1.TNO, Technical Sciences, Department of OptoMechatronics, NL-2600 AD, Delft, The Netherlands. 2.Institut für Plasmaforschung, Universität Stuttgart, D Stuttgart, Germany. 3.Max-Planck-Institut für Plasmaphysik, EURATOM Association, D Greifswald, Germany. 4.Differ, EURATOM Association, Nieuwegein, The Netherlands. 5.Max-Planck-Institut für Plasmaphysik, EURATOM Association, D 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 Controlled Mirror Motion 0

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

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 Controlled Mirror Motion

Disturbances / Gyrotron frequency variations EC 17; May Note resonance width (FWHM) is in the order of MHz Controlled Mirror Motion

Disturbances / Thermal effects EC 17; May 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

Actively controlled mirror motion system Main requirements Active control of single mirror Positioning resolution: 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 Controlled Mirror Motion

EC 17; May 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

Movable Mirror mechanism implemented EC 17; May Controlled Mirror Motion

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

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 Controlled Mirror Motion

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

EC 17; May Controlled Mirror Motion

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 Controlled Mirror Motion

EC 17; May Controlled Mirror Motion

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 Controlled Mirror Motion

EC 17; May Controlled Mirror Motion

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

EC 17; May Test IPP Greifswald June 2010 Controlled Mirror Motion

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

EC 17; May Test AUG Garching April 2012 Controlled Mirror Motion aliasing

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

EC 17; May Test IPP Greifswald June 2010 Controlled Mirror Motion

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

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

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

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 Controlled Mirror Motion

End of presentation EC 17; May Controlled Mirror Motion

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 Controlled Mirror Motion