1. Renzo F. Parodi INFN-Genova
STREGA JRA3 WP 1 - Task M3
Task T3
“Superconducting Parametric-Converter Detector M3 and Wide area parametric transducer T3.”
Renzo F. Parodi
INFN-Genova

2. Renzo F.Parodi, ILIAS GW General meeting
Collaboration
The INFN_Genoa Group is the only Group involved in the development of the M3-Task.
For the T3 task the Genoa Group works together the CNR-IFN Trento, INFN (Legnaro and LENS-Florence) CNRS (LKB-Paris) Groups.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

3. Task M3 Activities Full project
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

4. Seamless cavity production
The cavity was sputtred with
one micron Niobium film and tested
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

5. Niobium on Copper prototype (continued)
The Qo at low field was 1011 ad dropped smoothly below 1010 at a stored energy of 14 Joules (exceeding the design surface field of 100 mT).
The cavity met, since the first RUN, the design goal Q> 10 Jules *
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

6. Parametric converter prototype
The cavity was built using the procedure established along the Task M3
using the tooling developed for the construction of the cavity mock-up
The prototype was delivered to the Genoa-INFN lab on October 16, 2006
Test will start at the beginning of November.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

7. The cavity prototype as received
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

8. Tunable Niobium detector Prototype
integration of the cavity prototype in the Cryogenic setup
A magnetic shield is needed to reduce the Trapped magnetic flux producing additional RF Losses.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

9. Wide area parametric transducer T3
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

10. Advantages of a RF parametric Transducer
The noise figure of commercial RF amplifier is close to the quantum limit (10 times)
Manipulation of RF signals is “easier” than at Low frequency
Feedback systems allow to control, and reduce, some noise contribution.
It is a wideband with constant electric impedence (50 W).
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

11. Resonant cavities as an electromechanical transducer.
The change of a resonant cavity critical dimension changes the resonant frequency of the cavity.
For a sinusoidal variation of frequency fm and deviation Df the voltage at the cavity output is
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

12. Resonant cavities as electromechanical transducers
The signal produced by the mechanical modulation of the cavity gives an electric signal at the frequencies (fo±fm).
The cavity energy is distributed on the carrier at fo and on the sidebands at
The sidebands amplitude is proportional to Df/fm (for low Df/fm )
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

13. Renzo F.Parodi, ILIAS GW General meeting
Cavity Transducer
The optimum wide area transducer is a piece of shortened Ridged Guide with mm gap between ridge and wall.
Using this cavity a sensitivity of ~3x1013 Hz/m is easily obtained
The RF Output from different cavities can be algebraically added to reject the signal coming from unwanted mechanical modes
Cross section in the XY plane of a
Ridged-Guide cavity (half cavity)
The RF electric field linea are
superimposed
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

14. Transducer cavity (continued)
Adding a “CHOKE” flange the cavity is closed without the need of a metallic junction between the cavity and the moving wall.
This allows the movement of the waveguide wall producing the frequency modulation
Cavity Cross section
XY plane
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

15. Renzo F.Parodi, ILIAS GW General meeting
Wide area detector Parametric
Transducer cavity
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

16. Sensitivity limitations
The main limitation comes from the Phase Noise of the Drive Oscillator : the sidebands of the converted signal need to be greater than this noise.
The Frequency spectrum of the phase noise, for a “Very Good” drive oscillator, is shown in the next slide.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

17. Phase Noise of a “Very Good” Drive Oscillator
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

18. How to reduce the Drive Oscillator Phase noise ?
Using the superconducting cavity of the transducer in a control Loop (AFC), and carefully tailoring the loop gain, the oscillator Phase noise can be reduced.
Pushing the system to the limit we can (at least on the paper) obtain the phase noise spectrum reported in the next slide.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

19. Error reduction effect
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

20. Renzo F.Parodi, ILIAS GW General meeting
Challenges
The Drive oscillator phase noise set the ultimate limit for the transducer.
The possibility to get the needed sensitivity critically depend upon the capability of achieving the foreseen Phase noise reduction.
Despite the use of Superconducting cavities with the best achievable surface resistance, the RF power load from ~ one meter long cavities is still ~ 2-5 mw per cavity; this dissipation set some hard limit on the operating temperature.
This value allows a rather comfortable operation at superfluid helium, but is by far too high for the operation in a deep ultra-cryogenic environment (10mK)
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

21. Renzo F.Parodi, ILIAS GW General meeting
Experimental check
Most of the key features of this transducer are independent by the Cavity dimensions and shape
Using a small area cavity, already easier to build, the cavity independent problems can be investigated (Oscillator noise reduction, feedback loop…).
We are building an testing a prototype (small area) transducer to test the soundness of the concept and the electronic system on a real GW detector.
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

22. Renzo F.Parodi, ILIAS GW General meeting
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting

23. Renzo F.Parodi, ILIAS GW General meeting
First test of the small area
parametric converter
The antenna modes are 830 and 873 Hz
30 November, 2018
Renzo F.Parodi, ILIAS GW General meeting