Search

Various continuous-wave (CW) electron gun technologies are reviewed, including DC, superconducting radio frequency RF (SRF), hybrid DC-SRF and normal-conducting RF. Also, the SLAC Linac Coherent Light Source II (LCLS-II) normal-conducting RF gun and injector are described, and the performance to date, including the bunch emittance achieved and the dark current observed, is presented.

As an excellent demonstration of SRF gun technology, HZDR's SRF Gun-II has been rountinely operated as an electron gun for the ELBE THz radiation and the ELBE neutron source since 2018, delivering CW beams with bunch charges of up to 300 pC at 50-100 kHz. As is well known, the quality of the photocathodes is crucial for the stability and reliability of the gun operation. Different cathodes have been used in the HZDR SRF gun and the cathodes have been replaced three to four times per year. In the last five years, the quality of the superconducting cavity has remained almost stable, but some characteristics of the gun have been observed related to the cathodes. In this contribution, we will introduce the operational aspect of the photocathodes in HZDR SRF gun, look back at the achievements and discuss open issues and possible improvements for future application.

In the high gradient rf photoinjectors, dark current is the “unwanted beam” not produced by the cathode drive laser. It is a part of field emission from the cavity and photocathode, which is accelerated through the gun. Dark current can cause beam loss, increase the risk of damage to accelerator components, and create additional background for beam users. Furthermore, during operation of the ELBE srf gun, the dark current has been found to correlate with the photocathode QE and life time. Therefore, understanding the sources as well as the dynamics of dark current is crucial to machine safety and gun quality. In this paper we present our experimental investigations of the dark current at the ELBE SRF gun-II. The beam dynamics of the dark current is studied with the ASTRA code, which helps us to track the field electrons starting from the cathode area and from other sources, so that we can understand their different contributions to the dark current.

Superconducting radio frequency photo injectors (SRF gun) offer advantages for operating in continuous wave (CW) mode and generating high-brightness and high-current beams. A new SRF gun is designed as a low emittance photo injector for LCLS-II-HE and a prototype gun is currently being developed under collaboration between SLAC, FRIB, HZDR and ANL. The aim is to demonstrate stable CW operation at a cathode gradient of 30 MV/m. One of the crucial components for successful SRF gun operation is the photocathode system. The new SRF gun will adopt the HZDR-type cathode, which includes a cathode holder fixture (cathode stalk) developed by FRIB and a cathode exchange system designed by HZDR. This innovative cathode insertion system ensures accurate, particle-free and warm cathode exchanges. A novel alignment process targets the cathode to the stalk axis without touching cathode plug itself. To commission the prototype gun, metallic cathodes will be used. A specifically designed vacuum system ensures vacuum pressure of 10-9 mbar for transport of a single cathode from the cleanroom to the gun.

At the electron accelerator for beams with high brilliance and low emittance (ELBE), the second version of a superconducting radio-frequency (SRF) photoinjector was brought into operation in 2014. After a period of commissioning, a gradual transfer to routine operation took place in 2017 and 2018, so that more than 3000h of user beam have already been generated since 2019. During this time, a total of 20 cathodes (2 Cu, 12 Mg, 6 Cs₂Te) were used, but no serious cavity degradation was observed. In this paper, we summarize the operational experience of the last 6 years of SRF gun operation, with special emphasis on the main RF properties of the cavity. This includes the evolution of QvsE, dark current, multipacting, but also mechanical properties such as Lorentz force detuning, helium pressure sensitivity as well as microphonics. The latter is closely connected to an active compensation by a so-called low-level RF feedback loop, which is also briefly presented., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

As well known, the quality of the photocathodes is essential for the stability and the reliability of photo injector operation. Especially for the superconducting ratio frequency photo injectors (SRF guns), the photocathode represents one of the most critical parts. Benefit from the fast de-veloping photocathode technology in last years, several SRF guns were successfully operated or tested for the beam generation at kHz - MHz repetition rate. In this paper, we will review the achievements as well as the open questions in the applications of the photocathodes for SRF gun operation. Furthermore, we will discuss the possible improvement from cathodes side for the future CW electron sources.

The quality of the photocathodes is critical for the stability and reliability of the photoinjector’s operation. Thanks to the robust magnesium and Cs2Te photocathodes, SRFgun-II at HZDR has been proven to be a successful example in CW mode for high current user operation. In this contribution, we will present our observation of the QE evolution of Cs2Te photocathodes during SRF gun operation. The variables including substrate surface, film thickness, Cs/Te stoichiometric, multipacting, RF loading and charge extract are considered in the analysis.

The success of proposed high power free-electron lasers (FELs) and energy recovery linac (ERL) largely depends on the development of the electron source, which requires the best beam quality and CW operation. An elegant way to realize both high brilliance and high current is to com-bine the high beam quality of the normal conducting radio frequency photoinjector with the quick developing superconducting radio frequency technology, to build superconducting rf photoinjectors (SRF guns). In last decade, several SRF gun programs based on dif-ferent approaches have achieved promising progress, even succeeded in routine operation at BNL and HZDR. In the near future SRF guns are expected to play an im-portant role for hard X-ray FEL facilities. In this contribu-tion, we will review the design concepts, parameters, and status of the major SRF gun projects.

Magnesium bulk cathodes and caesium telluride cathodes work routinely in SRF Gun II at ELBE. However, the particle accelerator community is always looking for new materials which can promise higher quantum efficiency, longer lifetime and good vacuum stability, fast response time and low thermal emittance. P-type GaN on different substrate material is activated by a thin layer of caesium and illuminated at the same time by ultra-violet light. As a consequence of a negative electron affinity and photoeffect, the generated photoelectrons enter into vacuum and are collected by a copper ring anode. The resulting photocurrent is detected during the activation process and stopped when a maximum photocurrent is reached. Quantum efficiency can be calculated from the photocurrent and its decay is tracked in the following days after activation. By a comparison of differences in substrate material, chemical pre-cleaning, thermal heat treatment and activation parameters (e.g. caesium-flux), the photocurrent, quantum efficiency and its decay is studied.

A short report on experiences with UV photocathode lasers and laser beam line for ELBE SRF Gun in 2020-2021

The SRF gun-II at HZDR has been stably applied as the electron source for high power THz radiation since 2018, generating CW beams with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration that SRF guns can work reliably in a high power user facility. As well known, that the quality of the photocathodes is critical for the stability and reliability of the gun operation. In last years, thank to the successful ps UV laser cleaning, Mg photocathodes were successfully used for gun operation at kHz repitition rate. In order to satisfy user request of MHz operation, Cs2Te is still in demand. However, the Mo plugs were overheated in superconducting rf cavity due to thermal contact problem, and SRF Gun-II faced twice serious contamination in 2017. The Cs2Te could not be used in gun untill Cu is adopted in stead of Mo as new substratum. Up to now three Cs2Te cathodes on Cu plugs have been applied in the Gun-II. In this contribution, we will present the operational aspect of the photocathodes for SRF gun, and discuss the possible improvement in the future application.

The SRF gun-II at HZDR has been stably applied as the electron source for high power THz radiation since 2018, generating CW beams with bunch charges up to 300 pC at 100 kHz. It is an excellent demonstration that SRF guns can work reliably in a high power user facility. In order to generate higher current beam with MHz repetition rate, Cs2Te photocathodes are required. However, in last two experiments with Cs2Te, the Mo substrate plugs were overheated in superconducting rf cavity. The reason is that different thermal expansion coefficient of Mo and Cu led to a bad thermal contact between the Mo plug and Cu holder. Thus we decided to use Cu as new substratum of Cs2Te cathodes. In last year we prepared several Cs2Te photocathodes on Cu plugs and improved the vacuum of cathode transfer system in order to achieve satisfied lifetime. In this contribution, we will present the study result of QE and life time of Cs2Te photocathodes with different thickness.

SRF injectors need materials which can promise high quantum efficiency, long lifetime and good vacuum stability, fast response time and low thermal emittance. It is assumed that GaN, like GaAs, as a novel electron source for particle accelerators shows an enormous potential. P-type GaN on different substrate material is activated by a thin layer of caesium and illuminated at the same time by ultra-violet (UV) light. As a consequence of a NEA surface and photoeffect, the generated photoelectrons enter into vacuum and are collected by an anode. The resulting photocurrent is detected during the whole activation process and stopped when a maximum photocurrent is reached. Quantum efficiency (QE) can be calculated from the photocurrent. Its decay is tracked in the following days after activation. It is also studied to re-activate the sample again by using thermal heat treatment and caesium Deposition once more. High 11.5% QE can be provided from GaN:Cs on sapphire substrate at the moment. After 600 h of lifetime this photocathode shows still 1.4% QE. Besides the outstanding experimental results so far further investigations are still required.

At present, ELBE radiation source at HZDR is optimizing the SRF cavity for the next generation ELBE SRF GUN. This paper presents a preliminary study on the geometry optimization of a 3.5-cell SRF gun cavity based on beam dynamics. By changing the lengths of the half cell and the first TESLA like cell, two new cavity models with higher electric field in the half cell are built and their RF fields are compared with SRF GUN I and SRF GUN II. Through the scanning of the RF phases and the electric fields, the simulation results indicate that new models have smaller transverse emittance at relatively lower electric field gradients and better performance on longitudinal emittance than SRF GUN I and SRF GUN II., Proceedings of the 39th Free Electron Laser Conference, FEL2019, Hamburg, Germany

The first all-SRF accelerator driven THz source has been operated as a user facility since 2018 at ELBE radiation center. The CW electron beam is extracted from SRF gun II, accelerated to relativistic energies and compressed to sub-ps length in the ELBE SRF linac with a chicane. THz pulses are produced by pass-ing the short electron bunches through a diffraction radiator (CDR) and an undulator. The coherent THz power increases quadratically with bunch charge. The pulse energy up to 10 µJ at 0.3 THz with 100 kHz has been generated., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Quality of photocathode in a photoinjector is one of the critical issues for the stability and reliability of the whole accelerator facility. In April 2013, the IR FEL lasing was demonstrated for the first time with the electron beam from the SRF gun with Cs2Te at HZDR. Cs2Te photocathode worked in SRF gun-I for more than one year without degradation. Currently, Mg photocathodes with QE up to 0.5% are applied in SRF Gun-II, generating e⁻ beam with bunch charge up to 300 pC in CW mode with sub-ps bunch length for the high power THz radiation. It is an excellent demonstration that SRF guns can work reliably in a high power user facility., Proceedings of the 63th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2019, Berlin, Germany

In order to optimize the next generation SRF gun at HZDR ELBE radiation source, the impact on beam dynamics from the SRF cavity geometry needs to be investigated. This paper presents an analysis on the electromagnetic fields and output electron beam qualities, by changing the geometry parameters of a 3.5-cell SRF gun cavity. The simulation results show the higher electric field ratio in the first half cell to the TESLA like cell, the better beam parameters we can obtain, which, however, will also lead to a higher Emax/E0 and Bmax/E0.

The initial commissioning of the Superconducting RF (SRF) photoinjector is done with a Cu photocathode due to its robustness with regard to interactions with the SRF cavity of the injector. Here we present the preparation and characterization of a Cu photocathode plug and the diagnostics to insert the photocathode in the back wall of the SRF cavity. A polycrystalline bulk Cu plug was polished, particle free cleaned and characterized by x-ray photoelectron spectroscopy. During the transfer of the photocathode insert into the gun module the whole process was controlled by several diagnostic tools monitoring the insert position as well as RF, vacuum and cryogenic signals. We discuss the challenges of the photocathode transfer into an SRF cavity and how they can be tackled., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The superconducting RF photoinjector (SRF Gun II) has successfully served for the ELBE user facility at HZDR. Nevertheless, the quality of photocathodes is one of the most critical issues in improving the stability and reliability for its application. Magnesium has a comparably low work function (3.6 eV) and shows a quantum efficiency up to 0.3% after laser cleaning. However, the present cleaning process with a high intensity laser beam is time consuming and produces unwanted surface roughness, which leads to a higher thermal emittance. Thermal treatment and Excimer laser cleaning for Mg cathodes are investigated as alternative methods. In this work, the new cleaning procedures are tested and optimized, and the quantum efficiency of Mg samples with different microstructure, composition and suppliers are compared., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Contemporary particle injector technologies provide different advantages depending on the chosen design. In the case of copper rf injectors these is primarily the high accelerating field, enabling the generation of high charge bunches with very low emittance. However, the cost of that is a comparably low repetition rate. DC guns, on the other hand, can provide higher repetition rates and consequently increased beam currents at lower beam quality, i.e., increased emittance. The concept of a superconducting rf injector offers the opportunity to combine the advantages of both these concepts. However, it demands special concepts for emittance compensation, as the common approach with overlapping magnetic fields during the rf acceleration interferes with the limitations of superconductivity. The ELBE SRF Gun project is one of the most advanced in this field. Gun II, the second SRF injector at the Electron Linear accelerator with high Brilliance and low Emittance (ELBE), introduces new features for emittance compensation which were studied in detail over the last years. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method uses rf focusing by retracting the photocathode's tip from the last cell of the resonator. This paper discusses both of these schemes by briefly outlining their setups, discussing results of numerical simulations of their impact, and presenting results of initial experimental beam measurements with Gun II.

The multipurpose CW accelerator ELBE at HZDR, which is delivering a large set of secondary beams, is driven by a thermionic DC injector. In order to enhance the machine's beam quality, the development of a superconducting RF injector has been pursued since the early 2000ies. The corresponding ELBE SRF Gun I of 2007 and Gun II of 2014 already delivered beam for the operation of several user beamlines, such as the FEL, positron generation, and THz facility. Currently, the next version ' Gun III ' and its cryomodule are being assembled, characterized, and prepared for the final commissioning throughout late 2017/early 2018. The new module benefits from the experiences in terms of emittance compensation and surveillance of operation variables made with the two predecessors. Results of the latest Gun II operations as well as first commissioning data of the Gun III module will be presented., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

Future light sources such as synchrotron radiation sources driven by an energy recovery linac, free electron lasers, or THz radiation sources have in common that they require injectors, which provide high-brilliance, high-current electron beams in almost continuous operation. Thus, the development of appropriate highly brilliant electron sources is of key importance. With its superconducting radio-frequency photo-injector (SRF gun) the Helmholtz-Zentrum Dresden-Rossendorf provided a promising approach for this key component, which has since been adopted in other laboratories. Nevertheless, some limitations occur caused by electron multipacting, which should be suppressed in order to further improve the gun. In this contribution, we present a detailed analysis of multipacting in the critical area of the SRF gun and different suppression techniques for it. The analytical predictions on the threshold for multipacting are qualitatively comparable with numerical simulation results and experimental data. Finally, we present specific surface structuring as an effective method to mitigate the multipacting phenomenon from the photocathode channel.

The second version of the superconducting RF pho-toinjector (SRF Gun II) was successfully commissioned at the ELBE radiation source in 2014. The gun features an improved 3.5-cell niobium cavity combined with a super-conducting solenoid integrated in the cryostat. With a Mg photocathode the SRF Gun II is able to generate bunches with up to 200 pC and with sub-ps length in CW mode with 100 kHz pulse frequency for the THz radiation fa-cility at ELBE. In the ELBE linac, the beam is accelerat-ed, gets a proper correlated energy spread, and is com-pressed in a magnetic chicane. Sub-ps pulses are obtained producing coherent diffraction radiation and superradiant undulator radiation., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

As a new electron source with higher brilliance, the second version of the superconducting RF photoinjector (SRF Gun-II) has been successfully commissioned at the ELBE Center for high power radiation sources since 2014. SRF Gun-II features an improved 3.5-cell niobium cavity as well as a superconducting solenoid in the same cryomodule. With Mg photocathode SRF Gun-II can provide high current beam with bunch charge up to 300 pC at 100 kHz repetition rate. For user operation the SRF Gun-II successfully generated stable beam with 200 pC in CW mode and sub-ps bunch length. In this presentation the gun's status and beam parameters will be presented.

Quality of photocathodes is one of the critical issues for the stability and reliability of the light source facility. In 2014, SRF gun-I with Cs2Te provided stable electron beams successfully for IR FEL at HZDR. Cs2Te worked in SRF gun for more than one year without degradation. Currently, Mg photocathodes with QE up to 0.5% are applied in SRF Gun II, which is able to generate e- beam with bunch charges up to 200 pC in CW mode with sub-ps bunch length for the high power THz radiation facility for the ELBE users.

Since 2015, Mg photocathodes have been applied for the ELBE SRF gun. Recently, user experiments with a bunch charge of 100 pC and beam transport experiments with 200 pC have been performed. The electron beam diagnostics will be presented, including the slit-scan measurements of the transverse phase space, the quadrupole-scan emittance measurement and the phase-scan bunch length measurement. Principles and results of these diagnostics will be introduced, as well as the error analysis. A UV laser is used to emit electron, the pulse length of which directly impacts the electron beam. A commercial cross correlator has been installed to measure the temporal profile of the UV laser. The alignment of the beam measurement results for this will be presented. Bases on the operation experiences from the current SRF gun, a new gun-lab has been proposed to build and test the next SRF gun in a separated room from the ELBE accelerator. The preliminary design of a new corresponding diagnostics beamline will be presented, featuring a fast beam-scan transverse phase space measurement and a transverse deflecting structure based measurement of longitudinal phase space., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

An improved SRF gun (ELBE SRF Gun II) has been installed at the ELBE radiation center as an additional electron source since 2014. This new gun is able to produce up to 300 pC bunch charges in CW mode. This poster summarizes the latest results of user application with SRF Gun II

An SRF gun at the ELBE center has been operated with a magnesium cathode. Electron beams were produced with a maximum bunch charge of 200 pC and an emit-tance of 7.7 μm. Simulations have been conducted with ASTRA and Elegant for applying the SRF gun to ELBE user experiments, including neutron beam generation, positron beam generation, THz radiation and Compton backscattering experiment. Beam transport has been optimized to solve the best beam performance for these user stations at the bunch charge of 200 pC. Simulation results indicate that the SRF gun is potential to benefit the high bunch charge applications at ELBE., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In this contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results.

In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In our contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results as well as detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will present the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.

Report on the beam transport simulation of the ELBE accelerator for injection with the SRF gun for THz, neutron and CBS applications.

Status Report on Superconducting Rf Photoinjector application at ELBE

In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In this contribution we will report on the commissioning of the SRF gun by presenting detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will report the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.

For future linear CW accelerators, superconducting (SC) RF guns are discussed to be the most promising solution to fulfil the demands on high average current and high brightness at the same time. But in difference to the NCRF guns, the application of static magnetic fields near the cathode to compensate for space charge forces is not possible. Instead, magnetic fields of transverse electric (TE) modes excited in parallel to the accelerating mode were proposed. Experiments at the 1st Rossendorf SRF gun using the existing fundamental mode coupler in combination with a RF diplexer have shown that this is feasible. However, since the cavity was not designed for this purpose, the mode was strongly damped by HOM couplers and cavity beam tubes and thus only low field strength could be achieved. In this contribution we will present a modified cavity design that avoids these problems and provides a separate RF coupler for the TE mode. Additionally, we will report on the first vertical test that demonstrated the functionality of the whole RF setup as well as realized significant higher field of the excited TE011 mode in parallel to the TM010 mode.

In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time. With the improved parameters first user experiments of the superconducting CW accelerator ELBE are to be served, that benefit from an increased average beam current at a given repetition rate of some hundred kHz. Although the cavity performance stays behind its specifications (Ecath~12 MV/m), beam commissioning is underway. In order to lower the risk of particle contamination and to get enough robustness against vacuum events in this early stage, we started with a laser cleaned magnesium cathode (QE~1e-3) instead of our standard Cs2Te cathode. In this contribution we will report on detailed parameter measurements of the electron beam that has a repetition rate of 100 kHz and a bunch charge up to 300 pC.

For the accelerator-based light sources and the electron colliders, the development of photoinjectors has become a key technology. Especially for the superconducting radio frequency cavity based injector (SRF Gun), the searching for better photocathodes is always a principal technical challenge. To use metallic photocathodes for ELBE SRF Gun is the primary choice to prevent cavity contamination. In this contribution, we will report the investigation of Magnesium (Mg) in ELBE SRF gun, including laser cleaning treatment and the measurement on quantum efficiency, Schottky effect, dark current and damage threshold., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

We report the Status of Mg and Cu Photocathodes used in the HZDR SRF Photo-injector.

The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.

RF photoelectron sources with superconducting cavities provide the potential to generate high quality, high brightness electron beams for future accelerator applications. At Helmholtz-Zentrum Dresden Rossendorf, such an electron source was operated for many years. The commissioning of an improved SRF Gun with a new high-performance gun cavity with low field emission and a superconducting solenoid inside the gun cryomodule (SRF Gun II) has started in June 2014. Simulations of the experimental set-up with ASTRA and ELEGANT were performed. First low current measurements as well as studies of unwanted beam transport using SRF Gun II with Cu photocathode and an acceleration gradient up to 9 MV/m will be presented. First beam characterization of the SRF Gun in combination with ELBE, a two-stage superconducting linear accelerator will be discussed.

Superconducting RF injectors are promising candidates for the particle sources of future accelerators. While machines like high power free electron lasers or energy recovery linacs are planned to be operated with large duty factors, or even continuous wave mode, to increase the beam intensity, they also demand high beam quality. As this is already determined at the very start of the generation of each particle bunch, the concept of an SRF gun becomes appealing. Transverse Emittance marks the beam quality which is of tremendous relevance for all beam optics and further more sets the level of angular resolution of any scattering experiment performed with the beam. Several concepts to enhance this quality with the lately comissioned Rossendorf SRF Gun II have been presented in recent year’s conferences. The talk will summarize the expended efforts, discuss some of the reflections on installation and operation of the used tools and present preliminary results of the recent achievements.

An improved SRF gun (ELBE SRF gun II) has been installed and commissioned at HZDR. This new gun replaced the first SRF gun of the ELBE accelerator which had been in operation since 2007. The new gun has an improved 3.5-cell niobium cavity those SRF performances have been studied first with a copper cathode. After the replacement by our standard Cs2Tecathode we observed a tremendous degradation of the cavity gradient paired with an increase of field emission. In this contribution we will report on our in-situ investigations to find the origin and the reason for the particle contamination that happened during the first cathode transfer.