ITMO-JINR multidisciplinary project: development of the source of relativistic vortex electrons (carrying orbital angular momentum - OAM) based on the LINAC-200 electron accelerator in JINR. First stage: testbench with RF-gun based acceleration yielding vortex electrons with energies up to 5 MeV. Concept: generating vortex electrons via photoemission process with OAM transfer from photons to electrons.

Very thin nanostructured carbon films were deposited on quartz substrate by reactive magnetron sputtering using graphite target and gas mixture of Ar and reactive gas N 2 or N 2 +H 2 .Film thicknesses were in the range of 20-25 nm.Rutherford backscattering spectrometry and Elastic recoil detection analytical method determined the concentration of elements in the films.Scanning electron microscopy scanned the surface morphology of carbon films.Raman spectroscopy was used for chemical structural properties determination of very thin carbon films.Raman spectra intensities were fitted with Gaussian peaks.The photo-induced (pulsed laser -266 nm) electron emission properties of very thin nanostructured carbon films were investigated by the measurement of cathode bunch charge at different electric field and calculate quantum efficiency.The influence of different electric field on the photo-induced electron emission characteristics of prepared transmission photocathodes are discussed.

The linear accelerator Linac-200 at JINR is a new facility, constructed to provide electron test beams to carry out particle detectors R&D, to perform studies of advanced methods of electron beam diagnostics, and for applied research. The core of the facility is a refurbished MEA accelerator from NIKHEF. The key accelerator subsystems including controls, vacuum, precise temperature regulation were completely redesigned or deeply modernized. Two test beam channels are available for users: the first one with electron energy in range 5–25 MeV and maximum pulse current 60 mA; and the second one with electron energy in range 40–200 MeV and maximum pulse current 40 mA. The pulse current varies smoothly from the maximum value down to almost zero (single electrons in a pulse). This report presents the status and operation parameters of the facility.

A new 1.5-cell 2.856 GHz S-band RF photogun is simulated for the generation of ultrashort electron beams at the Linac-200 accelerator at JINR. The beam parameters at the photogun output are determined to meet the requirements of the Linac-200 injection. The general design of the photogun is presented. The electrodynamic parameters are determined and the accelerating field distribution is calculated. The particle dynamics is simulated and analysed to obtain the required beam properties.

The construction of an experimental facility with test electron beams is under way at the Dzhelepov Laboratory of Nuclear Problems at the Joint Institute for Nuclear Research (Dubna, Russia). The facility is based on the MEA accelerator that was transferred from NIKHEF to JINR at the beginning of the 2000s. Despite the long service life of the accelerator, it is in good condition and still has a significant operation potential. The linac is being commissioned and the first 200-MeV beam has been generated. For now, the machine is controlled by a set of standalone subsystems that were created as required. Certain systems (e.g., vacuum) are controlled and monitored locally. However, a global control system is required to operate the accelerator as a user facility. The system requirements are formulated in this paper. The key issues of controlling the accelerator and its auxiliary (evacuation, cooling, etc.) systems are considered. The design of a new Tango-based control system of the Linac-200 is presented.

Very thin nanostructured carbon films were deposited on quartz substrates by electron beam-plasma (EBP) vacuum deposition. In EBP system, electrons emitted by the incandescent cathode are focused by the electrostatic lens and accelerated by the electric field between the cathode and the crucible filled with evaporated material. At an initial instant, the evaporated material is melted due to electron bombardment effect. On achieving a certain vapor density (specific for each material) a non-independent discharge in material's vapor is developed within the anode-cathode gap (-,6-10 mm). The directly heated cathode changes it's purely thermo emission mode of operation into a combined - i.e. thermo- plus ion-electronic emission - mode. In our experiment, the evaporated material was pyrolitic graphite. Substrate holder temperature during deposition was 500°C (samples Q1, Q2) and 350°C (samples Q3, Q4,). Film thickness were 20 nm (samples Q1, Q3) and 25 nm (samples Q2, Q4). The elements concentrations in the films were determined by RBS and ERD analytical method. Raman spectroscopy was used for chemical structural features determination of carbon films. Elements concentration results were practically the same for the all samples: carbon - 93 at.%, nitrogen - 2 at.%, hydrogen - 2 at.%, oxygen - 3 at.%. Raman spectrum of carbon film, which is typical for all samples, was deconvoluted. We used five peaks fitting for the range 1000–1800 cm−1 and four peaks fitting for the range 2500–3300 cm−1, Nanostructured carbon film contained several carbon phases. The photo-induced (pulsed laser −266 nm) electron emission properties of carbon very thin films were determined by the measurement of cathode bunch charge and calculate quantum efficiency (QE) of the prepared back-side illuminated transmission photocathode. Best result of QE showed photocathode Q4 and was $\text{QE}(\%)\mathrm{x}10^{-2}=1.5$ at extraction field 4 kV/mm. Results in this study call for optimize EBP technology for the fabrication of the robust and high QE transmission photocathode.

Very thin N-doped nanostructured carbon films were deposited on quartz and sapphire substrate by radio-frequency reactive magnetron sputtering using carbon target and gas mixture of Ar and N-2 or N-2 + H-2 reactive gasses. Rutherford backscattering spectroscopy and Elastic recoil detection analytical methods determined the concentration of elements in the films. Scanning electron microscopy was used to investigate the surface morphology of nanostructured very thin carbon films. Raman spectroscopy was used for the determination of chemical structural properties of the thin nanostructured carbon films. Pulsed laser induced electron emission method was used for the study of photoelectron emission properties of nanostructured carbon films. Measured bunch charge results of fabricated transmission photocathodes showed better photoelectron emission properties of very thin nanostructured carbon films prepared on sapphire substrates. Effects of substrate and technology of very thin nanostructured carbon films on the properties of photo-induced electron emitters as backside illuminated transmission photocathode are discussed.

Very thin carbon-based nitrogen-doped films of different thicknesses were deposited on double-side polished sapphire substrates by RF reactive magnetron sputtering. RBS and ERD were used to determine the elemental concentration in the films, and Raman spectroscopy, to determine their chemical structure. The RBS and ERD analyses indicated that the films contained carbon, nitrogen and small amounts of hydrogen and oxygen. The Gaussian-fitted and identified Raman spectra of the films showed the D and G bands in the range 1000-1800 cm −1 , and the 2 D and D+G bands, in the range 2500-3100 cm −1 . The photo-induced (pulsed laser, 266 nm) electron emission properties of the films were determined by measuring the cathodes’ bunch charge and calculating their quantum efficiency. The paper discusses the structural properties of the very thin nitrogen-doped carbon-based films deposited on a sapphire substrate with different thicknesses in view of their use as backside-illuminated transmissive vacuum photocathodes.

A prototype of a direct-current photoinjector (DC) with an electron energy of up to 400 keV is being developed at JINR for future electron accelerators (electron-positron colliders and free-electron lasers). This article describes the injector, one distinctive feature of which is the use of the transmission photocathode operation mode. A unique laser system is implemented on the photoinjector. The system makes it possible to synchronize the repetition rate and the phase of the laser pulses (of 10 ps duration, 262 nm wavelength, and 1.85 μJ energy) with the frequency of the accelerator RF system. The first experimental results of a DC photoinjector are presented and further plans for the development of the installation are discussed.

The carbon-based very thin films were deposited on silicon substrate and double side polished sapphire or quartz glass by RF reactive magnetron sputtering using a carbon target and gas mixtures Ar, N-2 and H-2. Concentration of elements in the films was determined by RBS and ERD method simultaneously. SEM was used to investigate the morphology of carbon thin films. Raman spectroscopy was used for intensity ratios determination I(D)/I(G) of D and G peaks of carbon films. Photo-induced electron emission method was used for the study of electron emission properties of carbon-based very thin films. An examination of the results highlights how the technology and the structure of carbon films on quartz or sapphire glass play a key role in enhancing efficient escape of generated photoelectrons.

Photocathode research in the frame of the "transmis-sion" photocathode conception (backside illuminated cathode based on a quartz/sapphire plate or a metal mesh which is a substrate for thin film made of a photomaterial) is being conducted in the Veksler and Baldin Laboratory of High Energy physics (LHEP) of the Joint Institute for Nuclear Research (JINR). Status of the 30-kev DC Photogun test bench and recent results of the extremely thin carbon film based cathodes research are described. Progress in the full-scale photoinjector prototype (max electron energy of 400 keV) is given. Startup of the photoinjector was performed, 70 keV electrons were extracted (650 pC).

N-doped carbon thin films were deposited on a silicon substrate and quartz glass by RF reactive magnetron sputtering using a carbon target and an Ar+N-2 gas mixture. During the magnetron sputtering, the substrate holder temperatures was kept at 800 degrees C. The carbon film thickness on the silicon substrate was about 70 nm, while on the quartz glass it was in the range 15 nm. 60 nm. The elemental concentration in the films was determined by RBS and ERD. Raman spectroscopy was used to evaluate the intensity ratios I-D/I-G of the D and G peaks of the carbon films. The transmission photocathodes prepared were placed in the hollow-cathode assembly of a Pierce-structure DC gun to produce photoelectrons. The quantum efficiency (QE) was calculated from the laser energy and cathode charge measured. The properties of the transmission photocathodes based on semitransparent N-doped carbon thin films on quartz glass and their potential for application in DC gun technology are discussed.

Photocathode electron guns are key to the generation of high-quality electron bunches, which are currently the primary source of electrons for linear electron accelerators. The photogun test bench built at the Joint Institute for Nuclear Research (JINR) is currently being used to further develop the hollow (backside irradiated) photocathode concept. A major achievement was the replacement of the hollow photocathode by a technologically more feasible transmission photocathode made from a metal mesh that serves as a substrate for films of various photomaterials. A number of thin-film cathodes on quartz glass substrates are fabricated by photolithography. The vectorial photoeffect (related to the surface-normal component of the wave electric field) is observed and found to significantly affect the quantum efficiency. The dependence of the quantum efficiency of diamond-like carbon photocathodes on the manufacturing technology is investigated. The Rutherford backscattering and elastic recoil detection techniques are combined to carry out an elemental analysis of the films. An estimate of the emittance of a 400 pC electron beam is obtained using the cross-section method.

The influence was investigated of N-doped diamond-like carbon (DLC) films properties on the quantum efficiency of a prepared transmission photocathode. N-doped DLC thin films were deposited on a silicon substrate, a stainless steel mesh and quartz glass (coated with 5 nm thick Cr adhesion film) by reactive magnetron sputtering using a carbon target and gas mixture Ar, 90%N2+10%H2. The elements' concentration in the films was determined by RBS and ERD. The quantum efficiency was calculated from the measured laser energy and the measured cathode charge. For the study of the vectorial photoelectric effect, the quartz type photocathode was irradiated by intensive laser pulses to form pin-holes in the DLC film. The quantum efficiency (QE), calculated at a laser energy of 0.4 mJ, rose as the nitrogen concentration in the DLC films was increased and rose dramatically after the micron-size perforation in the quartz type photocathodes.

A photoinjector prototype for future electron–positron colliders and free-electron lasers (FEL) is being developed at the Joint Institute for Nuclear Research (JINR). A 30-keV photogun stand, transmission (backside irradiated) photocathode concept, and stand investigations of such cathodes in collaboration with Institute of Electrical Engineering (IEE SAS) (Bratislava, the Slovak Republic) are described. A progress report on creating the photoinjector at an electron energy of up to 400 keV with a unique 10-ps laser driver is given.

Recently three RF guns were prepared at the Photo Injector Test Facility at DESY, location Zeuthen (PITZ) for their subsequent operation at FLASH and the European XFEL. The gun 3.1 is a previous cavity design and is currently installed and operated at FLASH, the other two guns 4.3 and 4.4 were of the current cavity design and are dedicated to serve for the start-up of the European XFEL photo-injector. All three cavities had been dry-ice-cleaned prior their conditioning and hence showed low dark current levels. The lowest dark current level – as low as 60µA at 65MV/m field amplitude – has been observed for the gun 3.1. This paper reports in details about the conditioning process of the most recent gun 4.4. It informs about experience gained at PITZ during establishing of the RF conditioning procedure and provides a comparison with the other gun cavities in terms of the dark currents. It also summarizes the major setup upgrades, which have affected the conditioning processes of the cavities.

Photocathode electron guns are key devices for high quality electron bunches generation. Development of the original photocathode conception — backside illuminated transmissive (for laser beam) photocathode — is going on at the Photo-gun test bench of the Joint Institute for Nuclear Research (JINR). Such cathode has an improved (in comparison with “classic” photocathode) quantum efficiency due to vectorial photoelectric effect. The influence of the diamond-like carbon (DLC) films production technology on quantum efficiency of prepared photocathode has been investigated. DLC films were deposited on silicon substrate and stainless steel mesh by plasma enhanced chemical vapor deposition from gas mixture CH 4 +D z (H z )+Ar and reactive magnetron sputtering using carbon target and gas mixture Ar and Dz(H z ). The concentration of elements in films was determined by Rutherford backscattering spectrometry and Elastic recoil detection analytical methods simultaneously. Raman spectroscopy at visible excitation wavelength was used for I(D)/I(G) ratio determination. Emission properties of the films were investigated, new results concerning extracted charge and quantum efficiency are presented.

Development of the original transmissive photocathode conception is going on in JINR. Results of charge extraction from thin-film diamond-like carbon (DLC) photocathodes are presented. DLC films were prepared using both methods of reactive magnetron sputtering of carbon target in the mixture of Ar and H2(D2) gases and vapor deposition CH4+D2(H2)+Ar.