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

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

Why these axes? 4

The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability 1.Average neutron power loading ~ 4 MW/m 2 PSI Challenge 1.Global average exhaust power P/S ~ 1 MW/m 2 5

PFCs must be thin (~5 mm) to satisfy heat exhaust but thick to resist erosion & material removal & Continually maintain conformability to B field ITER is marginal. FNSF is even tougher due to T breeding & 4-5x P/S. Steady-state 10 MW/m 2 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. 6

The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability 1.Average neutron power loading ~ 4 MW/m 2 2.Continuous 24/7 power production. PSI Challenge 1.Global average exhaust power P/S ~ 1 MW/m 2 1.Global energy throughput > 30 TJ/m 2 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, s 4,300 s9,000 s2,000 s22,000 s Example of W surface evolution over ~1/4 day 9

The PSI Science Challenge & Fusion Viability are inextricably linked Fusion Viability 1.Average neutron power loading ~ 4 MW/m 2 2.Continuous 24/7 power production. 3.Thermo- dynamics demand high ambient temperature. PSI Challenge 1.Global average exhaust power P/S ~ 1 MW/m 2 1.Global energy throughput > 30 TJ/m 2 delivered by plasma 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 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 Whyte PSI

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 Tungsten surface after exposure to ~1 hour Helium plasma. He + ion fluence ~ 1–2×10 26 m K 1120 K 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 access, PF coils and PFC materials flexibility –Demonstrate integration of FNSF/Pilot Plant PMI solution with optimized core plasma Each of these activities will serve to improve and validate our predictive understanding of Plasma Material Interactions. Together, they will provide confidence in a solution for fusion applications 15

Example PSI Science Initiatives at MIT 16 Multi-institutional PSI Science Center Vulcan: 800 °C “24/7” PSI tokamak Conceptual Design Novel In-situ surface diagnostic development for C-Mod