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Design of plasma facing components of the ITER antenna

Design of plasma facing components of the ITER antenna. Sheath modeling scheme (Colas et al.) SEM theory (Faudot et al.) Basic results from modeling (Colas report) Using SEM or not Extrapolation from machines (TS, JET) How to refine predictions? Grounding and sheath effects

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Design of plasma facing components of the ITER antenna

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  1. Design of plasma facing components of the ITER antenna • Sheath modeling scheme (Colas et al.) • SEM theory (Faudot et al.) • Basic results from modeling (Colas report) • Using SEM or not • Extrapolation from machines (TS, JET) • How to refine predictions? • Grounding and sheath effects • Shimming and evolution of blanket design CCIC-03 PFC for ITER antenna (R. Koch)

  2. References • Colas L., et al., Note de travail CEA PHY/NTT-2008.008 (2008).”Estimation of expected power / particle fluxes on ITER PFCs caused by local acceleration of particles in RF fields. Contract EFDA 07/1700-1572” • Faudot E., Heuraux S., Colas L., Physics of Plasmas, 13(2007)042512. “Parametric study of two-dimensional potential structures induced by radio-frequency sheaths coupled with transverse currents in front of the Ion Cyclotron Resonance Heating antenna” • Personal contacts with Colas • Info from Maggiora about grounding effects on sheaths CCIC-03 PFC for ITER antenna (R. Koch)

  3. Colas et al sheath modeling scheme • Compute E// at antenna mouth (TOPICA) • Assume SW skin depth (at k//=0) to compute E// (or ) in plasma Gives RF • Run SEM: RF    rectified sheath potential • Use  to compute density modification by sheaths (convective cells) • Compute power dissipation due to ion acceleration in sheaths CCIC-03 PFC for ITER antenna (R. Koch)

  4. What is the SEM (Sheath Effect Modelling) code? • Adjacent flux tubes exchange RF current due to the polarization drift • E builds up because sheaths put adjacent field lines to different potential • SEM solves the equation resulting from •   is “diffused” poloidally and radially over a region of width CCIC-03 PFC for ITER antenna (R. Koch)

  5. SEM: What are the results? (I) • Sheath effects are negligible for all short scenarios (SW field penetration > )  < 0.1 MW/m2  no longer discussed • For long scenarios SW skin depth very short. SEM substantially spreads it  CCIC-03 PFC for ITER antenna (R. Koch)

  6. SEM: What are the results? (II) •  very deep penetration for large L// (field lines crossing divertor)  discarded •  deep penetration for L// = 2.8m  brings // field where there is substantial ne ! CCIC-03 PFC for ITER antenna (R. Koch)

  7. Colas et al sheath modeling scheme • Use  to compute density modification by sheaths (convective cells) • Density depletion where E// large • High density fingers around depleted region • SEM increased penetration brings larger density in fingers •  Amplified peak power fluxes •  Amplified total sheath power dissipation CCIC-03 PFC for ITER antenna (R. Koch)

  8. Discussion • Can SEM accurately compute the parallel electric field penetration? My answer: no • Over simplified model: , E incomplete, sheath model? • Meaning of RF ? • What would happen without SEM? CCIC-03 PFC for ITER antenna (R. Koch)

  9. Extrapolations from TS results (Colas report) My quick and dirty estimate: 1 ITER antenna = 6 TS antennas TS 1MW  ITER 6 MW Sheath losses  V QITER = (20/6)1/2QTS = 1.8  0.4 = 0.7 MW/m2 Agrees with Colas estimates, Table II.4 QITER,max = 1.6 MW/m2 But:  CCIC-03 PFC for ITER antenna (R. Koch)

  10. Extrapolations from JET results (Colas report) Much more difficult to compare with ITER antenna Table II.7 worst case Q// ITER,max = 6.7 MW/m2 Not in disagreement with TS extrapolation modeling without SEM CCIC-03 PFC for ITER antenna (R. Koch)

  11. How can we go further? • TS extrapolations seem most reliable because of similarity with ITER antenna but scarce database and Q • Pursue theory/experiment comparisons on TS (ILP removed!) • Get experimental data on ILA • Further theory developments and experiment/modelling comparisons welcome (but timing?) • Determine which density profile is realistic • Investigate coupling vs sheath dissipation trade-off • Optimize antenna for sheath reduction CCIC-03 PFC for ITER antenna (R. Koch)

  12. CCIC-03 PFC for ITER antenna (R. Koch)

  13. Preliminary results without SEM (Private communication from Colas) • VDCreduced fromVRF/2 to VRF/ (factor 1.5) • E// penetration reduced from 35 mm to 6 mm • Reduction in peak power load: from 16MW/m2 to 8.7MW/m2 (at antenna mouth) due to • Reduced VRF • Reduced density in fingers • Result close to extrapolation from JET (see below) • Total power loss reduced from 597 kW to 231 kW • Further analysis ongoing CCIC-03 PFC for ITER antenna (R. Koch)

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