11) Centre for Fusion Space and Astrophysics, University of Euratom-ENEA-CNR, Milano, Italy

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2 P.Mantica 1), C.Angioni 2), B.Baiocchi 1),3), C.Challis 4), J.Citrin 5), G.Colyer 4), A.C.A. Figueiredo 6), L. Frassinetti 7),.Joffrin 8),9), T.Johnson 7),.Lerche 1), A.G.Peeters 11), A.Salmi 12), D.Strintzi 13), T.Tala 14), M.Tsalas 13),9), D.Van ester 1), P.C.deVries 5), J.Weiland 15), M.Baruzzo 16), M.N.A. Beurskens 4), J.P.S.Bizarro 6), P.Buratti 17), F. Crisanti 17), X.Garbet 8),C.Giroud 4), N.Hawkes 4), J. Hobirk 2),F.Imbeaux 8), J. Mailloux 4), V.Naulin 1), C.Sozzi 1), G.Staebler 19), T.W.Versloot 5),and JT FDA contributors# JT-FDA, Culham Science Centre, Abingdon, OX14 3DB, UK 1) Istituto di Fisica del Plasma 'P.Caldirola', Associazione 11) Centre for Fusion Space and Astrophysics, University of uratom-na-cnr, Milano, Italy Warwick, Coventry 7AL, UK 2) Max-Planck-Institut für Plasmaphysik, URATOM 12) Association URATOM-Tekes, Helsinki Univ. of Association, Garching, Germany Technology, FIN-215 TKK, Finland 3) Università degli Studi di Milano,, Milano, Italy 13) Association URATOM-Hellenic Republic, Athens, Greece 4) uratom/ccf Association, Culham Science Centre, 14) Association URATOM-Tekes, VTT, P.O. Box 1, Abingdon, OX14 3DB, UK FIN-244 VTT, Finland 5) FOM Institute Rijnhuizen, Association URATOM-FOM, 15) Chalmers University of Technology and uratom-vr Nieuwegein, the Netherlands Association, Göteborg Sweden 6) Assoc. uratom-ist, Instituto de Plasmas e Fusão Nuclear, 16) Consorzio RFX, NA-uratom Association, Padua, Italy Inst. Superior Técnico, Lisboa, Portugal 17) Associazione URATOM-NA sulla Fusione, C.R. 7) Association URATOM - VR, Fusion Plasma Physics, S, Frascati, Frascati, Italy KTH, Stockholm, Sweden 18) Association uratom-risø DTU, DK-4 Roskilde, 8) Association uratom-ca, CA/IRFM, F-1318 Saint Paul Denmark Lez Durance, France 19) General Atomics, P.O. Box 8568, San Diego, California 9)FDA-CSU,Culham Science Centre,Abingdon,OX143DB,UK , USA 1) LPP-RM/KMS, Association uratom-belgian State, TC, #See the Appendix of F. Romanelli et al., Overview of JT B-1 Brussels, Belgium results, OV/1-3, this conference

3 The meaning of the title The core of large machines can escape the ion temperature profile rigidity if a rotation gradient and a flat q profile are present This can be a unified physics basis for empirically discovered regimes with improved core ion transport, such as Hybrid and ITBs This is at least one reason why some commonly used transport models have difficulties in simulating Hybrid/ITB scenarios. Some theory understanding of these observations is developing. Future machines will require rotation gradient and q profile manipulation to achieve AT scenarios with improved core ion confinement

4 heat flux turbulent transport high stiffness moderate stiffness Onset of turbulent transport above a critical value of R/LT=R T/T High stiffness implies the need of high pedestal low stiffness Reducing stiffness allows higher core T for same heat flux, easing the requirement on pedestal residual transport threshold R/L T In ITR an increase of R/LTi from 4 to 5 across the plasma radius doubles QDT and Pα

5 ffect of toroidal rotation In theory, rotation reduces transport via a threshold upshift associated to the xb flow shear according to the quenching rule (α ~1) [Waltz et al., 1994] ωxb= r/q d(q vxb/r) /dr turbulent transport heat flux γxb=γnoxb-α ωxb Common expectation high stiffness Low rotation ` moderate stiffness High low stiffness rotation residual transport threshold R/L T

6 3 sets of shots at different rotation χs= γ=ωxb/(cs/a)~ ω [1 rad/s] 6 ϕ ρ.8 1 tor Rotation mitigates stiffness in core plasma but not in outer region. Confirmed by Ti modulation qigb= qi / [(ρi/ R)2 vith ni Ti]

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8 6 Hybrid Pulse No: t = 6.5s OS ITB Pulse No: t = 4.8s NS ITB Pulse No: t = 4.2s Fully diffused H-mode Pulse No: t = 18s 4 scenarios with different q profile: ρtor.6.8 JG c q 4 1.

9 6 full line: with rotation Hybrid Pulse No: t = 6.5s dashed line:h-mode without Fully diffused Pulserotation No: t = 18s 5 3 Ti sketch 2 1 Stiffness mitigated by rotation.2.4 ρtor.6.8 JG c q 4 How improved core ion confinement originates in hybrid Stiff, R/LTi not easily changed 1.

10 6 Hybrid Pulse No: t = 6.5s OS ITBwith Pulse No: t = 4.8s full line: rotation NS ITB Pulse No: t = 4.2s dashed line: H-mode without rotation Fully diffused Pulse No: t = 18s Stiff, R/LTi not easily changed 5 3 Ti sketch 2 1 Stiffness mitigated by rotation.2.4 ρtor.6.8 JG c q 4 The same mechanism could explain all 4 scenarios 1. nhanced core confinement was lost at reduced rotation in JT and DIII-D hybrids and ITBs D VRIS,P.C.,et al,nucl.fusion 49(29)757 POLITZR,P.A.et al,nucl.fusion48 (28)751

11 Dedicated experiments of q scans both with and without rotation -3MW ICRH(3He)-D : off-axis threshold / on-axis stiffness at low rotation -3MW ICRH MW NBI stiffness at high rotation Range of s explored ρtor=.33 : ρtor=.64 :.5<s<.8.75<s<1.45.2<s/q<.5.25<s/q<.7

12 Threshold follows High rotation Low rotation the expected behaviour with s/q At high rotation R/LTi well above threshold and decreasing with q profile peaking Consistent changes in turbulence by reflectometry ITG threshold after Guo, Romanelli, 1993 R /LT i ITG 4 Ti s = Te q s~.7 appears the value for which rotation is no longer effective. In agreement with database analysis.

13 Ti modulation confirms higher stiffness (flatter phase profiles) after the decay of R/LTi associated with q profile evolution The hypothesis that ion stiffness is lowered by the concomitant effect of rotation and low magnetic shear seems supported by the results of dedicated experiments

14 JT Hybrids and ITBs are characterized by high rotation NS ITB 8 at trigger NS ITB fully developed γ up to.15 Hybrid ϕ 4 ω [1 rad/s] ρ tor.8 1

15 JT Hybrids and ITBs are characterized by high rotation Correlation is found between R/LTi and rotation gradient Hybrid database NS ITB 8 at trigger NS ITB fully developed γ up to.15 Hybrid ϕ 4 ω [1 rad/s] 12 4 High delta Low delta ρ.8 1 tor.joffrin, X/1-1, this conference

16 Linear threshold does not vary much from Hmode to Hybrid ωxb <4 14 s-1 apart High rotation and low s from strong ITBs threshold up-shift alone not enough ITBs and Hybrid fill the very low stiffness region Ion stiffness mitigation contributes to achieve high H98 together with improved pedestal and absence of NTMs In Hybrids it can contribute up to ΔH98 =.2, more in ITBs

17 Steady-state Amplitudes ITB ITB No ITB No ITB ITB ITB No ITB No ITB ICRH modulation in (3He)-D Large gradients in modulation amplitude in the ITB region indicate low stiffness. Similar evidence in Hybrid core by Ti modulation using NBI.

18 Weiland model 12 γ = γ =.4 γ =.8 Weiland Scan in R/LTi (with R/ LTe in prescribed ratio) using the parameters of one shot and increasing γ progressively. lectron collisions included. 8 4 xpt i q [gyro-bohm units] ρtor=.33 γ = γ =.4 γ =.8 5 R/L 1 15 Ti Weiland model one kθ only only threshold up-shift

19 ρtor=.33 Weiland +TGLF Scan in R/LTi (with R/ LTe in prescribed ratio) using the parameters of one low rotation shot and increasing γ (and dvtor/dr) progressively. lectron collisions included. 12 γ = γ =.4 γ =.8 γ = γ =.1 γ =.5 γ =.15 8 TGLF 4 xpt i q [gyro-bohm units] Weiland γ = γ =.4 γ =.8 5 R/L Ti 1 15 Weiland model one kθ only only threshold up-shift TGLF full spectrum of kθ indicates sizeable change in slope, especially in knee region. Still a problem to recover the high stiffness of low rotation data

20 Weiland +TGLF+GYRO non-linear flux-tube 12 γ = γ =.4 γ =.8 γ = γ =.5 γ =.1 γ =.15 8 GYRO TGLF 4 xpt i q [gyro-bohm units] Weiland γ = γ =.4 γ =.8 ρtor=.33 Scan in R/LTi (with R/ LTe in prescribed ratio) using the parameters of one low rotation shot and increasing γ (and dvtor/dr) progressively 5 R/L 1 15 Ti Weiland model one kθ only only threshold up-shift TGLF and GYRO full spectrum of kθ indicate change in slope Differential suppression of low (stiff) and high (less stiff) kθ?

21 Decrease in time of R/LTi is often abrupt. No MHD! It is due to a sudden shrinking of the low stiffness region Possibly connected to a beneficial role of low order rationals at low magnetic shear in presence of rotation

22 Ion stiffness is reduced by the combined effect of low magnetic shear and high rotational shear, allowing higher Ti peaking and thereby improving fusion performance/easing pedestal requirements Ion stiffness mitigation is at the basis of enhanced ion core confinement, such as in Hybrid and ITB scenarios The effect of rotation on stiffness is observed also in numerical simulations. The role of magnetic shear and possibly low order rationals remains to be investigated. AT scenarios in ITR should seek for maximum rotational shear compatible with the available heating systems and minimum magnetic shear in the broadest region to enhance the rotational shear effect

23 Correlation reflectometry Lrefl= f(lturb, Aturb) ρtor=.29 Red: high rotation Black: low rotation ρtor=.69 Lrefl is lower at high rotation (lower Lturb) Lrefl decreases in time at high rotation at inner radii but not at outer radii (increasing Aturb)