Working Group: High Brightness Electron Beams
Particle accelerators play a fundamental role within the modern research and development era, advancing such varied fields as the future of energy, health and our industry. The development of novel accelerator concepts already today gives science impulses for the exploration of new research fields and will be indispensable in the future. The development of innovative particle sources with extreme performance parameters such as high beam current, low emittance, variable pulse length or selectable polarization is the main task for future accelerators.
The goal of our research is to understand the fundamental limits of beam brightness in electron sources, electron guns and accelerators. We approach this goal from various angles: they range from photoemission studies via beam dynamics investigations to experiments with electron accelerators.
Physics and Applications of Photoelectron Injectors
Development of a high brightness, high average current superconducting radio-frequency photoelectron injector (SRF photoinjector) for applications requiring continuous wave operation of a source of extremely bright electron pulses. Possible applications are energy-recovery linacs (ERL), free electron laser (FEL) or other direct beam or secondary radiation source. For the research on the SRF photoinjector we are working on the photoemission source of electrons, the photocathode and the photocathode drive laser, as well as on the beam dynamics of space-charge dominated beams. We complement the activities with the development of beam instrumentation tools to understand and optimize the performance of such sources. For this we develop non-destructive beam size monitors for ERL and laser-plasma accelerators. Furthermore we look into the deployment of SRF photoinjectors for ultra-fast sciences. For example for ultra-fast electron diffraction or ultra-fast electron microscopy.
- T. Kamps et al., SRF Gun Development for Energy Recovery Linac Applications, Compact EUV & X-ray Light Sources 2016. OSA
- R. Barday et al., Characterization of a Superconducting Pb Photocathode in a Superconducting RF Photoinjector Cavity, Phys. Rev. ST Accel. Beams 16, 123402 (2013).
- M. Abo-Barkr et al., Nonlinear harmonic generation in the STARS FEL, Nuclear Instruments and Methods in Physics Research Section A, 593, 1-2, 6, (2008).
Photocathode Research & Development for Electron Accelerators
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. 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. Our goal is to provide high quantum efficiency Cs-K-Sb photocathodes for the operation of bERLinPro and beyond that to understand fatigue effects and fundamental electronic and optical properties in collaboration with Prof. C. Cocchi from Humboldt-Universität zu Berlin.
- M. A. H. Schmeißer et al., Towards the operation of Cs-K-Sb photocathodes in superconducting rf photoinjectors, Phys. Rev. Accel. Beams 21, 113401, (2018). PRAB
- C. Cocchi et al., First-principles many-body study of the electronic and optical properties of CsK2Sb, a semiconducting material for ultra-bright electron sources, J. Phys.: Condens. Matter, 31, 014002, (2018). JPCM
- H. Kirschner, Spectral quantum efficency measurements on Cs-K-Sb photocathodes for the energy-recovery linac test facility bERLinPro, Master-Thesis, Humboldt Universität zu Berlin, Germany, (2017). HUB
Beam instrumentation plays an important role during all phases of an accelerator project. Diagnostics are needed during checkout, startup and for the approach of the target beam parameters. Diagnostics help to debug the gun and to identify sources of performance deviations from the ideal gun. The focus must therefore be on straightforward, rapid and easy-to-interpret measurement techniques and procedures for the complete phase space. This must include not only the core beam but also tails in the distributions and dark current. Currently we are working on the development of a compact diagnostics trolley for the bERLinPro and Athena_e accelerators. The trolley will include an interferometric beam size monitor and a THz camera for bunch compression studies.
- G. Kourkafas et al., TRANSVERSE DEFLECTING CAVITY FOR LONGITUDINAL BEAM DIAGNOSTICS AT bERLinPro, Proceedings of LINAC2018, Beijing, China, pp. 875. JACoW.org
- J. Völker, Development of a compact test facility for SRF Photoelectron injectors, PhD-Thesis, Humboldt Universtität zu Berlin, Germany, (2018). HUB
- G. Kourkafas et al., SOLENOID ALIGNMENT FOR THE SRF PHOTOINJECTOR OF bERLinPro AT HZB, Proceedings of IPAC2017, Copenhagen, Denmark, pp. 1778. JACoW.org
- T. Kamps et al., Electron beam diagnostics for a superconducting radio frequency photoelectron injector, Review of Scientific Instruments 79, 093301 (2008).
- A. Bosco et al., A two-dimensional laser-wire scanner for electron accelerators, Nuclear Instruments and Methods in Physics Research Section A: 592, 3, 162 (2008).
Drive Laser and Laser Beam Transport
The operation of a photoelectron injector 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. Our drive laser systems are developed in collaboration with 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.
Contact: Dr. Guido Klemz
- 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
- 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
- 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
- I. Will and G. Klemz, Drive lasers for photoinjectors, Proceedings of ERL 2007, Daresbury, UK, pp. 1 JACoW.org
- 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
- SS2019: Elektronenbeschleuniger und Nanospektroskopie für Energierelevante Materialien
- WS2018/2019: Elektronenbeschleuniger und Nanospektroskopie für Energierelevante Materialien
- SS2017: Lecture Week GRK 2128 Accelence at Johannes-Gutenberg University Mainz