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The interview with Bob Rosner, a former chair of the Bulletin's Science and Security Board, explores his skepticism about fusion energy becoming a commercial energy source in the near future. Rosner discusses the complexities of fusion research, focusing on the challenges faced by tokamaks and stellarators in achieving fusion ignition and stability. He also touches on the issues related to tritium supply, neutron embrittlement, and the potential applications of fusion research beyond energy production. Rosner emphasizes the importance of fusion research for national defense and nonproliferation efforts, highlighting the role of facilities like NIF in advancing scientific knowledge and preventing nuclear weapons testing. [Extracted from the article]

Concern about adequate tritium resources to start up deuterium-tritium (DT) fusion reactors in the near term is misplaced: Proposed demonstration reactors and pilot plants will not realistically be buildable for a great many decades. More disturbing, tritium fuel self-sufficiency of eventual DT reactors may be unattainable, because it is unlikely that tritium-breeding blankets can completely replenish burned-up fuel as well as unburned tritium that is lost in numerous reactor subsystems. The concept of doubling time is unworkable. The only viable fuel solution for sustained operation demands deuterium-based reactors where the tritium is concurrently generated and burned up in the fusioning plasma. [ABSTRACT FROM AUTHOR]

Long-wavelength density fluctuations ( k ρ i 0.97, indicating the prevalence of density ‘voids’ at inner radii and density ‘blobs’ at outer radii and outside of the separatrix. The turbulence intensity flux ⟨ v ~ r n ~ 2 ⟩ is calculated to characterize turbulence spreading at the plasma edge. During ECH/NBI power ramps and at counter- I p injected torque, ⟨ v ~ r n ~ 2 ⟩ is directed inward inside the separatrix, which is evidence of inward spreading of turbulence intensity from the edge gradient region caused by the inner propagation of density ‘voids’. Significantly weaker ⟨ v ~ r n ~ 2 ⟩ is observed with co- I p torque. A correlation between co- I p torque, turbulence intensity δ n / n at ρ = 0.97, and increased srape-off layer (SOL) heat flux decay length λ q is found in the torque scan scenario, showing that edge turbulence plays a material role in determining the SOL conditions and heat flux width.

Since the first plasma realized in 2020, a series of key systems on HL-3 (known as HL-2M before) tokamak have been equipped/upgraded, including in-vessel components (the first wall, lower divertor, and toroidal cryogenic/water-cooling/baking/glow discharge systems, etc.), auxiliary heating system of 11 MW, and 28 diagnostic systems (to measure the plasma density electron temperature, radiation, magnetic field, etc.). Magnet field systems were commissioned firstly for divertor plasma discharges. During the 2nd experimental campaign of HL-3 tokamak, several great progresses have been achieved. Firstly, the successful operation with plasma current larger than 1 MA was achieved under a divertor configuration. Secondly, the advanced divertor concept with two distinct snowflake configurations was realized. It is found that the distribution of ion saturation current and heat flux on bottom plate becomes wide due to magnetic surface expansion, demonstrating the advantage of such configuration in the heat flux mitigation. In addition, using the combination of NBI, ECRH and LHCD, the standard sawtoothing high confinement mode of megampere plasma was firstly accessed on the HL-3. The successful commissioning of HL-3 is beneficial for the initial operation of ITER.

A real-time capable core Ion Cyclotron Range of Frequencies (ICRF) heating model on NSTX and WEST is developed. The model is based on two nonlinear regression algorithms, the random forest ensemble of decision trees and the multilayer perceptron neural network. The algorithms are trained on TORIC ICRF spectrum solver simulations of the expected flat-top operation scenarios in NSTX and WEST assuming Maxwellian plasmas. The surrogate models are shown to successfully capture the multi-species core ICRF power absorption predicted by the original model for the high harmonic fast wave and the ion cyclotron minority heating schemes while reducing the computational time by six orders of magnitude. Although these models can be expanded, the achieved regression scoring, computational efficiency and increased model robustness suggest these strategies can be implemented into integrated modeling frameworks for real-time control applications.

Experimental studies of the dynamics of shear flow and turbulence spreading at the edge of tokamak plasmas are reported. Scans of line-averaged density and plasma current are carried out while approaching the Greenwald density limit on the J-TEXT tokamak. In all scans, when the Greenwald fraction f G = n ¯ / n G = n ¯ / ( I p / π a 2 ) increases, a common feature of enhanced turbulence spreading and edge cooling is found. The result suggests that turbulence spreading is a good indicator of edge cooling, indeed better than turbulent particle transport is. The normalized turbulence spreading power increases significantly when the normalized E × B shearing rate decreases. This indicates that turbulence spreading becomes prominent when the shearing rate is weaker than the turbulence scattering rate. The asymmetry between positive/negative (blobs/holes) spreading events, turbulence spreading power and shear flow are discussed. These results elucidate the important effects of interaction between shear flow and turbulence spreading on plasma edge cooling.

An equation for estimating the effective diffusivity χ φ eff based on the thermal and frictional forces arising from the interactions with neutral particles is provided. These interactions are primarily attributed to charge-exchange processes between ions and neutral particles. Our analysis indicates that the proposed forces are strong candidates to act as sources or sinks of momentum at the plasma edge. Furthermore, although we only have an estimated profile of neutral particles, the results demonstrate a strong dependence of the effective diffusivity on the ion-neutral collision frequency and a comparatively weaker dependence on ion temperature. We showed that the toroidal rotation profile in the TCABR tokamak is well described by the Helander model for toroidal rotation velocity in the Pfirsch-Schlüter regime, which depends on the ion temperature gradient in the presence of the neutral particles. The toroidal rotation profile has been reconstructed by a sum of Bessel functions, derived from the solution of a second-order differential equation for the toroidal velocity. In this initial study on momentum transport in TCABR, our findings indicate that χ φ eff —which accounts for both the diffusivity and pinch terms in the momentum equation—increases significantly in the outer plasma region. Additionally, it achieves a reasonable maximum value of approximately χ φ eff ≈ 20 m 2 / s near the plasma edge at r / a ≃ 0.87 , in the same radial position of the maximum ion-neutral collision frequency, demonstrating that the applied method successfully captures the general behaviour of this component as reported in other works, and guiding future experimental validation. [ABSTRACT FROM AUTHOR]

The intermediate mode between the ohmic, or low confinement (L-mode), and the increased confinement (H-mode) regimes, or the so called I-phase, which is characterized by the existence of zonal flows in the form of limit cycle oscillations (LCOs), was observed on the Globus-M tokamak. Depending on the LCO frequency, the I-phase resulted in either a transition to H-mode or back to L-mode. The possibility of L-I-H transition initiation induced by LCOs and the effect of LCO frequency were studied by means of numerical modeling of the density profile evolution, taking into account turbulence suppression by the inhomogeneous radial electric field. The modeling results show that lower LCO frequency could be a factor facilitating the L-H transition, whereas higher frequency LCOs are more likely to cause the backward transition to L-mode. The results are in qualitative agreement with the results of the studies of geodesic acoustic mode (GAM)–initiated L-H transition in the TUMAN-3M tokamak, where a lower GAM frequency was found to be beneficial for L-H transition initiation. [ABSTRACT FROM AUTHOR]

DIII-D research is being accelerated by leveraging high performance computing (HPC) and data resources available through the National Energy Research Scientific Computing Center (NERSC) Superfacility initiative. As part of this initiative, a high-resolution, fully automated, whole discharge kinetic equilibrium reconstruction workflow was developed that runs at the NERSC for most DIII-D shots in under 20 min. This has eliminated a long-standing research barrier and opened the door to more sophisticated analyses, including plasma transport and stability. These capabilities would benefit from being automated and executed within the larger Department of Energy Advanced Scientific Computing Research program's Integrated Research Infrastructure (IRI) framework. The goal of IRI is to empower researchers to meld DOE's world-class research tools, infrastructure, and user facilities seamlessly and securely in novel ways to radically accelerate discovery and innovation. For transport, we are looking at producing flux matched profiles and also using particle tracing to predict fast ion heat deposition from neutral beam injection before a shot takes place. Our starting point for evaluating plasma stability focuses on the pedestal limits that must be navigated to achieve better confinement. This information is meant to help operators run more effective experiments, so it needs to be available rapidly inside the DIII-D control room. So far this has been achieved by ensuring the data is available with existing tools, but as more novel results are produced new visualization tools must be developed. In addition, all of the high-quality data we have generated has been collected into databases that can unlock even deeper insights. This has already been leveraged for model and code validation studies as well as for developing AI/ML surrogates. The workflows developed for this project are intended to serve as prototypes that can be replicated on other experiments and can be run to provide timely and essential information for ITER, as well as next stage fusion power plants. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

ObjectivesMagnetic confinement fusion is regarded as a critical solution to future global energy challenges. As the central component of magnetic confinement fusion devices, magnets play a crucial role in generating and sustaining plasma stability. A review of the magnetic system structures and specifications in representative magnetic confinement fusion devices worldwide was provided.MethodsThe technological evolution of fusion magnets was reviewed, from copper-based to low-temperature superconducting, and finally to high-temperature superconducting magnets. The structure and performance parameters of magnetic systems in various typical fusion devices were summarized systematically. Additionally, the technical challenges in magnet development were explored and an outlook on future development trend was offered.ConclusionsAdvances in magnet technology are vital for enhancing the performance of fusion devices and accelerating the commercialization of fusion energy. With the increasing application of high-temperature superconducting materials and continuous optimization of magnet designs, the practical realization of fusion energy is becoming increasingly feasible.

The dependence of the focal length of the thallium Tl+ ion beam on the parameters of the ion-optical system of the injector for diagnostics of plasma by heavy ion beam probe has been studied. The possibility of obtaining quasi-parallel beams and converging beams with a focal length of more than 4 m has been shown. Experimental results are compared with the results of computer modeling of the beam trajectory in the injector. [ABSTRACT FROM AUTHOR]

Investigation of discharges with a negative triangularity plasma configuration is carried out on various tokamaks: TCV, D-IIID, and ASDEX-U. Negative triangularity (NT) experiments in the TCV show a reduction in electron heat transport by a factor of two compared with the positive triangularity D-shaped configurations. Recent experiments on DIII-D with a NT configuration showed improved confinement compared to the positive triangularity (PT) D-shaped plasmas over a range of auxiliary heating powers and, in particular, for the case Te ~ Ti. In addition, it was found that the NT-shaped plasma has the capability to achieve significant normalized β. The purpose of this study is a computational confirmation of the possibility of implementing scenarios with NT discharges in the ohmic heating mode in the T-15MD tokamak with its standard poloidal system. Simulation results show that the poloidal system of the T-15MD tokamak is rather flexible for study of scenarios with D-shaped NT. It is proposed to expand the research program in the T-15MD by including in it the study of scenarios with NT. [ABSTRACT FROM AUTHOR]

The unique properties of high-temperature superconductors (HTSCs) and progress in the manufacture of HTSC-based wires made it possible to develop a new generation of tokamaks. In Russia, a tokamak project with reactor technologies (TRT), in which the magnetic field induction reaches 8 T on the plasma axis and 15 T and higher on the windings of the electromagnetic system, is being developed. The creation of HTSC current-carrying elements (CCEs) that meet the stringent requirements for the TRT magnetic system is one of the key issues of the entire project. A number of short experimental CCE samples that are potentially applicable in TRT magnetic systems was developed. A series of physical and mechanical tests were carried out to check the mechanical properties and develop a universal certification methodology for CCEs accepted for operation. [ABSTRACT FROM AUTHOR]

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%) is due to the two outer layers of the collector mesh. A simple mathematical model is proposed that describes the distribution of the collected lithium over the mesh layers. [ABSTRACT FROM AUTHOR]

A review of various mechanisms of suprathermal electron generation in tokamak plasma and an analysis of diagnostic systems for the study of the spatial evolution of electron beams are presented. It is planned to use detectors based on CdTe crystals to detect suprathermal x-ray emission (20–300 keV) at the T-15MD tokamak (R = 1.5 m, a = 0.67 m). Spatial resolution is provided by a system of tube collimators placed in detector chambers mounted in vertical, inclined, and equatorial diagnostic ports. To measure suprathermal x-ray emission spectrum, a set of CdTe spectrometric detectors and LaBr3(Ce) scintillation crystal detectors are used. The tomographic program is used to reconstruct spatial localization of the X-ray emission. The received spatial and temporal distribution of local suprathermal electron beams will be used to study a variety of physical phenomena, such as reconnection of magnetic field lines, nonlinear transport processes, distortion of the electron energy distribution function during powerful additional heating and current drive, and plasma perturbances that are important for the study of kinetic instabilities in plasma with fast ions. [ABSTRACT FROM AUTHOR]

The analysis of possible divertor working regimes and edge plasma parameters for TRT tokamak project is performed basing on modeling. It is shown that for the separatrix power of 18 MW corresponding to approximately twice higher full input power the low divertor integral heat flux 5 MW/m2 can be provided for the separatrix plasma density lower than 7 × 1019 m–3 and the effective charge Zeff lower than 2. These parameters are realistic for this device. In case of bigger separatrix power the working regime is possible with higher divertor heat load still within the technological limits of the machine. Modeling also shows positive effect of the increase of the distance between the separatrix and the vacuum vessel structures and better performance of the corner divertor configuration comparing to the "ITER-like" one. [ABSTRACT FROM AUTHOR]

The question of the existence of internal transport barriers (ITBs) around low-rational number values of the stability factor q = 1, 2, ... in the usual L-mode of tokamaks with central additional heating and positive magnetic shear remains open. To clarify the existence of such ITBs, experiments were carried out with a programmed linear time shift of the plasma column, in which the positions of the electron temperature measurements Te of the emission at the second electron cyclotron harmonic are shifted relative to the plasma column, which allows one to study the Te profile details. A series of experiments with perpendicular input of EC radiation with a power of 0.4 and 0.85 MW at a central ECRH and a fast (60 ms) shift of the column by 0.13a (minor plasma radius a) were carried out on the T-10 tokamak in plasma with a carbon limiter. In both cases, outside the q = 1 surface narrow (about 0.03a wide) and weak (a decrease in the coefficient of electron thermal conductivity χe by approximately two times) ITBs detected, which disappeared when the discharge parameters changed. These ITBs are 2–3 times narrower and an order of magnitude weaker than the ITBs near the surface q = 1, which was previously proposed to explain the RTP tokamak results. ITBs were not detected in the L-mode in experiments with simultaneous generation of a co-current and counter-current in the plasma center by two gyrotrons with a total power of 1.5 MW in a plasma with a tungsten limiter (column shift by 0.1a in 30 ms). This article appears to be the first journal publication on the study of Te profile details with rapid movement of the plasma column. [ABSTRACT FROM AUTHOR]

We investigated the correlation between density perturbations (bursts), having stochastic or intermittent character and magnetic fluctuations detected by Mirnov coils. To achieve this, we designed and constructed a novel Mixed-Probe system in the IR-T1 tokamak. Our experimental approach involved two steps: first with Resonant Helical magnetic Fields (RHF) and then without RHF. The conditional averaged analysis of the probe ion saturation current () revealed that stochastic density bursts or intermittencies were more likely to exist during the time interval between t = 10 and 12 ms. Before applying RHF, the intermittencies exhibited a strong cross-correlation with magnetic fluctuations. The predominant frequencies observed are below 7 kHz. Interestingly, after applying RHF, the peaks in the frequency of the signal disappeared, and there was no predominant peak in the FFT of . We further analyzed the radial and poloidal velocities of bursts and magnetic fluctuations using diagnostic data. The results suggested that magnetic fluctuations induced oscillations in the background plasma, affecting the radial motion of the density perturbations. Notably, the poloidal velocity of the magnetic field perturbations exceeded that of the bursts, allowing it to shear the poloidal plasma flux and generate the density bursts. The differing velocities confirmed their coupling for a specific time, followed by decoupling. Overall, in the IR-T1 tokamak, applying RHF reduced the cross-correlation between magnetic fluctuations and stochastic density bursts. [ABSTRACT FROM AUTHOR]

The possibility of using the method of dual-wavelength digital holographic interferometry to assess the wear of protective elements of the Globus-M2 spherical tokamak after working plasma discharges is demonstrated. At this stage of the work, the protective elements were removed from the tokamak discharge chamber and used as samples in the holographic setup. A diagram of a holographic interferometer for recording primary holographic images is presented, in which control of the radiation wavelength recording and monitoring systems is carried out through a hardware and software complex in real time. The results of measurements of the shape of tokamak elements are presented. It is shown that when the difference in wavelengths changes, the sensitivity of the measurement method changes, and in the proposed configuration of the optical scheme it is possible to determine the minimum value of the shape change at a level of 10–30 μm. At the same time, the error in determining the phase difference, by which the surface profile is assessed, in the digital method can reach about 2π/40. [ABSTRACT FROM AUTHOR]

The results of heat and particle transport simulations for ohmic plasma in the T-10 tokamak with a circular limiter and for D-shaped plasma in the COMPASS tokamak with a divertor are presented. In addition, the H-mode with ohmic heating and with additional heating by the neutral beam injection (NBI) in the COMPASS was simulated. The simulations were carried out with the Canonical profile transport model (CPTM) using the ASTRA code. The obtained electron temperature and density profiles agree with the measured ones with standard deviations within the experimental accuracy of 10–15%. The calculations demonstrated very similar density profiles in the H-mode both with the ohmic and with additional NBI heating. The electron temperature profiles in the H-mode with additional heating have higher pedestals than in the ohmic H-mode, that agree with the measurements. The comparison showed that the ohmic regimes in COMPASS and T-10 can be described by the same stiffness coefficients in the heat and particle transport equations. [ABSTRACT FROM AUTHOR]

The influence of the toroidal magnetic field ripples on the spatial structure and frequency of the geodesic acoustic mode (GAM) in tokamak plasma has been investigated. It is shown that the toroidal asymmetry of the magnetic configuration leads to coupling of oscillations of the GAM electric potential with toroidal and poloidal inhomogeneous perturbations of the plasma pressure. For tokamaks with a large aspect ratio, the GAM dispersion law is derived, taking the non-uniformity of the ripple in the tokamak cross-section into account. Increasing the number of coils of the toroidal field reduces the effect of ripple as . The applicability of the standard theory to finding the frequency and spatial structure of GAM in large tokamaks is shown. [ABSTRACT FROM AUTHOR]

One of the conditions of safe operation for the experimental tokamak reactor ITER is the possibility of mitigating disruption instability by massive injection of inert gases, in particular, of argon and neon. Here we present the results of assessing the influence of multiplet splitting and line radiation imprisonment during the discharge quenching by intense argon injection in ITER. In this paper, the fine structure of energy levels and the noncoronal collisional-radiative kinetics for the radiating excited state are used. For the radiation of two argon ions, Ar+15 and Ar+3, which have spectral lines of high intensity and could be used for plasma diagnostics, it is shown that the optical thickness for the ionic strongest lines has no significant effect on the total power losses of plasma radiation in the considered quenching scenario (massive argon injection in the 15 MA, Q ~ 10 basic scenario in ITER, carried out at the quasi-stationary stage of the discharge, flat-top of the current). The most significant effect appears to be the multiplet splitting of atomic levels, which provides an increase in the radiative losses, e.g., by a factor of ~2 for low-ionized atoms at low temperatures, because the resolution of the fine structure of atomic levels for Δn = 0 transitions leads to a contribution of lower excitation energy than that in the model of multiplet-average radiative transitions. [ABSTRACT FROM AUTHOR]

The paper analyzes the well-known vacuum technology method of "drying" vacuum volumes by purging them with "dry" gases, applied to the discharge chambers of tokamaks during their initial preparation phase before plasma experiments. This method competes with the traditional technique of thermal desorption by heating the tokamak chamber under high-vacuum conditions. Using the examples of the TSP and T-11M tokamaks, it is shown that, in the initial phase of preparing the tokamak chamber, before transitioning to plasma methods for wall conditioning, the simple "drying" method, especially when using forced convection of "dry" gases, can have significant advantages over the traditional approach. [ABSTRACT FROM AUTHOR]

The properties of boron carbide and its coating, which seem important for the plasma-facing material in thermonuclear facilities, are presented. The basic steps for boron carbide (B4C) coating using carborane (C2B10H12) as the initial material are reported. It has been shown that is not susceptible to "chemical sputtering." The sputtering rate of B4C is 3–4 times and the emission of carbon atoms is 15–20 times less than that of graphite and changes slightly up to 1500 K. Trapping of hydrogen isotope ions into the B4C coating tends to saturation at irradiation doses of about 7 × 1023 at/m2. A method for low-temperature "detritization" of the coating is proposed. Conditioning the coating by irradiating it with hydrogen ions with an energy of 50 eV left ≈8% of the introduced deuterium ions in it. The results of several cycles of thermal cycling of coatings are presented. In particular, a B4C coating with a thickness of 5 µm on tungsten up to 2000 K retained the composition B:C ≈ 3.8:1, melted in the range of 2500–3670 K, and changed the composition to B : C ≈ 1.2:1, but remained continuous, without peeling. The results of improvement of plasma parameters after deposition of a boron carbide coating on the first wall of the T-11M tokamak and in the PISCES-B facility are presented. The coating deposition rate reached 30 nm/s. The possibility of plasma-chemical conversion into gas and removal of boron carbide erosion products from facilities is reported. [ABSTRACT FROM AUTHOR]

The paper provides a brief overview of research activity related to the use of the flowing liquid lithium as a plasma facing material of the limiter and divertor in tokamaks. A substantiation for a system with liquid lithium, possible variants of such systems, demonstration of positive test results, prospects for using in other tokamaks, related research, and open questions are considered. [ABSTRACT FROM AUTHOR]

The article presents the results of the first experiments on the T-15MD tokamak. Plasma discharges with current up to 250 kA, discharge duration up to 2 s, and plasma electron temperature up to 3 keV have been obtained in the experiments. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)