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Papers by jean-marcel rax

Plasma Physics and Controlled Fusion, May 1, 1994

The interaction between a lower hybrid wave and a fusion alpha particle displaces the alpha parti... more The interaction between a lower hybrid wave and a fusion alpha particle displaces the alpha particle simultaneously in space and energy. This results in coupled diffusion. Diffusion of alphas down the density gradient could lead to their transferring energy to the wave. This could, in turn, put energy into current drive. An initial analytic study was done by Fisch and Rax. Here we calculate numerical solutions for the alpha energy transfer and study a range of conditions that are favourable for wave amplification from alpha energy. We find that it is possible for fusion alpha particles to transfer a large fraction of their energy to the lower hybrid wave. The numerical calculation shows that the net energy transfer is not sensitive to the value of the diffusion coefficient over a wide range of practical values. An extension of this idea, the use of a lossy boundary to enhance the energy transfer, is investigated. This technique is shown to offer a large potential benefit.

Physics of Plasmas, Apr 1, 2014

IEEE Transactions on Plasma Science, 1993

Relativistic third harmonic generation in a plasma is investigated. The growth of a third harmoni... more Relativistic third harmonic generation in a plasma is investigated. The growth of a third harmonic wave is limited by the difference between the phase velocity of the pump and driven waves. This phase velocity mismatch results in a third harmonic amplitude saturation and oscillation. In order to overcome this saturation, we describe a phase-matching scheme based on a resonant density modulation. The limitations of this scheme are analyzed.

Physics of fluids. B, Plasma physics, Dec 1, 1992

This report was prepared as an account of work sponsored by an agency of the United i.

Physical Review Letters, Aug 3, 1992

When an intense, plane-polarized, laser pulse interacts with a plasma, the relativistic nonlinear... more When an intense, plane-polarized, laser pulse interacts with a plasma, the relativistic nonlinearities fP induce a third harmonic polarization. A phase-locked growth of a third harmonic wave can tak; place, but the difference between the nonlinear dispersion of the pump and driven waves leads to a rapid li

Physics of Plasmas, Mar 1, 1996

A new nonlinear Raman instability in underdense plasma is investigated theoretically. Unlike the ... more A new nonlinear Raman instability in underdense plasma is investigated theoretically. Unlike the usual linear Raman instabilities which grow exponentially in time, this instability takes a finite amount of time to diverge. T h e explosion time t, depends on the initial level of the perturbation. A general set of equations for spatietemporal evolution of the forward nonlinear Raman scattering is derived and its temporal evolution is studied in detail. This new instability results in the generation of forward Raman radiation shifted by half the plasma frequency for laser intensities of order or exceeding 10'8W/cm2, something that has been recently observed (Astorre Modena, private communication, 1995).

Physical Review Letters, 2005

Capacitive discharges have classically been modeled in the electrostatic approximation. However, ... more Capacitive discharges have classically been modeled in the electrostatic approximation. However, electromagnetic effects become significant if the excitation wavelength and the plasma skin depth are not infinite. An electromagnetic model valid in the entire range of and of practical interest is solved. We find that the plasma may either be sustained by the usual capacitive E field or by an inductive H field, and that the discharge experiences E to H transitions as the voltage between the electrodes is raised.

This report has been reproduceddirectlyfromthe best available copy.

Physics of Plasmas, 2008

Recent theoretical analyses which predicted unexpected effects of neutral depletion in both colli... more Recent theoretical analyses which predicted unexpected effects of neutral depletion in both collisional and collisionless plasmas are reviewed. We focus on the depletion of collisionless neutrals induced by strong ionization of a collisionless plasma and contrast this depletion with the effect of strong ionization on thermalized neutrals. The collisionless plasma is analyzed employing a kinetic description. The collisionless neutrals and the plasma are coupled through volume ionization and wall recombination only. The profiles of density and pressure both of the plasma and of the neutral-gas and the profile of the ionization rate are calculated. It is shown that for collisionless neutrals the ionization results in neutral depletion, while when neutrals are thermalized the ionization induces a maximal neutral-density at the discharge center, which we call neutral repletion. The difference between the two cases stems from the relation between the neutral density and pressure. The pres...

Nuclear Fusion, 1992

Many experiments have proved the effectiveness of lower hybrid waves for driving toroidal current... more Many experiments have proved the effectiveness of lower hybrid waves for driving toroidal current in tokamaks, However, the use of these waves to provide all the current in a reactor is thought to be uncertain because it may happen that the waves do not penetrate into the centre of the more energetic reactor plasma and, if they do, the wave power may be absorbed by alpha particles rather than by electrons. The paper addresses mathematically the interaction between lower hybrid waves and alpha particles.

arXiv (Cornell University), Sep 30, 2022

Wave propagation properties in a medium are fundamentally affected when this medium is moving ins... more Wave propagation properties in a medium are fundamentally affected when this medium is moving instead of at rest. In isotropic dielectric media rotation has two noteworthy contributions: one is a mechanically induced circular birefringence which materialises as a rotation of the polarisation, the other is image rotation which corresponds to a rotation of the transverse structure of a wave. Here we review the effect of rotation in a magnetised plasma. We first show that the mechanical effect of rotation on polarisation is in a magnetised plasma superimposed onto the classical Faraday rotation, and that failing to account for this new contribution could lead to errors in the interpretation of polarimetry data. We also demonstrate that image rotation is recovered in plasmas for a number of low-frequency magnetised plasma waves carrying orbital angular momentum, and that this phenomenon holds promise for the development of new rotation diagnostic tools in plasmas.

Journal of Plasma Physics, Nov 30, 2023

Physics of Plasmas

Very large DC and AC electric fields cannot be sustained between conducting electrodes because of... more Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures, such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines, and usually providing the voltage drop feed between the field lines impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity betwe...

Physics of Plasmas, 2007

A new isotope separation process based on selective cyclotron resonant interaction between ions a... more A new isotope separation process based on selective cyclotron resonant interaction between ions and a tapered helicoidal magnetic structure is identified, analyzed, and evaluated. On the basis of a Hamiltonian analysis, the existence of a class of tapered magnetic modulation that provide a full conversion of linear momentum into angular momentum is discovered. The characteristics and parameters of this field configuration are analyzed and described. The dynamic of the nonresonant isotope is investigated in order to set up a separation criterion. This autoresonant ion cyclotron isotope separation mechanism provides an efficient alternative to other niches of enrichment process.

Physique des plasmas, 2005