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ITER needs for power threshold to achieve good H-mode. R Sartori. Outline. 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)

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Presentation Transcript
slide2

Outline

  • 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
slide3

What is good confinement?

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

  • “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)
slide4

What is good confinement?

R Sartori PPCF 2004

G Saibene PPCF 2002

  • 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
slide5

What is good confinement?

Summary

  • 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 ?
slide6

JET: Type III ELM operational space

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

R Sartori PPCF 2004

ELMy H-mode, power scan

ELMy H-mode, power scan

Plasma with ITB

Type III

Teped ~ 1/nped at low density/collisionality

Type I

slide7

JET: Type III ELM operational space

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

ELMy H-mode, density scan

L Horton, PPCF 1999

JET

Te~ constant at high density/collisionality

slide8

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

slide9

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
slide10

JET, ASDEX: Collisionality

JET

ASDEX-U

Sartori, IAEA 2004

F Ryter, H-mode Workshop 2007

Model based on resistive ballooning instability

Type III ELMs operational space depends on collisionality?

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

JET

Chankin, Saibene, PPCF 1999

slide11

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

slide12

JET: Type III-Type I ELM threshold

MarkII GB

MarkII A

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

  • 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
slide13

JET: Type III-Type I ELM threshold

D:T

D:D

D:T

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

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

4.5 MA/3.45T

slide14

Type III-Type I ELM threshold

Summary

  • 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 powerlarger 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.
slide15

Type I/III transition: achievable density

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

slide16

Summary

  • 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 collisionality
  • ASDEX Type III ELMS at high collisionality
  • No full understanding of physics or scaling of domain of existence for Type III ELMs
  • Power requirements
  • Which (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?
  • Density
  • Is there any link between the density that can be achieved with Type I ELM confinement and power requirements?
slide17

DD operation in ITER

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

slide18

Future experiments

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

slide19

Proposed JET experiment

bN

Total number of discharges = 31

(q95 ~ 2.7-3)

Push to highest bN in unfuelled conditions

2.2

Select Ip so that bN = 1.8 at ne = 0.7 nGW and explore ne range (4 levels)

2.0

Keep bN and explore ne range (3 levels) + exact n* match

1.8

Get discharge with Type I ELMs and best H-factor, bN and explore ne range (4 levels)

1.6

Keep bN and explore ne range (3 levels) + exact n* match

1.4

I1= 2.3 MA

I2= 3.4 MA

I3= 3.7-4.0 MA

Ip(MA)

2.5

3.0

3.5

4.0

4.5

slide20

Confinement studies: dimensionless scaling  power requirements

L-H/Type I threshold scaling

Gyro-Bohm scaling

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

G Petty, T Luce, NF 1997

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.

slide21

Type III-Type I ELM threshold

MarkII A

MarkII GB

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

slide22

Type III-Type I ELM threshold

MarkII GB

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

slide23

L Horton, PPCF1999

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

slide24

DIII-D, Osborne, EPS 1997

Type III ELMs at low density disappear above a critical pressure gradient which scales as Ip2