u u r r e e E E g g i i FOM-Institute for Plasma Physics Rijnhuizen l l o o a a C C r r e e lu lu t t a a s s l l t t ri ri e e Association Euratom-FOM T T r r TEC TEC Control of MHD instabilities by Electron Cyclotron Resonance Heating and Current Drive in TEXTOR Egbert Westerhof with thanks to: A. Lazaros, A. Merkulov, F.C. Schüller, I.G.J. Classen, M.R. de Baar, J.A. Hoekzema*, G.M.D. Hogeweij, R.J.E. Jaspers, H.R. Koslowski*, A. Krämer- Flecken*, N.J. Lopes Cardozo, J.W. Oosterbeek, J. Scholten , O. Zimmermann*, and the TEXTOR-team
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC This Talk • Will show that heating inside a magnetic island is the way in which 2/1 islands are stabilized in TEXTOR – Heating comes at no extra cost with ECCD – Extrapolation of our results to ITER: at least 20%, possibly 50% less power needed for stabilisation • Will show that sawteeth can be controlled with ECCD – Crash occurs when the shear exceeds a critical value (Porcelli …) – A criterion for the required current is provided by I cd > 2 ( ∆ r/r q=1 ) 2 I q=1
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC The Toolbox 140 GHz, 800 kW, 10 s Gycom gyrotron Flexible launcher: –vertical: -30 o tot +30 o –horizontal: -45 o tot +45 o TEXTOR tokamak R = 1.75, a= 0.46 Dynamic Ergodic Divertor 12/4, 6/2, 3/1 DC, AC 50Hz … 10 kHz
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC … and diagnostics • Interferometer • Electron Cyclotron Emission radiometers – ECE-I: talk by Ivo Classen on Wednesday morning • Soft x-ray camera • TV Thomson Scattering • Mirnov coils • Etc.
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Set up of m=2, n=1 tearing mode suppression experiment DED in 3/1 mode, AC 1 kHz – large 2/1 side band penetration stabilization B T = 2.25 T; I p = 300 kA n e = 2.0 10 19 m -3 ECE • ECRH at q=2 – 140 GHz, 770 kW sxr • We will use: w ECRH /w DED = ∆ T ECRH [%]/ ∆ T DED [%] resolution ~2cm
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Mode suppression for pure ECRH Deposition scan by • vertical inj. angle • ECE data consistent with sxr data
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Mode suppression by ECCD? • J cd,max at q=2 is 6% of J q=2 • Dominant effect for suppression is heating
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Dominance of heating confirmed by ECCD scan showing little effect • Reduced power, 200 kW, to enhance contrast • J cd,max at q=2 in scan is 3% of J q=2 co-drive counter-
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Gyrotron modulation in phase with DED • Magnetic islands are locked to DED, thus DED current can serve as reference signal for phase of island
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC O-point heating more effective than X-point
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Summary and conclusion from mode control Main observations: 1. Power must be deposited exactly at q=2; 2. Little or no effect from driven current; 3. Deposition at O-point more efficient than at X-point. • Conclusion : the 2/1 modes are suppressed by heating inside the island and by the temperature perturbation at the O-point that this produces – The temperature perturbation has been observed by ECE-I and TVTS see tomorrows talk by Ivo Classen
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Extrapolation to ITER • ITER will have 20 MW ECRH system for NTM stabilization • TORBEAM analyses of ITER UL designs show that on basis of ECCD NTM stabilisation can be achieved – Values for η NTM > 1 in all scenarios for RS-design, typically 1.8 times higher for FS-design • Present work completely neglects the effect of the concurrent heating • For χ e = 0.1 m 2 /s, the temperature perturbation in the island is predicted to be ~1 keV, and the effect of the heating is as large as the effect of the ECCD (RS). • For χ e = χ e,q=3/2 = 0.5 m 2 /s, still a 20% effect remains
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Set up of sawtooth control experiments • Slow magnetic field ramps to scan the EC deposition through the plasma • Change toroidal injection angle to vary EC driven current
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Experimental Data Analysis • Current Drive and Heating inseparable and both affect s.t. TORBEAM: ρ dep (t) • ECE (or sxr): τ saw (t) • Combine to find τ saw ( ρ dep ) • • Normalization to pure ECRH discharge gives the effect of the current drive: τ saw,ECCD / τ saw,ECRH ( ρ dep ) • To be compared with model estimate of driven current on evolution of shear at q=1
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Experimental Data Analysis II • TORBEAM estimates of the driven current I cd and profile width W cd • Account for profile broadening due to radial diffusion with D = 1 m 2 /s, or W D = 1 cm: W eff = (W cd 2 + W D 2 ) 0.5
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Example I: co-drive
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Example II: counter-drive I cd ≈ 2 ( ∆ r/r q=1 ) 2 I q=1 , marginal?
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC Summary and Conclusions from Sawtooth Control • Effect of current drive separated from effect of concurrent heating by normalization of sawtooth period response function on a discharge with pure heating • Effect on sawtooth period proportional to effect on shear evolution • In qualitative agreement with Porcelli’s critical shear sawtooth model • Required non-inductive current for sawtooth control scales like: I cd > 2 ( ∆ r/r q=1 ) 2 I q=1
E E u u r r e e g g i i l l o o a a C C r r e e lu lu t t a a Association Euratom-FOM Trilateral Euregio Cluster s s l l ri ri t t e e T T r r TEC TEC This Talk • Has shown that heating inside a magnetic island is the way in which 2/1 islands are stabilized in TEXTOR – Heating comes at no extra cost with ECCD – Extrapolation of our results to ITER: at least 20%, possibly 50% less power needed for stabilisation • Has shown that sawteeth can be controlled with ECCD – Crash occurs when the shear exceeds a critical value (Porcelli …) – A criterion for the required current is provided by I cd > 2 ( ∆ r/r q=1 ) 2 I q=1 • Establishes TEXTOR as an ideal tokamak for MHD experiments – because of its unique combination of tools
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