In the ISX-B tokamak, the poloidal fields are supplied by sets of coils which are functionally coupled, in the sense that each set contributes to both the Ohmic-heating (OH) flux and the vertical field (VF), in contrast to the traditional way of grouping coils into 'decoupled' OH and VF windings. As a result, control of the plasma current Ip and control of the horizontal position ΔR are also strongly coupled. A transfer matrix model of this system is described, and the model is used to guide both the design and analysis of Ip and ΔR feedback control for ISX-B. The equations are linearized about a plasma equilibrium operating point to facilitate the analysis of stability and noise sensitivity. On slow time scales, the non-linearities are tractable enough to be used in large-signal analysis as well. The model accurately simulates actual ISX-B behaviour and can be generalized to any tokamak, since IP – ΔR coupling in fact always exists. It is especially applicable to future large machines, such as the TFCX and INTOR, which of engineering necessity will have functionally coupled windings.
Measurement of the open loop plasma equilibrium response in TCV