MODELLING OF TIME DEPENDENT HIGH Q OPERATIONAL SCENARIO FOR ITER-LIKE DEVICE.

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MODELLING OF TIME DEPENDENT HIGH Q OPERATIONAL SCENARIO FOR

ITER-LIKE DEVICE.

V.M. Leonov

Nuclear Fusion Institute, RRC “Kurchatov Institute”, Moscow, Russia.

ITPA Confinement Database and Modelling Topical Group 3d Meeting, 21-23 October 2002, Cadarache, France.

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Motivation

One of the ITER goals is “to explore the possibility of high-Q

operation if favourable confinement conditions can be achieved”.

High-Q operation is interesting for investigations of burning

stability, control of plasma parameters and burning conditions

by different feedback loops at the small Paux 0.

RUSSIAN RESEARCH CENTRE «KURCHATOV INSTITUTE»

NUCLEAR FUSION INSTITUTE

3d ITPA Meeting (Conf. DB and Modelling) 21-23 Oct. 2002, Cadarache.

V. Leonov: Modelling of High-Q Scenario

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Issues

Analysis of ITER operational diagrams show that for

high Q (Paux 0) operation it is desirable to have:

--- plasma current higher than 15MA (q<3) (MHD stability-?)

--- enhanced density (close to the Greenwald limit) (E (n) - ?)

--- enhanced confinement (RS regimes with ITB) (Paux = 0 -?).

The subject of this work is to investigate the possibility of

ITER operation in enhanced confinement regime with ITB

at Paux = 0 during the time ~ some hundreds sec ( >> E ).

(to test burning dynamics and possibility to control performance and plasma

parameters in regimes with Paux= 0 ).





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Simulations show that RS configuration can’t be achieved

by bootstrap current only and some auxiliary off-axis CD (or Paux)

is necessary. It does difficult to achieve high Q values

but ...

... the main idea:

To use very long skin time (~ 3000s) which >> E (~ some s).

If the RS configuration is once achieved on the initial stage of the

discharge the operation in this configuration with the enhanced

confinement can be then continued for some hundred sec during

j(r) profile reorganization at Paux = 0.





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-0,2

0,0

0,2

0,4

0,6

0

100

200

300

0

5

10

15

0

2

4

6

8

10

Ulo

op (

V)

Uloop

Ip

I p (M

A)

Paux

Pfus

P fus (

MW

)

020406080100

P aux (

MW

)

<Te>

<n e>

<Ti>

<T>

(keV

)

02468101214

<n

e> (

1019

m-3)

0,0

0,5

1,0

1,5

li3

p

p

0,0

0,5

1,0

1,5

l i3

0123456

q 0

q min

q

q95

-200 0 200 400 600 800 1000 1200

time (s)

Example of simulation of plasma parameters evolution for WNS-like scenario after switch on Paux and <ne>.

Time of j(r) profile reorganization

~ 3000 s





0,0 0,2 0,4 0,6 0,8 1,00

1

2

3

4

>3000s

200s

1600s

800s

t = 0

q

(see also D.Moreau, I. Voytsekhovitch Nucl. Fus.V.39 (1999), 685)

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In D.Moreau, I. Voytsekhovitch paper (Nucl. Fus.V.39 (1999), 685) strategy of the initial stage of the discharge (which consists of some stages) with the total time duration ~ some thousand sec is suggested.

This strategy for discharges with a plasma current flat-top ~ some hundred sec (as in our case) is not effective.





We use other strategy including a simultaneous ramp-up of the plasma current in accordance with the plasma minor radius and plasma density increase which gives possibility to decrease time of j(r) profile formation to some tens sec (in our case ~ 50 s). (In this case profile forms layer after layer)

J(r)

rmax

0 0.5 1

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The model :1.5D ASTRA transport code : 2D equilibrium + 1D transport

i,e =i,e,o f (). Fi, e (S) + i,e

neo, D = Dof ().Fe(S) io = eo = Deo

f () = 1 + 3.2 - radial dependence, DHe= e , Vp= Vp He= 0

Fi, e (S) = exp{4. (S-1)}/(1 + exp{4. (S-1)}) , S = r .(q`/ q)

eo is fitted to provide E=scaling (OH, L or H-98(y2))

Boundary conditions : on the basis of B2-Eirine results approximation:

(Ts/1eV)3/2ns/1019m-3=90 Ploss/1MW

Thermalized Helium pumping speed: to produce He/E = 5.

Impurity: in the coronal approximation

Mean plasma density : is controlled by the gas puff in the kinetic approach.

H & CD : NBI, ECR, LH





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0,0

0,1

0,2

0,3

0,4

0,5

0,6

0

100

200

300

400

500

600

0

5

10

15

0

5

10

15

Ulo

op (V

)

Wth

Uloop

Ip

I p (M

A)

Paux

Pfus

PauxP fu

s (M

W)

0

20

40

60

80

100

P aux (M

W)

PLH

N

<Te>

n C

<Ti>

<T>

(keV

)

0

1

2

3

4

P loss/P

LH-t

hr

0

2

4

6

8

10 <ne>

<ne>

(10 1

9 m -

3 )

0

200

400

600

Wth (M

J)

0 50 100 150 200 250 3000

20

40

60

80

100

n Ar

P (M

W)

Prad

Ploss

time (s)

0,00,10,20,30,40,50,6

n Ar (

%)

0,0

0,2

0,4

0,6

0,8

1,0

li3

p

p

0,0

0,5

1,0

l i3

0

1

2

3

4

E

024681012

E (

s)

0,0

0,5

1,0

1,5

2,0

Zef

f

Zeff

fHe

0

2

4

6

8

10

12

f He,

f C

(%)

0

2

4

6k

q

a

q95

0

1

2

a (

m),

k

0 50 100 150 200 250 3000

5

10

15

20

25

res (W

b)

res

time (s)

0,00

0,05

0,10

0,15

0,20

0,25

High-Q operational scenario

with RS configuration

Pfus feedback control by ne (Paux=0)

ne feedback control by fuelling

Ploss feedback control by Ar seeding





t = 250 s R (m) / a (m) 6.2 / 2.0 k95 / 95 1.7 / 0.33 BT (T) / Ip (MA) 5.3 / 15.0 q95 3.6<ne> (1019m-3) / (n / nGr) 10.0 / 0.84<Ti > / <Te> (keV) 12.2 / 11.2< T > ( % ) / N 3.56 / 2.53 Pfus (MW) 628 Paux (MW) 0 Q = Pfus / Paux

P loss(MW) / P rad (MW) 74.9 / 52.1 Ploss / P L-H-thr 1.55 fHe (%) / fBe (%) 7.4 / 2 fAr (%) 0.1 Zeff (ave) 1.68

E (s) 4.8HH-98 (y2) 1.3

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Radial profiles during high-Q operation





t = 250 s (end of high-Q operation)

t = 70 s (start of high-Q operation)

0,0 0,2 0,4 0,6 0,8 1,00

5

10

15

20

25

0,0 0,2 0,4 0,6 0,8 1,00

1

2

3

4

5

Te

Ti T

(keV)

q

0,0 0,2 0,4 0,6 0,8 1,00

10

20

30

40

500,0 0,2 0,4 0,6 0,8 1,00

1

2

3

4

5

Te

Ti

T (keV)

q

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CONCLUSIONS

Operational strategy including j(r) profile formation layer after layer by

ramp-up of the plasma current simultaneously and in accordance with the

increase of plasma minor radius gives possibility to decrease time of j(r) profile formation to some tens sec.

Long time scale of j(r) profile reorganization gives possibility after

the achieving of RS configuration to work in this configuration some hundreds sec with enhanced confinement at very high Q (Paux= 0).

Simulations demonstrates possibility to control fusion power, plasma

density, power losses to the divertor and some other parameters by

feedback loops in high-Q regime at Paux = 0.





MODELLING OF TIME DEPENDENT HIGH Q OPERATIONAL SCENARIO FOR ITER-LIKE DEVICE.

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