POWER SCALING OF DIVERTOR PLASMA CONDITIONS DURING H-MODE IN DIII-D

An array of fixed Langmuir probes spanning the inner and outer divertor strike points has been used to measure the electron temperature, plasma density, and particle/heat flux profiles of the divertor plasma in DIII-D. We report here on observations made during the steady state phase of high-power neutral-beam heated H-mode plasmas. These data are important for predicting the expected impurity sources and target plate material lifetimes in future high power tokamaks such as ITER. H-mode plasmas formed with a high divertor neutral pressure in the absence of external gas feed in DIII-D were found to have beneficial consequences in reducing the peak values of divertor electron temperature without loss of core energy confinement. We have observed a steady state, high density (n(pl,d) almost-equal-to 10(14) cm-3), moderate temperature (< 50 eV) divertor plasma in DIII-D at divertor power levels of 3 MW/m2. A better understanding of the importance of collisional effects may be needed to interpret these results.