The paper discusses the results of a heating experiment in the ion cyclotron range of frequencies (ICRF) conducted on the JIPP T-IIU device with a five-element antenna array. This antenna system provides precisely shaped k∥, spectra which vary according to the relative phasing angle of the neighbouring antennas, Δφ. In the experiment, Δφ is scanned in a close pitch and it is found that the electron heating efficiency is drastically improved with Δφ = π and the lowest efficiency is obtained with Δφ = 0. This observation is analysed by calculating the k∥ spectra and then the power deposition profiles using a ray tracing code. It is also found that the effect of the phasing on the impurity problem is unexpectedly small. The reasons for the discrepancies between these data and theoretical expectations are also discussed.
Power deposition profiles and Poynting vector distribution of phased antenna arrays in the ion-cyclotron resonance heating of a NET/INTOR-type tokamak