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Single-cycle high-intensity electromagnetic pulse generation in the interaction of a plasma wakefield with regular nonlinear structures (vol 73, art no 036408, 2006)
No full textSHORT, RELATIVISTICALLY STRONG LASER-PULSE IN A NARROW CHANNEL
No full textWe present the results of an analytical study and of a two-dimensional particle-in-cell simulation of a relativistically strong laser pulse propagating in a narrow channel which eliminates the pulse spreading due to diffraction. In an empty channel with sharp boundaries, the main absorption mechanism is ''vacuum heating'' of the electrons expelled from the walls. These electrons fill the channel and form a charged cloud which moves at a relativistic velocity behind the pulse and produces a longitudinal electric field that can be used to accelerate charged particles. This cloud can also act as a mirror and, interacting with electromagnetic radiation, upshift its frequency. The interaction with the channel wall depends on the pulse intensity and polarization. TM-polarized pulses undergo greater losses than TE-pulses, and cause the formation of a charged cloud, of high harmonics and of a quasi-static magnetic field. In the case of a channel filled by an underdense plasma, an ultrashort pulse excites a strong wake wave with a longitudinal electric wake field which can accelerate charged particles
Single-cycle high-intensity electromagnetic pulse generation in the interaction of a plasma wakefield with regular nonlinear structures
No full textThe interaction of regular nonlinear structures (such as subcycle solitons, electron vortices, and wake Langmuir waves) with a strong wake wave in a collisionless plasma can be exploited in order to produce ultrashort electromagnetic pulses. The electromagnetic field of the nonlinear structure is partially reflected by the electron density modulations of the incident wake wave and a single-cycle high-intensity electromagnetic pulse is formed. Due to the Doppler effect the length of this pulse is much shorter than that of the nonlinear structure. This process is illustrated with two-dimensional particle-in-cell simulations. The considered laser-plasma interaction regimes can be achieved in present day experiments and can be used for plasma diagnostics
Generation of high-quality charged particle beams during the acceleration of ions by high-power laser radiation
No full textNumerous applications of protons and ions accelerated by laser radiation require charged particle beams of high quality (i.e., such that the ratio of the energy width of the beam to its mean energy is small). In order to produce beams with controlled quality, it is proposed to use two-layer targets in which the first layer consists of heavy multicharged. ions and the second layer (thin and narrow in the transverse direction) consists of protons. The possibility of generating a high-quality proton beam in the interaction of ultraintense laser radiation with such a two-layer target is demonstrated by two- and three-dimensional particle-in-cell computer simulations. (C) 2002 MAIK "Nauka/Interperiodica"
Interaction of petawatt laser pulses with underdense plasmas
No full textResults are presented from analytical study and particle-in-cell simulations of the interaction of ultrashort petawatt laser pulses with underdense plasmas. It is shown that this interaction exhibits effects typical of the interaction of moderate-power pulses with overdense plasmas. The results obtained demonstrate relativistic self-focusing, the formation of a vacuum channel in a plasma, excitation of a superstrong longitudinal electric field, acceleration of ions and electrons up to ultrarelativistic energies, and generation of a quasistatic magnetic field. The generation of relativistic electromagnetic solitons is demonstrated. It is shown that a significant part of the laser-pulse energy is transformed into the energy of these solitons. The space and time dependences of the fields inside the solitons are found to agree with our analytical description
Reconnection of magnetic field lines near critical points
No full textA review of theoretical studies and computer simulations of the plasma dynamics near critical points of the magnetic field is presented. The global characteristics of reconnection of the magnetic field lines and vortex lines are discussed. Examples of typical patterns of the magnetic field near critical points are presented. The propagation of MHD waves and the formation of singularities near null lines and separatrix surfaces are discussed. Nonlinear regimes of the plasma dynamics are described, and exact solutions of the MHD equations in which the Hall effect is taken into account are presented. The magnetic reconnection in the frame of the electron magnetohydrodynamics model is also discussed. The results of computer simulations of the current sheet formation near null lines and separatrices of the magnetic field are presented. The nonadiabatic motion and the acceleration of charged particles near critical points are discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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