[en] Free-boundary nearly rigid displacements are considered in a plasma confined by a magnetic field consisting of one part generated by the plasma current density, and one part being due to steady currents in fixed external conductors. An induced surface current effect and a related force on the plasma arise when the externally applied field is inhomogeneous in the direction of displacement. This additional force has not been taken into account in conventional MHD theory. In the particular case of tokamaks , the induced surface current effect has two impacts on vertical nearly rigid displacements. First, there arises an additional restoring force and a positive contribution to the change in potential energy when the externally applied field is inhomogeneous in the vertical direction. A special design of poloidal field coils can thus provide new means for vertical position control in tokamaks, also in the case of strongly elongated cross-sections. Second, an earlier simplified model, in which the plasma is represented by a line current, has to be modified since the plasma is a highly conducting body of finite size. 4 refs

[en] A theoretical approach is outlined which attempts to explain elementary particles with a rest mass as eigenmodes of self-confined electromagnetic radiation. For this purpose an extended interpretation of Maxwell's equations is being suggested. The theory is illustrated by a simple special case where the particle interior contains a unipolar-like electric field having a non-vanishing divergence and being coupled to a poloidal dipole-like magnetic field having a non-vanishing curl. At large distances from the particle centre these fields approach their classical vacuum solutions. Numerical order-of-magnitude estimations being based on this model are at least consistent with the experimental data of the electron and the proton. (author)

[en] A review is given of the theoretical analysis on the Extrap concept which consists of a Z-pinch being immersed in an octupole field generated by currents in a set of external conductors. This analysis includes research on plasma breakdown and start-up, equilibrium and stability, in terms of MHD and kinetic theory. Extrap theory includes an extensive area of diversified problems, being related to a high beta value, a non-circular plasma cross section with a magnetic separatrix, and strongly inhomogeneous plasma conditions in space. This also leads to unexplored and important areas of plasma physics, reaching far beyond the special applications to the Extrap configuration. At present progress has been made in the analysis of breakdown, of dissipation-free equilibria, and in identifying the instability modes and possible stabilizing meachanisms in Extrap. Nevertheless much work still remains within the area of dissipative equilibria and transport, as well as in the efforts to reach a complete theoretical understanding of the experimentally observed stability. (115 refs.)

[en] Steady bootstrap states of a Z-pinch are investigated both in absence and in presence of an imposed axial magnetic field, in terms of MHD theory with classical resistivity. The results indicate that bootstrap operation should become possible for certain classes of plasma profiles and that such operation can lead to higher bootstrap currents in a Z-pinch without axial magnetic field than in a tokamak-like case under similar plasma conditions. The ratio between the latter and the former currents is of the order of the square root of the beta value in the tokamak-like case. A simple numerical example is given on boot-strap operation in the Z-pinch. Neoclassical or anomalous diffusion will increase the diffusion velocity of the plasma but are not expected to affect the main physical features of the present results. This applies also to the kinetic effects in the weak-field region near the axis of the Z-pinch, because these effects can largely be described by MHD-like equations for a steady equilibrium. Bootstrap operation and the technical difficulty in realizing a volume distribution of particle sinks introduce certain constraints on the plasma and current profiles. This has to be taken into account in a stability analysis. The latter cannot only be performed in terms of MHD-like theory but has to be based on kinetic theory including large Larmor radius (LLR) effects. (author)

[en] An extended Lorentz invariant formulation of Maxwell's equations is presented which both includes time dependent and steady-state solutions. In this approach the charge and current densities are treated as intrinsic properties of the electromagnetic field itself, in vacuo. Two main results follow from such an approach. First, a longitudinal electric wave is predicted to propagate in vacuo. Second, an axially symmetric steady state can be outlined in which 'self-confined' electromagnetic radiation circulates in closed orbits around the axis of symmetry. For this state values are obtained of the charge, the spin, and the product between magnetic moment and mass which are of the same order of magnitude as those observed for some elementary particles such as the proton and electron. Consequently, this may provide certain areas of conventional elementary particle analysis with some complementary ideas. Whether the predicted new phenomena also correspond to physical realities is so far an open question which requires further investigation. With 6 refs. (Author)

[en] The particle and heat balance during plasma start-up are investigates, to specify the conditions for reaching various ion density ranges and high plasma temperatures in cases of a limited heating power. Particular attention is paid to the permeable-impermeable transition regime of plasmas being subject to Ohmic heating and confined in closed or open bottles with a main poloidal field. The ionization and burnout conditions are found to depend critically on the confinement and the filling density. They become optimal in closed bottles under symmetric and stable conditions, where the transition into a fully ionized state should be reached even at moderately large ionization rates, burnout powers and currents. Start-up methods based on constant as well as on variable filling densities are discussed as means of ion density control.(author)

[en] Classical scaling laws are deduced for the equilibrium relations between pinch current J, pinch radius a, axial density n₀ and temperature T₀ of linear Z-pinches having a finite length L, as well as for toroidal Z-pinches having a large aspect ratio. In both cases the radius a is found to increase almost linearly with the current J at a fixed density n₀, and the temperature T₀ to increase with J at fixed values of the radius a. In principle, anomalous transport can be simulated in a first approximation by multiplying the transport coefficients by corresponding numerical factors. At a fixed density n₀ and a fixed external conductor current of an Extrap pinch, the radius a is found to increase more rapidly with J than the radius of the magnetic separatrix. Within the range of increasing pinch currents there are therefore three regimes of an Extrap system. For small J the system becomes unstable in the conventional way of unstabilized Z-pinches. For intermediate values of J, the magnetic surfaces become deformed by the external conductor field, and the constraints of this field combine with FLR and cold-mantle effects to provide a macroscopically stable state. Finally, for sufficiently large currents J, i.e. when the pinch radius a approaches and even tends to exceed the separatrix radius, the system is expected to become ballooning unstable in regions of -bad- field line curvature. The present analysis thus provides relations between the basic pinch parameters which can be tested by experiments, and it also contributes to the understanding of Extrap stability in terms of increasing pinch currents. (author)

[en] An extended analysis is presented of the earlier investigated induced surface current effects which arise in a magnetized plasma when the confining field has an imposed inhomogeneous part being generated by currents in external conductors. The electromagnetic induction law requires a corresponding contribution from these effects to be added to the formulation of the energy principle for plasma MHD stability. For a plasma with a free boundary, conventional theory therefore holds only in the case of a homogeneous external magnetic field. When the characteristic length of the imposed field is comparable to or smaller than that of the field generated by the plasma currents, the induced surface current effects on electromagnetic free-boundary modes become at least as important as any other effect due to the plasma displacements. Any non-uniform displacement which includes a translatory component of the plasma motion across the imposed magnetic field then leads to a restoring partial force and a positive contribution to the change in potential energy. An illustration is given by two-dimensional straight Extrap geometry with a peaked current distribution, being subject to a combined translation and ballooning-like displacement. In this case there are strong restoring forces, leading to stable oscillations around the plasma equilibrium position. A peaked profile also becomes consistent with an efficient power production of thermonuclear plasma core. (au) (12 refs., 4 figs.)

[en] A set of plasma balance equations is proposed which is based on orbit theory and the particle distribution function, to provide means for theoretical analysis of a number of finite Larmor radius (FLR) phenomena without use of the Vlasov equation. Several important FLR effects originate from the inhomogeneity of an electric field in the plasma. The exact solution of a simple case shows that this inhomogeneity introduces fundamental changes in the physics of the particle motion. Thus, the periodic Larmor motion (gyration) is shifted in frequency and becomes elliptically polarized. Further, the non-periodic guiding-centre drift obtains additional components, part of which are accelerated such as to make the drift orbits intersect the equipotential surfaces of a static electric field. An attempt is finally made to classify the FLR effects, also with the purpose of identifying phenomena which have so far not been investigated. (author)

[en] A review is given of the potentialities of fusion energy, the approaches to controlled fusion, the present state and perspectives of fusion research, and aspects of future possibilities and plans. Fusion research does not concern a single problem area but rather covers a complex of problems, ranging from basic plasma physics to technology and system studies. Considerable progress has been made in all these areas. In the latest large tokamak experiments the 'breakeven' parameter range of marginal balance between fusion power and power losses has now been reached and the first experimental reactor is planned to be ready for operation in 14 years time. Thus, it has already become possible to realize a power producing fusion reactor. However, such a reactor, being based on the current tokamak concept, is not likely to become technically or financially relevant. In a balanced global research programme, a broader approach including work on concept improvement becomes crucial to final success and for the full potential of fusion energy to be utilized