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Developing and Validating Advanced Divertor Solutions for Next-Step Fusion Devices DiMES DIII-D Experiments By H.Y. Guo and BPMIC Team Edge Theory Presented to the Boundary DIII-D IAEA-TM on Divertor Boundary/PMI Concepts Initiative

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H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Edge Theory Boundary DIII-D Experiments DiMES

DIII-D Boundary/PMI Initiative

Materials (SciDAC) Surface Analysis

Developing and Validating Advanced Divertor Solutions for Next-Step Fusion Devices

By

H.Y. Guo and BPMIC Team

Presented to the

IAEA-TM on Divertor Concepts Vienna, Austria September 29 – Oct. 2, 2015

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SLIDE 2

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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ITER CFETR FNSF

Metrics ITER CFETR FNSF

P/R (MW/m) ~20 ~20 30~45 BT (T) 5.3 ~5 ~5 Pulse length (s) 400 ~103 ~106 n/nG ~1 ~ 0.5 ~ 0.5 βN 2 – 3 2 – 3 2 – 4

Increased Challenges for Divertor

  • Lower ne/nG
  • Long pulse

Boundary/PMI will be a Critical Issue for Next-Step Devices – Solutions Urgently Needed to Meet this Challenge

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H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices

Develop an advanced divertor concept to achieve detachment at lower upstream density

➡Physical structure ➡Magnetic configuration

Identify paths toward reactor-relevant PFM

➡High-Z erosion & migration ➡Advanced Materials

Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions

➡Divertor dissipation ➡Detachment dynamics

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SLIDE 4

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices

Develop an advanced divertor concept to achieve detachment at lower upstream density

➡Physical structure ➡Magnetic configuration

Identify paths toward reactor-relevant PFM

➡High-Z erosion & migration ➡Advanced Materials

Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions

➡Divertor dissipation ➡Detachment dynamics

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SLIDE 5

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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2D Divertor Thomson Scattering 2D Coherence Imaging (v and Ti)

Flow ¡interferometry ¡(CIII) Tangential ¡TV ¡(Da, Dγ, ¡CII, ¡CIII)

Leverage DIII-D Unique Capabilities to Advance Scientific Understanding & Develop Predictive Capability for Next Step

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SLIDE 6

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Model Validation is Aimed at Understanding of Detachment Dynamics

  • Understand

atomic/molecular physics that controls volumetric power and momentum losses

– Radiative models fail to capture observed dependencies

  • Quantify parallel,

perpendicular transport, especially near detachment

  • Effect of drifts

Electron Temperature

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SLIDE 7

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Dedicated Scans Have Identified Critical Role of qpol in Divertor Detachment

3 4 5 6 7 8 9 10 T

e , d i v e r t

  • r

(z = +1cm) (eV)

Density (1019m-3) 5 10 15

Btor= -1.25T Btor= -2.1T Btor= -1.67T Ip=0.8MA

5 10 15 20

0.95 MA 1.3 MA 0.67 MA

BT Scan (q||∝ BT) Ip Scan (λq∝ 1/Ip)

  • 1.5 Tesla
  • 1.1 Tesla
  • 2.1 Tesla
  • Increasing qpol by increasing Ip raises detachment threshold density,
  • In contrast, increasing q// by raising BT does not.
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SLIDE 8

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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New Diagnostics Revealed 2D Dynamics of Drift Effects Approaching Detachment

(n/nGW~0.7)

Forward BT Reverse BT Te pe V//

  • 2D TS shows

significantly greater divertor asymmetry in fwd. BT than in rev. BT

– About 15% higher nup is required to reach Te,OSP < 2 eV than in forward BT

  • Also manifested in

parallel flow seen by 2D coherence imaging

(100 eV) (1 kPa)

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SLIDE 9

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices

Develop an advanced divertor concept to achieve detachment at lower upstream density

➡Physical structure ➡Magnetic configuration

Identify paths toward reactor-relevant PFM

➡High-Z erosion & migration ➡Advanced Materials

Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions

➡Divertor dissipation ➡Detachment dynamics

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SLIDE 10

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Optimize Divertor to Maximize Dissipation

(1-frad)Ploss sin(θdiv) 4π λq fexp Rtarget qtarget = Ploss = PCD + 0.2xPα (λq ~ 1/Ip)

Magnetic Configuration (fexp)

  • Maximize poloidal/toroidal

flux expansion

  • Increase field line length

Divertor Geometry (R, θdiv)

  • Control neutrals and

impurities

  • Enhance divertor radiation

(frad) Active Radiation Control (frad)

  • Enhance radiation in

divertor

  • Enhance radiation in core

plasma (Ploss)

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SLIDE 11

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Optimize Magnetic Configuration è èPromote Detachment at Lower Upstream Density & Facilitate Core/Edge Coupling

  • Detachment onset:

– Flux expansion, Connection length, poloidal field angle – Enhanced turbulence & new instabilities

  • Control of detachment front:

– Magnetic shaping, field line flaring

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SLIDE 12

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Snowflake divertor significantly reduces divertor heat fluxes while maintaining good core confinement

  • V. Soukhanovskii

Standard Snowflake (radiative)

SP1 Parallel ¡heat ¡flux ¡(MW/m2) λq = 2.40 mm λq = 3.20 mm

  • Geometry enables

inter-ELM heat flux spreading over larger plasma- wetted area, multiple strike points

  • Broader parallel heat

flux profiles may imply increased radial transport

  • Significant reduction
  • f ELM divertor peak

target heat flux, especially in radiative snowflake configurations

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SLIDE 13

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Preliminary Results with XD Shows That Detachment May be Achieved at Lower Density

  • B. Covele
  • DIII-D accommodates highly flux-

expanded, highly flared XD

  • Further investigation will be made

to assess effects of flux expansion and flaring Low-δ High-δ

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SLIDE 14

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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  • UEDGE Modeling of USN indicates Important

Impact of Target Plate Configurations ➡ OSP-target intersection angle is a key parameter

Divertor Structure: Can We Optimize Physical Structure to Maximize Neutral Trapping and Divertor Dissipation?

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SLIDE 15

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Divertor Structure: Can We Optimize Physical Structure to Maximize Neutral Trapping and Divertor Dissipation?

  • SOLPS modeling also shows that modest changes near target can

improve divertor performance significantly Divertor Closure Modification (2017)

  • Will be tested on DIII-D in 2017

– Increase divertor neutral retention & impurity screening ➡ Achieve detachment at lower upstream density – Assess Impact on pedestal performance ➡ Ratio of nsep/npeda key issue

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SLIDE 16

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices

Develop an advanced divertor concept to achieve detachment at lower upstream density

➡Physical structure ➡Magnetic configuration

Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions

➡Divertor dissipation ➡Detachment dynamics

Identify paths toward reactor-relevant PFM

➡High-Z erosion & migration ➡Advanced Materials

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SLIDE 17

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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ERO Modeling of DiMES PMI Reveals Key Physics Mechanisms for Erosion/Redeposition

  • The re-deposition ratio is mainly determined by electric field and

density drop in magnetic pre-sheath ➡ DiMES biasing experiment is being prepared to test this prediction

Toroidal

DiMES ERO

Radial

DiMES ERO

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SLIDE 18

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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DIII-D Provides Unique Capability to Study High-Z PMI in a Low-Z Environment

  • Metal Divertor Rings in 2017

will examine:

– High-Z source & migration path – Impact of high-Z PFC on core performance ➡ Use different W isotopes

  • Test advanced materials

– W-based metal and – Low-Z based coatings

  • Assess effects of high

temperature PFCs

– Recycling, permeation – Surface morphology & synergistic effects

W-183 W-186 W-182 W-184

147634.02230.EFIT01

1 c m

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SLIDE 19

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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Validation of Reactor-Relevant PFMs Will Involve Integration with Linear Material Facility and Long-Pulse Tokamaks

Test W-fuzz prepared in the PISCES-A linear device in DIII-D using DiMES

  • Good survival of W-fuzz under a

variety of the plasma conditions

  • Gross erosion rate of W-fuzz in He

plasmas was ~4X lower than clean W surface

  • W-fuzz is prone to unipolar arcing
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SLIDE 20

H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015

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DIII-D Boundary/PMI Initiative Takes an Integrated Approach towards Advanced Divertor Development

Develop an advanced divertor concept to achieve detachment at lower upstream density Identify paths towards reactor- relevant plasma facing materials Advance scientific understanding and validate models for extrapolation to reactor-relevant conditions

  • Leverage DIII-D diagnostic capability

(2D TS, 2D flow, 2D Ti…)

  • Understand physics mechanisms of

divertor dissipation, detachment dynamic, stability & control

  • Leverage DIII-D flexible shaping &

robust control system

  • Optimize physical structure &

magnetic configuration to maximize dissipation (slot, XD, SXD…)

  • Leverage DiMES materials

collaborative efforts & new initiative

  • n high Z & hot divertor
  • Validate advanced materials in

collaboration with materials research community