Zeff profile measurements from bremsstrahlung imaging in the MAST spherical tokamak

A bremsstrahlung diagnostic has been deployed on the Mega Ampere Spherical Tokamak (MAST), with matrix viewing of the full plasma cross section in a narrow region of the continuum free of spectral lines. An uncooled CCD detector is used to provide 100 Hz 128x128 matrix viewing of the plasma emissivity which is spectrally selected using an interference filter of only ∼0.5 nm bandwidth. The apparently conflicting demands of a large field of view for the plasma and the small solid angle for narrow spectral bandwidth is accommodated in a compact lens, filter, and detector arrangement. Using measured electron temperature and density profiles the Zeff profile evolution is determined