Experimental measurements are presented of the parasitic loading resulting from an RF Langmuir current which flows from an unshielded antenna to the scrape-off layer (SOL) during Alfven wave heating (AWH) in TCA. The measurements are of relevance to ICRH where RF currents drawn by electrostatic screens lead to parasitic loading and harmonic generation in the SOL. An experimental study of the plasma response to AWH after the installation of screens on the AWH antennas is also presented. The results demonstrate that the fault current and some of the parasitic phenomena observed in the SOL during AWH with unshielded antennas are eliminated by screens. The plasma bulk response however is dominated by a large density rise which is unaffected by screens. The implications of these results for AWH are also discussed. (author) 10 figs., 27 refs.