Density profile from microwave reflectometry and confinement properties of a lower hybrid current drive sustained tokamak discharge

Two millimeter wave reflectometers using the extraordinary mode of propagation, have been installed on Petula in order to investigate their potentialities for application to larger tokamaks. By sweeping the frequency range 75-110 GHz, it was possible to measure the central part of the density profile. The addition of a second reflectometer working in the range 60-90 GHz allowed the determination of the external part of the profile. The resulting profile is presented with and without L.H. current drive application. The effect of L.H. current drive application is particularly marked on the scrape-off layer plasma, whose density can be decreased by more than a factor of 2. It is generally observed that in these conditions of moderate R.F level, the scrape-off density has the same temporal and parametric dependence than the loop voltage, but when the input R.F. power is further increased, this effects saturates while the loop voltage continue to decrease