TJ-II:Magnetics
Mirnov coils
TJ-II is fitted with an ample set of Mirnov coils: [1]
- Two straight arrays above the plasma column, each with 12 coils, mounted in a 0.5 mm thick stainless steel tube attached to a port flange. The 12 coils are distributed in 4 groups of 3 coils each, separated by a distance of 30 mm. The three coils in each group measure the three cylindrical components (R, Z, and φ) of the magnetic field. They are located in sectors B5 and C4, at φ = 232° and 308°.
- One poloidal array with 15 coils measuring the poloidal field component. This array is located between sectors D4 and D5, at φ = 45°.
Rogowski coils
Two Rogowski coils have been installed in sectors A5 (148.7°) and B4 (211.3°). Since the coils have to surround the plasma column completely, they are located under the protecting tiles of the groove that runs toroidally all along the vacuum vessel. For this purpose, 2 mm deep channels were machined on the vacuum side of the groove, at the above mentioned poloidal cross sections, in order to allow enough space for the coils.
The signals 'Ip_a5_' and 'Ip_b4_' in the TJ-II database provide the corresponding measurements of the net plasma current.
Diamagnetic loops
Two internal diamagnetic loops are installed at sector A5 (135°) and B4 (225°). They consist of a main loop which encircles the plasma column and runs under the protecting tiles in the groove region and a compensating loop which measures only the vacuum magnetic flux.
The signals 'W_a5_corr' and 'W_b4_corr' in the TJ-II database returns the energy content of the plasma, based on the diamagnetic loop in sector B4, corrected for the net plasma current.