1. 1.TNO, Technical Sciences, Department of OptoMechatronics, NL-2600 AD, Delft, The Netherlands. 2.Institut für Plasmaforschung, Universität Stuttgart, D-70569 Stuttgart, Germany. 3.Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-17491 Greifswald, Germany. 4.Differ, EURATOM Association, Nieuwegein, The Netherlands. 5.Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany. Niek Doelman 1, R. van den Braber 1, W. Kasparek 2, V. Erckmann 3, W. Bongers 4, B. Krijger 4, J. Stober 5, E. Fritz 1, B. Dekker 1, W. Klop 1, F. Hollmann 3, G. Michel 3, F. Noke 3, F. Purps 3, M. de Baar 4, M. Maraschek 5, F. Monaco 5, S. Müller 5, H. Schütz 5, D. Wagner 5, the ASDEX Upgrade Team 5 and other teams at the contributing institutes. Controlled Mirror Motion System for Resonant Diplexers in ECRH Applications EC 17; May 9 2012 Controlled Mirror Motion 0

2. EC 17; May 9 2012 1 FADIS diplexer functionality * Operational point at output power curves * see Kasparek, Bongers this conference Controlled Mirror Motion

3. FADIS system requirement For proper operation the FADIS resonant diplexer needs to have the correct round-trip length L, despite all disturbances Disturbances 1.Gyrotron frequency variations 2.Expansion of diplexer cavity due to temperature gradients 3.Structural vibrations EC 17; May 9 2012 2 Controlled Mirror Motion

4. Disturbances / Gyrotron frequency variations EC 17; May 9 2012 3 Note resonance width (FWHM) is in the order of 10-20 MHz Controlled Mirror Motion

5. Disturbances / Thermal effects EC 17; May 9 2012 4 Uncontrolled system; mirror motion depends on mount stiffness Disturbances / Structural vibrations Diplexer resonator length expansion Aluminium casing under  T  L ~ 5e-5  T Controlled Mirror Motion

6. Actively controlled mirror motion system Main requirements Active control of single mirror Positioning resolution: 1 - 10 µm (few % transmission) Positioning stroke> 1.5 mm (1 period) Mirror rotation(3 DOF)< 1 mrad Lateral motion< 1 mm Bandwidth > 10 – 100 Hz (in closed-loop) Linear response characteristics EC 17; May 9 2012 5 Controlled Mirror Motion

7. EC 17; May 9 2012 6 Mechanics of mirror motion Main principles Linear motion: voice-coil actuator Leaf springs as elastic guiding mechanism; free of friction Internal optical encoder as position sensor flange voice coil actuator elastic guiding mechanism mirror flange Cavity Mirror F act Sensor Frame Controlled Mirror Motion

8. Movable Mirror mechanism implemented EC 17; May 9 2012 7 Controlled Mirror Motion

9. Mirror motion in action Scanning motion EC 17; May 9 2012 8 Test IPF Stuttgart January 2012 Controlled Mirror Motion

10. Increasing the system’s bandwidth Position sensor feedback Low order feedback controller gives higher effective stiffness Higher bandwidth -> faster response -> higher performance Functions as inner control-loop for main power control approach EC 17; May 9 2012 9 Controlled Mirror Motion

11. Controlling the mirror motion Output powers are the controlled variables Feedback of power signals is most direct approach EC 17; May 9 2012 10 Controlled Mirror Motion

12. EC 17; May 9 2012 11 Controlled Mirror Motion

13. Gradient-type optimisation Given a cost function J(x), to be minimised Recursive minimisation by gradient search In case of FADIS, cost function J(x) could be the output power OUT 1 However, the gradient of the power curves is unknown. EC 17; May 9 2012 12 Controlled Mirror Motion

14. EC 17; May 9 2012 13 Controlled Mirror Motion

15. Dither-based gradient optimization (2) Add sinusoidal perturbation to current mirror position Use small amplitude, typically 1  m Step-size of gradient algorithm is limited to have proper estimation => possibly slow convergence The higher the dither frequency, the faster the convergence Very robust approach; performs irrespective of shape of cost function Also referred to as Extremum Seeking Control EC 17; May 9 2012 14 Controlled Mirror Motion

16. EC 17; May 9 2012 15 Controlled Mirror Motion

17. Experiment (0) The effect of a stationary mirror position EC 17; May 9 2012 16 Test IPP Greifswald June 2010 Controlled Mirror Motion

18. EC 17; May 9 2012 17 Test IPP Greifswald June 2010 Controlled Mirror Motion

19. Experiments (1) Mirror motion follows the frequency variations EC 17; May 9 2012 18 Test IPP Greifswald June 2010 Controlled Mirror Motion

20. EC 17; May 9 2012 19 Test AUG Garching April 2012 Controlled Mirror Motion aliasing

21. Experiments (3) Power switching by mirror motion Power trajectory is a 32 Hz sinusoid EC 17; May 9 2012 20 Test AUG Garching April 2012 Controlled Mirror Motion

22. EC 17; May 9 2012 21 Test IPP Greifswald June 2010 Controlled Mirror Motion

23. Experiments (5) Resonance control for in-line ECE Minimisation of P1 power Combined frequency feedforward and power feedback EC 17; May 9 2012 22 Test AUG Garching April 2012 Controlled Mirror Motion

24. Experiments (5) Combined frequency feedforward and power feedback Fast initialisation by feedforward Fine adjustment by power feedback EC 17; May 9 2012 23 Test AUG Garching April 2012 Controlled Mirror Motion

25. Experiments (6) Low power test using Magic-T based interferometric set-up EC 17; May 9 2012 24 Test IPF Stuttgart January 2012 W. Kasparek, EC-17 Controlled Mirror Motion

26. Conclusions Mirror motion system to keep diplexer at required resonator length Linear, friction-free actuation and guidance Weight of mirror limits motion speed Non-linear power curves complicate control Several approaches possible: Control at 1 slope of the curves (50% coverage) Small perturbation based adaptive control (100% coverage) Frequency signal feedforward Interferometric Magic-T set-up Combinations of the above Generic controlled motion concept for active manipulation of mm-waves..(?) EC 17; May 9 2012 25 Controlled Mirror Motion

27. End of presentation EC 17; May 9 2012 26 Controlled Mirror Motion

28. Controlling the mirror motion Response of mirror position sensor to actuator voltage is ‘slow’ but highly linear The response of both output powers to mirror position is ‘fast’ but not linear EC 17; May 9 2012 27 Controlled Mirror Motion