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[en] By using the strain-range partitioning method, the fatigue life of high-heat-load components made of oxygen-free copper have been successfully predicted within a factor of two. Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment
[en] It is known that NBI ion losses may pose a problem to the Wendelstein 7-X first wall, but the so-far utilized wall models had insufficient details for reproducing the locations and magnitude of the hot-spots. This study aims to exhaustively analyse the detailed wall loads in the reference magnetic configurations and in various plasma scenarios. The goal is to pinpoint the endangered plasma facing components and to calculate heat loads to them in preparation for the first NBI operations. This study can be used to prepare monitoring of the heat loads and paves the way to future searches of improved configurations. (paper)
[en] The first review is presented for the recent stellarator designs of FFHR, HSR, ARIES-CS, which are based on the experimental device projects of LHD, W-7X, NCSX, respectively. The main advantageous features of those designs are common on (1) current-free plasmas, which leads to steady, high Q and disruption-free reactors and (2) high density operations, which largely reduces the diverter heat load. Design optimization and engineering feasibility are highlighted including maintainability, fabricability and showing future R and D key issues with prospect towards DEMO.
[en] Full text: The mitigating properties of the divertor advanced magnetic configurations on the target heat load have been analyzed with the 2D edge code TECXY for the European DEMO. Particular emphasis is put on the snowflake minus, for which several variants have been proposed just to study this particular effect, where the distance between the two X-points, the primary and secondary ones, is varied. In such a way the magnetic topology in the outboard part of the divertor is varied and regions with low poloidal field and then much longer connection length are created with different extension and localization with respect to the primary X-point. The scenario considered is a low density one, without any added impurity in order to keep at a negligible level the effect of radiative volume losses and then to ascribe any possible change to the transport properties of each configuration. A significant widening of the power flow channel in term of the poloidal flux coordinate, i.e., independent of any expansion effect, is found and correspondingly a drop of the peak power load. The mitigation effect increases for these configurations that more affect the region in close touch with the main separatrix. The possible causes for this effect are discussed in the paper. However some manipulation is required to make the real magnetic topology compatible with the constraints of TECXY, which allows for only two targets. Even if the modifications affect only the more external flux tubes that have less weight in the power transport, the results clearly claim for confirmation by other more complex codes. (author)
[en] Life extension package LE3 (9975-03203) has been instrumented and subjected to an elevated temperature environment for approximately 8 years. During this time, the cane fiberboard has been maintained at a maximum temperature of ~160 - 165 °F, which was established by a combination of internal (19 watts) and external heat sources. Several tests and parameters were used to characterize the package components. Results from these tests generally indicate agreement between this full-scale shipping package and small-scale laboratory tests on fiberboard samples, including the degradation models based on the laboratory tests. These areas of agreement include the rate of change of fiberboard weight, dimensions and density, and change in fiberboard thermal conductivity. Corrosion of the lead shield occurred at a high rate during the first several weeks of aging, but dropped significantly after most of the moisture in the fiberboard migrated away from the lead shield. Dimensional measurements of the lead shield indicate that no significant creep deformation has occurred. This is consistent with literature data that predict a very small creep deformation for the time at temperature experienced by this package. The SCV O-rings were verified to remain leak-tight after ~5 years aging at an average temperature of ~170 °F. This package provides an example of the extent to which moisture within a typical fiberboard assembly can redistribute in the presence of a temperature gradient such as might be created by a 19 watt internal heat load. The majority of water within the fiberboard migrated to the bottom layers of fiberboard, with approximately 2 kg of water (2 liters) eventually escaping from the package. Two conditions have developed that are not consistent with package certification requirements. The axial gap at the top of the package increased to a maximum value of 1.549 inches, exceeding the 1 inch criterion. In addition, staining and/or corrosion have formed in a few spots on the drum. However, the package remains capable of performing its function. Aging of this package continues.
[en] The choice of the best material exposed to the plasma in a future reactor is still an open question. One of main requirements to be satisfied is the capability to withstand high heat loads, in the range 10-20 MW/m2, during normal operations in a future reactor, as well as the peak power released by ELMs in H-mode operation. On FTU, since the end of 2005, we have started an innovative program having as main goal the possibility to expose a liquid surface to the plasma. The small wetted area, of the FTU three liquid lithium limiter units, does not allow to use it as main limiter for all the duration of the discharge so that it is always set in the shadow of the main toroidal limiter. In this condition, heat loads up to 2 MW/m2 are normally withstood by the liquid lithium limiter without any surface damage and problems to the FTU operations. In order to increase the heat load on the liquid lithium limiter for a controlled limited period, the plasma column is shifted towards the liquid lithium limiter during the discharge. The surface temperature remains constant although the plasma column is pushed on the liquid lithium limiter. This saturation of the surface temperature can be understood considering the dependence of the evaporation rate versus the surface temperature between 250 deg. C and 550 deg. C that increases by five orders of magnitude. The evaporated lithium forms a strongly radiative cloud all around the three units limiting the power load on the surface. We do not observe any accumulation of lithium into the discharge as it can be also inferred from the time evolution of the Li III line growing up until the temperature is reaching the maximum value and then remaining almost constant.
[en] The simulation of the thermal response of the JET bulk tungsten divertor modules to real operational conditions demonstrates that the analyzed design provides more favourable conditions than before (≤600 deg. C) for the temperature-vulnerable materials of the stack attachment (esp. Inconel spring discs), thereby increasing the attachment lifetime. The computation shows that the JET divertor unit can withstand up to five consecutive cycles, 10 s long, of an evenly distributed heat loading (averaged heat flux of ∼6.5 MW/m2) with half-an-hour intervals before the springs reach their uppermost temperature limit. However, if we take into account: (i) the real heat load distribution over the upper lamellae surface (shadowing effect), (ii) an initial temperature of the structure of 200C, it may be that the temperature approaches 600C after a single full-energy pulse.