ITER as a Step to Fusion Power

1. ITER as a Step to Fusion Power Prof. Robert J. Goldston, Director Princeton Plasma Physics Laboratory Fusion Power Associates Annual Meeting and Symposium Forum on the Future of Fusion November 19, 2003

2. Questions for Magnetic Fusion • How is plasma pressure limited? •Sets maximum fusion power •Solar flares / magnetic substorms • How do hot particles sustain plasmas? • For plasma self-heating, current sustainment •Coronal heating / cosmic rays • What causes plasma transport? • Must confine heat in 200M C plasma • Astrophysical accretion disks • How do plasmas interact with materials? • Must handle high heat loads • Materials processing / plasma thrusters • How do fusion neutrons affect components? • Long-life, low activation, tritium regeneration. • Materials science / fission energy • How can we make practical S/C magnets? • Need large, high field, reliable, low-cost magnets. • Accelerators / electric transmission ITER Final Design Today’s Position – ITER’s Advances – Requirements for Fusion

3. How is Plasma Pressure Limited? Plasma pressure limit determines fusion power in a sustainable configuration. Fast instability limits are understood. Slower instabilities are being controlled. New plasma configurations are under study that can operate at higher pressure, have less impact from disruption. ITER will extend the understanding of pressure limits to much larger plasmas. Data from ITER will contribute to understanding other configurations. For practical fusion energy, fusion plasmas need to produce ~4x more power in an ITER-size system. Toroidal rotation can stabilize a tokamak plasma in the presence of an electrically conducting shell.

4. How do Hot Particles Sustain Plasmas? Plasma temperature and current must be sustained steadily. Modest plasma self-heating wasdemonstrated in TFTR & JET. Hot particles have been usedto sustain plasma currents. Instability thresholds are generally understood, nonlinearconsequences are under study. New plasma configurations are under study which do not require external drive for sustainment of plasma current. ITER will study regimes with very strong heating by fusion products, in new regimes where multiple instabilities can overlap, with possibly new nonlinear consequences. ITER will study steady-state operation at moderate gain. ITER will contribute to the development of other plasma configurations. For practical fusion energy, need plasmas that can be efficiently sustained at high gain in full steady-state. Fusion energy production has outpaced Moore’s law.

5. What Causes Plasma Transport? Low heat loss is required for high plasma gain. A “standard model” has been developed forunderstanding ion heat loss. The mechanism of electron heat loss is under study. Plasma fusion gain ~ 1 has been achieved. Advanced computing and detailed plasmadiagnostics are critical elements inthe advance of understanding. ITER will extend the study of turbulent plasma transport to much larger plasmas, providing a strong test of intensive vs. extensive turbulence scaling at Q > 10 for long pulses, Q > 5 in steady state. Other plasma configurations will benefit from studies in ITER. For practical fusion energy, need to be able to sustain plasmas efficiently, with low heat loss (Q ~ 30). Simulation of field-aligned turbulence in Spherical Torus plasma.

6. How do Plasmas Interact with Materials? Fusion plasmas generate intense steady heat loads, with high off-normal loads, which must be handled reliably. The mechanisms of heat flow along magnetic field lines to material surfaces are understood. Techniques have been developed to disperse heat as it flows to a material surface. Some magnetic configurations have more favorable exhaust geometries, and/or are less subject to off-normal events. Liquid lithium surfaces are under study as a potential revolutionary approach. ITER will extend the study of plasma-materials interactions to much higher power and much greater pulse length, but still well below power plant heat fluxes and durations. All other plasma configurations will benefit from ITER’s practical experience with plasma facing components. For practical fusion energy, need to be able to support ~3x higher heat flux, with multi-year component lifetimes. Tungsten “brush” capable of handling 25 MW/m2 heat flux.

7. Molecular dynamics calculation of displacement damage due to neutron impact. How do Fusion Neutrons Affect Power Plant Components? Fusion plasmas generate high-energy neutronswhich damage materials and must becaptured to regenerate tritium. New ferritic steels have improved propertiescompared with those developed for fission breeders, with much lower radioactivity. New blanket designs allow higher temperatureoperation, and so greater efficiency. Advanced computation is being used to optimize the design of fusion materials. ITER will allow the first break-in testing of blanket modules, but at ~4x lower neutron flux and much lower fluence than practical fusion power systems. All other fusion plasma configurations will benefit from ITER’s experience. For practical fusion energy, materials and components will need to be qualifiedat power-plant neutron flux and fluence.

8. ITER toroidal field magnet design How Can We Make Practical, Large-scale Superconducting Magents? Almost any magnetic fusion configuration will need large-scale, reliable, low-cost superconducting magnets. R&D tests have been undertaken for ITER at very large scale. Fusion and high-energy physics have a track record of advancing the frontiers of superconducting magnet technology. ITER will test full-scale superconducting magnets in a practical fusion environment. Other magnetic fusion plasma configurations will benefit from ITER’s experience. For practical fusion energy the cost of such magnets needs to be driven down through R&D and experience.

9. ITER will make Critical Contributions in Each Area • Extend the understanding of pressure limits to much larger size plasmas. • Study regimes with very strong heating by fusion products, in new regimes where multiple instabilities can overlap. • Extend the study of turbulent plasma transport to much larger plasmas, providing a strong test of intensive vs. extensive turbulence scaling. • Extend the study of plasma-materials interactions to much higher power and much greater pulse length. • Provide the first break-in testing of blanket modules. • Test full-scale superconducting magnets in a practical fusion environment. • ITER is a major step to fusion power. ITER Final Design