Anomalous collisional absorption of laser pulses in underdense plasma at low temperature

Abstract

In a previous paper [M. Kundu, Phys. Plasmas 21, 013302 (2014)], fractional collisional absorption (α) of laser light in underdense plasma was studied by using a classical scattering model of electron-ion collision frequency ν(ei), where total velocity v=√[v(th)(2)+v(0)(2)] (with v(th) and v(0) as the thermal and the ponderomotive velocity of an electron) dependent Coulomb logarithm lnΛ(v) was shown to be responsible for the anomalous (unconventional) increase of ν(ei) and α(∝ν(ei)) with the laser intensity I(0) up to a maximum value about an intensity I(c) in the low temperature (T(e)<15eV) regime and a conventional ≈I(0)(-3/2) decrease when I(0)≫I(c). One may object that the anomalous increase in ν(ei) and α were partly due to the artifact introduced in lnΛ through the maximum cutoff distance b(max)∝v. In this work, we show similar anomalous increase in ν(ei) and α versus I(0) (in the low temperature and underdense density regime) with more accurate quantum and classical kinetic models of ν(ei) without using lnΛ, but with a proper choice of the total velocity dependent inverse cutoff length k(max)∝v(2) (classical) or k(max)∝v (quantum). For a given I(0)<5×10(14)Wcm(-2), ν(ei) versus T(e) also exhibits so far unnoticed identical anomalous increase as ν(ei) versus I(0), even if the conventional k(max)∝v(th)(2) or k(max)∝v(th) (without v(0)) is chosen. The total velocity dependent k(max) in the kinetic models, as proposed here, is found to explain the anomalous increase of α with I(0) measured in some earlier laser-plasma experiments.

Nematic and gas-liquid transitions for sticky rods on square and cubic lattices

“…This demixing is found for L ≥ 7 in simulations [28]. The critical packing fraction for the onset of demixing scales approximately as 4.8/L for large L [29,33]. At very high packing fractions η ≈ 1, theoretical arguments predict a re-entrant transition from the demixed to a disordered state bearing some characteristics of a 2D cubatic phase on a lattice [28].…”

“…In Sec. III we revisit the case of 2D, where, for the case of purely hard-core rods, the demixing transition has been studied extensively [28][29][30][31][32][33]. Upon adding attractions, the demixing transition competes with the liquid-vapor transition, yet the full phase diagram in the temperature-density plane had not been resolved [34] up to now.…”

Phase transitions in a system of hard Y-shaped particles on the triangular lattice

“…HCLGs sometimes show multiple phase transitions with increasing density, but only when the excluded volume per particle is large. For instance, for multiple phase transitions to be present, the minimum range of interaction is seventh nearest neighbour for rods [30,32], fifth nearest neighbour for rectangles [33,34], fourth nearest neighbour for HCLG models for discs [38,45] while nearest neighbour exclusion models like the 1-NN model on the square lattice [13,15,37,[46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] or the hard hexagon model on the triangular lattice [39] show only one transition from a disordered phase to a sublattice phase. The excluded volume of Y -shaped particles consists of nearest neighbour sites, as in the hard hexagon model and half of the next-nearest neighbour sites depending on the pair of particles being considered.…”

“…Many different shapes have been studied in the literature. Examples include triangles [12], squares [13][14][15][16][17][18], dimers [19][20][21][22], mixture of squares and dimers [23,24], Yshaped particles [25,26], tetrominoes [27,28], rods [29][30][31][32], rectangles [33][34][35][36], discs [37,38], and hexagons [39]. The hard hexagon model on the triangular lattice is the only solvable model.…”

Diffusion dynamics and steady states of systems of hard rods on a square lattice

“…For rods in two dimensions, from grand canonical Monte Carlo simulations, it is known k min = 7 [9]. For rectangles of size 2×2k and 3×3k, where k is now the as-pect ratio, k min is still 7 [10,26,27]. In three dimensions, large scale simulations of rods on cubic lattices show that k min = 7 [24,25].…”