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

2. York, June the 23 rd 2013Chiara Piron The RFX-mod experiment 1 0 -0.1 1 r/a a r Padova RFX-mod: a Reversed Field Pinch (RFP) that can operate also as a Tokamak Bt direction reversed Comparable Bt, Bp amplitude Bt Bp 1/10

3. York, June the 23 rd 2013Chiara Piron The MHD stability problem Ip[kA] q(a) 2/1 RWM Br [mT] # 29774 ctrl OFF # 29797 ctrl ON Ip[kA] q(a) 1/6 RWM Br [mT] # 18542 ctrl OFF # 18541 ctrl ON RFP TOKAMAK 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 2/10

4. York, June the 23 rd 2013Chiara Piron The RFX-mod feedback control How is it possible to control MHD instabilities? 3/10

5. York, June the 23 rd 2013Chiara Piron The RFX-mod feedback control 192 MAGNETIC SENSORS (Br, Bt, Bp) How is it possible to control MHD instabilities? 3/10

6. York, June the 23 rd 2013Chiara Piron The RFX-mod feedback control 192 MAGNETIC SENSORS (Br, Bt, Bp) How is it possible to control MHD instabilities? 3/10

7. York, June the 23 rd 2013Chiara Piron The RFX-mod feedback control 192 MAGNETIC SENSORS (Br, Bt, Bp) + 192 ACTIVE COILS How is it possible to control MHD instabilities? 3/10

8. York, June the 23 rd 2013Chiara Piron The RFX-mod feedback control 192 MAGNETIC SENSORS (Br, Bt, Bp) + 192 ACTIVE COILS MARTe f CYCLE = 5kHz It is like opening and closing the shower turncock… 5000 times per second! How is it possible to control MHD instabilities? 5kHz 3/10

9. York, June the 23 rd 2013Chiara Piron Par == 1 ? CMC Par == 2 ? Par == 4 ? Par == 3 ? PLASMA RESPONSE DOUBLE SHELL CMC POLOIDAL CTRL Extrapolation? EXTRAPOLATOR PID FEEDFORWARD CURRENT FREEZING PID Cleaning? Par == 0? Reading Parameters All Pars = 0 RAW CTRL 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 TF T T T T T T F F F F F Br, Bt spectrum Bp spectrum active coils 4/10 [1] A. Netò et al., IEEE Trans. Nucl. Sci. 57 (2010)

10. York, June the 23 rd 2013Chiara Piron Par == 1 ? CMC Par == 2 ? Par == 4 ? Par == 3 ? PLASMA RESPONSE DOUBLE SHELL CMC POLOIDAL CTRL Par == 0? RAW CTRL The MARTe framework T T T T T F F F F [2] Strait E.J. et al. 2003 Nuclear Fusion 43 430 [3] Liu et al. Plasma Phys. Control. Fusion 51 (2009) 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 The Fourier harmonics of the signals An analytic cylindrical model is applied to clean the sideband aliasing A refinement of CMC where both the vessel and the shell are considered in the model A control scheme that uses a 8X4 array of poloidal sensor The field produced by the active coils is subtracted from the measurements 5/10

11. York, June the 23 rd 2013Chiara Piron Par == 1 ? CMC Par == 2 ? Par == 4 ? Par == 3 ? PLASMA RESPONSE DOUBLE SHELL CMC POLOIDAL CTRL Extrapolation? EXTRAPOLATOR PID FEEDFORWARD CURRENT FREEZING PID Cleaning? Par == 0? Reading Parameters All Pars = 0 RAW CTRL 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 TF T T T T T T F F F F F Br, Bt spectrum Bp spectrum active coils 6/10 [1] A. Netò et al., IEEE Trans. Nucl. Sci. 57 (2010)

12. York, June the 23 rd 2013Chiara Piron 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] 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 [4] G.Marchiori, et al., Nucl. Fus, 52 (2012) RMC:unstable Plasma Response:unstable CMC: stable Gain [4] 7/10

13. York, June the 23 rd 2013Chiara Piron 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 Error Field Correction (EFC) Ip[kA] q(a) 2/1 RWM Icoil [A] 2/1 RWM Br [mT] # 33576 # 33634 freezing ON 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 8/10 EFC control scheme was developed at the DIII-D tokamak to operate at high beta values and to investigate the RWM physics [5] [5] A. Garofalo et al., PRL, 23 (2002) Can the 2/1 RWM at q(a)<2 be destabilized by error fields?

14. York, June the 23 rd 2013Chiara Piron Poloidal magnetic sensor control #33808 Θ=342° Θ=297° Θ=252° Θ=207° #33808 Bp signals [T] array @ φ=322.5° 2,1 RWM Bp [mT] #33808 9/10 2D FFT before after algorithm processing before before (realtime) after algorithm processing

15. York, June the 23 rd 2013Chiara Piron 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 10/10