E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April Outline Background What we have learnt at JET of the effect of RF on impurity transport Open Issues

E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April For core issues, what really matters is the relationship between D_impurities, D_fuel and  e,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. Background 2 + accurate atomic physics Used 1D transport model with Main diagnostics for metal impurities: SXR, emission lines, bolometry At stationarity

E1/E2 Meeting, 7 April What we have learnt at JET

E1/E2 Meeting, 7 April Change RF deposition profile (heat modulation to work out heat transport – P Mantica Gas modulation or pellet for D D – L Garzotti) Shown that D imp and  e,i in some situations go together See ME Puiatti et al PoP 2006 RF (3He minority) deposition radius

E1/E2 Meeting, 7 April M-E. Puiatti PoP ; C. Angioni et al PRL 2006 RF power on electrons is effective as a means to control heavy impurities in JET low collisionality regimes  eff [= –2 Zeff R ] ≤0.2 MH MC Dominant ITG  inward v Subdominant TEM  outward v

E1/E2 Meeting, 7 April RF power as a means to control heavy impurities also in JET Elmy H mode / HIGH DENSITY and Ar puffing in JET Core diffusion decreases Core convection also decreases and may become outward NO ICRH Shot 52136: Strong INward convection Shots 53548, WITH ICRH: convection may become OUTward M.E. Puiatti et al.Plas. Phys.Contr. Fus. 44(2002)1863

E1/E2 Meeting, 7 April 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  = 0.2 Ni and Mo and 81 – marginal H mode (L-mode, but P>>LH threshold) Low collisonality, Similar triangularity and elongation Mo( 42) and Ni ( 28): similar behaviour Open symbols Shots around He3 minority RF power scan

E1/E2 Meeting, 7 April GS2 Simulation of the shots with RF power scan No sign of flow inversion with increaasing RF Quasi linear, electrostatic

E1/E2 Meeting, 7 April Mo( 42) and Ni ( 28) have very similar behaviour  = 0.5 Ni and Mo

E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April Discharges of the RF power scan

E1/E2 Meeting, 7 April RF power scan and LBO injection of Ni  = 0.2 Nickel 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?

E1/E2 Meeting, 7 April  = 0.2 Good correlation of v/D with R/LTe

E1/E2 Meeting, 7 April Correlation with toridal rotation  = 0.2

E1/E2 Meeting, 7 April Correlation with q and q shear  = 0.2

E1/E2 Meeting, 7 April  = 0.2 Good correlation of v/D with R/LTe NO RF 1 MW RF 3MW RF Stationary profiles : extrapolation using evaluated vand D’s

E1/E2 Meeting, 7 April neoclassical V and D from NCLASS Neoclassical transport parameters too small: do not macth the experiment

E1/E2 Meeting, 7 April Sensitivity study on neoclassical transport chord integrated central SXR emission during the injection of Ni in discharge Experiment Simulation - normalized V neo and D from Exp. v neo and v/D from Exp LBO

E1/E2 Meeting, 7 April D’s and V’s in the ICRH scan database Impact of RF scan seems to be more on v than on D

E1/E2 Meeting, 7 April Open issues

E1/E2 Meeting, 7 April Open Issues - 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 1)Understand the pump out effect of ICRH

E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April 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). Detection and analysis of W on JET

E1/E2 Meeting, 7 April 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. Detection and analysis of W on JET See L Lauro-Taroni H Summers et al presentation at the General Task Force T Meeting 16 February 2009

E1/E2 Meeting, 7 April Tungsten data available at JET Most recent W LBOs have been performed during C17 (Nov 2006): T/2.3MA 4.5 MW ICRH, 8.9MW NBI, 0.5 MW LHCD MW ICRH, 8.9 MW NBI, 0.8MW LHCD MW ICRH, 9 MW NBI, 1.1MW LHCD SXR BOLO W LBO data available at JET available for testing tools

E1/E2 Meeting, 7 April SXR Horizontal cameras - B.Alper W ablation at t=55 s Example of SXR after LBO of W shwoing central peaking

E1/E2 Meeting, 7 April SXR Vertical Camera ( B.Alper)68373 W ablation at t=55 In-Out Asymmetry Example of SXR after LBO of W showing polidal asymmetry

E1/E2 Meeting, 7 April 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). 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? All partitions yield the same n W (x,t), same total number of particles, same Power Effect of ionization stages partitioning has been tested

E1/E2 Meeting, 7 April SXR Black: V Ch. 3 (peripheral) Red: V Ch 12 (central) Light blue: H Ch11 (central) W source ΔP bolo P sim D (m2/s) V (m/s) Example of ongoing work: simulation of Prad and SXR after W LBO time ρ Jetto By L Lauro-Taroni

E1/E2 Meeting, 7 April 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

E1/E2 Meeting, 7 April SHOTIp(MA)Bt(T)NBI (MW)ICRH (MW)H/He He He He He H H H H H H H Ni injections

E1/E2 Meeting, 7 April H H H Mo injections SHOT Ip(MA)Bt(T) NBI (MW)ICRH (MW)H/He3

E1/E2 Meeting, 7 April Soft-X rays: a vertical camera with 34 l-o-s (250μ filter) and a horizontal camera with 17 channels (350μ filter).