FZD, Dresden
The success of most of the proposed electron accelerator projects for future FELs, ERLs or 4th generation light sources is contingent upon the development of an appropriate source to generate the electrons with an unprecedented combination of high-brightness, low emittance and high average current. An elegant way is to combine the high brightness of RF guns with the superconducting technology. This concept was first proposed at the University of Wuppertal*. In 2002, the successful operation of a SRF photo-injector could be demonstrated at FZD for the 1st time**. However, this type of injectors is still in the R&D phase. Challenges are the design of the cavity with its specific geometry, the choice of the photocathode type, its life time, a possible cavity contamination, the problems on coupling of high-average power into the cavity and the risk of beam excitation of higher order cavity modes. During the last years several R&D projects have been launched. Most of them pursue different approaches to deal with these issues. This contribution gives an overview on the progress of the SRF photo-injector development based on the most prominent projects in the world.
* H. Piel et al., FEL’88, Jerusalem, Israel, 1988.
** D. Janssen, et al., Nucl. Instr. and Meth. A507 (2002) 314.
FZD, Dresden
The RF-system of the superconducting electron LINAC ELBE (40 MeV, 1 mA CW) is in permanent operation since 2001 without mentionable problems but it is not completely free of RF-trips. Experience gained within eight years of operation shows that the better the RF-components were conditioned the better is their electrical stability during long time operation. To be prepared for a future ELBE upgrade several test benches have been built to study the performance of RF-amplifiers, RF-couplers and waveguide windows. A resonant ring (travelling wave resonator) allows component tests with RF power up to 100 kW in continuous wave (CW) mode and 200 kW in pulsed mode. The ring, driven by a 10 kW CW klystron is equipped with different sensors to detect light, temperatures and to produce infrared images of waveguide windows. A test bench with a waveguide sliding short is used to run component tests at full reflections (all phases). In 2008 the prototype of a 30 kW IOT–based RF transmitter was installed and connected to an ELBE cavity. The experience gained during routine FEL operation is used to improve the design of the high voltage power converter of the IOT transmitter.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
JLAB, Newport News, Virginia
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
BNL, Upton, Long Island, New York
DESY, Hamburg
FZD, Dresden
MBI, Berlin
In this paper we describe the R&D roadmap at HZB for the development of a high-brightness, high average current SRF electron gun for an energy-recovery linac based synchrotron radiation source.
FZD, Dresden
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
The superconducting rf photoinjector (SRF photoinjector) is one of the latest application of SC technology in the accelerator field. Since superconducting cathodes with high QE are not available up to now, normal conducting cathode material is the main choice for the SRF photoinjectors. However, the compatibility between the cathode and the cavity is one of the challenges for this concept. The SRF gun with Cs2Te cathode has been successfully operated under the collaboration of BESSY, DESY, FZD, and MBI. In this paper, some experience gained in the gun commissioning will be concluded. The results of the properties of Cs2Te photo cathodes in the cavity will be presented, such as the Q.E., life time, regeneracy, dark current and thermal emittance. At the same time, the cavity quality is showed to be steady before and after the cathode working.
FZD, Dresden
JLAB, Newport News, Virginia
An SRF photoinjector has been successfully tested in FZD under the collaboration of BESSY, DESY, FZD, and MBI. In order to improve the gun cavity quality and thus reach a higher gradient, a new 3+1/2 superconducting cavity is being fabricated in cooperation with JLab. The modified cavity is made of large grain niobium, composed of one filter choke, one special designed half-cell (gun-cell) and three TESLA cavities. In this paper, the main updates of the new cavity design will be explained in detail. The deformation of the filter choke and the gun-cell, which is caused by pressure fluctuation in the He-line and also by the effect of the Lorentz force, will be minimized by stiffening between the filter choke and the gun-cell. Meanwhile, the cathode hole in the choke and gun-cell is enlarged for better rinsing. To simplify assembly, the NbTi pick-up will be welded directly on the wall of filter choke.