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The current development state of the finite difference, multi-fluid, 3D plasma code Findif is detailed. The code was run on four meshes prepared for the OP 1.1 wall geometry of the Wendelstein 7 X stellarator. The meshes were produced for 4 magnetic configurations; two of them are finite-beta (non vacuum). The simulated volume covers plasma edge; the computations of limiter heat load distributions were the main goal. Plasma radiation was not taken into account.

Multidimensional modeling of phenomena and processes occurring during the expansion of the laser-produced plasma for different irradiation conditions related to both the laser beam parameters and the target constructions is a very complex issue, especially when modeling requires consideration of kinetic processes associated with the development of various types of microscopic instability. Multidimensional PIC codes create such a possibility, but their use is limited to modeling phenomena even in a very narrow timescale due to the limited computational capabilities of current supercomputers. For this reason, the paper attempts to interpret the results of the spontaneous magnetic field (SMF) measurements obtained during the PALS (Prague Asterix Laser System) experiment [Pisarczyk et al., AIP Adv. 10, 115201 (2020); Pisarczyk et al., Phys. Plasmas 22, 102706 (2015)] based on the 2D magneto-hydrodynamic (MHD) model [Jach et al., Computer Modeling of Dynamic Interaction of Bodies by Free Point Method (PWN, Warsaw, 2011)]. The MHD equations were used with included arbitrary (i) current of hot electrons treating it as an additional external current and (ii) ion-sound instability responsible for the increase in anomalous resistance in areas with high temperature and low-density plasma. The spatial distribution of magnetic fields and current density obtained from 2D modeling are in acceptable agreement with the experimental results [Pisarczyk et al., Plasma Phys. Controlled Fusion 62, 115020 (2020); Zaraś-Szydlowska et al., AIP Adv. 10, 115201 (2020); Pisarczyk et al., Phys. Plasmas 22, 102706 (2015)]. The inclusion of temporal changes in anomalous resistance in modeling allowed us to explain the persistence of high SMF amplitude at the level of several megagauss after the laser pulse ended due to the effect of magnetic field freezing.

The JT-60SA tokamak, being built under the Broader Approach agreement jointly by Europe and Japan, is due to start operation in 2020 and is expected to give substantial contributions to both ITER and DEMO scenario optimisation. A broad set of preparation activities for an efficient start of the experiments on JT-60SA is being carried out, involving elaboration of the Research Plan, advanced modelling in various domains, feasibility and conception studies of diagnostics and other sub-systems in connection with the priorities of the scientific programme, development and validation of operation tools. The logic and coherence of this approach, as well as the most significant results of the main activities undertaken are presented and summarised. EURATOM 633053

The JT-60SA tokamak, being built under the Broader Approach agreement jointly by Europe and Japan, is due to start operation in 2019 and is expected to give substantial contributions to both ITER and DEMO scenario optimization. A broad set of preparation activities for an efficient start of the experiments on JT-60SA is being carried out, involving the elaboration of the Research Plan, advanced modelling in various domains, feasibility and conception studies of diagnostics and other sub-systems in connection with the priorities of the scientific programme, development and validation of operation tools. The logic and coherence of this approach, as well as the main activities undertaken are presented and summarized.

Results are presented from two-dimensional MHD simulations of X-pinch implosion. The simulations were performed in the (r, z) and (x, y) geometries for homogeneous (dense plasma) and heterogeneous (core-corona) loads. The formation of a minidiode, the development of a neck and an X-radiating hot spot, and the influence of the plasma corona on the implosion dynamics of the dense X-pinch plasma were investigated. For through simulations, the conical neck model was used, whereas a detailed analysis of the X-ray burst was performed in the parabolic neck model. The MHD processes occurring during the implosion of oblique shock waves and the onset of instability of the plasma column were examined. It is found that, due to the quasi-periodic character of these processes, the neck compression proceeds in a cascade fashion. The plasma state in a hot spot just before the break of the neck is analyzed, and the possibility of generating fast particle beams is considered.

The dynamics of a new type of pinches—hybrid X-pinches (HXPs)—has been studied experimentally and numerically. The initial configuration of an HXP consists of a high-current diode with conical tungsten electrodes separated by a 1- to 3-mm-long gap and shunted with a 20- to 100-μm diameter wire. It was shown earlier that a hot spot (HS) with high plasma parameters also formed in the HXP, although its initial configuration is simpler than that of a standard X-pinch. Although details of the HXP dynamics still remain insufficiently studied, the main factors governing the HXP formation were investigated both experimentally and using magnetohydrodynamic simulations. The formation of a specific pressure profile in the electrode plasma after the wire explosion was investigated both experimentally and theoretically. It is shown that the effect of the pressure profile on the expanding wire plasma is similar for both standard X-pinches and HXPs, which allows one to assign them to the same class of loads of pulsed facilities. It is also established that the final stages of HS formation and the parameters of the HS plasma in standard X-pinches and HXPs are practically identical.

This paper aims at investigation of efficiency of an ablative plasma energy transfer into a massive aluminum target using different atomic number ablators. For this reason, several target materials representing a wide range of atomic numbers (Z= 3.5–73) were used. The experiment was carried out at the iodine Prague Asterix Laser System. The laser provided a 250 ps pulse with energy of 130 J at the third harmonic frequency (λ3= 0.438 μm). To study the plasma stream configurations a four-frame X-ray pinhole camera was used. The electron temperature of the plasma in the near-surface target region was measured by means of an X-ray spectroscopy. The efficiency of the plasma energy transport to the target was determined via the crater volume measurement using the crater replica technique. The experimental results were compared with two-dimensional numerical simulations where the plasma dynamics was based on the one-fluid, two temperature model, including radiation transport in diffusive approximation and ionization kinetics. It was shown that the plasma expansion geometry plays an important role in the ablative plasma energy transfer into the target.

The paper presents a physical model for numerical simulations, based on a set of the non-ideal MHD equations in the two-fluid approximation, which has been used for determination of the pinch evolution and its structure. To study the evolution of plasma within a PF-1000 discharge there was applied an optical frame camera with the exposure time of 1 ns. On the basis of plasma images and calculations it was possible to determine the dynamics of the plasma sheath (CS) evolution and plasma dimensions. The experimental observations within the large PF-1000 machine have been compared with numerical calculations of the plasma evolution, and a relatively good agreement has been obtained.

R. Zagorski∗1, M. Jakubowski2, N. McTaggart3, R. Schneider4, W. Stȩpniewski1, and P. Xanthopoulos4 1 Institute of Plasma Physics and Laser Microfusion, EURATOM Association, 01-497 Warsaw, Poland 2 Institut fur Plasmaphysik, Forschungszentrum Julich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Julich, Germany 3 Department of Engineering Materials, University of Sheffield, Sheffield S1 3JD, United Kingdom 4 Max-Planck-Institut fur Plasmaphysik, Teilinstitut Greifswald, EURATOM Association, Wendelsteinstrase 1, D-17491 Greifswald, Germany

The present paper presents a high-speed photography sub-system which allows recording of frame sequence and streak images of plasma in a narrow band of the visible spectrum with high temporal and spatial resolution. Two methods are proposed for determining the distribution of the electron temperature or electron density of the plasma sheath originating in the plasma-focus phenomenon. These methods are based on theoretical considerations and processing of the results of experiments using a high-speed photography sub-system. A comparison between an experimental study of the plasma sheath structure and calculations obtained using magnetohydrodynamic (MHD) code is presented. Detailed explanations and considerations are exemplified by a number of results obtained both in experimental investigations and in numerical calculations.

The motion of a current sheet in a plasma focus device has a complicated two-dimensional character. After the axial phase it rapidly changes to implosion and radial compression. Understanding of plasma evolution is impossible without computer simulation. In this paper results are presented of the computer simulation of current sheet dynamics in a plasma focus-1000 device. The MHD code is based on the modified free points method. This gridless method is very useful for the problem of large deformation. The physical model uses a full dissipative set of MHD equations with Braginski transport. The computations start from a partially ionized plasma and the kinetics of ionization is taken into account. In the region of low density, the anomalous resistivity due to the plasma turbulence is included. Current evolution is found from the circuit equation. Then numerical results differ a little from experimental results.

This invited lecture concerns Plasma-Focus (PF) devices belonging to the family of the dynamic Z-pinches which produce dense, hot and magnetized plasmas. The plasma is formed by an inter-electrode discharge of a capacitor bank, and the dynamics of the current sheet has two different phases: 1—A long-time phase (lasting several microseconds) of a breakdown and the axial acceleration, during which the current sheath is formed and pushed out by the Lorentz force; 2—A short-time phase, lasting a few hundreds nanoseconds, during which the pinch is created and (after the maximum compression) disrupted by instabilities. This lecture presents physics governing the behavior of current-carrying plasma in PF discharges. The lecture describes different phases of the PF phenomena: the breakdown and the early stage of the current sheath formation, dynamics of the axial acceleration (run-down) and the radial implosion, the formation of a transient quasi-equilibrium near the stagnation point, and a post-pinch phase. Some experimental results obtained with a large (mega-joule) PF-1000 facility are presented and discussed.

The compression of molybdenum X-pinches with paraboloidal and conical initial geometries is investigated using numerical radiative MHD models. The model with conical initial geometry provides a more complete description of the axial plasma motion, better reflects the actual discharge geometry, and applies to molybdenum loads with larger masses. Both models make it possible to describe the main compression stages, including the formation of a “minidiode,” the formation of a narrow neck in the constriction, the microexplosion of a “hot spot,” and the generation of shock waves followed by the breaking of the constriction.

MHD compression of a heterogeneous Z-pinch produced by the explosion of a thin metal wire in the diode of a high-power current generator is investigated. The process is calculated starting from the instant when the breakdown of the evaporation products from the metal surface has come to an end and the current is just switched from the central core to the surrounding plasma corona, whereas the core material is still in the liquid-vapor state. The influence of the cold core on the plasma implosion is studied. The results obtained are compared with similar calculations carried out under the assumption that, in the initial state, either the core material is completely ionized or the core is absent at all.

Results are presented from laboratory and numerical experiments on the influence of the core and associated hydrodynamic instabilities on the high-current implosion of a plasma of exploding metal wires. The experimental investigation of the discharge structure was carried out using the multiframe X-ray backlighting technique with high temporal and spatial resolution (

A micro-Z-pinch has been recognized as a possible spark for the ignition of a dense D-T plasma [1–3]. The use of such a spark to ignite advanced fuels has been explored only superficially [4, 5]. In this paper, we address the problem of the transition between an ignited D-T plasma and a section of an advanced fuel such as D or D + He3. Some general rules are derived for the parameters of a conical channel of D-T that amplifies the spark energy to a level suitable for the ignition of a detonation wave in an inertially confined cylinder of highly compressed advanced fuel plasma.

An MHD model of the implosion of a dense hot plasma column is developed. Because of a better description of radiation transport, this model has a higher spatial resolution compared to the previously developed, simpler, two-temperature model. The new model is applied to calculating the load (a single metal wire or an X-pinch, in particular, a heterogeneous corona-core structure with a sharp boundary) of a nanosecond high-voltage generator. An algorithm of the type previously used to solve the problem in the two-temperature model is supplemented by the iteration procedure for calculating the quasisteady radiation under the assumption that the plasma is optically thick.

Ideas are put forward regarding the possibility of a cold dense core, surrounded by a plasma corona, forming near the axis at the initial stage of a nanosecond electric explosion of metal wires, and the influence of such a radial structure on the plasma compression dynamics is discussed. Experimental evidence supporting these suppositions is presented. It includes both indirect confirmations, based on optical and x-ray diagnostics data, and direct observations of the core by new means of x-ray probing employing an X pinch as a source of radiation.

The numerical data on electrical explosion ofX-pinches have been obtained to analyze the physical phenomena, which lead to a generation of short high-intensity X-ray pulses observed in experiments. The main attention is given to MHD cumulative processes occurring in point-like regions of a non-equilibrium compressed plasma with high temperatures. The model gives the scaling laws for X-pinch cascade evolution, in particular, for hot-spot plasma parameters and X-ray burst. Namely, the duration of an x-ray pulse is of several picosecond, the size of a spark region is not larger than a few microns, and the X-ray pulse intensity is about 10 17 W/cm 2 .

High-current nanosecond discharges through metal wires and insulator fibres were investigated in the NIKE-3 (100 kA, 50 ns) and BIN (250 kA, 100 ns) facilities. Glass fibres were used as an example in a study of the dependence of the discharge conditions on the linear density μ of the load. An increase in μ altered the nature of the discharge through the diode from a mismatched regime accompanied by generation of an electron beam (μ 30 μg cm-1). A strong influence of the state of the surface on the nature of an explosion of a metal wire was observed. The experimental results obtained at the beginning of wire explosions were accounted for by a model of the metal—plasma transition. The plasma motion and the development of instabilities of a plasma filament during a discharge were investigated by optical methods. Some of the experiments indicated simultaneous development of helical and 'sausage' instabilities. A two-dimensional ideal magnetohydrodynamic model was employed in calculations dealing with the process of formation of a constriction (pinching) and the results were in good agreement with the observations.

Plasma‐Focus (PF) devices, which are based on high‐voltage high‐current pulse discharges, belong to the non‐cylindrical Z‐pinches. They can produce high‐temperature dense magnetized plasma and intense radiation pulses (of X‐rays, electrons, ion beams and fusion products). The paper reports on numerical modeling of different phases of high‐current pulse discharges in a PF‐type device. The numerical results concerning the breakdown and collapse phases are presented and discussed.

The processes of wire X‐pinch electrical explosion are analyzed to develop the understanding of physical phenomena which leads to generation of short, high intensive X‐ray pulse. The model of formation and subsequent development of hot plasma in the region of narrow X‐pinch neck is investigated. Main attention is given to MHD cumulative processes which is reasonable for creation of point‐like regions of non‐equilibrium compressed plasma with high temperatures and densities. The main physical properties of such type plasma are discussed.

Plasma‐Focus (PF) devices, which are based on high‐voltage high‐current pulse discharges, belong to the non‐cylindrical Z‐pinches. They produce high‐temperature dense magnetized plasma and radiation pulses (of X‐rays, electrons, ion beams and fusion protons). The paper reports on studies of intense soft (a few keV) X‐ray emission, as performed with a four‐frame X‐ray camera, and their correlation with time‐resolved measurements of current waveforms, neutrons, soft and hard X‐rays. Possible mechanisms of the production of fusion neutrons (thermal and non‐thermal) were also investigated on the basis of neutron pulses measured at different angels to the electrode outlet axis, and their comparison with time‐resolved measurements of the soft and hard X‐ray radiation.

It is suggested that a self-development process of high-autonomy systems based on dynamic neural networks can be formulated within a framework of generalized nonholonomic dynamic systems and extended to reach the nature of dynamic interactions in complex design tasks involving some cognitive, intellectual invention and discovery or other decision processes. This feature is considered to be critical for any true autonomy; however it also introduces a potential for tremendous risk of unknown new events. To better determine some of the undesirable consequences, a concept of nonholonomic constraints for representing dynamic changes in relationships within neural networks and super neural networks is generalized to quantum nonholonomic constraints. This is intended to develop barrier mechanisms of a psychological nature in the mutual interactions of high-autonomy systems. A target-dedicated self-development of nonholonomic constraints is introduced. It is intended to provide mechanisms for optimal self-control development. In this formulation both supervised and unsupervised learning processes could be a part of the optimal self-control mechanisms. >

Summary form only given. A new PF 1000 Mather-type plasma focus device with a 1.2 MJ capacitor bank, charging voltage U=45 kV, short circuit current I=15 MA, is now operated at IPPLM. The series of experiments with a hydrogen-argon mixture was performed within the energy range 250-450 kJ. The partial argon pressure was up to 20%. The hard and soft X-ray radiation was registered by means of scintillation probes, pinhole cameras and spectrometer equipped with a spherical crystal. The plasma current sheath dynamics was studied with streak cameras. To measure a discharge current a Rogowski coil and miniature magnetic probes were used.

Summary form only given. A two-dimensional MHD code, as developed at the IPPLM, was used to model the dynamics of a plasma column created in a radiating exploding wire experiment. The physical model is based on nonideal MHD equations. Ionization kinetics was included using an average-charge approximation. The radiation transport was treated with the diffusion 3T approximation. The numerical algorithm was based on the modified free point method (FPM). We started our computation from an initially ionized tungsten plasma column with a parabolic density profile. An initial distribution of plasma parameters was randomly disturbed at an amplitude below 1%. Realistic dimensions of the wire were considered (length-4 mm, radius-250 /spl mu/m) together with a sinusoidal current rising from 10 to 300 kA in 100 ns time. Transport coefficients and the equation of state were taken from a wide range formulas.

Summary form only given. An X-pinch plasma is produced by exploding two 10-50 micron metal wires that cross and touch at a single point (in the form of an X) using a 200-400 kA, 100 ns (FWHM) current pulse. In the region of the original cross point of the wires, a magnetically driven plasma implosion occurs, and one or more

Using an X-pinch configuration, we have determined that micropinches produced by exploding-wire z pinches can have densities approaching solid density and temperatures of 0.5-1.8 keV, depending upon the wire material used. These plasma parameters, determined from x-ray spectra recorded using an x-ray streak camera, vary drastically on time scales ranging from

The progress in pulsed power technique in the last decade can make the idea oftrigger the fusion reaction in the Z-pinch column. To show possibilities of burn wave propagation in this case, we used 2-D MHD code. The physical model includes: kinetics ofthermonu-clear reaction in D-T mixture, non-local deposition ofalpha particles, radiation transport and the influence ofmagnetic field on transport coefficients. We presented the results of simulation ofburn wave propagation in conical Z-pinch channel initiated fom hot, central region. These results are compared with the previous ones for the case without magnetic field.

A new hybrid method is presented for designing feedforward, backpropagation neural models with small training data sets. The method minimizes the generalization error, a fundamental quantity that characterizes the effectiveness of the regression models. It combines into one framework a bootstrap technique that estimates network generalization performance and a collection of stochastic and deterministic optimization techniques that adjust neural network interconnection geometry. The approach is derived as a form of multi-objective optimization strategy. This allows for more direct treatment of contradictory design criteria than traditionally employed single-objectivetechniques.Astochasticoptimization methodsuch asageneticalgorithmisusedto selectactivation functions for hidden-layer nodes, whereas fast deterministic techniques, optimal brain surgeon and singular value decomposition, are used to perform connection and node pruning. The method is demonstrated by optimizing neural networks that model the high-lift aerodynamics of a multi-element airfoil. The neural model is constructed using a small computational data set consisting of 227 data points. In the numerical experiments presented, the solutions produced by this hybrid approach exhibit an improvement in the generalization ability on the average of e ve to six times when compared to the pruned models with only one type of activation function. When traditional fully connected networks with hyperbolic tangent activation functions are considered, the improvement in the generalization performance of the new models is even greater. The neural models exhibit superior generalization qualities that are virtually impossible to e nd by manual trial-and-error approaches.

Results of first experiments on powerful plasma focus PF-1000 (IFPiLM) [1], loaded by low mass foam liners, produced for “Angara” (TRINITI) liner implosion program [2], are presented in this report. An interaction of PF current plasma shell and the liner was the problem of main interest in our joint experiment. The main goal is to elaborate new method of plasma liner production for its compact implosion using multiterawatt pulsed power driver.

A 2D (r-z) and 2-temperature (Te,i) nonideal MHD numerical model of dense Z-pinch dynamics and its applications to exploded wire plasmas with a cold dense core are presented. The numerical simulation algorithm is based on an Eulerian-Lagrangian method that is related to one suggested by D’yachenko for hydrodynamic calculations. As expected, a high density core that appears in the initial stage of the electrical explosion of a metal wire is found to be colder than the surrounding plasma. Model results are in good agreement with experimental data for exploded wires in a high current nanosecond diode.

The four-frame high-speed camera has been used to study the evolution of the plasma sheath structure and dynamics in the visible spectral range for final stages of plasma-focus phenomena. In order to simulate the main features of the plasma sheath evolution, a two-dimensional, two fluids, and nonideal magnetohydrodynamics (MHD) code has been developed. The comparison between experimentally recorded plasma images and the results taken by MHD numerical modeling has been made.

Summary Important indicators of soil aeration status, such as air-filled porosity, air permeability, relative gas diffusion coefficient, soil air composition, oxygen availability (ODR) and redox potential (Eh) are presented. Relationships among these indicators and techniques of measurement are discussed. Field and laboratory experimentation is described. Compaction is shown to restrict aeration and thereby impair crop growth. Examples are given of field experiments, generally involving cereals, with compaction treatments applied either before sowing to simulate unalleviated previous compacton by harvest machinery or during seedbed preparation. Crops, particularly winter crops, are most vulnerable in wet, warm periods shortly after sowing or fertilizer application. Impaired crop growth resulting from compaction is attributed to the interacting effects of poor aeration and mechanical impedance. Poor aeration can also result in gaseous losses of plant-available nitrogen. Experimental evidence of recovery from compaction in undisturbed soils is also presented. Subject areas requiring further research efforts are identified.

The effect of magnetic field line ergodization that eliminates magnetic surfaces (either by a resonant magnetic perturbation like in TEXTOR-DED or by intrinsic plasma effects like in W7-X) imposes the need for plasma transport models being able to describe this properly. To handle the ergodicity the concept of local magnetic coordinates allowing a correct discretization of the transport equations with minimized numerical errors is used. For the simulation of plasma transport in perturbed volume, a numerical method based on the finite difference concept has been developed, using a custom-tailored unstructured grid in local magnetic coordinates. This grid is generated by field line tracing to guarantee complete separation of the large parallel transport along B and that perpendicular to B and the ergodicity of the magnetic field does not limit applicability of the method in contrast to the methods based on finite volume ansatz. Perpendicular and parallel fluxes can be effectively separated in our approach and treated independently in the numerical method which has been implemented in the FINDIF code.The finite difference code FINDIF is used to investigate the energy transport in the complex 3D TEXTOR-DED tokamak geometry, where the plasma structures and transport are closely related to the structure of the magnetic field lines. Numerical grids have been prepared in order to simulate 12/4 and 6/2 modes of the DED operation, respectively. In particular, the question, what is the role of long and short magnetic field lines in the heat transfer from the core plasma to divertor surface, is addressed. Simulation results are compared with experimentally determined temperature profiles and heat fluxes at the target.

Effective dynamic system modelling and simulation reouires reliable algorithms for the automatic mathematical model generation to minimize the manual effort and analysts time usage as well as removal of the probability of undetected errors introduction. The bond-graph technique forms a well developed tool for nonlinear systems modelling, simultaneously providing capability for a formal procedure for automatic computer model generation. The GEN proaram applies that formalism for the automatic qeneration of nonlinear state space equations. The GEM's algorithm is described. An example of equations generating is given. Some aspects of the effectiveness of simulation process following model formulation are discussed.

The paper is aimed at optimization of parameters of a copper plasma jet produced at the DPF-1000U device, in which the inner electrode face was conically shaped. Preliminary information was obtained by numerical simulations of the plasma jet creation for different copper cones with the use of the two-dimensional magneto-hydrodynamic code KAROL. The simulations suggested that the cone height in the range of 4–7 cm should ensure a good plasma jet quality. The experimental data delivered by means of a 16-frame laser interferometer and a four-frame X-ray pinhole camera fully confirmed this conclusion. In the paper, we demonstrate the results for a 5 cm height cone. The eroded Cu plasma, swept up by the deuterium plasma sheath, was accelerated axially and compressed to very small diameter (3 mm) with an electron density of 7 × 1018 cm−3. The Cu plasma jet achieved a velocity of 5 × 107 cm/s and reached in the period of about 230 ns a distance (length) of 7 cm. The above results prove a successful adaptation of the plasma focus device to the metallic plasma jet generator.

In strength problems of stresscd‐skin constructions, the outside shape of a part to be stressed as well as the loads sustained by it are generally given. Having this data, the designer or stress analyst in most cases has to choose the type of skin and the best distance between ribs or bulkheads to obtain the lowest weight of construction.

Effective dynamic system modelling and simulation requires reliable algorithms for the automatic mathematical model generation to minimize the manual effort and analysts time usage as well as removal of the probability of undetected errors introduction. The bond-graph technique forms a well developed tool for nonlinear systems modelling, simultaneously providing capability for a formal procedure for automatic computer model generation. The GEM program applies that formalism for the automatic generation of nonlinear state space equations. The GEM's algorithm is described. An example of equations generating is given. Some aspects of the effectiveness of simulation process following model formulation are discussed.

Downward transport of oxygen in flooded soils is extremely difficult due to saturation of the soil with water. Compared to well-drained soils, there is a great difference in the depth of oxygenation and the consequences are of great practical importance.

Two classic methods have been used for evaluating the area of heat exchange between a subject and substrate. Kelly et all proposed to measure the animal-floor contact area by simply drawing the animal’s contour. Grommers et al2 photographed, from the underside, the subject reclining on a transparent ‘perspex’ panel. The contact area was then determined by planimetry. Neither of these methods allows direct estimation of the area of heat exchange because it is impossible to define the proportion of contour area which exchanges heat. Furthermore, Grommers’ method assumes that heat is exchanged by conduction only.

An analysis of radiative power exhaust for the JT-60SA tokamak with a tungsten divertor is performed with the help of the self-consistent, core-edge integrated COREDIV code. Two scenarios of operation (low and high density) were investigated in the scope of different parameters (electron density at the separatrix and the perpendicular transport in the scrape-off layer) with impurity seeding (Ne and Kr). The calculations show that in the case of the tungsten divertor the power load to the divertor plate is mitigated and the central plasma dilution is smaller compared to the carbon divertor. In the most cases the energy flux through the separatrix is above the L–H transition threshold. For the high density case with neon seeding operation in full detachment mode is observed. Changing the diffusion coefficient in the SOL has a strong influence on the result of the calculations as increased radial transport causes stronger screening effect. Also by changing the electron density on the separatrix the influx of heavy impurities (W, Kr) into the core region can be reduced. The results demonstrate that it is easier to achieve sustainable conditions in the divertor region for the high density scenario, whereas for the low density one reducing the auxiliary heating power seems unavoidable to prevent damaging of the target plate, even for strong seeding gas influx.

Scenario modelling for the demonstration fusion reactor (DEMO) has been carried out using a variety of simulation codes. Two DEMO concepts have been analysed: a pulsed tokamak, characterized by rather conventional physics and technology assumptions (DEMO1) and a steady-state tokamak, with moderately advanced physics and technology assumptions (DEMO2). Sensitivity to impurity concentrations, radiation, and heat transport models has been investigated. For DEMO2, the impact of current driven non-inductively by neutral beams has been studied by full Monte Carlo simulations of the fast ion distribution. The results obtained are a part of a more extensive research and development (R&D) effort carried out in the EU in order to develop a viable option for a DEMO reactor, to be adopted after ITER for fusion energy research.