Evolution of wave energy deposition profile in HT-7 lower hybrid current drive experiment

Lower hybrid waves (LHWs) with a selected nil spectrum have been used to control the energy deposition profiles, and then the wave driven current profiles effectively in tokamak discharges. In our lower hybrid current drive experiment in the HT-7 tokamak, it was found that the set-up of the wave energy deposition profile is a graduation process. In the beginning phase of the wave injection duration, the waves (with different n(parallel to) spectra) deposit almost all their energy in the central region of the plasma column, even if their n(parallel to) are very different. Up to around one hundred milliseconds, the wave energy deposition profiles can only take their corresponding shapes according to the n(parallel to) spectra of LHWs. It also shown that this evolution process is affected obviously by the LHW driven current profile, which has been formed early.