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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 Vienna, Austria Materials (SciDAC) Surface Analysis September 29 – Oct. 2, 2015 H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 1

Boundary/PMI will be a Critical Issue for Next-Step Devices – Solutions Urgently Needed to Meet this Challenge Metrics ITER CFETR FNSF P/R ITER ~20 ~20 30~45 (MW/m) B T (T) 5.3 ~5 ~5 Pulse 400 ~10 3 ~10 6 length (s) n/n G ~1 ~ 0.5 ~ 0.5 CFETR β N 2 – 3 2 – 3 2 – 4 Increased Challenges for Divertor FNSF • Lower n e /n G • Long pulse H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 2

New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions ➡ Divertor dissipation Develop an advanced divertor ➡ Detachment concept to achieve detachment dynamics at lower upstream density ➡ Physical structure Identify paths toward reactor-relevant PFM ➡ Magnetic configuration ➡ High-Z erosion & migration ➡ Advanced Materials H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 3

New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions ➡ Divertor dissipation Develop an advanced divertor ➡ Detachment concept to achieve detachment dynamics at lower upstream density ➡ Physical structure Identify paths toward reactor-relevant PFM ➡ Magnetic configuration ➡ High-Z erosion & migration ➡ Advanced Materials H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 4

Leverage DIII-D Unique Capabilities to Advance Scientific Understanding & Develop Predictive Capability for Next Step 2D Divertor Thomson Scattering 2D Coherence Imaging (v and T i ) Flow ¡interferometry ¡(CIII) Tangential ¡TV ¡(D a , D γ , ¡CII, ¡CIII) H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 5

Model Validation is Aimed at Understanding of Detachment Dynamics • Understand atomic/molecular physics that controls Electron Temperature volumetric power and momentum losses – Radiative models fail to capture observed dependencies • Quantify parallel, perpendicular transport, especially near detachment • Effect of drifts H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 6

Dedicated Scans Have Identified Critical Role of q pol in Divertor Detachment 15 B tor = -1.25T B T Scan B tor = -1.67T 10 ( q || ∝ B T ) B tor = -2.1T (z = +1cm) (eV) I p =0.8MA 5 0 20 0.95 MA I p Scan 15 r ( λ q ∝ 1/I p ) o t r 10 1.3 MA e v -1.1 Tesla i d , e 5 -1.5 Tesla T 0.67 MA -2.1 Tesla 0 3 4 5 6 7 8 9 10 Density (10 19 m -3 ) Increasing q pol by increasing I p raises detachment threshold density, • In contrast, increasing q // by raising B T does not. • H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 7

New Diagnostics Revealed 2D Dynamics of Drift Effects Approaching Detachment Forward B T Reverse B T T e (100 eV) 2D TS shows • significantly greater divertor asymmetry in fwd. B T than in rev. B T – About 15% higher (1 kPa) p e n up is required to reach T e,OSP < 2 eV than in forward B T Also manifested in • parallel flow seen by V // 2D coherence imaging (n/n GW ~0.7) H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 8

New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions ➡ Divertor dissipation Develop an advanced divertor ➡ Detachment concept to achieve detachment dynamics at lower upstream density ➡ Physical structure Identify paths toward reactor-relevant PFM ➡ Magnetic configuration ➡ High-Z erosion & migration ➡ Advanced Materials H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 9

Optimize Divertor to Maximize Dissipation Magnetic Configuration ( f exp ) Maximize poloidal/toroidal • flux expansion Increase field line length • Divertor Geometry ( R, θ div ) (1- f rad ) P loss sin( θ div ) q target = Control neutrals and • 4 π λ q f exp R target impurities Enhance divertor radiation • P loss = P CD + 0.2 x P α ( f rad ) Active Radiation Control ( f rad ) Enhance radiation in • ( λ q ~ 1/I p ) divertor Enhance radiation in core • plasma ( P loss ) H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 10

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 H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 11

Snowflake divertor significantly reduces divertor heat fluxes while maintaining good core confinement • Geometry enables • Broader parallel heat • Significant reduction inter-ELM heat flux flux profiles may imply of ELM divertor peak spreading over increased radial target heat flux, larger plasma- transport especially in wetted area, radiative snowflake multiple strike points configurations SP1 Parallel ¡heat ¡flux ¡(MW/m 2 ) λ q = 2.40 mm Standard Snowflake (radiative) λ q = 3.20 mm V. Soukhanovskii H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 12

Preliminary Results with XD Shows That Detachment May be Achieved at Lower Density Low- δ DIII-D accommodates highly flux- • High- δ expanded, highly flared XD Further investigation will be made • to assess effects of flux expansion and flaring B. Covele H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 13

Divertor Structure: Can We Optimize Physical Structure to Maximize Neutral Trapping and Divertor Dissipation? • UEDGE Modeling of USN indicates Important Impact of Target Plate Configurations ➡ OSP-target intersection angle is a key parameter H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 14

Divertor Structure: Can We Optimize Physical Structure to Maximize Neutral Trapping and Divertor Dissipation? Divertor Closure Modification (2017) SOLPS modeling also shows that modest changes near target can • improve divertor performance significantly 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 n sep /n ped a key issue H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 15

New Initiative on DIII-D: Developing and Validating Advanced Divertor Solutions for Next-Step Devices Advance scientific understanding & validate models for extrapolation to reactor-relevant conditions ➡ Divertor dissipation Develop an advanced divertor ➡ Detachment concept to achieve detachment at dynamics lower upstream density ➡ Physical structure Identify paths toward reactor-relevant PFM ➡ Magnetic configuration ➡ High-Z erosion & migration ➡ Advanced Materials H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 16

ERO Modeling of DiMES PMI Reveals Key Physics Mechanisms for Erosion/Redeposition DiMES DiMES ERO ERO Toroidal Radial 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 H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 17

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 W-182 W-183 • Test advanced materials W-184 W-186 – W-based metal and 147634.02230.EFIT01 – Low-Z based coatings • Assess effects of high temperature PFCs m c 1 – Recycling, permeation – Surface morphology & synergistic effects H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 18

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 H.Y. Guo/IAEA-TM on Divertor Concepts/Sept. 29 – Oct. 2, 2015 19