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EXPERIMENTS OF ACTIVE QSH CONTROL IN EXTRAP-T2R

EXPERIMENTS OF ACTIVE QSH CONTROL IN EXTRAP-T2R. L. Frassinetti, P.R. Brunsell, E.K.J Olofsson and J.R. Drake. OUTLINE. INTRODUCTION (1) The device and the feedback system (2) Diagnostics for MHD modes (3) Spontaneous QSH in EXTRAP T2R EXPERIMENTAL RESULTS (1) Open loop experiments

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EXPERIMENTS OF ACTIVE QSH CONTROL IN EXTRAP-T2R

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  1. EXPERIMENTS OF ACTIVE QSH CONTROL IN EXTRAP-T2R L. Frassinetti, P.R. Brunsell, E.K.J Olofsson and J.R. Drake

  2. OUTLINE • INTRODUCTION • (1) The device and the feedback system • (2) Diagnostics for MHD modes • (3) Spontaneous QSH in EXTRAP T2R • EXPERIMENTAL RESULTS • (1) Open loop experiments • (2) Close loop experiments • CONCLUSIONS

  3. EXTRAP T2R – the device • R=1.24m • a=0.18m • Ip  80kA (standard current plasma) • ne≈1019m-3 • Te ≈200-400eV • tpulse≈20ms (w/o FeedBack) • tpulse≈up to 90ms (with IS)

  4. EXTRAP T2R – the feedback shell by Olofsson E. Active coils • tshell≈6ms • 4 poloidal x 32 toroidal • sensor saddle coils (m=1 connected) • located inside the shell • 4 poloidal x 32 toroidal • active saddle coils (m=1 connected) • located outside the shell • Digital controller Sensor coils

  5. Open Loop (OL) external helical magnetic perturbations Sensor coils plasma Active coils shell Close Loop (MC) external helical magnetic perturbations Sensor coils plasma Active coils shell bc Digital controller Fourier harmonics in real time input to active coils b1,nbc Vc(t)  V1,n(t)=-Knp[ref-b1,n(t)] EXTRAP T2R – algorithms • At present, three algorithms • are routinely used in EXTRAP T2R: • Open Loop • Intelligent Shell (close loop) IS • Mode Control (close loop) MC by Olofsson E.

  6. DIAGNOSTICS RWM TM -12 -13 -14 Raw signals Magnetic perturbations: br  4 poloidal x 32 toroidal sensor saddle coils (m=1 connected) located inside the shell give the time integrated signals. bq  4 poloidal x 64 toroidal local sensors (m=1 connected) located inside the shell give the time derivative of the signals.

  7. SPONTANEOUS QSHs IN EXTRAP T2R QSH example in EXTRAP T2R The dominant mode is the first resonant. With the typical equilibrium: nDOM=-12 n=-12 Average duration tQSH≈0.1ms Fraction of the discharge characterized by QSHs: MH Ns>2 QSH Ns<2 SH Ns=1

  8. OPEN LOOP EXPERIMENTS plasma V=1.4V V=1.2V V=1.0V V=0.8V V=0.6V V=0.4V V=0 Average between 5ms-end of discharge Open Loop (OL) external helical magnetic perturbations Sensor coils plasma vacuum Active coils shell • Basic idea: • Apply a static helical perturbation (n=-12) • Study the plasma behaviour

  9. OPEN LOOP EXPERIMENTS spontaneous QSH induced QSH “Often”, the TM is larger than “usual” in the sense that more and longer QSHs are generated But the TM still rotates! A static helical field with n=-12 is applied at the plasma boundary. What happen to the corresponding rotating TM?

  10. OPEN LOOP EXPERIMENTS Amplitude of dominant TM during QSHs spontaneous 120 QSHs are considered But when br-12 is too large, even secondary modes increase Dominant TM Secondary TMs Is the amplitude of the rotating TM during QSH affected by the external helical perturbation? More QSHs when the external helical perturbation is used

  11. CLOSE LOOP EXPERIMENTS (MC) The mode suppression is controlled by kp-12 Each can be controlled separately. One mode free to grow All other modes suppressed n=-12 Secondary modes Close Loop (Mode Control) external helical magnetic perturbations Sensor coils plasma Active coils shell bc Digital controller Fourier harmonics in real time Calculates input to active coils b1,nbc Vc V1,n=-Kpn b1,n

  12. CLOSE LOOP EXPERIMENTS (MC) Amplitude of dominant TM during QSHs All modes suppressed 210 QSHs are considered …20 Gain reduction br-12 increase Are QSH and rotating TMs affected? The gain of mode n=-12 is reduced -12

  13. CLOSE LOOP EXPERIMENTS (MC) Dependence of resonant radii with F (1,-15) (1,-14) (1,-13) (1,-12) (1,-11) Using the optimal kp-12, F is scanned to test the dependence of PQSH. PQSH is clearly dependent on F This is mainly due to a change in the position of the resonant radius.

  14. CONCLUSIONS QSH MC QSH OL MH std MH MC • A static helical perturbation can affect the corresponding rotating TM • - Higher QSH probability • - The TM velocity is affected • - But NOT the TM mode amplitude during the QSH • (2) With the MC better results are obtained • - QSH probability higher than in Open Loop • - QSH are more “pure” (i.e. lower secondary modes) • - The amplitude of the rotating TM is affected

  15. OPEN LOOP EXPERIMENTS Fitzpatrick model [NF 33, 1049 (1993)] Is the TM velocity affected by the external perturbation?

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