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Creative Commons license Marco de Baar, Engineering technical artefacts and scientific instruments [July 23, 2011]

 Summary

Conférence plénière du 23 juillet - CLMPS 2011 / Plenary lecture, Sat.. 23 July - CLMPS 2011

In this paper a comparison is made between engineering and scientific approaches to the design and construction of artefacts. The paper aims to show that the engineering of artefacts involves a separate body of knowledge, thus undermining the idea of engineering as being just applied natural science. This will be discussed on the basis of a case study, the test fusion reactor ITER that is currently being built in France.
Magnetohydrodynamics (MHD) is the science of conducting magnetized fluids. The theory combines Maxwell’s equations with the gas dynamics equations for the evolution of density and pressure. MHD allows physicists to understand elements of solar physics, the development of the earth magnetic field and the behaviour of fully ionised gasses (a.k.a. plasmas). In nuclear fusion research hot plasmas are confined by magnetic fields. MHD explains that in fusion plasmas at specific locations resistive instabilities (tearing modes) can develop. These modes are important from both a scientific and a reactor performance perspective.
The key notions of magnetohydrodynamics (MHD) will be explained. Then two instruments for MHD research will be compared. Both instruments are based on 140 GHz electro-cyclotron (EC) waves. The 2D ECE system is designed and built for scientific research in resistive MHD modes. The in-line ECE is a prototype of a real time control system for these modes, and designed and built for operational purposes (the suppress these modes and to increase the fusion power). The requirements and design of, and implementation of these systems on the small German tokamak TEXTOR will be discussed. If we were to bring these instruments to maturity for installation on ITER additional requirements emerge, associated with safety, licensing, lifecycle considerations, waste-management and operational availability.
On the basis of this comparison it will be argued that a specific body of engineering and design knowledge is involved in the second case. This knowledge is required to deal with complex trade-offs and cannot be derived from the natural sciences. The requirements for the mature scientific instrument, on the other hand, are only performance driven and similar to the typical requirements associated with prototypes. Finally, the design process seems firm and well established. External factors or the requirements can change, and this will affect the object of design, but not the design process.

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