Variety of electromechanical Lorentz force compensation systems dedicated for superconducting high field resonant cavities DEPARTMENT OF MICROELECTRONICS AND COMPUTER SCIENCE TECHNICAL UNIVERSITY OF LODZ, POLAND Sekalski Przemyslaw, DMCS-TUL, Poland Wilga 31.V.2005

Sekalski Przemyslaw, DMCS-TUL, Poland Outline Types of tuners Types of actuators Control system Current results Sekalski Przemyslaw, DMCS-TUL, Poland

Purposes of cavity tuner Pre-tuning- is necessary stage to reach proper frequency. Cavity with couplers are assembled at room temperature, during cooling down and pumping the cavity shape is deformed. Required system might work slow but must be able to change the cavity length in range of several millimeters (corresponds to a few MHz of detuning compensation). The pretuning phase will be performed i.e. once a week or even month. Lorentz Force compensation. During pulsed operation the cavity is reloaded with frequency of 1.3GHz. The current, which flows through cavity walls, interacts with electromagnetic field inside cavity and as a result changes its shape and its resonant frequency. Detuning depends on accelerating field gradient (Δf~Eacc2) and is below 1000Hz. LF is repetitive and periodic. System needs to act quite fast (up to 2kHz) and will be run each pulse (repetition rate up to 20Hz) Microphonics is a vibration of environment. It is fully stochastic. The detuning caused by microphonics is below 20Hz. Feedback loop is required. System should work permanently. Sekalski Przemyslaw, DMCS-TUL, Poland

CEA-Sacley current design Types of tuners Electromechanical system for LF compensation CEA-Sacley current design Double lever system Stepping motor PHYTRON with Harmonic Drive gear box ΔZ=±5mm, Δf=±2.6MHz Theoretical resolution 1.5nm Stiffness ~100kN/mm Ready for piezoelectric and magnetostrictive actuator UMI Milan tuner Coaxial Three coaxial rings connected by blades Stepping motor for pretuning stage Piezos up to 72mm length Shorter dead zone between cavities 350283mm (total accelerator length reduction by 5%) Expensive (factor of 2-3) Stiffer than others (easily upgradeable) CEA-Sacley new design Double lever with a screw-nut system Stepping motor PHYTRON or SANYO with Harmonic Drive gear box Δf=±2MHz @RT, Δf=±460kHz @2K Ready for piezoelectric and magnetostrictive actuator preload force for active elements is almost decoupled with motor position All tuners needs an smart material based actuator Sekalski Przemyslaw, DMCS-TUL, Poland

Smart materials principles Smart materials have one or more properties that can be dramatically altered. Most everyday materials have physical properties, which cannot be significantly altered; for example if oil is heated it will become a little thinner, whereas a smart material with variable viscosity may turn from a fluid which flows easily to a solid. A variety of smart materials already exist, and are being researched extensively. These include: Electrochromic materials, Thermoresponsive materials Shape memory alloys, Smart gels and many others Piezoelectric materials, Magnetostrictive and electrostrictive materials, Rheological materials (magneto- and electro-rheostatic), PH-sensitive materials, Sekalski Przemyslaw, DMCS-TUL, Poland

Smart materials principles R=R0 R=R1>R0 Piezoelectric effect (direct and inversed - electrostriction) discovered by Pierre Curie in 1880, is exhibited by certain crystals, e.g., quartz and ceramic materials. Magnetostrictive effect (direct and reciprocal) discovered by James Prescott Joule in 1840’s in iron samples Piezoresistive effect discovered by C. S. Smith in 1954 in germanium and silicon samples Sekalski Przemyslaw, DMCS-TUL, Poland

Types of actuators (1/2) Piezoelectric actuators Magnetostrictive actuators Dimensions: 10x10x36mm Manufacturer: PI Dimensions: 10x10x30mm Manufacturer: NOLIAC Dimensions: Φ10x20mm Material: KELVIN ALL Dimensions: 7.5x7.5x50mm Manufacturer: PiezoMechanik Dimensions: 7x7x30mm Manufacturer: EPCOS Dimensions: 6x6x20mm Material: GalFeNOL Sekalski Przemyslaw, DMCS-TUL, Poland

Sekalski Przemyslaw, DMCS-TUL, Poland Types of actuators (2/2) Piezoelectric tuner Magnetostrictive tuner Max strain at 2K Small, ~0.05% Large, 0.14 -0.2% (need to be checked) Lifetime Large, if preload correct >1010 cycles (small damage) Large >108 cycles (no damage) Preload Small range, 0.7-1.5kN NOTE: few kN per 1mm (416kHz) Large range, 0.2-10kN Susceptibility to electric damage High, electric break-through, safer when cooled down Low, magnetic field driven Stray magnetic field Small, only from wires Small with niobium shielding, <25mG at 30 mm from actuator Cryogenic heat loss low Low <0.1W, can be improved, probably active cooling needed Demonstration yes, with and without cavity yes, without cavity Electronic driving system Voltage driven, Current driven (design effort higher) Sensor redundant actuator (normally sensor) sensor needed Price 0.8 k€ + 0.4 k€ 1 k€ + 0.6 k€ Sekalski Przemyslaw, DMCS-TUL, Poland

Current results (1/2) Frequency content of cavity vibration Detuning only 30Hz during flat top (20MV/m) Without compensation detuning is 200Hz Resonance frequencies 291Hz 325Hz 496Hz MATLAB application Control system for piezoelement (ACC1, cav5) Sekalski Przemyslaw, DMCS-TUL, Poland

Current results (2/2) FLAT TOP 20 10 Field gradient [MV/m] After compensation, the detuning (red curve) is only 30Hz during flat top for field gradient 20MV/m (black curve). Resonance excitation method was used. Without compensation detuning is 200Hz (blue curve) Sekalski Przemyslaw, DMCS-TUL, Poland

New Piezo Control Panel ver. 0.1 Last week (24.05.2005) detuning caused by LF was dumped to less than 20 Hz (without piezo compensation it was more than 160Hz, 18MV/m, ACC1 cav5) Proper Matlab script was written to drive piezoelement via DOOCS servers dedicated for function generator Sekalski Przemyslaw, DMCS-TUL, Poland

Fast and slow tuner integration… Next possible step… Fast and slow tuner integration… Instead of using two separate tuner components (step motor and piezoelectric or magnetostrictive devices), there is possibility to use a smart material based linear motor (simple design) clamps Linear translator The stepper motors use three actuators to achieve bi-directional linear motion in a stepwise fashion. The center actuator provides the large-scale motion, 10-50 mm in discrete steps. Two side actuators provide positive clamping power allowing the motor to hold any position for "set and forget" placement. Fine tune mode achieves high resolution positioning of less than 0.05 µm. Sekalski Przemyslaw, DMCS-TUL, Poland

Sekalski Przemyslaw, DMCS-TUL, Poland Conclusions There are several options for cavity tuners (UMI – coaxial tuner, CEA tuner – old and new ones or even a linear step motor system). All tuner are simultaneously developing by CEA Sacley, France and University of Milan, Italy. A lot of problems are solved so far i.e. neutral point, force measurement at 2K, etc., but there are plenty difficulties, which need to be worked out. There are two types of actuators: magnetostrictive and piezoelectric one. The second one has been tested with cavity with success. The detailed study needs to be performed to compare both solutions and choose the best one. Both of types were tested successfully at Lhe temperature. Current setup (1st generation of CEA tuner) with piezostack is already mounted in ACC1 cavity 5. It is possible to reduce detuning from 170 to 20Hz during flat-top (almost 90%). The control signal is manually set nowadays. However, LF is very repetitive from pulse to pulse (the same settings are adequate for months). The feed-forward and feedback algorithm are under developing. Sekalski Przemyslaw, DMCS-TUL, Poland

Sekalski Przemyslaw, DMCS-TUL, Poland LLRF design: Stefan Simrock, Alexander Brandt, Mariusz Grecki, http://tesla.desy.de/~abrandt http://tesla.desy.de/~simrock LLRF model: Ryszard Romaniuk http://tesla.desy.de/~elhep Tuner control design: Przemek Sekalski, Lutz Lilje http://tesla.desy.de/~sekalski Sekalski Przemyslaw, DMCS-TUL, Poland

Control System Each cavity is different as a consequence each cavity needs a different (dedicated) control system settings. Fast automatic system identification procedure is needed for proper starting and operation point. Adaptive feed-forward algorithm will be used Results from FEM mechanical simulations (H. Gassot) Results from experiment in ACC1/Cav5 PhD thesis of H. Gassot Sekalski Przemyslaw, DMCS-TUL, Poland

System identification Let’s assume that system is linear Detuning caused by the piezoelement might be calculated as a difference between detuning caused by RF field with piezo action and RF field only. X1(s) Y(s) L(s) Detuning is measured using forward power and probe signal. Forward power last only 1,3 ms, therefore there is need to shift piezo pulse versus RF field by T and perform next measurement. To eliminate microphonics and other noises there is need to average data from several measurements T Test was performed last week Sekalski Przemyslaw, DMCS-TUL, Poland