Magnetic Fields and Magnetic Diagnostics for Tokamak Plasmas

Magnetic fields and tokamak plasmas
Alan Wootton
Figure 18.7. The internal electric field prior to a disruption (from Hutchinson)
Figure 18.7 shows some spatial profiles of E φ from this analysis just before and at a disruption.
Although the edge electric field goes negative (the negative voltage spike) the internal electric
field strongly positive. In principle, having measured j and E we could derive the local
conductivity.
Mirnov Oscillations
The same probes used to measure the internal equilibrium properties can be used to look at the
Mirnov fluctuations (as long as the coils have a sufficiently high frequency response). Data from
such experiments has isolated the radial dependence of the fluctuating b r , b θ fields, as shown in
Figure 18.8. It agrees with our discussion in section 17, namely b ∝ (r mn /r) m+1 for r > rmn
without a vacuum vessel. In the presence of a conducting vessel at r = r w we must account for
the image currents which flow, so for example we would expect
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