DiMES and MiMES Recent Experiments D. Rudakov (UCSD) A. Leonard (GA) A. Litnovsky (FZJ) A. McLean (U Toronto) W. Wampler (SNL) C. Wong (GA) DiMES Team and Collaborators Presented at the PFC Meeting UCLA, August 4-6, 2010

This talk  PPI studies of carbon chemical erosion  Enhanced carbon erosion in detached H-mode divertor: Ne injection versus elevated temperature  DiMES and MiMES activities in support of Oxygen bake and 13 C injection experiments  Introduction of of pre-characterized dust in divertor and SOL by DiMES and MiMES Later in the meeting  C. Wong: Transient Tolerant Surface Development  K. Umstadter: Effects of transient heating events on W PFCs in a steady-state divertor-plasma environment Experiments to be covered Dedicated time

A Porous Surface is used to Replicate the Intrinsic Erosion Process a Non-Perturbative Way  The porous plug injector (PPI) injects hydrocarbons at known rates to provide direct calibration of spectroscopic signals from optical diagnostics  Porous plasma-facing surface: 1004 holes, 0.25 mm diameter  Designed based on the mean-free-path of CH 4 in a divertor target plasma  The holes comprise <10% of the surface area so that the probe closely approximates a solid surface  The gas flow rate corresponds to 1-3% erosion yield for D→C over the holed area for typical low density, attached conditions (i.e., /s) A. McLean, PSI-19

PPI Mark II: Passively Controlled Predictable Injection A. McLean, PSI-19

Injected ethylene into semi-detached shots via the PPI (1/2 day) C 2 H 4 elucidates role of higher-hydrocarbons in chemical sputtering Significantly less CH-band emission than with CH 4 injection, but significantly more C 2 dimer emission Consistent with a resilient C=C double bond, esp. in cold plasma Suggests higher-hydrocarbons play minor role in chemical erosion Operated the PPI in plasmas that evolve from semi-detached (T e ~2-5 eV), to fully detached (T e ~1 eV) (1/2 day) Strong signs that full detachment was reached Near extinction of CH-band emission in detachment indicates chemical sputtering yield decreases substantially (from 2-3% to 0.5%) Suggests lower expected gross erosion, and tritium retention in ITER Operated the PPI in L-mode plasma with resonant magnetic perturbations First attempt to measure chemical erosion in-situ in the presence of RMP ½ day piggyback exp. in collaboration with O. Schmitz (FZ Juelich) Significant reduction in chemical erosion yield at strike point lobes found DiMES Experiments Examined Carbon Chemical Erosion A. McLean, PSI-19

Effect of neon injection and elevated surface temperature on carbon erosion  Carbon erosion was studied in ELMing H-mode with detachment induced by Ne injection  Two exposures of multiple button samples were performed, first at ambient temperature, second with pre-heating to 300C  Net deposition was observed on the holder and buttons after non-heated exposure  Very high erosion rate of up to 30 nm/s was measured on graphite samples exposed at 300 C  Most recently, an exposure to similar discharges with detachment induced by D gas injection and pre-heating to 300 C was performed  Erosion rate of carbon was again up to 30 nm/s, similar to that with Ne injection Neon does not cause any significant increase of net erosion of carbon under detachment, while elevated surface temperature does OSP R Non-heated Heated

Goals:  Demonstrate an oxygen bake on the DIII-D tokamak and recover high performance plasma operation (with only clean vents). Assess “collateral damage” to tokamak systems Operate tokamak systems – Pumps, ECH, ICH Demonstrate 13 C removal on a few inserted tiles Perform tests of coated and non-coated diagnostic mirrors Measure reaction products – RGA and FTIR  Deposit a 13 C layer under conditions similar to C experiment  Demonstrate removal of 13 C from several tiles with a second oxygen bake DiMES and MiMES provided the only in-situ measurements of 13 C deposition during 18 repeat plasma shots Tiles removed for analysis at start of LTOA Oxygen bake and 13 C injection experiments in DIII-D

Oxygen bake timeline

Oxygen bake #1  Pre-characterized tiles from previous 13 C injection experiments inserted into the vessel on stalk mounts Results of tile analysis will be presented by D. Buchenauer later in the session  Copper and molybdenum mirror samples supplied by FZJ installed on stalk mounts (4 off), flanges (4 off) and DiMES (2 off)  Some of the mirrors were pre- coated with hydrocarbon layers  During O-bake stalk mounts and DiMES we at ~350 C and flanges at ~150 C Mirrors

 So far, only a visual inspection of the exposed mirrors has been performed Cu mirrors look oxidized, Mo mirrors mostly unaffected Cu mirror looks oxidized, Mo mirror looks unaffected Pre-coated Mo mirrors look unaffected Cu mirror looks slightly oxidized near edge, Mo mirror unaffected Coated and uncoated Mo mirrors look unaffected Cu and Mo mirrors got coated from a nearby component Detailed analysis at FZJ forthcoming DiMES Flanges Stalks

Surprising result: “protected” area oxidized strongly  Exposed part of the copper mirror shows visible oxidation after O-bake  “Protected” part under the flap oxidized much stronger than open area Before O-bake After

13 C injection and Oxygen bake #2 13 C injection:  A depth-marked graphite DiMES sample was exposed during 13 C injection experiment to measure 13 C coverage and net carbon deposition/erosion  Mid-plane probe/MiMES was inserted in the SOL during 13 C injection to get 13 C deposition on the probe shield  Asymmetries of the deposition may provide information on carbon flows in the SOL  Analysis pending new accelerator becoming operational at SNL Albuquerque O-bake #2:  Tungsten castellation sample with gap sides pre-coated with hydrocarbon layers ~70 nm thick were exposed in DiMES  No visible change after exposure, detailed analysis underway at FZJ B

Injections of pre-characterized dust in divertor and SOL  Experiments performed as a part of ITPA DSOL-21 joint experiment: Introduction of pre-characterized dust for dust transport studies in the divertor and SOL  Goals: Characterization of core penetration efficiency and impact of dust of varying size and chemical composition on the core plasma performance in different conditions and geometries Benchmarking of DustT and DTOKS modeling of dust transport and dynamics  Participating machines: DIII-D, TEXTOR, MAST, NSTX, LHD, AUG  Coordinator: D. Rudakov (DIII-D)  Different types of carbon dust are used in DIII-D: 5  m 10  m Graphite flakes Graphite spheres Diamond

Mid-plane probe LCFS Dust Injection in the SOL from mid-plane probe/MiMES  Probe moves with a velocity of ~ 1 m/s, turns around in ~ 5 ms  A few mg of graphite flake dust placed on the probe  Dust was expected to be released at turn-around  Better defined dust quantity and velocity than in DiMES dust 10  m

Dust Injection in the SOL from mid-plane probe/MiMES UCSD fast camera, shot #141525, full light, 8000 f/s  Dust injection observed locally with fast-framing camera  Unlike in DiMES experiments, dust had no effect on core plasma parameters  This result is in line with earlier observations on TEXTOR

Mobilization of Dust from Tile Gaps  Is dust fallen in tile gaps permanently retained or can it be re-mobilized by plasma contact?  A DiMES sample with poloidal and toroidal gaps ~0.8 mm wide and ~8 mm deep filled with dust has been exposed in a few discharges with OSP sweeps  Dust was pressed into the gap  Dust loss from the gap quite small (no visible loss, could not quantify mass)  Measurable loss of loose dust from a comparable gap exposed to a disruption observed in NSTX (C.H. Skinner, ITPA DSOL meeting Dec 2009) R BTBT 10  m