High precision pick-up (Mirnov) coils for disruption studies in the T-11M and TCABR tokamaks

Newly developed methods of visualization and determination of widths of int ernal magnetic islands are based on measurements of the perturbed magnetic fields near the plasma border. Reliable analysis of pick-up (Mirnov) coils data is rather complicated and measurement errors have to be minimized. Pla sma wall interaction, electrical sparks in the discharge chamber, and reson ances in the measurement systems could be main sources of errors but, also, the design of coils should take into account that the typical frequency ba nd of the disruptive processes is in the range of similar to 100 kHz - 1.5 MHz. A double Faraday coaxial screening with a symmetrically input system o f pick-up coils was developed for disruption studies in the TCABR tokamak i n Sa S (a) over tilde o Paulo. The main design features of this high precis ion pick-up coil system are discussed. (C) 1999 American Institute of Physi cs. [S0034-6748(99)61401- 0].