Key Capabilities are Needed to Address PMI Issues

Key Capabilities are Needed to Address PMI Issues

Implications of Plasma-Material Interactions Dennis Whyte, MIT PSFC & PSI Science Center With contributions from Jeff Brooks (Purdue), Russ Doerner (UCSD), Rob Goldston (PPPL), Amanda Hubbard (MIT), Tony Leonard (GA), Bruce Lipschultz (MIT), Rajesh Maingi (ORNL), Jon Menard (PPPL), Mike Ulrickson (SNL) Fusion Power Associates Meeting, December 2010 1 Summary: Plasma Material Interactions (PMI) deals with the complex, coupled region extending from the pedestal into the plasma-facing materials. The PMI challenges lay along three axes to fusion energy: these are not gaps, but chasms. POWER & PARTICLE FLUX DENSITY FUSION POWER DENSITY DURATION RELIABLE BASELOAD ENERGY SOURCE

TEMPERATURE HIGH EFFICIENCY ELECTRICITY PRODUCTION PMI science literally lies as the boundary of plasma physics and nuclear material science Advancing plasma-facing (PFC) material technology is necessary but insufficient to tackle this problem. A four-prong science-based approach is required. 1. Theory & modeling 2. Science & Technology Test Stands 3. Exploit existing and planned experiments. 4. Integration: Validation in fusion-relevant conditions. 2 PMI Science & PFC Technology Gap to FNSF/Reactors is More like a 3-D Chasm 3

PMI Science & PFC Technology Gap to FNSF/Reactors is More like a 3-D Chasm Why these axes? 4 The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability PSI Challenge 1. 1.

Average neutron power loading ~ 4 MW/m2 Global average exhaust power P/S ~ 1 MW/m2 5 PFCs must be thin (~5 mm) to satisfy heat exhaust but thick to resist erosion & material removal & Continually maintain conformability to B field Steady-state 10 MW/m2 heat exhaust pushes high-T He gas cooling to limits, no allowance for transients.

Small Transient heat loading limits lifetime of even best materials While loss of conforming surface to B greatly accelerates loss of PFC viability & severe plasma effects. ITER is marginal. FNSF is even tougher due to T breeding & 4-5x P/S. 6 The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability

PSI Challenge 1. Average neutron power loading ~ 4 MW/m2 1. Global average exhaust power P/S ~ 1 MW/m2 2. Continuous 24/7 power

production. 1. Global energy throughput > 30 TJ/m2 delivered by plasma 7 Erosion physics and rates are set by complex PMI interplay & total energy throughput: Extrapolation from present devices to FSNF/reactors > x10,000 Net erosion set by small differences in large fluxes Exceeding PFC critical heat flux failure

8 Erosion physics and limits are set by complex PMI interplay & total energy throughput: Extrapolation from present devices to FSNF/reactors at least x10,000 300 s 2,000 s 4,300 s 9,000 s 22,000 s Example of W surface evolution over ~1/4 day 9

The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability PSI Challenge 1. Average neutron power loading ~ 4 MW/m2 1. Global average exhaust power

P/S ~ 1 MW/m2 2. Continuous 24/7 power production. 1. Global energy throughput > 30 TJ/m2 delivered by plasma 3. Thermodynamics demand high ambient

temperature . 2. Fundamental new regime of physical chemistry for plasma-facing materials. 10 Required High-T walls present a fundamentally new regime of physical chemistry for PMI science that has not even been approached in an integrated manner Whyte PSI2008 ITER-size reactor with irradiated W ~1% bulk trap density from neutron damage

High-temperature disallows tritium storage in W through de-trapping & diffusion ..instead permeation into coolant is concern 11 The Core of Multi-scale PMI Science is Hyper-Sensitive to Material Temperature 12 Example from PISCES PMI test-stand: Nano-morphology highly T dependent 900 K Tungsten surface after exposure to ~1 hour Helium plasma. 1120 K

He+ ion fluence ~ 121026 m-2 1320 K 13 How do we get from here/now to there? 14 A Four-Pronged Attack is Required to Resolve PMI/PFC Issues for FNSF/Pilot Plant 1. Theory and Modeling: Understand & manipulate plasma/materials physics Plasma Science and Innovation: spread heat loads, control long-term erosion and redeposition, avoid and mitigate ELMs and disruptions Strong connection with FSP, new PMI Science centers Material Science and Innovation: materials operate at high heat flux and temperature, control tritium retention/ permeation, reduce erosion and dust, survive ELMs/disruptions Strong connection with overall materials thrust 2. S&T Test Stands: Provide data on PSI science and PFC technology

Provide data on high power plasma-surface interaction in simple geometry Coordinated national program to develop PFC technologies based on fundamental PFC R&D. Test technologies (He-cooled tungsten, liquid metals) at high ambient temperatures for practical use 3. Existing and Planned Experiments: Test New Science and Technology Validate theory and modeling in toroidal geometry at moderate power and pulse length Need dramatically more plasma edge and material surface diagnostics Test interaction of new geometries and PFC technologies with plasma/toroidal configuration. 4. Integration: Validation in Fusion-Relevant Conditions Flexibly test physics and technologies of new PMI solutions at fusion-relevant power density, pulse length, duty factor and ambient temperature Requires extensive diagnostic and service coils and PFC materials flexibilityof Each of these

activities will serve to improve and access, validatePFour predictive understanding 15 Demonstrate integration of FNSF/Pilot Plant PMI solution with optimized core plasma Plasma Material Interactions. Together, they will provide

confidence in a solution for fusion applications Example PSI Science Initiatives at MIT Multi-institutional PSI Science Center Vulcan: 800 C 24/7 PSI tokamak Conceptual Design Novel In-situ surface diagnostic development for C-Mod 16

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