Plasma Position

The mission of this script is to process data from Mirnov coils, determine plasma position and thus help with plasma stabilization. Mirnov coils are type of magnetic diagnostics and are used to the plasma position determination on GOLEM. Four Mirnov coils are placed inside the tokamak 93 mm from the center of the chamber. The effective area of each coil is $A_{eff}=3.8\cdot10^{-3}$ m. Coils $mc_9$ and $mc_1$ are used to determination the horizontal plasma position and coils $mc_5$ and $mc_{13}$ to determination vertical plasma position.

Procedure (This notebook to download)

Data integration and $B_t$ elimination

The coils measure voltage induced by changes in poloidal magnetic field. In order to obtain measured quantity (poloidal magnetic field), it is necessary to integrate the measured voltage and multiply by constant: $B(t)=\frac{1}{A_{eff}}\int_{0}^{t} U_{sig}(\tau)d\tau$

Ideally axis of the coils is perpendicular to the toroidal magnetic field, but in fact they are slightly deflected and measure toroidal magnetic field too. To determine the position of the plasma, we must eliminate this additional signal. For this we use vacuum discharge with the same parameters.

Plasma life time

Plasma Position

To calculate displacement of plasma column, we can use approximation of the straight conductor. If we measure the poloidal field on the two opposite sides of the column, its displacement can be expressed as: $\Delta=\frac{B_{\Theta=0}-B_{\Theta=\pi}}{B_{\Theta=0}+B_{\Theta=\pi}}\cdot b$

Horizontal plasma position $\Delta r$ calculation

Vertical plasma position $\Delta z$ calculation

Plasma column radius $a$ calculation

Data

Graphs

Results

Icon fig

Plasma position during discharge