**Acknowledgements**

study, the He-I 4<sup>3</sup>

**Figure 11.** Experimental 4<sup>3</sup>

D - 2<sup>3</sup>

D-2<sup>3</sup>

162 Plasma Science and Technology - Basic Fundamentals and Modern Applications

to be used for E-field measurements [16, 17].

source will be the subject of future research.

**5. Conclusions and future plans**

P transition is simulated with the EZSSS code for several values of

P He I line profile for EDC = 0 kV/cm and EDC = 2.7 kV/cm (black and red diamonds,

the DC electric field, and the best match between the measured and simulated lines corresponds to a simulated spectral line exposed to the external electrical field of E = 2.7 kV/cm, as depicted in **Figure 3** with the solid lines. The estimated electrical field agrees with theoretical prediction and showing possibility of passive emission spectroscopy with high resolution

respectively) fitted with the simulated theoretical spectra calculated with the EZSSS code (solid lines).

A dedicated test facility has been constructed for studying RF sheath effects [24]. For this purpose plasma conditions representative of the edge of a tokamak are needed. A helical antenna creates plasmas with the required parameters. Helium and argon operation are used routinely, also hydrogen is foreseen, as well as gas mixtures. Plasma densities of the order of 1017–1018 m−3 and temperatures around 5–10 eV have been obtained. The main limiting factor is the generator power (3 kW) of the helical antenna. Performance optimisation is possible by adapting the magnetic field strength and topology; the detailed study of the helical plasma

A simple ICRF antenna is installed and operational, it is coupled to a broadband generator with frequencies in the range of 100 kHz to 100 MHz and a maximal power of 1 kW. If needed The authors want to thank the technical staff at IPP - Garching, LPP-ERM/KMS and Ghent University, in particular F. Fischer, G. Siegl, M. Berte and J. Peelman.
