Techniques for the Measurement of Disruption Halo Currents in the National Spherical Torus Experiment
Authors: S.P. Gerhardt, E. Fredrickson, L. Guttadora, R. Kaita, H. Kugel, J. Menard, H.Takahashi
This paper describes techniques for measuring halo currents, and their associated toroidal peaking, in the National Spherical Torus Experiments [M. Ono, et. al, Nuclear Fusion 40, 557 (2000)]. The measurements are based on three techniques: i) measurement of the toroidal field created by the poloidal halo current, either with segmented Rogowski coils or discrete toroidal field sensors, ii) the direct measurement of halo currents into specially instrument tiles, and iii) small Rogowski coils placed on the mechanical supports of invessel components. For the segmented Rogowski coils and discrete toroidal field detectors, it is shown that the toroidal peaking factor inferred from the data is significantly less than the peaking factor of the underlying halo current distribution, and a simple model is developed to relate the two. For the array of discrete toroidal field detectors and small Rogowski sensors, the compensation steps that are used to isolate the halo current signal are described. The electrical and mechanical design of compact undertile resistive shunts and mini-Rogowski coils is described. Example data from the various systems is shown.Abstract:
__________________________________________________
Submitted to: Review of Scientific Instruments (May 2010)
__________________________________________________
Download PPPL-4694 (pdf 275 KB 22 pp)
__________________________________________________