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New schemes for MHD stability control in RFX-mod using the real-time MARTe framework

New schemes for MHD stability control in RFX-mod using the real-time MARTe framework. Chiara Piron. In collaboration with: G.Manduchi, L.Marrelli, P.Piovesan, P.Zanca, A.Garofalo, M. O kabayashi. 3 rd PhD Event in Fusion Science and Engineering York, June the 23 rd 2013. 1. -0.1. 0.

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New schemes for MHD stability control in RFX-mod using the real-time MARTe framework

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  1. New schemes for MHD stability control in RFX-mod using the real-time MARTe framework Chiara Piron In collaboration with: G.Manduchi, L.Marrelli, P.Piovesan, P.Zanca, A.Garofalo, M. Okabayashi 3rd PhD Event in Fusion Science and Engineering York, June the 23rd 2013

  2. 1 -0.1 0 r/a 1 The RFX-mod experiment RFX-mod: a Reversed Field Pinch (RFP) that can operate also as a Tokamak Padova Bt Comparable Bt, Bp amplitude Bp Bt direction reversed a r Chiara Piron 1/10

  3. The MHD stability problem TOKAMAK RFP # 29774 ctrl OFF # 29797 ctrl ON # 18542 ctrl OFF # 18541 ctrl ON Ip[kA] Ip[kA]   q(a) q(a) 1/6 RWM Br [mT] 2/1 RWM Br [mT] AIM OF MY PhD ACTIVITY: develop and implement in realtime new feedback control strategies to counteract MHD instabilities to optimize the performance both in tokamak and RFP plasmas. Such control strategies can be used as control schemes in reactor-relevant scenarios, such as advanced tokamak regimes Chiara Piron 2/10

  4. The RFX-mod feedback control How is it possible to control MHD instabilities? Chiara Piron 3/10

  5. The RFX-mod feedback control How is it possible to control MHD instabilities? 192 MAGNETIC SENSORS (Br, Bt, Bp) Chiara Piron 3/10

  6. The RFX-mod feedback control How is it possible to control MHD instabilities? 192 MAGNETIC SENSORS (Br, Bt, Bp) Chiara Piron 3/10

  7. The RFX-mod feedback control How is it possible to control MHD instabilities? 192 MAGNETIC SENSORS (Br, Bt, Bp) + 192 ACTIVE COILS Chiara Piron 3/10

  8. The RFX-mod feedback control How is it possible to control MHD instabilities? 192 MAGNETIC SENSORS (Br, Bt, Bp) + 192 ACTIVE COILS 5kHz MARTe fCYCLE = 5kHz It is like opening and closing the shower turncock… 5000 times per second! Chiara Piron 3/10

  9. The MARTe framework Multi-threaded Application Real-Time Executor [1]: a C++ development enviroment for real-time applications. It has been introduced in RFX-mod, where both software and hardware upgrades in the feedback control have been recently carried out Br, Bt spectrum Bp spectrum T F Cleaning? Reading Parameters All Pars = 0 T Par == 0? RAW CTRL F T Par == 1 ? CMC T F EXTRAPOLATOR T Par == 2 ? Extrapolation? PLASMA RESPONSE F F T Par == 4 ? DOUBLE SHELL CMC active coils PID F T Par == 3 ? POLOIDAL CTRL CURRENT FREEZING PID FEEDFORWARD CURRENT [1] A. Netò et al., IEEE Trans. Nucl. Sci. 57 (2010) Chiara Piron 4/10

  10. The MARTe framework Why so many control schemes? To contribute to the scientific debat on the optimal sensors for feedback: Poloidal sensor control is successful in tokamak experiments[2, 3] BUT the sensor are located inside the vessel, thus they can not be used in a fusion reactor. Radial sensors can be used instead BUT they are less effective because of sideband aliasing. challenge: find the optimal algorithm to clean the radial measurements and make the radial magnetic field sensor control as much effective as the poloidal one T The Fourier harmonics of the signals Par == 0? RAW CTRL F An analytic cylindrical model is applied to clean the sideband aliasing T Par == 1 ? CMC F The field produced by the active coils is subtracted from the measurements T Par == 2 ? PLASMA RESPONSE F A refinement of CMC where both the vessel and the shell are considered in the model T Par == 4 ? DOUBLE SHELL CMC F T A control scheme that uses a 8X4 array of poloidal sensor Par == 3 ? POLOIDAL CTRL [2] Strait E.J. et al. 2003 Nuclear Fusion 43 430 [3] Liu et al. Plasma Phys. Control. Fusion 51 (2009) Chiara Piron 5/10

  11. The MARTe framework Multi-threaded Application Real-Time Executor [1]: a C++ development enviroment for real-time applications. It has been introduced in RFX-mod, where both software and hardware upgrades in the feedback control have been recently carried out Br, Bt spectrum Bp spectrum T F Cleaning? Reading Parameters All Pars = 0 T Par == 0? RAW CTRL F T Par == 1 ? CMC T F EXTRAPOLATOR T Par == 2 ? Extrapolation? PLASMA RESPONSE F F T Par == 4 ? DOUBLE SHELL CMC active coils PID F T Par == 3 ? POLOIDAL CTRL CURRENT FREEZING PID FEEDFORWARD CURRENT [1] A. Netò et al., IEEE Trans. Nucl. Sci. 57 (2010) Chiara Piron 6/10

  12. RMC: unstable Plasma Response: unstable CMC: stable [4] Gain The Plasma Response control scheme Feedback variable = the component of the radial magnetic field that is obtained by subtracting the field produced by the active coils from the measurements • The Plasma Response control scheme fails in suppressing the instability, regardless the applied proportional gain. • Experiments with derivative gains are planned in the next future. • Preliminary results seem to suggest that a proportional gain threshold exists for the growth rate saturation, as predicted by [1] [4] G.Marchiori, et al., Nucl. Fus, 52 (2012) Chiara Piron 7/10

  13. Error Field Correction (EFC) EFC control scheme was developed at the DIII-D tokamak to operate at high beta values and to investigate the RWM physics [5] • Two similar discharges: • #33576 reference shot • #33634 frozen currents at t=[0.5, ..] s • When q(a)<2 the 2/1 RWM always grows despite error fields are compensated # 33576 # 33634 freezing ON Ip[kA] Can the 2/1 RWM at q(a)<2 be destabilized by error fields? q(a) 2/1 RWM Icoil [A] Why does EFC seem not to work in RFX-mod? Probably because we are using the wrong feedback variable Try to use the poloidal sensors instead 2/1 RWM Br [mT] [5] A. Garofalo et al., PRL, 23 (2002) Chiara Piron 8/10

  14. Poloidal magnetic sensor control Bp signals [T] array @ φ=322.5° 2,1 RWM Bp [mT] #33808 #33808 #33808 before after algorithm processing Θ=342° 2D FFT Θ=297° Θ=252° Θ=207° before before (realtime) after algorithm processing Chiara Piron 9/10

  15. Conclusions and future plans.. • Active feedback control is an essential and effective tool to counteract the growth of MHD instabilities both in RFP and tokamak plasmas • The development and of new MHD feedback algorithms contributes to the scientific debat on the optimal feedback control strategies (ITER relevance for advanced tokamak scenarios) • The Plasma Response and the EFC are just two of the available RFX-mod control schemes that put light on the inner physics of RWM dynamics and act as benchmarks for theoretical models • To do.. • Plasma Response, EFC and other control schemes are planned to be further tested in real experiments both in Tokamak and RFP campaigns • Data analyses on the collected data will be carried out to characterize the nature of the MHD instabilities and to extract theoretical model to describe their dynamics Chiara Piron 10/10

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