U i APCS f Pl V i l C lU i APCS f Pl V i l C l TCVTCVUsing APCS for Plasma Vertical Control atUsing APCS for Plasma Vertical Control at TCVTCVUsing APCS for Plasma Vertical Control atUsing APCS for Plasma Vertical Control at TCVTCVUsing APCS for Plasma Vertical Control at Using APCS for Plasma Vertical Control at TCVTCVN Cruz1 J ‐M Moret2 S Coda2 J I Paley2 B P Duval2 A P Rodrigues1 F Piras2 F Felici2 C M B A Correia3 C A F Varandas1N. Cruz , J. M. Moret , S. Coda , J. I. Paley , B.P. Duval , A. P. Rodrigues , F. Piras , F. Felici , C. M. B. A. Correia , C. A. F. Varandas

1Associação EURATOM/IST, Instituto de Plasmas e Fusão Nuclear‐Laboratório Associado, Instituto Superior Técnico, P‐1049‐001 Lisboa, Portugalç / , , p , , g2Association Euratom‐Confédération Suisse Centre de Recherches en Physique des Plasmas École Polytechnique Fédérale de Lausanne (EPFL) CH‐1015 Lausanne SwitzerlandAssociation Euratom‐Confédération Suisse, Centre de Recherches en Physique des Plasmas, École Polytechnique Fédérale de Lausanne (EPFL), CH‐1015 Lausanne, Switzerland

3G d El t ó i I t t ã D t d Fí i U i id d d C i b 3004 516 C i b P t l3Grupo de Electrónica e Instrumentação, Dept. de Física, Universidade de Coimbra, 3004‐516 Coimbra, Portugal

Ab t tAbstractl k k i h i l i l i i i ll i ll bl d bl h l f i l i i d h f i ll l d l iEarly Tokamaks with circular cross‐section plasmas were intrinsically vertically stable and no problems to the control of vertical position were reported. However, the new concept of vertically elongated plasma cross‐section

with benefits to the energy confinement time led to vertical instabilities. Such instabilities can only be overcome by means of a complex closed feedback loop control system with a vertical position measurement, signalprocessing, control algorithm, power supplies and active actuating coils.

Th “T k k à C fi ti V i bl ” (TCV) ith f l ti l iti t l t ith f t li bl f ti d 0 1 it th t bili ti f hi hl l t d l WithThe “Tokamak à Configuration Variable” (TCV), with a powerful vertical position control system, with fast power supplies capable of response times under 0.1 ms, permits the stabilization of highly elongated plasmas. Withh i d i f h d d l l ( ) i h i l i i b b il f h l h bili i f h d l h li i i h d d bthe introduction of the new Advanced Plasma Control System (APCS) in the TCV a new vertical position observer was built to further explore the capabilities of the new system and solve the limitations that were detected bythe introduction in the feedback loop of signal digitizing. The need for a new measure of the plasma vertical position is discussed as well as the method for building the observer and the validation of the measured positionwhich is compared with the previous methods and measures.

A f th i k i d It i l di d it i d th l th t t d t b hi d b l i th di it l li t l l ith biliti f APCSA summary of the ongoing work is made. It is also discussed its aim and the goals that are expected to be achieved by exploring the new digital non‐linear control algorithm capabilities of APCS.

Overview of APCS SystemOverview of APCS System TCV Magnetic Diagnostics,The Advanced Digital Plasma Control System (APCS) was developed and installed to increase

TCV Magnetic Diagnostics,Pl Sh d P iti C t lThe Advanced Digital Plasma Control System (APCS) was developed and installed to increase

the scope of the TCV control of physical plasma parameters such as shape position currentPlasma Shape and Position Control

the scope of the TCV control of physical plasma parameters such as shape, position, currentd d [ ][ ]

pand density. [1][2]

The picture on the left depicts the cross section of theThe picture on the left depicts the cross‐section of thek kTCV tokamak.

It is possible to seeIt is possible to seevacuum vessel;‐ vacuum vessel;f t t bili ti il i id th l (G1 d G2)‐ fast stabilization coils inside the vessel (G1 and G2)

(the black turns at the top and bottom outer corners);( p );‐ 16 poloidal field shaping coils (the inboard E1‐E816 poloidal field shaping coils (the inboard E1 E8

and outboard F1 F8 stacks of 8 coils each)The above figure shows the original TCV control system with high capability and performance and outboard F1‐F8 stacks of 8 coils each);The above figure shows the original TCV control system with high capability and performancet li t l l ith b t l ki th bilit f i li l ith ‐ flux‐loops (marked x);to run linear control algorithms, but lacking the capability of running non‐linear algorithms.

‐ 38 magnetic probes around the vessel contourThe figure below depicts the APCS integrated into the TCV control system permitting to run 38 magnetic probes around the vessel contour(marked inside the tiles)

g p g y p gnon‐linear algorithms by the use of a grid of APC channels with digital signal processing (marked inside the tiles).

l f f h C i di i

non linear algorithms by the use of a grid of APC channels with digital signal processingcapabilities and sharing the acquired data among all units for each control cycle A complete reference of the TCV magnetic diagnosticscapabilities and sharing the acquired data among all units for each control cycle.

can be found in [3][ ]

Di i d F t W kDiscussion and Future Work

The digital system is installed at TCV and adaptations to the vertical control observerThe digital system is installed at TCV and adaptations to the vertical control observerand algorithm have been made to allow the implementation of new nonlinearand algorithm have been made to allow the implementation of new nonlinearvertical plasma control algorithms.

Figure on the left depicts theFigure on the left depicts thecomparison between the controlcomparison between the controlsignals path for both observers andA) signals path for both observers anddi it l/ l t l th

A)digital/analogue control path:A) Bd Ob i l b

New Plasma Vertical Position ObserverA) Bdot‐Observer signal as seen by

New Plasma Vertical Position Observer analogue (red) and digital (blue andblack) control systemsB)

The initial analogue vertical position control loop for the internal fast coils was composed by a ZiB) Digital control output (blue and

)The initial analogue vertical position control loop for the internal fast coils was composed by a Zipobserver (from integrated magnetic probe signals) and a D (derivative) controller[4] When migrating to

) g p (black) following the analogue output

observer (from integrated magnetic probe signals) and a D (derivative) controller[4]. When migrating toth di it l t l t th D l ith di iti d b i l l d t b t i

black) following the analogue output(red) with improved signal to noise

the digital control system the D algorithm ran over digitized observer signal revealed to be too noisy.h l i f ll d hi l i h i h f f i f h ll ld b

(red) with improved signal to noiseratioC)Further analysis followed this conclusion showing the transfer function of the D controller could not beratioC) B Observer signal as seen by

C)used over the digital data.

C) B‐Observer signal as seen byl ( d) d di it l (bl danalogue (red) and digital (blue and

bl k) lblack) control systemsD) Digital control output (blue)D)amplifies the input signal noise too

D)

much justifying the implementationj y g pof a new observer

W k i i l d h i l i f li ll di

of a new observer

Work in progress include the implementation of a new nonlinear controller accordingto the work proposed in [5] to test the quality of the “bang bang” algorithmp p [ ] q y g g gdescribed for vertical position control in the presence of power supply voltagedescribed for vertical position control in the presence of power supply voltaget ti hi h t ibl t hi ith th i li lsaturation, which was not possible to achieve with the previous linear analogue

control system.yThe robustness of the observer and control loop in the presence of ELMs will beThe robustness of the observer and control loop in the presence of ELMs will bestudied and improvements using non linear capability is envisaged [6][7]U i h 20 i d i b i l il bl h TCV l Zi b studied and improvements using non‐linear capability is envisaged [6][7].Using the 20 non‐integrated magnetic probe signals available on the TCV control system a new Zip observer

was built for use with a P (proportional) controller.Picture on top left depicts the derivative of magnetic field as seen by the magnetic probes and the

Referencescoefficients of the new observer while the top right shows the magnetic field and the standard plasma

Referencesp g g p

vertical observer coefficients.vertical observer coefficients.Picture below reveals the result of the observer signals and the PID control output voltage for both control [1] AP Rodrigues N Cru B Santos CAF Varandas J M Moret J Berrino BP Duval “TCV Advanced Plasma Control SystemPicture below reveals the result of the observer signals and the PID control output voltage for both controlloops during a TCV shot where plasma had a small “yo‐yo” movement Note that observer on the left had to

[1] AP Rodrigues, N Cruz, B Santos, CAF Varandas, J‐M Moret, J Berrino, BP Duval, “TCV Advanced Plasma Control SystemSoftware Architecture and Preliminary Results” IEEE Transactions On Nuclear Science vol 55 pages 316 321 (2008)loops during a TCV shot where plasma had a small yo‐yo movement. Note that observer on the left had to

be integrated to give plasma position once the observer is in reality an observer of plasma velocity BothSoftware Architecture and Preliminary Results , IEEE Transactions On Nuclear Science, vol. 55, pages 316‐321 (2008).[2] N Cruz AP Rodrigues B Santos CAF Varandas BP Duval J‐M Moret J Berrino Y Martin X Llobet “The Integration of thebe integrated to give plasma position once the observer is in reality an observer of plasma velocity. Both

b d t th l iti i b LIUQE ilib i l t ti d

[2] N Cruz, AP Rodrigues, B Santos, CAF Varandas, BP Duval, J‐M Moret, J Berrino, Y Martin, X Llobet, The Integration of theNew Advanced Digital Plasma Control System in TCV” Fusion Engineering and Design 83 (2008) 215–219observers are compared to the plasma position given by LIUQE equilibrium plasma reconstruction code. New Advanced Digital Plasma Control System in TCV , Fusion Engineering and Design 83 (2008) 215 219.[3] J.‐M. Moret, F. Buhlmann, D. Fasel, F. Hofmann and G. Tonetti, ”Magnetic measurements on the TCV Tokamak”, Rev. Sci.[3] J. M. Moret, F. Buhlmann, D. Fasel, F. Hofmann and G. Tonetti,  Magnetic measurements on the TCV Tokamak , Rev. Sci. Instrum. 69, 2333 (1998), ( )[4] F. Hofmann , M.J. Dutch , A. Favre , Y. Martin , J.‐M. Moret and D.J. Ward, “Feedback stabilization of axisymmetric modes in[ ] , , , , , ythe TCV tokamak using active coils inside and outside the vacuum vessel”, 1998 Nucl. Fusion 38 399[5] J‐Y Favez, J B Lister, Ph Mullhaupt and B Srinivasan, “Improving tokamak vertical position control in the presence of powersupply voltage saturation”, Plasma Phys. Control. Fusion 47 (2005) 1709–1741[6] F. Hofmann, I. Furno, S. Gerasimov, Y. Martin, F. Milani, M.F.F. Nave, H. Reimerdes, F. Sartori, O. Sauter, “Effect of ELMs onthe measurement of vertical plasma position in TCV and JET”, Nucl. Fusion 42 (2002) 59–65[7] G T i S C d J M M Y M i d O S “Th ff f MHD i h i l b i k k ” Pl[7] G Turri, S Coda, J‐MMoret, Y Martin and O Sauter, “The effect of MHD noise on the vertical observer in tokamaks”, PlasmaPh C t l F i 50 (2008) 035012 (20 )Phys. Control. Fusion 50 (2008) 035012 (20pp)

AcknowledgementsThis work has been sponsored by the Contract of Association between European Atomic Energy Community and Instituto

AcknowledgementsThis work has been sponsored by the Contract of Association between European Atomic Energy Community and InstitutoSuperior Técnico (IST) and by the Contract of Associated Laboratory between Fundação para a Ciência e Tecnologia (FCT) and ISTSuperior Técnico (IST) and by the Contract of Associated Laboratory between Fundação para a Ciência e Tecnologia (FCT) and IST.The content of publication is the sole responsibility of the authors and it does not necessarily represent the views of theThe content of publication is the sole responsibility of the authors and it does not necessarily represent the views of theCommission of the European Union or FCT. This work was partly supported by the Swiss National Science Foundation.p p y pp y