SRF Gun Development for BERLin Pro T Kamps

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Ultra Bright Sources Workshop | Cockroft Institute 29. 06. – 01. 07. 2011 SRF Gun Development for BERLin. Pro

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Helmholtz-Zentrum Berlin build and operates accelerator facilities for fundamental and applied research • Synchrotron radiation sources Bessy I (now Sesame), Bessy II and MLS for the generation of soft X-rays: 2500 users doing 700 experiments / year • Vicksi, an ion and proton accelerator complex currently used for eye cancer treatment: several hundred patients treated • Ho. Bi. Ca. T, a facility for the development of Superconducting radio-frequency (SRF) components for continous-wave operation of linear accelerators We will build BERLin. Pro, a feasibility study for an Energy-Recovery Linac (ERL) Thorsten Kamps | kamps@helmholtz-berlin. de 22. 09. 2010 2

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de BERLin. Pro – an accelerator science and technology experiment – fully integrated ERL demonstrator 1. 5 Me. V spent beam 5 -10 Me. V merger section beam dump 5 -10 Me. V SRF booster main linac SRF modules SRF photo gun recirculation 100 Me. V beam manipulation funded by the Bundesminesterium für Bildung und Forschung and the State of Berlin High flux flexibility max. beam energy 50 -100 Me. V max. current 100 m. A nominal bunch charge 77 pc up to ~10 p. C pulse length 2 ps down to ~ 100 fs Rel. energy spread ~10 -4 range ~10 -2 rep. rate 1. 3 GHz variable normalized emittance < 1 mm mrad some mm mrad Joint Accelerator Developments | T. Kamps | HZB 27. 06. 2011 3

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de After evaluation of several options during CW Source Workshop in 2008 we concluded that SRF is the way to go for the electron source Courtesy S. S. Kurennoy / LANL NCRF DC SRF is the right choice to reach an average current of 100 m. A with 1 mm mrad emittance, maximum control and. Courtesy flexibility D. Dowell / Boeing / SLAC SRF Courtesy B. Dunham / Cornell Courtesy J. Lewellen / NPS Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 Courtesy A. Burril / BNL / AES 17. 05. 2011 4

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de The longest running SRF gun: The HZDR/ELBE SRF injector. First beam in 2007, injection into ELBE in 2010 • 3. 5 cell geometry to achieve 9. 5 Me. V beam energy • 10 k. W average power required for 1 m. A average current • Sacrifice on transverse brightness, ok for the IR FEL application. • Require 1 m. A of average current normal-conducting Cs 2 Te cathode on LN 2 cathode stock. • No degradation in cavity performance due to cathode stock and material. ½ cell Tuner Cathode Choke filter 3 full cells stock RF / HOM ports From J. Teichert, see NIM A 577 (2006) Setup by collaboration between HZDR, MBI, HZB, DESY and funded by BMBF, CARE, Eu. CARD Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 5

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de The cathode: Motivation to choose Cs. K 2 Sb as baseline photocathode material • QE of 4… 12 % at 532 nm compatible with our requirements, o need at least 10% of QE in the VIS to relax requirements on laser system o fast, robust (see Cornell results), rel. low thermal emittance • Experience in other labs shows good performance o delivered 32 m. A in Boeing NCRF gun o delivered >22 m. A in DC gun at U Cornell, proved to be more robust than Ga. As against RF trips in booster module • Need to establish comprehensive R&D programm o undestand correlation between preparation and beam parameters o determine reliable means and procedures to operate this type of NC cathode inside SRF cavity Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 6

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de What are the challenges and current limits for SRF guns with respect to our target beam parameters? • HZDR/ELBE gun shows feasiblity of the SRF gun concept SRF cavity with normal-conducting cathode works! • For our application, we need different performance: o Beam dynamics: How can we have more control on the transverse and longitudinal beam parameters? Mainly determined by field on cathode and setup of any focusing elements. o Average current: How can we generate 100 m. A? Need cathode with high QE at VIS, which can operate in SRF environment. o Average power: How can we couple Pavg = 100 m. A x Eb power into the SRF cavity? Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 7

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Put these three questions into three stages Gun 0 is a beam demonstrator experiment with SC Pb cathode (2011), study beam dynamics, cavity performance For Gun 1 add NC cathode with high QE at VIS, study cathode lifetime, slice/projected emittance performance (2013) For Gun 2 add RF input power coupler for 200 k. W (2014), study high power operation Goal Ho. Bi. Ca. T Gun 0 Source lab Gun 1 BERLin. Pro Gun 2 Beam Demonstrator Brightness R&D gun Current Production gun Electron energy ≥ 1. 5 Me. V RF frequency 1. 3 GHz Design peak field ≤ 50 MV/m Operation launch field ≥ 10 MV/m Bunch charge ≤ 77 p. C Repetition rate 30 k. Hz 54 MHz / 25 Hz 1. 3 GHz Cathode material Pb Cs. K 2 Sb Cathode QE 5*10^-4 at 258 nm 10^-1 at 532 nm Laser wavelength 258 nm 532 nm Laser pulse energy 0. 15 µJ 1. 8 n. J Laser pulse shape Gaussian Flat-top Laser pulse length 2. 5 ps FWHM ≤ 20 ps Average current 0. 5 µA ≤ 10 m. A / 0. 1 m. A 100 m. A Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 8

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Gun 0 takes advantage of the work done by Jacek Sekutowicz & Co for the hybrid Nb/Pb gun cavity • • Utilitzes a thin Pb film on the backwall of cavity as photo-electron emitter Pb is also a superconductor of type I with Hcrit = 8 m. T at 1. 3 GHz and 2 K, and has QE at least one order of magnitude higher than bare Nb backwall Discussed first during Source workshop in Sep 2008, sketched during ERL 09 at Cornell and then agreed on in June 2009. o Jacek and HZB elevate cavity design from sketch to engineering design o Peter Kneisel builds and tests a cavity ready for beam tests at Ho. Bi. Ca. T o Robert Nietubyc coats backwall of cavity with Pb film. o HZB prepares Ho. Bi. Ca. T for beam tests Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 J. Smedley et al. , PRSTAB 11, 013502 (2008) • 17. 05. 2011 9

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Beam dynamics simulation of gun performance: UV laser on Pb cathode, thermal emittance sqrt(2) higher than VIS on Cs. K 2 Sb (MV/m) ASTRA simulation of energy and emittance versus injection phase. Electron bunch has 10 p. C charge in 2. 5 ps FWHM pulse length. Similar peak current as for Gun 1/2. Learn about slice beam dynamics Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 10

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Turning the physics design of the SRF cavity into engineering design compatible with operation in Ho. Bi. Ca. T Target for em design was to optimze electric field on cathode Need to add stiffening to back-plane as Helium pressure fluctuations cause frequency shift of fundamental mode (All values are given in Hz/mbar) With Ib < 2 µA and Eb < 3. 8 Me. V can run with 700 W forward power from solid state amp. A. Neumann et al, Proc. of LINAC 2010 Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 11

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de The cavity collected some 20. 000 air miles… keeping its Q vs Epk performance… EM Design at DESY in Hamburg Production, RF-tests, Cleaning at JLAB in Newport News Cathode depo at Soltan INS at Swierk before after Test of cold mass and beam operation at HZB in Berlin Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 12

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Results from vertical tests at JLAB, from assembly of cavity to delivery for Berlin 02/10 Initial test after assembly, tuning, BCP etching and rinsing of the cavity. The field flatness was only 66%. 02/10 Further tuning improved field flatness to 94%, the following BCP treatment improved the RF performance. 03/10 After installation of the helium vessel, limitation by moderate field emission. 07/10 With first cathode coating 07/10 Test after accidential loss of lead cathode and removal of remnants by grinding and BCP. 10/10 With second cathode coating P. Kneisel et-al, Proc. of PAC 2010 Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 01. 07. 2011 17. 05. 2011 13

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Installation of cold mass into Ho. Bi. Ca. T SRF cavity, solenoid and steerer package Solenoid sits close to cavity. Both cavity and solenoid are shielded. No performance degradation with respect to Q of cavity found, OK. Solenoid gets warm if driven > 5 A due to heat transfer from current leads. Improved cooling of those leads during last week. Check performance of this measure. HZB Accelerator Physics Seminar 24. 05. 2011 14

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Drive laser and diagnostics beamline for Gun 0 0. 26 µm, 30 k. Hz, 2… 3 ps, 0. 15 µJ pulses from Yb: YAG oscillator + regen. amp. + 4 th harm conv. (m) Robust and reliable beam diagnostics to study cavity and cathode performance Short pulses of 1 ps rms length less than 1 deg. L slice equals projected beam dynamics Cathode jobs: measure QE, QE map, emission surface, thermal emittance ( master thesis) before and after laser cleaning Cavity jobs: study microwave properties, Q vs E, LLRF, microphonics, dark current Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 15

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de The drive laser: cw with short pulses in UV to do beam diagnostics experiments with the Pb/Nb system • Requirements from Gun 0 operation o UV light for metallic cathode / existing cavity design o short pulses (2 ps) o easy and straight forward design of laser o avg. power high enough to do beam diagnostic (QE !) • Specifications: o Wavelength: 260 SESAM nm (UV) modelocked oscillator o Pulse length: 2 -3 ps o Pulse Energy: 0, 15 µJ o Reprate: 120 Hz – 30 k. Hz o Synchronized to 1. 3 GHz • Good for average currents of 0. 1 µA or bunch charges up to 20 p. C Regenerative amplifier Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 16

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Q vs Epk and dark current measurements at Ho. Bi. Ca. T • • • Qo slightly lower compared to last measurement at JLAB So far we set safety limit to 15 MV/m Dark current kicks in above 10 MV/m, increases exponentially field emission from cathode spot? SEM/EDX reveal Pb droplets and flawed Pb film on Nb surface Energy spectrum of dark current suggests emission around 90 deg of RF R. Barday, T. Kamps, A. Neumann, S. Schubert et al Proc. of DIPAC 2011 Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 17

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de First beam of photoelectrons from Pb cathode generated and accelerated at 21 st Aptil 2011, < 2 years after project approval Switch on RF, adjust phase, steer and focus with solenoid Measure QE of 1*10^(-5) at 260 nm Next lasercleaning of cathode Start with steering of laser beam spot on backwall of cavity T. Kamps et al, Proc. of IPAC 2011 (planned) First beam 21 st April 2011 Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 18

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de In parallel with commissioning of Gun 0: Start activities for Gun 1/2 • Gun 0 was more akin to a task force project. o Two years from project approval by lab director to first beam. • Gun 1/2 will be embedded inside BERLin. Pro project structure. • Main activities in the next two years (for first beam with Gun 1 in 2013) o Setup of preparation and analysis lab for o Beam dynamics simulation to fix parameters o Development of new gun cavity o Design and engineering of cathode insert, cold mass and cryomodule o Get new drive laser o Change diagnostics beamline setup • Put all this together in Gun. Lab gun test area inside Ho. Bi. Ca. T bunker • For Gun 2 start thinking about RF feeds for high average power Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 19

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Use surface and material science techniques to study growth of Cs. K 2 Sb photocathodes The use of surface science already showed high potential to improve the injector performance Bessy II: XPS: determination of growth behaviour and stoichiometry UPS: determination of valence band maximum ARPES: angular distribution of emitted electrons and depending on the film appearence maybe band structure Bessy II infrastructure: PEEM: determination of areas of high and low work function IPES: determination of conduction band minimum White light interferrometry Ion source mounted on UHV chamber: LEIS: determination of the formation of 1 monolayer, the deposition rate and composition of topmost layer Other: S. Lederer et al, Proc. of PAC 99 SEM/EDX: surface topography and composition Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 20

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de Setup preparation system and DC setup to chase photoelectron properties from growth to use Mass spectrometer Transfer and transportation U=60 k. V Photocathode X-ray tube Evaporation sources Ion gun QE Mapper Response time Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 Thermal emittance Ion and electron Energy analyser 17. 05. 2011 21

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de beam diagnostics for gunlab build and comission Gun 2 build and commission Gun 0 2009 2010 2011 2012 2013 build and comission Gun 1 high QE cathode new cavity, cold mass and Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 cryomodule 17. 05. 2011 22

SRF Gun Development for BERLin. Pro | T. Kamps | kamps@helmholtz-berlin. de work done by T. Kamps, W. Anders, R. Barday, D. Böhlick, A. Frahm, M. Dirsat, F. Hoffmann A. Jankowiak, S. Klauke, J. Knobloch, O. Kugeler, J. Rudolph, A. Matveenko, A. Neumann, T. Quast, M. Schenk, M. Schuster, S. Schubert , P. Kneisel (JLAB), R. Nietubyc (Soltan), J. Sekutowicz (DESY), J. Smedley (BNL), J. Teichert (FZD), V. Volkov (BINP), I. Will (MBI) supported by the Accelerator Physics and SRF institutes and Experimental Support groups at HZB. Ultra Bright Electron Sources Workshop | Cockroft Institute | 29. 06 - 01. 07. 2011 17. 05. 2011 23