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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 MeetingUCLA, 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 13C 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 CH4 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., 1017-1018/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)
• C2H4 elucidates role of higher-hydrocarbons in chemical sputtering
• Significantly less CH-band emission than with CH4 injection, but significantly more C2 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 (Te~2-5 eV), to fully detached (Te~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 13C removal on a few inserted tiles
Perform tests of coated and non-coated diagnostic mirrors
Measure reaction products – RGA and FTIR
Deposit a 13C layer under conditions similar to 2008 13C
experiment
Demonstrate removal of 13C from several tiles with a second
oxygen bake
DiMES and MiMES provided the only in-situ measurements of 13C
deposition during 18 repeat plasma shots
Tiles removed for analysis at start of LTOA
Oxygen bake and 13C injection experiments in DIII-D
Oxygen bake timeline
Oxygen bake #1
Pre-characterized tiles from previous 13C injection experiments inserted into the vessel on stalk mountsResults 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
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
13C injection and Oxygen bake #2
13C injection:
A depth-marked graphite DiMES sample was exposed during 13C injection experiment to measure 13C coverage and net carbon deposition/erosion
Mid-plane probe/MiMES was inserted in the SOL during 13C injection to get 13C 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 m10 m10 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
BT
10 m