Topic

# Plasma parameters

About: Plasma parameters is a(n) research topic. Over the lifetime, 9050 publication(s) have been published within this topic receiving 128542 citation(s).

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Abstract: Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.

1,062 citations

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Abstract: The conception of random positive ion velocities corresponding to ion temperatures in a plasma has serious theoretical difficulties and is lacking in direct experimental verification It is more reasonable to assume that each ion starts from rest and subsequently possesses only the velocity which it acquires by falling through a static electric field which is itself maintained by the balance of electron and ion charges This new viewpoint thus ascribes motions to the positive ions which, for long free paths, are ordered rather than chaotic, each negative body in contact with the discharge collecting ions from a definite region of the plasma and from it only The resulting integral ? the plasma-sheath potential distribution have been set up for plane, cylindrical, and spherical plasmas, for long, short and intermediate length ion free paths, and for both constant rate of ionization throughout the plasma and rate proportional to electron density, and these equations have been solved for the potential distribution in the plasma in all important cases The case of short ion free paths in a cylinder with ion generation proportional to electron density gives the same potential distribution as found for the positive column by Schottky using his ambipolar diffusion theory, with the advantages that ambipolarity and quasineutrality need not appear as postulates The calculated potential distribution agrees with that found experimentally The potential difference between center and edge of plasma approximates $\frac{{T}_{e}}{11,600}$ volts in all long ion free path cases The theory yields two equations One, the ion current equation, simply equates the total number of ions reaching the discharge tube wall to the total number of ions generated in the plasma, but it affords a new method of calculating the density of ionization The second, the plasma balance equation, relates rate of ion generation, discharge tube diameter (in the cylindrical case), and electron temperature It can be used to calculate the rate of ion generation, the resulting values checking (to order of magnitude) those calculated from one-stage ionization probabilities The potential difference between the center of the plasma and a non-conducting bounding wall as calculated from the ion current equation agrees with that found experimentallyThe solution of the general plasma-sheath equation has been extended into the sheath surrounding the plasma to determine the first order correction which is to be subtracted from the discharge tube radius to obtain the plasma radius The wall sheath in the positive column is several times the thickness given by the simple space charge equationActually the ions do not start from rest when formed but have small random velocities corresponding to the gas temperature, ${T}_{g}$ In the long ion free path cases this leads to an error of the order of only $\frac{{T}_{g}}{{T}_{e}}$ in the calculated potential distributionsIn the plasma surrounding a fine negatively charged probe wire the potential difference between plasma potential maximum and sheath edge may be so small that the ions generated within the plasma potential maximum are not trapped but can traverse the maximum by virtue of their finite initial velocities This justifies the use of a sufficiently fine negatively charged wire in the usual way to measure positive ion concentrations, although certain difficulties appear which are thought to be connected with the collector theory rather than the present plasma theory

813 citations

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Abstract: The addition of a small concentration of suitably chosen noble gas to a reactive plasma is shown to permit the determination of the functional dependence of reactive particle density on plasma parameters. Examples illustrating the simplicity of this method are presented using F atomic emission from plasma‐etching discharges and a comparison is made to available data in the literature.

766 citations

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Abstract: A review is presented of plasma chemical processes occurring in the volume part of electrical nonequilibrium discharges. The role of energetic electrons as initiators of chemical reactions in a cold background gas is discussed. Different discharge types of (glow, corona, silent, RF, and microwave discharges) are investigated with respect to their suitability for plasma processing. Emphasis is placed on the requirements of initiating and maintaining the discharge and, at the same time, optimizing plasma parameters for the desired chemical process. Using large-scale industrial ozone production as an example, the detailed process of discharge optimization is described. Other applications of volume plasma processing include other plasma chemical syntheses as well as decomposition processes such as flue gas treatment and hazardous waste disposal. The author only deals with plasmas which are not in equilibrium. >

742 citations

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Abstract: The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than in current accelerators has been well documented. We develop a phenomenological framework for laser wakefield acceleration (LWFA) in the 3D nonlinear regime, in which the plasma electrons are expelled by the radiation pressure of a short pulse laser, leading to nearly complete blowout. Our theory provides a recipe for designing a LWFA for given laser and plasma parameters and estimates the number and the energy of the accelerated electrons whether self-injected or externally injected. These formulas apply for self-guided as well as externally guided pulses (e.g. by plasma channels). We demonstrate our results by presenting a sample particle-in-cell (PIC) simulation of a $30\text{ }\mathrm{fs}$, 200 TW laser interacting with a 0.75 cm long plasma with density $1.5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ to produce an ultrashort (10 fs) monoenergetic bunch of self-injected electrons at 1.5 GeV with 0.3 nC of charge. For future higher-energy accelerator applications, we propose a parameter space, which is distinct from that described by Gordienko and Pukhov [Phys. Plasmas 12, 043109 (2005)] in that it involves lower plasma densities and wider spot sizes while keeping the intensity relatively constant. We find that this helps increase the output electron beam energy while keeping the efficiency high.

726 citations