SRF-Seminars Jacek Sekutowicz JLab, CASA Seminar, March 2nd, 2006. 1/32 J. Sekutowicz, DESY
5. SUPERCONDUCTING PHOTO-INJECTORS JLab, CASA Seminar, March 2nd, 2006. 2/32 J. Sekutowicz, DESY
SRF Photo-Injectors; Topics 1. Introduction 2. Projects; Specs and measured data 3. Cathodes 4. RF-performance of sc-cavities 5. RF-focusing 6. ε growth compensation with DC- and RF-magnetic field 7. Nb-Pb gun 8. Conclusions JLab, CASA Seminar, March 2nd, 2006. 3/32 J. Sekutowicz, DESY
SRF Injectors Acknowledgements BNL: A. Burrill, I. Ben-Zvi, R. Calaga, T. Rao, J. Smedley AES: T. Favale, A. Todd, J. Rathke FZR: D. Janssen, J. Teichert DESY: D. Kostin , B. Krause, A. Matheisen, W.-D. Möller, R. Lange IHIP: J. Hao, K. Zhao INFN: M. Ferrario JLAB: P. Kneisel INS: J. Langner, P. Strzy ż ewski SUNY: R. Lefferts, A. Lipski UNI- Ł ÓD Ź : K. Sza ł owski SLAC: K. Ko, Z. Li. JLab, CASA Seminar, March 2nd, 2006. 4/32 J. Sekutowicz, DESY
1. Introduction SRF Injectors Motivation to develop SRF electron guns: Operation in CW mode with high acc. gradient on photo-cathode. Low power dissipation and excellent thermal stability. What is technically challenging: Integration of non-superconducting cathodes into the sc environment. Lower QE of superconducting cathodes than alkali cathodes. Emittance growth compensation with magnetic field is more difficult and needs novel approaches. JLab, CASA Seminar, March 2nd, 2006. 5/32 J. Sekutowicz, DESY
1. Introduction SRF Injectors FZR (since 1998) IHIP PU (since 2001) f =1.3 GHz f =1.3 GHz Cs 2 Te ◄ E RF Cs 2 Te ◄ E DC Courtesy of Dietmar Janssen Courtesy of Hao Jiankui BNL/AES (since 2004) BNL (since 2002) f =1.3 GHz f =703.75 MHz Nb ◄ E RF Alkali+ ♦ ◄ E RF Courtesy of Triveni Rao Courtesy of Alan Todd JLab, CASA Seminar, March 2nd, 2006. 6/32 J. Sekutowicz, DESY
2. Four projects: Spec/Measured SRF Injectors E Δ E q/Bunch Bunches/s I b ε @ q [MeV] [keV] [nC] [10 6 ] [mA] [µrad] @ [nC] BESSY S: 5 S: ? S: 2.5 S: 0.025 S: 0.063 S: 1.5 @ 2.5 FZR S: 9.5 S: 5 S: 0.077 S: 13 S: 1.0 S: 1.0 @ 0.077 FZR S: 9.5 S: S: 1.0 S: 1 S: 1.0 S: 1.5 @ 1.0 M: 0.85 M: 8.5 M: 0.020 M: 26 M: 0.52 M: 1.0 @ 0.020 S: 2.61 S: 30 S: 0.060 S: 17 S: 1.0 S: 3.0 @ 0.060 M: 0.58 M: 35 M: 0.001 M: 81 M: 0.08 M: 2.7 @ 0.001 Cavities have been built mainly for measurements of QE of cold Nb S: 352 S: 500 S: 2.0 S: 62 S: 1.33 S: 5.0 @ 1.33 S: 704 S: 1000 M: ( - ) M: ( - ) M: ( - ) M: ( - ) M: ( - ) M: ( - ) JLab, CASA Seminar, March 2nd, 2006. 7/32 J. Sekutowicz, DESY
3. Cathodes: Spec / Measured SRF Injectors < QE> @ λ Ph E pulse / P laser Cathode E cath Spot size Emitter/T [mm] at operation [µJ] / [W] Life Time [MV/m] S BESSY : 0.01/262 S: 1.19/0.03 S: Ø 3.0 S: 25 S FZR : 0.01/262 S: 0.5 / 0.5 Cs 2 Te / 78 K >50 days M: Ø 2.0 M: 22 M: 0.003/260 M: 0.06/1.5 S: 0.01 / 266 S: 0.015/1.2 S: Ø 5.6 Cs 2 Te /273 K ~100 days M: 2.7 M: 0.01/ 266 M: 0.010/0.8 M: Ø 6.0 10 -5 / 266 Nb / 2-4 K 0.002 /0.15 ∞ (?) 4x1.5 M: 48 S: 0.05 / 527 0.071 /25 S: Alkali / ? ? S: Ø 2.0 S: 40 S: Alkali+D/? S: 5 / 527 0.0006 /0.2 JLab, CASA Seminar, March 2nd, 2006. 8/32 J. Sekutowicz, DESY
4. Cavities: Measured RF-performance SRF Injectors IHIP-Peking FZR 4 K-test 4.2 K- test 2.5·10 8 @ E peak =22 MV/m 10 8 @ Eacc= 5 MV/m 2 K-test 5·10 9 @ E peak =46 MV/m AES: 703.85 MHz not yet fabricated but 748.5 MHz 1.E+11 1 .E+1 1 BNL/AES is very similar Test at JLab Test at JLab 2005 T=1.99K 2003 Q0 Qo 1 .E+1 0 1.E+10 1 .E+0 9 1.E+09 0 1 0 2 0 3 0 4 0 5 0 6 0 0 10 20 30 40 50 60 Epe ak [MV/ m ] Epeak [MV/m] JLab, CASA Seminar, March 2nd, 2006. 9/32 J. Sekutowicz, DESY
4. Cavities: Next Steps SRF Injectors IHIP-Peking University FZR DC+1.5-cell � 3.5-cell Test cavity (RRR=40) received BCP in Sept. 2005 Eacc [MV/m] 15 High RRR=300 cavity will be V-DC [kV] 100 treated and tested at DESY soon I beam [mA] 1 Energy [MeV] 4.9 Energy spread [%] 2.27 Emittance (rms) [µrad] 3.4 BNL/AES 1.3 GHz BNL/AES 703.85 MHz QWC will be added for cathode with diamond: - 2005 RF Design will be finished in 2005 ? ε =1.99 [µrad] Δ E/E= 3.8% JLab, CASA Seminar, March 2nd, 2006. 10/32 J. Sekutowicz, DESY
5. E-field Focusing; Recessed cathode SRF Injectors 60 60 MV/m Cathode shifted MV/m by 3 mm only r r 20 57 MV/m z z 0 0 MV/m 60 60 Ez(r,+1mm) Ez(r,+1mm) 50 50 Er(r,+1mm) Er(r,+1mm) 40 40 30 30 Ez, Er Ez, Er [MV/m] [MV/m] 20 20 10 10 0 0 -10 -10 0 2 4 6 0 2 4 6 r [mm] r [mm] JLab, CASA Seminar, March 2nd, 2006. 11/32 J. Sekutowicz, DESY
5. E-field Focusing; Recessed cathode SRF Injectors Since position of the cathode is a very sensitive “knob” Cathode longitudinal position tuner as proposed by RFZ JLab, CASA Seminar, March 2nd, 2006. 12/32 J. Sekutowicz, DESY
5. E-field Focusing; Inclined back wall SRF Injectors FZR: 1.3 GHz 1.5-cells and 3.5-cells BNL/AES: 1.3 GHz and 703.85 MHz will have recessed cathode and inclined back wall have recessed cathode and inclined back wall Without RF With RF With RF focusing focusing focusing µrad] 3.66 1.49 ε n ε n [µrad] 1.99 Recess [mm] 0 2-3.5 Recess [mm] 3 R. Calaga, Proceed. SRF2005,Cornell D. Janssen, V. Volkov , NIM A452(2000)34 JLab, CASA Seminar, March 2nd, 2006. 13/32 J. Sekutowicz, DESY
6. Emittance compensation with H-field: SRF Injectors Exposing a sc cavity to H-field may cause degradation in the performance. 1. One can put solenoid and the sc-cavity at different locations � split injector (M. Ferrario, J.B. Rosenzweig): 6 q = 1nC E cath = 60 MV/m r spot = 1.5mm E cry = 13.5 MV/m ε n t pulse = 20ps [µrad] ε th = 0.45µrad σ r I = 50 A [mm] E = 120 MeV ε n ε n = 0.6 µrad σ r 0 z [m] 16 Sc-cavity Solenoid; 0.3 T JLab, CASA Seminar, March 2nd, 2006. 14/32 J. Sekutowicz, DESY
6. Emittance compensation with H-field: SRF Injectors Example: 1 mm thick 2K ≤ 4K µ-metal shield Solenoid (0.3 T) Cathode (20 µT) stainless steel Nb 410 mm (optimum 360 mm) JLab, CASA Seminar, March 2nd, 2006. 15/32 J. Sekutowicz, DESY
6. Emittance compensation with H-field: SRF Injectors 2. One can use solenoidal modes of (TE0xx) for the ε compensation (D. Janssen) 1.3 GHz TM010; E field 3.8 GHz TE011; B field TE 021 ~ 350mm The low emittance results from: ε n for 1 nC [µrad] 0.78-0.98 RF-focusing and B RF compensation and weakly depends on the phase ε n minimum at z [m] 4.25 of the solenoidal mode. B TE on axis [T] 0.324 D. Janssen et al, Proc. of FEL2004 Surf. B max = [B 2 TM + B 2 TE ] 0.5 [T] 0.144 JLab, CASA Seminar, March 2nd, 2006. 16/32 J. Sekutowicz, DESY
7. Nb-Pb RF-gun: DESY, BNL , INFN, SUNY, JLab, INS… SRF Injectors Motivation is to build cw operating RF-source of ~0.5-1 mA class for an XFEL facility. An all superconducting RF-gun follows the all niobium RF-gun of BNL QE = 10 -5 @ λ =266 nm In 2003 we proposed to investigate quantum efficiency of Pb (TTF Meeting, Frascati, June 2003, Phys. Rev. ST-AB, vol. 8, January 2005) Lead is commonly used superconductor for accelerating cavities: T c = 7.2 K , B c = 70 mT JLab, CASA Seminar, March 2nd, 2006. 17/32 J. Sekutowicz, DESY
7. Nb-Pb RF-gun: Quantum Efficiency of Lead at 300 K SRF Injectors QE measured at 300K using setup at BNL (J. Smedley, T. Rao) Light sources: • ArF- laser: 193 nm, KrF-laser: 248 nm, 4-th harmonic Nd: YAG laser : 266 nm • Deuterium light source with monochromator (2 nm bandwidth): 190-315 nm 190 nm 193 nm 0.006 0.55% Pb: vacuum-deposited 200 nm Pb: bulk Pb: electro-plated Nb: bulk 210 nm Pb: arc-deposited 213 nm Pb: magnetron-deposited QE 220 nm 230 nm Measured also at ~100 K 240 nm 248 nm 0.000 4.0 4.5 5.0 5.5 6.0 6.5 7.0 Ep [eV] JLab, CASA Seminar, March 2nd, 2006. 18/32 J. Sekutowicz, DESY
7. Nb-Pb RF-gun: Quantum Efficiency of Lead at 300 K SRF Injectors Surface Uniformity (Courtesy J. Smedley) Arc Sputtered Deposited Vacuum Solid Deposited 10 μ m All cathodes laser cleaned with 0.2 mJ/mm 2 of 248nm light JLab, CASA Seminar, March 2nd, 2006. 19/32 J. Sekutowicz, DESY
7. Nb-Pb RF-gun: Quantum Efficiency of Lead SRF Injectors Preparation Nb used as substrate • Four deposition methods: • Electroplating – Vacuum deposition (evaporation) – Sputtering – Vacuum Arc deposition – Solid lead, mechanically polished • In situ laser cleaning • KrF Excimer (248 nm), 12 ns pulse, ~0.2 mJ/mm 2 – JLab, CASA Seminar, March 2nd, 2006. 20/32 J. Sekutowicz, DESY
7. Nb-Pb RF-gun: Quantum Efficiency of Lead SRF Injectors Lead Surface Finish and Damage Threshold (Courtesy J. Smedley) (Electroplated Lead) Prior to Laser Cleaning 0.26 mJ/mm 2 0.11 mJ/mm 2 0.52 mJ/mm 2 1.1 mJ/mm 2 1.8 mJ/mm 2 JLab, CASA Seminar, March 2nd, 2006. 21/32 J. Sekutowicz, DESY
Recommend
More recommend
