Characterization of 3-strap antennas in ASDEX Upgrade

The response of the local RF current measured at limiters of 3-strap ICRF antenna to variations of power balance and phasing at f ICRF =30MHz agrees qualitatively well with EM calculations by TOPICA and RAPLICASOL codes. Measurements of tungsten sputtering yield and DC current at the limiters correlate strongly with the local RF current. In contrast to findings for the 2-strap antennas, values of DC current are predominantly positive, and negative only for some locations and feeding parameters. Explanations can involve more physical mechanisms than only parallel sheath dynamics.