Control of MHD instabilities by Electron Cyclotron Resonance Heating - - PowerPoint PPT Presentation

FOM-Institute for Plasma Physics Rijnhuizen Association Euratom-FOM

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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

Association Euratom-FOM Trilateral Euregio Cluster

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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 Icd > 2 (∆r/rq=1)2 Iq=1

Association Euratom-FOM Trilateral Euregio Cluster

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The Toolbox

140 GHz, 800 kW, 10 s Gycom gyrotron Flexible launcher: –vertical: -30o tot +30o –horizontal: -45o tot +45o TEXTOR tokamak R = 1.75, a= 0.46 Dynamic Ergodic Divertor 12/4, 6/2, 3/1 DC, AC 50Hz … 10 kHz

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… 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.

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ECE sxr penetration stabilization resolution ~2cm

Set up of m=2, n=1 tearing mode suppression experiment

DED in 3/1 mode, AC 1 kHz

– large 2/1 side band

BT = 2.25 T; Ip = 300 kA ne = 2.0 1019 m-3

• ECRH at q=2

– 140 GHz, 770 kW

• We will use:

wECRH/wDED = ∆TECRH[%]/∆TDED[%]

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Mode suppression for pure ECRH

Deposition scan by

• vertical inj. angle
• ECE data consistent

with sxr data

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Mode suppression by ECCD?

• Jcd,max at q=2 is

6% of Jq=2

• Dominant effect for

suppression is heating

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Dominance of heating confirmed by ECCD scan showing little effect

• Reduced power, 200 kW,

to enhance contrast

• Jcd,max at q=2 in scan is

3% of Jq=2

co-drive counter-

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Gyrotron modulation in phase with DED

• Magnetic islands are locked to DED, thus DED current

can serve as reference signal for phase of island

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O-point heating more effective than X-point

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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

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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 ηNTM > 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 χe = 0.1 m2/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 χe = χe,q=3/2 = 0.5 m2/s, still a 20% effect remains

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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

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Experimental Data Analysis

• Current Drive and Heating

inseparable and both affect s.t.

• TORBEAM: ρdep(t)
• ECE (or sxr): τsaw(t)
• Combine to find τsaw(ρdep)
• Normalization to pure ECRH

discharge gives the effect of the current drive: τsaw,ECCD /τsaw,ECRH(ρdep)

• To be compared with model

estimate of driven current on evolution of shear at q=1

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Experimental Data Analysis II

• TORBEAM estimates of the driven current Icd and profile

width Wcd

• Account for profile broadening due to radial diffusion with

D = 1 m2/s, or WD = 1 cm: Weff = (Wcd

2 + WD 2)0.5

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Example I: co-drive

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Example II: counter-drive

Icd ≈ 2 (∆r/rq=1)2 Iq=1, marginal?

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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: Icd > 2 (∆r/rq=1)2 Iq=1

Association Euratom-FOM Trilateral Euregio Cluster

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lu s t e r

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T ri l a t e r a l E u r e g i

• C

lu s t e r

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 Icd > 2 (∆r/rq=1)2 Iq=1

• Establishes TEXTOR as an ideal tokamak

for MHD experiments

– because of its unique combination of tools