Table of contents

The biennial International Congresses on Plasma Physics (ICPPs) are the most international of the full-spectrum plasma physics conferences, having no permanent tie to any one regional physical society, but rather making different regional links as they move around the world. The 2002 Congress, held in the southern Asia-Pacific region, incorporated the 6th Asia Pacific Plasma Theory Conference, the 24th Australian Institute for Nuclear Science and Engineering (AINSE) Plasma Science and Technology Conference, and the 6th Japan-Australia Plasma Theory and Computation Workshop.

About 290 delegates met at the Manly Pacific Park Royal, Sydney, Australia between 15-19 July, 2002. In an age of specialization, ICPP 2002 was a general conference in plasma physics. A theme of the conference was the unity of plasma physics, covering all aspects, from low-temperature plasmas to fusion plasmas, from industrial applications to astrophysics, and all three approaches to investigating physical phenomena: experiment, observation and theory.

The International Programme Committee, co-chaired by Robert Dewar of The Australian National University and Michael Tendler of the Royal Institute of Technology, Stockholm, met in Sydney in February 2002 to select the programme of 49 invited Plenary and Review talks for the morning programme. These were selected from nominations submitted by the International Advisory Committee, the Local Organizing Committee, the Programme Committee itself, and self-nominations in abstracts submitted.

This cluster of papers in Plasma Physics and Controlled Fusion is the result of an invitation kindly extended by Institute of Physics Publishing to the Plenary and Review Speakers to submit papers based on their talks. The refereeing of these papers was administered by the editors of Plasma Physics and Controlled Fusion in accordance with their usual high standards.

The Congress was underwritten by the Australian Institute of Physics, the Department of Theoretical Physics and the Plasma Research Laboratory at The Australian National University's Research School of Physical Sciences and Engineering, and by the Head of the School of Physics, University of Sydney. The organizers thank the main sponsors - the International Union of Pure and Applied Physics (IUPAP) and the New South Wales Department of State and Regional Development.

The standard model for radio pulsars implies that the `pulsar plasma' in the source region is a highly relativistic, strongly magnetized, one-dimensional, electron–positron pair plasma. Relativistic quantum effects lead to a correction of first order in ℏ to the linear response of a pulsar plasma due to its spin dependence, but this is small for highly relativistic particles. Wave dispersion in the radio range involves the X-mode, Alfvén mode and L–O mode. It is argued that the most plausible radio emission mechanism involves a nonresonant beam instability due to a beam mode that couples to the L–O mode. It is suggested that `orthogonal modes' in the observed radio emission arise from mode coupling at sharp gradients at the edges of ducts, and that the observed circular polarization is associated with gyrotropy (a difference in the electron and positron distributions) and it develops as a propagation effect.

If the mechanism responsible for creating the high-temperature solar corona is a magnetic one, the resulting coronal heating events are likely to be highly sporadic and fragmented. Therefore, nanoflare heating, where both these features are present, by the very meaning of the concept, is a strong candidate. The major problem is how to test this theory while individual nanoflares remain beyond observational recognition. Here, we discuss a possibility of probing the nanoflare heating scenario by considering statistical characteristics of coronal active regions, which presumably originate from a large number of random impulsive heating events. This approach allows one to derive various parameters of x-ray coronal loops (temperature, emission measure, filling factor, etc) without specifying particular details of the heating events. How the energy of individual nanoflares can be estimated from observed fluctuations in the coronal x-ray emission is also discussed. Comparison of our results with recently reported analysis of small fluctuations of coronal x-ray intensity observed with Yohkoh SXT telescope yields an estimate of (10²²–10²³) erg for the energy of nanoflares in the active region.

To understand how large systems of neurons communicate, we need to develop, among other things, methods for growing patterned networks of large numbers of neurons. Success with this challenge will be important to our understanding of how the brain works, as well as to the development of novel kinds of computer architecture that may parallel the organization of the brain. We have investigated the use of metal ion implantation using a vacuum-arc ion source, and plasma deposition with a filtered vacuum-arc system, as a means of forming regions of selective neuronal attachment on surfaces. Lithographic patterns created by the treating surface with ion species that enhance or inhibit neuronal cell attachment allow subsequent proliferation and/or differentiation of the neurons to form desired patterned neural arrays. In the work described here, we used glass microscope slides as substrates, and some of the experiments made use of simple masks to form patterns of ion beam or plasma deposition treated regions. PC-12 rat neurons were then cultured on the treated substrates coated with Type I Collagen, and the growth and differentiation was monitored. Particularly good selective growth was obtained using plasma deposition of diamond-like carbon films of about one hundred Angstroms thickness. Neuron proliferation and the elaboration of dendrites and axons after the addition of nerve growth factor both showed excellent contrast, with prolific growth and differentiation on the treated surfaces and very low growth on the untreated surfaces.

Plasma immersion ion implantation (PIII) is an established technique in certain niche microelectronics applications such as the synthesis of silicon-on-insulator. In other applications such as shallow junction formation by plasma doping, trench doping, and fabrication of blue light emitting materials, PIII has unique advantages over conventional techniques and may be the technique of choice in the future. There have been significant developments in these areas and recent breakthroughs in plasma and trench doping are discussed in this review paper. Results pertaining to direct-current PIII that excels in planar sample processing as well as the optical characteristics of nano-cavities produced by hydrogen PIII are also presented.

Tabletop laboratory experiments have been used to simulate natural lightning, interacting explosions and astrophysical jets. When a high-energy laser pulse is focused in air, a laser-induced plasma (LIP) is produced, that generates a shock wave and an adiabatic expansion of the gas. In our work we have used LIPs in order to simulate lightning, for the study of chemical reactions relevant to atmospheric science.

Several diagnostics have been applied to our LIPs, such as deflectometry, shadowgraphy and interferometry, which yield full spatial information of the process (electron density and temperature, the position of the shock wave fronts and the expansion of the hot gas), with a time resolution that ranges from nanoseconds to milliseconds. A new diagnostic alternative was implemented for shadowgraphy, which uses either continuous lasers or conventional light sources. The experimental results have been reproduced by hydrodynamic codes that we have developed.

With astrophysical applications in mind, we have simulated and diagnosed the interaction of two explosions, with the aforementioned techniques. For this purpose, two LIPs are synchronized and diagnosed spatially and temporarily. Also, by producing the LIP in a glass sphere with a nozzle that ejects a shock wave and hot gas, we are able to simulate astrophysical jets. With such experiments, astrophysical models developed by us have been validated, showing excellent agreement between experiments and numerical simulations.

The PERUN and PALS iodine laser systems and a Nd : YAG laser have been used for studies of ions emitted from various single element laser plasmas, at both low (I_L∼10⁹ W cm⁻²) and high (I_L∼10¹⁶ W cm⁻²) laser intensities. Sufficiently high current densities of low-charge ions, with energies only of hundreds of electronvolt, were produced for starting tests of a considered new hybrid ion source, based on coupling of laser ion source to electron cyclotron resonance plasma. Highly charged ions with charge states about 50+ and with energies even higher than 20 MeV were generated at the highest laser intensities (I_L>2×10¹⁴ W cm⁻²). Seven ion sub-groups at least (faster and slower) were recorded and distinguished at these conditions. The existence of an `optimum focus position' in front of the target surface is consistent with the idea that laser interaction with a prepulse-produced plasma improves the conditions for self-focusing. The experimental arrangements and ion diagnostics used for the various laser ion generation experiments are briefly reviewed, as well as our both older and more recent results on the characteristics of the ions, produced at the various laser irradiances, are presented. The results of laser ion implantation experiments using these ions directly (without additional electrostatic acceleration) are also mentioned.

Results from recent experiments on the DIII-D tokamak have revealed many important details on transport barriers at the plasma edge and in the plasma core. These experiments include: (a) the formation of the H-mode edge barrier directly by pellet injection; (b) the formation of a quiescent H-mode edge barrier (QH-mode) which is free from edge localized modes, but which still exhibits good density and radiative power control; (c) the formation of multiple transport barriers, such as the quiescent double barrier (QDB) which combines an internal transport barrier with the quiescent H-mode edge barrier. Results from the pellet-induced H-mode experiments indicate that: (a) the edge temperature (electron or ion) does not need to attain a critical value for the formation of the H-mode barrier, (b) pellet injection leads to an increased gradient in the radial electric field, E_r, at the plasma edge; (c) the experimentally determined edge parameters at barrier transition are well below the predictions of several theories on the formation of the H-mode barrier, (d) pellet injection can lower the threshold power required to form the H-mode barrier. The quiescent H-mode barrier exhibits good density control as the result of continuous magnetohydrodynamic activity at the plasma edge called the edge harmonic oscillation (EHO). The EHO enhances the edge particle transport whilst maintaining a good energy transport barrier. The ability to produce multiple barriers in the QDB regime has led to long duration, high-performance plasmas with β_NH₈₉ values of 7 for up to 10 times the confinement time. Density profile control in the plasma core of QDB plasmas has been demonstrated using on-axis electron cyclotron heating.

Experiments in the tokamaks TEXTOR, CASTOR, T-10 and ISTTOK, as well as in the reversed field pinch RFX have provided new and complementary evidence on the physics of the universal mechanism of E×B velocity shear stabilization of turbulence, concomitant transport barrier formation and radial conductivity by using various edge biasing techniques.

In TEXTOR the causality between transport reduction and induced electric fields in the edge has been for the first time clearly demonstrated. The high electric field gradients have been identified as the cause for the quenching of turbulent cells. A quantitative analysis of the measured transport reduction is in good agreement with theoretical predictions. The scaling of plasma turbulence suppression with velocity shear has been established, revealing the density-potential cross-phase as a key element. Reduction in poloidal electric field, temperature, and density fluctuations across the shear layer lead to a reduction of the anomalous conducted and convected heat fluxes resulting in an energy transport barrier that is measured directly.

In CASTOR the biasing electrode is placed at the separatrix in a non-intrusive configuration which has demonstrated strongly sheared electric fields and consequent improvement of the global particle confinement, as predicted by theory. The impact of sheared E×B flow on edge turbulent structures has been measured directly using a comprehensive set of electrostatic probe arrays as well as emissive probes. Measurements with a full poloidal Langmuir probe array have revealed quasi-coherent electrostatic waves in the SOL with a dominant mode number equal to the edge safety factor.

In T-10 edge biasing is clearly improving the global performance of ECR heated discharges. Reflectometry and heavy ion beam probe measurements show the existence of a narrow plasma layer with strong suppression of turbulence.

On ISTTOK, the influence of alternating positive and negative electrode and (non-intrusive) limiter biasing has been compared. Electrode biasing is found to be more efficient in modifying the radial electric field E_r and confinement, limiter biasing acting mainly on the SOL.

In the RFX reversed field pinch it has been demonstrated that also in RFPs biasing can increase the local E×B velocity shear in the edge region, and hence substantially reduce the local turbulence driven particle flux mainly due to a change in the relative phase between potential and density fluctuations.

Several important topics relating to MHD behaviour in JT-60U are presented. An extremely hollow current profile was found for the first time in JT-60U with a very small plasma current in the central region, which is called the current hole. Analyses of equilibrium and stability of the current hole discharge show that, as β_p increases, the Pfirsh–Schlü;ter current increases, which reduces the poloidal field on the inboard side. It may cause the null point of the magnetic field. β limits due to ideal MHD instability in the current hole do not change very much compared to that of the weakly reversed shear plasma. In high β long pulse plasmas, it is important to suppress the resistive MHD instability, neo-classical tearing mode (NTM), induced by the lack of bootstrap current inside the magnetic island. Analyses of two typical JT-60U discharges with and without NTM show that the polarization current due to the plasma rotation is a plausible candidate to suppress the NTM though it is very sensitive to the value of mode rotation. To establish an advanced control of NTM, a real-time control system, which can identify the island by ECE measurement and control EC ray to the island by a steerable mirror, was prepared in JT-60U, and it successfully stabilized the NTM. Instability due to fast ions is an important subject for sustaining the fusion reaction. In JT-60U, slow frequency sweeping (slow-FS) modes and bursting MHD modes in the frequency range of the toroidicity-induced Alfvén eigenmodes (TAEs) are observed by injections of negatively-charged ion based neutral beam of ∼360 keV. Analyses by the HINST code show that the resonant TAE mode is a candidate of the slow-FS mode. A bursting mode was observed to change its frequency by 10–20 kHz in 1–5 ms (fast FS mode) and evolve explosively in ∼400 μs (abrupt large amplitude event). Analyses of the bursting mode show that the non-linear deformation of the energetic ion distribution may cause the repetition of bursting phenomena and the recovery of lost energetic ions.

The National Spherical Torus Experiment (NSTX) is a low aspect-ratio fusion research facility whose research goal is to make a determination of the attractiveness of the spherical torus concept in the areas of high-β stability, confinement, current drive, and divertor physics. Remarkable progress was made in extending the operational regime of the device in FY 2002. In brief, β_t of 34% and β_N of 6.5 were achieved. H-mode became the main operational regime, and energy confinement exceeded conventional aspect-ratio tokamak scalings. Heating was demonstrated with the radiofrequency antenna, and signatures of current drive were observed. Current initiation with coaxial helicity injection produced discharges of 400 kA, and first measurements of divertor heat flux profiles in H-mode were made.

The most important finding in the Large Helical Device (LHD) experiments so far is that an inward-shifted configuration exhibits good plasma performance with a scaling similar to that of ELMy H-mode tokamaks. The inward-shifted configuration has been predicted to have unfavourable magnetohydrodynamic (MHD) properties, even though it has significantly better particle-orbit properties. However, no serious confinement degradation due to the MHD activities was observed, resolving favourably the potential conflict between stability and confinement. Neoclassical transport loss can be suppressed even in a low-collisionality regime, and in this way the inward-shifted configuration was shown to make the LHD plasma properties favourable. Then, it is very important to realize more improved plasma performance and higher temperature plasmas for extending the plasma-parameter regime in order to obtain data that can be extrapolated to a reactor. In the fifth campaign in 2001–2002, an increase in the heating power achieved an electron temperature T_e of over 10 keV and an ion temperature T_i of 5 keV. A T_e profile, which is characteristic of internal transport barriers, was also observed when the electron cyclotron resonance heating power was highly focused on the centre of the plasma sustained by neutral beam injection.

The ITER project has an overall programmatic objective `to demonstrate the scientific and technological feasibility of fusion energy for peaceful purposes'. The ITER tokamak design is the embodiment of the finding, endorsed by all the parties to the project, that `the full non-linear interplay between alpha-particle heating, confinement barriers and pressure and profile control, and their compatibility with a divertor can be addressed only in an integrated step'. This step involves not only the study of fusion burning plasma physics but also the demonstration of key items of fusion reactor technology.

This paper introduces: magnetic fusion plasma (section 1), the physics goals of ITER (section 2) and the burning plasma physics which will be studied (section 3), examines the present ITER design and how it meets the plasma performance requirements in terms of extended burn at specific fusion power amplification (section 4), describes plasma measurements for ITER and some of the issues involved in their implementation (section 5), indicates how ITER provides a focus for international research into tokamak plasma physics (section 6), and presents a brief report on the status of the ITER Project (section 7). To conclude, this paper presents some final remarks (section 8).

The various methods put forward for the description of paraxial wave beams propagating in weakly inhomogeneous media are shown to be equivalent to each other. This issue is discussed in terms of a comparative analysis with respect to the complex eikonal-based solution relevant to the propagation of a Gaussian wave beam in a lens-like isotropic medium (such a solution being readily extendible to the propagation in a plasma slab). The accuracy of the paraxial solution thus considered is assessed numerically in comparison with the corresponding exact solution of the Helmholtz equation.

Two-dimensional coherent structures in potential and saturation current have been observed in the turbulent plasma of the simple magnetized torus Blaamann, using the conditional averaging technique. The structures observed in helium plasmas are evolving in time and rotating in the poloidal cross-section with a period of about 100 μs. The time resolved average radial particle transport generated by these structures has been calculated, and it is shown that large bursty flux events occur at the vortex separatrices whenever a double vortex in the potential is formed. The time evolution of fluxes has been correlated with the dynamical evolution of the structures and their topology. The results suggest that the intermittent behaviour of the transport is due to events involving the dynamics of coherent structures on a short-timescale. The observed structures are temporally intermittent. When they occur, they cover most of the plasma cross-section.

Moderately peaked electron density profiles are observed in virtually all plasma conditions in TCV. The existence of an anomalous pinch is unambiguously demonstrated by the observation of peaked density profiles in stationary, fully relaxed, fully current driven electron cyclotron current drive (ECCD) discharges with V_loop = 0. The behaviour of the density profiles from a database of 300 Ohmic L- and H-mode, as well as electron cyclotron heating and ECCD discharges, is compared to predictions of models based on the Ware pinch, the curvature pinch and anomalous thermodiffusion. Best overall agreement throughout the database is obtained with models combining an anomalous pinch mechanism, such as the curvature pinch, with the Ware pinch.

A novel statistical treatment of the full raw edge localized mode (ELM) signal from a series of previously studied JET plasmas is tested. The approach involves constructing probability distribution functions (PDFs) for ELM amplitudes and time separations, and quantifying the fit between the measured PDFs and model distributions (Gaussian, inverse exponential) and Poisson processes. Uncertainties inherent in the discreteness of the raw signal require the application of statistically rigorous techniques to distinguish ELM data points from background, and to extrapolate peak amplitudes. The accuracy of PDF construction is further constrained by the relatively small number of ELM bursts (several hundred) in each sample. In consequence the statistical technique is found to be difficult to apply to low frequency (typically Type I) ELMs, so the focus is narrowed to four JET plasmas with high frequency (typically Type III) ELMs. The results suggest that there may be several fundamentally different kinds of Type III ELMing process at work. It is concluded that this novel statistical treatment can be made to work, may have wider applications to ELM data, and has immediate practical value as an additional quantitative discriminant between classes of ELMing behaviour.

Coexistence of two modes of ion-acoustic waves in two-ion-species plasmas is investigated both theoretically and experimentally. Two ions are combinations of H₂, He, Ne, Ar and Xe. The boundary of existence of two modes in the plane of an electron–ion temperature ratio and heavy–light ion mass ratio is obtained from the two-species ion-acoustic dispersion relation with a real frequency and a complex wavenumber. The boundary is given approximately by T_e/T_i = 2M_h/M_l, where T_e and T_i are temperatures of electrons and ions, respectively, and M_h and M_l are masses of heavy and light ions, respectively. The experiment is perfomed with a double-plasma device. Ion-acoustic waves are transmitted by applying a sinusoidal pulse to the anode of the source plasma. A single mode is observed for Ne–Ar, He–Ne, Ne–Xe and Ar–Xe plasmas and two modes are detected for H₂–Ar, H₂–Ne and He–Ar plasmas.

The electron cyclotron current drive (ECCD) with extraordinary mode at the second cyclotron harmonic launched from the high-field-side (HFS) is investigated in W7-AS stellarator. Trapped particle effects and quasi-linear effects are taken into account in linear ray-tracing and quasi-linear bounce-averaged Fokker–Planck computations of the driven current. The results for both low-field-side (LFS) and HFS injection in W7-AS are compared with the experimental results. A slightly lower current drive efficiency is obtained, both theoretically and experimentally, in the case of HFS injection, confirming the LFS launch as the preferred mode of operation for ECCD.

When a surface of a radiation-absorbing material is illuminated by a sufficiently intense radiation, the gas ablated from the surface produces reactive a force causing an acceleration of the initial matter and setting a stage for instabilities of the Rayleigh–Taylor type. New effects associated with the non-normal incidence of the radiation are analysed. It has been shown that, at large enough tilt, the instability becomes significantly faster than in the `normal' case and unstable modes acquire finite phase velocity along the surface. The most unstable perturbations are rolls whose orientation depends on the angular distribution of radiation. These results are of interest for laboratory studies of ablation fronts and for the theory of photoevaporation fronts in astrophysics.

High density experiments were carried out in T-10 with gas puffing and electron cyclotron resonance heating (with absorbed power value up to 1.4 MW) with oblique and perpendicular power launch. Densities exceeding the Greenwald limit (n_Gw) by up to a factor of 1.8 were achieved in a regime with a high value of the edge safety factor at the current flat-top, q(a)≅8.2. The decrease of q(a) to a value of 3 led to the reduction of the ratio (_e) _lim /n_Gw to 1. Confinement degradation with density increase was not significant up to the density limit. However, the typical T-10 linear increase of energy confinement time with density saturates at _e⩾0.6n_Gw. This saturation is the result of the development of an additional transport in the electron heat channel. However, the saturated τ_E values exceeded the ITER L-mode scaling predictions by up to a factor of 1.2 and were close to the value predicted by the ITER H-mode scaling. Effect of the strong gas puffing on the plasma confinement and experiments with neon seeding are also discussed in this paper.

A method is proposed for obtaining radial profiles of plasma temperatures of both plasma ion (T_i) and electron (T_e) simultaneously by the use of a semiconductor detector array. The method is based on our developed particle-response model for a semiconductor detector; in particular, the response theory is constructed for giving the applicability in particle energies ranging down to a kiloelectronvolt. Calculated results from our model are in fairly good agreement with experimental data on the detector response of incident particle beams with energies in the range 100 eV to a few kiloelectronvolts. On the basis of the verification of the proposed model, an idea of the use of a developed semiconductor detector array covered with `reliably unbreakable' ultrathin SiO<sub>2</sub> `dead-layer filters' having various nanometre-order thicknesses is applied for simultaneous T_i and T_e analyses by using charge-exchange neutral particles and x-rays from plasmas. Radial profiles of T_i and T_e are obtained in a single plasma discharge alone, and the data reliability is independently cross-checked by a radial scan of a conventional charge-exchange neutral-particle analyser system as well as a 50-channel microchannel plate x-ray diagnostics system in the GAMMA 10 tandem mirror.

A statistical model for the bifurcation of the radial electric field E_r is developed in view of describing L–H transitions of tokamak plasmas. Noise in micro-fluctuations is shown to lead to random changes of E_r, if a deterministic approach allows for more than one solution. The probability density function for and the ensemble average of E_r are obtained. The L-to-H and the H-to-L transition probabilities are calculated, and the effective phase limit is derived. Due to the suppression of turbulence by shear in E_r, the limit deviates from Maxwell's rule. The ensemble average of heat flux as well as that of E_r do not show a hysteresis in contrast to the deterministic model. Experimental condition for observing the hysteresis is also addressed.