The EU DEMO equatorial outboard limiter — Design and port integration concept

The equatorial outboard limiters (also called outboard midplane limiters (OMLs)) are an essential part of the DEMO wall protection concept. Limiters are foreseen in different areas of the DEMO first wall, namely in the equatorial ports, on the high-field side, in vertical ports and additional protection limiters between equatorial and lower ports. The limiters shall prevent the plasma to touch the first wall of the breeding blankets during all plasma transients.The port integration concept of the OMLs, used for plasma ramp-up/-down, is explained including (i) thermal, structural and electromagnetic loads, (ii) neutronic requirements and related material properties, (iii) remote handling considerations, (iv) space and mass constraints and (v) the required alignment precision to allow equal distribution of the heat exposure amongst the individual of the plasma facing (PFC) limiter components.While the hot fusion plasma during ramp-up is impinging directly on the limiter, its PFC components temperature is rising and can be measured by means of either thermocouples or by infrared (IR) thermography an estimation of the heat flux on the contact point can be made. This is the basis for the proposed alignment strategy. Previous article in issu

Initial port integration concept for EC and NB systems in EU DEMO tokamak

The integration of the heating and current drive (HCD) systems in the EU DEMO tokamak must address a number of issues, namely space constraints in the tokamak building, remote handling requirements, breeding blanket penetration, neutron and photon radiation shielding, compliance of penetrations of the primary vacuum with safety and vacuum criteria, and a large number of loading conditions, in particular heat, electromagnetic (EM), and pressure loads in normal and off-normal conditions. A number of pre-conceptual design options for the vacuum vessel (VV) port and the port-plug are under assessment and need to be verified against all requirements and related criteria. The identification of the functional (or physics) requirements of the HCD systems remains an on-going process during the pre-conceptual design phase, hence some initial assumptions had to be made as a basis for development of the design of the VV ports and the HCD port plugs. The paper will provide an overview of present margins in the functional/physics requirements and the rationale behind the assumptions made in order to facilitate development of the pre-conceptual design options. Furthermore it will introduce the initial design concepts of the electron cyclotron (EC) Launchers and the neutral beam (NB) injectors integrated in equatorial ports. The NB duct design in DEMO and related issues such as transmission and re-ionization losses will be also addressed

Activation material selection for multiple foil activation detectors in JET TT campaign

In the preparation for the Deuterium-Tritium campaign, JET will operate with a tritium plasma. The T + T reaction consists of two notable channels: (1) T + T -> He-4 + 2n, (2) T + T -> He-5 + n -> He-4 + 2n. The reaction channel (1) is the reaction with the highest branching ratio and a continuum of neutron energies being produced. Reaction channel (2) produces a spectrum with a peak at 8.8 MeV. A particular problem is the ratio between the individual TT reaction channels, which is highly dependent on the energy of the reacting tritium ions. There are very few measurements on the TT spectrum and the study at JET would be interesting. The work is focused on the determination of the spectral characteristics in the TT plasma discharges, especially on the presence of the 8.8 MeV peak, a consequence of channel (2) of the TT reaction. The possibility to use an optimized set of activation materials in order to target the measurement of the 8.8 MeV peak is studied. The lower limit of detection for the channel (2) ratio within the TT reaction is estimated and the influence of DT source neutrons, which are a consequence of deuterium traces in the plasma, is investigated

Activation inventories after exposure to Dd/Dt neutrons in safety analysis of nuclear fusion installations

Irradiations with 14 MeV fusion neutrons are planned at Joint European Torus (JET) in DT operations with the objective to validate the calculation of the activation of structural materials in functional materials expected in ITER and fusion plants. This study describes the activation and dose rate calculations performed for materials irradiated throughout the DT plasma operation during which the samples of real fusion materials are exposed to 14 MeV neutrons inside the JET vacuum vessel. Preparatory activities are in progress during the current DD operations with dosimetry foils to measure the local neutron fluence and spectrum at the sample irradiation position. The materials included those used in the manufacturing of the main in-vessel components, such as ITER-grade W, Be, CuCrZr, 316 L(N) and the functional materials used in diagnostics and heating systems. The neutron-induced activities and dose rates at shutdown were calculated by the FISPACT code, using the neutron fluxes and spectra that were provided by the preceding MCNP neutron transport calculations