MEASUREMENT OF THE VERTICAL MAGNETIC-FIELD IN TEXTOR USING THE ELECTRON-BEAM TECHNIQUE

The results of the poloidal field (PF) coil efficiency measurements an d the values for stray field compensation during premagnetization are presented. The results have been verified by field calculations and co mpared with plasma breakdown experiments. Determination of the vertica l field in the plasma center produced by PF coils is essential for the definition of breakdown conditions and for the control of the horizon tal plasma position and of the plasma shape in tokamaks. The electron beam technique has been chosen for the measurements, providing suffici ent precision and visibility Magnetic field lines became visible due t o the effect of electron movement in a magnetic field and light emissi on in a gas. Vertical fields Mere determined from the measured toroida l field and vertical electron beam displacements. Precise determinatio n of the values for the stray field compensation was achieved by detec tion of very low stray fields from the deflection of the electron beam .