Effects of substrate biasing on deuterium content in W-D layers co-deposited at 380 K was investigated for biasing potentials from +5 V to-500 V. The mean deuteron implantation energy at 500 V was similar to 100 eV. It was found that deuterium content increased with increase of the bias voltage absolute value with no clear sign of saturation, and approximately a 2-fold increase was observed at -500 V. Co-deposited deuterium was suggested to be trapped both from three sources: from gas, largely unaffected by substrate biasing, from atomic particles formed in the plasma near the substrate, also mostly unaffected by substrate biasing, and by ion implantation due to bias applied. Deuterium trapped by implantation desorbs at higher temperatures as TDS demonstrated.

The experimental results of collecting lithium on the smooth and mesh collectors installed in the T-11M tokamak chamber with a vertical lithium limiter are presented. The collector (longitudinal) in the form of a long cylinder was installed in the near-wall region of the chamber along the toroidal axis of the tokamak. It was shown that a collector with a surface covered by several layers of stainless steel mesh collects lithium five times more than one with a smooth surface. The collection of lithium by a mesh collector with a different number of mesh layers was studied. It has been established that the most part of lithium collection (75

A novel design of a continuous toroidal solenoid for the small spherical tokamak MEPhIST-0 is presented. The solenoid's geometry is optimized in regard to stray magnetic fields perpendicular to the toroidal fields based on Maxwell's equations and interface conditions for magnetic fields. The solutions obtained may in theory provide the level of stray fields similar to 10(-10) of the toroidal fields. The design of the solenoid is tested by means of COMSOL modeling. The observed ratio of stray fields to the toroidal component of magnetic fields, B-p/B-T is approximately similar to 0.4% at the plasma center. A ripple of the toroidal magnetic field at the edge of the plasma of delta similar to 0.8% is observed. The possibility of plasma breakdown with the chosen toroidal solenoid configuration was evaluated using the DINA calculation code.

A probabilistic and diffusion-based model describing concentrations of multiple hydrogen isotopes simultaneously co-depositing with slowly grown metal layer is given. The conditions modeled are identical to stationary ion implantation into bulk material with infinite fluence. Ratios of different multiple hydrogen isotopes occupying same trapping sites in metal layers co-deposited from plasma are estimated. It is shown that if hydrogen isotopes have different detrapping energies in regards to the same trap (vacancy, dislocation, etc.), only the concentration of the isotope with highest detrapping energy decreases monotonously with deposition temperature. The uncertainty of tritium concentration in co-deposited layer based on the uncertainty in detrapping energy of tritium and deuterium is evaluated; for an 0.01 eV difference, a >10% tritium concentration uncertainty is predicted.

In the MEPhIST-0 tokamak, toroidal magnetic coil system is implemented as a single continuous toroidal solenoid. This design ensures synchronized operation of each segment of the solenoid and requires only one power supply line to operate. However, this configuration has the downside of introducing stray vertical and radial magnetic field components, which result from the inclination of the solenoid segments. Such stray fields can be measured using an electron beam, as previously demonstrated in experiments on T-15, TEXTOR, KSTAR, and SST-1. This paper describes the parameters of the experiment and presents the main results obtained from the MEPhIST-0 tokamak. Two experimental techniques for measuring the vertical magnetic field are discussed: one with a change in the current direction in the toroidal solenoid and one without. The ratio of the stray vertical field to the toroidal field was found to be approximately 0.5%. The conducted experiments highlight the necessity of compensating for the stray vertical field using additional poloidal coils.

The deuterium loss from W-D co-deposited films after exposure to atmospheric air (-50 % humidity) for 1, 24 and 576 h has been investigated for 50 nm, 250 nm, and 750 nm thick films. Approximately 50 % and 75 % of deuterium is lost after 24 h and after 576 h, respectively. The rate of deuterium loss is similar for thin and thick films. Significant amount of protium is trapped from air during exposure, which releases in H2 and H2O during thermal desorption spectroscopy analysis. Even after 24 days in air, the films do not transform into tungsten oxide.

The article is devoted to the calculation of equilibrium configurations of the MEPHIST-0 tokamak plasma with a poloidal magnetic system taking into account the part responsible for compensating the magnetic field of the central solenoid using the DINA plasma physics code. The parameters of the poloidal magnetic system necessary for the formation of initial equilibrium after the discharge breakdown are obtained. The results of calibration experiments without taking into account the vacuum chamber using a pulsed current source are presented, on the basis of which the dynamic problem of plasma equilibrium calculation is formulated. The simulation results are compared with the experimental data, and the influence of the chamber on the results is considered.

Hydrogen isotope exchange as a method for removal of heavy hydrogen isotopes from tungsten co-deposits in fusion devices was investigated by exposing fresh W-D co-deposited films in protium atmo-sphere. The temperature was in the range from room temperature to 473 K (200 degrees C), the protium pressure was 1 atm, the time of exposure was 18 hours. It was shown that the efficiency of exchange increases with temperature, and at least 99% of deuterium was removed at 473 K from 250 nm thick films. Vacuum annealing was much less efficient at all experimental conditions. Similar to polycrystalline materials, mul-tiple occupation of traps by hydrogen isotopes is suggested to be a key mechanism of D to H exchange in the co-deposits.(c) 2022 Elsevier B.V. All rights reserved.

A comparative study of the deuterium content in tungsten-deuterium layers 50, 250, and 750 nm thick co-deposited from a magnetron discharge plasma on molybdenum substrates has been carried out. The measurements were carried out by in vacuo thermal desorption spectroscopy without contact with the atmosphere. Simulation of experimental data in the TMAP7 code has been carried out; concentrations and energies of traps have been obtained at which the best agreement with experiment is achieved. The content of deuterium in the films deposited at a temperature of 100°C was 3–5 at

An overview of the MEPhIST-0 educational and research small-scale spherical tokamak project is presented including the vacuum vessel, magnetic field systems, and diagnostics. In contrast to other small machines, it is an advanced tokamak with D-shaped plasma equipped with an electron-cyclotron resonance pre-ionization system for plasma startup and an ion-cyclotron resonance system for plasma heating and wall conditioning. The design choices taken are discussed from the perspective of a primarily educational installation. The machine design is simplified while remaining relevant to larger devices. First plasma results obtained in 2021 are presented.

The technique and results of measuring the soft X-ray spectra of plasma on the small spherical MIFIST-0 tokamak are presented. The measurements were carried out by the gray filter method using a multichannel spectrometer based on LiF (Mg, Ti) thermoluminescent lithium fluoride detectors. This technique made it possible to study X-ray radiation in the energy range of quanta 0.2−15 keV. The spectrum of the soft X-ray component was obtained.

The growing fusion research industry faces an extensive need for specialists with practical skills. However, the high complexity of the relevant experiments makes it difficult to maintain laboratories in which students can get their first hands-on experience of interacting with relevant devices. One of the options is using small, simplified machines that are designed for low-qualified personnel. This paper presents the architecture and implementation of a control and data acquisition system for an educational tokamak MEPhIST-0. It integrates different plasma diagnostic systems as well as tokamak's control nodes using the EPICS framework. Different approaches to data archiving and access are discussed, and the overall design is presented from the perspective of a primarily educational installation, as well as the preliminary results.

Microwave preionization is a common technique used for electron-cyclotron resonance assisted plasma start-up in spherical tokamaks. The purpose of this work is to test the developed MEPhIST-0 tokamak preionization system and to study the preliminary preionization plasma. The gas discharge parameters are measured using Rogowski coils, optical spectroscopy, and Langmuir probes. A fast CCD camera is additionally used to capture the emission during the discharge. The results show that the preliminary plasma discharge is localized at a certain distance inside the vacuum chamber, which satisfies the condition for the existence of electron cyclotron resonance. The estimated plasma density and electron temperature are 5.5 × 1016 m–3 and 8 eV, respectively.

The effect He in plasma has on the co-deposition of D–W films is investigated for the room–800 K range of substrate temperatures and two He/D2 ratios of 5 and 20%. He can both raise and lower the content of D in a film, and a mechanism is proposed for this effect. The ratio of He/D in the film is higher than in gas, due to the stronger diffusivity and bonding energy of He. A similarity is observed between the dependences of D and He content on temperature, and it is suggested that the low temperature release of D and He during TDS could be due to annealing-induced relaxation of stresses in the film structure. It is expected that the desorption of He above 1300 K could lead to underestimates of the He content.