R Sartori

ITER needs for power threshold to achieve good H-mode

R Sartori

R Sartori

This presentation is based mainly on JET results+ ASDEX Upgrade results presented at this H-mode workshop (F Ryter)

What is good confinement in this context (power requirements for ITER)

Operational space for Type III ELMs

Power requirements for Type I ELMy H-modes

Outline

R Sartori

What is good confinement?

“Good” confinement means highest likelihood to achieve H98=1

H98=1 is more likely in H-modes Type I ELMs than with Type III ELMs

Type III ELMs have on average lower confinement (H98~0.8)

ASDEX Upgrade data- F Ryter, H-mode workshop 2007

R Sartori

ELM Type (i.e.Type I ELMs vs Type III ELMs) is the only key parameter in this context

Confinement can be optimised in other ways (e.g triangularity) or depends on other variables (density)

Type III ELMs follow similar trends as Type I ELMs but with overall lower H98

What is good confinement?R Sartori PPCF 2004 G Saibene PPCF 2002

R Sartori

ITER standard scenario requires H98=1 requires “Type I ELMy like” confinement

Confinement scaling laws are derived form a database dominated by Type I ELMy H-modes

-Most devices also observe H-modes with Type III ELMs

-H98 is lower in Type III ELMy H-modes in JET and ASDEX Upgrade

Is H98 overall lower with in H-modes Type III ELMs also in other devices?

In which conditions the H-mode has Type III ELMs (operational space)?

Is there an additional power requirement above L-H threshold power for transition to Type I ELMy regime ?

What is good confinement?

Summary

R Sartori

Teped ~ 1/nped at low density/collisionality

JET: Type III ELM operational space

Boundary between Type III and Type I ELMy H-modes in pedestal ne-Te

Type III

Type I

ELMy H-mode, power scan

Plasma with ITB

ELMy H-mode, power scanR Sartori PPCF 2004

R Sartori

JET: Type III ELM operational space

Boundary between Type III and Type I ELMy H-modes in pedestal ne-Te

Te~ constant at high density/collisionality

ELMy H-mode, density scanJETL Horton, PPCF 1999

R Sartori

JET: Type III ELM operational space

Boundary between Type III and Type I ELMy H-modes in pedestal ne-Te

Compound ELMs

Interval of power exists where Type I and Type III ELMs coexist compound ELMs

Type I to III Degraded confinement loss of density

R Sartori

JET: Are all Type III ELMs the same?

Low and high density Type III ELMs

Common experimental observations

Same ELM frequency dependence on power !

H factor degraded compared to Type I ELMs

Smaller ELM size than Type I ELMs

Lower power above the L-H threshold power

Effect of isotopic mass

Experimentally observed differences

Low density increase of density at constant power triggers Type III to I transition

Low density Ip ramp down triggers Type III to I transition

Low density confinement degradation is due to loss of density

High density effect of collisionality

High density confinement degradation mainly due to loss of temperature

R Sartori

JET, ASDEX: Collisionality

Type III ELMs operational space depends on collisionality?

Low density behaviour of critical temperature (JET) suggests also a beta dependence

ASDEX-UJET

JET

Model based on resistive ballooning instability

Chankin, Saibene, PPCF 1999

F Ryter, H-mode Workshop 2007

Sartori, IAEA 2004

R Sartori

JET, ASDEX: Normalised beta

D McDonald, PPCF 2004

In JET Type III ELMs operational space is separated from Type I ELMs in normalised beta more than in ASDEX Upgrade

R Sartori

JET: Type III-Type I ELM threshold

Type I to Type III power threshold follows L-H like threshold scaling Ip /density, Bt (and mass) dependence

MarkII A

MarkII GB

PIN PL-H, with ranging from ~1.3 to ~2.5 required for Type I ELMy H-modes . Value of changes with triangularity (), density()/collisionality()

No scaling exists. No physics reason links the L-H and Type I threshold

R Sartori

JET: Type III-Type I ELM thresholdD:T

Power required for transition to Type I ELMy H-mode decreased proportionally to isotope mass

D:T

D:D

4.5 MA/3.45T

PIN>2.5 PL-H for low triangularity ne/nG=0.5 (20% radiation, 40% dW/dt between ELMs)NTM limited for q95<2.4

R Sartori

Is additional power above the threshold power required for Type I ELMy H-modes?

I think that there is no disagreement between JET and ASDEX- U results

JET Type-I ELMs requires power larger than ~1.3 to ~2.5 PL-H. Sufficient condition requires P> 2.5PL-H, but lower values are also possible ASDEX Upgrade this statement (JET) is sufficient (in ASDEX-U), but is not necessary, as Type-I ELMs also exist at lower values of P/PL-H.

It is possible to find lower values of P/PL-H required for Type I ELMs, but -how often ? -in which conditions?(In JET it is possible to obtain H=1 at ne/nG=1…..)

Conditions required to achieve Type I ELMs with low P/PL-H in ITER need to be specified, understood and extrapolated from present data.

Type III-Type I ELM threshold Summary

R Sartori

Type I/III transition: achievable density

It is not always easy to achieve high density with good confinement. Increased power affects this behaviour?

R Sartori

Confinement Both in JET and ASDEX Upgrade the confinement is statistically lower (~20%) in H-modes with Type III ELMs than in H-modes with Type I ELMs

Operational space JET Type III ELMs at low and high collisionalityASDEX Type III ELMS at high collisionalityNo full understanding of physics or scaling of domain of existence for Type III ELMs

Power requirementsWhich (if any) power above the threshold power for ITER? In JET the requirement P> 1.5PL-H is common and not conservative. And, for whichever reason, most machines do operate above this level. ASDEX-U? Other machines?

DensityIs there any link between the density that can be achieved with Type I ELM confinement and power requirements?

Summary

R Sartori

DD operation in ITER

Access to H mode in DD at full field and current could be marginal

R Sartori

1- Dedicated experiments in each machine, for example variation of Bt, Ip, n to determine power required for Type I ELMs to clarify relation with L-H threshold if any

Requires: Quasi steady phases, clear ELM classification, L-H threshold determination

2- Combined threshold/confinement experiment with N and scans

3-Inter machine experiments

Future experiments

R Sartori

Proposed JET experiment

2.2

1.8

2.0

1.6

1.4

4.54.03.52.5 3.0

Get discharge with Type I ELMs and best H-factor, N and explore ne range (4 levels)Keep N and explore ne range (3 levels) + exact * match

Select Ip so that N = 1.8 at ne = 0.7 nGW and explore ne

range (4 levels)Keep N and explore ne range (3 levels) + exact * match

Push to highest N in unfuelled conditions

Total number of discharges = 31

(q95 ~ 2.7-3)

I1= 2.3 MA

N

Ip(MA)

I2= 3.4 MA I3= 3.7-4.0 MA

R Sartori

If L-H or Type I threshold scaling has stronger negative * scaling than gyro-Bohm dimensionally similar path could change to follow the L-H/Type I scaling instead of gyro-Bohm like scaling increased power is required.

Which loss power is required to keep the non-dimensional parameters and * constant as * is decreased?

L-H/Type I threshold scaling

Gyro-Bohm scaling

Confinement studies: dimensionless scaling power requirements

G Petty, T Luce, NF 1997

R Sartori

At low density increase in density decreases the power threshold for Type I ELMs. Consistent with pedestal ne-Te boundary

Type III-Type I ELM threshold

MarkII GBMarkII A

R Sartori

At low density Ip ramp down at constant power produces transition to Type I ELMs (and Ip ramp up transition to Type III ELMs)

Type III-Type I ELM thresholdMarkII GB

R Sartori

ASDEX-U- Pressure gradient with Type III ELMs can be as high as with Type I ELMs, but pedestal T higher with Type I ELMs

L Horton, PPCF1999

R Sartori

DIII-D, Osborne, EPS 1997

Type III ELMs at low density disappear above a critical pressure gradient which scales as Ip

2