[en] Published in summary form only

[en] The problem of the treatment and disposal of radio-active waste from nuclear power stations is reviewed. Types of radio-active waste (weakly-active and highly-active), their treatment and containment, disposal in geological sites and the risks involved are discussed. (H.E.G.)

[en] In ITER the main loss mechanism of fast fusion alpha particles is expected to be due to toroidal field (TF) ripples caused by the finite number of TF coils. The associated radial diffusion of fast alphas is specified by an energy and space dependent diffusion coefficient which can be extended to account also for toroidal Alfven eigenmode (TAE) diffusion. Energy transfer from the fast alphas to the thermal background plasma is considered to occur due to Coulomb collisions and nuclear elastic scattering (NES). The α-transport is described here by a reduced slowing down kinetic equation of which the numerical solution provides for the energy-, space- and time-dependent alpha particle distribution in the tokamak plasma. This alpha distribution then constitutes the basis for a determinative calculation of the actual fusion power allocation to each distinct background species. Though TAE diffusion alone is not a significant fusion power loss mechanism, recent calculations indicate that the coaction of TF-ripple (TFR) and TAE transport processes synergisticly results in a substantial reduction of fusion alpha power deposition

[en] The continuous progress in the attainment of plasma parameters required for establishing nuclear fusion in magnetically confined plasmas as well as the prospect of feasible steady-state operation has instigated the interest in the physics of burning plasmas [1]. Aside from the required plasma current drive, fusion energy production with tokamaks demands particular attention to confinement and fuelling regimes in order to maintain the plasma density n and temperature T at favourable values matching with specific requirements such as the triple product nτ_ET, where τ_E represents the plasma energy confinement time. The identification of state and parameter space regions capable of ignited fusion plasma operation is evidently crucial if significant energy gains are to be realized over longer periods. Examining the time-evolving state of tokamak fusion plasma in a parameter space spanned by the densities of plasma constituents and their temperatures has led to the formation of an ignition criterion [2] fundamentally different from the commonly used static patterns. The incorporation of non-stationary particle and energy balances into the analysis here, the application of a 'soft' Troyon beta limit [3], the consideration of actual fusion power deposition [4,5] and its effect of reducing τ_E are seen to significantly influence the fusion burn dynamics and to shape the ignition conditions. The presented investigation refers to a somewhat upgraded (to achieve ignition) ITER-like tokamak plasma and uses volume averages of locally varying quantities and processes. The resulting ignition criterion accounts for the dynamic evolution of a reacting plasma controlled by heating and fuel feeding. Interestingly, also self-organized ignition can be observed: a fusion plasma possessing a density and temperature above a distinct separatrix in the considered parameter phase space is seen to evolve - without external heating and hence practically by itself - towards an ignited stable equilibrium state, even if the initial state is outside the positive power balance region. Since fuel is assumed to be constantly supplied for that, cold fuelling is the sole required injection to the system during the ignition dynamics. The known parameter discrepancy between stable and unstable ignited operation is found to be controllable by the fuelling rate, and thus may be reduced for a D-T fusion plasma to only a very few keV difference in the plasma temperature T. Further, the minimum heating path toward stable ignition was inspected; however, it was identified as an impracticable operational scenario due to substantial oscillations of the plasma density and temperature. Avoiding the latter, a heating regime with optimized low energy expense is proposed that leads conveniently to the stable ignition point at reasonable plasma temperatures in the 20 keV range. To minimize the energy required to heat the plasma beyond a state, from where it evolves by itself to ignited stable equilibrium, a relatively high power neutral beam applied for a short duration is found to be more efficient than a less powerful beam over a longer time period. References: [1] IAEA Workshop on Burning Plasma Physics and Simulation, Tarragona, Spain, July 4-5, 2005; Workshop Summary in Fusion Sci. Techn. 49, 79 (2006) [2] K. Schoepf, T. Hladschik, Ann. Nucl. Energy 23, 59 (1996) [3] D. Anderson et al., Fusion Technology 23, 5 (1993) [4] K. Schoepf et al., Kerntechnik 67, 285 (2002) [5] K. Schoepf et al., TH/P6-3 at 21st IAEA Fusion Energy Conf., Chengdu, China, Oct. 2006

[en] Published in summary form only

[en] Burn dynamic studies of magnetically confined fusion (MCF) have shown that - for certain fueling regimes - there exists a stable equilibrium point in the density-temperature state plane associated with high fusion power production. In approaching this operation point the plasma is heated by auxiliary mechanics. The question of interest is: When can the external heating power be turned off and the plasma temperature and density will evolve into the stable equilibrium point only due to internal fusion power deposition. The associated conditions suggest the definition of a new ignition criterion which seems to be more adequate for accomplishing steady-state operation of fusion reactors than todays ignition criteria. (author). 10 refs, 4 figs

[en] The evolution of plasma density and temperature in fusion burns is essentially influenced by the amount of fusion alpha heating. Hence detailed knowledge of the fusion power transferred to the several plasma constituents is of great to fusion dynamics. Different α-transport models determine the actual alpha power deposition in the plasma and consequently affect the ignition dynamics. In this model alphas are lost from the tokamak plasma by toroidal field ripple (TFR) diffusion due to finite number of toroidal field coils, and by toroidal Alfven Eigenmode (TAE) diffusion. Though TAE transport alone does not constitute a significant fusion power loss mechanism, recent investigations have indicated that coaction of TFR and TAE diffusion processes synergistically results in a substantial reduction of fusion power deposition. (author). 3 figs. 9 refs

[en] Global fusion dynamics are examined for a d-t- plasma confined in an ITER-like tokamak reactor. The analysis is based on the solution of a set of coupled nonlinear first order differential equations describing the evolution of plasma density and plasma temperature as affected by the several particle and energy gain/loss mechanisms occurring in the burning d-t fusion plasma. (author)

[en] The present paper investigates the combined effect of toroidal field (TF) ripples as well as MHD induced low frequency perturbations on fast ion confinement in tokamak plasmas. The transport coefficients of fusion alphas in presence of TF ripples and TAE modes are calculated using the simplectic method for the integration of Hamiltonian systems. It is shown that MHD induced modes can result in both, either a degradation or an improvement of fast ion confinement in a rippled tokamak magnetic field, which is in qualitative agreement with observations of charged fusion products confinement in TFTR. (author)

[en] Published in summary form only