Presentation on theme: "Chalkidikhi Summer School Plasma turbulence in tokamaks: some basic facts… W.Fundamenski UKAEA/JET."— Presentation transcript:
Chalkidikhi Summer School Plasma turbulence in tokamaks: some basic facts… W.Fundamenski UKAEA/JET
Chalkidikhi Summer School Applied Science: community with a mandate Goal: Artificial Star on Earth, i.e. exo-thermal reactor No gravity: Magnetic (MCF) vs. Inertial (ICF) Confinement MCF: Closed B-field lines, toroidal geometry Tokamak: strong toroidal field, with weaker poloidal transform, hence net Helical field Today: JET, AUG, JT-60, DIII-D, MAST, NSTX,… Tomorrow: ITER, a burning plasma experiment (EU, Japan, Korea, China, Russia, Canada, US) Decision on site in final stages, expected by end of the year Controlled Nuclear Fusion
Chalkidikhi Summer School Excellent textbook by J.Wesson, eg. JET (Joint European Torus) near Oxford, UK Core fields Btor 3 T, Edge Bpol 1 T 10,000 Gauss Core temperatures Ti,Te 10 keV, Edge Ti,Te 100 eV Core density ni,ne 1e20 m-3, Edge ni,ne 1e19m-3 Low beta plasma, β = p_plasma / p_B < 3 % Btor 1/R, Bpol(jtor), poloidal transform necessary to prevent free (hoop) expansion via ExB drift Tokamaks I
Chalkidikhi Summer School Core: closed field lines, radial transport Edge or SOL: open field lines, parallel >> radial transport Energy source: neutral beams, ICRH, ECRH (in ITER and beyond fusion reactions themselves) heat the core Particle source: edge recycling >> core fuelling Hence, mostly interested in power flow across B-field Due to high temperatures, the core is very difficult to diagnose for fluctuations Must rely on global transport reconstruction, to extract radial velocities, diffusivities, viscosities, conductivites, etc. In the colder edge, some measurements are possible Tokamaks II
Chalkidikhi Summer School Core transport found >> classical (Spitzer, Braginskii) Also >> neo-classical (corrections for toroidal geometry) Must infer the flow is not laminar but turbulent Electrostatic vs. Electromagnetic turbulence Comparison with theory suggests ion (critical gradient modes) dominate 3-D Numerical codes (gyro-fluid and gyro-kinetic) are reaching a stage where global turbulence resolved Transport barriers (local reduction of transport to laminar, neo-classical levels) Edge (ETB) vs. internal (ITB) transport barriers ETB: L-H bifurcation, highly intermittent MHD bursts these edge localized modes (ELMs) eject particles and energy on transit time scales – similarity to solar flares ?! Tokamaks III
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