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

DiMES and MiMES Recent Experiments

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

206-10/DR/jy

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-19 206-10/DR/jy

PPI Mark II: Passively Controlled Predictable Injection

A. McLean, PSI-19 206-10/DR/jy

• 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 ITE

• Operated the PPI in L-mode plasma with resonant magnetic perturbations

– First attempt to measure chemical erosion in-situ in the presence of RMP

– 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-19 206-10/DR/jy

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 300°C

• 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 206-10/DR/jy

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

206-10/DR/jy

Oxygen Bake Timeline

206-10/DR/jy

Oxygen Bake #1

• Pre-characterized tiles from

previous 13C 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

Mirrors

206-10/DR/jy

• 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

206-10/DR/jy

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

206-10/DR/jy

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

• Midplane 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 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 μm 10 μm 10 μm

Graphite flakes Graphite spheres Diamond

206-10/DR/jy

Midplane

probe

LCFS

Dust Injection in the SOL from Midplane 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 μm

206-10/DR/jy

Dust Injection in the SOL from Midplane 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

206-10/DR/jy

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 μm

206-10/DR/jy

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