The behaviour and structure of waves launched from a novel double-loop
antenna in the SHEILA heliac are presented. Radial wave field and azi
muthal phase measurements are compared with cylindrical helicon wave t
heory after an appropriate magnetic coordinate transformation. This co
mparison provides strong evidence for the involvement of helicon waves
. Damping of the waves is investigated by comparing measured spatial d
amping rates with theoretical estimates. Comparison of measured densit
y with predictions from the helicon dispersion relation reveals how ge
ometry influences propagation of the waves in SHEILA.