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