This paper presents the findings of the synthesis of multicomponent (Al, W, Ni, Ti, Nb) alloy coatings from mosaic targets. For the study, a pulsed magnetron sputtering method was employed under different plasma generation conditions: modulation frequency (10 Hz and 1000 Hz), and power (600 W and 1000 W). The processes achieved two types of alloy coatings, high entropy and classical alloys. After the deposition processes, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy techniques were employed to find the morphology, thickness, and chemical and phase compositions of the coatings. Nanohardness and its related parameters, namely H3/Er2, H/E, and 1/Er2H ratios, were measured. An annealing treatment was performed to estimate the stability range for the selected coatings. The results indicated the formation of as-deposited coatings exhibiting an amorphous structure as a single-phase solid solution. The process parameters had an influence on the resulting morphology—a dense and homogenous as well as a columnar morphology, was obtained. The study compared the properties of high-entropy alloy (HEA) coatings and classical alloy coatings concerning their structure and chemical and phase composition. It was found that the change of frequency modulation and the post-annealing process contributed to the increase in the hardness of the material in the case of HEA coatings.

A photocathode composed of a Pb layer deposited on Nb substrate is an attractive solution proposed for fully superconducting, radio frequency electron gun to be used in the linear accelerator of the European X-ray free electron laser (Eu-XFEL) operating at Deutsches Elektronen Synchrotron (DESY) and in other, similar devices. Much effort has been put in development of deposition and post-processing of Pb films as superconducting photoemitters. These works led to a satisfactory solution based on lead deposition in a cathodic-arc followed by ex-situ smoothing of the obtained film through its re-melting with a pulsed plasma ion beam. Pb layers obtained by different procedures have been tested for their morphology, microstructure, dark current emission, quantum efficiency and impact on SRF e− gun performance.

The paper concerns measurements of runaway electrons (REs) which are generated during discharges in tokamaks The control of REs is an important task in experimental studies within the ITER-physics program. The NCBJ team proposed to study REs by means of Cherenkov-type detectors several years ago. The Cherenkov radiation, induced by REs in appropriate radiators, makes it possible to identify fast electron beams and to determine their spatial-and temporal-characteristics. The results of recent experimental studies of REs, performed in two tokamaks-COMPASS in Prague and FTU in Frascati, are summarized and discussed in this paper. Examples of the electron-induced signals, as recorded at different experimental conditions and scenarios, are presented. Measurements performed with a three channel Cherenkov-probe in COMPASS showed that the first fast electron peaks can be observed already during the current ramp-up phase. A strong dependence of RE-signals on the radial position of the Cherenkov probe was observed. The most distinct electron peaks were recorded during the plasma disruption. The Cherenkov signals confirmed the appearance of post-disruptive RE beams in circular-plasma discharges with massive Ar-puffing. During experiments at FTU a clear correlation between the Cherenkov detector signals and the rotation of magnetic islands was identified.

Direct measurements of fast electrons, which are produced in high-temperature plasma and escape from tokamak-type facilities, are of particular interest for ITER and future fusion devices, where intense runaway electrons (RE) can significantly damage the firstwall components. Therefore, the runaway control and mitigation based on credible measuring methods should be developed already in present devices. A team from the National Centre for Nuclear Research (NCBJ), Poland, developed special probes equipped with Cherenkov-type detectors for measurements of the fast electrons within edge plasmas of tokamaks. Studies of the fast runaway electrons were extensively carried out at the COMPASS tokamak at the Institute of Plasma Physics (IPP) in Prague during experimental campaigns in 2014-2016. In order to investigate an electron-beam energy distribution a three-channel probe equipped with the Cherenkov-type detectors sensitive to electrons of different energies has been constructed. The measurements performed by means of these detectors showed that the first fast electron peak appears usually in the current ramp-up phase, even before the hard Xrays (HXR) pulse. Some electron signals can also be observed during subsequent HXR emissions. However, the most distinct electron peaks in all energy channels appear mainly during the plasma disruption. A correlation of Cherenkov signals with the MHD activity was also studied.

The paper presents feasibility and design studies of Cherenkov-type probes, a development of the measuring head construction designed for different tokamak devices, and in particular the acquisition of optical signals to a data storage system. In order to lower the energy threshold of the electron detection the authors applied radiators with the highest values of the refractive index. Different radiator materials, such as aluminium nitride and CVD diamond were applied. Several versions of measuring heads and different manipulators, e.g., a movable vacuum-tight shaft or a fast-moving reciprocating probe, were manufactured and used. The practical application of the Cherenkov probes required also a consideration of spectral characteristics of optical fibres and photomultipliers. The Cherenkov radiation, as generated inside the radiators, is lead out through separate fibres (optical cables) to the atmospheric pressure side. The emitted radiation in the blue (near ultraviolet) spectrum range should be collected and delivered through appropriate optical cables to a control room, amplified within photomultipliers and recorded in a digital form. In order to investigate an electron energy distribution the multi-channel probes have also been designed and applied.

Results are reported on using evaporation and UHV arc lead deposition to create thin-layer superconducting Pb photocathodes on niobium wall of electron gun. Evaporated photocathodes were prepared and tested for the first time in 2014. A complete XFEL-type photoinjector with an evaporated photocathode underwent successful quality check at DESY - an acceptable working point was reached. On the other hand poor adhesion to niobium proved to be the most serious shortcoming of the evaporated Pb layers. UHV arc deposition seems to be much more promising in this context as it allows energetic coating. Filtered arc coating lead to creation of uniform, 2 mu m thick lead layers with casual spherical extrusions which enhance locally electric field and leads to high dark current. Conditioning in electric field is needed to reduce the field emission effects from these layers to acceptably low value. Using non-filtered UHV lead deposition enabled fast coating up to a thickness above 10 mu m. Pb films obtained in this way require further post-processing in pulsed plasma ion beams in a rod plasma injector. In order to reach a sufficiently planar film surface the pulsed heat flow through a lead layer on niobium was modeled and computed.

A combination of a ultra high vacuum arc deposition system and a recrystallization method was used to optimize the smoothness and thickness of thin-layer lead cathodes for superconducting niobium electron injectors. A non-filtered arc system was chosen to deposit Pb films on niobium. The films then underwent melting and recrystallization by treating them with pulsed argon ion beams in a rod plasma injector.

This paper presents a summary of the most important results of fast electron measurements performed so far within different tokamaks by means of Cherenkov-type detectors. In the ISTTOK tokamak (IPFN, IST, Lisboa, Portugal), two measuring heads were applied, each equipped with four radiators made of different types of alumina-nitrate poly-crystals. A two-channel measuring head equipped with diamond radiators was also used. Within the COMPASS tokamak (IPP AS CR, Prague, Czech Republic) some preliminary measurements have recently been performed by means of a new single-channel Cherenkov-type detector. The experimental data from the TORE SUPRA tokamak (CEA, IFRM, Cadarache, France), which were collected by means of a DENEPR-2 probe during two recent experimental campaigns, have been briefly analyzed. A new Cherenkov probe (the so-called DENEPR-3) has been mounted within the TORE SUPRA machine, but the electron measurements could not be performed because of the failure of this facility. Some conclusions concerning the fast electron emission are presented.

The Note reports on experimental studies of ripple born fast electrons within the TORE-SUPRA facility, which were performed by means of a modified measuring head equipped with diamond detectors designed especially for recording the electron-induced Cherenkov radiation. There are presented signals produced by fast electrons in the TORE-SUPRA machine, which were recorded during two experimental campaigns performed in 2010. Shapes of these electron-induced signals are considerably different from those observed during the first measurements carried out by the prototype Cherenkov probe in 2008. An explanation of the observed differences is given.

We report the efforts undertaken at NCBJ and some of its collaborating laboratories dedicated to prepare pure and flat lead film coated onto niobium to operate as superconducting photocathodes. Three approaches to lead cathodic arc deposition have been implemented and tested: active plasma flux filtering, passive filtering and unfiltered flux. None of them allowed us to find a proper balance between thickness and surface roughness of a cathode. At that point efforts were taken to establish post-deposition heat treatment of lead film.

Photocathodes deposited as thin lead films on a wall of a niobium RF cavity were accepted as a way to construct superconducting RF e injectors [1-2]. Ultra High Vacuum cathodic arc was implemented and developed at NCBJ to deposit thin Pb films which can be used as superconducting photocathodes in electron guns of superconducting radio-frequency linear accelerators [3]. The main drawback of this method is the presence of lead droplets within the films. In electromagnetic field the micrometer-sized droplets cause such effects as dark current or field emission. To cope with this problem filtering of metal plasma flux is applied inside deposition devices that typically reduces the film deposition rate by orders of magnitude which in turn leads to thinner layers with degraded purity.

The paper reports on progress in design and use of novel detectors for experimental studies of fast (run-away and ripple-born) electrons in various experiments of the tokamak type. The idea of the use of a Cherenkov effect for direct on-line measurements of the fast electrons within tokamaks was presented by scientists from the NCBJ (former IPJ) several years ago. Successive efforts led to the development of prototype detector heads equipped with diamond or aluminium nitrate (AlN) crystals, which were shielded with very thin metal filters in order to eliminate the visible light from plasma and to enable a rough energy analysis of electrons. Those Cherenkov radiators were coupled through optical-fibre cables with fast photomultipliers. Those prototypes were applied for test measurements within the CASTOR experiment in Prague, and later in the ISSTOK device in Lisbon, but the main aim remained to develop the Cherenkov detectors for the TORE-SUPRA experiment in Cadarache. PACS: 41.75.Ht, 40.60.Bq, 52.70.La

The paper presents advance in a new method developed in the Institute for Nuclear Studies (IPJ) for direct detection of high-energy (super-thermal, runaway) electrons generated in tokamaks. The technique in question is based on registration of the Cherenkov radiation, emitted by energetic electrons, moving through a transparent medium (radiator body) with a velocity higher than the velocity of light in this material. The main aim of the presented studies was to develop a diagnostic technique applicable for investigation of fast electron beams within magnetic confinement fusion (MCF) facilities.

The paper presents a schematic design and tests of a system applicable for measurements of fast electron pulses emitted from high-temperature plasma generated inside magnetic confinement fusion machines, and particularly in the TORE-SUPRA facility. The diagnostic system based on the registration of the Cherenkov radiation induced by fast electrons within selected solid radiators is considered, and electron low-energy thresholds for different radiators are given. There are some estimates of high thermal loads, which might be deposited by intense electron beams upon parts of the diagnostic equipment within the TORE-SUPRA device. There are some proposed measures to overcome this difficulty by the selection of appropriate absorption filters and Cherenkov radiators, and particularly by the application of a fast-moving reciprocating probe. The paper describes the measuring system, its tests, as well as some results of the preliminary measurements of fast electrons within TORE-SUPRA facility.

A structure of deposited film is determined by an interaction of arriving atoms with these of substrate and with those already stacked on. In case of ions having the kinetic energy in the range of tens electronvolts and falling into hot target, the interaction is dominated by an inelastic scattering with the stacked atoms, which happen during the subplantation few tens of angstroems inwards the film. Continuous ions influx to the near-surface part of the film accompanied by an enhanced vibration and mobility of constituent atoms and followed by a gradual cooling and crystallisation occurring when the new material accumulates above, facilitates the growth of compact and dense material composed of large crystallites. Ultra High Vacuum Cathodic Arc (UHVCA) deposition method utilises the ions produced in explosive spots on the cathode, gaining there an energy about 100 eV and subsequently transported in the discharge channel towards the substrate to form pure films of regular and dense morphology. One of the most demanding application of such deposited films is particle accelerator technology where the Nb films have been proposed to coat inner walls of copper RF cavities. Such obtained superconducting cavities may, in some applications, replace the bulk niobium ones. The aim of these studies is to describe the growth of the Nb film on the single crystal sapphire. It was accomplished by complementary measurements of X-ray Diffraction patterns (XRD) and Extended X-ray Absorption Fine Structure (EXAFS) performed for a series of Nb/sapphire(001) samples having various thicknesses ranging from about 3 nm up to more than 500 nm. These two methods, enabled the structural analysis of samples showing long or short range of crystalline order, respectively.

This work presents the results of our research concerning the synthesis of metallic Fe-Cu coatings by use of the magnetron sputtering method. The structure of the coatings synthesized during two modes of pulsed magnetron sputtering was compared. In our experiment the pulsed magnetron power supply generated a series of pulses gated at 1kHz - standard pulsed mode (SPM) and 2 Hz - low frequency pulsed mode (LFPM). The analysis of the microstructure by means of SEM and TEM show that obtained coatings are characterized by nanocrystalline structure. Additionally the optical emission spectra (OES) during the copper and iron sputtering were measured.

This work was supported by a grant no. 4743/B/T02/2009/37 from the State Committee for Scientific Research in Poland.