The experiments on medium-size stellarator Uragan-2M (U-2M) in Kharkiv, Ukraine, are carried on in support of the Wendelstein 7-X (W7-X) experimental program. The scenario ion cyclotron frequency range (ICRF) plasma production at the hydrogen minority regime had been experimentally tested on U-2M and was qualified at the Large Helical Device (LHD). The paper presents the results of further research on the ICRF plasma production. The ICRF discharge studies were carried out in a H2 + He mixture with a controlled hydrogen concentration ranging from few percents to 75%. The two-strap like antenna mimicks the W7-X antenna operated in monopole phasing. The applied RF power was in the range of ∼100 kW. Relatively dense plasma of up to Ne ∼ 1019 m−3 was produced near the first harmonic of the hydrogen cyclotron frequency. The maximum temperature of the electrons and ions was not more than a few tens of electron volt. The characteristic features of RF plasma production and the propagation of electromagnetic waves in the experimental conditions are discussed. The experiments on U-2M and LHD indicate that the minority scenario of ICRF plasma production appears to be scalable and could be used in large stellarator machines. This is, in particular, important for the future experiments ICRF production of target plasma in W-7X in conditions where electron cyclotron resonance heating start-up is not possible.

Tokamak a configuration variable (TCV), recently celebrating 30 years of near-continual operation, continues in its missions to advance outstanding key physics and operational scenario issues for ITER and the design of future power plants such as DEMO. The main machine heating systems and operational changes are first described. Then follow five sections: plasma scenarios. ITER Base-Line (IBL) discharges, triangularity studies together with X3 heating and N2 seeding. Edge localised mode suppression, with a high radiation region near the X-point is reported with N-2 injection with and without divertor baffles in a snowflake configuration. Negative triangularity (NT) discharges attained record, albeit transient, beta(N) similar to 3 with lower turbulence, higher low-Z impurity transport, vertical stability and density limits and core transport better than the IBL. Positive triangularity L-Mode linear and saturated ohmic confinement confinement saturation, often-correlated with intrinsic toroidal rotation reversals, was probed for D, H and He working gases. H-mode confinement and pedestal studies were extended to low collisionality with electron cyclotron heating obtaining steady state electron iternal transport barrier with neutral beam heating (NBH), and NBH driven H-mode configurations with off-axis co-electron cyclotron current drive. Fast particle physics. The physics of disruptions, runaway electrons and fast ions (FIs) was developed using near-full current conversion at disruption with recombination thresholds characterised for impurity species (Ne, Ar, Kr). Different flushing gases (D2, H2) and pathways to trigger a benign disruption were explored. The 55 kV NBH II generated a rich Alfvenic spectrum modulating the FI fas ion loss detector signal. NT configurations showed less toroidal Alfven excitation activity preferentially affecting higher FI pitch angles. Scrape-off layer and edge physics. gas puff imaging systems characterised turbulent plasma ejection for several advanced divertor configurations, including NT. Combined diagnostic array divertor state analysis in detachment conditions was compared to modelling revealing an importance for molecular processes. Divertor physics. Internal gas baffles diversified to include shorter/longer structures on the high and/or low field side to probe compressive efficiency. Divertor studies concentrated upon mitigating target power, facilitating detachment and increasing the radiated power fraction employing alternative divertor geometries, optimised X-point radiator regimes and long-legged configurations. Smaller-than-expected improvements with total flux expansion were better modelled when including parallel flows. Peak outer target heat flux reduction was achieved (>50%) for high flux-expansion geometries, maintaining core performance (H-98 > 1). A reduction in target heat loads and facilitated detachment access at lower core densities is reported. Real-time control. TCV's real-time control upgrades employed MIMO gas injector control of stable, robust, partial detachment and plasma beta feedback control avoiding neoclassical tearing modes with plasma confinement changes. Machine-learning enhancements include trajectory tracking disruption proximity and avoidance as well as a first-of-its-kind reinforcement learning-based controller for the plasma equilibrium trained entirely on a free-boundary simulator. Finally, a short description of TCV's immediate future plans will be given.

After a long device enhancement phase, scientific operation resumed in 2022. The main new device components are the water cooling of all plasma facing components and the new water-cooled high heat flux divertor units. Water cooling allowed for the first long-pulse operation campaign. A maximum discharge length of 8 min was achieved with a total heating energy of 1.3 GJ. Safe divertor operation was demonstrated in attached and detached mode. Stable detachment is readily achieved in some magnetic configurations but requires impurity seeding in configurations with small magnetic pitch angle within the edge islands. Progress was made in the characterization of transport mechanisms across edge magnetic islands: Measurement of the potential distribution and flow pattern reveals that the islands are associated with a strong poloidal drift, which leads to rapid convection of energy and particles from the last closed flux surface into the scrape-off layer. Using the upgraded plasma heating systems, advanced heating scenarios were developed, which provide improved energy confinement comparable to the scenario, in which the record triple product for stellarators was achieved in the previous operation campaign. However, a magnetic configuration-dependent critical heating power limit of the electron cyclotron resonance heating was observed. Exceeding the respective power limit leads to a degradation of the confinement.

In 2021 JET exploited its unique capabilities to operate with T and D-T fuel with an ITER-like Be/W wall (JET-ILW). This second major JET D-T campaign (DTE2), after DTE1 in 1997, represented the culmination of a series of JET enhancements-new fusion diagnostics, new T injection capabilities, refurbishment of the T plant, increased auxiliary heating, in-vessel calibration of 14 MeV neutron yield monitors-as well as significant advances in plasma theory and modelling in the fusion community. DTE2 was complemented by a sequence of isotope physics campaigns encompassing operation in pure tritium at high T-NBI power. Carefully conducted for safe operation with tritium, the new T and D-T experiments used 1 kg of T (vs 100 g in DTE1), yielding the most fusion reactor relevant D-T plasmas to date and expanding our understanding of isotopes and D-T mixture physics. Furthermore, since the JET T and DTE2 campaigns occurred almost 25 years after the last major D-T tokamak experiment, it was also a strategic goal of the European fusion programme to refresh operational experience of a nuclear tokamak to prepare staff for ITER operation. The key physics results of the JET T and DTE2 experiments, carried out within the EUROfusion JET1 work package, are reported in this paper. Progress in the technological exploitation of JET D-T operations, development and validation of nuclear codes, neutronic tools and techniques for ITER operations carried out by EUROfusion (started within the Horizon 2020 Framework Programme and continuing under the Horizon Europe FP) are reported in (Litaudon et al Nucl. Fusion accepted), while JET experience on T and D-T operations is presented in (King et al Nucl. Fusion submitted).

Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under the auspices of a single Task Force called ‘Tokamak Exploitation’. The goal is to benefit from the complementary capabilities of each machine in a coordinated way and help in developing a scientific output scalable to future largre machines. The programme of this Task Force ensures that ASDEX Upgrade, MAST-U, TCV, WEST and JET (since 2022) work together to achieve the objectives of Missions 1 and 2 of the EUROfusion Roadmap: i) demonstrate plasma scenarios that increase the success margin of ITER and satisfy the requirements of DEMO and, ii) demonstrate an integrated approach that can handle the large power leaving ITER and DEMO plasmas. The Tokamak Exploitation task force has therefore organized experiments on these two missions with the goal to strengthen the physics and operational basis for the ITER baseline scenario and for exploiting the recent plasma exhaust enhancements in all four devices (PEX: Plasma EXhaust) for exploring the solution for handling heat and particle exhaust in ITER and develop the conceptual solutions for DEMO. The ITER Baseline scenario has been developed in a similar way in ASDEX Upgrade, TCV and JET. Key risks for ITER such as disruptions and run-aways have been also investigated in TCV, ASDEX Upgrade and JET. Experiments have explored successfully different divertor configurations (standard, super-X, snowflakes) in MAST-U and TCV and studied tungsten melting in WEST and ASDEX Upgrade. The input from the smaller devices to JET has also been proven successful to set-up novel control schemes on disruption avoidance and detachment.

We present and discusses the magnetic surface structures of different Uragan-2M stellarator plasma configuration modes, where large magnetic islands or their remains at the edge of the plasma volume, thus, will lead to deterioration of performance control. The VMEC code is adopted for Uragan-2M in ideal l=2, m=4 stellarator approach without distortions introduced by feeding connectors. This code can be used in magnetic configurations where large core islands are absent.

An ozone destructor for a plasma ozone sterilizer has been developed. This is an improved model of an ozone destructor, consisting of two parts, which significantly increases the contact area of activated carbon with ozone. This destructor design is suitable for ozone concentrations of 100…120 mg/l at an oxygen flow rate of 1 l/min. A study was conducted to determine the dependence of the temperature of carbon at the contact point with ozone depending on the amount of decomposed ozone at various oxygen flow rate. It was monitored that output ozone did not exceed the maximum permissible concentration in the working area proving the effectiveness of the developed ozone destructor.

Ozone therapy for treating wounds is not commonly used in many regards and such a technology is still being developed even with extremely promising results. The most important key of wound treatment with ozone is its ability to eliminate bacterial growth and population. In this regard there is an urgent need for alternative options for antiseptic treatment of wounds at the stage of evacuation and pre-medical care for their further effective treatment. In this research, a portable ozone generating device for wound treatment has been developed and the main technical characteristics have been discussed.

The studies of the scenario of hydrogen plasma creation with two sequential RF discharges during one pulse were carried out for the Uragan-2M stellarator. The first-stage discharge initiated the hydrogen pre-ionization at the generator anode voltage of 4 kV. The second-stage discharge was performed at the generator anode voltage selected from 6 to 9 kV. As result, plasma with an electron density up to 3.9·1018 m-3 was produced in a confinement volume. An increase of voltage resulted in an earlier appearance of signals of electron density, the intensity of the Hα spectral line, and the intensity of the molecular hydrogen spectral line. The increase of the time-dependent intensities of these signals was also registered.

This report compares results ion-cyclotron range of frequencies (ICRF) plasma production at hydrogen mi-nority regime in Uragan-2M (U-2M) and Large Helical Device (LHD). The condition of the presence of the fundamental harmonic ion cyclotron resonance zone for the hydrogen inside the plasma column should be ful-filled for this method. The scenario is successful at both machines and weakly sensitive to the variation of the hydrogen concentration in the H2+He gas mixture. It should be noted that at LHD the start up is slower than at U-2M. The comparison of plasma production in ICRF with hydrogen minority at U-2M and LHD indicate that this scenario can be scaled to larger stellarator devices. The experiments made are the base for the proposal for usage this scenario for plasma production in ICRF at Wendelstein 7-X at magnetic field reduced to 1.7 T.& COPY; 2023 The Japan Society of Plasma Science and Nuclear Fusion Research

In this paper, a well-known design procedure is proposed for the design of wideband constant-beam width conical corrugated horn antennas, with minimum design and construction complexity. The inputs to the procedure are the operating frequency band, the required minimum beam width in the entire frequency band, and the frequency in which the maximum gain is desired to occur. Based on these values, the procedure gives a relatively good design with a relative bandwidth of up to 2.1:1. Based on the proposed procedure, a corrugated horn antenna with a constant beam width over the frequencies of 10 to 14 GHz was designed and simulated using commercial software. This paper presents initial design for the development of quasi-optical corrugated conical horn for reflectometry diagnostics for the Uragan-2M stellarator plasma experiments.

Plasma production experiments in helium at Uragan-2M have been performed to investigate the role of the hydrogen minority in helium. The experiments presented here were carried on with a controlled minority hydrogen concentration. The hydrogen minority allowed one to increase plasma density more than three times as compared with pure helium. The obtained plasma density is highest for whole time of Uragan-2M operation. The developed scenario allowed to decrease the neutral gas pressure at which the plasma production is possible. This is a requirement for achieving regimes of plasma production with full ionization. Although the initial gas mixture 14%H 2 + 86%He can be treated as optimum, there is no sensitive dependence on hydrogen minority concentration, which makes the scenario robust. This study, together with initial LHD experiments, confirm the prospects of target plasma production by ICRF waves for stellarator type machines.

The results of the plasma start-up with ICRH of U-2 M RF discharges in H-2 +He mixture with newly implemented controlled gas H-2 concentration are presented. The W7-X like ICRH antenna operated in monopole phasing with applied RF power of similar to 100 kW. We investigated plasma start-up in the pressure range p = 6 x 10(-4) - 9 x 10(-2) Pa. Plasma production with an average density of up to N-e similar to 10(13) cm(-3) was observed at frequencies the fundamental harmonic of the hydrogen cyclotron frequency. (C) 2022 The Japan Society of Plasma Science and Nuclear Fusion Research

We consider a scenario of the initial stage of the RF breakdown of a working gas in torsatrons Uragan-3M and Uragan-2M and the roles of runaway electrons in this process. In our previous works, we studied only the acceleration factor of the breakdown process which occurs, when the intensity of the flow of runaway electrons increases due to the stimulation by an additional ultrahigh-frequency discharge at the front edge of a magnetic field pulse. This work attempts to describe the individual phenomena that accompany the initial stage of plasma formation in the confinement areas of torsatrons Uragan-3M and Uragan-2M in the presence of the flow of runaway electrons.

This paper presents initial proposal for the development of quasi-optical (QO) microwave technology for Electron Cyclotron Emission (ECE) and reflectometry diagnostics in the Uragan-2M (U-2M) stellarator. For the existed ECE radiometer systems and for the operational plasma parameters of U-2M new quasi-optical beam separation dichroic filter is designed. For such filter the mechanical parameters and performed attenuation characteristic are calculated. Frontend antenna/splitter system for the combined ECE/reflectometry radiation detection is presented. As an example, QO beam pattern for the ECE receiving antenna is numerically calculated.

We present recent highlights from the most recent operation phases of Wendelstein 7-X, the most advanced stellarator in the world. Stable detachment with good particle exhaust, low impurity content, and energy confinement times exceeding 100 ms, have been maintained for tens of seconds. Pellet fueling allows for plasma phases with reduced ion-temperature-gradient turbulence, and during such phases, the overall confinement is so good (energy confinement times often exceeding 200 ms) that the attained density and temperature profiles would not have been possible in less optimized devices, since they would have had neoclassical transport losses exceeding the heating applied in W7-X. This provides proof that the reduction of neoclassical transport through magnetic field optimization is successful. W7-X plasmas generally show good impurity screening and high plasma purity, but there is evidence of longer impurity confinement times during turbulence-suppressed phases.

The improved thermal desorption diagnostics has been manufactured, installed and tested in the Uragan-2M (U2M) stellarator [1-5] for in-situ characterisation a stainless steel (SS) wall outgassing rate and a number of molecular layers of residual gases on its surface in four different positions. The detailed description of this diagnostics, the location of thermal desorption stainless steel probes, the methodology of determining the outgassing rates and the number of molecular layers of residual gases on the probe surfaces are presented. It has been found that the difference between of the data taken from the probes being at different position in the U-2M vacuum chamber lies within the measurement accuracy. Using the present diagnostics together with the mass-spectrometer measurements, some studies were made to investigate the release of gases from the thermal desorption probes before and after radio frequency (RF) or glow discharge (GD) cleaning with hydrogen, helium and argon plasmas. It has been observed that hydrogen sorption by the SS probes surface during the discharge cleaning leads to significant hydrogen desorption even at the temperature of 250-300 degrees C. In this case, hydrogen can be the one of the main gases which desorbs. After U-2M glow discharge cleaning with Ar plasma, the thermal desorption experiment has shown Ar as a significant component which is desorbed from the SS probe surface. Two kinds of desorbed Ar were registered with two different activation energies. The characteristics of the U-2M vacuum system are presented, too, including the block scheme, the list of pumps used to attain the ultimate vacuum, the equipment for measuring the total and partial pressures of residual gases.

Charge exchange (CX) neutral fluxes were measured by neutral particle analyzer (NPA) in plasma discharges sustained by the W7-X-like radio frequency (RF) antenna in the Uragan-2M (U-2M) stellarator. CX fluxes in pure hydrogen discharge (B0 = 0.36 T, f = 4.926 MHz) in stellarator configuration (effective perpendicular ion temperature TꞱ ≈ 450 eV) is less energetic in comparison with U-2M hybrid configuration (TꞱ ≈ 800 eV). RF discharge in stellarator configuration with helium and hydrogen mixture (B0 = 0.351 T; f = 5.156 MHz, P = 6·10-4Torr) shows more energetic CX fluxes (TꞱ ≈ 1 keV). The ion cyclotron frequency distribution across the U-2M plasma has been studied numerically. These calculations are accompanied by direct measurement of the RF frequency by magnetic sensor. The ion cyclotron frequency is present in plasma bulk of all discharges under consideration.

Conceptual development activities on a stellarator-mirror-based fission-fusion hybrid system (SM hybrid) are reviewed.Intended for transmutation of spent nuclear fuel and safe fission energy production, SM hybrid consists of a fusion neutron source and a powerful subcritical fast fission reactor core.Its fusion component is a stellarator with an embedded magnetic mirror.The stellarator allows for the confinement of a moderately hot (1-2 keV) deuterium plasma.In the magnetic mirror, the hot sloshing tritium ions are trapped and fusion neutrons are generated.The magnetic mirror is surrounded by a fission mantle, where transmutation of minor actinides and energy generation take place.One candidate magnetic confinement device for the SM hybrid is the advanced DRACON magnetic trap system, which, unlike the «classical» DRACON version, has one short, rather than two longer mirrors with a relatively short size of 3-6 m.A comparative numerical analysis of collisionless losses occurring in the magnetic trap part of the single-mirror DRACON leads to a conclusion about the possibility for high-energy tritium ions to be fairly well confined in the magnetic trap area.The Uragan-2M (U-2M) stellarator is used to test the SM hybrid concept with experiment.To fit a magnetic trap into U-2M system, one of the toroidal coils had to be switched off.A radial escape of charged particles may spontaneously give rise to a weak radial electric field, which may result in closing the particles' drift trajectories and thereby substantially improve their confinement.Background plasma confinement without destructive instabilities is demonstrated in the stellarator-mirror regime of U-2M) operation.The sloshing ions driven by radio-frequency heating are detected in the mirror part of the device with NPA diagnostics.A novel fission mantle design for the SM hybrid is proposed.

In support of the ICRF experiments planned on the Wendelstein 7-X (W7-X) stellarator, i.e. fast ion generation, wall conditioning, target plasma production and heating, a first experimental study on plasma production has been made in the Uragan-2M (U-2M) stellarator using W7-X-like two-strap antenna. In all the experiments, antenna monopole phasing was used. The W7-X-like antenna operation with launched radiofrequency power of ~100 kW have been performed in helium (p = (4–14) × 10−2 Pa) with the vacuum vessel walls pre-loaded with hydrogen. Production of plasma with a density higher than 1012 cm−3 was observed near the first harmonic of the hydrogen cyclotron frequency. Operation at first hydrogen harmonic is feasible in W7-X future ICRF experiments.