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Achievements and open issues in impurity profile control at JET. M. Valisa and

Achievements and open issues in impurity profile control at JET. M. Valisa and Angioni Carraro Coffey Lauro-Taroni Predebon Puiatti Alper Belo Corrigan vanEester Garzotti Giroud Lerche Mantica Naulin Tala Tsala et al. JET E1/E2 meeting - Culham 7 April 2011. Background

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Achievements and open issues in impurity profile control at JET. M. Valisa and

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  1. Achievements and open issues in impurity profile control at JET. M. Valisa and Angioni Carraro Coffey Lauro-Taroni Predebon Puiatti Alper Belo Corrigan vanEester Garzotti Giroud Lerche Mantica Naulin Tala Tsala et al JET E1\/E2 meeting - Culham 7 April 2011

  2. Background What we have learnt at JET of the effect of RF on impurity transport Open Issues Outline

  3. Impurity accumualtion avoidance may require Active Control to guarantee stationary plasma fusion experiments and optimization of reactor efficiency. Codes validation is required to include impurities and their control in a ITER/ DEMO flight simulator RF well know empirical means to pump out impurities in present day experiments. Underlying mechanims still uncertain. Background 1

  4. Background 2 • For core issues, what really matters isthe relationship between • D_impurities , D_fuel and ce,i , since the relevant parameter is dilution. • Used impurity density perturbations (= trace impurity )to work out impurity transport • as with laser ablation. Modelling of the transient evolutions of the impurities provides an estimate of the transport coefficients. Used 1D transport model with + accurate atomic physics At stationarity Main diagnostics for metal impurities: SXR, emission lines , bolometry

  5. What we have learnt at JET

  6. Shown that D imp and ce,iin some situations go together RF (3He minority) deposition radius Change RF deposition profile (heat modulation to work out heat transport – P Mantica Gas modulation or pellet for DD – L Garzotti) See ME Puiatti et al PoP 2006

  7. RF power on electrons is effective as a means to control heavy impurities in JETlow collisionality regimes n eff [=10-14 <ne > <Te >–2 Zeff R ] ≤0.2 MH 58144 MC 58149 Dominant ITG  inward v Subdominant TEM  outward v M-E. Puiatti PoP 13 2006 ; C. Angioni et al PRL 2006

  8. RF power as a means to control heavy impurities also in JET Elmy H mode / HIGH DENSITY and Ar puffing in JET Shots 53548 , 53015 WITH ICRH: convection may become OUTward • Core diffusion decreases • Core convection also decreases and may become outward NO ICRH Shot 52136: Strong INward convection M.E. Puiatti et al .Plas. Phys.Contr. Fus. 44(2002)1863

  9. LBO & ICRH power scan: Ni and Mo are expelled from the centre as power increases H minority / H mode / low collisionality/ about 12 MW NBI, 1.5MA, 3T r = 0.2 Mo( 42) and Ni ( 28): similar behaviour RF power scan Ni andMo Open symbols Shots around 58140 He3 minority 68383 and 81 – marginal H mode (L-mode, but P>>LH threshold) Low collisonality, Similar triangularity and elongation

  10. GS2 Simulation of the shots with RF power scan Quasi linear, electrostatic No sign of flow inversion with increaasing RF

  11. Mo( 42) and Ni ( 28) have very similar behaviour r = 0.5 Ni andMo

  12. Discharges of the RF power scan “ “ = RF Power increase Target Plasma: Ip=1.5 MA B= 3T NBI= 12 MW Low triangularity No sawteeth Central ICRH

  13. Discharges of the RF power scan

  14. RF power scan and LBO injection of Ni r = 0.2 Out of many correlation attempts ( with rotation, Ti/Te, q and q shear etc ) the best correlation is with R/LTi Signature of a neoclassical trend? Nickel

  15. Good correlation of v/D with R/LTe r = 0.2

  16. Correlation with toridal rotation r = 0.2

  17. Correlation with q and q shear r = 0.2

  18. Good correlation of v/D with R/LTe r = 0.2 Stationary profiles : extrapolation using evaluated vand D’s 3MW RF 1 MW RF NO RF

  19. neoclassical V and D from NCLASS Neoclassical transport parameters too small: do not macth the experiment 0.2 0.15 0.05 0

  20. Sensitivity study on neoclassical transport Simulation - normalized chord integrated central SXR emission during the injection of Ni in discharge 74360 Experiment V neo and D from Exp. v neo and v/D from Exp LBO

  21. D’s and V’s in the ICRH scan database Impact of RF scan seems to be more on v than on D

  22. Open issues

  23. Open Issues • Understand the pump out effect of ICRH • - Role q and q shear? • Required shots with similar settings but different timing of LBO during pulse • or different timing of ICRH and or NBI • Role of rotation and shear rotation ? • Counter beam or different share of ICRH and NBI keeping total power constant. ICRH

  24. Open Issues • Is there a direct role of the RF itself ? • Test different heating schemes – ICRH on fundamental harmonic , • He3 minority heating • Are neoclassical terms correctly evaluated? • - In/out asymmetries / role of centrifugal forces. Impact on analysis • Can sawteeth be as efficient as RF ? • How large and frequent must ST be? Shown in the past that if small their • efficiency is smaller than 2MW RF (Puiatti et al PPCF 2003) 2) Issue of poloidal asymmetries 3) Efficiency of RF compared to sawteeth

  25. Open Issues • 4) Effect of ICRF on Zeff • In #68383 ( 8 MW ICRH ) Zeff increase from 2 to 4-5 with Zeff from C • nearly constant ( L Carraro et al EPS Warsaw) • See also JET works by Czarneka where the problem has been investigated • in some details. Lot of work also on other machines. • 5) Analysis Tools for dealing with Tungsten • - Do we have reliable tools for detection and analysis ? • - Will W radiation be overwelming to make traditional techniques • ( such as LBO with Ni and Mo) useless? • 6) How to implement a feedback control system on impurity accumulation

  26. Detection and analysis of W on JET • Data available are: • some SXR/VUV spectroscopic lines (KT2 and KT4) with a fairly coarse time resolution. Have lines been identified ? • Soft-X rays: a vertical camera with 34 l-o-s (250μ filter) and a horizontal camera with 17 channels (350μ filter).

  27. Detection and analysis of W on JET • Heavy impurity transport simulations. • Available the predictive impurity transport simulation JETTO/SANCO • The ADAS tables can be used to calculate the local emissivities that integrated along the various l-o-s can simulate the experimental SXR channels • Standard treatment: • ZI +1 equations with ionisation and recombination to and from neighbouring ionised states provided by ADAS/adf11 tables. • Superstages treatment: • Reduced set of equations each representing a ‘bundle’ of contiguous ionised stages (a ‘superstage’) in coronal equilibrium between each other. • W from 74 to 35 , or more aggressively down to 10 superstages. See L Lauro-Taroni H Summers et al presentation at the General Task Force T Meeting 16 February 2009

  28. Tungsten data available at JET Most recent W LBOs have been performed during C17 (Nov 2006): 68373 3.2T/2.3MA 4.5 MW ICRH, 8.9MW NBI, 0.5 MW LHCD 68374 6 MW ICRH, 8.9 MW NBI, 0.8MW LHCD 68387 7.7 MW ICRH, 9 MW NBI, 1.1MW LHCD W LBO data available at JET available for testing tools SXR 68373 BOLO

  29. Example of SXR after LBO of W shwoing central peaking SXR Horizontal cameras - B.Alper 68373. W ablation at t=55 s

  30. Example of SXR after LBO of W showing polidal asymmetry In-Out Asymmetry SXR Vertical Camera ( B.Alper) 68373 W ablation at t=55

  31. Effect of ionization stages partitioning has been tested Different superstages partitions of W 74 ion (no bundling) 35 superstages: natural bundling 26 superstages: natural bundling, with 55+ upwards bundled into 2 SS 10 superstages: ions with ionisation potential >800 eV bundled into 1 SS ( for edge plasmas). All partitions yield the same nW(x,t), same total number of particles, same Power But the partition into 10 SS yields a slightly different SXR simulation, with a faster rise in the initial phase. ONGOING WORK Could be superstage treatment be included in feedback controlled system?

  32. Example of ongoing work: simulation of Prad and SXR after W LBO 50 ΔP bolo P sim D (m2/s) V (m/s) W source time 100 ρ Jetto SXR Black: V Ch. 3 (peripheral) Red: V Ch 12 (central) Light blue: H Ch11 (central) time By L Lauro-Taroni

  33. Summary and conclusions • Central ICRH effective on JET to pump out Ni and Mo which feature peaked profiles in JET NBI only H mode plasmas • About 3 MW ICRH required in the analysed shots • W : only very Preliminary analysis by Lauro Taroni • Mechanism for impurity pump out? Trends recall neoclassical transport ( proportional to R/LTi) but absolute values do not fit • Ni (28) and Mo(42) seem to behave similarly , and W?? • ICRH is accompanied by higher Zeff . • Possibility of treatment of W in superstages successfully implemented in JETTO/SANCO (ADAS files for bundled impurities can be generated ) • Simulations of a Tungsten injection in JET started

  34. Ni injections

  35. Mo injections SHOT Ip(MA) Bt(T) NBI (MW) ICRH (MW) H/He3

  36. Soft-X rays: a vertical camera with 34 l-o-s (250μ filter) and a horizontal camera with 17 channels (350μ filter).

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