1. 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

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

3. 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

4. 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 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
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

5. 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

6. 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 in germanium and silicon samples
Sekalski Przemyslaw, DMCS-TUL, Poland

7. 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

8. Sekalski Przemyslaw, DMCS-TUL, Poland
Types of actuators (2/2)
Piezoelectric tuner
Magnetostrictive tuner
Max strain at 2K
Small, ~0.05%
Large, % (need to be checked)
Lifetime
Large, if preload correct
>1010 cycles (small damage)
Large
>108 cycles (no damage)
Preload
Small range, kN
NOTE: few kN per 1mm (416kHz)
Large range, kN
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€ k€
1 k€ k€
Sekalski Przemyslaw, DMCS-TUL, Poland

9. 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

10. 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

11. New Piezo Control Panel ver. 0.1
Last week ( ) 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

12. 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, 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

13. 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

14. Sekalski Przemyslaw, DMCS-TUL, Poland
LLRF design: Stefan Simrock, Alexander Brandt, Mariusz Grecki, LLRF model: Ryszard Romaniuk Tuner control design: Przemek Sekalski, Lutz Lilje
Sekalski Przemyslaw, DMCS-TUL, Poland

15. 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

16. 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