[Show abstract][Hide abstract] 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 04/2010; 13(4). DOI:10.1103/PhysRevSTAB.13.043501 · 29.60 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: As the first superconducting rf photo-injector (SRF gun) in practice, the FZD 3+1/2 cell SRF gun is successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for ELBE users. It is the first example for an accelerator facility fully based on superconducting RF technology. For high average power FEL and ERL sources, the combination of SRF linac and SRF gun provides a new chance to produce beams of high average current and low emittance with relative low power consumption. The main parameters achieved from the present SRF gun are the final electron energy of 3 MeV, 16 μA average current, and rms transverse normalized emittances of 3 mm mrad at 77 pC bunch charge. A modified 3+1/2 cell niobium cavity has been fabricated and tested, which will increase the rf gradient in the gun and thus better the beam parameters further. In this paper the status of the integration of the SRF gun with the ELBE linac will be presented, and the latest results of the beam experiments will be discussed.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: More and more electron accelerator projects for FELs, ERLs or 4th generation light sources require super electron beams with high brightness, low emittance, and high average current. Under this background, much attention is paid on the research and development of new electron sources. A Superconducting RF photoinjector within a collaboration of HZB, DESY, FZD, and MBI is designed to improve the beam quality for ELBE IR FEL users, and at the same time to test this kind of promising injector concept. The main design parameters of this 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. In this paper the results of the RF and beam parameter measurements with Cs2Te photo cathodes will be presented, and the experience for the gun running gained at the first beam experiment will be concluded, including the life time and the compatibility of the normal conducting photocathode in SC cavity, the cavity properties after the cathode s inserting
[Show abstract][Hide abstract] 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 08/2008; DOI:10.1016/j.nima.2008.04.035 · 1.22 Impact Factor
[Show abstract][Hide abstract] 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 06/2008; 11(6). DOI:10.1103/PhysRevSTAB.11.061302 · 29.60 Impact Factor
[Show abstract][Hide abstract] 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(2-3):259-265. DOI:10.1016/j.nima.2007.10.030 · 1.22 Impact Factor
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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).
[Show abstract][Hide abstract] 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 07/2007; 577(3-577):440-454. DOI:10.1016/j.nima.2007.04.171 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: For the ELBE superconducting linear accelerator at FZD a radiofrequency photoelectron injector with a superconducting cavity (SRF gun) is under development. The SRF gun combines the excellent beam quality which can be delivered by RF photoinjectors with the possibility of continuous wave operation. The superconducting niobium cavity of the injector consists of 3½ cells and contains a Cs 2 Te photocathode which is normal-conducting and cooled by liquid nitrogen. The RF frequency of the cavity is 1.3 GHz. The final electron energy will be about 9.5 MeV and the average electron current will be 1 mA. In the past years the SRF photo injector has been designed and fabricated. Several critical subsystems have been tested. For the cavity, the results of the RF measurements will be shown. An UV driver laser system has been developed which fulfils the different requirements (77 pC @ 13 MHz, 1 nC @ 500 kHz) for the future operation at ELBE. A photo cathode preparation system was developed and installed. The equipment is now in operation and the first series of Cs 2 Te photo cathodes have been produced.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 07/2006; 441(1):216-219. DOI:10.1016/j.physc.2006.03.051 · 0.94 Impact Factor
[Show abstract][Hide abstract] 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 02/2006; 8225. DOI:10.1016/j.nima.2005.10.120 · 1.22 Impact Factor
[Show abstract][Hide abstract] 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; DOI:10.1016/j.nima.2005.10.054 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The designs and a report on the progress in construction and testing of the cryomodule and the tuning system for the SRF gun are presented. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a CW photo injector at the ELBE linac. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from the ELBE module. A cooling and support system for the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20 W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with step motors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.