Technique for inferring outward displacement of magnetic flux surfaces in toroidal plasmas, using multichord interferometry

When flow can be neglected and when heat conduction parallel to the magnetic field is sufficiently strong, a confined plasma's surfaces of constant magnetic flux are also surfaces of constant plasma density. Thus, in principle, measurements of the internal density asymmetries can also determine the internal profile of flux-surface displacement along major radius caused by toroidal effects. This paper develops a simple algorithm for doing this with multichord interferometer data in toroidal plasmas having circular minor cross section and illustrates the technique with data from the ZT-40M reversed-field pinch