EFFECT OF ANTENNA PHASING AND WALL CONDITIONING ON ICRH IN TEXTOR

Four new low field side antennae grouped in pairs have been installed on TEXTOR. It is found that the interaction with the wall (density rise, impurity generation) is significantly reduced when operating each pair out of phase ( pi ) as opposed to in phase (0). The beneficial effect in the pi configuration is obtained without drop in plasma loading. This experimental property is shown, from theory, to be explained by the judicious choice of the geometrical configuration. A further improvement in the wall interaction is made possible by an appropriate choice of wall conditioning (wall carbonization with liner at 400 degrees C or, above all, boronization). As a result record low values of Prad/Ptotal were achieved during ICRH. The large reduction in wall interaction during ICRH allows routine long pulse (>1 s) ICRH operation at the maximum power level available ( equivalent to 2.5 MW).