understanding physics issues of relevance to iter · 2011-11-30 · p.mantica jet anniversary 20th...

JET anniversary 20th May 2004P.Mantica 1/20

Understanding physics issuesof relevance to ITER

• Brief summary of ITER relevant physics issues addressed at JET

• Detailed example: recent improvements in the understanding of transport and confinement

presented by P. ManticaIFP-CNR, Euratom/ENEA-CNR Association, Milano, Italy

on behalf of contributors to the EFDA-JET Work Programme

JET Anniversary P.Mantica 2/20

JET as a bridge to ITERJET is the tokamak nearest to ITER in size and achievable plasma parameters.

This allows

the best confidence in the extrapolation of results;

to carry out physics studies that are not possible in other machines;

to act as a focus for EU fusion research favouring exchange of results from various groups and the build-up of a EU team.


ITER relevant physics issues addressed at JET

Disruptions

Edge Localized Modes

Stabilization of MHD activity

Burning plasma physics

Tritium retention and migration

Understanding energy and particle transport


Why is understanding transport important?

Progress towards ignition relies on improving energy and particle confinement.

Understanding transport physics allows to control transport.


What do we need to understand?Transport is measured to be well above the levels foreseen by theory of neoclassical collision processes ==> “anomalous transport”

The anomaly comes from the existence of turbulence processes

Electrostatic fluid turbulence simulation

hat type of instabilities e the main players?

w do we control them?

D.McDonald


Current predictions of ITER performance assume a flat density profile

a 20% gain in central density would bring a 40% increase in fusion power

Particle and impurity transport

Density peaking

Pfus ~ nD nT

D and T transport

Impurity accumulation

He ash removal

JET has unique capability to study differences between T and D transport

Outward convection

0

1

4 5 6 7 8

n e (1

020 -

3 )

Major radius (m)

JG04

.169

-7c


Is an anomalous pinch predicted by theory?

Does an anomalous pinch exist in experimental data?

Anomalous Curvature Thermo- Warediffusion driven pinch diffusion Pinch

Density peaking: anomalous pinch or not?


Theoretical predictions from turbulence simulations

X. Garbet

• electrostatic turbulence simulations indicate curvature pinch

• Thermo-diffusion changes sign when ∇Te/∇Ti is increased

0.6

0.4

0.2

0.00.80.60.40.2

Spe/Spi τe 0.5 2.0 1.0 2.7 2. 3.2 TEP

ρ

ne-n95

electron heating

No core particle source nor Ware pinch

==> no flattening due to αparticle electron heating expected in ITER plasmas dominated by Ion Temperature Gradient modes

ion heating

JET anniversary 20th May 2004P.Mantica 10/20H.Weisen / A. Zabolotsky

Curvature driven pinch in L-mode

No core particle source nor Ware pinch, still peaked ne

Peaked density in H-mode at low collisionality

Experimental results

Current peaking

Den

sity

pea

king

Strong dependence on collisionality


Tritium transport studiesT penetration after trace T gas puff in D plasma is resolved by powerful 14 MeV neutron diagnostics

T transport investigatedin all main JET plasma regimes, clarifying several physics issues for particle transport.

Dependence on ρ* can be assessedB τp

T ~ ρ*-2.9

Anomalous pinch present also for T transport

L.Bertalot


Impurity accumulationOccurs when impurity transport is neoclassical and the density gradient is peaked

Control of impurity accumu-lation as well as He ash removal is a result of control of density peaking.Method: application of central ion heating through RF in ITG dominated plasmas. Reduction of v observed.

No ICRH2 MW ICRH

Ar d

ensi

ty

M.E. Puiatti


Heat transport

Confinement scaling laws

Turbulence stabilization

Formation of Internal Transport Barriers

Temperature profile stiffness

How to stabilize turbulence and attain higher ∇T/T

Turbulence limits attainable ∇T/T

τE,th = 0.0562 M0.19κa0.78R1.39a0.58Ip

0.9 BT0.15ne

0.41P-0.69

ITPA

ITER 98

ITER


Dimensionless Scaling Laws

Dimensionless form of ITER 98 scaling law

BτE~ρ*-2.7 β-0.9 ν*

0.0

New results from JET

τE= τB ρ*a βb ν*

c τE= τB 1/ρ* βb ν*c

gyroBohm scaling

BτE~ρ*-2.7 β0 ν*

-0.35

needs to be confirmed by fut higher power experiments

gyroBohm scaling law, e collisions

0

5

10

15Pr

ojec

ted

Fusi

onPe

rform

ance

βN

Conventionalprediction

0 1 2 3

Ipu

= JET= DIII–D

20

G.Cordey, C.Petty


Turbulence and transport increase above a threshold value of ∇T/T preventing to reach high values of ∇T/T

Temperature Profile Stiffness

0.1

100

0 0.2 0.4 0.6 0.8 1

ρ

Assuming T profile

P.Mantica

A gain in threshold or an attenuation of the stiffness factor imply a gain in ITER central temperature/fusion power or alternatively allow a less demanding constraint on pedestal heigth.


A powerful tool to study

stiffness: power

modulation

Modulation data allow a stringent test of transport models and their validation for extrapolation to ITER predictions

P.Mantica


Results

• Coupled IonTemperature Gradient and Trapped Electron Modes are the main players. Stiffness models can be discriminated.

P.Mantica

Critical thresholdElec

tron

hea

t flu

xWeaker stiffness for dominant electron heatingStronger

stiffness with ion heating


One solution to overcome stiffness: Transport BarriersTransport barriers are regions where turbulence is stabilized and consequently transport is reduced.

ExB flow shear

Negative magnetic shear

X.Garbet

Turbulent vortices are broken and transport reduced

r

r

q q

r

zITB1

00.80.60.4

T

r/a

L RS q min =1.35 RS q min =1.5


JET has shown the importance of q profile for ITB triggering in large machines

Stabilizing effect of negative shear on electrons and ionsradius radius

0 0.2 0.4 0.6 0.8 1

Ion

tem

p er a

t ur e

(k e

V )

q

C.Challis


CONCLUSIONSJET is providing important information to clarify several ITER relevant transport issues due to

Continuing JET operation during ITER construction would allow significant progress in physics understanding, thereby making use of ITER more effective

• Proximity to ITER range of ρ*,ν*,β• T injection facility• Good diagnostic capabilities• Flexibility of heating systems

understanding physics issues of relevance to iter · 2011-11-30 · p.mantica jet anniversary 20th...

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