1. Engineering of the power prototype of the ESRF HOM damped cavity* V. Serrière, J. Jacob, A. Triantafyllou, A.K. Bandyopadhyay, L. Goirand, B. Ogier * This work, carried out within the framework of the ESRFUP project, has received research funding from the EU Seventh Framework Programme, FP7. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

2. Introduction The new ESRF cavity Objectives Aluminum prototype Design optimization Experimental validation Copper power prototype Design aspects Technology of fabrication Perspectives and future work Summary 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009 1 Anna Triantafyllou-E.S.R.F.

3. Introduction The development of the new 352 MHz cavity for the ESRF is based on the 500 MHz European HOM damped normal conducting cavity. 2 Cavity body HOM damper Tuner Coupler Vacuum pump Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

4. Introduction 3  300 mA of beam current : - Design margin in terms of power per coupler window : 500 mA of stored beam. - Design margin in terms of HOM damping : 1A of bunch instability threshold to anticipate possible discrepancies between numerical and experimental data.  9 MV of accelerating voltage :  New ESRF cavities objectives : - Installation of 18 new single-cell cavities. - The system should be operational with 12 cavities. Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

5. Aluminum prototype  Design optimization : 1 damper for the remaining HOMs : f c = 1.05 GHz d = 160 mm The vacuum pump port is not degrading the quality factor Length before C48 ferrites = 840 mm Dissipated power @ 352 MHz < 100 Watt 4 2 dampers not in the same plane : to avoid the high impedance 758 MHz mode measured on the previous prototype 2 dampers for the lowest HOMs : f c = 452 MHz d = 230 mm Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

6. Aluminum prototype 5 - Good correlation between measured and calculated data. - All the measured impedances of the HOMs are lower than the L.C.B.I.  Validation of the numerical model : @ 352 MHz : R s /Q =145 Q Cu : 30 k R s =4.35 MΩ Ridge width = 60 mm Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

7. 6  Design aspects - The gap problems between the ridges and the cavity body are eliminated by splitting the HOM dampers in three parts. Copper prototype Coupling section Intermediate section Absorber Coupling section e-beam welded to the cavity body. In the ridge zones, the electrical continuity will be established by means of RF fingers. Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

8. Copper prototype Anna Triantafyllou-E.S.R.F.  Design aspects - In house design of the cooling system. *Thanks to Lin Zhang for his advice in thermal computations Maximum temperature : 56°C Cooling channels Heat flux computed for the degraded operation 9MV with 12 cavities : 7 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

9. 1. Machining of the pieces Copper prototype 8  Establishment of technological process (1/3) 2.The gap is avoided by splitting the dampers in three parts. The first part is e- beam welded to the body. e- Cavity body Coupling section Beam stop: will be removed after welding by turning e-e- constant 15 mm thickness all around the e-beam welding Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

10. 3.The vacuum flanges, outlets and pipes are brazed in a single step Turning this assembly Brazing of the S.S. and the Cu TIG welding of the flanges Copper prototype Copper plating the SS surface 9  Establishment of technological process (2/3 ) Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

11. Machining of the end discs Brazing step to attach the cooling system and the outlets. Intermediate coupling sections Brazing of the vacuum flanges and the cooling system. Brazing of C48 ferrites on Copper Brazing on the ridges TIG welding of the Cover.  Establishment of technological process (3/3) Copper prototype Frequency tuning by machining the end disc The end discs are added in a last brazing step. 10 Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

12. Copper prototype  Alternative Fabrication process 11 Division of the cavity body in 3 parts Machining of the cooling system in each part. e beam welding to add the water box covers in each part. Coupling sections and outlets are joined by e beam from the internal face. e- Outlets brazing before the cavity assembly e beam welding for the 3 shells assembly - e beam welding to join the angles. - e beam welding for the end discs after the frequency tuning steps. Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009

13. Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009 Copper prototype  Stress calculation : Stress < 27 MPa 40 MPa < Stress < 57 MPa 12 - max water pressure = 15 Bars The Maximum stress computed in the e beam weld area is reduced by increasing the e beam welding surface.

14. 13 Conclusions and Perspectives Validation of the simulation model by an aluminum prototype. Two different fabrication processes for the power prototype. Ferrite infra red test bench under development. Delivery of three prototypes expected by the end of 2010 followed by tests. Anna Triantafyllou-E.S.R.F. 13th ESLS RF Meeting, Desy, Hamburg, 30 th September - 1 st October 2009