Introduction to the Diagnosis of Magnetically Confined Thermonuclear - PowerPoint PPT Presentation

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Introduction to the Diagnosis of Magnetically Confined Thermonuclear Plasma Core diagnostics I: Heavy Ion Beam Probe (HIBP) J. Arturo Alonso Laboratorio Nacional de Fusión EURATOM-CIEMAT E6 P2.10 arturo.alonso@ciemat.es version 0.1 (March 2, 2011) Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 1 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Outline 1 Motivation: Radial electric fields and trasnport barriers Electric fields and plasma motion Electric fields and confinement transitions Experimental determination of the radial electric field The Heavy Ion Beam Probe 2 General Principle Injection, energy analyser and measurement localisation Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 2 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Outline 1 Motivation: Radial electric fields and trasnport barriers Electric fields and plasma motion Electric fields and confinement transitions Experimental determination of the radial electric field The Heavy Ion Beam Probe 2 General Principle Injection, energy analyser and measurement localisation Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 3 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Electric fields in a quasineutral plasma We have said that plasma has a strong tendency to remain quasineutral n e ≈ n i , or more precisely | n i − n e | / n ≪ 1 with n = 1 2 ( n i + n e ) . However, tiny deviations from neutrality render measurable macroscopic electric fields. • Take δ = ( n i − n e ) / n , then Poisson’s equation reads ∇ 2 φ = ρ ⇒ d drE r = δ en , ǫ 0 ǫ 0 • now take n = 10 19 m − 3 and dE r / dr ≈ E r / a with a = 1 m to get E r (( V / m )) = 1 . 8 × 10 11 δ A deviation from neutrality δ = 10 − 9 would cause an electric field of ∼ 100 V/m. Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 4 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Ambipolar electric field The electron and ion cross-field fluxes Γ e , i are functions of the radial electric field E r . These two fluxes need not be the same, but whenever there is a preferential loss of charge, an electric field will build up to equilibrate the losses and preserve the plasma quasineutrality. The equilibrating radial electric field is called ambipolar field and, for a two species ( e , i ) plasma, is given by the condition Γ e ( E r ) = Γ i ( E r ) This equation is the basis of most calculations of the equilibrium E r in a plasma Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 5 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe The E × B drift The fluid velocity of an isotropic and frictionles plasma ( m , q ) -specie evolves acroding to mn ( ∂ t u + u · ∇ u ) = −∇ p + qn ( E + u × B ) (1) Neglect inertial forces (drift ordering δ = ρ/ L ≪ 1 ) and multiply by B × (1) u ⊥ = E × B + ∇ p × B = u E + u ∗ . B 2 nqB 2 A radial electric field E r causes a plasma-fluid rotation perpendicular to the magnetic field and contained within the flux surface Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 6 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Characterised by strong turbulent transport and power degradation Above a P th the plasma suddenly transits to a improved mode of confinement (H-mode) where τ ( H ) ∼ 2 τ ( L ) E . L to H transition is not E yet understood!! H-mode and the edge transport barrier Turbulence supression by shear decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe L to H transition Low confinement mode (L-mode) was the only mode before the 80’s Internal Characterised by strong turbulent Transport transport and power degradation Barrier Above a P th the plasma suddenly e r u transits to a improved mode of s s confinement (H-mode) where e r H-mode τ ( H ) ∼ 2 τ ( L ) P E . L to H transition is not (Advanced a E m yet understood!! Scenarios) s a H-mode and the edge transport l P barrier Turbulence supression by shear Surface radius decorrelation Also ITBs (Advanced Scenarios). Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 7 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Experimental determination of E r Because of these and other things it is very interesting to measure radial electric fields in fusion plasmas. Sevela diagnostics are used for that: Langmuir probes (only for the far SOL in hot H-mode plasmas) Impurity ( s ) line doppler broadenning ( T s ) and shift ( v s ). From the velocity expression u ⊥ = E × B + ∇ p s × B ⇒ E r = − 1 dp s dr + v ϕ s B θ − v θ s B ϕ . B 2 n s q s B 2 n s q s Heavy Ion Beam Probe – direct measurement Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 8 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe Outline 1 Motivation: Radial electric fields and trasnport barriers Electric fields and plasma motion Electric fields and confinement transitions Experimental determination of the radial electric field The Heavy Ion Beam Probe 2 General Principle Injection, energy analyser and measurement localisation Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 9 / 20

Motivation: Radial electric fields and trasnport barriers The Heavy Ion Beam Probe General principle 1 Heavy ions are injected into the plasma at a known energy 2 Ions collide with plasma electrons and get further ionised 3 They are deflected away from the primary beam and their energy is measured 4 From the difference in the injection and detection energy we can infer the electric potential at the ionization point (sample volume) Core diagnostics I: Heavy Ion Beam Probe (HIBP), A. Alonso, copyleft 2010 10 / 20