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a. Scale size 



b. Strength of magnetic field 



c. Aspect ratio (long skinny to sliort fat) 



d. Shape of cross section -- round, elliptical, bean and others 



e. Method(s) of heating 



f . Wall material 



g. Diverters or I Imiters (many different varieties) 



Modest size experiments are essential in filtering out the various possibi- 

 lities. It is completely impractical to design all these variations into 

 one - or even a few - experimental devices. Thus the dozens of modest size 

 experiments around the world have combined to form a data base that was 

 utilized to make parameter choices for the next phase of larger and better 

 machines. This has, in turn, provided a way to check the earlier data as 

 to its relevance. So to answer the question: 



In the early phases of modest, exploratory devices, it is important to have 

 many different exploratory experiments. The normal scientific competitive 

 urge will ensure that these experiments are not really duplicates. These 

 small machines can be modified fairly rapidly and at a relatively low cost. 

 Thus dozens of small Tokamaks have been well utilized around the world. 



With increased knowledge it has been possible to design and build a smaller 

 number of larger devices with plasma parameters closer to reactor require- 

 ments. Here again they effectively supplement one another in building an 

 International data base. 



The main point of all this is that Tokamaks would not have occupied their 

 present dominant position (and conceivably could have been cast aside 

 completely) had it not been for the strong interaction between competing 

 groups. 



So much for the Tokamaks — but the variety of parameter choices involved in 

 the Tokamaks is substantially exceeded by those in stellarators and other 

 confinement geometries. Thus it would not make sense, in the exploratory 

 phases in particular, to subdivide the work with each nation taking on the 

 task of developing one approach. 



Second, Materials - Here the situation is different. The problems are to a 

 greater extent separable. For example, the task of development and charac- 

 terization of new alloys for fusion application can be (and are to some 

 extent) organized and subdivided between the international participants. 

 Some larger test facilities will be needed. At present, Japan and the EC 

 are following a somewhat different approach that the U.S. The EC and Japan 

 are focusing their development activities on those required to build next 



