plasma profiles, including poloidal magnetic flux, safety factor, and toroidal current density, are obtained and plotted. In the next step, we turn to the stability calculations and characterize the stable and unstable ideal MHD modes of Damavand plasma.