ITER Design

The shielding blanket is composed of water-cooled steel modules, which are directly supported by the vacuum vessel and are effective in moderating the 14MeV neutrons, with a water-cooled copper mat bonded to the surface of the modules on the plasma side, and protected from interaction with the plasma by beryllium. Manufacturing considerations can be found elsewhere [48]. The first wall incorporates two start-up limiters located in two equatorial ports. With the aim to reduce cost and nuclear waste, the design includes a modular and separable first wall. This allows damaged or eroded blanket modules to be repaired inside the hot cell either by replacement of panels or by plasma spraying or other methods. 

The factors that affect the selection of plasma facing materials for ITER come primarily from the requirements of plasma performance (e.g., need to minimize impurity contamination and the resulting radiation losses in the confined plasma), engineering integrity, component lifetime (e.g., need to withstand thermal stresses, acceptable erosion), and safety (e.g., need to minimize tritium and radioactive dust inventories and avoid explosion hazards). 

Currently, the ITER design uses beryllium for the first wall, and CFC as well as tungsten in the divertor. Each of these three candidate materials has some inherent advantages and disadvantages [1] (see Table 12.1), and their application depends on the specific operational requirements [53,54] (see Table 12.2). The plasma-material interaction (PMI) issues are comprehensively reviewed in [1]. 

The longer pulse duration and cumulative run-time, together with the higher heat loads and more intense disruptions, represent the largest changes in operation conditions compared to today s experiments. Erosion of PFCs over many pulses, and distribution of eroded material, are critical issues that will affect the performance and the operating schedule of the ITER tokamak. Primary effects ensuing from erosion/re-deposition include plasma contamination, tritium co-deposition with carbon (if used in some parts of the divertor), component lifetime, dust, and formation of mixed-materials, whose behavior is still uncertain. 

Disruptions (VDEs) Peak surface heat load - 10 uncertain uncertain 

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It is greatly recommended that strong feedback between the designer who needs the results and the CFD engineer is maintained to improve the results incrementally and also to produce results that are really needed. It is in fact an iterative design procedure. 

Iterative design is essential It is a rarity that the first ligand to be designed is the final one. As indicated above, it is common to go through several iterations of the structure-based design cycle before settling on the desired molecule that will be advanced to development. 

Identify the five basic steps in an iterative design process. 

We will not describe the iterative design process in any more detail than this. There are many fine books on the subject, and the interested reader is referred to the list at the end of the chapter for further information. After a brief diversion into alternative design strategies in the next section, we will return to the iterative design process to see how the concepts of materials selection fit into mechanical design. 

Figure 8.2 The iterative design process applied to mechanical design of components. Reprinted, by permission, from M. F. Ashby, Materials Selection in Mechanical Design, 2nd ed., p. 9. Copyright 1999 by Michael F. Ashby.

Outer iteration Design points x xl03, mol/1 QX108... 

Melnick M, Reich SH, Lewis KK, Mitchell L, Ngyen D, Trippe AJ, Dawson H, Davies JF, Appelt K, Wu B-W, Musick L, Gehlhaar DK, Webber S, Shetty B, Kosa M, Kahil D, Andrada D. Bis-tertiary amide inhibitors of the HIV-1 protease generated via protein structure-based iterative design. J. Med. Chem. 1996 39 2795-2811. 

The sieve plates are designed in accordance with the recommendations made in Refs. A3 to A6. The iterative design approach was suggested in Ref. A3 (p.458). The procedure is summarized below. 

The first two of the above disadvantages of fixed design methods can be overcome by the use of iterative designs. These are methods in which an initial design that contains a minimum number of data points is used, then the results are investigated and the results of that investigation are used to conclude whether or not one or more new experiments are required, as well as where these additional experiments should be located in the parameter space. 

Figure 5.28 Illustration of the operation of iterative designs for the optimization of chromatographic selectivity.

The model is then used in a calculation step to predict the location of the optimum. This step involves the calculation of the response surface from the retention surfaces using a suitable criterion, the location of the (predicted) optimum on this surface, and a decision about new experiments to be performed. Only this last aspect distinguishes iterative designs from the previously described fixed experimental designs. 

The philosophy of iterative designs is to locate the true (global) optimum using a minimum number of experiments and making maximum use of available insight and experimental data. Such a philosophy can be justified if... 

We may summarize the characteristics of iterative design methods as follows ... 

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