in situ, real-time measurement of plasma facing component … · 2017. 6. 16. · 9may 30, 2017,...

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In situ, Real-time Measurement of Plasma Facing Component Erosion using Digital HolographyPresented to theFusion Energy Sciences Advisory Committee (FESAC), Transformative Enabling Capabilities (TEC) subpanel

T.M. Biewer1, J. Rapp1, J.C. Sawyer2, C.E. Thomas3

1Oak Ridge National Laboratory2University of Tennessee-Knoxville3Third Dimension Technologies, LLCFESAC TEC, Rockville, MD, USA, May 30th, 2017

2 May 30, 2017, T.M. Biewer, FESAC TEC

Holography “a long time ago . . .”


Outline• Significance

– Fusion Energy and the Plasma Facing Component (PFC) “gap”

– Address with Plasma-Material Interaction (PMI) science

• Need for in-situ diagnostics of material surfaces– Digital Holography to provide real-time, in situ

measurement of surface erosion

• Digital Holography (DH)– Principles– Design– Status of implementation


Viable fusion energy source depends on solving plasma facing component gap• Fusion needs a PFC solution, which motivates plasma

material interaction (PMI) research.• Research device trajectory (ORNL) for fusion energy:

– DEMO (goal) ç ITER ç FNSF ç MPEX ç Proto-MPEX

DEMO reactor

ITERFNSF

MPEX

JET, et al.

Proto-MPEX


The harsh plasma/nuclear environment necessitates in-situ, non-invasive diagnostic techniques

• The change in material surfaces during plasma bombardment cannot be captured with ex-situ techniques

• Power flux in ITER is estimated to be 10 MW/m2 for the standard baseline operating scenario: H-mode with Type I “edge-localized modes” (ELMs).– Estimated net Tungsten divertor surface erosion: 1-10 µm/hour– i.e. ~ 3 µm every ITER discharge (~3000 sec)

• Off-normal ITER events: “disruption” event or vertical displacement event (VDE)– Estimated net Tungsten divertor surface erosion: ~0.6 mm/event– Estimated net Beryllium surface erosion: ~0.4 mm/VDE

(May 2013, Kaur, Vayakis, et al., ITPA Diagnostics, GA)


Strongly coupled Plasma Surface Interactions (PSI)

Erosion(chemical and physical)AblationMelting (metals)

Re-depositionCo-deposition ofhydrogen

Implantation

Strongly Coupled regime:1) Eroded material is trapped in plasma (highly collisional) near target, and re-deposited on surface

due to incoming flows and electro-static acceleration2) Long exposure to damaging plasma flux Þ thick layers of re-deposited material

Every surface atom is displaced ~ 107 times in a divertor lifetimeØ Material in a reactor divertor is NOT what was installed, we need a way to create and test

plasma-reformed surfaces


Digital Holography (DH) optical table layout for “single laser” holography at ORNL

Notable features:CO2 holography laser

IR cameraIR camera image display

HeNe alignment laserBeam splitterTarget stage


LDRD7784: First hologram for “single laser” Digital Holography system was achieved on 12/27/2016

Rawhologram

FFT

amplitude phase

Group 0Resolution Target

Rendered Hologram of USAF resolution target

T.M. Biewer (ORNL),C.E. Thomas (TDT)

DH laser table layout


Digital Holography has been used to image surface modification on target plates exposed to plasma in Proto-MPEX

Group 0Resolution Target

USAF resolution target has etched features

1 µm deep

T.M. Biewer (ORNL), C.E. Thomas (TDT)

“Helicon Mode” plasma exposure feature is

raised ~ 40 µm

“Trivelpiece-Gould” plasma exposure feature

is eroded ~10 µm

HeNe laser indicates DH sample location


Staging for single-laser DH system in Bldg. 5800, D115 lab at ORNL.

CO

2 laser

IRCamera

AOM

EMdump

HeNe laser

PulseGenerator

Energymonitor

O-scope


Layout for dual-laser DH system in Bldg. 5800, D115 lab at ORNL.


CO2 Laser Two

CO2 Laser One

HeNeLaser

Ref Beam

Object Beam

2nd laser arrived last week and is being installed.


Single Wavelength v. Dual Wavelength• Single wavelength system using CO2 laser (l~10.6 µm)

– Field of View (1:1 imaging of CCD): x*y ~ 1 cm x 1 cm– X,Y feature resolution (f/100 optics): ~ 30 µm x 30 µm– Z: max feature size=l ~ 10 µm, accuracy 0.1-1 µm/frame– 30 Hz LWIR camera w/ AOM

• Vibration tolerance (10 µm in 1/30 sec): 300 µm/s• Erosion rates: ~<100 µm/s, accuracy of ~1 µm/s

• Dual wavelength systems using two CO2 lasers: 9R(16)/9R(18) molecular lines, Dl~10 nm, ls = 1 cm– FoV and X,Y resolution same as single laser system– Z: max feature size=ls ~ 1 cm, accuracy 0.1-1 µm/frame– 30 Hz LWIR camera w/ AOM

• Vibration tolerance (1 cm in 1/30 sec): 300 mm/s• Erosion rates: ~<100 mm/s, accuracy of ~1 µm/s


Uniform IR beam delivered at ~3 m


Conceptual layout for Proto-MPEX installation


Conceptual layout for Proto-MPEX installation

Plasma-material interactionon target surfacePlasma discharge in central chamber


FESAC TEC guidelines addressed explicitly in the associated “white paper.”1) Description of the technology

2) Application of the technology for fusion energy, e.g. in a fusion power plant

3) Expected performance of the technology – what is the critical variable (or variables) that determines or controls the output of the technology?

4) Design variables – what are the parameters that can be controlled in order to optimize the performance of the technology?

5) Risks and uncertainties with the technology development and performance

6) Current maturity of the technology, using e.g. Technical Readiness Levels (TRL – see Appendix 2 for DoE TRL guidelines)

7) Required development for the technology


FESAC TEC guidelines addressed explicitly in the associated “white paper.” Summary:1) Digital Holography is a diagnostic technique being developed at ORNL …

2) … to measure surface erosion/redeposition from plasma facing components in-situ, in real-time, ultimately in fusion reactors.

3) ITER baseline W divertor erosion rates are estimated to be ~3 µm/hr, with ELM/VDE rates of ~600 µm/event.– Single-laser DH demonstrated capability of ~6 µm/s, with ~0.2-10 µm/event.

4) Dual-laser DH estimated to achieve ~5 mm/ms, with ~0.2-1000 µm/event.

5) Some concern about incoherent IR radiation of ITER/DEMO divertorsurfaces, but this is small compared to ~10 W of coherent laser light used.

6) Single-laser DH: TRL 4. Dual-laser DH: TRL3.

7) Deployment on Proto-MPEX in FY17 should show TRL5.– If TRL6=“in toroidal geometry”, then follow-on funding has been applied for (DOE LAB17-

1624 “Diagnostic Innovations”) to demonstrate “real time” measurement and assess a toroidal implementation.

in situ, real-time measurement of plasma facing component … · 2017. 6. 16. · 9may 30, 2017,...

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