Data on the emission of energetic ions produced in laser–matter interactions have been analyzed for a wide variety of laser wavelengths, energies, and pulse lengths. Strong correlation has been found between the bulk energy per AMU for fast ions measured by charge cups and the x-ray-determined hot electron temperature. Five theoretical models have been used to explain this correlation. The models include (1) a steady-state spherically symmetric fluid model with classical electron heat conduction, (2) a steady-state spherically symmetric fluid model with flux limited electron heat conduction, (3) a simple analytic model of an isothermal rarefaction followed by a free expansion, (4) the lasnex hydrodynamics code [Comments Plasma Phys. Controlled Fusion 2, 85 (1975)], calculations employing a spherical expansion and simple initial conditions, and (5) the lasnex code with its full array of absorption, transport, and emission physics. The results obtained with these models are in good agreement with the experiments and indicate that the detailed shape of the correlation curve between mean fast ion energy and hot electron temperature is due to target surface impurities at the higher temperatures (higher laser intensities) and to the expansion of bulk target material at the lower temperatures (lower laser intensities).

Viscosity reduction and swelling are the principal mechanisms contributed to the improvement of heavy-oil recovery by immiscible C02 displacement. This paper presents the results of experimental measurements for the physical properties of heavy oils before and after CO 2 saturation. Based on measured data, correlations were developed for the predictions of CO 2 solubility, oil swelling factor, and viscosity change for CO 2 -saturated heavy oils.

The existence of a new type of surface wave in plasmas is demonstrated. These waves are intimately connected with the self-generation of magnetic fields in the laser-plasma interaction. The waves resemble waveguide modes in that a number of discrete modes can exist. The modes are localized to within a collisionless skin depth of the surface and, in the collisionless fluid limit, there is no restriction on the distance the waves can propagate.PACS numbers: 52.35.Hr, 52.35.Bj, 52.40.Fd, 52.40.Kh Spontaneously generated magnetic fields in laser-produced plasmas have been observed for many years. 1 "" 3 These observations, along with their obvious impact on the inertial-confinement fusion program, have been the motivation for the many papers that have appeared on the subject in the last decade. 4 " 8 Transport of energy along surfaces, 8 ' 9 anomalously fast plasma blowoff, 8 and insulation of the laser-heated electrons from the target interior 7 * 8 (known in the laser fusion community as flux limitation) have all been attributed to properties of self-generated magnetic fields. All these phenomena require sharp discontinuities in plasma properties (e.g., density, temperature, and atomic charge) for their existence. Therefore, the understanding of the normal surface modes in a plasma is crucial to the understanding of these phenomena. In this Letter, I demonstrate the existence of an entirely new set of plasma surface modes. It will be shown that (1) the self-generated magnetic field plays an essential role in the propagation of these waves; (2) a number of discrete modes exist, as in a waveguide; (3) in the collisionless fluid limit, there is no restriction on the distance the waves can propagate; (4) the waves are localized around the surface on scale lengths of the order of a collisionless skin depth; and (5) the phase and group velocities are very dependent on the density and temperature profiles at the surface. While this work has been motivated by programmatic aspects of the inertial-confinement fusion program, it is felt that the results are quite general and applicable to any plasma that contains sharp density and/or temperature gradients.We choose a density profile similar to the one illustrated in Fig. 1(a). In regions A and C we require the density gradient scale lengths to be large compared with the scale length of the density jump in region B. We will permit the density to vary in the x direction only. The ions are assumed to be cold and fixed. Quasi charge neutrality is also assumed. Collisions have been neglected. The temperature profile is permitted to be arbitrary and no heat flux is permitted. We choose the magnetic field to lie in the z direction and to vary only as a function of x y y, and time. We will look for waves localized inx around region B and propagating in the y direction. The equations for the electron hydrodynamics are V«OT = 0, (1) 9 --+ 1 -7(?-fl)-VXvX(^ -fi) = -VX Vp, (2) dt r mn (a) (b) FIG. 1. (a) Density profile. The surface, region B, separates region A from region C. (b) Den...

Organic deposition has been shown to be a major problem associated with oil recovery by gas flooding. Industry is lookingfor ways of controllingorganicdepositionand economicmethods that can remedy the problem. A predictivetechniqueis crucialto the solutionof this problem, and this research projectwas designed to focus on the developmentof a predictivetechnique. A thermodynamicmodel has been developed to describe the effects of temperature, pressure,and compositionon asphaltene precipitation. The model employes a polymer solutiontheory for asphaltene-oil solution and treated asphaltene as a polydispersedmedium. The proposed model combines regular solutiontheory with Flory-Hugginspolymer solutionstheory to predictmaximumvolumefractionsof asphaltenedissolvedin oil. The model requires evaluationof vapor-liquidequilibria,first usingan equationof state followedby calculationsof asphaltene solubilityin the liquid-phase. A state-of-the-arttechnique for C7+ fraction characterizationwas employed in developingthis model. The preliminarymodeldeveloped in this work was able to predict qualitativelythe trends of the effects of temperature, pressure, and composition.

A theoretical explanation is presented of some observations from recent CO,-laser experiments by introducing a novel mechanism for harmonic light emission. The theoretical model provides new insight into the properties of large-amplitude waves in the extremely inhomogeneous environment caused by strong profile modification of the critical-dens ity plasma. PACS numbers: 52.25.Ps, 52.35.Ht, 52.35.Mw, 52.70.Kz Harmonic generation in laser-irradiated plasmas has been the subject of a number of experimental" and theoretical papers. ' These studies have been confined primarily to second-harmonic (SH) emission. The analytic efforts to understand SH have relied on perturbation theory based on the assumption of a weakly nonlinear response by the plasma in which the source current for the SH is due to beats between the first-harmonic field. Higher harmonics up to the eleventh harmonic of CO, -laser light have been reported by Burnett etal. ' The relative efficiency of the emitted lines in this work was a decreasing function of harmonic number, again a result corresponding to a weakly nonlinear plasma response.A recent paper reported the observation of CO, harmonic light as high as the 29th harmonic, ' and more recently, as high as the 46th harmonic. 'The unique feature of these data is the constant relative efficiency of the lines. It is obvious that to understand these data one must introduce a new approach which goes beyond any analysis based on mode coupling and perturbation theory.Furthermore, these data are compelling evidence for nonlinearity heretofore unexplored in the study of laser-plasma interactions. The purpose of this Letter is to understand some of the properties of this nonlinearity. Before we discuss the nonlinear mechanism for the high-harmonic C 0, emission, let us consider the absorption of the incident light. It is generally accepted that the dominant absorption mechanism of intense CO, -laser light in laser-fusion applications is resonant absorption. ' Resonant absorption in a fixed plasma density profile is a linear mechanism whereby incident light tunnels from the electromagnetic turning point and excites plasma density oscillations at the critical density, n"where =~, with~the incident light frequency and u~the local plasma frequency, respectively. Throughout the pulse time of the laser the plasma density is certainly not fixed and can develop a sharp plasma boundary as a result of the very substantial pressure of the in-