International Thermonuclear Experimental Reactor ITER Research Articles

Experimental Estimation of Dust Generation Under ELM-Like Transient Heat Loads in Divertor Plasma Simulator-2

Although plasma-facing components composed of tungsten are less likely to generate dust when compared to other materials, dust generation is still possible during severe transient phenomena in fusion devices. The generation of tungsten dusts was experimentally investigated by exposing tungsten targets to a transient heat flux factor (FHF) simulated by a high-energy pulsed laser so that the rate of dust generation would be analyzed. The rate of dust generation is observed to be increased linearly with respect to FHF: G [mg/min] = C (FEX – F0), where FEX is the experimental value of FHF, F0 is the threshold FHF, and C [mg∙m2∙s1/2/min∙MJ] = 0.0031 ± 0.0002. FHF indicates that the characteristics of dusts such as size and FHF are similar to those observed in several toroidal fusion devices. The threshold of FHF for dust generation was also observed as 41 MJ/m2∙ s1/2, which is similar to that of the international thermonuclear experimental reactor ITER (50 MJ/m2∙ s1/2).

Simulation of Dust Particle Trajectories in an Electrostatic Probe with the Purpose of Increasing Its Efficiency

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of movement of dust particles in an electrostatic probe. Dust particle trajectories inside the probe are analyzed. Several electrostatic probe design modifications are proposed on the basis of the analysis in order to increase the efficiency of dust collection.

Increasing of an electrostatic probe capacity and efficiency for metal dust collection in ITER

Formation of dust particles and clusters is observed in almost all modern fusion devices. Accumulation of dust in next-generation thermonuclear installations can significantly affect plasma parameters and lead to accumulation of unacceptably large amounts of tritium. The use of a specially developed electrostatic probe is planned in the international thermonuclear experimental reactor ITER to collect dust for further analysis. The article describes a numerical model of dust particles movement in an electrostatic probe. Dust particles trajectories inside the probe were analyzed. Several electrostatic probe design modifications were proposed on the basis of the analysis in order to increase the efficiency of dust collection.

Control of Warm Compression Stations Using Model Predictive Control: Simulation and Experimental Results

This paper deals with multivariable constrained model predictive control for Warm Compression Stations (WCS). WCSs are subject to numerous constraints (limits on pressures, actuators) that need to be satisfied using appropriate algorithms. The strategy is to replace all the PID loops controlling the WCS with an optimally designed model-based multivariable loop. This new strategy leads to high stability and fast disturbance rejection such as those induced by a turbine or a compressor stop, a key-aspect in the case of large scale cryogenic refrigeration. The proposed control scheme can be used to achieve precise control of pressures in normal operation or to avoid reaching stopping criteria (such as excessive pressures) under high disturbances (such as a pulsed heat load expected to take place in future fusion reactors, expected in the cryogenic cooling systems of the International Thermonuclear Experimental Reactor ITER or the Japan Torus-60 Super Advanced fusion experiment JT-60SA). The paper details the simulator used to validate this new control scheme and the associated simulation results on the SBTs WCS. This work is partially supported through the French National Research Agency (ANR), task agreement ANR-13-SEED-0005.

Grand challenges in low-temperature plasma physics

INTRODUCTION A plasma is a hot ionized gas and classification of this fourth state of matter can be initially done using the basic concept of temperature. A prime example is the Sun which exhibits a very hot plasma in its core with temperatures of about 1.5 × 107 K (a result of fusion reactions with a proton density of ∼1026 cm−3) and cooler surface temperatures of about 6000 K [1]: the Solar wind originates from the Solar Corona, expands into the universe and impacts the Earth’ magnetosphere and ionosphere, the two plasma layers surrounding Earth’s gaseous atmosphere. Aurorae in the Northern and Southern skies near the magnetic poles are examples of this interaction. The electron density in the ionosphere is low (104–106 cm−3) and the background neutral gas density is also low (about 108 cm−3 or 3 × 109 Torr at 300 km altitude) approaching the “space-like” environment created in laboratories to develop and test hardware for space use (i.e., satellites and payloads). At the surface of the Earth lightning strikes of a storm are naturally occurring plasmas operating near atmospheric pressure (neutral density of about 2 × 1019cm−3) with large electron densities (about 1015– 1017 cm−3) characteristic of streamers, arcs and filamentary discharges. The temperatures and densities of neutral and charged particles are critical parameters affecting the physical mechanisms within the plasma such as particle transport and collisional processes [2] and their range spans many orders of magnitude, opening doors to an extremely wide range of plasma applications. Plasmas in which fusion reactions take place are often referred to as “hot” plasmas. The high-temperature plasma community has a well-defined aim of triggering and controlling fusion plasmas (as can be found in the Sun’s core) for energy production, with various worldwide large scale programs or experiments in place (i.e., the International Thermonuclear Experimental Reactor ITER, the National Ignition Facility ICF. . .) [3]. Hot plasmas in space also include relativistic plasmas (highest electron temperatures) and quantum plasmas (highest electron densities). All other plasmas are classified as low-temperature or “cold” plasmas: those gaseous plasmas or electrical discharges have been successfully harnessed and studied in the laboratory since the 1920s and in space using satellites since the 1960s. The latter two plasma examples essentially sit at the opposite ends of the “cold” plasma spectrum. The wide range of available plasma parameters has largely contributed to the long and expanding list of plasma applications as a result of both scientific and economic drivers: the temperature range of the neutral and/or ionized species allow heat and particle control to burn, melt, cut, coat, grow materials from the macroscopic to the microand nanoscale via “so called” plasma processes. Amongst thousands of plasma applications processes, a few examples are presented to show the past, present and future key role cold plasma physics must play in addressing the challenges facing the modern world: predicted energy crisis, environmental issues and ecosystems, global climate variation, population growth and biomedical concerns. In addressing those issues we must better understand the physics of the atmosphere, ionosphere and magnetosphere, the physics of the plasma interacting with a boundary and develop new clean sources of energy.

JT-60SA TF Magnet Joints Developments and Prequalification

In the framework of the so-called “broader approach” in connection with the International Thermonuclear Experimental Reactor ITER, the European and Japanese part- ners have agreed to in kind contribute to the construction of the JT-60SA tokamak in Naka (Japan). JT-60SA is a major upgrade of the former tokamak JT-60U, equipped with, in particular, superconducting coils. France and Italy, as European Voluntary Contributors, are sharing the supply of the 18 superconducting Toroidal Field coils, along with the corresponding mechanical structures and supports. These D shaped coils use a NbTi Cable-In-Conduit Conductor (CICC) and are electrically connected in series. Each coil is composed of double pancakes connected in series and two coil terminals, all located in a joint area at their outer radius at the upper part of the outer leg. The joints proposed by CEA is the twin box design which was initially developed by CEA for ITER Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn conductors and which is now adapted to the NbTi conductor. This design relies on the use of copper/steel explosion bonded plate as base material to constitute each conductor termination, the joint being assembled by soldering of the adjacent terminations. Such a design was successfully qualified on a pre-prototype sample in the CRPP SULTAN facility. To simplify the inner joints regarding the winding pack manufacture process, an evolution towards a monobloc twin box concept is proposed. After production and qualification of the needed prototype steel/copper/steel 3-layer explosion bonded plate, a dedicated joint mock-up was used to define the corresponding manufacture process. Specific processes were also developed for the coil terminals which have to be connected in a dismountable way for the cold acceptance tests of the coils in Europe, as well as in a definitive way at the Japan site. A low cost dedicated facility was developed to measure the DC resistance in order to perform a simple prequalification in cryogenic conditions on the produced mock-ups. A benchmark of the facility using the previously prequalified sample was done to validate this facility as a simple tool usable for this resistance measurement. The paper reports the different joint proposals and the manufacture processes developed as well as the pre-qualification results.

Draining of a Helium-Cooled Lead Lithium Test Blanket Module by Gravity Under the Influence of a Strong Magnetic Field

A helium-cooled lead lithium blanket has been proposed as a European liquid-metal test blanket module for the experimental campaign in the international thermonuclear experimental reactor ITER. The current design consists of columns of rectangular boxes called breeder units filled with the liquid-metal PbLi. The blanket modules are placed in the region of the strong plasma-confining magnetic field, which causes intense interactions of the flowing liquid metal with induced currents and creates Lorentz forces opposing the flow. Under emergency conditions, the liquid metal has to be removed from the blanket as fast as possible to minimize losses to the surrounding. In case of a leak, the liquid metal has to flow out, driven only by its own weight. This paper analyzes the draining by gravity under the conservative assumption that the magnetic field is not switched off. The geometric elements creating the major magnetohydrodynamics resistance to the draining fluid are identified to support further improvements in the design.

Anita-4/F: A Code for Material Irradiation Characterization in Fusion Neutron Spectra Using Fendl-2 Activation Data

The ANITA-4/F is a code package for the activation characterisation of materials exposed to neutrons in fusion machines. The package has been intensively used by ENEA for safety assessment of the International Thermonuclear Experimental Reactor ITER to evaluate the activated corrosion product source terms. This paper presents a summary description of the package and gives the details of its capabilities. The main component of the package is an updated version of the activation code ANITA that computes the radioactive inventory of a material subject to neutron irradiation, continuous or stepwise. It provides activity, atomic density, decay heat, biological hazard and gamma-ray source of each nuclide; total activity, decay heat, contact dose equivalent, gamma-ray spectra and other relevant parameters, for the irradiated material, versus cooling time. As an option, those parameters may be plotted by the GRANITA module, as a function of the cooling time. The code is provided with a complete data base that includes: 1) the FENDL/A-2 neutron activation data libraries (both for the standard 100 GAM-II and 175 VITAMIN-J groups structure), 2) the FENDL/D-2 decay data library, 3) the ICRP dose coefficients for ingestion and inhalation of radionuclides. Arbitrary structure can be used for the neutron irradiation spectrum. It is internally converted to one of the standard structures. Continuous or multi-steps (up to 2000 burn-dwell intervals) can be considered for the operational scenario. A different level of the irradiation flux can be used for each one of the exposure time step. The paper presents also, as an example, an application to the neutron exposure characterisation for the AISI 316 LN of the first wall, with reference to the basic performance phase of ITER.

Radiation-enhanced sublimation of graphite in PISCES experiments

Radiation enhanced sublimation (RES) of graphite leads to potentially high erosion rates in advanced fusion devices (Compact Ignition Tokamak, CIT) and (the International Thermonuclear Experimental Reactor ITER) and may be important in the ‘‘carbon blooms’’ observed in Tokamak Fusion Test Reactor (TFTR) and the Joint European Torus (JET). Erosion rates measured by weight loss are reported for POCO graphite exposed to helium plasmas for a temperature range from 900–2000 °C, ion energies of 30–300 eV, ion fluxes of 1–6×1018 cm−2 s−1, densities of 2–10×1012 cm−3, and electron temperatures of 4–10 eV. These are the first data on RES at fusion-relevant particle fluxes. The data show little reduction from a direct linear dependence upon flux. For these conditions, the amount of redeposition and carbon self-sputtering was minimal. Over 1700 °C, there is evidence of electron emission from the sample.