R Sartori Thank you to the people who contributed

1. Impact of rotation and momentum input on the L-H transition R Sartori Thank you to the people who contributed

2. Outline of the talk L-H threshold and: • Changes in rotation by changing NBI torque (DIII-D) • Changes in rotation due to changes in SOL flow (Alcator C-Mod) • Changes in rotation due to TF ripple (JET) • Changes in rotation due to changes in momentum input: NBI vs no momentum input ICH and ECH (Asdex Upgrade and JET) • Changes in rotation due to RMP

3. DIII-D: L-H threshold depends on applied beam torque and toroidal rotation • The L-H threshold power is reduced by a factor of 3 going from prevalent co-injectionto prevalent counter in USN (ion grad-B drift away from X-point) • Smaller reduction of PLH in LSN  ~80% • No difference between USN and LSN for counter and balanced injection • Reduction in edge toroidal rotation is correlated with the observed reduction in L-H threshold power P Gohil, H-mode workshop 2007

4. DIII-D: L-H threshold depends on applied beam torque and toroidal rotation The L-H transition can be induced by reduction of applied torque at constant power

5. DIII-D: L-H threshold dependence on torque/rotation is independent of ion mass The experiment P Gohil, NF, to be published • The increase of PLH with torque is seen also in Hydrogen plasmas • In Hydrogen a factor of 2 larger threshold observed in the range of torque explored

6. DIII-D: Changes in rotation/torque correlate with edge turbulence dynamics Description of the Experiment GR McKee, IAEA 2008 D J Schlossberg, Phys. Of Plasmas, 2009 • Changes in fluctuation level and flow pattern between co-injection and balanced injection • Turbulence flow reversal in balanced injection  poloidal flow shear • Correlation between changes in injected torque and poloidal group velocity of turbulence near edge • spectra obtained in 100 ms before L-H. Phase shift of poloidally displaced channels Z=1.2cm.

7. DIII-D: Increased Er shear at lower rotation Description of the Experiment • Interplay between pressure gradient and v X B terms in Er: • lower contribution of toroidal rotation term  increase in Er shear at the edge de-correlation and suppression of turbulence .

8. Alcator C-Mod: Changes in L-H threshold correlated with changes in SOL flows/rotation From H Hubbard, EPS 2004 • Changes in core rotation correlated with changes of SOL flows (largest in inner SOL) • PLH two times higher in USN (ion B drift away from X-point ) • Strong parallel flows are driven in the inner SOL, co-current for LSN, counter current for USN • At the L-H threshold flows and rotation near a constant value, independent of configuration  strong suggestion that SOL flows are causing differences in PLH with configuration

9. JET: Variation of toroidal rotation due to TF ripple changes Comparison of density and temperature and toroidal rotation profiles • Lower rotation with increasing ripple. Edge rotation becomes negative at high ripple • ASCOT calculation  that dominant mechanism for reduction of rotation is banana orbit diffusion  induces a radial return current  JXB torque in counter current direction. For ripple of 0.5% this torque was found to be 20-30% of that supplied by the NB system 1.5% ripple: L-modes with low level of beam power P De Vries et al, NF 48 2008

10. JET: L-H threshold is not affected by large variation in toroidal rotation due to TF ripple Comparison of power and torque density • 0.08% ripple  v in co-current direction • 1 % ripple  v in counter-current direction • Similar Te and Ti the transition • v unaffected by ripple Y Andrew et al, PPCF 50 2008

11. Asdex Upgrade: L-H threshold is independent of heating method momentum input/rotation Global and pedestal confinement is similar • No difference in L-H power threshold and in the density dependence of PLH between ICH and NBI, for both D and He plasmas F Ryter et al, NF 49 2009

12. JET: L-H threshold is independent of heating method momentum input/rotation • JET results shows that L-H access is independent of heating method, as seen previously in JET for all H isotopes • New data confirms the results and shows typical changes from ~6-8 kHz (NBI+ICH) down to ~2.5KHz (ICH) at 3T with similar threshold Data from 1MA/1T to 3.8MA/3.8T LH scaling from Righi et al NF 39, 1999 Andrew et al, PPCF 48 2006

13. Effect of RMPs on the L-H transition Summary from Carlos Hidalgo- H-mode workshop talk JET No effect observed (2009 experimental campaign) MAST On MAST there is observation of the delay of the L-H transition time if the n=1 coils are applied before the L-H transition but not with n=3. DIII-D In Helium plasmas PL-H increased by >50% in the presence of n=3 RMP perturbations.   NSTX PL-H increases from ~1.4 to 2.6 MW with higher n=3 current (~65% increase for Pheat/ne)

14. Summary and future work NXTS and JET results on L-H threshold with RMP • PLH increases from ~1.4 to 2.6 MW with higher n=3 current • PLH unaffected by application of RMP if effect exists it depends on the strenght of the perturbation • 30% decrease in rotation

15. Summary • Evidence from DIII-D of strong effect of beam torque on L-H threshold • The effect persist when mass (and X-point height) are changed • For counter-injection, it reduces differences between favourable and unfavourable grad-B direction • The effect is less strong in favourable grad-B direction (why?), therefore effect on threshold scaling not as large as largest reported variations • When rotation is changed by changing heating methods and ripple the L-H threshold is unchanged, with RMP it increases or is unvaried  suggest weaker link with rotation in DIII-D results

16. JET data : LSN configuration and reversed Bt and Ip Comparison with same density and total power • Reversed Bt direction ion B drift away from X-point and counter injection • Forward Bt direction ion B drift towards X-point and co injection • No difference between L-H power threshold with ion B drift direction in the JET data.