LH Power Deposition and CD Efficiency Studies by Application of Modulated Power at JET

The LH power deposition and the CD efficiency were assessed by application of modulated LH power. Density and magnetic field scans were performed and the response of the electron temperature provided by the available ECE diagnostic was investigated by means of FFT analysis. An innovative technique based on comparison between modelled and experimental data was developed and used in the study. The LH waves are absorbed by fast electrons with energies of a few times the thermal one, causing a modification in the Electron Distribution Function (EDF) by creating a plateau in parallel direction. The phase of the temperature perturbations, ϕ, as well as the ratio between the amplitudes of the third and the main harmonics, δTe3/δTe1, are found to be strongly affected by the plateau of the EDF as the broader the plateau the larger |ϕ|, (ϕ<0), and the smaller δTe3/δTe1 are. Transport and Fokker-Planck modelling was used to support this conclusion and to interpret the experimental data hence to assess the LH CD efficiency and deposition profile. The results from the analysis are consistent with broad off-axis LH power deposition profile. For densities between 1 x 1019m-3 and 4 x 1019m-3, which is the accessibility limit at the highest magnetic field discharges a gradual shift of the maximum of the power deposition to the periphery and a degradation of the CD efficiency was observed.
Name Size  
EFDP09033 1.41 Mb