1. 1 TTC Meeting at CEA Saclay 6 july 2015 ESS Double spoke tuner development N. Gandolfo

2. 2 Outline Working principle Tuner stiffness measurement A world of tuner technical issues Dedicated test bench Disengaging system Preparing the masse production

3. 3 Main purpose : Compensation of large frequency shifts with a low speed Actuator used : Stepper motor with planetary gearbox (1:256) Slow tuner action Fast tuner action Main purpose : Compensation of small frequency shifts with a high speed Actuator used : Piezoelectric actuators

4. 4 Vacuum Motor Ball screw (p = 2 mm) Rods Flange frame Cavity flange Lever arm (D/d = 10) Bellow LHe bath Cavity vacuum Insulation vacuum A ball screw system driven by a stepper motor acts on a double lever arm mechanism to provide a significantly reduced displacement of the cavity flange along the beam axis. Slow tuner principle D d Cavity body LHe vessel

5. 5 The tuner is put on a large horizontal tensile/compressive test bench A displacement is manually progressively applied to push against the tuner, thus representing the same stress than pulling a cavity. Load sensor give a direct force measurement. Displacement sensors (not shown on the picture) measure at different locations of the tuner. F Mobile frame Load cell Fixed frame Results : Tuner #03 : 28 kN/mm Tuner #04 : 30 kN/mm Force (kN) Tuner deformation (mm) Conclusion : 3D finite element computation gave 110 kN/mm for machined parts deformation but it seems the mechanical joints (ball bearings, etc.) are the weakest elements of the system.

6. 6 Last year, several case of failure of the tuner has been found (  my talk from TTC meeting December 2015) The problem appeared to come from slight oil film found on the large roller bearing. Ultrasonic cleaning solved the problem but a lack of lubrication was still there. Coating vendor has been asked to prepare the spherical roller bearing with dry lubrication such as MoS2 or WS2 but all answered there was a need to disassemble these bearing prior coating. A disassembling way has been found, bearing were sent to be prepared with a LAM'LCOAT ® coating which is likely a variant of WS2 lubricant. We are planning to test the prepared bearings on a tuner with the next incoming cavity vertical test this summer. Outer ring of the bearings after coating

7. 7 On the last tuner test at low temperature (January 2015) the tuner get stuck from the start without giving us a chance to move it. Industrial high precision grade ball screw with following specifications : -Screw made in stainless steel (AISI 440C) -Balls in zircone (ZrO) -MoS2 lubricant coating A LN2 bath test of this element has been made : Strong frictional torque appeared Irregular motion  seems either the ball or the rolling path were damaged 21 LN2 bath method Also, a difference has been found with previous “normal static load” ball screw with trapezoidal thread [1] From the actual screws which are in “high static load” profile with circular thread (same vendor) [2]. The point is, in the first case the ball are sharing a line of contact. This might make the system more vulnerable against differential thermal shrink. Both of design have been tested in LN2 bath, the design with trapezoidal thread profile seems less affected to the low temperature but still show some frictional torque.

8. 8 C B A Now we are looking at other candidates to make comparative low temperature stress tests in order to get data : [A] Actuated screw/nut system from Phytron [B] Satellite roller screw (picture aside) : quite good experience from SOLEIL facility (SRF15 paper) [C] More classical screw/nut system + dry lubricant (currently working in our lab but with small forces and in LHe bath)

9. 9 At first, 2 prototypes of tuner were made to receive 50 mm long piezo actuators. Cold tests showed the fast tuning range was OK but in order to reduce the voltage for LFD compensation, it has been decided to use larger piezos (90 mm) just by “enlarging” the tuner. Static detuning test at RT Second tuner prototype « only » modification : allow to put longer piezo 50 mm  90 mm Two enlarged tuners have been made and tested with long piezo, but the results are pretty disturbing : -At room temperature we observe a gain that match well with the expectations as shown on the graph -At low temperature we observe no gain at all between 50 mm piezo and 90 mm piezo on the fast tuning range  U(V) df (Hz) First tuner prototype 90 mm

10. 10 Trying to find some explanations Boundary conditions are not changing a lot, especially from RT to LT. Nevertheless, due to change of length the differential thermal shrinks rise significantly, it could lead to excess the piezo blocking force. Especially thinking about piezo actuator dilates itself on its longitudinal axis when the temperature drops. We assume the load of the piezo is an accumulation of the following factors : -Manual preload when installing the piezo on the tuner frame  monitored through voltage measurement -Differential thermal shrink  appeared to be negligible with 50 mm stacks but maybe not with 90 mm stacks -Slow tuner action (cavity forces counteract)  appeared to be negligible, at least near the starting point of cavity stretching Next tests : -Try to monitor actuator preload online -If thermal shrinks appeared to be the main cause, then act on the manual preload in consequence -More tests to better understand piezo actuator especially at low temperatures and with different loading conditions.

11. 11 R&D program : Dedicated tool built for testing piezo at low temperatures. Design have been made in the continuity of the piezo test stand we already had at Orsay. Main specifications : -Compressive force (0 to 4kN) applied with electric motor + spring (with a stiffness of 130 N/mm) -Online force measurement thanks to a RT load cell and coaxial transmission tube -Displacements in the cold box up to 20 mm, also measured on RT side -Possibility to cool with LHe (for characterization) or LN2 (for accelerate life test) Piezo characterization tests were scheduled early this year but have been delayed in order to test in priority an innovative safety system for tuners.

12. 12 Introduction : During operation, part of the cavity body is potentially highly stressed (up to 311 MPa) by the tuner action, much far away from the RT elastic domain (around 40 MPa). This can lead to cavity damage risk in a case where the tuner is getting stuck. Goal : Get the possibility to release the cavity from the tuner prior any warming-up, even in case of failure of motor/gearbox/ballscrew. Idea : Put inside the tuner a disengage system that act likely as a mechanical switch and rely on the association of two different materials to : -Release the system above a temperature (> T high ) -Couple the system at low temperature (< T low ) A heater located on the outside member provides heating to the whole assembly. (old design values)

13. 13 Where would it goes ? Preliminary computations showed some difficulties to find a model that fit well to the already existing design and transmit up to 20 kN force which is the tuner specification. An idea is to put it on the screw/nut system, thus before the lever action there is only 1kN max force to transmit. What does it look like ? Thermal sensor Heaters (x2) Ballscrew Disengage system

14. 14 Test protocol : 1- Cooling down to 4K : no force applied 2- Applying 1 kN force : equivalent to max force on the tuner screw nut in theory 3- Heating up to 300 K : dissipating 30 W on two resistive film heaters  30 minutes The system disengage smoothly with good reproducibility from 230 K to 300 K. However : While removing the system from its chamber, we discovered it was a bit stuck instead of staying free as before the test. We decided to proceed as following : 1- Heating up using the same film heater 2- At around 60 °C, it totally disengaged 3- Back to room temperature, it was still free again. Plastification ? Metal adhesion ? Next actions : Larger test campaign to better understand, repeat cycles and test different sizes to converge on definitive values of diameter/tolerances that meet tuner requirement. Heating up from 4K to 300K Start to disengage around 230K F(N) Ø(mm) T(K) Inside member ø Outside member ø Shrink over T(K)3 runs of heating on same setup and same day

15. 15 Ability to test 4 tuners without cavity (more safe) at 300 K and 77 K Goal is to validate main functions of the tuner : Motor sensitivity and cabling, Piezo sensitivity and cabling, disengaging system. This kind of device would also have the potential to make an accelerated life test of whole tuners. Burn-in test dedicated tooling Ø700 mm

16. 16 Procurement stage : Motor / Ball screw / Piezos / Pre assembled mechanics  For piezo, we will ask the suppliers to supply customized solution according to our specifications Assembly stage Burn-in test RT + LT Cavity + tuner vertical test Cryomodule integration Mass production plans  One does not want a tuner to be stuck during a cavity test  But still we want to ensure a cavity+tuner pair fulfill the final resonant frequency requirement prior a cryomodule assembly

17. 17 Lesson learned When testing a tuner, do not just play with it few hours like it would work the same way for few years. Assemble, test, disassemble, re-assemble, re-test, test it again and again as often it is possible. Spend time over tests especially while it is still at the prototype state ! Not a new statement but more like encouraging a well known rule : extensive test of each critical elements. Cold burn-in test of each tuner might be a must have in the mass production loop. Many thanks to T. Fletcher for the work on stiffness measurement, Y. Zeraia for the work on disengage system qualification tests, to the whole ESS Orsay team, and to the SRF community (you).