SRF Gun Development for BERLinPro | T. Kamps | SRF Gun Development for BERLinPro T. Kamps | Ultra Bright Sources Workshop | Cockroft Institute –

SRF Gun Development for BERLinPro | T. Kamps | 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 HoBiCaT, a facility for the development of Superconducting radio-frequency (SRF) components for continous-wave operation of linear accelerators Thorsten Kamps | We will build BERLinPro, a feasibility study for an Energy-Recovery Linac (ERL)

SRF Gun Development for BERLinPro | T. Kamps | BERLinPro – an accelerator science and technology experiment – fully integrated ERL demonstrator Joint Accelerator Developments | T. Kamps | HZB3 SRF photo gun recirculation merger section main linac SRF modules spent beam beam dump SRF booster 1.5 MeV 100 MeV beam manipulation 5-10 MeV High fluxflexibility max. beam energy50-100MeV100MeV max. current100mA nominal bunch charge77pcup to ~10pC pulse length2psdown to ~ 100fs Rel. energy spread~10 -4 range~10 -2 rep. rate1.3GHzvariable normalized emittance< 1mm mradsome mm mrad funded by the Bundesminesterium für Bildung und Forschung and the State of Berlin

SRF Gun Development for BERLinPro | T. Kamps | After evaluation of several options during CW Source Workshop in 2008 we concluded that SRF is the way to go for the electron source Ultra Bright Electron Sources Workshop | Cockroft Institute | Courtesy B. Dunham / Cornell Courtesy S. S. Kurennoy / LANL Courtesy D. Dowell / Boeing / SLAC Courtesy A. Burril / BNL / AES Courtesy J. Lewellen / NPS DC NCRF SRF

SRF Gun Development for BERLinPro | T. Kamps | The longest running SRF gun: The HZDR/ELBE SRF injector. First beam in 2007, injection into ELBE in Ultra Bright Electron Sources Workshop | Cockroft Institute | cell geometry to achieve 9.5 MeV beam energy 10 kW average power required for 1 mA average current Sacrifice on transverse brightness, ok for the IR FEL application. Require 1 mA 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. From J. Teichert, see NIM A 577 (2006) Cathode stock Choke filter RF / HOM ports Tuner ½ cell 3 full cells Setup by collaboration between HZDR, MBI, HZB, DESY and funded by BMBF, CARE, EuCARD

SRF Gun Development for BERLinPro | T. Kamps | The cathode: Motivation to choose CsK 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 mA in Boeing NCRF gun o delivered >22 mA in DC gun at U Cornell, proved to be more robust than GaAs 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 |

SRF Gun Development for BERLinPro | T. Kamps | 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 mA? Need cathode with high QE at VIS, which can operate in SRF environment. o Average power: How can we couple P avg = 100 mA x E b power into the SRF cavity? Ultra Bright Electron Sources Workshop | Cockroft Institute |

SRF Gun Development for BERLinPro | T. Kamps | Put these three questions into three stages Gun0 is a beam demonstrator experiment with SC Pb cathode (2011), study beam dynamics, cavity performance For Gun1 add NC cathode with high QE at VIS, study cathode lifetime, slice/projected emittance performance (2013) For Gun2 add RF input power coupler for 200 kW (2014), study high power operation Ultra Bright Electron Sources Workshop | Cockroft Institute |

SRF Gun Development for BERLinPro | T. Kamps | Gun0 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 H crit = 8 mT at 1.3 GHz and 2K, and has QE at least one order of magnitude higher than bare Nb backwall Discussed first during Source workshop in Sep 2008, sketched during ERL09 at Cornell and then agreed on in June 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 HoBiCaT o Robert Nietubyc coats backwall of cavity with Pb film. o HZB prepares HoBiCaT for beam tests Ultra Bright Electron Sources Workshop | Cockroft Institute | Smedley et al., PRST- AB 11, (2008) J. Smedley et al., PRST- AB 11, (2008)

SRF Gun Development for BERLinPro | T. Kamps | Beam dynamics simulation of gun performance: UV laser on Pb cathode, thermal emittance sqrt(2) higher than VIS on CsK 2 Sb Ultra Bright Electron Sources Workshop | Cockroft Institute | ASTRA simulation of energy and emittance versus injection phase. Electron bunch has 10 pC charge in 2.5 ps FWHM pulse length. Similar peak current as for Gun1/2. Learn about slice beam dynamics (MV/m)

SRF Gun Development for BERLinPro | T. Kamps | Turning the physics design of the SRF cavity into engineering design compatible with operation in HoBiCaT Ultra Bright Electron Sources Workshop | Cockroft Institute | 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 I b < 2 µA and E b < 3.8 MeV can run with 700 W forward power from solid state amp. A. Neumann et al, Proc. of LINAC 2010

SRF Gun Development for BERLinPro | T. Kamps | The cavity collected some air miles… keeping its Q vs E pk performance… Ultra Bright Electron Sources Workshop | Cockroft Institute | Production, RF-tests, Cleaning at JLAB in Newport News Test of cold mass and beam operation at HZB in Berlin Cathode depo at Soltan INS at Swierk before after EM Design at DESY in Hamburg

SRF Gun Development for BERLinPro | T. Kamps | Results from vertical tests at JLAB, from assembly of cavity to delivery for Berlin Ultra Bright Electron Sources Workshop | Cockroft Institute | /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

SRF Gun Development for BERLinPro | T. Kamps | Installation of cold mass into HoBiCaT SRF cavity, solenoid and steerer package HZB Accelerator Physics Seminar14 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.

SRF Gun Development for BERLinPro | T. Kamps | Drive laser and diagnostics beamline for Gun Ultra Bright Electron Sources Workshop | Cockroft Institute | (m) Robust and reliable beam diagnostics to study cavity and cathode performance Short pulses of 1 ps rms length  less than 1 degL  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 0.26 µm, 30 kHz, 2…3 ps, 0.15 µJ pulses from Yb:YAG oscillator + regen. amp. + 4 th harm conv.

SRF Gun Development for BERLinPro | T. Kamps | The drive laser: cw with short pulses in UV to do beam diagnostics experiments with the Pb/Nb system Requirements from Gun0 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 nm (UV) o Pulse length: 2-3 ps o Pulse Energy: 0,15 µJ o Reprate: 120 Hz – 30 kHz o Synchronized to 1.3 GHz Good for average currents of 0.1 µA or bunch charges up to 20 pC Ultra Bright Electron Sources Workshop | Cockroft Institute | SESAM modelocked oscillator Regenerative amplifier

SRF Gun Development for BERLinPro | T. Kamps | Q vs Epk and dark current measurements at HoBiCaT Ultra Bright Electron Sources Workshop | Cockroft Institute | 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

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

SRF Gun Development for BERLinPro | T. Kamps | In parallel with commissioning of Gun0: Start activities for Gun1/2 Gun0 was more akin to a task force project. o Two years from project approval by lab director to first beam. Gun1/2 will be embedded inside BERLinPro 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 GunLab  gun test area inside HoBiCaT bunker For Gun2 start thinking about RF feeds for high average power Ultra Bright Electron Sources Workshop | Cockroft Institute |

SRF Gun Development for BERLinPro | T. Kamps | Use surface and material science techniques to study growth of CsK 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: SEM/EDX: surface topography and composition Ultra Bright Electron Sources Workshop | Cockroft Institute | S. Lederer et al, Proc. of PAC99

SRF Gun Development for BERLinPro | T. Kamps | Setup preparation system and DC setup to chase photoelectron properties from growth to use Ultra Bright Electron Sources Workshop | Cockroft Institute | Ion gun Evaporation sources Ion and electron Energy analyser X-ray tube Mass spectrometer Transfer and transportation

SRF Gun Development for BERLinPro | T. Kamps | Ultra Bright Electron Sources Workshop | Cockroft Institute | build and comission Gun build and comission Gun1 beam diagnostics for gunlab new cavity, cold mass and cryomodule high QE cathode build and commission Gun0

SRF Gun Development for BERLinPro | T. Kamps | Ultra Bright Electron Sources Workshop | Cockroft Institute | 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.