CARBON YIELDS AND INFLUXES AS A FUNCTION OF TARGET TEMPERATURES IN JET X-POINT DISCHARGES

During X-point discharges in JET the wall region near the X-point has been studied with CCD cameras and an OMA system. Tile temperatures, carbon influx, recycled deuterium and a beryllium line were measured. Strike zones which occur only with additional heating receive from fast ions the highest power flux of up to 3 kW/cm2 resulting in tile temperatures of 2400-degrees-C. This type of strike zone releases most of the carbon observed. The Carbon yield begins to rise significantly at about 1850-degrees-C due to RES and continues to rise up to 2350-degrees-C when thermal sublimation takes over. The carbon influx is amplified by selfsputtering resulting in a carbon bloom almost immediately when the regime of thermal sublimation is entered. It is suggested that the presence of beryllium on the graphite target mitigates the carbon influx.