Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.

Effects of crystallinity and electron mean-free-path on dielectric strength of low-density polyethylene

Abstract: The relation between crystallinity and the mean free path of high-energy electrons in low-density polyethylene and their effects on dielectric strength was studied. Thin LDPE films obtained by vacuum evaporation were annealed at temperatures between room temperature and 100 degrees C. Crystallinity was measured by X-ray diffraction. Electrons were injected into the film by photo-emission and the energy of electrons emitted into vacuum through the film was analyzed to obtain their energy distribution. The mean free path was then calculated from the energy distribution. It was found that the crystallinity increases and the mean free path becomes longer as the annealing temperature increases. Dielectric strength was measured by applying an impulse voltage of 1.2/50 mu s at room temperature and -50 degrees C. It was found that the breakdown field decreases with an increase in annealing temperature at both measurement temperatures. Thus, increases crystallinity makes electron transport easier and the mean-free path longer, resulting in a lower dielectric strength. >

Molecular free path distribution in rarefied gases

Abstract: We present the results of investigations into the distribution of molecular free paths in rarefied gases using molecular dynamics simulations. Our tests on a range of different gas densities and confinements (unbounded, single bounding wall and parallel bounding walls) indicate that the molecules perform Levy-type flights, irrespective of the presence of a bounding wall. The free paths most closely follow a power-law distribution. Simulations of gases confined by planar surfaces indicate that the local molecular mean free path varies sharply close to a solid surface. These results may yield new insight into diffusive transport in rarefied gases, in particular, the constitutive behaviour of gas flows in micro- and nanoscale devices.

Resistive ballooning modes in an axisymmetric toroidal plasma with long mean free path

Abstract: Tokamak devices normally operate at such high temperatures that the resistive fluid description is inappropriate. In particular, the collision frequency may be low enough for trapped particles to exist. However, on account of the high conductivity of such plasmas, one can identify two separate scale lengths when discussing resistive ballooning modes. By describing plasma motion on one of these, the connection length, in terms of kinetic theory the dynamics of trapped particles can be incorporated. On the resistive scale length, this leads to a description in terms of modified fluid equations in which trapped particle effects appear. The resulting equations are analyzed and the presence of trapped particles is found to modify the stability properties qualitatively.

Spatial dependence of the pitch-angle and associated spatial diffusion coefficients for cosmic rays in interplanetary space

Abstract: The spatial dependence of the pitch-angle and associated spatial diffusion coefficients for cosmic ray particles in interplanetary space is calculated in the WKB approximation. The model considers only Alfven waves of solar origin to be responsible for scattering of moderate energy particles. After developing the general theory results are presented for the asymptotic case corresponding to radial distancesr greater than about 1 to 2 AU. The radial diffusion coefficientиr increases with energyE likeиr∼Eυ, wherev≈2/3. The radial mean free path turns out to increase proportional tor3 at medium and low heliographic latitudes. This behaviour is consistent with a very small radial cosmic ray gradient and the existence of a ‘free boundary’ for particle diffusion. At equal radial distances the high latitude mean free path is not only much smaller than the one calculated at the lower latitudes but in addition increases only weakly with distance. Some conceivable dynamical implications for the outer solar system are indicated.