Spectroscopic ion beam imaging for investigations into magnetic field mapping of a plasma

Abstract

The trajectory of an ion beam as it passes through a magnetically confined plasma is determined by the ion mass, energy, and charge state, and the magnetic field structure. In undergraduate physics laboratories, students use a measure of beam deflection in a well-defined magnetic field to determine the charge-to-mass ratio of a particle. The complementary analysis is equally valid; the field may be determined given a known charge-to-mass ratio. Additional complexity is introduced in a spatially nonuniform, time-varying magnetic field, such as that of a plasma. The technique of field mapping via spectral imaging is being developed with a heavy ion beam probe on the Madison Symmetric Torus. Technical issues, such as choice of wavelengths, optics, viewing geometry, and imaging hardware, are being addressed. Calculations indicate that beam emission is brighter than background bremsstrahlung for several transitions of interest. However, a wavelength region containing lines from the beam ions, but free of atomic lines from the plasma, remains to be identified.