Results 1 - 10 of 40
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[en] During the pre-conceptual design phase of fusion devices such as the European demonstration fusion power plant (DEMO), systems codes provide a fast evaluation of optimal design points and highlight high impact areas. However, determining or evaluating a design point at such an early stage comes with uncertainties in many of the design parameters. These uncertainties are both associated with the physics as well as the engineering basis of the European DEMO design. The work applies an uncertainty quantification analysis to the 2017 pulsed European DEMO design using the PROCESS systems code. It assumes that DEMO will be built as suggested by the baseline and explores what implications the currently known physics and engineering uncertainties have on the expected performance parameters (net electric output and pulse length), while optimising the fusion gain Q. A more detailed single parameter analysis clearly identifies high impact parameters. This confirms previous investigations as well as revealing new areas that warrant deeper investigation in particular in the technology area. (paper)
[en] Reflectometry simulations are particularly important since they allow to assess the measuring capabilities in experimental fusion devices and to predict the performance of future ones. We present a brief overview of reflectometry and introduce the family of REFMUL* codes for time-dependent reflectometry simulation. REFMUL* codes are Finite Difference Time Domain (FDTD) that allow to set up synthetic diagnostics to assess the behaviour of reflectometry diagnostics. This is illustrated in the current manuscript using the example of the Plasma Position Reflectometers of DEMO.
[en] WCrY Smart Alloys are developed as first wall material of future fusion devices such as DEMO. They aim at behaving like pure W during plasma operation due to depletion of the alloying elements Cr and Y. The Cr concentration gradients induced by preferential plasma sputtering cause Cr-diffusion. The exposure of WCrY and W samples to pure D plasma, with a plasma ion energy of , is simulated using the dynamic version of SDTrimSP. Cr-diffusion is included into the model. Simulation results are compared with experimental results. At sample temperatures of more than 600∘C and sputtering by D plus residual oxygen in the plasma ion flux, the Cr-transport to the surface leads to enhanced erosion for WCrY samples. A diffusion coefficient for Cr in WCrY of the order of is determined. The suitability of WCrY as first wall armour and the influence of further effects, considering especially Cr-diffusion, is discussed.
[en] Toward the use of RAFM (reduced-activation ferritic/martensitic) steels as a plasma-facing material (PFM) in future fusion devices, fundamental properties of RAFM steels as a PFM have been investigated in laboratory experiments. In this study, we have explored D retention in various RAFM steels (CLF-1, Eurofer, F82H, and Rusfer) exposed to plasmas (D fluence ∼ 1x1025 m-2, ion flux ∼ 2x1021 m-2s-1, sample temperature ∼ 373 K, incident ion energy ∼ 100 eV) in the PISCES-A linear plasma device.
[en] Structural materials present in and around any fusion device will face stringent conditions due to the high-energy and high-flux neutrons emitted from the fusion plasma. These neutrons can cause induced radioactivity, gas production, energetic knock out atoms, atomic displacement and decay heat in these materials. This would have a significant life-limiting impact on the materials and would also cause biological hazards and radioactive waste. Hence designing low activation materials for fusion devices is warranted. This paper presents a novel tool for quantification of radiological responses in terms of the elements present in the initial material composition. Such a framework would help in the identification and optimization of the fraction of most dangerous elements/isotopes from the material composition. In practical scenarios, the material encounters a large spatial and temporal variation of neutron fluxes. This problem has been effectively treated in the present work using a multi-parameter optimization scheme. The scheme optimizes the material composition (elemental or isotopic) based on various nuclear responses and there spatial and temporal variations within the user-defined constraints. This scheme is further included in the multi-point activation code ACTYS-1-GO. The tool provides a comprehensive picture of the material response during neutron irradiation and after shutdown, enabling the assessment of structural integrity of components in a fusion device. As an aide to the material optimization process, this paper also introduces a visual representation of the evaluated information like quantification of radiological responses produced by the parent elements/isotopes in a material. This has been implemented through a series of spectrum independent and spectrum-dependent diagrams called the radiation response diagrams. These diagrams show the variation of contributing parents toward the radiological responses as a function of cooling time. Such a graph could be very useful as a first approximation for material design. (paper)
[en] Due to their low sputtering yield, low intrinsic tritium retention, high melting point, and high thermal conductivity, W and W alloys are promising candidates for the divertor region in a magnetic fusion device. Transmutation reactions under neutron irradiation lead to the formation of He and H particles that potentially degrade material performance and might lead to failure. High He fluxes ultimately lead to the formation and bursting of bubbles that induce swelling, a strong decrease in toughness, and a nanoscale microstructure that potentially degrades the plasma. Understanding the behavior of He in polycrystalline W is thus of significant importance as one avenue for controlling the material properties under operating conditions. This paper studies the interaction of substitutional He atoms with various grain boundaries in pure W and the effect of the He presence on the system response to external loading. We observe that He segregates to all the interfaces tested and decreases the cohesion of the system at the grain boundary. Upon tension, the presence of He significantly decreases the yield stress, which depends considerably on the bubble pressure. Increasing pressure reduces cohesion, as expected. More complex stress states result in more convoluted behavior, with He hindering grain boundary sliding upon simple shear. (paper)
[en] A proof of principle experiment has been performed for the in situ measurement of the work function in vacuum conditions (∼10−7 torr) relevant to cesium-seeded negative ion sources for fusion applications. The work function is measured using the principle of the photoelectric effect. The performance of the work function measurement setup and temperature-controlled cesium (Cs) oven has been characterized using various diagnostics such as a quartz crystal microbalance, a surface ionization detector and pressure measurements. The background impurities responsible for work function degradation are detected using the residual gas analyzer. The work function (⩽3.06 eV) and Cs flux (∼1012 atoms s−1) have been measured directly at the sample surface during controlled Cs evaporation using a novel, inexpensive and portable design of the cathode–anode assembly. (paper)
[en] A Consultancy Meeting was held on 20 August 2014 at IAEA Headquarters in Vienna to review data needs for plasma-wall interaction with reduced-activation steel surfaces in fusion devices and delimit the scope of a possible coordinated research project on that topic. The proceedings and discussions during the meeting are summarized here. (author)
[en] The edge plasma simulation is coupled to fuel retention code to assess the fuel retention in tungsten divertor, which is a critical safety issue for the future fusion device. SOLPS suite of code is applied to calculate the divertor plasma condition as the input parameters for the fuel retention simulation, and HIIPC code is employed to calculate the fuel retention during the discharge. EAST upper divertor is chosen for the application of the coupled code. A realistic cycle of plasma discharges consisting of 60 s of plasma exposure followed by a resting period of 500 s is simulated to study the fuel retention from attached to detached divertor regime. The simulation results show significant difference of fuel retention between attached and detached plasma. Moreover, the ‘hot wall’ operation is proposed as a candidate method to reduce the retention.
[en] The effect of strong anomalous absorption (up to three-quarters of the pump power) of microwaves in electron cyclotron resonance heating (ECRH) experiments in toroidal devices is predicted. It originates from the low-power-threshold two-plasmon parametric decay instability, for which the only effective saturation mechanism is provided by the pump wave depletion. This makes the power deposition profile different from that predicted by the linear theory and provides an alternative interpretation for its evident broadening observed on ECRH in toroidal devices. (letter)