Contributions to ELI-NP on RF accelerator activities

1. Contributions to ELI-NP on RF accelerator activities Andrea Mostacci Università di Roma, Sapienza The joint Sapienza/INFN-LNF group is active in the field of S-band, C-band,X-band accelerator devices design and construction. The group is interested both in designing beam generation and manipulation devices as well as the technological issues related to the construction of devices standing the high RF power needed in modern accelerators. Through numerical simulation, we study and optimize the electron beam dynamics in a single device as well as in the whole machine. Moreover we are commissioning the LNF photo-injector (SPARC), the first S-band/C-band high brilliance linear accelerator. As a university based group, we have also experience in training students in their first steps in the accelerator physics and technology.

2. Outline Goal Show our experience and ongoing activities on RF issues of accelerator physics which can be useful for ELI-NP Group L. Palumbo (Sapienza) and its group M. Ferrario, B. Spataro, L. Serafini (INFN/LNF) and researchers from INFN/LNF accelerator division High brightness photo-injector (SPARC) commissioning. S-band devices: installation and operation of S-band accelerator and in-house RF gun construction. C-band devices: high gradient accelerating sections and RF guns, installation and commissioning. X-band devices: beam manipulation devices (e.g. harmonic cavities) and beam generation devices (hybrid SW/TW gun). R&D activities on RF issues Beam dynamics studies and optimisation (S-band, C-band, X-band and mixed solutions). Training and educational experience. Contribution to ELI-NP.

3. Commissioning of SPARC 150 MeV S-band linac Velocity Bunching Diagnostic and Matching Undulators u = 2.8 cm Kmax = 2.2 r = 500 nm 10 m 15 m S-band Gun Long Solenoids Seeding THz Source High Brilliance photo-injector

4. S-band devices (~ 3 GHz) We presently are runnig a S-band linear accelerator producing high brightness 180 MeV electorons. We design, built and operate RF deflectors for beam length measurement. Our device, first tested at SPARC, has been rebilt and installed in PSI SWISS-FEL and FERMI FEL injectors. A novel improved RF gun is at the executive design stage (design scalable to higher frequencies). SPARC RF Deflector RF gun Beam

5. C-band devices (~ 6 GHz) For SPARC energy upgrade (180 250 MeV), we will install and operate in-house built TW sections. (>35 MV/m accelerating field) S-band injector in a C-band linac will be tested next year @ SPARC and it is the solution adopted by SWISS-FEL @ PSI. After the succesful Spring 8 FEL, the C-band seems a mature and reliable technology. For a given bunch charge, wake fields and beam loading are relaxed with respect to higher frequency solutions. The same arguments holds for timing, synchronization and jitters issues. We are investigating a fully C-band linac design, including C-band RF gun. Power test @ KEK Symmetric input coupler Output couplers 48 MV/m Beam RF power

6. X-band devices: design & production X-band (11.424 GHz) harmonic cavities for longitudinal phase space compensation in high brilliance photo-injectors Accelerating cells RF CAD design TUNER Beam Coupling cells RF power Low power test and multi-cell cavity tuning Technological issues (high power test @ SLAC), novel materials Cu z axis (cm) Mo

7. X-band devices: design & production X-band (11.424 GHz) harmonic cavities for longitudinal phase space compensation in high brilliance photo-injectors Accelerating cells RF power 9 cells TUNER Beam Coupling cells ~17 cm Low power test and multi-cell cavity tuning Technological issues (high power test @ SLAC), novel materials Cu z axis (cm) Mo

8. X-band devices: R&D on manufacturing We join the world wide effort to avoid hot brazing to Photographs of three manufactured X band cavities: (a) Cu brazed; (b) Mo brazed; (c) Cu electroformed. V. Dolgachev, SLAC B. Spataro, invited contribution to X-Band Structures, Beam Dynamics and Sources, December 2010

9. X-band hybrid gun (Sapienza/INFN/UCLA) SW RF gun section fed on-axis from coupling cell that also feeds (the majority of the power) to a lower gradient downstream TW section (no circulators needed). The gun strongly longitudinally focuses, from velocity bunching due to  90° phase shift between SW cell and input coupler.  Device under study Emittance-Compensating Solenoids RF input RF power Photo-cathode Electrons TW structure 2.5 SW structure 1.6 SW structure (higher field) Laser (266 nm) RF input coupler RF output coupler RF Input coupler TW structure (lower field) Next steps: RF design optimisation (with beam dynamics), hot tests … The S-band version will be commissioned in 2011 @ UCLA (J. Rosenzweig) The hybrid gun is part of the CRISP proposal.

10. Beam dynamics studies Simulations of particle beam evolution in linear and circular accelerators based on macro-particle models. Beam optimisation in S-band, C-band, X-band linac and for mixed frequency machines (SPARC is the first linac operating at two frequencies) Study of collective effect due the particle wake fields. Micro-bunching instability due to coherent synchrotron radiation (CSR) and space charge in linear or in circular machines (e.g. RF and/or magnetic compressors). Beam dynamics optimization of accelerator devices (e.g. hybrid gun). CSR in a ring Bunch Length in hybrid gun 1OC temperature shift energy time

11. Beam dynamics studies for SPARX SPARX is a mixed frequency machine (S-band/C-band) to be commissioned before 2015 (C-band gun is under investigation). C-band has been chosen for reliability consideration (as SWISS-FEL @ PSI). SPARX has a nominal energy of 750 MeV (FEL operation) to 900 MeV (on crest operation, corresponding to 18 MeV Compton photons). Thermal emittance 0.6 um/mm, minimum emittance (Ferrario) working point. Parmela/Astra simulation + scaling laws Luminosity/spectral density

12. Educational and training experience All the previous activities are pursued with the aid of students, either master thesis or PhD level, that every year get their diploma at Sapienza (Faculty of Engineering). At the moment we have PhD and master students working on accelerator physics topics. The core topics where most of the students have been trained range from beam dynamics in linear and circular machines (including collective effects) to design methodology and bench measurements of RF devices in particle accelerators at frequencies from S-band (3 GHz) to X-band (12 GHz). In the framework of our long standing collaboration with INFN/LNF accelerator physics division, we can also profit of the experience gained at SPARC (an accelerator physics research machine) where many talented PhD students from our university have been trained. We give lectures in international accelerator schools, such as Joint Universities Accelerator School (JUAS) or Cern Accelerator School (CAS). We give also a course on Physics and Technology of Accelerators at the University of Rome, Faculty of Engineering and Faculty of Physics.

13. Conclusions We design and construct RF devices for beam generation (photo-gun) and beam manipulation (IV harm. cavity, RF deflectors, …) in the 3-12 GHz frequency range. We are interested in sharing our experience in design and the realization of RF devices for the ELI-NP accelerator We have experience in beam dynamics optimisation of linear/circular machines We are interested in contributing to beam dynamics studies and commissioning of the accelerator in ELI-NP We take part to commissioning of High Brilliance photo-injector SPARC We are interested in contributing to the setting up of accelerator physics expertise in ELI-NP We train PhDs and technical engineers in accelerator physics Ongoing collaborations: INFN (other labs/sections), UCLA, CERN, LULI, ELI, EuroFEL (IRUVX FEL), SLAC, KEK

14. Additional material

15. X-band hybrid gun (Sapienza/INFN/UCLA) SW RF gun section fed on-axis from coupling cell that also feeds (the majority of the power) to a lower gradient downstream TW section (no circulators needed). The gun strongly longitudinally focuses, from velocity bunching due to  90° phase shift between SW cell and input coupler.  Device under study Emittance-Compensating Solenoids RF input RF power Photo-cathode Electrons TW structure 2.5 SW structure 1.6 SW structure (higher field) Laser RF input coupler RF output coupler RF Input coupler TW structure (lower field) Next steps: RF design optimisation (with beam dynamics), hot tests … The S-band version will be commissioned in 2011 @ UCLA (J. Rosenzweig) The hybrid gun is part of the CRISP proposal.

16. X-band hybrid gun (Sapienza/INFN/UCLA) SW RF gun section fed on-axis from coupling cell that also feeds (the majority of the power) to a lower gradient downstream TW section (no circulators needed). The gun strongly longitudinally focuses, from velocity bunching due to  90° phase shift between SW cell and input coupler.  Device under study Emittance-Compensating Solenoids RF input RF input coupler Photo-cathode Electrons TW structure 2.5 SW structure 1.6 SW structure (higher field) Laser RF Input coupler TW structure (lower field) Temperature sensitivity 200 kHz/oC Next steps: RF design optimisation (with beam dynamics), hot tests … The S-band version will be commissioned in 2011 @ UCLA The hybrid gun is part of the CRISP proposal.

17. X-band hybrid gun (Sapienza/INFN/UCLA) SW RF gun section fed on-axis from coupling cell that also feeds (the majority of the power) to a lower gradient downstream TW section (no circulators needed). The gun strongly longitudinally focuses, from velocity bunching due to  90° phase shift between SW cell and input coupler.  Device under study Emittance-Compensating Solenoids RF input @z=30cm σz< 10 mm (90 A) εn,x< 0.08 mm-mrad Photo-cathode σx< 80 mm Electrons Brilliance=2.8 1016 A/m2 1.6 SW structure (higher field) Laser 6.7 pC RF Input coupler TW structure (lower field) Solenoid @ 6 kG Next steps: RF design optimisation (with beam dynamics), hot tests … The S-band version will be commissioned in 2011 @ UCLA The hybrid gun is part of the CRISP proposal.