The Mini-Radio Frequency Test Facility (Mini-RFTF) has contributed to helicon plasma source optimization for the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). In this paper, we report how the source, using hydrogen and helium, can be optimized for non-uniform geometries that are constrained to be suitable for VASIMR. The behavior of the density transition into high-density helicon operation was found to significantly depend on the magnetic field geometry. Operation indicates that a strongly focused magnetic geometry produces a continuously increasing density with increasing net power. For helium operation, mirror confinement effects possibly explain the observed plasma sustainment on upstream and downstream for several magnetic field geometries. (c) 2005 Published by Elsevier B.V.