Reply to: Comment on `Long-range electrostatic interactions between like-charged colloids: steric and confinement effects'

In his Comment (cond-mat/0104060) to [Phys. Rev. E 60, 6530 (1999)], Mateescu shows that while the effective interactions remain repulsive when the specific size of the micro-ions is taken into account via a Modified Poisson-Boltzmann equation, a similar conclusion cannot be reached for the situation of complete lateral confinement. This point is correct but has already been considered in a more general study [Phys. Rev. E 62, R1465 (2000), where repulsion is generically obtained]; moreover, we argue that it illustrates the irrelevancy of the notion of pair potential in completely confined configurations, as shown on a simple example

On the Boltzmann relation in a cold magnetized plasma

International audienceA systematic and exact comparison between the forces acting on magnetized electrons in a current-free plasma is considered within a fluid model. We show that the Boltzmann relation is fulfilled in the drift-diffusion approximation when (hi/he)(1 he2)/(1 hi2)⪡1 where he (or hi) is the ratio of the electron (or ion) cyclotron to the collision frequency. When the nonlinear inertia terms are taken into account, the previous criterion is too rough and must be modified. In particular it is proved that the Boltzmann relation is not uniformly valid in the plasma. The case of bounded plasmas where the electron temperature must be determined self-consistently is discussed in detail

A generalization of the rocket formula and its application to advanced space propulsion systems

International audienceA generalized rocket formula is derived from a first principles approach. The resulting expression of the thrust is applied to advanced space propulsion systems and a possible link between the asymptotic propellant velocity and the velocity at thruster exit is given. An estimation of the thrust modification due to spacecraftplume interactions is also considered

Plasmas froids radiofréquence

International audienceL'interaction d'un plasma froid faiblement ionisé et d'une surface semiconductrice est à l'origine des technologies de nanostructuration de la matière en microélectronique. Ces plasmas sont générés et entretenus par des champs électromagnétiques radiofréquence. La compréhension des mécanismes fondamentaux du couplage de l'énergie électromagnétique au plasma et de son transport vers les surfaces du réacteur est un enjeu majeur pour la maîtrise des procédés industriels utilisant les plasmas froids radiofréquence

Edge-to-center plasma density ratio in high density plasma sources

International audienceThe flux of positive ions leaving a classical low-temperature plasma discharge is proportional to the plasma density at the plasmasheath edge, and the edge-to-center plasma density ratio, the so-called hl factor, normally depends only on the discharge size and the neutral gas pressure. The ion flux leaving the discharge is therefore linearly proportional to the central plasma density. The hl factor has been previously derived by solving the plasma transport equations over a large pressure range, with the assumption of constant neutral gas density within the discharge. Tonks and Langmuir derived the low pressure (collisionless) solution of this problem in 1929. More recent works have shown that the neutral gas density is no longer constant when the plasma pressure becomes comparable to the neutral gas pressure. In this paper, we solve the plasma transport equations in this new situation and we propose a new expression for the hl factor. It is shown that hl becomes a function of the central plasma density which implies that the ion flux leaving the discharge is no longer proportional to this density. This effect has to be included in particle and energy balance equations used in global models of high density plasma sources

Chaotic polaronic and bipolaronic states in coupled electron-phonon systems

International audienc

Competitive effects of an axial magnetic field and of neutral gas depletion in a positive column

International audienceNeutral gas dynamics has been incorporated in plasma transport equations in recent studies of nonmagnetized plasma discharge equilibrium. It was found that when the plasma density increases, the neutral gas density becomes depleted in the discharge center, leading to plasma deconfinement. Consequently, larger electron temperature, flatter plasma density profiles, and larger edge-to-center plasma density ratios were observed. In this paper, we investigate the effect of adding a static axial magnetic field to the discharge. We find that at fixed plasma density at the center, the magnetic field reduces the calculated neutral depletion and all the associated effects. Nevertheless, the action of the magnetic field is less pronounced if one keeps the power deposited into the discharge fixed instead. This is because at fixed power, the plasma density increases with the magnetic field

Chaotic polaronic and bipolaronic states in the adiabatic Holstein model

International audienc

Effective discommensurations in the incommensurate ground states of the extended Frenkel-Kontorowa models

International audienceFor the Frenkel-Kontorowa model and its extensions in several dimensions, with several neighbor interactions, etc., it is proven that the hull function of an incommensurate ground state is purely discrete when the phonon spectrum exhibits a non-zero gap. The same result also holds when the Lyapunov coefficient of the corresponding set of trajectories in the associated twist map (when it is definable) is strictly positive. When this theorem applies, the Fourier coefficients of the incommensurate modulation can be described by an analytic hull function. This is in some sense a dual result to the Kolmogorov-Arnol'd-Moser theorem, which proves under different hypotheses that incommensurate modulation in real space (instead of reciprocal space) can be described by an analytic hull function. The physical implication of this theorem i s that the incommensurate ground states can be decomposed into a linear superposition of localized effective discommensurations. The shape of these discommensurations depends on the model parameters and on their density. Approaching the transition by breaking of analyticity (TBA) from above, the size of these discommensurations diverges. Below the TBA, these discommensurations cannot be described anymore as localized objects in the analytic phase. These results confirm that TBA in non-linear models extends the concept of localization of eigenstates, which up to now was only meaningful for linear operators