Measurement of tokamak poloidal field by spectroscopic observation of a neutral helium beam

F. C. Jobes, M. H. Redi, A. L. Roquemore, G. Schilling, B. C. Stratton, E. J. Synakowski

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Abstract

The pitch angle of the magnetic field of a tokamak can be determined by observing the light emitted by He+ ions injected into the plasma by a perpendicular He0 beam. These ions will orbit in small circles near the ionization point. The observed spectrum of a He II line (4686 Å) has a very wide and distinctive shape; the width of the spectrum depending only upon the particle velocity and the geometry of the view point. The geometry depends upon both the pitch of the poloidal field and the choice of observation point. Preliminary observations of a 60 keV He0 beam show that the above effect indeed exists, and is intense enough to be seen all the way into the center of the plasma (even in a helium plasma), and that pitch measurements derived from the observed widths in the outer part of the plasma agree with the pitch derived from magnetic measurements of q(a).

Original languageEnglish
Pages (from-to)2981-2983
Number of pages3
JournalReview of Scientific Instruments
Volume61
Issue number10
DOIs
StatePublished - 1990

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