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ITPA-Transport TG Particle & impurity workgroup Discussion, future plans

ITPA-Transport TG Particle & impurity workgroup Discussion, future plans. Milano, 20.10.2008. Issue1: Density peaking with electron heating.

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ITPA-Transport TG Particle & impurity workgroup Discussion, future plans

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  1. ITPA-Transport TGParticle & impurity workgroupDiscussion, future plans Milano, 20.10.2008

  2. Issue1: Density peaking with electron heating • Peaking at low neff is robustly documented in ITG and consistent with theory. Truly relevant to ITER in electron heated regime? Smaller machines experience ‘pumpout’ with strong electron heating How to address question? - Empirical: study trends with relevant parameters Ti/Te, Ti/Te,tei/tE- Study ITG/TEM transitional region (scan electron/ion heating ratio) - Resolve correlation between Ti/Te in expts and NBI source, compare to theory

  3. Particles:talks summary • H.Weisen et al presented 1000+ GS2 linear simulations, reproduced JET density peaking dependencies on nueff, source,li, gradTi/Ti • C.Angioni presented collisional, non-linear GYRO calculations of particle flux. High k, outward flux from trapped electron, low k inward. Explains agreement in linear case, if representative max gamma mode chosen. • K. Tanaka showed detailed comparison between LHD&JT-60U. LHD at large major radius shows clear, non-axissymmetrical NC transport. Comparison useful as tokamak community struggles and/or makes use of non-axisymmetrical effects: TF ripple, MHD modes, Resonant magnetic perturbations. Watch out! • Y. Camenen et al presented GK equations with inclusion of Coriolis and centrifugal forces. Important for heavy impurities in strong rotation. • N. Tamura showed CORE BORN impurity accumulation of in LHD occurs at highest densities and with strongest ne peaking (pellets). Ergodic edge layer can screen impurities born at PFC, thereby preventing accumulation. • D. Mikkelsen reported GYRO GK simulations for CMOD, consistent with observations. Density peaking if R/LTi not to far above threshold, otherwise flattening.

  4. Particles: discussion summary • Electron heating: Effect of electron heating by alphas in ITER. Will ITER remain in ITG (in which case we expect density peaking) or will TEM’s flatten density peaking? If ITER remains in ITG, will alpha power drive out core impurities? • L versus H: How can we understand differences in peaking behaviour in L and H-mode? • Fuelling: What evidence do we really have that gas fuelling will be ineffective in ITER? • Z-scaling of impurity transport. Research on several devices and operating regimes. Very wide subject, too large for a focussed task. • He-transport: Received little attention in recent years, especially in advanced scenarios. Felt we had some catching-up to do. Chosen as a priority 1 subject for joint research, because answers can be obtained by experiments and by mining existing data in resonable time frame.

  5. CDB-? He profiles and transport coefficients (draft) Confinement Database & Modeling TG Spokesperson: H. Weisen Background - Previous results

  6. Outline of Experiment

  7. Issue 2: Density peaking in H versus L-modes 2) Can we understand the apparent conflicting behaviour between most of the H-mode database (strong nueff scaling, weak or no li or magnetic shear scaling) and most of the L-Modes (strong magnetic shear scaling, weak or no nueff scaling)? Ideas: -Clues to be obtained from exceptions: C-MOD and other devices? -Repeat GS2 comparison with good L-mode profile data (JET) -

  8. Issue 3: Fuelling • Plasma fuelling • Do we understand gas fuelling? • Is gas fuelling aided by an inward pinch in the pedestal or not? • Are we sure we can write off gas fuelling in ITER? • Are large devices truly harder to gas fuel than small ones? • Prediction of pellet fuelling in ITER? • Relation with ELM pacing? • How to address issues?

  9. Issue 4: De-ashing • He transport poorly documented • He profiles harder to obtain than C profiles in JET He transport coefficients directly impact reactor performance.( For instance inward pinch/outward convection would worsen/relieve divertor compression requirements) • Do He transport coefficients vary as you go from ion heated to electron heated? • Believe this should be high priority • How to address issue? • -Analysis effort at JET (Carine Giroud) • Proposal for measuring He profile in ECH –H-mode in TCV

  10. Issue 5: Impurity transport, Z scaling • W adressed in AUG, will be at JET • Medium Z in several devices • Impact of rotation, may introduce bias that’s wrongly attributed to Ti/Te or other parameters correlated with heating method • So far no multi-machine effort as for density profiles • How to address issue? • -Need HFS & LFS profiles in machines with strong rotation (DIII-D, AUG, JET?) • Proposal for measuring He profile in ECH –H-mode in TCV

  11. Issue 6: Particle, He, impurity transport in ITB’s - So far little systematic studies? How to address issue? Priority?

  12. Issue N: -

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