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Energy Recovery Linacs and SRF

Energy Recovery Linacs and SRF. Dmitry Kayran Collider-Accelerator Department Brookhaven National Laboratory. Outline Introduction ERLs around the world Goals of R&D ERL at BNL BNL ERL general layout, parameters and SRF components Conclusion. Main accelerator types.

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Energy Recovery Linacs and SRF

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  1. Energy Recovery Linacs and SRF Dmitry Kayran Collider-Accelerator Department Brookhaven National Laboratory RHIC & AGS Annual Users’ Meeting, June 3, 2009

  2. Outline • Introduction • ERLs around the world • Goals of R&D ERL at BNL • BNL ERL general layout, parameters and SRF components • Conclusion RHIC & AGS Annual Users’ Meeting, June 3, 2009

  3. Main accelerator types ERL Basic idea: Bring the beam through the accelerating structures timed in a way so that the second-pass beam is decelerated, i.e. delivering its energy to the cavity fields. 1) Accelerate in 1st pass of RF cavity 2) The return loop is N plus ½ RF wavelengths. 3) Recovery energy in 2nd pass RF cavity RHIC & AGS Annual Users’ Meeting, June 3, 2009

  4. Energy recovery* linacs (ERLs) (with the same cavity energy recovery) Problems: a – colliding beams, b – focusing of two beams with different energies in the RF accelerator. *Energy Recovery - process by which the energy invested in accelerating particles is returned to the RF cavities by decelerating them, and re-used to accelerate others RHIC & AGS Annual Users’ Meeting, June 3, 2009

  5. First Energy Recovery demonstration Same-cell energy recovery was first demonstrated at Stanford University the SCA/FEL project in July 1986 Beam was injected at 5 MeV into a ~50 MeV linac (up to 95 MeV in 2 passes), 150 μA average current (12.5 pC per bunch at 11.8 MHz) All energy was recovered. FEL was not in place. • Now the world-record energy recovery demonstration current is 30 mA at the Novosibirsk BudkerINP NovoFEL (2003) RHIC & AGS Annual Users’ Meeting, June 3, 2009

  6. Power Multiplication Factor An advantage of energy recovered recirculation is nicely quantified by the notion of a power multiplication factor: where Prf is the RF power needed to accelerate the beam. By the first law of thermodynamics (energy conservation!) k < 1 in any linac not recirculated. Beam recirculation with beam deceleration somewhere is necessary to achieve k > 1. If energy IS very efficiently recycled from the accelerating to the decelerating Examples CEBAF no recovery (matched load) k=0.99; (typical) k=0.8 JLAB IR DEMO k=16; JLAB 10 kW Upgrade k=33 RHIC & AGS Annual Users’ Meeting, June 3, 2009

  7. JLab demonstration: Energy Recovery Works With energy recovery the required linac RF power is ~ 16 kW, nearly independent of beam current. It rises to ~ 36 kW with no recovery at 1.1 mA. Gradient modulator drive signal in a linac cavity measured without energy recovery (signal level around 2 V) and with energy recovery (signal level around 0.) RHIC & AGS Annual Users’ Meeting, June 3, 2009

  8. Benefits of Energy Recovery • Required RF power becomes nearly independent of beam current. • Increases overall system efficiency. • Reduces electron beam power to be disposed of at beam dumps (by ratio of Efin/Einj). • More importantly, reduces induced radioactivity (simplify shielding) if beam is dumped below the neutron production threshold. • Promises efficiency near that of storage rings, while maintaining beam quality of linacs: superior emittance and energy spread, short bunches. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  9. Operational high power ERLs RHIC & AGS Annual Users’ Meeting, June 3, 2009

  10. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  11. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  12. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  13. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  14. Some more uses of ERLs • Operational ERLs now are used for FEL application • The advantages of ERLs well beyond of that : • Average current-carrying capability of storage-ring. • Smaller beam emittance and energy spread. • Higher photon brilliance and coherence, round sources, and short-pulse-length radiation. 100-fsec pulse width domain. • Efficient way to use RF power Make the ERLs great machines for the future: • Light sources • High energy electron coolers of ions (previous talk) • Electron ion colliders (next talk) RHIC & AGS Annual Users’ Meeting, June 3, 2009

  15. e-cooling (RHIC II) PHENIX Main ERL (3.9 GeV per pass) STAR e+ storage ring 5 GeV - 1/4 RHIC circumference Four e-beam passes Goals for ERL R&D at BNL • R&D ERL will serve as a test-bed for future RHIC projects: • ERL-based electron cooling (conventional or coherent). • 10-to-20 GeV ERL for lepton-ion collider eRHIC. • Test the key components of the High Current ERL based solely on SRF technology • SRF Photoinjector (703.5 MHz SRF Gun, photocathode, laser, merger etc.) test with 500 mA. • -Preservation of high-charge, low emittance. • High current 5-cell SRF linac test with HOM absorbers • -Single turn - 500 mA • Stability criteria for CW beam current. • Attainable ranges of electron beam parameters in SRF ERL. RHIC & AGS Annual Users’ Meeting, June 3, 2009

  16. ERLs beam parameters *) To demonstrate 3 min cooling time for proof pf principal of CeC for single Au bunch at 40GeV/nucl (above transition) with 1e09 particles 66cm length energy recovery may not be necessary. To improve energy spread 3rd harmonic cavity and increase injection energy will help RHIC & AGS Annual Users’ Meeting, June 3, 2009

  17. High Power ERL landscape Commissioned Under construction In design stage RHIC & AGS Annual Users’ Meeting, June 3, 2009

  18. Cryo-module Beam dump e- 2.5 MeV SRF cavity 1 MW 703.75 MHz Klystron Schematic Layout of the BNL R&D ERL e- 15-20 MeV Return loop Laser Cryo-module Merger system e- 2.5MeV SC RF Gun 50 kW 703.75 MHz system Control room RHIC & AGS Annual Users’ Meeting, June 3, 2009

  19. BNL ERL Injector: beam dynamics simulation results 5 cell SRF cavity SRF Gun 70 cm 15º 190 cm 99.5 cm 70 cm -15º -30º Laser port 15 120 100 Horizontal Vertical 80 10 60 40 5 20 0 0 10 2 8 4 6 10 2 8 4 6 30º RMS normilized emittance, mm-mrad RMS normilized emittance, mm-mrad Distance from the cathode, m Distance from the cathode, m PARMELA simulations shown: the small emittances can be achieved using bear-can initial distribution Blue 5 nC Red 1.4 nC Green 0.7 nC 4.8/5.3 um 2.2/2.3 um 1.4/1.4um RHIC & AGS Annual Users’ Meeting, June 3, 2009

  20. ERL loop lattice is very flexible Lattice  and D functions of the ERL for the different cases longitudinal dispersions (Ds=M56): No dispersion b, m Dispersion, m Dispersion, m b, m Positive longitudinal dispersion Zero longitudinal dispersion Dispersion, m b, m Transverse normalized emittances from cathode to dump Q=0.7 nC (PARMELA simulation) Negative longitudinal dispersion RHIC & AGS Annual Users’ Meeting, June 3, 2009

  21. Layout of R&D ERL in Bldg. 912 at BNL RHIC & AGS Annual Users’ Meeting, June 3, 2009

  22. R&D ERL beam parameters (PARMELA simulation result two operational regimes ) Operation regime Parameter RHIC & AGS Annual Users’ Meeting, June 3, 2009

  23. Why use SRF Technology? Since RF power for ERL operation no longer depends on beam current, main losses are wall losses: for SRF cavities high Q’s mean small wall losses Quality Factor Q0: RHIC & AGS Annual Users’ Meeting, June 3, 2009

  24. Linac Cryomodule 5 cell SRF cavity 703 MHz, 20 MV/m @ Qo=1e10 Ferrite Dampers for HOMs RHIC & AGS Annual Users’ Meeting, June 3, 2009

  25. BNL 5 Cell SRF Linac F = 703.75 MHz, E = 20 MeV Q0~ 1010, QHOM ~ 103 LHe Ballast Tank • The 5-cell cavity was specifically designed for • high current, high bunch charge applications such as eRHIC and high energy electron cooling. • The loss factor of the cavity was minimized. • The number of cells was limited to 5 to avoid HOM trapping. • Additionally, HOM power is effectively evacuated from the cavity via an enlarged beam pipe piece 24 cm diameter. • The simulated BBU threshold is of the order of 20 A • First horizontal test in April 2009 5 Cell SRF Cavity inside the cryomodule Build: AES Processed: JLAB Will be used: BNL More details about the 5cell cavity status in the next talk … RHIC & AGS Annual Users’ Meeting, June 3, 2009

  26. Brookhaven Science Associates Energy Recovery Linac 5-Cell Super Conducting RF Cavity Collider-Accelerator Department LHe Ballast Tank Magnetic Shield Tuning Assembly Helium Vessel 5 Cell RF Cavity Insulating Vacuum Fundamental Power Coupler RHIC & AGS Annual Users’ Meeting, June 3, 2009

  27. Cavity VTA tests The cavity was processed at JLab. After BCP, Rinsing, and low temp. bake (120 C) cavity reached 19 MeV/m at Q0=1010. 19 MeV/m Ebeam,max  20 MeV RHIC & AGS Annual Users’ Meeting, June 3, 2009

  28. SRF Injector fRF= 703.75 MHz Energy=2.5-3 MeV Average Current: 0.5 A Two fundamental power couplers: 0.5 MW each SRF Gun: axial electric field profile for different cathode insertion depth (SUPERFISH result) RHIC & AGS Annual Users’ Meeting, June 3, 2009

  29. Conclusion: A bright future for ERLs • ERLs provide a powerful and elegant solution for high average power free electron lasers. • The pioneering ERL FELs have established the fundamental principles of ERLs. • Operating ERL-FELs reach higher performance • Several more are in serious planning stages and will likely be constructed • ERLs based on SRF technology will be used for the future: light sources, high energy electron coolers of ions, electron ion colliders RHIC & AGS Annual Users’ Meeting, June 3, 2009

  30. Thank you RHIC & AGS Annual Users’ Meeting, June 3, 2009

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