Adiabatic Expansion Of Plasma Research Articles

Fullerene C20 carbon nucleation induced by IR ns pulsed laser-generated plasma

Intense laser pulses can be employed to generate plasma, carbon aggregates, and nanoparticles. The plasma produced by ns laser pulses impinging on carbon targets in a vacuum generates carbon vapors, atoms nucleation and growth of nano aggregates. Mass quadrupole spectrometry has permitted to analyze the mass of the carbon atoms and molecules produced in a vacuum by laser-generated plasma, discovering that the fullerene C20 and other small carbon aggregates have a high probability of being produced. In this paper, the conditions of C20 aggregate synthetization are presented, and their yield generation is approximately evaluated. It also calculated the process ablation yield, the maximum carbon energy acquired in the plasma, the plasma temperature and density, the adiabatic plasma expansion velocity, and the carbon ion charge state distributions. To this, measurements of time-of-flight (TOF) of ions have been performed using suitable ion collectors and ion energy analyzers.

A Set of Benchmark Tests for Validation of 3-D Particle in Cell Methods

While the particle-in-cell (PIC) method is quite mature, verification and validation of both newly developed methods and individual codes has largely focused on an idiosyncratic choice of a few test cases. Many of these test cases involve either one- or two-dimensional simulations. This is either due to availability of (quasi) analytic solutions or historical reasons. Additionally, tests often focus on investigation of particular physics problems, such as particle emission or collisions, and do not necessarily study the combined impact of the suite of algorithms necessary for a full featured PIC code. As three dimensional (3D) codes become the norm, there is a lack of benchmarks test that can establish the validity of these codes; existing papers either do not delve into the details of the numerical experiment or provide other measurable numeric metrics (such as noise) that are outcomes of the simulation. This paper seeks to provide several test cases that can be used for validation and bench-marking of particle in cell codes in 3D. We focus on examples that are collisionless, and can be run with a reasonable amount of computational power. Four test cases are presented in significant detail; these include, basic particle motion, beam expansion, adiabatic expansion of plasma, and two stream instability. All presented cases are compared either against existing analytical data or other codes. We anticipate that these cases should help fill the void of bench-marking and validation problems and help the development of new particle in cell codes.

Plasma jet characteristics in vacuum arc with diffused cathode spot

Diffused vacuum arc, which is characterized by the absence of microparticles in cathode erosion products and by the irregular voltage oscillations, is considered to be a perspective plasma source for plasma reprocessing technology of spent nuclear fuel (SNF). The development of this technology requires data on ions energy in plasma jet. In this work parameters of plasma jet in diffused vacuum arc with a gadolinium cathode were studied by a retarding field analyzer, Langmuir and condensation probes. Gadolinium is regarded as a substance simulating SNF plasma. Ion energy spectrum was studied at arc currents of 30-75 A and voltages of 4-15 V at the distance of 20 cm above the arc anode. Dependencies of spectrum widths and most possible ion energies on arc voltages were obtained. The measured electron temperature was 2 eV, the maximum ion energy reached 70 eV. Experimental data were used to calculate adiabatic plasma expansion through the anode outlet.

Temperature gradients due to adiabatic plasma expansion in a magnetic nozzle

A mechanism for ambipolar ion acceleration in a magnetic nozzle is proposed. The plasma is adiabatic (i.e., does not exchange energy with its surroundings) in the diverging section of a magnetic nozzle so any energy lost by the electrons must be transferred to the ions via the electric field. Fluid theory indicates that the change in plasma potential is proportional to the change in average electron energy. These predictions were compared to measurements in the VX-200 experiment which has conditions conducive to ambipolar ion acceleration. A planar Langmuir probe was used to measure the plasma potential, electron density, and electron temperature for a range of mass flow rates and power levels. Axial profiles of those parameters were also measured, showing consistency with the adiabatic ambipolar fluid theory.

Space- and Time-Resolved Dynamics of Fast Electrons and of the Energy Partition Into Cold Electrons

Through the time- and space-resolved interferometry of a short-pulse low-energy probe beam reflecting on the rear surface of a solid target irradiated on its front surface by a high-intensity laser, we have measured a very abrupt expansion of the target rear surface. The experiments were performed using the LULI 100-TW laser facility with a maximum of 10-20 J energy pulses of > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> W ldr cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> intensity, wavelength of 1.053 mum irradiating Al targets. The detected phase changes, with a few micrometers spatial resolution and picosecond temporal resolution, are interpreted as induced by the cloud of fast electrons having propagated through the target and expanding into vacuum. The measurements have been performed using a laser-pulse duration of 320 fs and a laser energy of 20 J, varying the target thickness from 25, 14, and 9.4 mum. The experimental phase measurements are compared to simulations obtained by post-processing simulation data, run with a 1-D adiabatic plasma-expansion code. The comparison allows one to access, for the first time, to the dynamics of the density and temperature of laser-accelerated fast electrons in solid targets and expanding into vacuum. The same technique also allows one to have information regarding the cold electrons and the energy-partition dynamics.

Study of recombination processes during the expansion phase of titanium-plasma produced by picosecond Nd:glass laser radiation

An investigation of the plasma dynamics during its expansion phase is presented. The analysis is based on a numerical model, which considers the adiabatic plasma expansion as well as a three-body recombination process as the main source for plasma cooling. The result shows that a fast energy transfer between electrons and ions is observed during the early stage of plasma expansion. Three-body recombination process exhibits a pronounced effect leading to a “freezing” feature in the average charge states of heavy particles. This process seems to control the fractional population of ionic species at the end of the expansion phase.

Ion acceleration during adiabatic plasma expansion: Renormalization group approach

The renormalization group approach is applied to derive an exact solution to self-consistent Vlasov kinetic equations for plasma particles in the quasineutral approximation. The solution obtained describes the one-dimensional adiabatic expansion into vacuum of a plasma bunch with arbitrary initial velocity distributions of the electrons and ions. The ion acceleration is investigated for both a Maxwellian two-temperature initial electron distribution and a super-Gaussian initial electron distribution.

Pulsed‐laser deposition of thin‐film process characterization by optical spectroscopy

Spectral analysis of CO2-TE-laser-ablated plasma on YBa2Cu3O72-x targets demonstrates a very complex spectrum with emission lines from atomic and ionic species. Plasma temperature is estimated at different moments in its evolution. A good accordance with the values achieved by considering an adiabatic plasma expansion is obtained. Plasma emission intensity is studied as a function of laser pulse energy and, for the same incident energies, a very reproducible amplitude is evidenced. Using a hydrodynamic model, plasma parameters are calculated.

Observation of Coulomb liquids and solids in lasergenerated plasmas: regime of adiabatic plasma expansion

In the high power laser treatment of metal surfaces (Ti, Ta, Mo) in of O 2 and N 2, at the pressure P = 2–6 atm, with the CO 2 laser beam of energy density Q ∼ 20–50 J/ cm 2, of the power density ∼ 10 9 W/ cm 2, and of the pulse duration τ ∼ 150 ns, some new effects have been observed. The laser-material interaction occurred in the highly absorptive plasma regime, meaning that the metal surface was effectively screened from the beam. Because of the neutral particles immersed, the plasma was a type of “colloidal” or “dusty” plasma. The neutral particles (probably the metal clusters or clusters of metal oxides) “dressed” with (+) ions, of the size ∼ 10 μm to ∼ 30 μm, of the volume density ∼ 20 × 10 6 cm −3, move radially with expanding plasma and strike the metal surface. A high particle's temperature ( T ∼ 3200 K) causes them to behave as micro-scale fireballs leaving the hot spots on the surface. Metal surface reveals two-dimensional orthogonal projection of the Coulomb system: (i) with random structure which represents either amorphous (glassy) solid, or liquid, (ii) with the short range-order of hcp hexagonal lattice which represents a Coulomb liquid, (iii) with the middle-range order showing the coexistence of the hcp hexagonal and bcc cubic lattices, which represents a polycrystal (near the solid-liquid transition), (iv) with the long-range order with the bcc cubic lattice, which represents the Coulomb solid and finally, (v) with the bcc → fcc deformation induced transition, caused by the shear waves. A local geometrical order was found to appear for the critical surface charge on the particles Q p ∼ 2,1 × 70 4 e (of elementary charge). Debye shielding radius λ D was estimated to be ∼ 70 μm (in adiabatic plasma expression), and ∼ 52 μm (in isothermal expression during the laser pulse).