Dynamic fuel retention and release under ITER like wall conditions in JET

Dynamic fuel retention and release under ITER like wall conditions in JET V. Philipps1, T. Loarer2, M. Freisinger1, H.G.Esser1, S. Vartanian2, U. Kruezi3, S. Brezinsek1, G. Matthews3 and JET EFDA contributors

JET-EFDA, Culham Science Centre, OX14 3DB, Abingdon, UK1Forschungszentrum Jülich, Association EURATOM – FZJ, Jülich, Germany 2CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3EURATOM/UKAEA Fusion Association, Culham Science Centre, UK. * See the Appendix to paper by F. Romanelli et al., Fusion Energy 2010 (Proc. 23st Int. Conf. Daejon, Republic of Korea, 2010) IAEA, Vienna 2010.

Background and MotivationBackground and Motivation JET with ITER-Like WallJET with ITER-Like Wall

Analysis of T retention under ITER like wall conditions is main objective of the JET ILW project .

Long term fuel (tritium) retention studied by gas balances using cryopump regeneration. Reduction of a factor >10 compared with C walls

This study: dynamic fuel retention (hydrogen retained during plasma operation and released in between discharges and over longer times (night etc.)

DiagnosticDiagnostic calibrated gas injection (JET GIMS)

Neutral pressure measurements in main chamber ( pennings) and subdivertor (baratrons)

Support form mass spectrometer data

Cross calibration of pennings versus baratrons

Consistency check: matching of particle balance in gas injection only ( no plasma)

Becoating

on Inconel

Bulk Be

Bulk W

Wcoating on CFC

Diverted plasma conditions Diverted plasma conditions Dynamic retention in Be walls ( limiter Dynamic retention in Be walls ( limiter

discharges)discharges)

82590 82600 82610 82620 826300

1x1020

2x1020

3x1020

4x1020

5x1020

6x1020

7x1020

8x1020

Shot Number

52 s

ec [7

.698

9e+02

0]

-8x1019

-7x1019

-6x1019

-5x1019

-4x1019

-3x1019

-2x1019

-1x1019

0

D

Wal

l re

ten

tio

n (

D/s

ec)

Gra

die

nt

of

rete

nti

on

(D

/sec

)

Initial wall retention rate (flat top density)

Gradient of retention (avarage over 5 sec)

Retention rate

Gradient

• Example of a long term limiter shot

• no sign of saturation

• 3x1022 D shot-end retention

40 50 60 700,0

0,5

1,0

0123

0

2

4

0

2

4

Plasma content

Wall retention

Cumulative injection

Subdivertor pressure

D x

10

23D x

10

21

D x

10

21

X 1

0-3 m

bar

Injection (circles) release until 770 sec (triangles) ,Extrapolated until next shot (squares)

Regeneration

Good agreement→ all dynamic retention released 82590 82600 82610 82620 82630

0

2

4

6

8

10

12

14

Inje

ctio

n (bar

l)

Shotnumber

injection

Release

Cryopump regeneration

Integral deuterium injection (dynamic wall retention in absence of pumping) and particle release for all limiter shots (limiterdatabase)

Retention at shot end up to 3x 10 22

• Strong wall retention in start of divertor phase

• Fast decay within few sec • ≈100% of retained deuterium released

in between shots (within data accuracy )

• Dverted plasmas: plasma interaction largely with W surfaces (+Be-deposits)

• reduced contact with Be walls

Stronger initial retention in divertor phase

Decay phase (1.4→ 0.4 x 1021/sec)

Flat phase : 4x 1020 D/sec No saturation

L-mode diverted, no cryopump active

0

2

4

6

Wal

l ret

enti

on

(x

1021

#/s

ec)

0

2

4

6

(x 1

021 )

Retention rate

Plasma content

40 45 50 55 60 65 700,0

0,5

1,0

1,5

2,0

2,5

(x

1022

D-a

tom

s)

Time

Cumulative retention

Limiter phase

Divertor phase

80655 80660 80665

0

4

8

12

16

20

24

Am

ount of gas ( b

arl

)

shotnumber

L-mode with cryopump

Injection

cryyopumping

Release after shot≈ dynamic retention

regeneration

With cryopump active, most injected D is pumped by cryopumps Evaluation of dynamic wall retention has larger uncertainty ( mismatch of regegeneration and integrated pressure data

Transient dynamic retention (> 1023 D-atoms, partly released during shot

100 1000 100001E-11

1E-10

1E-9

Ma

ss

4 s

ign

la (

arb

it u

n.)

Time after discharge (s)

Particle ( D) release after shots follows a power law

t– 0.7 ±0.1

t – 0.7 ±0.1

• Transient wall retention in density ramps with fast release during shot

• Particle release after shot with power law t– 0.7 ±0.1 for long times

• Reproducible retention of Be-walls ≈1.5 -0.4 x1021 D/sec (flat top, no memory effect of previous shots)• Retention rate decreases only slightly with time ( 0-8 % /sec) , no saturation in JET time scales • D-release behavior after discharge ≈ t– 0.7 ±0.1 (very similar to C wall conditions) • Nearly all dynamically retained D is released in between shots (within data accuracy) • Be retention will provide sufficient wall pumping for start up phase in ITER

Wall retention during limiter and divertor phase

Injection

Release 740 sec and til next shot

Limiter

Divertor

0,0

0,5

1,0

1,5

2,0

Re

ten

tio

n ( x

10

22 D

-at.)

81940 81950 81960 819700

4

8

12

16

Am

ou

nt

of

ga

s (

ba

rl)

shotnumber

Injection and release (740 sec and extrapolated to next shot ) + cryopump

regeneration

X 1

021

D-a

tom

s x

1022

D-a

tom

s x

1023

pre

ssur

e (m

bar)

82305

0

2

4

6

-8

-4

0

4

40 45 50 55 60 650,000

0,004

0,008

40 45 50 55 60 65 700,0

0,4

0,8

1,2

a b

c d

Time ( sec)

Plasma content

Div pressure

Retention rate

Total retention

40 45 50 55 60 65 70 75 80

0,0

0,2

0,4

0

1

2

0

1

2

012

(x 1

022 )

(x 1

021 /s

ec )

(x 1

0-3 m

bar )

Div pressure

Retention rate

Cumulative retention

Plasma content

30 consecutive repredocucible limiter shots

Time ( sec)

Time ( sec)

Typical shot

AcknowledgementsThis work was supported by EURATOM and carried out within the framework of theEuropean Fusion Development Agreement. The views and opinions expressed herein do

not necessarily reflect those of the European Commission.