Lennart Stenflo

Alfven vortices in a strongly magnetized electron-position plasma

Using the cold plasma and Maxwell equations, the authors derive a pair of coupled nonlinear equations governing the propagation of finite amplitude shear Alfven waves in a strongly magnetized electron-positron plasma. It is shown that the waves can propagate in the form of two-dimensional polar vortices. The latter may affect cross-field particle and energy transport in the pulsar magnetosphere. 27 references.

Drift wave driven zonal flows in plasmas

The generation of large-scale zonal flows by small-scale electrostatic drift waves in a plasma is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves. To describe this process a generalized Hasegawa–Mima equation containing both vector and scalar nonlinearities is used. The drift waves are supposed to have arbitrary wavelengths (as compared with the ion Larmor radius). A set of coupled equations describing the nonlinear interaction of drift waves and zonal flows is deduced. The generation of zonal flows turns out to be due to Reynolds stresses produced by finite amplitude drift waves. It is found that the wave vector of the fastest growing mode is perpendicular to that of the drift pump wave. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. A comparison with previous results is carried out. The present theory can be used for interpretations of drift wave...

Alfvén waves in cosmic and laboratory plasmas

This Topical Issue of Physica Scripta is dedicated to Professor Hannes Alfven (1908–1995). In order to review the state-of-the-art on Alfven waves in cosmic and laboratory plasmas, an International Workshop on Alfven Waves was organized at the State University of Rio de Janeiro (UERJ), Brazil, during November 8–10, 1994. The Alfven waves that Professor Alfven predicted in the 1940s are of fundamental importance to laboratory plasma physics, space plasma physics, and plasma astrophysics. It is remarkable that after half a century of its discovery, the subject of Alfven waves is still an active area of research in all branches of plasma physics. This Topical Issue consists of invited lectures delivered at the International Workshop on Alfven Waves. In addition, a number of leading experts on Alfven waves have been invited to contribute papers to this special issue. With the assistance of these colleagues, this issue has a good coverage of most aspects of Alfven wave research today. The workshop was made possible by the kind support of Professor H Cordeiro (Rector of UERJ), Miss G S Dutra (Workshop Secretary), the State University of Rio de Janeiro and the Research Foundation of State of Rio de Janeiro (FAPERJ).

Workshop on Large Amplitude Waves and Fields in Plasmas, sponsored by the Commission of the European Communities

During the last decade considerable progress has been made in the area of nonlinear plasma wave phenomena and their applications. In order to exhibit the present state-of-art in this field, a one-week (22–26 May) workshop on Large Amplitude Waves and Fields was organized at the International Centre for Theoretical Physics (ICTP), Trieste, Italy, during the bi-yearly activity of the Spring College on Plasma Physics (15 May–9 June, 1989). Most of the invited lectures are published in this Topical Issue of Physica Scripta so that scientists working, or who want to enter the field of nonlinear plasma wave theory, can find out what has been achieved and what are the current research trends in this area. The material included here consists of general plasma wave theory, results of computer simulations, and experimental verifications. Without going into any detail, we shall just highlight the topics and the general features of the lectures contained in these proceedings. Various aspects of the excitation, propagation and interaction of nonlinear waves in plasmas are reviewed. Their relevance to plasma-based beat wave accelerators, short pulse laser and particle beam wake-field accelerators, plasma lenses, laser fusion and ionospheric modification experiments is discussed. Some introductory lectures present the general physics of nonlinear plasma waves including the saturation mechanisms and wave breaking conditions for both non-relativistic and relativistic nonlinearities. Three wave and four wave processes which include stimulated Raman, Brillouin and Compton scattering, modulational instabilities, self-focusing and collapse of the waves are discussed, emphasizing the important effects due to the relativistic electron mass variation and ponderomotive force. Detailed numerical studies of the interaction of high frequency plasma waves with low frequency density fluctuations described by the Zakharov equations show the localization of the high frequency field in density cavities and their burn-out resulting in very strong turbulence. Remarkable agreement between the simulations and ionospheric modification experiments have been demonstrated. The articles presented also attempted to correlate the theories of parametric instabilities with experimental observations. The properties of plasma lenses used for focusing of high energy particle beams is also presented as part of the uses of the nonlinear plasmas. Self-organisation of plasmas resulting in coherent nonlinear structures and particle diffusion processes are reported. On the experimental side the nonlinear optics of plasmas as a new area of research has been reviewed. This is becoming an important area for research since it treats the plasma from the outset as a nonlinear medium. Experimental observations of phase conjugation of electromagnetic signals demonstrate once again the importance of the nonlinearities inherent in the interaction of large amplitude waves with plasmas. Finally the importance of turbulence in space plasmas is emphasized in a discussion of the auroral phenomenon, presenting the plasma physicists point of view on this topic. The workshop, attended by scientists from all over the world, stimulated a great deal of lively discussions about the theoretical foundations, experimental observations and interpretations together with computer simulation results on the physics of nonlinear plasma wave phenomena. The workshop was made possible by the kind support of Professors A Salam, L Bertocchi and M Hassan. We are grateful to them for giving us the opportunity to organize the workshop within the activities of the Spring College on Plasma Physics. Thanks are also due to the ICTP and the European Economic Community (EEC) for providing partial financial support. Finally, our most cordial thanks are extended to the invited speakers for coming to Trieste delivering excellent talks and enhancing the activity of the Spring College.

International Topical Conference on Plasma Physics: New Perspectives of Collective Effects

The International Topical Conference on Plasma Physics: New Perspectives of Collective Effects (ITCPP-97) was held at the Abdus Salam International Centre for Theoretical Physics (ASICTP), Trieste, Italy, during the period 10 – 14 November 1997 and was sponsored by the ASICTP (Trieste) and the IUPAP. The conference was organized by us with the help of an international advisory board and a program committee that included scientists from all over the world. The purpose of this conference was to provide an informal forum for members of the plasma physics, nonlinear optics, astrophysics, and fluid dynamics communities to meet and discuss with other researchers studying collective processes in nonlinear dispersive media. It was perceived that the conference filled an important need, not satisfied by large conferences sponsored by different professional societies. The challenge was how best to integrate the intellectual resources and unique strengths of groups who deal with similar kinds of methodologies to describe quite diverse nonlinear phenomena, and to push forward the frontiers of new collective effects in physics for the twenty-first century. The response of the conference was overwhelming. It was attended by approximately 120 scientists from 43 countries, and the participation from the industrial and the developing countries was about half each. The participants from the developing countries included a large number of young graduate students and post doctoral fellows, in addition to a limited number of well known senior scientists who delivered invited talks. The program included 5 invited review talks (45-minutes each) and 30 invited topical lectures (30-minutes each). In addition, there were 81 contributed posters in three sessions. The latter gave opportunities to younger physicists for displaying the results of their recent work and to obtain constructive comments from the other participants. During the five days at the ASICTP, we focused on various aspects of new collective effects that have potential applications in different branches of sciences. The review and topical lectures as well as the posters dealt with the most recent advances on coherent nonlinear structures in space and astrophysical plasmas, fluids and optics, ordered and melting states in low-temperature dusty plasmas, as well as parametric and transport processes in laser produced and magnetically confined laboratory plasmas. The focus was on wave-particle and wave-wave interactions and nonlocal particle and heat transports, phenomena governed by the generalized MHD and gyrokinetic equations, the generation and development of turbulence, ordered and chaotic states in nonuniform media, the formation of new molecules (dusty plasma crystals) in strongly coupled systems, new x-ray sources, plasma based charged particle acceleration by intense electrostatic waves that are created by intense short laser pulses, new trends in particle astrophysics (viz. studies of collective processes involving neutrinos for understanding the origin of the inhomogeneities and the magnetic fields in the early universe as well as during supernova explosions, etc.) Specifically, the review lectures presented the general picture of the subject matter at hand and the underlying physics, whereas the remaining topical talks and posters described the present state-of-art in the field. The first lecturer at the conference was Dr. W. L. Kruer (Los Alamos Laboratory at Livermore) who emphasized the importance of stimulated scattering instabilities of powerful laser beams in the presence of high-Z impurities, and the effects of nonlocal heat transport on collective processes in inertial confinement fusion (ICF). Furthermore, all the speakers kept a good balance in injecting the new physics and advanced mathematical techniques to their audience. Most of the contributions from the Trieste meeting appear in this Topical Issue of Physica Scripta, which will be distributed to all the participants. A visible trend at this conference was the attendance of a sizable number of fusion experimentalists. It is evident that the recent cuts in the support for fusion research means that additional scientists now look into fundamental problems that are unsolved in space and astrophysics as well as those dealing with new materials (dusty plasma crystals) and new particle acceleration schemes. Thus, the experience from tokamak experiments can be connected to other modern fields of plasma physics that are going to play a very important role in the twenty first century. In conclusion, we strongly feel that there is an important role to be played by the ITCPPs and that the next conference should be held in the autumn of 1999 at the ASICTP. It is expected that at that time there will be more scientific exchanges between the different areas representing our nonlinear world. We are grateful to the ASICTP director Professor M. A. Virasoro for his generous support and warm hospitality at the ASICTP. Thanks are also due to Professor F. Hussain of the ASICTP and Professor M. H. A. Hassan of the Third World Academy of Sciences (TWAS, ASICTP) for their constant and wholehearted support in our endeavour. Finally, we would like to express our gratitude to the ASICTP and the IUPAP for providing partial financial support to our conference at Trieste. Besides, our cordial thanks are extended to the speakers and attendees for their contributions which resulted in the success of the ITCPP-97. The excellent work of the scientific secretaries Dr. Srinivas Jammalamadaka and Dr. Nagesha N. Rao, and the ASICTP secretary Mrs. Pandora Pieri is gratefully acknowledged.

Workshop on Wave-Particle Interaction and Energization in Plasmas

Sponsored by the Commission of the European Communities. During the 1987 Spring College on Plasma Physics Professor Abdus Salam asked us to help organize the plasma physics activity at the ICTP with the hope that more Europeans would get involved in the endeavors of diffusing modern plasma physics knowledge to the participants who come mostly from developing countries. In order to fulfill his expectations, we formed a European team for organizing at least a one-week workshop during the biennial activity of the Spring College on Plasma Physics at Trieste. Since 1989, we have taken an active part in organizing the fourth week of the Spring College on Plasma Physics at the ICTP. We have also brought out the lecture notes in the form of Topical Issues in Physica Scripta, for distributing the advanced scientific materials to the participants. This fourth week has now become a permanent feature of the ICTP plasma physics activity and serves the purpose of bringing together scientists from different parts of the world in a forum so that they can exchange ideas and interact for mutual benefits. This year we focused on wave-particle interaction and energization in plasmas. The present topics fall within one of the most advanced areas of plasma physics, where there is an urgent need to understand the turbulent as well as the coherent plasma wave phenomena. We invited distinguished lecturers, who presented the fundamentals of interactions in plasmas. The lectures covered basic as well as advanced topics dealing with wave phenomena, which are of current interest in laboratory and space plasmas. Accordingly, the morning lectures were centered around a unified theme covering quasilinear theory in the context of weak turbulence, wave-wave interactions, theory and computer simulations of magnetic field reconnection, as well as the generation of coherent nonlinear structures in laboratory plasmas. In the afternoon sessions, the lecturers went on to describe the present state of the art with various aspects of wave-particle interactions. They focused on the generation of intense waves, arrest of wave collapse, distortion of the distribution functions, as well as charged particle acceleration in space and laboratory plasmas. The highlights of these activities were documented in the invited papers, which are presented in this issue of Physica Scripta. This material supplements the existing plasma physics literature and should be valuable to the plasma physics community. As in the past, we have received wholehearted support from Professors Abdus Salam, Luciano Bertocchi, and Mohamed H A Hassan. We are grateful to them for giving us the opportunity to organize the present workshop within the activities of the Spring College on Plasma Physics. Thanks are also due to the ICTP and the Commission of the European Community in Brussels for providing financial support to our activities at Trieste. Finally, our cordial thanks are extended to the invited speakers for coming to Trieste, delivering excellent talks, supplying well prepared manuscripts for publication, and enhancing the activity of the Spring College on Plasma Physics at the ICTP.