PhD studies report: "FUSION energy: basic principles, equipment and materials" Birutė Bobrovaitė; Supervisor dr. Liudas Pranevičius

Content 1.Fusion reactions; 2.Iter configuration; 3.Plasma operation scenario; 4.Fusion power plant; 5.Plasma wall interaction; 6.Materials and their properties.

The demand of energy will rise The enviroment must be protected Fossil fuels will eventually run out We must continue to develope alternative energy sources Energy is vital

Fusion D + T α particle ( 4 He) (3.5 MeV) + n (14.1 MeV) Plasma heating – 3,5MeV; Energy sources – 14,1MeV.

ITER – experimental reactor It is an international project involving: European Union, Japan, Russian Federation, China, South Korea, United States of America. The main goal to demonstrate the scientific and engineering feasibility of fusion as an energy source. ITER - way

JET: B – 3,8 T R – 2,9 m ITER: B – 5,5 T R – 6,2 m ITER

Major radius: 6.2 m Minor radius: 2.0 m Plasma volume: 840 m 3 Plasma current: 15 MA Toroidal field: 5.3 T Pulse length: > 300 s Fusion power: 500 MW Plasma energy: 350 MJ n-wall load~: 0.5 MW/ m 2 n-fluence: 0.3 MW-a/ m 2 Heating power: MW Machine height: ~25 m Machine diameter: ~26 m Machine mass: t Main parameters:

Tokamak configuration A toroidal device Large plasma current - poloidal magnetic field - confinement Strong toroidal magnetic field - stability Magnetic field configuration

Purpose: The vacuum vessel provides the high vacuum. The vessel cooling also provides decay heat removal by natural water convection for all the vessel and in-vessel components. The vessel also provides in- built attachment points for the blanket and divertor. Vessel

Blanket The blanket system is generally defined as the components that surround the plasma absorbing heat; radiation and neutrons from the plasma, and converting the nuclear energy of the neutrons into thermal energy.

Heat flow average:– 3-5 MW/m 2 Max heat flow: MW/m 2 Heat flow < 5MW/m 2 (W) Heat flow to 20 MW/m 2 (CFC) ITER divertor exhausts the flow of energy from charged particles produced in the fusion reactions and removes helium and other impurities resulting from the reactions, and from interaction of plasma particles with the material walls. Divertor

Plasma heating

A fusion power plant

Tritium breeding The most promising source of tritium seems to be the breeding of tritium from lithium-6 by neutron bombardment which can be achieved by slow neutrons.

PlasmaBlanket Shield Vacuum Vessel Magnet coils Cryostat Biological shield Divertor He Fuel processing plant T D+T Steam generator Turbines Electric Power coolant Blanket heat recovery tritium generation shielding energy multiplication Blanket heat recovery tritium generation shielding energy multiplication Shield reduces radiation load on VV and coils Shield reduces radiation load on VV and coils Vacuum vessel contains plasma chamber vacuum Vacuum vessel contains plasma chamber vacuum Magnets cryogenic superconducting (mass ~20,000 Te) Magnets cryogenic superconducting (mass ~20,000 Te) Biological shield protects personnel from radiation Biological shield protects personnel from radiation n Li Fusion Power Plant operation

Plasma wall interaction based on erosion: - melting or sublimations (heat loads); - particle fluxes to the wall. Transport process : - impurity remove; - neutralization, recycling. Plasma wall interaction

The main characteristics of materials High thermal conductivity Resilience to thermal shocks Low neutron activation Low chemical erosion Low affinity to hydrogen towards formation of volatile products Low affinity to oxygen towards formation of volatile products Oxygen gettering(formation of stable oxides) Low sorption of hydrogen Materials for fusion reactor

Structural materials The main structural material in ITER is austenitic stainless steel. For magnets are used niobium alloy. Plasma facing materials: Tungsten Beryllium CFC These materials are connected to cupper alloy cooling system and connected to the main structural material stainless steel.

Materials 700m 2 Be – first wall: - low Z - good oxygen getter ~ 100m 2 W – divertor (baffle, dome): - low erosion - long lifetime ~ 50 m 2 CFC – divertor target - no melting - C good radiator, emitter

Berilium Low plasma contamination; Low radiative power losses; Good oxygen gettering; Low bulk tritium inventory; Lowest BeO and metallic impurity content among the other structural grades; High elevated temperature ductility; Thermal shock resistance.

Tungsten chemical properties: -Atomic weight – 183,85; -Highest melting point in comparison with other infusible materials K; -Boiling temperature – 5933K; -Tungsten density – 19,35 g/cm 3 ; -Crystal lattice – body- centered crystal.

Tungsten physical and mechanical properties: –High temperature stability and tightness; –High thermal conductivity; –Low tritium retention; –Compability with plasma.

Tungsten disadvantages: Low erosion rate - low sputtering productivity; During breakdown tungsten melt faster then CFC; Low ductility at low temperature; Recrystalisation at high temperature.

Production of layers 1.Thin layers (CVD, PVD): –carbon substrates; –short lifetime. 2.Thick layers (PS, LPPS) –High porousity; –Limited thermal conduction.

Thank You for Your attention