Comparison of the performance of ICRF antennas with and without Faraday shield on TEXTOR

After the first demonstration of successful operation with ion cyclotron resonance heating (ICRH) on TEXTOR using an antenna without Faraday shield (FS), a further comparison of an antenna with FS and an antenna without FS has been made over a wide range of plasma conditions (including the improved confinement regime on TEXTOR), in zero phase and pi phase operation, using various heating scenarios. No restriction in the operational conditions was found to exist for the screenless antenna. A theoretical analysis shows that antenna side limiters are sufficient to protect the antenna conductor from the plasma and that the plasma in front of the antenna can take over the role of the FS without introducing additional losses. The impact of the operation with both antennas on plasma temperature, density, energy, impurities, etc., is discussed in detail.