1. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Cornell Laboratory for Accelerator-based ScienceS and Education (CLASSE) Pushing beam brightness from ERL source & photocathode R&D world‘s highest brightness & current operating cw photoinjector Ivan Bazarov 1

2. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Main points Low emittance achieved Photocathode R&D Plans to improve the performance further 2

3. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Source brightness Key parameter for ERL Improvements in the source immediately translate to a better performance of the entire facility Source development at Cornell –5-15 MeV injector –New 500kV DC gun + beamline 5-15 MeV injector DC gun dev lab 3

4. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Ingredients for pushing the brightness Theoretical insights Computer modeling Beam diagnostics Working hardware Right crew of people 4

5. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Example: analytical scaling of optics aberrations aberrations slice-induced Solenoid chromatic: Solenoid geometric: RF focusing: 5

6. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Example: high fidelity beam dynamics modeling 200-CPU computer cluster dedicated to beam dynamics simulations Use of experimentally benchmarked beam dynamics codes Pioneered the use of evolutionary multi-objective algorithms for flexible (nonlinear) beam optics design Cornell approach is now used in a number of labs world-wide 6

7. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Example: 6D beam diagnostics key to success y pypy t y pypy t E transverse phase space (animation) slice emittance with resolution of few 0.1ps projected emittance longitudinal phase space 7

8. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL PhD students Jared MaxsonColwyn Gulliford Siddharth KarkareHeng Li Example: beam running crew Luca Cultrera Adam BartnikFlorian Loehl CHESS/ERL1 8

9. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Just last month: emittance spec achieved! Keys to the result –Beam-based alignment (took us several months) –Working diagnostics!! –Fight jitters in the injector x2 thermal emittance! x1.3 simulated emittance correct scaling with bunch charge  ny (100%) = 0.4 um @ 20pC/bunch  ny (100%) = 0.8 um @ 80pC/bunch 9

10. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Understanding beam brightness Single RMS emittance definition is inadequate for linacs –Beams are not Gaussian –Various groups report 95% emittance or 90% emittance (or don’t specify what exactly they report) The right approach –Measure the entire phase space, then obtain emittance of the beam vs. fraction (0 to 100%) 20pC/bunch  core = 0.15 um f core = 73% 80pC/bunch  core = 0.3 um f core = 67% 10

11. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Shaking old-established notions: no Gaussians anywhere… animation: scanning around 1 st harm. ~6keV (zero emittance) Spectral flux (ph/s/0.1%BW/mm 2 ) at 50m from undulator (5GeV, 100mA, p = 2cm) 11

12. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Understanding coherence: fully consistent formalism (Wigner) Phase space (ph/s/0.1%BW/mm/mrad) at the undulator (5GeV, 100mA, p = 2cm) animation: scanning around 1 st harm. ~6keV (zero emittance) 12

13. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Emittance vs. fraction for light phase space of light emittance vs fraction (of light!) Bazarov, Synchrotron radiation in phase space (in preparation) Final radiation phase space: convolution with electron phase space 13

14. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Just how bright is Cornell ERL injector beam? Effective brightness (for comparison) Today’s 20mA ERL injector beam is as bright as 100mA 0.6nm- rad  0.006nm-rad storage ring Gaussian beam! Parity in transverse brightness with the very best storage rings is already achieved; the result can only improve ERL10ERL2 14

15. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Main points Low emittance achieved Photocathode R&D Plans to improve the performance further 15

16. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Photocathode R&D Brightness is ultimately set by the photocathode intrinsic properties Cornell has emerged as a leader in photocathode R&D for accelerator applications Expertise now covers a range of NEA materials, alkali-based: next is ‘material engineering’ of photocathodes for accelerators x-ray topography map showing ion damage profile for a cathode with 1000 coulombs 1/e lifetime 16

17. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Photocathode research at Cornell: building up the infrastructure multialkali growth chamber with vacuum suitcase GaAs system with load-lock in-vacuum LEED/Auger MBE III-V system Also on campus AFM, EDX, SEM, STM, SIMS, ARPES + CHESS (XRF, x-ray topography, EXAFS, and much more) 17

18. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Photocathode research: a sample of results from the group Wide selection of photocathodes evaluated for MTE and response time: GaAs, GaAsP, GaN, Cs 3 Sb, K 2 CsSb 10%QE in green now routine GaAs intrinsic emittance time response vs theory GaN’s MTE GaAsP response K 2 CsSb MTE Just 2011 alone APL 98 (2011) 224101 APL 98 (2011) 094104 APL 99 (2011) 152110 PSTAB (2011) submitted PRL (2011) in preparation 18

19. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Photocathode research: moving forward Ultra-cold electrons are in the view; About to grow our first MBE III-V with tuned parameters; Impact way beyond accelerators; Transverse Energy Longitudinal Energy unique 2D energy analyzer for photoelectrons structural studies of the bandgap structure ps-resolution of response time 19

20. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Building collaboration on photocathodes for accelerators Collaboration with ANL BNL JLAB SLAC Berkeley Excitement and momentum in the community; Cathode workshop at Cornell in 2012; Leading the effort on creating collaborative community- driven Internet resource; 1 st workshop 2 nd workshop 20

21. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Undergrads in cutting-edge photocathode research Ashwathi Iyer: in situ work function mapping Rick Merluzzi: Auger/LEED characterization Yoon Woo Hwang: 2D energy analyzer, RHEED CHESS/ERL1 21

22. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL High current operation: photocathode performance ~600 coulombs delivered (same spot) QE before QE after ERL2 22

23. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Ion back-bombardment halo, beam losses cathode life-time degrading mechanisms computed ion dose delivered to the cathode 23

24. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Real-life accelerator testing for photocathodes: high average current CsKSb cathode after delivering ~600C. cathode after 20mA 8hour run SEM close-up x-ray topography showing rings of ion back-bombardment damage 24

25. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Realistic operating conditions Good news: running 5mm off-center on the photocathode – same emittance (20pC/bunch) due to intrinsically low geometric aberrations in the DC gun 25

26. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Main points Low emittance achieved Photocathode R&D Plans to improve the performance further 26

27. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Improving brightness further Already close to the fundamental emittance limit (0.5 mm-mrad for given photocathode, cathode electric field) Detailed model/measurement verification is underway Merger characterization – promising simulations at ~12MeV show minimal emittance degradation Improvements to laser 3D shaping, element stability Examples of optimal laser shapes ERL10 27

28. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL 3D laser shaping for space charge control Optimal 3D laser shape: practical solution identified >50% of light gets through, emittance (sims) ~20% higher than the optimal temporal – birefringent crystal pulse stacking transverse – truncated Gaussian temporal profile transverse profile PRSTAB 11 (2008) 040702 Appl. Opt. 46 (2011) 8488 28

29. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL New DC gun Reviewed in January 2011 by a group of external experts New segmented ceramic received – fully shielded from field emission Construction is underway 29

30. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Projected performance of the new DC gun (475kV) beamline Cornell’s construction of the MK II DC Gun: –Adjustable cathode/anode gap  “dial-in” a field! –Segmented insulator: pushing the voltage limits. –Full 6D phase space characterization out of the gun 30

31. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL Outlook: defining the state-of-the-art Cornell ERL photoinjector project has achieved beam brightness that exceeds that of the best storage rings; Diverse and aggressive program to improve beam brightness and injector performance further; –Detailed model/measurement benchmarking (6D phase space) –Improving laser shape, element stability, diagnostics –New gun & photocathode materials ERL10 31

32. I.V. Bazarov, Beam Brightness and Cathode R&D, NSF Annual Review, Oct 25, 2011 CLASSE Cornell University CHESS & ERL END 32