D. Janssen

MBI Yeshiva, Berlin, New Hampshire, United States

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Publications (70)163.61 Total impact

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    ABSTRACT: The superconducting radio frequency photoinjector (SRF gun) is one of the latest applications of superconducting rf technology in the accelerator field. Since superconducting photocathodes with high quantum efficiency are yet unavailable, normal conducting cathode material is the main choice for SRF photoinjectors. However, the compatibility between the photocathode and the cavity is one of the challenges for this concept. Recently, a SRF gun with Cs2Te cathode has been successfully operated in Forschungszentrum Dresden-Rossendorf. In this paper, we will present the physical properties of Cs2Te photocathodes in the SC cavity, such as the quantum efficiency, the lifetime, the rejuvenation, the charge saturation, and the dark current.
    Review of Modern Physics 01/2010; · 44.98 Impact Factor
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    ABSTRACT: The superconducting RF photo-injector (SRF gun) at FZD is the first operating electron injector of its kind. The gun with a 3½-cell cavity and a frequency of 1.3 GHz produces an electron beam of 3 MeV with a maximum bunch charge of about 400 pC. Also the design values for the acceleration gradient could not be reached with the cavity which is in use at present, the SRF gun will improve the beam quality for ELBE users. In the winter shutdown of 2009/10 the beam line was installed which connects the SRF gun with the ELBE accelerator. The paper reports on the first tests and on the progress in applying the SRF gun for ELBE operation.
    01/2010;
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    ABSTRACT: An RF photoinjector with a superconducting cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. This new and promising injector type allows CW operation and has the potential for the production of high-brightness electron beams. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed. In November 2007 the first beam was produced. Results of the beam parameter measurements with Cs2Te photo cathodes are presented.
    AIP Conference Proceedings. 08/2009; 1149(1).
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    ABSTRACT: At the Forschungszentrum Dresden‐Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF‐Photo‐Gun) is finished. This new injector is placed next to the existing thermionic gun of the superconducting linear accelerator ELBE. A connection between the accelerator and the SRF‐Gun will provide improved beam parameters for the users at the second half of 2009. At the moment the commissioning is fully under way. We will report on important results concerning cavity commissioning like measurements of: Q vs. E, microphonics, Lorentz detuning, tuner parameters, pressure sensibility and in‐situ fundamental mode field distribution calculated from measured pass band.
    AIP Conference Proceedings. 08/2009; 1149(1):1125-1132.
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    ABSTRACT: This paper presents the results of electron beam tracking simulations with the ASTRA code for the cell superconducting RF gun at the Forschungszentrum Dresden-Rossendorf. The SRF gun will improve the quality of the electron beam parameters for the ELBE superconducting electron linear accelerator. The ELBE electron accelerator is a general purpose facility for secondary radiation production. The facility produces X-rays, gamma-rays, neutrons, positrons and IR FEL radiation. The SRF gun will run in two operation modes with different repetition rates and bunch charges of the pulsed electron beam. The commonly used ELBE mode will operate with electron bunches with 13 MHz repetition rate and a bunch charge of about 77 pC with a maximal average current of 1 mA. The high charge mode with 500 kHz repetition rate and a bunch charge up to 1 nC will be used to generate neutrons by inducing nuclear reactions. For the future BESSY Soft X-ray FEL, a bunch charge of about 2.5 nC is required. For these operation modes of the SRF gun preferential operation parameters are determined by the results of beam dynamics studies.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2008; 584:259-265. · 1.14 Impact Factor
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    ABSTRACT: Most of the proposed electron accelerator projects for future free electron lasers, energy recovery linacs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. For that reason existing electron injectors must be considerably improved or new injector concepts developed. One very promising approach represents the superconducting radio frequency photoinjector (SRF gun). This injector type combines the advantages of a conventional photoelectron injector with that of superconducting acceleration, i.e. the very low RF losses and simple continuous wave operation. A SRF gun was developed and installed at Forschungszentrum Dresden-Rossendorf for operation at the ELBE superconducting linear accelerator. In November 2007 the first beam was produced. First commissioning results have been collected. Besides an improvement of beam quality and parameter range the SRF gun serves as a test bench for further development, evaluation and optimization since it is the first injector of its type which is operating at an accelerator worldwide
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2008;
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    ABSTRACT: In November 2007 the first electron beam was generated from the superconducting RF photo electron gun. The injector together with the UV driver laser system and the diagnostic beam line were developed and constructed within a collaboration of BESSY, DESY, MBI and FZD. After the cool-down of the cryostat the RF properties of the 3½-cell niobium cavity like pass band mode frequencies, unloaded quality factor versus accelerating gradient, Lorentz force detuning, and He pressure influence were measured. The first beam was extracted of a Cu photo cathode using the laser with a repetition rate of 100 kHz and 0.4 W laser power. Later, caesium telluride photo cathodes have been applied. First results of of beam parameter measurements are presented.
    01/2008;
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    V. Volkov, D. Janssen
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    ABSTRACT: Different applications of TE modes in accelerator physics are discussed. In this discussion, the Fourier transform of the squared axial component of magnetic field, Bz2(z), plays an important role. If it turns out to be zero, the rf field-particle energy transfer is negligible and the focal length of the TE mode lens is phase independent. Such rf lens focuses continuous beams just as a solenoid. In order to compensate spherical aberrations and emittance growth caused by field nonlinearities of a focusing solenoid, the rf focusing is used also even if the beam space charge is taken into account. If the transform has its maximum, excitations of TE mode resonances and electron beam self-focusing are possible. Furthermore, the rf field of the TE mode can be used to expand the radial acceptance of a FEL for the THz region.
    Review of Modern Physics 01/2008; 11(6). · 44.98 Impact Factor
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    ABSTRACT: Most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources require electron beams with an unprecedented combination of high brightness, low emittance, and high average current. In all projects photoguns will be applied: DC-photoguns, normal conducting RF-photoguns (NC-guns), and superconducting RF photoguns (SRF-guns). While the concepts of DC- and NC-guns are well proofed, the SRF-gun development still possesses a high risk. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high average power into the gun, and, finally, the risk of beam excitation of higher-order cavity modes. In combination with SRF linacs, the SRF-guns seem to be the best solution for high average currents. Several R&D projects of SRF-gun have been launched. In this paper, we will give an overview of the progress of the SRF photoinjector development. In detail, the technical concept, the performance and the status of the Dresden Rossendorf SRF-gun project, a collaboration of BESSY, DESY, MBI and FZD, will be presented. The main design parameters of this SRF-gun are the final electron energy of 9.5 MeV, 1 mA average current, and transverse normalized emittances (rms) of 1 mm mrad at 77 pC and 2.5 mm mrad at 1 nC bunch charge. The 1.3 GHz cavity consists of three TESLA-shaped cells, a specially designed half-cell where the photocathode is placed and a choke filter in order to prevent RF losses at the cathode side. The normal-conducting photocathode with a Cs2Te photoemission layer is cooled by liquid nitrogen. The SRF-gun cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid nitrogen-cooled thermal shield and a titanium He tank with a two-phase supply tube. The 10 kW fundamental power coupler is adopted from the ELBE cryomodule. In a first commissioning and test period the gun will be operated in parallel to the accelerator. A diagnostic beamline will allow beam parameter measurement and further optimization of the SRF-gun. In a final step, the gun will be connected to the ELBE superconducting linear accelerator to deliver an improved electron beam to the user labs.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2008; · 1.14 Impact Factor
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    ABSTRACT: A radio frequency photo injector with a superconducting acceleration cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. Beside the operation at ELBE, the SRF gun together with its diagnostic beam line is an excellent test bench for extended studies and improvements of this new and promising injector type. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed in summer and fall 2007. In November the first beam was produced. It will be reported on the experience gained at the first phase of commissioning. Results of rf and beam parameter measurements with Cs 2 Te photo cathodes are presented.
    01/2008;
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    V. Volkov, K. Floettmann, D. Janssen
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    ABSTRACT: The first electron beam of an RF gun with a 3.5 cell superconducting cavity is expected in July 2007 in FZD. This cavity has been designed for small bunch charges. In this paper we present the design of a similar cavity and of 1.5 cell gun cavities for large bunch charges. For a charge of 2.5 nC, which is the design value of the BESSY-FEL, and a bunch length of 21 ps a projected transverse emittance less then 1 pimu has been obtained (without thermal emittance).
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: A superconducting radio frequency (RF) photoelectron injector (SRF gun) is under development at the Research Center Dresden–Rossendorf. This project aims mainly at replacing the present thermionic gun of the superconducting electron linac ELBE. Thereby the beam quality is greatly improved. Especially, the normalized transverse emittance can be reduced by up to one order of magnitude depending on the operating conditions. The length of the electron bunches will be shortened by about two orders of magnitude making the present bunchers in the injection beam line dispensable. The maximum obtainable bunch charge of the present thermionic gun amounts to 80 pC. The SRF gun is designed to deliver also higher bunch charge values up to 2.5 nC. Therefore, this gun can be used also for advanced facilities such as energy recovery linacs (ERLs) and soft X-ray FELs. The SRF gun is designed as a cell cavity structure with three cells basically TESLA cells supplemented by a newly developed gun cell and a choke filter. The exit energy is projected to be 9.5 MeV. In this paper, we present a description of the design of the SRF gun with special emphasis on the physical and technical problems arising from the necessity of integrating a photocathode into the superconducting cavity structure. Preparation, transfer, cooling and alignment of the photocathode are discussed. In designing the SRF gun cryostat for most components wherever possible the technical solutions were adapted from the ELBE cryostat in some cases with major modifications. As concerns the status of the project the design is finished, most parts are manufactured and the gun is being assembled. Some of the key components are tested in special test arrangements such as cavity warm tuning, cathode cooling, the mechanical behavior of the tuners and the effectiveness of the magnetic screening of the cavity.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2007; · 1.14 Impact Factor
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    ABSTRACT: Continuous effort has been paid in last decades for a better polarized electron source for the high energy physics experiments. The DC guns with GaAs type photocathodes have been successfully operated in several laboratories, but the beam emittance is regretfully very poor. Although rf gun has been considered for the generation of the polarized electron beams with low emittance, the limit on vacuum is still an open question for the currently designed RF guns. In this paper a new proposal is reported: polarized SRF gun, i.e. superconducting rf gun with polarized photocathode. The polarized SRF gun would eliminate this vacuum barrier because of its low working temperature. Some questions including the cathode response time and the electron back bombardment are discussed in some detail, and the beam dynamics simulation gives positive forecast of the future application of polarized SRF gun.
    01/2007;
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    ABSTRACT: The design, fabrication and commissioning of a 703.75 MHz SRF photoinjector with a retractable multi-alkali photocathode designed to deliver 0.5 A average current at 100% duty factor is the present undertaking of the electron cooling group in the Collider Accelerator Division of Brookhaven National Labs. This photoinjector represents the state of the art in photoinjector technology, orders of magnitude beyond the presently available technology, and should be commissioned by 2007. The R&D effort presently underway, and the focus of this paper, will address the numerous technological challenges that must be met for this project to succeed. These include the novel physics design of the cavity, the challenges of inserting and operating a multi-alkali photocathode in the photoinjector at these high average currents, and the design and installation of a laser system capable of delivering the required 10 s of watts of laser power needed to make this photoinjector operational.
    Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 02/2006;
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    ABSTRACT: After successful tests of a SRF gun with a superconducting half-cell cavity a new SRF photoinjector for cw operation at the ELBE linac is under development. The paper discuss the design of the injector, the technological challenges of different components, the status of manufacturing and the expected parameters.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; 8225. · 1.14 Impact Factor
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    ABSTRACT: This paper presents results of the photocathode cooling system test of the 312 cell SRF gun at the Forschungszentrum Rossendorf. The SRF gun will produce short electron pulses with high bunch charges and low transverse emittance. The requirement for the superconducting electron linear accelerator in Rossendorf (ELBE) is to provide a low emittance electron beam up to 1mA current and 9.5MeV energy. Additionally, it will easily operate in continuous wave (cw) mode because of the low RF power losses in the superconducting material. Therefore, the normal conducting copper cathode must be cooled by liquid nitrogen in order to preserve the temperature of the cavity at 2.2K. The estimated power input from the RF field into the cathode could be more than 10W [P. vom Stein, Thesis, TU-Dresden, 1998]. First results of temperature measurements of the photocathode, respectively, from the cooling system at a heat load up to 30W are presented.
    Physica C Superconductivity 01/2006; 441(1):216-219. · 0.72 Impact Factor
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    ABSTRACT: The RF power input into an accelerating cavity is usually performed with special couplers that deliver the power in an asymmetric manner. Further, for superconducting cavities, the delivery point is typically into the beam tube beyond the cavity cells. In photocathode electron guns, where the cathode is isolated from the surrounding cavity by a coaxial vacuum gap, another power coupling possibility exists, since the cathode gap forms a coaxial line which can be used for RF power input. In the present paper, we show the advantages of this input coupling method. We then discuss a particular coupler design and present numerical results for normal and superconducting cavities.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    ABSTRACT: A key technology issue of energy recovery linac (ERL) devices for high-power free-electron laser (FEL) and fourth generation light sources is the demonstration of reliable, high-brightness, high-power injector operation. Three ongoing programs that target up to 0.5 Ampere photocathode injector performance with required ERL brightness, are described. The first is a DC gun and superconducting RF (SRF) booster cryomodule. Such a 748.5 MHz device is being assembled and will be tested up to 100 mA at the Thomas Jefferson National Accelerator Facility (JLAB) beginning in 2006. The second approach is a high-current normal-conducting RF (NCRF) injector. A 700 MHz gun will undergo thermal test in late 2005 at the Los Alamos National Laboratory (LANL), which when equipped with a suitable cathode, would be capable of exceeding 0.5 Ampere operation. Finally, a half-cell 703.75 MHz SRF gun with a diamond amplifier and other cathodes, will be tested to 0.5 Ampere at the Brookhaven National Laboratory (BNL) in 2007. The status and projected performance for each of these injector projects is presented.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    ABSTRACT: In the paper, we report on the status and progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 9.5 MeV electron energy, and it will be installed at the ELBE superconducting electron linear accelerator. The gun will have a 3½ cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. The production of two Nb cavities, with RRR 300 and 40 respectively, has be finished at the beginning of 2005. After delivery, the RF tests will be performed and the preparation of the cavities will be started. At the same time, the design of the cryostat and the fabrication of its components are already finished. Further activities are the design of the diagnostic beam line, the testing of the new photocathode preparation system, and the upgrade of the 262 nm driver laser system.
    01/2005;
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    ABSTRACT: Next generation x-ray sources require very high-brightness electron beams that are typically at or beyond the present state-of-the-art, and thus place stringent and demanding requirements upon the electron injector parameters. No one electron source concept is suitable for all the diverse applications envisaged, which have operating characteristics ranging from high-average-current, quasi-CW, to high-peak-current, single-pulse electron beams. Advanced Energy Systems, in collaboration with various partners, is developing several electron injector concepts for these x-ray source applications. The performance and design characteristics of five specific RF injectors, spanning "L" to "X"-band, normal-conducting to superconducting, and low repetition rate to CW, which are presently in various stages of design, construction or testing, is described. We also discuss the status and schedule of each with respect to testing.
    Proc SPIE 11/2004;

Publication Stats

536 Citations
163.61 Total Impact Points

Institutions

  • 2010
    • MBI Yeshiva
      Berlin, New Hampshire, United States
  • 1994–2010
    • Helmholtz-Zentrum Dresden-Rossendorf
      Dresden, Saxony, Germany
  • 2008
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 2003–2006
    • Budker Institute of Nuclear Physics
      Novo-Nikolaevsk, Novosibirsk, Russia
  • 1971
    • Joint Institute for Nuclear Research
      Dubno, Moskovskaya, Russia