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HL-2M tokamak is one of largest magnetic confinement fusion devices designed and constructed by Southwestern Institute of Physics (SWIP), China National Nuclear Corporation (CNNC), the first plasma was obtained on December, 4th, 2020. The magnets system which plays an important role for the plasma confinement consists of 20 toroidal field (TF) coils and 18 poloidal field (PF) coils. The magnets system commissioning was carried out by two phases: self-commissioning and integrated commissioning. The first phase: self-commissioning including joint resistance commissioning, turn to turn insulation commissioning, ground insulation commissioning, deionized water sealing commissioning was accomplished during the installation and test of the magnets system. The second phase: the integrated commissioning with power supply system, ground system, measurement and data acquisition system, plasma control system, interlock and safety system was accomplished based on the results of the first stage. The total commissioning of magnets system in HL-2M tokamak for the first plasma have been accomplished successfully.

ITER is an experimental tokamak device that has many collaborators from different countries and aims to produce energy from nuclear fusion inside a reactor with magnetic confinement. Corresponding ...

Magnetic confinement nuclear fusion is an important way to realize controllable nuclear fusion. Due to the large current and complicated coil arrangement, there is a complicated electromagnetic environment around the fusion device. In this paper, the B-dot sensor is used to measure the magnetic field, the D-dot sensor is used to measure the electric field, the MAXWELL electromagnetic simulation software is used to simulate the electromagnetic field strength; the simulation and measurement of the spherical Tokamak SUNIST device and the measurement of MARX generator are carried out, then we give corresponding electromagnetic protection suggestions.

The toroidal field (TF) coil is a crucial system in the tokamak, which provides the main magnetic field to confine the plasma. One TF coil of the China Fusion Engineering Test Reactor (CFETR) will be constructed with the support of the Chinese government in the next five years. In order to study the quench behavior of the CFETR TF coil, the assumed quench initiation at the maximum and minimum temperature margin position of the TF coil is analyzed, and the effect of the quench detection threshold on the hot spot temperature is studied. It is found that 0.5 V quench detection voltage leads to hot spot temperature above 250 K in the low-field region. In order to meet the design criteria of the hot spot temperature, the quench detection voltage should be less than 0.2 V.

As an in situ and remote diagnostic technique, laser-induced breakdown spectroscopy (LIBS) has been well proven to detect the elemental distribution on plasma-facing materials (PFMs) in the magnetic confinement nuclear fusion device of Experimental Advanced Superconducting Tokamak (EAST). However, due to the limited optical windows and irregular shape of the PFM surface, such as the monoblock structure of the divertor, the laser ablation angles (LAAs) of LIBS always vary with the laser spot scanning on the different regions of the PFMs. In this work, a LIBS system with a coaxial collection configuration based on the linear array fiber bundle is developed to investigate the features of laser-induced tungsten (W) plasma spectra at variable LAAs under vacuum conditions. The results show that the LIBS signal intensity, signal to background ratio, and signal to noise ratio of the W II line have different trends compared with W I under different LAAs. The intensities of the W I line decrease faster than those of W II with the increase of LAAs. Moreover, it is confirmed that the emission of the continuum background propagates mainly along the direction of the incident laser, while the plume of W I and W II propagates along the normal direction of the target. For the coaxial LIBS system, the results show that the plasma spectral collection area with a diameter of no less than 7 mm can minimize the spectral signal loss rate under different LAAs, no matter for W I or W II. This result will further improve the understanding of the spatial evolution of LIBS plasma at variable LAAs, to optimize and upgrade the current collection system of the in situ LIBS in the nuclear fusion device of EAST.

Two neutral-beam based diagnostic techniques are numerically evaluated for the stellarator TJ-II. The evaluation considers the beam from a dedicated diagnostic neutral beam injector that provides a 5 ms pulse of hydrogen accelerated to 30 keV as well as the light throughput of a dual purpose optical system that views the beam as it traverses the microwave, or neutral beam, heated plasmas of this magnetic confinement device. In the first instance, in which the implementation of the beam emission spectroscopy technique is considered for characterizing medium to long wavelength plasma turbulence, detailed estimates are made to determine the Balmer Hα light intensity reaching avalanche photodiode modules. In the second instance, similar detailed estimates are made for the spectrograph-based experimental set-up used for the Motional Stark Emission technique that has been successfully employed to determine the magnitude and direction of the internal magnetic field in TJ-II plasmas. In addition, optical measurements made to evaluate beam energy and composition are described. Finally, estimates and measurements are compared and discussed in order to complete this work.

Recycling coefficient is an important parameter for modeling of particle balance in the Tokamak. In this paper, recycling coefficient was considered as a function of time and energy to demonstrate its effect on density of plasma and wall of the Tokamak. Results showed that energy of incident particle plays a major part in plasma particles of the Tokamak. In addition, other calculations were performed to investigate the effects of different fuel injection rates on particle balance.

The ITER reactor relies in magnetic confinement of hot plasma. The main driver for the confinement is played by the Toroidal Field Coils. These magnets are composed by a Winding Pack, made of Nb3Sn superconductors, and a surrounding stainless steel structure or Coil Case which is closed by welding once the Winding Pack is inserted. The closure GTAW weld of the cases includes about 70m of weld ranging from 40 to 120 mm. Due to the tight tolerances that have to be respected on the final Toroidal Field Coils, a mechanical quasi-static Finite Element Model has been developed using ANSYS software by Enginsoft and SIMIC, under the work frame of a Fusion for Energy contract, to predict the welding distortion by simulating different welding scenarios and to confirm the definition of the required extra-material in the Toroidal Field Coil Cases. The FEM model was firstly benchmarked with validation coupons, then verified and fine-tuned with four 1:1 scaled Toroidal Field Coil Case cross section mock ups . Finally, a full Finite Element Model has been developed in order to predict the deformation of the cases during the welding process. The first Toroidal Field Coil has been welded during the first half of 2019. In this paper, a comparison between the deformation predicted by Finite Element Model and direct dimensional measurements of the distortions carried out during the welding process is presented.

Core-ion temperature measurements are based on resolving the energy components and the analysis of fast neutrals coming out of the magnetic confinement of plasma. ADITYA-tokamak (R/a = 75 cm/25 cm) uses Neutral Particle Analyzer (NPA) based charge exchange diagnostic system for measurement of the core ion-temperature in the range of 100–300 eV of Aditya plasma. Several ohmic plasma discharges are investigated for the Aditya tokamak, which provides an estimate of core ion-temperature (Ti0) evaluation with time and its comparison with the core electron-temperature (Te0). The analysis shows the ratio of Ti0/Te0 is typically in the rage of 30%–40%. Attempts have been made to estimate the neutral hydrogen (nH°) density in the core regime and its evolution with time using a simple approach. The core neutral densities estimated in the order of 108–109 cm−3 for ohmic discharges in ADITYA-tokamak. Effect of the ion cyclotron radio frequency heating (ICRH) on the experimental charge-exchange spectrum is also observed, which shows a typical increase of the perpendicular ion temperature (Ti⊥) by ~ 50 eV.

To enhance parameters of the plasma and improve the magnetic confinement performance, a 105-GHz electron cyclotron resonance heating (ECRH) system is being built on the J-TEXT. We designed a quasi-optical launcher which mainly consists of a focusing mirror and a steering mirror. The focusing mirror is optimized by considering the localized deposition, and the steering mirror is close to the plasma boundary for flexible adjustment of the toroidal and poloidal injection angles of the wave. The toroidal and poloidal rotation angles of the steering mirror are independently controlled by the mechanical structure. For our design, the beam radius at the plasma center for perpendicular incidence is about 20 mm; the adjustable range of the toroidal and poloidal injection angles is ±14° and ±31°, respectively. These can meet the requirements for physics experiments on J-TEXT.

Plasma radiation plays an important role in the operation and control of magnetic confinement fusion and is typically measured by bolometers. Here, we study the influence of mechanical vibration and magnetic field, which are typically present in magnetic confinement fusion devices, on the performance of a fiber-optic bolometer (FOB) based on silicon Fabry-Perot interferometer (FPI) demodulated by a scanning diode laser. It is found that both the vibration and magnetic field could cause large noise due to the birefringence of the silicon FPI. To mitigate the birefringence effects, we demonstrated two effective methods: polarization maintaining FOB and polarization scrambling. We show that two methods can be effective in mitigating the effect caused by the sensor birefringence: (1) replacing the regular single-mode fiber in the FOB system with polarization-maintaining fiber and (2) using a polarization scrambler after the laser source. For both methods, no significant increase in the noise was observed in the vibration and magnetic field tests. Our research highlights the importance of the polarization management for the FOB systems toward their practical applications in magnetic-confinement fusion systems.

In this study, we have spectroscopically investigated the plasma generated by a Q-switched Nd:YAG laser operating at its fundamental wavelength of 1064 nm focused on magnesium (Mg) and titanium (Ti) target samples in the air under atmospheric pressure. We employed circular cavities of radii (2.5, 3.0, and 3.5 mm) and a square cavity to investigate the cavity confinement effect on the spectral emission intensities of the plasmas. We observed that the circular cavity of radius 2.5 mm had the maximum signal enhancement, and this can be attributed to the compression of the plasma and reheating by the reflected shock waves. The maximum enhancement factor of the Mg I-518.4 nm line was reached at approximately 3.8, 3.4, and 2.8 with a circular cavity of radius 2.5, 3.0, and 3.5 mm, respectively, at a delay time of 350 ns and a laser energy of 350 mJ. By applying varying external magnetic fields (0.47, 0.62, 0.91, and 1.23 T) across the generated plasma, the plasma parameters such as electron temperature and number density have been investigated. From our results, we observed that the radius of the cavity had a tremendous effect on the enhancement of the emission signal intensities. We also found that the increase in the electron temperature and the number density can be attributed to the increase in the applied magnetic field and the laser energy. From our calculations, the value of β, which was less than 1 for all the cases, confirms that there was a plasma confinement at the presence of the magnetic field.

In order to achieve the goals of a non-carbonized energy system, there are also major challenges in how to replace coal-fired power plants as base load production facilities. One option is to replace with gas power plants that are more efficient than coal-fired TPPs with lower greenhouse gas emissions as well as fUssion nuclear power plants. In this regard, fusion nuclear power plants (NPP) are a perspective for the development of new technology in nuclear production facilities. Although fusion development has been expanding for the last 60 years, it is to be expected that the next 20 years will achieve the goal of commercially using this technology for peaceful energy purposes. The paper presents an overview of the development of fusion technology, as well as the challenges and obstacles that need to be overcome in order to achieve a commercial nuclear reactor. A magnetic confinement device – Tokamak, is represented as the most advanced device for sustainable plasma burning. Properties and expectations of the latest international Tokamak (ITER) are presented.

We employ our recently developed explicit 2nd-order charge-conservative symplectic electromagnetic particle-in-cell (PIC) scheme in the cylindrical mesh to simulate the whole-volume magnetic confinement toroidal plasmas on the new Sunway supercomputer. From a large-scale simulation of magneticized toroidal plasma with 111.3 trillion particles and 25.7 billion grids, we have obtained a sustained performance exceeding 201.1 PFLOP/s (double precision) with the fastest iteration step achieving 298.2 PFLOP/s (double precision). For the first time, unprecedented high resolution evolution of 6D electromagnetic fully kinetic plasmas based on 2D equilibrium profiles from Experimental Advanced Superconducting Tokamak (EAST) and designed operation state of China Fusion Engineering Test Reactor (CFETR) are presented, and edge micro-instabilities can be investigated directly. This shows the possibility to study crucial problems and phenomena in the magnetic confinement toroidal plasma directly using the symplectic electromagnetic fully kinetic PIC method on world's leading supercomputers.

Power Electronics Converters employed in nuclear fusion applications have been recently assuming a crucial role for reactors’ coils power supply systems as they are particularly challenging not only due to the very high current amplitude, but also to guarantee a proper plasma acceleration and its magnetic confinement for tens of years. To face such demanding requirements, with focus on the Poloidal Field Power Supplies of the Divertor Tokamak Test (DTT) facility, this paper analyzes a parallel-connected H-Bridges (HBs) DCDC converter characterized by relatively low voltages and very high current ratings (tens of kA), quite unusual in industry applications. A specific mathematical model, including the high frequency disturbances identification, has been pointed out for the first time in literature. A current control strategy, which aims at maximizing the current sharing among all HBs legs, is proposed as well. The simulation results have confirmed the validity of the presented control by keeping the load current error below 0.015% and by correctly balancing each HB leg current. These results have been furtherly validated through a Hardware-in-the-loop test facility.

Radio frequency (RF) sheaths occur under a wide variety of conditions when RF waves, material surfaces and plasma coexist. RF sheaths are of special importance in describing the interaction of ion cyclotron range of frequency (ICRF) waves with the boundary plasma in tokamaks, stellarators and other magnetic confinement devices. In this article the basic physics of RF sheaths is discussed in the context of magnetic fusion research. Techniques for modelling RF sheaths, their interaction with RF wave fields and the resulting consequences are highlighted. The article is intended as a guide for the early-career ICRF researcher, but it may equally well serve to provide an overview of basic RF sheath concepts and modelling directions for any interested fusion scientist.

Plasma turbulence plays a key, governing role in determining the spatial-temporal evolution of plasmas in astrophysical, geophysical and laboratory contexts. In particular, turbulence on disparate spatial and temporal scales limits the level of confinement achievable in magnetic confinement fusion experiments and therefore limits the viability of sustainable fusion power 1 . The TDoTP project* (Turbulent Dynamics of Tokamak Plasmas) aims to advance understanding of plasma turbulence coupling across a wide range of scale sizes. As part of this effort, a mm-wave based scattering diagnostic is being designed for the MAST-U spherical tokamak, to measure binormal oriented high-k (electron scale) turbulence in the core plasma. We present the results of Gaussian wave optics and beam-tracing calculations 2 that demonstrate the predicted spatial and wavenumber resolution of the diagnostic, as well as estimates for the sensitivity of measurement. Current specifications for the diagnostic include an operating frequency of 260GHz, a turbulence wavenumber measurement range of k ⊥ ρ e = 0.1 -> 0.5 (where k ⊥ is the poloidal turbulence wavenumber and ρ e the electron gyroradius) and a minimum spatial localisation of ~3cm along the primary beam path.

X-ray radiography has been used to diagnose a wide variety of experiments at the Z facility including inertial confinement fusion capsule implosions, the growth of the magneto-Rayleigh-Taylor instability in solid liners, and the development of helical structures in axially magnetized liner implosions. In these experiments, the Z Beamlet laser (1 kJ, 1 ns) was used to generate the x-ray source. An alternate x-ray source is desirable in experiments where the Z Beamlet laser is used for another purpose (e.g., preheating the fuel in magnetized liner inertial fusion experiments) or when multiple radiographic lines of sight are necessary.

In this paper, a cylindrical microrobot based on noncontact manipulation for controllable motion is reported. In the system, the diameter and length of the microrobot are 200 µm and 400 µm respectively. The rotating magnetic field generated by an electromagnetic actuator consisting of five electromagnets to control the rolling motion of microrobot in two-dimensional. The proposed microrobot can move along a planned trajectory in the fluids, which proves its efficiency of advanced functionality. Some key parameters including aspect ratio and magnetic field affect the rolling velocity. By adjusting the frequency of sinusoidal current and aspect ratio of cylinder, the forward velocity can be controlled accurately and up to maximum value of 7.64 mm/s. The experimental results show that the cylindrical microrobot can roll along different shaped trajectories accurately, which demonstrates the capability and flexibility of controlling method. This proposed method has a potential for transport of micro objects in a confined environment.

This contribution describes the basic applications of passive optical emission spectroscopy in the visible and far-UV region of electromagnetic radiation to diagnostics of the magnetic confinement fusion plasma. To simplify and condense the broad topic it presents the most common ways of analyzing the spectra of atoms, ions and molecules in fusion plasma and disseminating results of those analysis to the non-spectroscopists. It provides the reasons for choosing some particular regions, elements and charge states to determine the impurity content and plasma-surface interactions in MCF (Magnetic Confinement Fusion) reactor. Examples used in the contribution are predominantly from measurements performed in JET tokamak, but the approach presented is generalized and not really device-dependent.

The overview discusses development of the unique fusion plasma diagnostics—Heavy Ion Beam Probing (HIBP) in application to toroidal magnetic plasma devices. The basis of the HIBP measurements of the plasma electric potential and processing of experimental data are considered. Diagnostic systems for probing plasma in tokamaks TM-4, TJ-1, TUMAN-3M and T-10, stellarators WEGA, TJ-II and Uragan-2M are presented. Promising results of the HIBP projects for various existing modern machines, such as TCV, TCABR, MAST, COMPASS, GLOBUS-M2, T-15 MD and W7-X and the international fusion tokamak reactor ITER are given. Results from two machines with similar size and plasma parameters, but with different types of the magnetic con-figuration: axisymmetric tokamak T-10 and helically symmetric stellarator TJ-II are compared. The results of studies of stationary potential profiles and oscillations in the form of quasimonochromatic and broadband fluctuations, turbulent particle flux, fluctuations of density and poloidal magnetic field are presented. The properties of symmetric structures—zonal flows and geodesic acoustic modes of plasma oscillations as well as Alfvén Eigenmodes excited by fast particles from neutral beam injection heating are described. General trends in the behavior of electric potential and turbulence in magnetized fusion plasmas are revealed.

The solution of the problem of heat exhaust has been pointed out as one of the main challenge towards the realization of magnetic confinement fusion. In the last years, two concepts have been proposed in alternative to the conventional divertor solution adopted for ITER: modification of the magnetic topology in the divertor region and liquid metal as plasma facing component. The role of the Divertor Tokamak Test facility (DTT) in the power exhaust implementation strategy is discussed. The evolution of the project, since the original proposal in 2015 to the present design, is shown. The DTT facility is well integrated in the European strategy and the final decision on the divertor configuration will be made, within 2022-23, on the basis of the indication of the Power Exhaust Group constituted by the EUROfusion Consortium. Finally, the main milestones and the timeline of the project are illustrated. © 2019 Elsevier B.V.

To realize the commercialized operation, it is preferable that tokamak devices achieve the operating scenarios with steady-state, long-pulse, H-mode and high magnetic confinement plasma current. For enhancing the magnetic confinement capability and improving the poloidal beta βp in quasi-snowflake configuration, under the consideration of the effect on other performance parameters, the method of shifting magnetic axis is employed. According to the calculated method proposed in this paper, the plasma current density distribution is modified to realize the supposed radial movement of the magnetic axis. Then the value of βp, the coordinates of X2 point, the flux expansion of outside and inside strike points (fmout and fmin), poloidal field currents and safety factor q profile are formulated, the relations between these parameters and the horizontal displacement of the magnetic axis are analyzed. Finally, in lower single-null quasi-snowflake configuration, by shifting the magnetic axis from 1.9242 to 1.9412m, βp has an increase of 86.96 %, the confinement capability of the plasma is significantly enhanced, Meanwhile, the position of X2 point is varied from (2.6789 m, −1.6439 m) to (2.2955 m, −1.6039 m), which is closer to X1 point and the plasma. Therefore, fmout is enlarged from 6.646 to 7.706, which has an increase of 15.9%. And fmin has a decrease of 0.62%, which can be neglected. The safety factor at magnetic axis q0 is decreased by 1.75%, from 1.0897 to 1.0701, which is larger than 1 and satisfies the requirement of magnetohydrodynamic stability. In addition, EFIT code is used to verify the feasibility and the accuracy of the optimized results.

Low-resistance metal-to-metal contacts, both static and sliding contacts, are of interest to many scientific and technical applications as magnetic confinement fusion, railguns, and electrical motors. In fusion applications, silver-coated copper contacts and low-current-density designs are preferred, while in other applications, high current densities are required. For high-pressure high-current-density sliding contacts, contact pairs such as aluminum/copper are preferred as in railguns, while for electrical motors, copper–copper alloys are preferred. Copper–beryllium alloy, C172, is investigated as static contacts for high-current-density pulsed-power applications. To subject the contacts to suitable current pulses and pressures, a special electrical contact assembly has been developed allowing contact pressures from 0 to 66 MPa and current densities from 62 to 263 kA/cm2. The contacts were studied under different current density pressure combinations with repeated 60- $\mu \text{s}$ pulses in air, while current evolution and surface modifications were followed. Besides some surface oxidation, no evidence of other surface modifications like welding or surface melting were found.

The Loss Of Vacuum Accident is one of the hazardous events that may occur in nuclear fusion power plants which work with the magnetic confinement technology. During these accidents, the intake of air may re-suspend toxic, explosive and radioactive dust, involving a hazardous release in the external environment. Several studies have been conducted in scaled facilities, in order to investigate and understand how the phenomenon works. In the previous studies, the authors replicated these events in several different conditions by means of the scaled facility called “STARDUST-Upgrade”, providing a good description of the phenomenon. A Computational Fluid Dynamic (CFD) code able to replicate these events has been developed and validated. Once a scaled experiment is realized, a specific analysis must be performed to understand if the phenomenon can be scaled and in what conditions. A result obtained in STARDUST-Upgrade, that is much different in terms of size and shape from a real TOKAMAK, must be modified by an adequate scaling law. The aim of this work is to analyse how to deduce a scaling law (for large scale flow) by a theoretical analysis based on the Buckingham π theorem. The authors will present also the experimental analysis provided to validate some features of this model. The conclusion of the work will be the use of the scaling law to obtain technical information (pressurisation time) about a LOVA inside an ITER-like reactor and further fusion power plants.

One of the main aims of Wendelstein 7-X (W7-X), an advanced stellarator, is to investigate the quasi-steady state operation of magnetic confinement devices for nuclear fusion, for which power exhaust is an important issue. A dominant fraction of the energy leaving from the confined plasma region will be removed by 10 so-called island divertor units, which are designed to sustain a maximum heat flux of up to 10 MWm−2. An essential prerequisite for the safe operation of a steady-state device is automatic detection of hot spots and other abnormal events. Simple temperature limits in infrared (IR) thermographic images will not be enough on their own, because of plasma-generated surface coatings and other effects summarized in the following. To protect divertor elements from overheating, and to monitor power deposition onto the divertor elements, near real-time hotspot detection algorithms for the analysis of carbon plasma facing components (PFCs) were implemented and tested in the GLADIS facility.One of the difficulties in hotspot detection in a carbon-based machine is the deposition of plasma impurities as layers with a reduced thermal connection to the underlying bulk material. We have developed and successfully tested a method to classify surface layers and benchmarked the performance of the method with the Tore Supra IR data operating with actively cooled carbon PFCs. The surface layers can be detected in a steady plasma discharge during the initial rise and decay in temperature when a strike line touches parts of the divertor or wall. It can also be detected by modulating electron cyclotron resonance heating (ECRH) input power. This feature allows detection of overheated areas while reducing false positives. For the recent operational campaign, inertially cooled test divertor units (TDU) were installed to prepare for steady-state operation with water-cooled divertor units. Automatic, near real-time detection of hot spots and identification of surface layers in the W7-X divertor are presented. Results are compared with a best fit estimate of the heat transmission coefficient α which is used to calculate heat flux onto the divertor in the presence of surface layers. Keywords: W7-X, Divertor, Plasma facing components, Heat load, Infrared, Surface layers, Tore supra

Considering the wear in mechanical bearings and the requirement for sensors or electrical power in active magnetic bearings, a novel nutation blood pump using a passive magnetic spherical bearing was developed in this paper. A mathematical model was derived to calculate the magnetic forces of the bearing between two pairs of magnetic sleeves in the nutation process. The calculation results demonstrate that the fluctuations of magnetic forces enlarge with the increase in the nutation angle; the magnetic forces obviously increase with the decrease in the air gap, especially along the z-axis. The dynamic magnetic finite element simulation was carried out to validate the mathematical model. The simulation and calculation results of the magnetic forces show consistent trends and provide a theoretical basis for the parameter design. To validate the performance of the pump, computational fluid dynamics (CFD) analyses and in vitro experiments were conducted. The predicted values of the flow velocity vector through the pump, and the wall shear stress, demonstrate that the pump has an antithrombotic property and would not cause serious blood damage. The hydraulic experiment shows that a pressure rise can be achieved in the range of 60-140 mmHg, at a rotational speed of 600-1600 rpm and a flow rate of 0.4-6.7 L/min. The normalized index of hemolysis (NIH) of the nutation pump was 0.0043 ± 0.0008 g/100L. The in vitro tests indicate the feasibility of a magnetically levitated ventricular-assist nutation blood pump for further suspension stability and animal trials.

International audience; A computer simulation technique has been applied to the modeling of radiation redistribution functions in low- and moderate-density magnetized hydrogen plasmas. The radiating dipole is described within the Heisenberg picture, and perturbations by the plasma microfield are accounted for through a time-dependent Stark effect term in the Hamiltonian. Numerical applications are presented for the first Lyman and Balmer lines at plasma conditions relevant to tokamak divertors and magnetized white dwarf atmospheres. In both cases, the collisional redistribution of the radiation frequency is shown to be incomplete. Comparisons with a previously developed impact model are performed, and results are discussed.

Academician A. D. Sakharov’s idea concerning the emission of atomic flux from hot plasma (1951) inspired scientists of A. F. Ioffe Physico-Technical Institute to create the first in the world instrument called Neutral Atom Analyzer in 1960 and then in 1961 to use it successfully on the Alpha device (USSR, 1958–1963). Now the analysis of fluxes of fast atoms referred to as Neutral Particle Analysis (NPA) is one of the main diagnostic methods for the ion component of plasma in tokamaks, stellarators, and other devices. NPA provides a unique opportunity for studying the ion distribution functions, ion temperatures and hydrogen isotope ratio in hot plasma. Neutral particle analyzers developed at the Ioffe Institute were widely used in the USSR until the late 1970s, and afterwards began to be employed worldwide. Since then, most of the information on the ion distribution functions and the behavior of fast ions in fusion plasma is obtained from NPA measurements on all leading magnetic confinement fusion systems worldwide. The specialized complex of atom analyzers currently being created at the Ioffe Institute is included in the primary list of ITER diagnostics. The integration of this complex on ITER is expected to begin in 2025.

Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, which carry extreme momentum and low loss in the Mid-infrared (MIR) to Terahertz (THz) spectra. In this work [1], we demonstrate a new way to excite AGPs from the far-field, which are confined to nanometric-scale cavities, via localized graphene-plasmon-magnetic-resonators (GPMRs). This approach enables the efficient excitation of single AGP cavities, which are able to confine MIR light to record-breaking ultra-small mode-volumes that are ∼5·1010 times smaller than their free-space volume.

For a few years the multi-physics modelling of the resonance cavity (resonator) of MW-class continuous-wave gyrotrons, to be employed for electron cyclotron heating and current drive in magnetic confinement fusion machines, has gained increasing interest. The rising target power of the gyrotrons, which drives progressively higher Ohmic losses to be removed from the resonator, together with the need for limiting the resonator deformation as much as possible, has put more emphasis on the thermal-hydraulic and thermo-mechanic modeling of the cavity. To cope with that, a multi-physics simulator has been developed in recent years in a shared effort between several European institutions (the Karlsruher Institut für Technologie and Politecnico di Torino, supported by Fusion for Energy). In this paper the current status of the tool calibration and validation is addressed, aiming at highlighting where any direct or indirect comparisons with experimental data are missing and suggesting a possible roadmap to fill that gap, taking advantage of forthcoming tests in Europe.

Although the nuclear fusion process has received a great deal of attention in recent years, the amount of mathematical analysis that supports the stability of the system seems to be relatively insufficient. This paper deals with the mathematical analysis of the magnetic confinement of the plasma via kinetic equations. We prove the global wellposedness of the Vlasov-Maxwell system in a two-dimensional annulus when a huge (but finite-in-time) external magnetic potential is imposed near the boundary. We assume that the solution is axisymmetric. The authors hope that this work is a step towards a more generalized work on the three-dimensional Tokamak structure. The highlight of this work is the physical assumptions on the external magnetic potential well which remains finite within a finite time interval and from that, we prove that the plasma never touches the boundary. In addition, we provide a sufficient condition on the magnitude of the external magnetic potential to guarantee that the plasma is confined in an annulus of the desired thickness which is slightly larger than the initial support. Our method uses the cylindrical coordinate forms of the Vlasov-Maxwell system., Comment: Accepted in a KRM special volume in the memory of Bob Glassey; 38 pages

Alfvén eigenmodes (AEs) driven by energetic alpha particles can lead to enhanced fast ion transport and losses, thereby degrading the plasma performance in ITER and future magnetic confinement fusion reactors. Unexpectedly, AEs with negative toroidal mode numbers, which are currently not considered for ITER, were observed in dedicated experiments with fusion-born alpha particles on the tokamak Joint European Torus (JET). The paper provides evidence for a complex interplay between fast ions, monster sawtooth crashes and AEs. Our results highlight the need for an improved description of the synergies between different fast ion phenomena in future burning plasmas.

Poloidal asymmetries of the propagation velocity of density fluctuations perpendicular to the magnetic field measured with Doppler reflectometry have been reported in several magnetic confinement plasma devices. Careful analysis of a large variety of different low confinement mode plasma scenarios performed at the ASDEX Upgrade tokamak does not reveal such an asymmetry outside the uncertainties of the evaluation process of the measurement data. The perpendicular velocity is investigated between mid-radius and the plasma edge and follows the poloidal dependence of the E × B drift velocity regardless of the probed turbulence structure size. Compared to measurements of a charge exchange recombination spectroscopy diagnostic this points towards a significantly smaller phase velocity than the E × B drift velocity. The analysis technique is presented in a representative discharge together with a sensitivity study of the impact of density, magneto hydrodynamic equilibrium and diagnostic alignment on the interpretation of the measured Doppler shift using ray tracing and thus on poloidal asymmetries. Three more highly different plasma scenarios with poloidally symmetric velocity profiles are shown.

A fusion reactor is an artificial sun created under laboratory conditions of high temperature and pressure to produce inexhaustible energy. When two nuclei of hydrogen isotopes are forced to fuse, under high temperature and high pressure, the reaction produces huge amount of energy and the heavier atoms of helium. The tokamak concept for magnetic confinement of plasma in a fusion reactor made the use of superconducting magnets most attractive and a natural choice. This chapter gives an account of the fusion process, the Lawson-Criterion for realizing ‘ignition’, different methods of plasma confinement and the superiority of tokamak concept. In a tokamak plasma is confined in a torus by an axial field generated by a set of toroidal coils distributed around the torus and a poloidal field generated by a set of poloidal coils. A high field central solenoid induces current in the plasma to heat it to high temperature through ramping of the field. This current in turn also produces poloidal field. We discuss the superconducting magnet systems built for most important fusion reactors so far, namely, T-7 of Russia, Tore Supra of France, JT-60 SA of Japan, KSTAR of Korea, EAST of China and SST-1 of India. The magnet systems of ITER, has been discussed in greater details. Two tokamaks, namely, TFTR of USA and JET at Culham UK both using normal magnets have also been included for they had many firsts and the data collected from them contributed significantly to the design of ITER. Two more futuristic reactors, the stellarator W7-X being built in Germany and IGNITOR an Italian–Russian joint fusion reactor being built in Russia have also been included towards the end of the chapter.

Nuclear fusion energy is an ideal energy source for the future due to the clean and efficient features, first proposed by Russian scientists in the 1950s. With the successful construction and operation of a batch of tokamak devices globally, a series of major achievements have been realized in magnetic confinement fusion (MF). On this basis, the recent progress and current status of tokamak devices are systematically reviewed from academic literatures and official websites. To better demonstrate, the principle of MF and the history of a tokamak are introduced firstly. Subsequently, developments of four typical state-of-art tokamak facilities (JT60, FTFR, JET, EAST) are discussed detailly. These results offer a guideline for tokamak device construction and MCF realization.

Research on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lacking a comparably high level of neoclassical optimization., Previously documented record values of the fusion triple product in the stellarator Wendelstein 7-X are shown to be evidence for reduced neoclassical energy transport in this optimized device.

In this work, a surface current plasma model is coupled to a volume integral formulation for studying the interaction between tokamak tearing modes (TMs) and the machine metallic structures surrounding the plasma. By evaluating the passive response on a set of pickup probes, TMs' amplitude is estimated.

The investigation of fuel retention in fusion experiments is important in view of plasma density control as well as tritium inventory for future fusion reactors. We present a first gas balance of the stellarator Wendelstein 7-X with its inertially cooled graphite divertor. The gas balance is used to estimate the wall inventory and it is found that the wall plays an important and dynamic role, absorbing or releasing particles depending on the plasma conditions. Several different scenarios are presented and the effect of fueling and heating on the wall inventory is assessed. We find that the record duration plasma experiment of 100 s required previous shorter plasmas to be successfully conducted.

In magnetic confinement thermonuclear fusion the exhaust of heat and particles from the core remains a major challenge. Heat and particles leaving the core are transported via open magnetic field lines to a region of the reactor wall, called the divertor. Unabated, the heat and particle fluxes may become intolerable and damage the divertor. Controlled ‘plasma detachment’, a regime characterized by both a large reduction in plasma pressure and temperature at the divertor target, is required to reduce fluxes onto the divertor. Here we report a systematic approach towards achieving this critical need through feedback control of impurity emission front locations and its experimental demonstration. Our approach comprises a combination of real-time plasma diagnostic utilization, dynamic characterization of the plasma in proximity to the divertor, and efficient, reliable offline feedback controller design., The exhaust of heat and particles is an important challenge in future nuclear fusion devices. Here the authors report the use of carbon emission as indicator for plasma detachment in a tokamak and its real-time feedback control.

A new variational theory is presented for beam loading in microwave cavities. The beam--field interaction is formulated as a dynamical interaction whose stationarity according to Hamilton's principle will naturally lead to steady-state solutions that indicate how a cavity's resonant frequency, $Q$ and optimal coupling coefficient will detune as a result of the beam loading. A driven cavity Lagrangian is derived from first principles, including the effects of cavity wall losses, input power and beam interaction. The general formulation is applied to a typical klystron input cavity to predict the appropriate detuning parameters required to maximize the gain (or modulation depth) in the average Lorentz factor boost, $\langle \Delta\gamma \rangle$. Numerical examples are presented, showing agreement with the general detuning trends previously observed in the literature. The developed formulation carries several advantages for beam-loaded cavity structures. It provides a self-consistent model for the dynamical (nonlinear) beam--field interaction, a procedure for maximizing gain under beam-loading conditions, and a useful set of parameters to guide cavity-shape optimization during the design of beam-loaded systems. Enhanced clarity of the physical picture underlying the problem seems to be gained using this approach, allowing straightforward inclusion or exclusion of different field configurations in the calculation and expressing the final results in terms of measurable quantities. Two field configurations are discussed for the klystron input cavity, using finite magnetic confinement or no confinement at all. Formulating the problem in a language that is directly accessible to the powerful techniques found in Hamiltonian dynamics and canonical transformations may potentially carry an additional advantage in terms of analytical computational gains, under suitable conditions., Comment: 18 pages, 6 figures (2nd version: corrected typos and notation; added one more example in Section V). To appear in Physical Review Applied

An offset-pole periodic cusped magnet (PCM) focusing system for an H-band (220–325 GHz) traveling wave tube was designed and optimized using CST-PS. It is composed of 82 magnetic blocks and 84 poles. The diffusion of the sheet electron beam is effectively suppressed. The transmittance can reach 100% under the elliptical electron emission source.

This paper presents the design of a radial flux Brushless dc (BLDC) motor with a special type of permanent magnet arrangement known as Halbach-array magnet arrangement. Halbach-array magnets are placed in between the rotor poles and its magnetization is set in such a way so that it increases the overall air gap flux density. The performance of the Halbach-BLDC motor is analyzed. The aim of this paper is to compare the design and performances of a Halbach-BLDC motor with a conventional BLDC motor. The designs are tested using FEA solutions. The experiment shows that the Halbach-BLDC motor enhances the performance by increasing its speed, overall torque and the magnetic flux density. A 48V 0.5kW 8 pole Halbach-BLDC motor is designed and analysed using Ansys Maxwell software.

Electron scattering cross sections for pyridine in the energy range 0–100 eV, which we previously measured or calculated, have been critically compiled and complemented here with new measurements of electron energy loss spectra and double differential ionization cross sections. Experimental techniques employed in this study include a linear transmission apparatus and a reaction microscope system. To fulfill the transport model requirements, theoretical data have been recalculated within our independent atom model with screening corrected additivity rule and interference effects (IAM-SCAR) method for energies above 10 eV. In addition, results from the R-matrix and Schwinger multichannel with pseudopotential methods, for energies below 15 eV and 20 eV, respectively, are presented here. The reliability of this complete data set has been evaluated by comparing the simulated energy distribution of electrons transmitted through pyridine, with that observed in an electron-gas transmission experiment under magnetic confinement conditions. In addition, our representation of the angular distribution of the inelastically scattered electrons is discussed on the basis of the present double differential cross section experimental results., This research was partially funded by the Spanish Ministerio de Ciencia, Innovación y Universidades-MICIU (Projects FIS2016-80440 and PID2019-104727RB-C21) and CSIC (Project LINKA 20085). F.C. acknowledges the Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, PD/00193/2012); UCIBIO (UIDB/04378/2020) and together with P.L.-V. the Portuguese National Funding Agency FCT through the Research Grants CEFITEC (UIDB/00068/2020) and PTDC/FISAQM/31281/2017. M.J.B. and R.D.W. thank the Australian Research Council for funding through grant DP180101655. L. Álvarez and A. García-Abenza thank the local CAM government and MICIU, respectively, for their corresponding grants within the “Garantía Juvenil” programmes. M.H.F.B. acknowledges support from the Brazilian Agency Conselho Nacional de Desenvolvimento Científico e Tecnollógico (CNPq). A.S.B. and M.H.F.B. acknowlegde computational support from Prof. Carlos de Carvalho at LFTC-DFis-UFPR and at LCPAD-UFPR and from C3SL at DInf-UFPR. A.D. and X.R. thank Igor Bray for providing helium ionization cross sections for calibration of the reaction microscope.

Experiments on DIII-D show that resonant magnetic perturbations (RMPs) reduce the impurity confinement time in the H-mode pedestal below that of naturally ELMy plasmas. STRAHL modeling of discharges with aluminum laser blow off (LBO) injection show increased diffusion in the pedestal of H-mode discharges with RMPs. The increased diffusion from the RMPs provides improved impurity control compared to the naturally ELMy discharges and prevents the buildup of impurities near the edge of the plasma. Tungsten LBO injection into discharges with and without RMPs led to striking differences in the evolution of the discharge. The naturally ELMy discharge became ELM free and showed an increase in edge radiation, leading to the eventual radiative collapse of the plasma. Injecting a similar number of W particles into discharges with RMPs, either with or without ELMs, led to a measurable accumulation of core W but did not significantly impact the evolution of the discharge. These results indicate that RMPs are beneficial for controlling the buildup of impurities in the pedestal region of the plasma.

Lower hybrid (LH) and magneto-sonic (MS) waves are well known modes of magnetized plasma. These modes play important roles in many phenomena. The lower hybrid wave is often employed in magnetic confinement fusion experiments for current drive and heating purposes. Both LH and MS waves are observed in various astrophysical and space plasma observations. These waves involve ion motion and have not therefore been considered in high power pulsed laser experiments. This paper shows, with the help of Particle - In - Cell (PIC) simulations, a simple mechanism for excitation of lower hybrid and magnetosonic excitations in the context of laser plasma interaction. A detailed study characterising the formation and propagation of these modes have been provided. The scheme for generating these perturbations relies on the application of a strong magnetic field in the plasma to constrain the motion of lighter electron species in the laser electric field. The magnetic field strength is chosen so as to leave the heavier ions un-magnetized at the laser frequency. This helps in the excitation of the LH waves. On the other hand at the slower time scale associated with the laser pulse duration, even the ions show a magnetized response and magnetosonic excitations are observed to get excited.

A Multi-Color (MC) gas puff imaging diagnostic has been developed on HL-2A tokamak. This diagnostic can simultaneously measure two-dimensional (2D, radial, and poloidal) electron density and temperature distributions with a good spatial resolution of 2.5 × 2.5 mm2 and a temporal resolution of about 100 µs at best in edge plasmas. The 2D electron density and temperature distributions are inferred from the ratios of intensities of three different neutral helium emission lines; therefore, it is also referred to as helium beam probe or beam emission spectroscopy on thermal helium. A compact light splitter is used to split the inlet visible emission beam into four channels, and the specific neutral helium lines of the wavelengths λ1 = 587.6 nm, λ2 = 667.8 nm, λ3 = 706.5 nm, and λ4 = 728.1 nm are measured, respectively. This MC diagnostic has been experimentally tested and calibrated on a linear magnetic confinement device Peking University Plasma Test device, and the measured 2D electron density and temperature distributions are compared with the Langmuir probe measurements.

The global confinement time is a critical parameter for characterization of plasmas in magnetic confinement fusion experiments. A practical nonlinear ensemble Kalman filter is developed for estimation of the global energy confinement time. The filter implementation runs in real time and provides quality estimates enabling novel modes of tokamak plasma feedback. Open and closed loop experimental results are reported for the regulation of a confinement time based plasma performance metric, using the total plasma current as actuator.

The structure of the edge plasma in a magnetic confinement system has a strong impact on the overall plasma performance. We uncover for the first time a magnetic-field-direction dependent density shelf, i.e., local flattening of the density radial profile near the magnetic separatrix, in high confinement plasmas with low edge collisionality in the DIII-D tokamak. The density shelf is correlated with a doubly peaked density profile near the divertor target plate, which tends to occur for operation with the ion $B\ifmmode\times\else\texttimes\fi{}\ensuremath{\nabla}B$ drift direction away from the $X$-point, as currently employed for DIII-D advanced tokamak scenarios. This double-peaked divertor plasma profile is connected via the $E\ifmmode\times\else\texttimes\fi{}B$ drifts, arising from a strong radial electric field induced by the radial electron temperature gradient near the divertor target. The drifts lead to the reversal of the poloidal flow above the divertor target, resulting in the formation of the density shelf. The edge density shelf can be further enhanced at higher heating power, preventing large, periodic bursts of the plasma, i.e., edge-localized modes, in the edge region, consistent with ideal magnetohydrodynamics calculations.