The compatibility of detached radiative divertor operation with a robust H-mode pedestal is examined in DIII-D. A density scan produced low temperature plasmas at the divertor target, T-e <= 2 eV, with high radiation leading to a factor of >= 4 drop in peak divertor heat flux. The cold radiative plasma was confined to the divertor and did not extend across the separatrix in X-point region. A robust H-mode pedestal was maintained with a small degradation in pedestal pressure at the highest densities. The response of the pedestal pressure to increasing density is reproduced by the EPED pedestal model. However, agreement of the EPED model with experiment at high density requires an assumption of reduced diamagnetic stabilization of edge Peeling-Ballooning modes. (C) 2014 Published by Elsevier B.V.

The ELM induced change in wetted area (A(wet)) and peak heat flux (q(peak)) of divertor heat flux is investigated as a function of the number of striations, which represent ELM filaments, observed in the heat flux profile in NSTX More striations are found to lead to larger A(wet) and lower q(peak). The typical number of striations observed in NSTX is 0-9, while 10-15 striations are normally observed in other machines such as JET, and the ELM contracts heat flux profile when the number of striations is less than 3-4 but broadens it with more of them. The smaller number of striations in NSTX is attributed to the fact that NSTX ELMs are against kink/peeling boundary with lower toroidal mode number (n = 1-5), while typical peeling ballooning ELMs have higher mode number of n = 10-20. For ELMs with smaller number of striations, relative A(wet) change is rather constant and q(peak) change rapidly increases with increasing ELM size, while A(wet) change slightly increases leading to a weaker increase of q(peak) change for ELMs with larger number of striations, both of which are unfavourable trend for the material integrity of divertor tiles. (C) 2014 Elsevier B.V. All rights reserved.

We survey the results of recent DIII-D experiments that tested the effectiveness of three innovative tokamak divertor concepts in reducing divertor heat flux while still maintaining acceptable energy confinement under neon/deuterium-based radiating divertor (RD) conditions: (1) magnetically unbalanced high performance double-null divertor (DND) plasmas, (2) high performance double-null Snowflake (SF-DN) plasmas, and (3) single-null H-mode plasmas having different isolation from their divertor targets. In general, all three concepts adapt well to RD conditions, achieving significant reduction in divertor heat flux (q(perpendicular to p)) and maintaining high performance metrics, e.g., 50-70% reduction in peak divertor heat flux for DND and SF-DN plasmas that are characterized by beta(N) congruent to 3.0 and H98((y,2)) approximate to 1.35. It is also demonstrated that q(perpendicular to p) could be reduced approximate to 50% by extending the parallel connection length (L parallel to-XPT) in the scrape-off layer between the X-point and divertor targets over a variety of the RD and non-RD environments tested. (C) 2014 Elsevier B.V. All rights reserved.

Edge fluid-plasma/kinetic-neutral modeling of well-diagnosed DIII-D experiments is performed in order to document in detail how well certain aspects of experimental measurements are reproduced within the model as the transition to detachment is approached. Results indicate, that at high densities near detachment onset, the poloidal temperature profile produced in the simulations agrees well with, that measured in experiment. However, matching the heat flux in the model requires a significant increase in the radiated power compared to what is predicted using standard chemical sputtering rates. These results suggest that the model is adequate to predict the divertor temperature, provided that the discrepancy in radiated power level can be resolved. (C) 2014 Elsevier B.V. All rights reserved.

Lithium has been introduced into the DIII-D tokamak, and migration and retention in graphite have been characterized since no lithium was present in DIII-D initially. A new regime with an enhanced edge electron pedestal and H-98y2 <= 2 has been obtained with lithium. Lithium deposition was not uniform, but rather preferentially deposited near the strike points, consistent with previous C-13 experiments. Edge visible lithium light (Lil) remained well above the previous background during the entire DIII-D campaign, decaying with a 2600 plasma-second e-fold, but plasma performance was only affected on the discharge with lithium injection. Lithium injection demonstrated the capability of reducing hydrogenic recycling, density, and ELM frequency. Graphite and silicon samples were exposed to a lithium-injected discharge, using the DiMES system and then removed for ex-situ analysis. The deposited lithium layer remained detectable to a depth up to 1 mu m. (C) 2014 Elsevier B.V. All rights reserved.

A study to examine some current issues in the physics of the-plasma sheath has been recently carried out in DIII-D low power Ohmic plasmas using both flush and domed Langmuir probes, divertor Thomson scattering (DTS), an infrared camera (IRTV), and a new calorimeter triple probe assembly mounted on the Divertor Materials Evaluation System (DIMES). The sheath power transmission factor was found to be consistent with the theoretically predicted value of 7 ( 2) for low power plasmas. Using this factor, the three heat flux profiles derived from the LP, DTS, and calorimeter diagnostic measurements agree. Comparison of flush and domed Langmuir probes and divertor Thomson scattering indicates that proper interpretation of flush probe data to get target plate density and temperature is feasible and could potentially yield accurate measurements of target plate conditions where the probes are located. (C) 2015 Elsevier B.V. All rights reserved.