1. The Frascati C-band structure and the high-power test of the cavity at KEK B. Spataro (LNF-INFN, Frascati, Italy) on behalf of the SPARC/X C-Band group SLAC, XB11 17/05/2011

2. Design: D. Alesini and V. Spizzo (Univ. of Rome “La Sapienza”) Mechanical design and Realization: D. Alesini, V. Lollo, R. Di Raddo, P. Chimenti Test at KEK: D. Alesini, L. Palumbo, R. Boni, A. Gallo, S. Quaglia, F. Marcellini, A. Battisti, G. Di Pirro, R. Clementi Toshiyasu Higo, Shuji Matsumoto, K. Kakihara (KEK) Silvia Verdu Andres (CERN) Klystron, Modulator, Installation, logistics, financial support: R. Boni, G. Di Pirro, L. Palumbo Beam dynamics: M. Ferrario, V. Fusco, C. Vaccarezza SLED design: B. Spataro, F. Marcellini THANKS TO ALL CONTRIBUTORS

3. OUTLINE 1)Design Overview 2)Realization 3)High power RF test at KEK

4. SPARC RF GUN: -2.856 GHz -1.6 cell LINAC: -S BAND -3 sections (3 m long) UNDULATORS -Diagnostics (RF deflector) -quadrupoles matching -seeding Solenoids SPARC PHOTO-INJECTOR

5. E ≈ 170 MeV GUN Klystron N°1 ≈ 13 MV/m ACC. SECTION 20 ÷ 22 MV/m ≈ 130 MeV ACC. SECTION Klystron N°2 PULSE COMPRESSOR ATT 3 dB splitter SPARC ENERGY UPGRADE WITH C BAND SYSTEM C-band Station C-band ENERGY COMPRESSOR C-band acc. structures > 35 MV/m 5712 MHz – 50 MW 1.4 m ≈ 50 MW (Half pulse) ≈ 50 MW ≈ 100 MW/0.20 μs 2.5 μs E > 240 MeV The new C-band system consists mainly of:  2 accelerating sections (1.4 m long)  1 C-band klystron (50 MW), by Toshiba Ltd (JP)  1 Pulsed HV modulator supplied by ScandiNova (S)  WR187 waveguide system  400 W solid state driver supplied by MitecTelecom (CDN)  SLED The SPARC energy will be upgraded from  170 to >240 MeV by replacing a low gradient S-band traveling wave section with two C-band units. We decided to implement this system at SPARC to explore the C Band acceleration (RF components, construction at LNF TW sections, SLED, syncronization) in hybrid scheme with S Band: -Higher gradients -Very promising from the beam dynamics point of view

6. Single cell design: optimized to work with a SLED RF pulse Splitter: to have a symmetric feeding system. Coupler design: based on the “new generation” of couplers proposed at SLAC for high gradient X Band structures (waveguide couplers ) C BAND structure THE C BAND STRUCTURE AND THE PROTOTYPE Previous the construction of the two TW sections, a prototype with a reduced number of cells, has been realized. The goals of this prototype were: -test all design and construction procedure -test the structure at high power at KEK (Japan) in the framework of a collaboration between LNF-KEK. (and many dicussions with V. Dolgashev during his visit in Italy)

7. SINGLE CELL DESIGN Elliptical shape The structure has been designed as TW constant impedance (cells with equal radius) in order to: -simplify the fabrication -reduce the peak surface field when the structure is feed by a SLED pulse -reduce the unbalance between the accelerating field at the entrance and at the end of the structure, due to the combination of power dissipation along the structure and SLED pulse profile. The single cell has been designed: -exploring the different TW cell parameters as a functiion of the iris aperture (a), thickness (t) and ellipticity (r 1 /r 2 ). -combining the parameters with the real RF SLED pulse and calculating the maximum surface field, accelerating field,.... Elliptical shape (V. Dolgashev)

8. STRUCTURE FINAL PARAMETERS ( with no coupler) PARAMETERprototypeFinal structure Frequency (f RF )5.712 [GHz] Phase advance per cell 2  /3 Number of accelerating cells (N)2271 Structure length included couplers (L)0.54 [m]1.4 [m] group velocity (v g /c):0.0283 Field attenuation (  ) 0.206 [1/m] series impedance (Z) 34.1 [M  /m 2 ] Filling time50 [ns]150 [ns] E s peak /E acc 2.17 H s peak @ E acc =35 MV/m87.2 [kA/m] Pulsed heating @ E acc =35 MV/m<1 o C Average Accelerating field with SLED input pulse and after one filling time 60.2 [MV/m]51.6 [MV/m] Peak surface field with SLED input pulse at the beginning of the pulse (max and @35 MV/m) 140 (96) [MV/m] Energy gain (max and @ 35 MV/m)23.2 [MeV]64.1 (42) [MeV] Output power 0.85  P in 0.60  P in Average dissipated power @ 10 Hz with SLED pulse length equal to one filling time 7.6 [W]59.6 [W] The dimensions of the single cell have been optimized to simultaneously obtain: -lowest peak surface electric field on the irises with the SLED input pulse; -an average accelerating field of, at least, 35 MV/m with the available power from the klystron; -the largest iris aperture for better pumping, reduced wakefields contribution and reduced filling time of the structure (related to the breakdown rate probability).

9. COUPLER DESIGN The design of the coupler has been divided in two parts: -the design of the waveguide coupler; -the design of the splitter. Advantages: -integrated symmetric feeding -low H field  pulsed heating -Better pumping Disadvantage: -multipolar field components (quadrupole) The analysis of the multipolar field components have been done (see technical note (D. Alesini et al. ). waveguide coupler splitter

10. COUPLER DESIGN: QUADRUPOPLE COMPONENT ANALYSIS The coupler is a compact transition between a rectangular geometry (the waveguide) and a circular one (the cavity). It introduces, in the waveguide region, multipolar field components. Due to the symmetric feeding of the system this components have an even periodicity with respect to the azimuthal angle. Beam axis H Ideal cavity Waveguide coupler Pure circular component B  in the center of the waveguide coupler calculate on three circles of different radius A 2 quad. component (A 2 =gradient of the quad. component) 

11. STRUCTURE REALIZATION

12. REALIZATION OF CELL AND COUPLERS @ COMEB S.r.l. Output coupler: Electro discharge machining Ra<1  m tolerances  20  m Input coupler cumputer controlled milling machine Ra<0.2  m tolerances  10  m Cells Turning machine “Shaumblain” Cell Ra<0.05  m tolerances  2  m Cooling pipes Tuning by deformation

13. BRAZING @ LNF The structure has been brazed @ LNF in several steps: -Cells -Couplers -Final brazing Intermediate RF measurements have been done during realization Main problem during the realization: -alignment of coupler and cells in the final brazing process

14. HIGH POWER TESTS AT KEK: OVERVIEW Control room C Band Klystron C Band test room X Band test room

15. Prototype SLED HIGH POWER TESTS AT KEK: TEST AREA (1/2)

16. prototype loads Ionic pumps HIGH POWER TESTS AT KEK: TEST AREA (2/2)

17. PeriodInvolved person ActivityProblemsResults 2/11- 9/11 D. Alesini-Operations startup -conditioning: flat pulse w/o SLED -structure cooling system failure -Increase of the breakdown activity at the end of the week at 30 MW Flat pulse P in_max =30 MW Pulse length=200 ns Rep. rate: 50 Hz 9/11- 16/11 F. Marcellini A. Battisti -Conditioning w/o OK (first day) -SLED switched on  high BDR even at low power <16 MW and pulse length 200 ns -SLED switched off because of high BDR -operation with flat pulse not recovered completely and critical at 300 ns -Acoustic sensor installation for BD monitoring -High BDR after the switch on- off of the SLED -cooling system not yet repaired (KEK people decision) Flat pulse P in_max =30 MW Pulse length=150-300 ns SLED P peak <16 MW due to the high BDR pulse length (peak)=200 ns Total=1.8-2.2  s Rep. rate: 25-50 Hz 16/11- 23/11 G. Di Pirro, R. Clementi -Conditioning with SLED -cooling system repaired SLED P peak =50 MW pulse length (peak)=200 ns Rep rate 50 Hz 23/11- 30/11 A. Gallo, S. Quaglia -Conditioning with SLED -input power calibrations SLED P peak =80 MW Pulse length=200 ns 30/11- 15/12 S. Verdu Andres (CERN) Final characterization of BDR probability P peak >100 MW Pulse length=150-300 ns HIGH POWER TESTS AT KEK: ACTIVITY OVERVIEW

18. STRUCTURE CHARACTERIZATION AT HIGH POWER (1/2) P kly_out =15 MW 2  s

19. PF=klystron output power STRUCTURE CHARACTERIZATION AT HIGH POWER (2/2) See S. Verdu Andres Talk for comparison with X-Band BDR

20. TE037 storage cavity TE028 storage cavity Frequency 5712 MHz Qo = 135000 (unloaded) β = 6 ΔF ~ 13 MHz (min. frequency separation ) Relevant sizes : L ~ 24 cm ( cavity axial length) L/D = 1 ( with D the cavity diameter) For the SLED design we investigated cavities with ellipsoid – like shape in order to increase the quality factor Qo and remove the modes degeneration. P. Fernandes, R. Parodi, C. Salvo, B. Spataro: "The Design of the TE Storage Cavities for a RF Pulse Compressor System". NIM A 288 (1990) pp. 549-554.

21. CONCLUSIONS FOR THE C BAND 1)Design: SLED oriented, large irises, low filling time (D. Alesini, et al., SPARC note RF-11-002, 2011) 2) Realization: LNF+ local companies 3) Results of high power RF test at KEK: 50 MV/m with BDR<1e-6 As responsible of the Frascati Laboratory for the technological transfer activity, we have given to the local private company (COMEB S.r.l. involved in our projects ) a strong economic impact, new know – how, new permanent recruitment, new orders from other institutions ( domestic and international) and so on, in the order of the following areas: 1) X - Band : thank you very much again to S. Tantawi and V. Dolgashev for them help !!! ; 2) RF deflectors designed and realized for the CERN,PSI,ELETTRA ; 3) First PETS prototype fabricated for the CERN ; 3) New Frascati RF gun ( fabrication in progress); 4) Design and realization of the Frascati C band section ; 5) Training for young scientist as : L. Faillace (Radiabeam), A. Falone( PSI), C. Vicario (PSI) and many other ones !!!

22. Some words for the X-Band activities status The work of the X-Band fabricated with the EBW is made possible by the efforts : SALAF Group, INFN - LNF V. Dolgaschev, S. Tantawi, A.D. Yeremian, SLAC Y. Yigashi, KEK L. Palumbo, University of Roma 1 5 th Collaboration Meeting on X-band Accelerator Structure Design and Test Program May 16 h -18 th, 2011- National Accelerator Laboratory Menlo Park, SLAC

23. Triple choke standing wave structure Studies on the mechanical drawings are in progress in order to separate vacuum and RF-joint to test molybdenum and hard alloy structures (A.D. Yeremian, V.A. Dolgashev, S.G. Tantawi, SLAC) http://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpea065.pdf Preliminary 3D Model

24. Triple choke standing wave structure Studies on the mechanical drawings in order to separate vacuum and RF- joint to test molybdenum and hard alloy structures are in progress, too. (A.D. Yeremian, V.A. Dolgashev, S.G. Tantawi, SLAC) http://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpea065.pdf Preliminary Solid Model  mode e.m. distribution  mode field profile on axis  mode coefficient reflection

25. Use of the Electron Beam Welding technique EBW was used for a welding test of an X-band cavity sample. Sample pre-bonding @ 300°C 0.04 mm 0.6 mm cavity Tool to keep together the 2 half-cavities during pre-bonding The pre-bonding is used in order to prevent : 1) microgaps left by welding (on the cell surface) [vacuum leakage tests gave about 10 -10 mbar litre/sec] 2) accidental pocket air inclusions 3) EBW damages in the internal surface of the structure 3 mm EB welded sample Prototype ready to be used for the EB technique Cross section of the prototype

26. …… use of the Electron Beam Welding technique The welding meets the requirements of the applicable specification SI 01.003 revA No cracks have been found in the fusion zone and in the heat affected zone. There are only small porosities at the root-side of the weld joint which are, however, within the limits of the specs. Moreover dimensional mechanical tests before and after welding gave negligible difference. Macrographic inspection of EB welded joints, made on a X-band test specimen pre-bonding zone EBW zone The joints in the pre-bonding region demonstrated to work well and additional tests are in progress, too.

27. Macrographic inspection of EB welded joints, made on a X-band test specimen Carrried out by HTC (High Technology Center April 14 – 2011)O Test Specimen (after welding process) Specimen Identification The joints in the pre-bonding region demonstrated to work well. Vacuum leakage tests after the Welding process gave about 5 10 -10 mbar litre/sec Cavity (inside) Electron Beam Welding region. Again no cracks have been found in the fusion zone and in the heat affected zone

28. Triple choke section mechanical drawing Gasket in order to separate vacuum and RF-joint to test molybdenum and hard alloy structures Triple choke section solid model Copper real triple choke cavity after Electron Beam Welding process Copper Triple choke fabrication

29. Assembling of all cells for making the pre-bonding process Single cavity Devices after the pre-bonding process ready for making the Electron Beam Welding process Prototype Real model

30. Bead-pull measurements of triple choke cavity made of Cu and E.B.W. process Frascati low power test data ModeFrequency [GHz] Qoβ1β1 β2β2  11.44283680.08220.039 2  /3 11.38182890.19080.059  /3 11.34279620.05210.076 An about 40 MHz frequency increase of the  mode has been obtained after the welding process. Investigations are in progress !!!

31. Fields profile on axis measurements Q 0 =8368  mode Q 0 =8289 2  /3 mode Q 0 =7962  3 mode Triple choke cavity The baking of the triple choke cavity structure is in progress, too.

32. Scattering Parameters and Field profile : π mode S 11 S 22 S 12 β 1 =0.0822 β 2 =0.039 Q 0 =8368 π mode electric field profile on axis

33. Scattering Parameters and Field profile : π mode S 11 S 22 S 12 β 1 =0.0822 β 2 =0.039 Q 0 =8368 Electric field profile on axis

34. Scattering Parameters and Field Profile :II mode S 11 S 22 S 12 β 1 =0.1908 β 2 =0.059 Q 0 =8289

35. Scattering Parameters and Field Profile :III mode S 11 S 22 S 12 β 1 =0.0521 β 1 =0.076 Q 0 =7962

36. Thanks a lot for your attention !!!!