1,555 research outputs found

### Stable transport in proton driven Fast Ignition

Proton beam transport in the context of proton driven Fast Ignition is
usually assumed to be stable due to protons high inertia, but an analytical
analysis of the process is still lacking. The stability of a charge and current
neutralized proton beam passing through a plasma is therefore conducted here,
for typical proton driven Fast Ignition parameters. In the cold regime, two
fast growing Buneman-like modes are found, with an inverse growth-rate much
smaller than the beam time-of-flight to the target core. The stability issue is
thus not so obvious, and Kinetic effects are investigated. One unstable mode is
found stabilized by the background plasma protons and electrons temperatures.
The second mode is also damped, providing the proton beam thermal spread is
larger than $\sim$ 10 keV. In Fusion conditions, the beam propagation should
therefore be stable.Comment: Submitted to Po

### Classical Strongly Coupled QGP: VII. Energy Loss

We use linear response analysis and the fluctuation-dissipation theorem to
derive the energy loss of a heavy quark in the SU(2) classical Coulomb plasma
in terms of the $l=1$ monopole and non-static structure factor. The result is
valid for all Coulomb couplings $\Gamma=V/K$, the ratio of the mean potential
to kinetic energy. We use the Liouville equation in the collisionless limit to
assess the SU(2) non-static structure factor. We find the energy loss to be
strongly dependent on $\Gamma$. In the liquid phase with $\Gamma\approx 4$, the
energy loss is mostly metallic and soundless with neither a Cerenkov nor a Mach
cone. Our analytical results compare favorably with the SU(2) molecular
dynamics simulations at large momentum and for heavy quark masses.Comment: 18 pages, 15 figures. v2: added references, changed title, replaced
figures for Fig. 7, corrected typo

### Spin-density functional approach to thermodynamic and structural consistence in the charge and spin response of an electron gas

We use spin-density functional theory to obtain novel expressions for the
charge and spin local-field factors of an electron gas in terms of its
electron-pair structure factors. These expressions (i) satisfy the
compressibility and spin susceptibility sum rules; (ii) keep account of kinetic
correlations by means of an integration over the coupling strength; and (iii)
provide a practical self-consistent scheme for evaluating linear response and
liquid structure. Numerical illustrations are given for the dielectric response
of the paramagnetic electron gas in both three and two dimensions.Comment: 9 pages, 3 figures, submitted to Solid State Commu

### Classical Strongly Coupled QGP: VII. Shear Viscosity and Self Diffusion

We construct the Liouville operator for the SU(2) classical colored Coulomb
plasma (cQGP) for arbitrary values of the Coulomb coupling $\Gamma=V/K$, the
ratio of the mean Coulomb to kinetic energy. We show that its resolvent in the
classical colored phase space obeys a hierarchy of equations. We use a free
streaming approximation to close the hierarchy and derive an integral equation
for the time-dependent structure factor. Its reduction by projection yields
hydrodynamical equations in the long-wavelength limit. We discuss the character
of the hydrodynamical modes at strong coupling. The shear viscosity is shown to
exhibit a minimum at $\Gamma\approx 8$ near the liquid point. This minimum
follows from the cross-over between the single particle collisional regime
which drops as $1/\Gamma^{5/2}$ and the hydrodynamical collisional regime which
rises as $\Gamma^{1/2}$. The self-diffusion constant drops as $1/\Gamma^{3/2}$
irrespective of the regime. We compare our results to molecular dynamics
simulations of the SU(2) colored Coulomb plasma. We also discuss the relevance
of our results for the quantum and strongly coupled quark gluon plasma (sQGP)Comment: 36 pages, 14 figure

### Nonextensive statistics in stellar plasma and solar neutrinos

Nonextensive and quantum uncertainty effects (related to the quasiparticles
composing the stellar core) have strong influence on the nuclear rates and, of
course, affect solar neutrino fluxes. Both effects do coexist and are due to
the frequent collisions among the ions. The weakly nonextensive nature of the
solar core is confirmed. The range of predictions for the neutrino fluxes is
enlarged and the solar neutrino problem becomes less dramatic.Comment: 4 pages. Proc. of TAUP99, Sept. 6-10 1999, Paris. To appear in Nucl.
Phys. B, Proc. Supp

### Relaxation of the distribution function tails for systems described by Fokker-Planck equations

We study the formation and the evolution of velocity distribution tails for
systems with long-range interactions. In the thermal bath approximation, the
evolution of the distribution function of a test particle is governed by a
Fokker-Planck equation where the diffusion coefficient depends on the velocity.
We extend the theory of Potapenko et al. [Phys. Rev. E, {\bf 56}, 7159 (1997)]
developed for power law potentials to the case of an arbitrary potential of
interaction. We study how the structure and the progression of the front depend
on the behavior of the diffusion coefficient for large velocities. Particular
emphasis is given to the case where the velocity dependence of the diffusion
coefficient is Gaussian. This situation arises in Fokker-Planck equations
associated with one dimensional systems with long-range interactions such as
the Hamiltonian Mean Field (HMF) model and in the kinetic theory of
two-dimensional point vortices in hydrodynamics. We show that the progression
of the front is extremely slow (logarithmic) in that case so that the
convergence towards the equilibrium state is peculiar

### Deuterium burning in Jupiter interior

We show that moderate deviations from the Maxwell-Boltzmann energy
distribution can increase deuterium reaction rates enough to contribute to the
heating of Jupiter. These deviations are compatible with the violation of
extensivity expected from temperature and density conditions inside Jupiter.Comment: 6 pages, use elsart + 1 encaspulated postscript figure. Submitted to
Physica

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