Stray magnetic field interference with ion source operation on the DIII-D beamline

Measurements were made of the stray magnetic fields originating from the tokamak magnetic coils at the location of the ion source. The ohmic coils are the primary source of stray fields. Without the shield housing the dominant stray field was in the vertical direction. When the shield housing was in place, the radial component and the vertical component inside the housing become comparable. The short pulse ion sources exhibited clear degradation in discharge stability when the stray fields exceeded 1 gauss, whereas the common long pulse ion source appears quite immune to the stray fields up to a few gauss. 7 refs., 4 figs