RECIPROCATING AND FIXED PROBE MEASUREMENTS OF DENSITY AND TEMPERATUREIN THE DIII-D DIVERTOR

This paper describes divertor density and temperature measurements usi ng both a new reciprocating Langmuir probe (XPT-RCP) which plunges ver tically above the divertor floor up to the X-point height and swept, s ingle, Langmuir probes fixed horizontally across the divertor floor. T hese types of measurements are important for testing models of the SOL and divertor which then are used to determine engineering design crit eria for plasma facing components in reactor size tokamaks. The 6 mm d iameter fixed single probes (19 domed and 2 flat at radially equivalen t locations) are incorporated into the lower divertor floor at 19 radi al locations and swept at 250 Hz. These probes are critical for determ ining plasma detachment from the floor during operation with high dens ity, highly radiating diverters. By sweeping the divertor strike point across the fixed probes, different regions of the target plate incide nt flux profile can be sampled and a high resolution spatial profile c an be obtained from each probe tip as the strike point moves past. The X-point reciprocating probe (XPT-RCP) provides n(e) and T-e profiles with high spatial (2 mm) and temporal (0.5 ms) resolution from the tar get plate to the X-point along a single vertical chord at the same rad ial location as a fixed probe tip at a different azimuthal location. T he probe n(e) and T-e are compared to the divertor Thomson scattering (DTS) n(e) and T-e (eight vertical points at 20 Hz, R-Thomson = RX-poi nt-rcp). Recent observations have also shown divertor densities from 3 x 10(19) to 4 x 10(20) m(-3) near the target plate with the highest d ensities observed with D-2 gas puffing. Electron temperature is typica lly of the order of 15-25 eV at the target rising to about 70 eV near the X-point. Lower temperature, higher density plasmas are observed al ong the inner leg. Generally good agreement among the XPT-RCP, the fix ed floor probes, and the DTS is observed. Differences between these di agnostic measurements will also be discussed with respect to different operating regimes and conditions.