H-mode characterization for dominant ECR heating and comparison

H-mode characterization for dominant ECR heating and comparison to dominant NBI or ICR heating F. Sommer Ph. D thesis advisor: Dr. Jörg Stober Academic advisor: Prof. Dr. Hartmut Zohm Max-Planck-Institut für Plasmaphysik Boltzmannstr. 2, 85748 Garching, Germany Advanced Course of EU Ph. D Network 29 Sep 2010

Outline • NBI and ECR heating systems • Heat transport theory • H-mode heat transport characterization – Te, Ti, C profiles • Further investigations and experiments • Summary and discussion F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 2

NBI – general introduction • Beam of neutrals (H 0, D 0, T 0, He 0 ) injected into plasma with – high power – up to 2. 5 MW – high (appropriate) energy – Ebeam > Ti, e – Inside plasma neutrals collide with plasma ions & electrons • H 0 + H + → H+ + H 0 – CX • H 0 + H + → H+ + H + + e – Ionisation by ions • H 0 + e → H+ + 2 e – Ionisation by electrons – exponential decay Ebeam ~ • 100 ke. V today 1 Me. V for ITER Resulting fast ions are confined within the plasma by magnetic field slowed down to thermal energies Coulomb collisions & electrons transfer of beam power to plasma F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 3

NBI – power deposition • critical energy: rate of energy loss to ions = rate of energy loss to electrons • Ecr = 14. 8 (k. Te) [ (A 3/2/Ai) ]2/3 – for pure D – beam: Ecr = 19 Te Ebeam/Ecr ~ 1 – 3 ITER: 1 Me. V = 3, 5 Me. V F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 ENBI = Ea 4

NBI – layout cut through 1 st injector PINIs (4 x) neutraliser box height: ~ 4. 5 m magnet – 10 MW at 60 k. V – arc sources pins have to be replaced quite often – 10 MW at 93 k. V ASDEX – RF sources simpler, cheaper, Upgrade less maintenance - pulse = 10 s ion dump F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 5

NBI – layout • 2 Beamlines, each 4 ion sources • SO-injector • 2 radial beams • 2 tangential beams • NW-injector • 2 tangential beams • 2 off-axis deposition • Also source of : • particles edge: 1/10, but deep fuelling (not relevant for ITER) • driven current • plasma rotation (by NBI torque) • CXRS • efficiency factor of only 40 % F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 6

ECRH – principle • Electron Cyclotron Maser Instability • • Electron gun: hollow e- beam Accelerated to relativistic speeds and focussed v. II converted to v┴ inside resonant cavity (axial B-field) Interaction between e- and em wave Phase focus of e. Slowing down of e- by E transfer to HF field Vgyrotron = 73 k. V Bgyrotron = 5. 3 T Efficiency factor of 50 % • • • F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 7

ECRH – layout • • • f. ECRH ~ 140 GHz Electron cyclotron frequency fce(B = 2. 5 T)= e. B / (2 pme) = 70 GHz location determined by – B µ 1/R – f. ECR – launching angle (mirror) • • Pold = 4 x 0. 5 MW for 2 s Pnew = 2 x 1 MW for 10 s • Pfuture = 2 x 1 MW for 10 s F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 8

ECRH – advantages • • Localized (few cm) deposition Localized current drive removal of NTMs by heating inside island structure • Electron heating simulate reactor conditions • Fast modulation ( 500 Hz) fast response in plasma • Central heating enhanced impurity transport F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 9

Heat transport - theory • Why are we interested in heat transport? – High E low heat transport – High central density low particle transport – Low accumulation of impurities enhancement of impurity transport • Heat transport is not governed by classical or neoclassical drive, but by micro instabilities and turbulent effects – ITG, TEM, (ETG) – Scale length ~ ion gyro radius << a • qe(r) = - ne(r) · Ce(r) · ÑTe(r) • G(r) = - F. Sommer D (r) · Ñne(r) + v · ne(r) Advanced Course of EU Ph. D Network, 29 Sep 2010 10

Heat transport - theory • • Gyro-Bohm scaling law in H-mode. Turbulence increases above a critical gradient length: • • CS, C 0, R/LTe, crit adjusted to experiment stiffness of profiles • Boundary condition at rpol = 0. 8 (H-mode pedestal) F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 11

ASTRA • Automated System for TRansport Analysis in a tokamak • • 2 D equilibrium 1 D (radial) profiles and transport equations of transport Modular build – Many implemented models – Easy inclusion of own models • • Equilibrium + radial profiles (Te, Ti, ne, j, Pheat, , Prad, …) qe, i, Ce, i, Dn, … Equilibrium + radial profiles (ne, j, Pheat , , Prad, …) + Ci, e, theory radial profiles (Te, Ti) F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 12

H-mode characterization • 4 similar discharges: Ip ~ 600 k. A, Btor ~ 2. 5 T, ne ~ 5 x 1019, PNBI = 5 MW – Different heating power (PECRH = 0, 0. 5, 1. 5 MW) – Different deposition location: PECRH = 1 MW, rpol = 0, 0. 3, 0. 6 F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 13

H-mode characterization - T profiles • • • Power dependence of Te profiles with varying ECRH: 0. 6 k. A, 2. 5 T, central ECRH ne = 5 x 1019 F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 14

H-mode characterization - T profiles II • • • Power dependence of Te profiles with varying ECRH deposition location: 0. 6 k. A, 2. 5 T, PECRH = 1. 2 MW ne = 5 x 1019 R. M. Mc. Dermott et al 2010 EPS F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 15

H-mode characterization - Ce profiles • Electron and ion heat diffusion coefficients derived with ASTRA with varying heating power Transport dominated by ion heat transport (ITG) F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 16

Further experiments and investigations • Increase of ECRH power (6 MW) Replacement of NBI in H-mode • • Higher current values up to Ip ~ 1. 2 MA Lower density values ne < 5 x 1019 Increased influence of ECRH on Ce (TEM) due to decreased n* • Variation of R/LTe by variation of r. ECRH • Dependence of ei on energy confinement time E • Influence of central ECRH on pedestal F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 17

H-mode characterization – ECRH on edge • Influence of ECRH power on edge profiles (Te, vtor, ne) Analysis by Elisabeth Wolfrum F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 18

Further experiments and investigations • Increase of ECRH power (6 MW) Replacement of NBI in H-mode • • Higher current values up to Ip ~ 1. 2 MA Lower density values ne < 5 x 1019 Increased influence of ECRH on Ce (TEM) due to decreased n* • Variation of R/LTe by variation of r. ECRH • Dependence of ei on energy confinement time E • Influence of ECRH on pedestal • Analysis of ICRH heated plasmas: torque e-/D+ heating F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 19

Summary and discussion • Difference between NBI and ECR heating its influence on transport • Gyro-Bohm scaling law • Examples of ECRH influence on heat transport • Increase of available ECRH power increases the range of accessible parameter space to analyse heat transport. Thank You F. Sommer Advanced Course of EU Ph. D Network, 29 Sep 2010 20