R Sartori et al, ITPA, Autumn 2009

R SartoriThank you to the people who contributed

Impact of rotation and momentum input on the L-H transition

R Sartori et al, ITPA, Autumn 2009

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

R Sartori et al, ITPA, Autumn 2009

• The L-H threshold power is reduced by a factor of 3 going from prevalent co-injection to 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

DIII-D: L-H threshold depends on applied beam torque and toroidal rotation

P Gohil, H-mode workshop 2007

R Sartori et al, ITPA, Autumn 2009

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

R Sartori et al, ITPA, Autumn 2009

The experiment DIII-D: L-H threshold dependence on torque/rotation is independent of ion mass

• 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

P Gohil, NF, to be published

R Sartori et al, ITPA, Autumn 2009

Description of the Experiment

• Correlation between changes in injected torque and poloidal group velocity of turbulence near edge

• Changes in fluctuation level and flow pattern between co-injection and balanced injection

• Turbulence flow reversal in balanced injection poloidal flow shear

• spectra obtained in 100 ms before L-H. Phase shift of poloidally displaced channels Z=1.2cm.

DIII-D: Changes in rotation/torque correlate with edge turbulence dynamics

GR McKee, IAEA 2008

D J Schlossberg, Phys. Of Plasmas, 2009

R Sartori et al, ITPA, Autumn 2009

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 .

DIII-D: Increased Er shear at lower rotation

R Sartori et al, ITPA, Autumn 2009

• 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

• Changes in core rotation correlated with changes of SOL flows (largest in inner SOL)

Alcator C-Mod: Changes in L-H threshold correlated with changes in SOL flows/rotation

From H Hubbard, EPS 2004

R Sartori et al, ITPA, Autumn 2009

• 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

Comparison of density and temperature and toroidal rotation profiles

JET: Variation of toroidal rotation due to TF ripple changes

P De Vries et al, NF 48 2008

1.5% ripple: L-modes with low level of beam power

R Sartori et al, ITPA, Autumn 2009

Comparison of power and torque density

JET: L-H threshold is not affected by large variation in toroidal rotation due to TF ripple

• 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

R Sartori et al, ITPA, Autumn 2009

Global and pedestal confinement is similar

Asdex Upgrade: L-H threshold is independent of heating method momentum input/rotation

• 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

R Sartori et al, ITPA, Autumn 2009

• 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

JET: L-H threshold is independent of heating method momentum input/rotation

R Sartori et al, ITPA, Autumn 2009

Effect of RMPs on the L-H transition Summary from Carlos Hidalgo- H-mode workshop talk

DIII-DIn Helium plasmas PL-H increased by >50% in the presence of n=3 RMP perturbations.  

JETNo effect observed (2009 experimental campaign)

MASTOn 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.

NSTX PL-H increases from ~1.4 to 2.6 MW with higher n=3 current (~65% increase for Pheat/ne)

R Sartori et al, ITPA, Autumn 2009

Summary and future work

• 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

NXTS and JET results on L-H threshold with RMP

R Sartori et al, ITPA, Autumn 2009

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

R Sartori et al, ITPA, Autumn 2009

Comparison with same density and total power

JET data : LSN configuration and reversed Bt and Ip

• 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.