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.
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
For good operating the ELBE linear accelerator it is essential to have RF signals with high phase stability and purity on all cavities and buncher RF signals. Therefore a large number of low level RF control loops are used. But sometimes problems with these circuits occur. For further investigations a multichannel phase supervising device is required to have knowledge of phase noise and long term drifts. The circuit under development at ELBE allows the simultaneous phase measurement of up to 32 signals of 1.3 GHz (accelerator), 260 MHz (buncher) or 13 MHz (gun) frequency with 2 deg accuracy. Using an additionally 1.3 GHz PLL locked to the 13 MHz master oscillator (OCXO) of the machine as reference the phase measurement device is completely independent from the circuits used in the accelerator low level RF. Under normal conditions a programmable logic controller (SIMATIC) is used for data acquisition. This leads to approx. 5 measurements per second for all channels. But the measurement device is much faster, feeding the signals to a National Instruments PXI-6115 12-Bit, 10 MS/s/channel multifunction DAQ card enables also microphonic and phase noise measurements up to 10 kHz.