Operation of the superconducting RF photo gun at ELBE

Abstract

As the first superconducting RF photo-injector (SRF gun) in practical operation, the SRF gun has been successfully connected to the superconducting linac ELBE at Forschungzentrum Dresden-Rossendorf. The injection with this new gun will improve the beam quality for the users of the radiation source. The SRF gun contains a 3½ cell superconducting accelerating cavity with a frequency of 1.3 GHz. The design is for use of normal conducting photocathodes. At present, caesium telluride photocathodes are applied which are illuminated by an ultraviolet laser beam. The kinetic energy of the produced electron beam is 3 MeV which belongs to a peak electric field of 16 MV/m in the cavity. The maximum bunch charge which is obtained and measured in a Faraday cup is about 400 pC (20 µA average current at a repetition rate of 50 kHz). The SRF gun injector is connected to the ELBE accelerator via a dogleg with two 45° deflection magnets. This connection beam line was commissioned in January 2010. A first beam injection into the ELBE accelerator has been carried out with a bunch charge of 120 pC (6 µA at 50 kHz). Detailed measurements showed that beam loss occurred in the dogleg above 60 pC due to the correlated energy spread. In order to find the optimal operation conditions, energy spread was measured in dependence of bunch charge, laser phase and further gun parameters. The Cs 2 Te photocathode shows an excellent life time. It is in the gun since May 2010 with about 300 h beam time and about 7 C extracted charge. In the present cavity, the limit for the acceleration gradient is field emission due to some defect on the cavity surface and problems during cleaning. Therefore a modified 3½ niobium cavity has been fabricated, which will increase the RF gradient in the gun and thus improve the beam parameters further.

Spatial Localization of EEG Electrodes in a TOF+CCD Camera System

“…With regard to the point cloud stitching problem, many works use an ICP algorithm or improved ICP algorithm (Cheng et al, 2016; Yang et al, 2016). However, here, due to the large deviation of the angle of view, the performance of ICP algorithm is not ideal, thus SVD is adopted to calculate the conversion relationship between the two sets of point clouds (Sorkine, 2009; Jung et al, 2015; Raposo et al, 2016). The principle is described firstly from this transform…”

Systematic study of multipactor suppression techniques for a superconducting rf gun

“…Due to this effect, it turns out that a strong input mismatch paired with a resonance drift makes it infeasible to raise the accelerating gradient by increasing the incident rf power. Therefore, this phenomenon is a serious problem that limits the accelerating gradient in the cavity to very low values [20]. Hence, minor design changes are under investigation that should allow the SRF gun to operate up to the desired electric field strength [19].…”

“…10, MP was totally suppressed in the case of 100 V and above but even 50 V could be sufficient. However, in practice it has been found that a voltage up to 7 kV was required to suppress MP reliably [20]. Therefore, further investigations are needed to match numerical and experimental data.…”