Working Group: High Brightness Electron Beams

Particle accelerators play a fundamental role in modern research and for applications in energy and life science research. The right particle beam with the right properties can help answer questions regarding the fundamental constituents of matter, create energy in subcritical reactors, investigate nuclear waste, analyze new drugs and help to detect and destroy cancer tumors.

The working group High Brightness Electron Beams (HBEB) investigates the physics of the generation, dynamics and diagnostics of high brightness electron beams. The work is currently focused on the development of a Superconducting Radio-Frequency (SRF) Photoinjector for bERLinPro, the ERL test facility at HZB.


Research & Development Platform for Photoinjectors


Gun0 measurement: Reconstruction of the vertical phase space.

GunLab is the research and development platform for SRF photoinjectors of bERLinPro. It will allow us to the push the limits of SRF photoinjector performance in the context of high brightness, high average current electron beams for future lightsources driven by energy recovery linacs (ERL). The goal for the diagnostics beamline of GunLab is to enable com- missioning of all bERLinPro electron guns. The focus is on the generation of electron bunches with low emittance and short pulse length at 77 pC bunch charge. For this diagnostics tools will be assembled allowing full six-dimensional phase space reconstruction. Besides the main beam the focus is also on the properties of any unwanted beam (dark current, halo) resulting from field emission or other processes. Another goal of GunLab is to provide research opportunities for accelerator physics students and external collaborators in a state-of-the-art accelerator environment.


Contact: kamps@helmholtz-berlin.de

Last publications:

  1. J. Völker et al., Introducing GunLab – A Compact Test Facility for SRF Photoinjectors, Proceedings of IPAC2014, Dresden, Germany, pp. 630  JACoW.org
  2. I.Yu. Vladimirov et al., Spectrometer for SRF Gun, Proceedings of IPAC2014, Dresden, Germany, pp. 3608  JACoW.org
  3. H. Vennekate et al., Transverse Emittance Compensation for the Rossendorf SRF Gun II, Proceedings of IPAC2014, Dresden, Germany, pp. 1582 JACoW.org
  4. M. Schmeißer et al., Results from Beam Commissioning of an SRF Plug-Gun Cavity Photoinjector, Proceedings of IPAC2013, Shanghai, China, pp. 282  JACoW.org
  5. J. Völker et al., Operational Experience with the Nb/Pb SRF Photoelectron Gun, Proceedings of IPAC2012, New Orleans, USA, pp. 1518  JACoW.org
  6. T. Kamps et al., Beam Dynamics Studies For SRF Photoinjectors, Proceedings of LINAC2012, Tel-Aviv, Israel, pp. 999 JACoW.org

Collaborations:

  • Dr. V. I. Shvedunov of Moscow State University MSU
  • Prof. Dr. T. Weis of TU Dortmund University Homepage

Support:

  • BMBF PCHB - FKZ: 05K12CB2
  • EUCARD2 EU Grant Agreement No. 312453

Photocathode Research & Development


Photocathode preparation and analysis chamber

The beam quality of an ERL in terms of brightness and current is ultimately given by the electron source. In an SRF photoinjector electrons are generated by illuminating a photocathode with light pulses from a drive laser. This photocathode must be embedded into the SRF cavity,such that the electrons can be quickly accelerated to mitigate space charge effects. An  SRF photoinjector for an average current of 100 mA at high brightness has not been demonstrated yet. The focus of the activities is to understand correlations between cathode material, preparation, treatment and electron beam parameters such as transverse emittance, which is linked to the brightness of the beam generated with the SRF photoinjector. For this reason we build a complex photocathode preparation and analysis chamber, where different materials and preparation techniques can be evaluated. For the evaluation a complex array of material science techniques is available.


Contact: julius.kuehn@helmholtz-berlin.de

Last publications:

  1. S.G. Schubert et al., Influence of Growth Method on K3Sb Photocathode Structure and Performance, Proceedings of IPAC2014, Dresden, Germany, pp. 624 JACoW.org
  2. M. Schmeißer et al., In-situ Characterization of K2CsSb Photocathodes, Proceedings of IPAC2014, Dresden, Germany, pp. 627 JACoW.org
  3. S.G. Schubert et al., Bi-Alkali Antimonide Photocathodes for High Brightness Accelerators, APL Materials 1, 032119 (2013) DOI:10.1063/1.4821625
  4. S.G. Schubert et al., XPS and UHV-AFM Analysis of the K2CsSb Photocathodes Growth, Proceedings of IPAC2013, Shanghai, China, pp. 291 JACoW.org
  5. J. Smedley et al., Correlating Structure and Function - In situ X-ray Analysis of High QE Alkali-antimonide Photocathodes, Proceedings of IPAC2013, Shanghai, China, pp. 464 JACoW.org
  6. S.G. Schubert et al., Investigation of Laser-cleaning Process on Lead Photocathodes, Proceedings of IPAC2012, New Orleans, USA, pp. 1515 JACoW.org

Collaborations:

        • Brookhaven National Laboratory, Long Island, USA  BNL
        • Photocathode Research For High Brightness Electron Beams PCHB - BMBF (Helmholtz-Zentrum Dresden-Rossendorf HZDR, Johannes Guttenberg-Universität Mainz JGU, Moscow State University MSU, Saint-Petersburg State Polytechnic University SPSPU)

        Support:

        • BMBF PCHB - FKZ: 05K12CB2
        • EUCARD2 EU Grand Agreement No. 312453

        Fieldemission Studies


        Dark current of Gun0 on view screen

        The systematic study of field emission processes is interesting in many ways. On the one hand, high electric field gradient increases the probability of unwanted field emission both from the surface of the superconducting resonator and photocathode or substrate that limits the achievable field gradient on the photocathode surface. Extensive methods of the surface treatment and quality control have been established to suppress unwanted field emission. On the other hand, new materials and structures with a strong field emission at low field gradients are sought to be used as an alternative electron source for high brilliance electron beams. An essential precondition for sustainable success in both the suppression of field emission and the use of field emission as an electron source is the clarification of the fundamental mechanisms of field emission.


        Contact: NN

        Last publications:

        1. R. Barday et al., Field Emission Studies of Heat Treated Mo Substrates, Proceedings of IPAC2014, Dresden, Germany, pp. 2955 JACoW.org
        2. R. Barday et al., Characterization of a Superconducting Pb Photocathode in a Superconducting RF Photoinjector Cavity, Phys. Rev. ST Accel. Beams 16, 123402 (2013) PRSTAB
        3. R. Barday et al., Characterization of a Superconducting Pb Photocathode in a SRF Gun Cavity, Proceedings of IPAC2013, Shanghai, China, pp. 279  JACoW.org
        4. R. Barday et al., Beam Size and Intensity Diagnostics for a SRF Photoelectron Injector, Proceedings of IBIC2012, Tsukuba, Japan, pp. 241  JACoW.org
        5. V. Volkov et al., Interpretation of Dark Current Experimental Results in HZB SC RF Gun, Proceedings of IPAC2012, New Orleans, USA, pp. 1545  JACoW.org
        6. V. Volkov et al., The Source of Emittance Dilution and photoemission tunneling effect in Photocathode RF Guns, Proceedings of IPAC2012, New Orleans, USA, pp. 1542  JACoW.org

        Collaborations:

        • Dr. Bo Choi of Vanderbildt University, USA, 'Diamond Field Emitter Array' homepage
        • Prof. Dr. G. Müller and S. Lagotsky of Wuppertal University, Germany, 'Modelle und Messungen mit Feldemitter' working group

        Support:

        • BMBF PCHB - FKZ: 05K12CB2
        • EUCARD2 EU Grand Agreement No. 312453

        Drive Laser and Laser Transport Beam-Line for GunLab


        Photoinjector drive lasers for GunLab delivering pulses of ≈3 ps (FWHM) duration at 258 nm wavelength and variable repetition rates between 120 Hz and 8 kHz.

        Being able to provide short electron bunches of high brilliance and low emittance, a photoinjector is a very suitable electron source for an ERL. The operation of such an electron source requires a dedicated drive laser. The mode-locked drive laser initiates the emission of photo-electrons from a cathode. This process occurs on such a short time-scale that the bunch duration is identical with the duration of the laser pulse, even in the ps-regime. Therefore, the temporal characteristic of the electron bunches can simply be controlled by shaping the laser pulses accordingly and by providing a suitable pulse-pattern. The optical pulse energy as well as the transverse shape and location of the laser spot on the photocathode influence space charge effects, beam dynamics and emittance. The quantum efficiency of the cathode, however, depends on the wavelength of the laser radiation. The drive laser currently used for GunLab has been developed and installed by the Max-Born-Institute.
        An optical system, which transports the laser pulses onto the cathode, is desirable to provide some flexibility with regard to the transverse shape and to the optical pulse energy. These requirements for GunLab will be met by a variable attenuator, optical imaging and some zoom capabilities.


        Contact: guido.klemz@helmholtz-berlin.de

        Last publications:

        1. E. Panofski et al., Virtual Cathode Drive Laser Diagnostics with a Large Dynamic Range for a Continuous Wave SRF Photoinjector, Proceedings of IPAC2014, Dresden, Germany, pp. 2251 JACoW.org
        2. M. Gross, G. Klemz et al., Laser Pulse train management with an Acousto-optic modulator, Proceedings of FEL 2012, Nara, Japan, pp. 189 JACoW.org
        3. I. Will and G. Klemz, Generation of flat-top picosecond pulses by coherent pulse stacking in a multicrystal birefringent filter, Optics Express 16, 14922-14937 (2008) DOI:10.1364/OE.16.014922
        4. I. Will and G. Klemz, Drive lasers for photoinjectors, Proceedings of ERL 2007, Daresbury, UK, pp. 1 JACoW.org
        5. G. Klemz and I. Will, A Beam Shaper for the Optical Beamline of RF Photoinjectors, Proceedings of FEL 2006, Berlin, Germany, pp. 53 JACoW.org

        Collaborations:

        • Dr. Ingo Will, Max-Born-Institute, Berlin, Germany; project group  Laser systems for accelerators MBI website
        • Dr. Siegfried Schreiber, technical head of FLASH at DESY FLASH website
        • Dr. Frank Stephan, Photo Injector Test Facility at DESY, Location Zeuthen (PITZ) PITZ website