1. 1 Garching, 20/3 2009EFDA Fuelling Meeting A Ekedahl 1, M Goniche 1, G Granucci 2, J Mailloux 3, V Pericoli 4, V Petrzilka 5, K Rantamäki 6, 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 local gas injection

2. 2 Garching, 20/3 2009EFDA Fuelling Meeting 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

3. 3 Garching, 20/3 2009EFDA Fuelling Meeting Simplified image of the grill (JET example) In each waveguide: E(t)=E 0 sin(2  ft+  ), f = 3.7GHz  increases by 90 o between each small waveguide t = 0  = 0  =  /2  =  = 3  /2 Wave with = 4 x width of waveguide = 4.5cm  n // = 0 /  = 1.8 BTBT +E 0 -E 0 array of 32 waveguides IPIP e-e-

4. 4 Garching, 20/3 2009EFDA Fuelling Meeting Slow wave has cut-off for ω = 2  f = ω pe below which wave is evanescent. –Wave has to tunnel through the evanescent region to the cut-off –For f = 3.7GHz (JET, TS)  n cut-off = 1.7*10 17 m -3 Everything that affects the SOL affects the LH coupling: –plasma edge density –plasma-launcher distance –connection length in front of the grill, q 95 –ELMs –ICRH power on magentically connected antenna n e = n cut-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: n e > n cut-off Low reflection coefficient: RC < 5%

5. 5 Garching, 20/3 2009EFDA Fuelling Meeting 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 n cut-off nene PAM on FTU In ITER, f = 5GHz  n cut-off = 3.1*10 17 m -3 Poor coupling for n e below ~ 1*10 17 m -3 V. Pericoli et al., Nucl. Fusion 45, 1085 (2005)

6. 6 Garching, 20/3 2009EFDA Fuelling Meeting 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 n e profiles (A. Loarte) Near SOL: B2-Eirene –Scenario 2 & 4 Far SOL extrapolation: 2 pinch velocities v x –Short SOL v x ~30m/s –Long SOL v x ~90m/s n cut-off (f = 5GHz) n e (m -3 )

7. 7 Garching, 20/3 2009EFDA Fuelling Meeting 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

8. 8 Garching, 20/3 2009EFDA Fuelling Meeting 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

9. 9 Garching, 20/3 2009EFDA Fuelling Meeting Reciprocating Langmuir probe measurements show a flattening of the SOL density profile. P LHCD (MW) D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)

10. 10 Garching, 20/3 2009EFDA Fuelling Meeting JET: LH power assists in increasing the SOL density M. Goniche et al., PPCF 51, (2009) Reciprocating Langmuir probe measurements show increase in J sat with LH power.

11. 11 Garching, 20/3 2009EFDA Fuelling Meeting Tore Supra: Large neutral density improves LH coupling (L-mode) J. Mailloux et al., 25 th EPS Conf., Prague (1998) Tore Supra C2 launcher LH coupling at plasma-launcher distance up to 14.8cm in TS L-mode plasmas.

12. 12 Garching, 20/3 2009EFDA Fuelling Meeting 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.

13. 13 Garching, 20/3 2009EFDA Fuelling Meeting JET: Large neutral density improves LH coupling in H-mode Coupling maintained also at large divertor gas injection, high D  level.

14. 14 Garching, 20/3 2009EFDA Fuelling Meeting Are ITER gas injection locations suitable for LH coupling improvement? B A D C LH GIM6 GIM7GIM8 I P, B T GIM6 LH GIM5 GIM8GIM7 GIM5 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.

15. 15 Garching, 20/3 2009EFDA Fuelling Meeting 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 P LH RC H98 GIM6GIM6, GIM7 or GIM8 Maybe a more favourable equilibrium exists  need new experiment to confirm. Poor coupling when using top GIMs.

16. 16 Garching, 20/3 2009EFDA Fuelling Meeting 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. Gas flow (10 22 el/s) GIM6 GIM7, GIM8, GIM5 Launcher pressure (10 -7 mbar) GIM6 With GIM6 With GIM7, GIM8, GIM5 Time (s) T Biewer

17. 17 Garching, 20/3 2009EFDA Fuelling Meeting  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