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Comparative assessment of SC Structures

Comparative assessment of SC Structures. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008. Juliette PLOUIN CEA/Saclay. Objectives of this presentation. Give an overview on the work achieved through the HIPPI project.

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Comparative assessment of SC Structures

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  1. Comparative assessment of SC Structures HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 Juliette PLOUIN CEA/Saclay HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  2. Objectives of this presentation • Give an overview on the work achieved through the HIPPI project. • Present together the main results collected for the cavities involved in the project, in order to prepare elements of comparison. • Introduce the discussion. • Prepare the final report. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  3. All the cavities have been fabricated Elliptic B Elliptic A 3 Spoke 1 Spoke CH HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  4. The HIPPI program HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  5. RF parameters HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  6. Fabrication parameters Inner magnetic shield (inside the He tank) Outer magnetic shield HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  7. Mechanical simulations • Calculations of mechanical parameters have been carried out for all the cavities in order to evaluate : • the influence of the Lorentz Force Detuning (LFD) during the tests • the influence of the Helium pressure • Main parameters are : • cavity stiffness [kN/mm] • pressure sensitivity [Hz/mbar] • Lorentz coefficient KL [Hz/(MV/m)²] • KL depends strongly on the external stiffness, which is not easy to evaluate • Meaningful informations must contain the extrem values of KL (free/fixed ends), and the theoretic curve between these points • Calculations on the dynamics parameters (mechanical modes) have also been performed (EllA, EllB, CH), but their comparison is of poor interest because they strongly depend on the cavity surroundings  not presented here • The values correspond to the final design of the cavity with its stiffening system, without helium tank. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  8. Mechanical parameters HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  9. CARE Conf-05-055-HIPPI Elliptic A : stiffening rings KL = -2.7 Hz/(MV/m)² KL = -20.3 Hz/(MV/m)² Elliptic B 3 Spoke KL = -3.1 Hz/(MV/m)² KL = -4.1 Hz/(MV/m)² (in red) stiffening rings Curves KL/Kext (1) HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  10. 1 Spoke KL = -72 Hz/(MV/m)² KL = -20 Hz/(MV/m)² stiffeners CH stiffening ribs – additional stabilization rings Curves KL/Kext (2) HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  11. Comments about the mechanical parameters KL(fixedends) KL(fixedends) KL(freeends) KL(freeends) The value for |KL(fixed ends)| determines the minimum Lorentz detuning expected on the cavity (external stiffness is infinite) If |KL(free ends)| is small : the external stiffness is not a critical value to have a small Lorentz detuning If |KL(free ends)| is high : the external stiffness (stiffness of the tuner) has to be high enough : ~100 kN/mm For high values of the cavity stiffness, it is necessary to have a high stiffness for the tuner, to be able to tune the cavity. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  12. Mechanical measurements (cold tests) • Static : Lorentz coefficients have been measured, in the mechanical environment of the low power tests conditions (Kext only approximatively known), with almost good agreement with the simulations. Several cavities presented a thickness lower than expected. • Dynamic : at this time, measurements in the pulsed mode have been performed only for the CH resonator. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  13. Elliptic A External stiffness has been evaluated for each test, and the exp. data are compatible with the simulated curve. Elliptic B measured KL -3.8 ± 0.4 Hz/(MV/m)2 simulation : this value could correspond to an external stiffness kext = 100 kN/mm, and a cavity thickness ~3.3mm (measured thickness) CARE Conf-05-055-HIPPI Experimental Lorentz Force Detuning – statics 1 Spoke measured KL : between -55 and -47 Hz/(MV/m)² simulations : -20 Hz/(MV/m)²(fixed ends) -72 Hz/(MV/m)²(free ends) 3 Spoke Presented by E. Zaplatin HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  14. Experimental Lorentz Force Detuning – dynamics CH structure RF pulse Reflected power gives the frequency detuning VCO signal Transmitted power exp. value for the static KL ? numerical value for the static KL with free ends ? Microphonics at cryogenic temperatures and the impact on the rf-resonance HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  15. stepping motor Elliptic A : blade tuner, between two parts of the He tank Tuning range 420 kHz piezo stepping motor Elliptic B : tuner between the He tank and the cavity flange Tuning range +/- 2.5 MHz Mechanical stiffness ~30 kN/mm (estimated) piezo Tuners - 1 HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  16. Spoke cavity (helium tank) CH structure : tuner between the inner cold mass containing the helium and the outer vacuum vessel. Tuning range +/- 1 MHz Piezoelectricactuators 1 Spoke piezo Cold tuning system (copper braid for cooling) CM0 Cryostat(80K shield) Tuners - 2 HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  17. Tuners - 3 Each tuning system has been especially adapted to its own cavity and to its surrounding. It is not meaningfull to compare the performances of the different tuning systems without considering at lot of parameters depending on the cavity and on the cryostat. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  18. field emission Quench Low power RF tests - 1 Elliptic A 3 Spoke 352 MHz Elliptic B HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  19. Low power RF tests - 2 1 Spoke CH 3 Spoke 760 MHz HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  20. Low power RF tests - 3 • The performances of the cavity strongly depend on the cavity preparation (BCP, HPR, EP...) – detailed in the report. • A realistic comparison should include a representative sample for each cavity to take into account the spread generally observed in the results for a batch of identical cavities prepared and tested in the same conditions. • In order to take the size of the cavity into consideration, it is meaningfull to evaluate the real estate gradient... HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  21. Real estate gradient DU is the energy received by a particle while crossing the cavity Eacc = |DU|/(q.Lacc) = Vacc/Lacc Is it possible to give an evaluated value for Lreal, with the same criteria for each structure type, taking into account the external environment of the cavities ? HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  22. Couplers Elliptic B 250 kW peak power duty cycle 10 % whole coupler copper plating of the outer conductor doorknobs RF window (T=300K) 2 loops to intercept the conduction flux from 300K  4K 1 Spoke 20 kW cw RF cavity port (T=4K) HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  23. Considerations about the estimated cost We know that a cost comparison between the cavities cannot really be used, because in some cases, the laboratories have carried out the fabrication by their own, while the fabrication has been performed by an industrial society in some other cases. Furthermore, each cavity is a prototype, and the cost for its fabrication is necessarily different from the cost of one item into a series of cavities. Indications for the effective cost of a prototype has been given for two cavities : • Elliptic B : • cavity manufacturing (with He tank) : 120 k€ • coupler + magnetic shield + tuner : 75 k€ • CH structure : • The costs for structure only without magnetic shielding and without helium vessel amounts to 350 k€. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  24. Contents of the final report • We have values for the RF and the mechanical parameters which can be presented together. The comparisons can be made by beta families : b=0.47 / b = 0.1-0.2 • The experimental results will be presented for the low power RF tests ; experiments for high power won’t have progressed enough at the end of the program to give meaningful results. • For the couplers, the tuners, .. it could be more meaningful to present the different technical solutions including their own constraints and their characteristics, rather than to make a real « comparison ». (e.g. 352 MHz-20kW / 704 MHz 250kW pk) • This comparison shows the performances that can be achieved from the different kinds of cavities. However it is difficult to conclude that one cavity is better than the others. In particular, it would be necessary to have statistical results about theses cavities. HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

  25. Preparation of the report • A –very- first draft has been prepared, with the contributions received before the meeting. • This draft and this presentation are a tool for the discussion, about the data that should appear in the report, and about the conclusions. • This last WP3 session should lead to an agreement concerning the headlines of the final report, in order to achieve the redaction before december 08 Thank you ! HIPPI 2008 Annual Meeting CERN,  29-31 October 2008 

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