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WP3 Pierini

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Published on November 12, 2007

Author: Chan

Source: authorstream.com

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INFN-MI: Status:  INFN-MI: Status Angelo Bosotti, Nicola Panzeri, Paolo Pierini Planning:  Planning Milestones : Report on final tuner design by end 2005 Tuner construction and testing by mid 2006 Parallel “historical” tuner activity Started within TTF, now ILC/XFEL In CARE/JRA1/WP8 Report in preparation for 1.3 GHz b=1 cavities (Angelo Bosotti) LFD compensation at high gradients (Dn = KL E2):  LFD compensation at high gradients (Dn = KL E2) Evolution of the tuner concept, with integration of the fast LFD action 1.3 GHz system under fabrication right now Cavity A characterization:  Cavity A characterization Previous estimation [7 Hz/(MV/m)2] only on half-cell geometry, but also, mechanical load condition was overestimated by a factor of 2. Present calculation on the full geometry. Where did we stand in tests with cavity A?:  Where did we stand in tests with cavity A? Vertical tests: 3 at Saclay, 3 at JLAB Huge spread in static measurements! And off by a factor 10 Influence of boundary conditions:  Influence of boundary conditions Linear superposition of 2 effects: Shape deformation (fixed boundary) Cavity shortening (cavity+boundary combined stiffness) Analytical derivation of full behavior requires solution of only 2 load cases Cavity frequency response under arbitrary b.c.:  Cavity frequency response under arbitrary b.c. Frequency response of the cavity can be then understood as a function of the external boundary condition Using values from the cavity mechanical characterization and Slater perturbation theorem The RF test frames:  The RF test frames Saclay tests in 2004 Jlab tests in 2003/2005 Q: Are they sufficiently stiff? JLAB frame:  JLAB frame Cavity is held at He tank disks with a bar Dish stiffness is greatly reduced! Saclay frame:  Saclay frame A: NO, both are not stiff enough Correlation with measured KL:  Correlation with measured KL Mechanical models assume perfect joints and no slack contacts between components In reality: joints, screws, etc. Alternative check:  Alternative check From the Saclay data at low temperatures (2.2 to 1.7 K, where the bath pressure is more stable), an average value of Dn/DP of -462 Hz/mbar can be evaluated Kext of 1.15 kN/mm can be estimated, coherent with the model discussed before From the JLab data an average of Dn/DP of -1020 Hz/mbar in the same temperature range can be estimated. Comparable to a nearly “free” cavity behavior (nominal -966 Hz/mbar), with a negligible external stiffness condition with respect to the cavity stiffness, again, coherent with the model discussed before Summary on static KL:  Summary on static KL RF test data is understood Weak constraints for the cavity length Low beta geometry very sensible to external boundary condition (low cavity stiffness) Behavior of KL agains Kext allows to set tuner stiffness requirements under operating conditions Interaction with CEA (GD) has shown a nearly perfect agreement of static LFD modeling both calculation modes based on Slater perturbation theorem, but different and independent implementations, especially concerning the mechanical part of the codes (ANSYS vs CASTEM) Planning for dynamic LFD calculations harmonic analysis + Slater for cavity transfer function and piezo tf time dependent analysis: overelongation? need time for the development and check the procedures Requirements for 704.4 MHz:  Requirements for 704.4 MHz One of the uncertainties of the piezo materials is still their stroke capabilities at the low operating temperatures Assuming a 3 mm stroke to cavity (long piezos) [safe? SRF/WP8 work in progress] a ~1000 Hz frequency offset can be compensated during the fast tuning action With a design accelerating field of 8.5 MV/m, this implies that the overall KL in the operating condition should be limited to around -10 Hz/(MV/m)2 We took a 50% margin for dynamic LFD? [M.Liepe: factor 2] In order to achieve this condition with these rather soft cavities the combined stiffness of the He Tank and tuner system needs to provide ~ 10 kN/mm At 20 kN/mm we are hitting limit with He tank dish stiffness Tuner requirements:  Tuner requirements Extracting out the Tank and end dish stiffness contribution (total of 15 kN/mm), the requirement for the tuner becomes about 20 kN/mm Actual experimental stiffness including leverage (TTF) On the road to finalize tuner design:  On the road to finalize tuner design Will ask for bids in late 2005 and Order main tuner mechanical components before end of year (INFN contribution is available) Then fabrication time will take 4-6 months Now we are fine-tuning the tuner stiffness by slight adjustments of the blade number length and slope for final optimization before emitting final drawings for Cavity A

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