112,611 research outputs found
Preliminary Comparison of the Conventional and Quasi-Snowflake Divertor Configurations with the 2D Code EDGE2D/EIRENE in the FAST Tokamak
No full textThe new magnetic configurations for tokamak divertors, snowflake and super-X, proposed to mitigate the problem of the power exhaust in reactors have clearly evidenced the need for an accurate and reliable modeling of the physics governing the interaction with the plates. The initial effort undertaken jointly by ENEA and IPPLM has been focused to exploit a simple and versatile modeling tool, namely the 2D TECXY code, to obtain preliminary comparison between the conventional and snowflake configurations for the proposed new device FAST that should realize an edge plasma with properties quite close to those of a reactor. The very interesting features found for the snowflake, namely a power load mitigation much larger than expected directly from the change of the magnetic topology, has further pushed us to check these results with the more sophisticated computational tool EDGE2D coupled with the neutral code module EIRENE. After a preparatory work that has been carried out in order to adapt this code combination to deal with non-conventional, single null equilibria and in particular with second order nulls in the poloidal field generated in the snowflake configuration, in this paper we describe the first activity to compare these codes and discuss the first results obtained for FAST. The outcome of these EDGE2D runs is in qualitative agreement with those of TECXY, confirming the potential benefit obtainable from a snowflake configuration. � 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Modelling of lithium erosion and transport in FTU lithium experiments
No full textThe ERO code has been used to simulate lithium erosion, transport and re-deposition from liquid lithium limiter experiments in FTU. Two different operational cases from LLL experiments with different plasma parameters and surface temperature are modelled. According to the effective lithium sputtering yields, for both cases the lithium erosion is mainly due to physical sputtering rather than evaporation. Furthermore, the modelled re-deposition fraction of evaporated lithium is much higher than that of sputtered lithium, which is due to the shorter ionisation mean free path of thermal lithium atoms. Therefore, the evaporation erosion effect can be neglected compared to physical sputtering when the surface temperature is below 450 °C. According to the simulations, most of the lithium impurities exist in the form of Li+, and the main plasma contamination by lithium ions is low because most of eroded lithium particles are not transported into the core plasma and stay outside of the LCFS. © 2013 Elsevier B.V. All rights reserved
Comparative analysis of the SOL plasma in DEMO using EDGE2D/EIRENE and TECXY codes
No full textIn this contribution a benchmark of the 2D edge codes TECXY and EDGE2D-EIRENE is presented. A conventional DEMO scenario is considered by assuming a simplified geometry, with the target plates perpendicular to the separatrix, and a pure Deuterium plasma. Despite the different models adopted in the two codes, mainly related to the description of the neutral dynamics and to the different boundary conditions, the results show a good match both in terms of power load profiles on the outer target and predicted trends for global quantities. A scan in density and in diffusion coefficients is performed in order to identify the characteristic conditions and the different regimes of the SOL. Comparable values and similar dependency of the global quantities as a function of the power decay length is also observed
Perspectives for the liquid lithium and tin targets in the Italian Divertor Test Tokamak (I-DTT) divertor
No full textThe behaviour of the scrape-off plasma of the projected Italian tokamak I-DTT is analysed by means of the two-dimensional edge code TECXY for either Li or Sn as the liquid target material. A scan in the outer midplane separatrix density range n e,omp ≈ (0.5-1.1) × 1020 m-3 is carried out for several power inputs into the scrape-off layer (SOL) up to a maximum of P SOL = 35 MW. The radiative capability and peak load mitigation are higher for Sn than for Li, but only slightly so at high density, so that the entire density range can be explored with liquid Sn targets, unlike Li whose employment at low density and high power is questionable. However, if a ceiling to the Sn concentration is set for high core fusion performance, Sn mitigation at low density may drop below Li. Nonetheless, concerns about the Li option derive from the very large material consumption and from the fact that the main mechanism of impurity release is sputtering, which is outside the full control of the operator. Considering specifically the three main scenarios-low, medium and high density-at the maximum auxiliary power of 45 MW, operations are successful with Sn, whereas Li requires an additional impurity able to radiate in the core, except at the highest density. The snowflake plus configuration, compared with the standard single null, as a sample for advanced divertors, appears more suited to exploit the advantages of the liquid metal option. Concerning additional impurities, only Ar and Ne are considered at present. They can strongly help in reaching and studying deep detached conditions even at the maximum power, but are not essential for operations. Wide flexibility in designing the target refrigeration system is required to fully exploit its great potential
A comparative study of the effects of liquid lithium and tin as DEMO divertor targets on the heat loads and SOL properties
No full textComparative study of a conventional and snowflake divertor for the FAST (Fusion Advanced Studies Torus) tokamak
No full textThe SOL features of FAST in the snow flake (SF) configuration of the divertor are compared with those of the conventional single null case for three main scenarios: reference, advanced and extreme H-mode by means of the 2D edge code TECXY. The heat load onto the divertor targets is dramatically mitigated, much more than expected from the change of magnetic topology only, especially at the highest plasma densities. The accompanying large density increase and temperature drop indicate a much closer approach to plasma detachment. The load level with SF appears always manageable by the present technology without the help of injected impurities. Sputtering from the target also should become negligible. These changes are attributed to the much longer time spent by the SOL particles in the cold region of the X point where the length of the magnetic lines is highly increased and hence to the much stronger interaction of the plasma particle with the neutrals. © 2013 EURATOM-ENEA Association. Published by Elsevier B.V. All rights reserved
Preliminary integrated core-SOL-divertor modelling for DTT tokamak with liquid metal divertor targets
No full textThe I-DTT tokamak has been analyzed by means of the integrated COREDIV code simulations when either Li or Sn are used as liquid divertor target materials. It has been found that power to divertor can be strongly mitigated with LMD. The reason is that the solution is determined by the LM divertor properties, leading to the requirements that the heat load to the liquid target is reduced below a threshold value. The threshold is due to the limits to the plasma contamination by the evaporated material. In the case of Li target, the limit is set to ∼8 MW/m2 and is achieved by strong Li radiation in the divertor (vapor shielding). For Li, there is a low density limit and solution is only achievable if the plasma density is high enough. The low density operation might be recovered if Kr seeding is applied. For the tin liquid divertor, H-mode operation is possible with efficient reduction of the heat flux to the divertor (∼11 MW/m2) in the evaporation efficiency reduced mode of operation and with the separatrix density high enough. The heat load reduction can be even more efficient (∼2.5 MW/m2) in the regime with strong evaporation but in this case the H-mode operation might be a problem. It appears that Ne seeding can hardly solve the H-mode operation problem but Li seeding seems to be better solution. The operation with higher edge plasma densities alleviates difficulties with the H-mode operation of liquid tin divertor
Comparison between liquid lithium and liquid tin targets in reactor relevant conditions for DEMO and I-DTT
No full textThe performance of divertor targets made of liquid metal, either lithium or tin, in highly powered tokamaks is analyzed for the proposed European DEMO and the projected Italian divertor test tokamak (I-DTT). The main tool is the 2D edge code TECXY, together with COREDIV. The results show that both materials are compatible with either DEMO or I-DTT under proper setting of the liquid divertor parameters. In general, operation at a high density is always highly recommended especially if detached conditions are desired. The latter can always be closely approached even when preserving an acceptable plasma purity with a proper setting of the target parameters and with the help of an additional impurity, which is able to radiate significantly inside the scrape-off layer plasma. For this action, Ar is preferred over Ne. Tin usually performs better than lithium for mitigation properties, reducing plasma pollution, material consumption, which in a DEMO-like device could be very high, and a definitely lower chemical affinity to hydrogen
Preliminary analysis of the efficiency of non-standard divertor configurations in DEMO
No full textThe standard Single Null (SN) divertor is currently expected to be installed in DEMO. However, a number of alternative configurations are being evaluated in parallel as backup solutions, in case the standard divertor does not extrapolate successfully from ITER to a fusion power plant. We used the SOLPS code to produce a preliminary analysis of two such configurations, the X-Divertor (XD) and the Super X-Divertor (SX), and compare them to the SN solution. Considering the nominal power flowing into the SOL (PSOL = 150 MW), we estimated the amplitude of the acceptable DEMO operational space. The acceptability criterion was chosen as plasma temperature at the target lower than 5 eV, providing low sputtering and at least partial detachment, while the operational space was defined in terms of the electron density at the outboard mid-plane separatrix and of the seeded impurity (Ar only in the present study) concentration. It was found that both the XD and the SXD extend the DEMO operational space, although the advantages detected so far are not dramatic. The most promising configuration seems to be the XD, which can produce acceptable target temperatures at moderate outboard mid-plane electron density ( m−3) and Zeff= 1.3
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