H-mode characteristics close to L-H threshold power ITPA T&C and Pedestal meeting, October 09, Princeton Yves Martin 1, M.Greenwald, A.Hubbard, J.Hughes,

H-mode characteristics close to L-H H-mode characteristics close to L-H threshold powerthreshold power

ITPA T&C and Pedestal meeting, October 09, PrincetonITPA T&C and Pedestal meeting, October 09, Princeton

Yves MartinYves Martin11, M.Greenwald, A.Hubbard, J.Hughes, , M.Greenwald, A.Hubbard, J.Hughes, A.Loarte, A.Polevoi, F.Ryter, R.Sartori, et al.A.Loarte, A.Polevoi, F.Ryter, R.Sartori, et al.

11Centre de Recherches en Physique des PlasmasCentre de Recherches en Physique des PlasmasAssociation Euratom - Confédération SuisseAssociation Euratom - Confédération Suisse

Ecole Polytechnique Fédérale de LausanneEcole Polytechnique Fédérale de Lausanne (EPFL) (EPFL)CH - 1015 Lausanne, SCH - 1015 Lausanne, Switzerlandwitzerland

OutlineOutline

Introduction

PL/PThresh in present H-mode experiments

ELM type

Weak points

Discussion

Yves Martin, ITPA Meetings, October 2009 2

Introduction: H-mode accessibility in ITER (I)Introduction: H-mode accessibility in ITER (I)

ITER baseline scenario:• Stationary H-mode, Q~10• Confinement factor H~1• Bt=5.3T and ne=1x1020m-3

ITER exploitation phases:• H or He• D• D-T

Baseline scenario to be tested in non or low activating phases• H-mode access in all phases

ITER available power: • ~45MW -> ~70MW (~110MW later)


H-mode accessibility in ITER (II)H-mode accessibility in ITER (II)

L-H transition threshold power:• With empirical scaling based on magnetic field, plasma density

and size, L-H threshold power is estimated: ~85MW in nominal magnetic field and density, D plasma ~50MW at ½ density

• Large uncertainty in threshold power

H-mode with Good Confinement - Experience in present tokamak • Good (H~1), ‘steady state’, confinement: Type I ELMs• Type I ELMs obtained at powers exceeding ‘significantly’ the

threshold power

Question: Can all these conditions be realised simultaneously in ITER?• Bt=5.3T and ne=1x1020m-3 • Confinement factor H~1• Additional power ≤70MW (110MW)

… in H/He, D, D-TYves Martin, ITPA Meetings, October 2009 4

ITER ScenariosITER Scenarios

Phase I – H or He• Threshold power increased by ~100% or 30-50%, resp.

~170MW, 110-130MW in nominal plasmas ~45MW at ½ magnetic field and ½ density (He)

Phase II – D• Threshold power with large uncertainty

~85MW (45-160MW) Several parameters known to play a role (X-point height, plasma

shape, dIp/dt, RMP, …, rotation / torque, …)

Phase II – D-T• Threshold power is lower: ~70MW (isotope mass effect)• Fusion power () can be added

In all phases, L-H transition could be obtained but little power available to access good confinement


QuestionQuestion

Background• Scaling based on pre-transition data, in L-mode• Extrapolated to ITER, predictions give power to enter the H-

mode• Expected H-mode regime: type III ELMs• More power required to access H~1 regime, type I ELMs

Question• What is the power ratio in the most common H-mode regime in

your device, what are the plasma parameters, heating scheme and H-mode characteristics?

• In case of PL/PT~1, what are the characteristics of these plasmas, and the differences with point 1?

• In case of PL/PT~1 and H~1, what are the characteristics of these plasmas, and the differences with point 1&2?


Good H-mode access - generalGood H-mode access - general

+ Large ELMs. Small ELMs


From confinement DB:TS used in

confinement studiesMeasure of E and

normalise by its value estimated with scaling

Measure PL and normalise by its value estimated with the scaling, Pthresh, taken at the same time

A lot of power is available in present day devices!

JETJET

Confinement experiments done at PL/PT=1-3Type III ELMs at low powers above PT

ELM free, then type I ELMs phases obtained when power increased

Mixed phases (III->I) also observed


Proportionality between threshold powers for L-H transitions and ELM type transitions (up to factor 2)

ELM type transition occurs at reduced power when triangularity is increased (30% reduction)

Increase of plasma density leads to transition from type I to type III

R.Sartori, PPCF, 2004

ASDEX UpgradeASDEX Upgrade

Confinement experiments done at PL/PT=1-4

F.Ryter’s paper [JPCS 2008]: PL/PT < 1.6

• Ion grad B drift towards X-pt


2

4

6

8

10

12

14

0.4 0.6 0.8 1 1.2 1.4

Type-IType-I/IIIType-IIInGW

n e [

101

9 m

-3]

IP [MA]

2

3

4

5

6

7

8

0.4 0.6 0.8 1 1.2 1.4

Type-IType-I/IIIType-III

q 95

IP [MA]


PL < 5MW because of PL/PT < 1.6PL/PT > 0.6 because of limit for H-L transition‘Empty’ zones because of operational constraints


2

4

6

8

10

12

14

1 1.5 2 2.5 3 3.5

Type-I

Type-I/III

Type-III

n e [

101

9 m

-3]

abs(BT) [T]

4 MW

2.5 MW

1.5 MW

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5 6

Type-I

Type-I/III

Type-III

PLT

H/P

thr

PLTH [MW]


Variation of H-factor as a function of PL/PT

Type III ELMs have lower confinementNo degradation of H-factor with decreasing PL/PT

TS with PL/PT<1.2 & H>1 have ne~8x1019m-3, N~1.5


0.6

0.8

1

1.2

1.4

1.6

0.6 0.8 1 1.2 1.4 1.6

Type-IType-I/IIIType-III

H98

Y2

PLTH/Pthr

0 10 20 30

Type-I/III

0 5 10 15 20

Type-III

0 20 40 60 80

Type-I

DIII-D and Alcator C-ModDIII-D and Alcator C-Mod

Confinement studies are performed atPL/PT ~ 1.5-2.5

In Alcator C-Mod, confinement studies are done for plasmas close the threshold power. This is due to the natural increase in density which follow the L-H transition

Dedicated experiments are currently performed


ELM typesELM types

Traditional ELM types:• Type III ELMs are found at powers close to PT, but confinement

low, H~1 cannot be reached • Type I ELMs have better confinement, H~1 is regularly

obtained, but input power must be significantly increased above PT. Intermediate ELM free phase has good confinement but is not stationary

Other H-mode regimes (grassy ELMs, type II ELMs, EDA, QH, no ELM

with RMP, …) ?• Reduced operational domain => Compatibility with ITER ?

Grassy: low e*, high , high q95 and high Type II: high density, high q95, high and high EDA: high q95, high and high QH: large gaps, RMPs: more in the type I domain

Literature give little detail on PL/PT …


Weak pointsWeak points

Little experience of tokamak operation close to threshold power (except Alcator C-Mod)• Recipes to obtain good confinement at low power not clearly

identified• Characteristics of such plasmas

Influence of the gas puffing• Recipes for gas puffing not always clearly described in the

literature• Impact of the gas puffing on the confinement

Behaviour at high density• back transition type I -> type III; H-L transition (hysteresis)

• Operational domain at high density Access to type I ELMs?


DiscussionDiscussion

Comments from devices

Pedestal: link between power, confinement, plasma parameters• Increase in power induces increase in total stored energy• Pedestal stored energy is proportional to the total stored energy• => Pedestal top pressure increases with the power

Requirements for RMP coil system to access better confinement

Polevoi’s comments: • Quantify PtI/PT density dependence• Quantify ne,crit for type I -> type III transitions• Change in scenario:

Enter H-mode at low density (0.5x1019m-3) Stay in type III ELMs Increase density Transition to type I ELMs


DiscussionDiscussion

Future plans• Explore PL/PT~1 operational domain

Existing discharges New dedicated experiments

• Determine requirements (plasma, heating scheme, scenario, …) to obtain H~1

• Test ITER scenarios (TC-2 JEX; link with hysteresis)


Documents

H-mode characteristics close to L-H threshold power ITPA T&C and Pedestal meeting, October 09, Princeton Yves Martin 1, M.Greenwald, A.Hubbard, J.Hughes,