C16. Commission on Plasma Physics

Report to the 1999 General Assembly for 1996-99

Members:

J.S. Bakos, Hungary
R. Bharuthram, South Africa
R. Cross, Australia
Ricardo Galvão, Brazil
J-C. Gauthier, France
V.E. Golant, Russia
Brian C. Gregory, Canada
A. Sen, India
K.M. Spatschek, Germany
M. Wakatani Japan

Associate Members:

D.B. Melrose, Australia
S. Penselin, Germany

Activities

The Commission elected at the 1998 General Assembly had the following composition: Africa 1, Asia 2, Australia 2, Europe 8, North America 2, South America 1.In addition, the link with Statistical Physics was reflected through associate membership of an expert from that Commission.

Although international collaborations and conferences in the field of plasma physics take place within the IUPAP family, there are also many activities, which take place outside that framework.Thus, for instance, both fusion and space plasma physicists gather under the auspices of other international bodies, as well.

Commission is an active one and it has met annually, typically in the context of IUPAP-sponsored Conferences, as well as keeping in touch by correspondence. A meeting was scheduled at the IUPAP-sponsored International Conferences on Plasma Physics in joint with the European Physical Society meeting on Fusion and Plasma Physics Czech Republic (1998).

The Commission sponsors two complementary major conference series on plasma physics: The International Conference on Phenomena in Ionized Gases (ICPIG) and the International Conference on Plasma Physics (ICPP). While the ICPIG series emphasises low-temperature partially - ionized gases, including many industrial applications, the ICPIG series concentrates on high-temperature, fully ionised gases, such as are of interest in fusion and space physics.

Fusion plasma physics is also the subject of other major conference, such as the IAEA sponsored series on Plasma Physics and Controlled Nuclear Fusion Research, and every attempt is made to ensure that ICPP does not clash with the latter. In addition to these two major series, the Commission also supports individual meetings, particularly in research areas of developing interest. For example the International Conference on Dusty Plasmas, Goa, India (1996), the next meeting to be held in Hakore, Japan (1999).

The Commission has also endeavoured to intensify interaction with industries involved in plasma applications. The objective is to ensure that (a) plasma physicists in the industry stay fully informed about the latest developments in the field so that the new results can be quickly applied to technical applications and (b) the problems faced in industrial applications are exposed to a wide cross-section of the plasma community so that they can participate in finding solutions.

Conferences sponsored by IUPAP following recommendations by C.16:

1996 International Workshop on Dusty Plasma, Goa, India October.
1996 International Conference on Phenomena in Ionised Gases, Hoboken, NJ, USA July-August.
1996 International Conference on Plasma Physics, Nagoya, Japan September.
1997 International Conference on Phenomena in Ionised Gases Toulouse, France
1998 International Conference on Plasma Physics,Prague, Czech Republic

New Developments in the Field

Plasma Physics continues to develop with immense vigour both in its fundamental aspects and various applications. As a paradigm for systems far from thermodynamic equilibrium, which are dominated by non-linear collective phenomena, plasmas have no parallel. They are giving us a wealth of experimental information on non-linear phenomena like chaos, turbulence, anomalous transport, solitions, vortices etc., and leading us towards quantitative descriptions of such effects and providing an intuition for new guiding principles necessary for describing far from equilibrium systems. At the same time, as we learn more about plasmas and how to manipulate them, we have been able to use them in a great number of applications ranging from fusion to free electron lasers, plasma processing to novel accelerators and radiation sources, MH power generators to propulsion devices, such as ion drive used in NASA's Deep Space satellite and ESA's smart mission. :Z-pinch research is enjoying a revival and is one of the fastest growing areas of research in plasma physics.

Progress in Magnetic Fusion Research

After initial deuterium-tritium experiments on JET (Joint European Torus) an extensive study of D-T plasmas has been performed on TFTR (Tokamak Fusion Test Reactor, Princeton). TFTR has explored a wide range of physics issues in plasmas with high concentrations of tritium and achieved Megawatts of fusion power. There is a strong positive isotope scaling in high performance plasmas. The energy confinement time was found to increase in D-T, relative to D plasmas, by 20% and the [Ni(0)Ti(0) tE] product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity. Alpha ash us rapidly transported out of the plasma.

Further major steps have been made in confinement optimisation. In addition to the H-mode scenario, which reveals itself in edge transport barrier formation, several new operational modes with improved central confinement have been found. Internal or Core Transport Barriers have been achieved in JT-60U and PBX-M. An extremely interesting regime is that of Reversed Magnetic Shear which has been observed in TFTR, JET, DIII-D, Tore-Supra and JT-60U. In this regime, the thermal conductivity in the core drops down to a very low value (comparable to neo-classical values or sometimes even smaller than that) and there is a concomitant reduction of turbulence levels.

Significant progress has been achieved in development of a Steady State operational scenario needed for reactor. In many tokamaks possibilities of noninductive current drive have been studied. Lower Hybrid RF Power was shown to be an effective means for current drive. Several mega amperes of current was obtained experimentally in JET, Tore Supra and JT-60U with assistance of lower hybrid waves. High beta-poloidal allows one to achieve large fractions of ``bootstrap'' current. The regimes with bootstrap fraction up to 0.7 of full current were obtained in JET and DIII-D.

A critical problem in the design of steady state fusion reactors is that of high power load on divertor plates. A `radiative divertor' concept has been proposed to solve this problem. Intensive puffing of hydrogen gas or low Z impurities like Neon into the divertor chamber allows the divertor plasma to radiate most of the power transported there from the main plasma chamber. This radiated power distributes itself uniformly on the divertor chamber walls and prevents high heat flux loads on the divertor plates. Experiments performed on many divertor tokamaks have demonstrated efficiency of this concept and also the possibility of combining radiative divertors with improved confinement modes of operation.

Z-pinches

This is one of the fastest growing areas of plasma physics, which revives interest in Z-pinch control fusion reactors along with new investigations of new z-pinch applications, such as high powered x-ray sources, high energy neutron sources and ultra high magnetic field generators.

Laser Plasma Interactions and Laser Fusion

Rapid advances have taken place recently in laser plasma interaction studies due to the relaxation, in the United States, of classification of experiments on x-ray driven hohlraums and also the developmeent of inexpensive ultra-short pulse high power lasers. It is the ultra short pulse laser development that has created some of the most promising advances. Fields in excess of 109 V/cm have been produced in laser plasma interactions producing electron energies of 100 MeV in distances of the order of mm. This opens the way for future experiments in this area and already experimentalists are talking about producing GeV electron beams in the near future. It is still a long way from producing TeV beams for high-energy experiments, using these techniques. The theory of intense ultra-short pulse interaction with plasmas is advancing rapidly with many new developments in highly non-linear, relativistic plasma interactions. X-ray production using short pulse laser is also being pursued by a number of groups and the observation of harmonics created by non-linear effects up to the 73rd have been observed. Isotope production and g-ray generations are new areas being studied.

Laser fusion is now progressing on two fronts, a) Direct drive and b) indirect drive using hohlraum targets. At present there does not seem to be a clear winner.

Short pulse high intensity lasers are also being investigated as possible triggers for ignition of the pellet fuel; at maximum compression the intense laser would tunnel through the pellet and provide enough energy to ignite the fusion fuel.

The National Ignition Facility if under construction at the Lawrence Livermore Laboratory.

Astrophysics and Space Plasmas

Plasma astrophysics is still a relatively young field. space plasma physics, on the other hand, is a fairly vigourous discipline with a very large number of papers being published every year. Both of these fields are strongly influenced by the launching of new satellites.

The Satellite SOHO (Solar and Heliospheric Observatory) after a brief period of inactivity due to command error is nor working satisfactorily. SOHO is designed to study Sun's interior using helioseismology data from various instruments, as well as its exterior. The results from this satellite may be able to solve two major problems in solar physics viz. the solar neutrino deficit problem and the problem of explaining the high temperatures (~1 keV) observed in the solar corona.

Another spacecraft launched in November 1995 called ISO Infrared Space Observatory) is also of interest to plasma astrophysicists since it will be studying the formation of stars from large dust clouds. The dust clouds will most likely be charged at some stage of star formation which will certainly alter the interaction physics involving electromagnetic as well as gravity interactions known as electro-gravity processes. Dusty plasmas is a relatively new area of study and is one that is expanding rapidly both in laboratory and astrophysical plasmas.

The Cluster satellites which, unfortunately were destroyed during the first Arianne 5 launch is back with a launch schedule of 2000. This mission is aimed at building up a better understanding of the earth's magnetosphere and in particular the interaction of the solar wind plasma with the magnetosphere.

The four spacecraft will have similar orbits and will be able for the first time to send back information on spatial scales. One of the main objectives is to understand the penetration of the solar wind plasma into the magnetosphere and the development of substorms which are a major source of concern for power companies in high latitude areas where disruptions to power line supplies can be initiated by substorms. The predictions of substorms is fast becoming an important area and goes by the name of space weather. Astronauts are also effected by energetic particles created during these substorms. The recent comet X-ray observations, a surprise to most comet researchers, has been shown to be due to the solar wind interacting with the neutral cometary atmosphere. This has lead to a significant amount of research into this and other space physics areas.

Plasma physics is now also beginning to have an impact on other areas of astrophysics such as in the understanding of supernovae explosions. It is widely recognised that the neutrinos must interact more strongly with the plasmas and heat the electrons. These electrons help to provide sufficient energy to blow the star apart. This is a new area of research and is expanding the domain of usefulness of plasma physics research.

There are many other areas of astrophysics research where plasma physics is beginning to play an ever expanding role, examples being a) the origin of magnetic fields in the universe, b) relativistic jets. There is also the problem of the missing matter in the universe, which may be explained by hot plasma. The X-ray background spectrum in the range 3 - 50 keV implies the existence of very hot plasma. The mass involved could be enormous (more than all other known or implied mass in the universe); if true, then this is indeed an important result for cosmology. An important meeting on laboratory experiments for astrophysics was held in Tucson, Arizona (1998). The meeting brought together laser plasma and astrophysicists.

Fundamental Plasma Physics

During the past three years major developments have taken place in fundamental studies related to exotic plasmas and complexity and self-organisation in plasmas.

Among exotic plasmas, non-neutral plasmas have received a lot of attention. The study of 2-D turbulence using experiments on non-neutral electron clouds has led to major insights on formation and merging of vortex structures. Electron clouds have also being observed in toroidal configurations and poloidally asymmetric states leading to a description in terms of 'optimal energy states'.Experiments on positron plasmas have also been initiated.

The physics of dusty plasmas is of consideerable interest because of it applications to planetary physics as well as to plasma etching systems. Collective effects in such plasmas are being studied, especially taking account of dust charge fluctuations.The nonlinear theories of such waves are also being examined.A number of experiments with novel diagnostics have started to explore the plasma physics of dusty plasmas.

The physics of strongly correlated plasmas is also attracting a lot of attention. The formation of `crystals' has already been seen in strongly correlated dusty plasmas. Molecule dynamics simulations have also demonstrated novel liquid crystal like behaviour in certain other situations such as pure one-component plasmas. Experiments and theory are proceeding hand in hand and generating interesting results in this area.

The problem of complexity and self-organization is fundamental to plasma physics. Computer simulations have generated a wealth of information on the possible coherent structures produced in nonlinear open and driven systems. These can be understood in, terms of minimisation of energy, optimisation of rate of entropy production and sometimes effects associated with entropy expulsion at boundaries. The description of intermittency in plasma turbulence is also related to such transient coherent vortex like structures. The physics of formation and destruction of vortices in turbulent configurations continues to be a topic of great interest. There is also considerable interest in modelling a number of such phenomena using the paradigm of self-organised criticality, so successful in critical phenomena.

R. Bingham