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

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

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

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  1. 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 local gas injection

  2. Outline 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 JET Tore Supra, C3 Tore Supra, C2 FTU, PAM

  3. +E0 -E0 Simplified image of the grill (JET example) In each waveguide: E(t)=E0sin(2pft+Dq), f = 3.7GHz Dq increases by 90o between each small waveguide Dq = 0 Dq = p/2 Dq = p Dq = 3p/2 BT t = 0 array of 32 waveguides IP e- Wave with l = 4 x width of waveguide = 4.5cm  n// = l0/l = 1.8

  4. Slow wave has cut-off for ω = 2f = 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 LH coupling depends on the density in front of grill ALOHA: D. Voyer, J. Hillairet et al. ALOHA ne = ncut-off For good LH performance: Sufficient density: ne > ncut-off Low reflection coefficient: RC < 5%

  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 PAM on FTU ncut-off ne 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)

  6. ITER far SOL is largely unknown Main plasma • Solution: 4 ne profiles (A. Loarte) • Near SOL: B2-Eirene • Scenario 2 & 4 • Far SOL extrapolation: 2 pinch velocitiesvx • Short SOL vx~30m/s • Long SOL vx~90m/s ncut-off (f = 5GHz) ne (m-3) Density at launcher mouth may vary by more than a factor 100.  Local gas puffing to ensure good coupling conditions.

  7. 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. Near gas feed was then installed for the LH launcher in JET L-mode LH GIM6 Same result as in ASDEX: coupling improvement with near gas feed.

  9. Now used routinely for LH in JET H-mode plasmas A. Ekedahl et al., PPCF, 51 (2009) Good LH coupling obtained at plasma-launcher distance up to 15cm, using local gas injection (GIM6) in H-mode plasmas. PLHCD (MW) RC (%) GIM6 12-13cm -2cm Da Reciprocating Langmuir probe measurements show a flattening of the SOL density profile.

  10. 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.

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

  12. 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 Da level.

  13. JET: Large neutral density improves LH coupling in H-mode Coupling maintained also at large divertor gas injection, high Da level.

  14. Are ITER gas injection locations suitable for LH coupling improvement? 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. GIM5 GIM8 GIM7 GIM6 LH IP, BT GIM5 GIM6 B A D C GIM7 GIM8 LH

  15. Gas injection from the top did not improve LH coupling GIM6 GIM6, GIM7 or GIM8 PLH RC H98 #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 Poor coupling when using top GIMs. Maybe a more favourable equilibrium exists  need new experiment to confirm.

  16. JET: New Da diagnostic viewing the launcher T Biewer Gas flow (1022 el/s) #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 GIM7, GIM8, GIM5 GIM6 GIM6 Launcher pressure (10-7 mbar) With GIM6 With GIM7, GIM8, GIM5 Time (s) Time (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.

  17. Summary • 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

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