A Ekedahl 1 , M Goniche 1 , G Granucci 2 , J Mailloux 3 , V Pericoli 4 ,

1Garching, 20/3 2009 EFDA Fuelling Meeting

A Ekedahl1, M Goniche1, G Granucci2, J Mailloux3, V Pericoli4, V Petrzilka5, K Rantamäki6, JET-EFDA contributors,

and many more…

1 CEA, IRFM, 13108 St Paul-lez-Durance, France

2 Associazione Euratom-ENEA sulla Fusione, IFP-CNR, Via R. Cozzi, 53 - 20125 Milano, Italy

3 Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

4 EFDA

5 Association Euratom-IPP.CR, Za Slovankou 3, P.O.Box 17, 182 21 Praha 8, Czech Republic

6 Association Euratom-Tekes, VTT, P.O. Box 1000, FI-02044 VTT, Finland

LH coupling improvement with LH coupling improvement with

local gas injectionlocal gas injection


1. Introduction to LH and wave coupling

2. Experimental results on LH coupling with local gas puffing

3. Comparison of different gas puff locations, in view of ITER

4. Summary

Outline

Tore Supra, C3

Tore Supra, C2

FTU, PAM

JET


-5

0

5

array of 32 waveguides

E (

kV

/cm

)

Simplified image of the grill (JET example)

In each waveguide: E(t)=E0sin(2ft+), f = 3.7GHz increases by 90o between each small waveguide

t = 0 = 0 = /2 = = 3/2

-5

0

5


E (

kV

/cm

)

-5

0

5


E (

kV

/cm

)

-5

0

5


E (

kV

/cm

)

-5

0

5


E (

kV

/cm

)

-5

0

5


E (

kV

/cm

)

Wave with = 4 x width of waveguide = 4.5cm n// = 0/= 1.8

BT

+E0

-E0

array of 32 waveguides IPe-


Slow wave has cut-off for

ω = 2f = ωpe below which wave is evanescent.

– Wave has to tunnel through the evanescent region to the cut-off

– For f = 3.7GHz (JET, TS) ncut-off = 1.7*1017m-3

Everything that affects the SOL affects the LH coupling:

– plasma edge density– plasma-launcher distance– connection length in front of

the grill, q95

– ELMs– ICRH power on magentically

connected antenna

ne = ncut-off

ALOHA: D. Voyer, J. Hillairet et al.

ALOHA

LH coupling depends on the density in front of grill

For good LH performance:

Sufficient density: ne > ncut-off

Low reflection coefficient: RC < 5%


Prediction of coupling for an ITER-like LH launcher (PAM)

J.Hillairet (CEA) & O.Meneghini (MIT)

LH coupling codes ALOHA (CEA) and TOPLHA (Politecnico di Torino) have been cross-checked for different types of LH launchers.

Good agreement between the codes tools for predicting LH coupling for an ITER LH launcher.

f = 3.7GHz

ncut-off ne

PAM on FTU

In ITER, f = 5GHz ncut-off = 3.1*1017m-3

Poor coupling for ne below ~ 1*1017m-3

V. Pericoli et al., Nucl. Fusion 45, 1085 (2005)


0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.1610

15

1016

1017

1018

1019

1020

x (m)

n (m

-3)

Sc2 long Sc4 long Sc2 shortSc4 short

Far SOL Near SOL

Antenna mouth Separatrix

ITER far SOL is largely unknown

Density at launcher mouth may vary by more than a factor 100. Local gas puffing to ensure good coupling conditions.

Main plasma

•Solution: 4 ne profiles

(A. Loarte)

•Near SOL: B2-Eirene

– Scenario 2 & 4

•Far SOL extrapolation:

2 pinch velocities vx– Short SOL vx~30m/s

– Long SOL vx~90m/s

ncut-off (f = 5GHz)

ne

(m-3)


ASDEX: near gas valve helped maintaining LH coupling

F. Leuterer et al., PPCF 33, 169 (1991)

With gas valve near launcher

With gas valve far from launcher

Plasma-launcher distance


Near gas feed was then installed for the LH launcher in JET

LH

GIM6

Same result as in ASDEX: coupling improvement with near gas feed.

L-mode


Reciprocating Langmuir probe measurements show a flattening of the SOL density profile.

PLHCD (MW)

D

12-13cm

-2cm

GIM6

Now used routinely for LH in JET H-mode plasmas

RC (%)

Good LH coupling obtained at plasma-launcher distance up to 15cm, using local gas injection (GIM6) in H-mode plasmas.

A. Ekedahl et al., PPCF, 51 (2009)


JET: LH power assists in increasing the SOL density

M. Goniche et al., PPCF 51, (2009)

Reciprocating Langmuir probe measurements show increase in Jsat with LH power.


Tore Supra: Large neutral density improves LH coupling (L-mode)

J. Mailloux et al., 25th EPS Conf., Prague (1998)

Tore Supra C2 launcher

LH coupling at plasma-launcher distance up to 14.8cm in TS L-mode plasmas.


JT60-U: Large neutral density improves LH coupling (H-mode)

S. Ide et al., Nucl. Fusion 40, 445 (2000)

Coupling maintained at larger distance in plasmas with higher D level.


JET: Large neutral density improves LH coupling in H-mode

Coupling maintained also at large divertor gas injection, high D level.


Are ITER gas injection locations suitable for LH coupling improvement?

B A D C

LH

GIM6

GIM

7

GIM

8

IP, BT

GIM6 LH

GIM5

GIM8GIM7

GIM

5

Similar layout of top gas injections in JET as those foreseen for ITER.

Experiment to compare top gas injections with GIM6 has been carried out in JET.


Gas injection from the top did not improve LH coupling

#76047: GIM6 = 6.5 and 4*10e21 el/s#76048: GIM7 = 9 and 6*10e21 el/s#76050: GIM8 = 10 and 6.5*10e21 el/s

PLH

RC

H98

GIM6 GIM6, GIM7 or GIM8

Maybe a more favourable equilibrium exists need new experiment to confirm.

Poor coupling when using top GIMs.


JET: New D diagnostic viewing the launcher

#76047: GIM6 = 6.5 and 4*10e21 el/s#76048: GIM7 = 9.0 and 6*10e21 el/s#76050: GIM8 = 10 and 6.5*10e21 el/s#76051: GIM5 = 9.5 and 6*10e21 el/s

Higher neutral pressure in the launcher with GIM6.

Somewhat higher D signal with GIM6,

but note that the diagnostic is not viewing the relevant part of the launcher.

Ga

s f

low

(102

2 e

l/s

)

GIM6

GIM7, GIM8, GIM5

La

un

ch

er

pre

ss

ure

(1

0-7 m

ba

r)

GIM6

With GIM6

With GIM7, GIM8, GIM5

Time (s) Time (s)

T Biewer


Experiments on JET, and ASDEX, indicate that LH coupling improvement with gas injection is a local effect. For the same central density, different gas injection location gives different LH coupling.

Experiments also show that LH coupling also depends on the wall conditions and on the LH power (TS, JT-60U, JET).

The LH power seems to plays a role in the ionisation process. Possible mechanism is through the fraction of LH power (~1%) which is lost at the plasma edge and known to cause electron acceleration and hot spots.

In order to guarantee the LH coupling in ITER in all conditions, a dedicated local gas feed seems necessary.

However, poor knowledge of ITER SOL parameters and poor level of modelling of existing experiments, make it difficult to optimise the design (toroidal and raidal location).

Diagnostics for the far SOL are crucial in the experiments (neutral density, electron density and temperature profiles) and the modelling needs to be improved…

…Next talk

Summary

A Ekedahl 1 , M Goniche 1 , G Granucci 2 , J Mailloux 3 , V Pericoli 4 ,

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