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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

SCALE 6.3 Validation: Spent Nuclear Fuel

This report is the fifth volume in a series documenting the validation of SCALE 6.3 with ENDF/B-VII.1 libraries for nuclear criticality safety, reactor physics, radiation shielding, and spent nuclear fuel applications. This fifth volume, which focuses on validating SCALE capabilities that impact spent nuclear fuel applications, provides an update of the similar validation reported for SCALE 6.2.4. The experimental data used as basis for validation herein consist of measurement data for nuclide inventories and decay heat, including the following: 1. radiochemical assay (RCA) measurements of nuclides important to burnup credit, decay heat, and radiation shielding in 205 light-water reactor (LWR) spent nuclear fuel samples that cover burnups ranging up to 80 GWd/MTU and initial fuel enrichments up to 4.9% 235U; 2. full-assembly decay heat measurements for 236 LWR assemblies with initial fuel enrichments ranging up to 4% 235 U, assembly burnups of 5–51 GWd/MTU, and decay times after fuel discharge in the 2- to 27-year range (of importance to spent nuclear fuel storage, transportation, and disposal); and 3. pulse fission irradiations for fissionable materials at cooling times of interest to severe accident analyses (<10 5 s).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Plasma-Coupled Flow Reactor Studies of Low-Temperature Plasma Assisted Kinetics of Methanol Blended with CO2

Ignition technologies based on low-temperature plasmas (LTP) have the potential to operate next generation engines at elevated pressures and increased dilution limits promoting higher efficiencies. From a practical standpoint, research on LTP igniters has shown to enhance combustion and ignition, improve flame stability, and extend the dilution limits of combustion. All of the aforementioned gains are complemented with higher ignition efficiencies. However, the biggest challenge with incorporating this technology into engines is the knowledge gap of how exactly plasma chemistry effects can enhance the basic combustion phenomena. This coupled with the lack of validated kinetic mechanisms for plasma-combustion chemistry is the biggest obstruction to recognize efficient ignition, especially for application relevant fuels and biofuels. In order to comprehensively evaluate the effects of LTP on an oxygenated fuel specific system, this present study examines the kinetics of methanol plasma-assisted pyrolysis and oxidation using a custom-built plasma flow reactor (PFR). Experimental regimes are also further extended to understand the effects of adding CO2 to the mixture and its consequence on reaction kinetics. The PFR is installed with a dielectric-barrier discharge (DBD) configuration to induce LTP into the fuel mixture. Non-equilibrium plasmas are generated by high-voltage pulses (nearing 20 KV) administered by a plasma pulser at high-pulse repetition rates (up to 10 kHz). In order to better understand and isolate plasma chemistry and its effect on neutral chemistry, the experiments were carried out by heavily diluting reactive mixtures in nitrogen at near isothermal conditions. This suppresses the effect of exothermic reactions on chemistry allowing stable intermediates and products to be detected and quantified using ex-situ GC/MS diagnostic methods. Experiments were carried out at 0.5 atm pressure and over a wide range of temperatures from 523 K to 1203 K. Experimental results depicted the enhancement in intermediates production as well as overall lower temperatures required for complete fuel consumption in the plasma specific cases as opposed to their pure thermal counterpart. Formation of oxygenated and nitrile compounds specific to plasma assisted pyrolysis cases illustrated the efficacy of LTP to introduce new reaction pathways accelerating fuel decomposition. Increase in reactivity at lower temperatures is sought to be an effect induced by plasma chemistry postulating the acceleration in intermediates production. The onset of thermal ignition in plasma assisted oxidation is seen 200 K earlier than thermal oxidation highlighting efficient fuel conversion to final byproducts. Enhanced collisional processes afforded by LTP is seen to perturb reaction pathways between oxygenated fuel radicals and N-atoms to alter overall chemical reactivity. New insights into kinetics are gained from this study highlighting governing plasma assisted combustion (PAC) pathways for oxygenated fuel reaction chemistry. The results from this study can be used to develop future mechanisms specific to plasma chemistry which can bridge the mechanistic knowledge gap for LTP ignition so that future engines can adopt LTPs in their design for efficient combustion.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Combined microwave and laser Rayleigh scattering diagnostics for pin-to-pin nanosecond discharges

In this work, the temporal decay of electrons produced by an atmospheric pin-to-pin nanosecond discharge operating in the spark regime was measured via a combination of microwave Rayleigh scattering (MRS) and laser Rayleigh scattering (LRS). Due to the initial energy deposition of the nanosecond pulse, a variation in the local gas density occurs on the timescale of electron decay. Thus, the assumption of a constant collisional frequency is no longer applicable when electron number data are extracted from MRS measurements. Furthermore, to recalibrate MRS measurements throughout the electron decay period, temporally resolved LRS measurements of the local gas density were performed over the event duration. The local gas density was calculated to be 30% of the ambient level during the later stages of electron decay, and it recovers at about 1 ms after discharge. A shock front traveling approximately 500 m/s was additionally observed. Coupled with plasma volume calibration via temporally resolved intensified charge-coupled device imaging, the corrected decay curves of the electron number and electron number density are presented with a measured peak electron number density of 4.5 × 1015 cm -3 and a decay rate of ~(0.1–0.35) × 10 7 s -1 . A hybrid MRS and LRS diagnostic technique can be applied for a broad spectrum of atmospheric-pressure microplasmas where a variation in the gas number density is expected due to energy deposition in the discharge.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Deployment of salt sample extraction system at an engineering-scale electrorefiner

The goal of the salt sampling program at Argonne is to develop and deploy automated molten salt sampling approaches for interfacing relevant unit operations with salt analysis to improve the timeliness of sampling-based accountancy measurements. Two technologies under development in support of this goal are a vacuum sampling loop module and a high-throughput pneumatic sample generator module. Compared to traditional point sampling approaches (i.e., dip probes), the vacuum sampling loop facilitates the collection of a larger cross-section of the bulk salt in order to collect more representative samples. The vacuum sampling approach also eliminates the risk of dross contamination of samples and avoids the use of moving parts in the salt. The pneumatic sample generator module is used to facilitate high-throughput sample analysis to improve the measurement precision of any given analytical technique by averaging out random sampling and measurement errors. In FY21, two methods for integrating these two modules were tested including direct fluidic coupling and coupling using a solid salt transfer mechanism. Solid salt transfer was ultimately selected over fluidic coupling, primarily to enable the transport of samples over longer distances to support automated at-line integration with high-precision techniques (such as microcalorimetry) that cannot withstand the conditions near an electrorefining process. To facilitate rapid solid salt coupling, new mechanisms were developed for rapidly charging and discharging salt sample tubes at the vacuum sampling loop and pneumatic sample generator modules, respectively. While the charging mechanism will be deployed in FY22, the discharge mechanism was tested in FY21 and is described here. The solid salt tube transfer method was deployed at one of Argonne’s engineering-scale electrorefiners to implement at-line high-throughput pneumatic micro-sample generation capabilities. The approach was used to generate precise uranium- and lanthanide-bearing electrorefiner micro-samples with the specific dimensions requested by researchers at Los Alamos National Laboratory for use in testing their novel microcalorimeter x-ray techniques. The solid salt transfer mechanism proved not only to be an effective means of integrating the precision sample generator with vacuum sampling, but also improved the performance of the sampler generator. To discharge salt from the sample tubes at the sampler generator, tube segments were inserted directly into the sample generator’s Helmholtz chamber and pressure pulse actuations were used to generate precision molten salt samples directly from the tube segments. The direct insertion of sample tubes into the sample generator enabled rapid loading of the salt and prevented salt from contacting most of the interior surfaces of the sample generator, which eliminated cross-contamination between runs. The vacuum sampling-loop tube charging mechanism will support high-throughput tube sampling operations by employing a dynamic vacuum filling process to fill short charge tubes that are configured to be rapidly connected and disconnected from the loop. The dynamic vacuum sampling operation will be automated, and sample tube handling can be executed with simple overhead actuation. Because the modular sampling approach described here eliminates the need for new high-radiation sample handling capabilities, salt-wetted seals, salt-wetted moving parts, and heated transfer lines outside the electrorefiner, it will address most of the remaining technical challenges for the at-line deployment of high-precision analytical techniques which will enable significant reductions in the time delay for sampling-based high-precision accountancy measurements.

42 ENGINEERING↗
DOE OSTI2020

Improved Fireset Acceptance Using Established Evaluation Measurements

As new insight is gained into the relationship between firesets and detonators, tighter control of the circuit parameters is desired to maintain consistent and optimum system performance. An analysis of the established acceptance method reveals that it has insufficient precision to guarantee a uniform population of units. While the production has been historically very uniform, the uniformity has been primarily due to the quality and consistency of the manufacturing process rather than to the stringency of the acceptance criteria. The established method of evaluating and accepting firesets for the stockpile has been to discharge the units into a representative load and to record the output current waveform. Three characteristics of the output waveform (Peak Current, Rise Time, and Pulse Width) are then analyzed and an acceptance window is applied directly to these measurements. The purpose of this paper is to introduce a new approach that incorporates these same established measurements. However, instead of applying acceptance criteria to the three measurements directly, rather these measurements are used to evaluate the circuit values of capacitance, inductance and resistance to provide a more stringent and uniform acceptance criteria.

42 ENGINEERING↗
DOE OSTI2023

In-situ coating of silicon-rich films on tokamak plasma-facing components with real-time Si material injection

Abstract Experiments have been conducted in the DIII-D tokamak to explore the in-situ growth of silicon-rich layers as a potential technique for real-time replenishment of surface coatings on plasma-facing components (PFCs) during steady-state long-pulse reactor operation. Silicon (Si) pellets of 1 mm diameter were injected into low- and high-confinement (L-mode and H-mode) plasma discharges with densities ranging from 3.9– 7.5 × 10 19 m −3 and input powers ranging from 5.5 to 9 MW. The small Si pellets were delivered with the impurity granule injector at frequencies ranging from 4 to 16 Hz corresponding to mass flow rates of 5–19 mg s −1 (1– 4.2 × 10 20 Si s −1 ) at cumulative amounts of up to 34 mg of Si per five-second discharge. Graphite samples were exposed to the scrape-off layer and private flux region plasmas through the divertor material evaluation system to evaluate the Si deposition on the divertor targets. The Si II emission at the sample correlates with silicon injection and suggests net surface Si-deposition in measurable amounts. Post-mortem analysis showed Si-rich coatings containing silicon oxides, of which SiO 2 is the dominant component. No evidence of SiC was found, which is attributed to low divertor surface temperatures. The in-situ and ex-situ analysis found that Si-rich coatings of at least 0.4–1.2 nm thickness have been deposited at 0.4–0.7 nm s −1 . The technique is estimated to coat a surface area of at least 0.94 m 2 on the outer divertor. These results demonstrate the potential of using real-time material injection to form Si-enriched layers on divertor PFCs during reactor operation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Residual Stress Measurements in Extreme Environments for Hazardous, Layered Specimens

In nuclear fuel plates of low-enriched U-10Mo (LEU) clad with aluminum by hot isostatic pressing (HIP), post-irradiation stresses arising during reactor shutdown are a major concern for safe reactor operations. Measurement of those residual stresses has not previously been possible because the high radioactivity of the plates requires handling only by remote manipulation in a hot cell. The incremental slitting method for measuring through-thickness stress profiles was modified, and a system for automated, remote operation was built and tested. Experimental modifications consisted of replacing electric-discharge machining (EDM) with a small end mill and strain-gauge measurements with cantilever displacement measurements. The inverse method used to calculate stresses was the pulse-regularization method modified to allow discontinuities across material interfaces. The new system was validated by comparing with conventional slitting on a depleted U-10Mo (DU) fuel plate. The new system was applied to two measurements each on six as-fabricated (pre-irradiation) LEU miniature fuel plates. Variations between the measurements at two locations in the same plate were strongly correlated with measured geometrical heterogeneity in the plate—a tilt in the fuel foil. Compressive stresses in the U-10Mo were shown to increase from 20 to 250 MPa as the ratio of aluminum thickness to U-10Mo thickness increased causing increased constraint during cooling. Faster cooling rates during processing also increased stress magnitudes. The measurements trends agreed with data in the literature from similar plates made with DU, which further validates the method. Because other methods are impractical in a hot cell, the modified slitting method is now poised for the first measurements of post-irradiation stresses.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Preliminary Kinetic Analysis of Non-Equilibrium Plasma- Assisted Methanol Pyrolysis and Oxidation Experiments

Efforts to enhance power generation efficiency and reduce emissions have driven interest in novel combustion techniques, including non-equilibrium plasma (NEP) ignitors. NEP ignitors show promise in improving energy conversion efficiency, fuel reforming, emission control, and lean-flammability limits. However, their adoption is hindered by a limited understanding of the interplay between plasma-enhanced combustion and thermal chemistry, particularly for complex fuels under engine-relevant conditions. Developing experimentally validated kinetic mechanisms is therefore critical. Additionally, the increasing interest in renewable biofuels like ethanol and methanol, coupled with the desirable qualities of NEP ignitors, presents a compelling opportunity for study. Therefore, this work acts as an extension of a previous work (Bopaiah et al., 2023) pertaining to the experimental results of NEP-assisted methanol pyrolysis and oxidation. Experiments were performed with a custom-built plasma flow reactor at 0.5 atm and temperatures from 523-1203 K. All reactive mixtures are extremely diluted to minimize exothermicity due to reactivity, allowing isothermal assumptions and the isolation of plasma chemistry from thermal chemistry. A dielectric barrier discharge plasma, at 14 kV and 15 ns full-width half maximum, was applied to the reactive mixture at varying frequencies to maintain the number of pulses with increasing temperature. Steady-state product speciation was performed downstream of the reactor with ex-situ GC/MS diagnostics. The attained experimental results were examined through in-depth analysis performed by means of an in-development plasma-coupled kinetic mechanism. As discussed in the previous work, the plasma significantly accelerates methanol pyrolysis, increasing stable intermediate production, including oxygenated and nitrile species. Plasma-assisted oxidation shows even faster fuel consumption compared to pyrolysis and a 200 K ignition shift compared to thermal oxidation. For plasma-assisted pyrolysis, the model demonstrates that accelerated fuel consumption stems from dissociative quenching of excited N2 states with fuel and H2, generating H radicals that react to rapidly form CH3 and CH2OH radicals. At low temperatures, these radicals recombine to produce oxygenates, while CH3 drives nitrile and hydrocarbon formation at higher temperatures. While the model captures pyrolysis trends well, discrepancies in methane, ethylene, and ethanol predictions are present. Similarly, the model faces challenges in accurately representing plasma-assisted oxidation, predicting a much steeper fuel gradient and ignition 100 K earlier than the experiment. While a similar scheme to pyrolysis is nested in the reaction pathway, the enhancement of the O and H radical fluxes and their initiation of the OH and HO2 radical pools dominate fuel and intermediate oxidation. The overestimation of these processes is shown to be responsible for the divergence of model from experiment. While the modelling predictions of this preliminary mechanism are not perfect, they serve as a valuable starting point. Primarily, they elicited new reaction pathways that are not otherwise possible in thermal chemistry induced reaction kinetics. The results also provide a basis for the future work that should be performed. For example, theoretical and experimental studies on excited nitrogen species and fuel/fuel radical interactions, quantification of the NOx production, and the kinetics behind the slow ignition observed in oxidation should be emphasized.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2026

Developing the hybrid scenario in DIII-D and KSTAR for W-compatible long-pulse operation

Long-pulse, high-performance operation with tungsten plasma-facing components is a crucial challenge for achieving steady-state (SS) goals in ITER and future fusion devices. This paper presents a joint international effort between the DIII-D and KSTAR tokamaks aimed at demonstrating the compatibility of the high q 95 ~ 6 hybrid scenario with a tungsten divertor and superconducting coils. A DIII-D hybrid scenario recipe is successfully tailored to KSTAR’s operational constraints, which facilitates cross-device studies. The results show successful 30 s long-pulse operation in KSTAR at a normalized beta (β N = 2.4) with a benign m/n = 4/3 mode and effective mitigation of tungsten accumulation. Despite this success, the KSTAR scenario exhibits a greater than 25% reduction in thermal confinement compared to the DIII-D reference. To investigate this discrepancy, we performed a predictive TGYRO validation study, which suggests that the difference is likely caused by a weaker temperature pedestal in the KSTAR discharge due to a higher and narrower density pedestal. In addition, such lower thermal confinement leads to higher impurity accumulation, possibly due to a change in neoclassical transport with increased inward pinch, which further degrades global confinement. We also report that stationary, long-pulse operation with sustained thermal confinement requires consistent fueling and wall conditioning. These findings highlight the importance of optimized fueling and real-time wall conditioning in achieving a high temperature pedestal and strong global confinement during stable long-pulse operation. We propose potential approaches toward fully SS, long-pulse operation, including real-time wall conditioning using an impurity dropper in KSTAR and future tokamaks.

DIII-D↗
DOE OSTI2024

Effects of growth rate and dynamic substrate tilt on properties of Au-Ta alloy films deposited by high-power impulse magnetron sputtering

Gold-tantalum (Au—Ta) alloys are promising for next-generation hohlraums for magnetically-assisted indirect-drive inertial confinement fusion. Hohlraum fabrication involves sputter deposition of ultrathick coatings on sphero-cylindrical substrates. The control of physical properties of such coatings remains a challenge. Here, in this work, we systematically study effects of the growth rate and dynamic substrate tilt on properties of AuTa 4 films deposited onto rotating planar substrates mounted at different tilt angles to mimic different regions of the sphero-cylindrical surface of a hohlraum. We use high-power impulse magnetron sputtering (HiPIMS) in the constant charge per pulse mode with a pulse duration of 100 μs, a charge per pulse of 190 μC, a peak target current of about 3 A, and the pulse frequency varied in the range of 400–1400 Hz. The Langmuir probe, mass-resolved ion energy spectrometry, and optical emission spectroscopy are used to monitor plasma discharge characteristics in order to isolate and study effects of the growth rate. The deposition rate and the ballistics and energetics of depositing species are estimated by Monte Carlo simulations. Results show that the film microstructure, crystallographic phase, residual stress, and electrical resistivity strongly depend on both the deposition rate and substrate tilt, highlighting their critical role in tailoring properties of Au—Ta films during hohlraum fabrication.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Long plasma duration operation analyses with an international multi-machine (tokamaks and stellarators) database

Combined high-fusion performance and long-pulse operation is one of the key integration challenges for fusion energy development in magnetic devices. Addressing these challenges requires an integrated vision of physics and engineering aspects with the purpose of simultaneously increasing time duration and fusion performance. Significant progress has been made in tokamaks and stellarators, including very recent achievement in duration and/or performance. This progress is reviewed by analyzing the experimental data (109 plasma pulses with a total of 3200 data points, i.e. on average 29 data per pulse) provided by ten tokamaks (in alphabetical order: Axially Symmetric Divertor Experiment Upgrade, DIII-D, Experimental Advanced Superconducting Tokamak, Joint European Torus, JT-60 Upgrade, Korea Superconducting Tokamak Advanced Research, tokamak à configuration variable, Tokamak Fusion Test Reactor, Tore Supra, W Environment in Steady-State Tokamak) and two stellarators (Large Helical Device and Wendelstein 7-X) expanding the pioneering work of Kikuchi (Kikuchi M. and Azumi M. 2015 Frontiers in Fusion Research II: Introduction to Modern Tokamak Physics (Springer)). Data have been gathered up to January 2022 and coordination has been provided by the recently created International Energy Agency-International Atomic Energy Agency international Coordination on International Challenges on Long duration OPeration group. By exploiting the multi-machine international database, recent progress in terms of injected energies (e.g. 1730 MJ in L-mode, 425 MJ in H-mode), durations (1056 s in L-mode, 101 s in H-mode), injected powers, and sustained performance will be reviewed. Progress has been made to sustain long-pulse operation in tokamaks and stellarators with superconducting coils, actively cooled components, and/or with metallic walls. The graph of the fusion triple products as a function of duration shows a dramatic reduction of, at least two orders of magnitude when increasing the plasma duration from less than 1 s to 100 s. Indeed, long-pulse operation is usually reached in dominant electron-heating modes at reduced density (current drive optimization) but with low ion temperatures ranging from 1 to 3 keV for discharges above 100 s. Difficulties in extending the duration may arise from coupling high heating powers over long durations and the evolving plasma-wall interaction towards an unstable operational domain. Possible causes limiting the duration and critical issues to be addressed prior to ITER operation and DEMO design are reported and analyzed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

First lower hybrid current drive experiments on the WEST tokamak

The first lower hybrid current drive experiments in the full tungsten WEST tokamak are reported. Good wave coupling is found at rather low plasma current (q 95 ~4.3) and medium density (n e ~3×10 19 m -3 ). Reflection coefficient is in agreement with the expectation from the linear theory of coupling. With low reflection coefficients, 5MW was coupled for 2 seconds. High central electron temperature, up to 5keV, is achieved at ne = 3-4×10 19 m -3 . Flat and even hollow profiles of tungsten density are derived from the bolometry diagnostic. The stored thermal energy follows the H96-P scaling law with very slight degradation with density. The current drive efficiency has been assessed in low loop voltage (V L ~0.15V) discharges. Low plasma current operation and rather high effective charge (Z eff ~3) lead to modest current drive efficiency (η = 0.5-0.65 × 10 19 A.W -1 m -2 ). Long pulse operation (~30s) with high LHCD power (P LH =2.7MW) is achieved with stationary parameters, in particular electron and impurity densities, with the upper water-cooled tungsten divertor.

Goniche, M.↗
DOE OSTI2025

Experimental progress and future plans on spherical tokamak, QUEST

QUEST (Q-shu university experiment with steady state spherical tokamak) aims at effective plasma current start-up and stable maintenance of plasma discharge. To solve the inherent problems in a spherical tokamak (ST) arising from insufficient space for placing the inductive center solenoid, electron cyclotron current drive (ECCD) and transient coaxial helicity injection (T-CHI) are implemented as a non-inductive plasma start-up method in QUEST. Efficient ECCD assisted by energetic electrons could be achieved. By combining control of the wave injection angle and application of a negative toroidal electric field, the bulk electron temperature could be raised up to 1 keV due to selective wave power absorption in the bulk electrons. The plasma current of over 50 kA contained within the closed flux surface could be obtained with a floating single biased electrode placed on lower divertor plates for T-CHI. Long-pulse operations on QUEST are impeded frequently due to wall saturation and subsequent density runaway caused by fuel particle imbalance. Since 2014, a unique tool called the ‘hot wall’ has been implemented to overcome the imbalance. The hot wall has a capability to regulate its surface temperature using a heater and two water cooling channels. With the help of the hot wall, 6 h discharges were obtained in 2020. Cooling down of the surface of the hot wall was significantly effective in recovering the wall pumping and was useful to extend the pulse duration. Augmentation of the toroidal magnetic field, B T up to 0.5 T from 0.25 T and a continuous wave (CW) gyrotron of 28 GHz are planned for QUEST in the near future. As raising B T provides a fundamental resonance of electron cyclotron waves (ECWs) with 28 GHz, more effective plasma current start-up and heating will be performed. Long-pulse operations with higher plasma parameters are expected.

QUEST↗
DOE OSTI2021

Resolving ECRH deposition broadening due to edge turbulence in DIII-D

Microwave heat pulse propagation experiments have demonstrated a correlation between millimeter-scale turbulence and deposition profile broadening of electron cyclotron (EC) waves on the DIII-D tokamak. In a set of discharges in DIII-D, a variation in edge density fluctuations on the mm-scale is associated with 40%–150% broader deposition profiles, expressed in terms of normalized minor radius, as compared with equilibrium ray tracing. The 1D power profile is determined from transport analysis of the electron temperature response to EC power modulation using perturbative analysis with a square wave power modulation at 20–70 Hz, producing a series of Fourier harmonics that are fit collectively to resolve transport. Fitting an integrated heat flux expressed in the Fourier basis of the modulation to diffusive, convective, and coupled transport terms in a linear model can resolve the broadened EC deposition width from the power perturbation to resolve a broadening in each case. The best fit degree of beam broadening observed scales approximately linearly with the Doppler backscattering measured fluctuation level in the steep gradient region. Quantifying the effect of edge fluctuation broadening on EC current drive power needs of future devices will require 3D full-wave codes that can be validated on the current generation of machines. These DIII-D experiments provide a quantitative measure of fluctuation effects and a dataset to benchmark full-wave simulations that can model and eventually predict nonlinear effects neglected by 1D equilibrium beam and ray tracing.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Fuel recycling and impurity characteristics in long-pulse H-mode plasmas with full metal and dynamically coated walls on EAST

We report the basic behaviors of fuel recycling and impurity accumulation during >100 s long-pulse H-mode plasma under full metal wall conditions on EAST. Significant fuel recycling and impurity rising, particularly from heavy impurities, have been observed when operating with a bare metal wall or a deteriorate real-time coated wall, which severely limits the duration of H-mode discharges. To address this issue, a novel dynamic wall coating technique combining feedforward and feedback controls has been successfully developed. The feedforward control presets the Li powder injection rate based on prior experimental observations, whereas the feedback control dynamically modulates the Li injection rate in response to real-time Li-II line emission measurements. Using this approach, a 605 s H-mode plasma has been achieved with fuel recycling and impurity level maintained stable. This result extends the previous record of a 403 s long-pulse H-mode plasma Gong et al (2024 Nucl. Fusion 64 112013) by over 200 s. It demonstrates the effectiveness of the dynamic powder injection technique in controlling fuel recycling and impurities accumulation, while prolonging plasma duration. These findings offer valuable insights into potential applications of other low-Z powder, such as boron, in ITER.

fuel recycling↗
DOE OSTI2022

Simultaneous single-shot rotation–vibration non-equilibrium thermometry using pure rotational fs/ps CARS coherence beating

Here, we report the development of a simple and sensitive two-beam hybrid femtosecond/picosecond pure rotational coherent anti-Stokes Raman scattering (fs/ps CARS) method to simultaneously measure the rotational and vibrational temperatures of diatomic molecules. Rotation–vibration non-equilibrium plays a key role in the chemistry and thermalization in low-temperature plasmas as well as thermal loading of hypersonic vehicles. This approach uses time-domain interferences between ground state and vibrationally excited N 2 molecules to intentionally induce coherence beating that leads to apparent non-Boltzmann distributions in the pure rotational spectra. These distortions enable simultaneous inference of both the rotational and vibrational temperatures. Coherence beating effects were observed in single-shot fs/ps CARS measurements of a 75 Torr N 2 DC glow discharge and were successfully modeled for rotational and vibrational temperature extraction. We show that this method can be more sensitive than a pure rotational fs/ps CARS approach using a spectrally narrow probe pulse. Lastly, we experimentally measured the beat frequencies via Fourier transform of the time-domain response and obtained excellent agreement with the model.

42 ENGINEERING↗
DOE OSTI2023

Long-pulse high-performance H-mode plasmas achieved on EAST

A record duration of a 310 s H-mode plasma (H 98y2 ~ 1.3, n e /n GW ~ 0.7, f BS > 50%) has been recently achieved on experimental advanced superconducting tokamak (EAST) with metal walls, exploiting the device's improved long-pulse capabilities. The experiment demonstrates good control of tungsten concentration, core/edge MHD stability, and particle and heat exhaust with an ITER-like tungsten divertor and zero injected torque, establishing a milestone on the path to steady-state long-pulse high-performance scenarios in support of ITER and CFETR. Important synergistic effects are leveraged toward this result, which relies purely on radio frequency (RF) powers for heating and current drive (H&CD). On-axis electron cyclotron heating enhances the H&CD efficiency from lower hybrid wave injection, increasing confinement quality and enabling fully non-inductive operation at high density (n e /n GW ~ 70%) and high poloidal beta (β P ~ 2.5). A small-amplitude grassy edge localized mode regime facilitates the RF power coupling to the H-mode edge and reduces divertor sputtering/erosion. The high energy confinement quality (H 98y2 ~ 1.3) is achieved with the experimental and simulated results pointing to the strong effect of Shafranov shift on turbulence. Transport analysis suggests that trapped electron modes dominate in the core region during the record discharge. The detailed physics processes (RF synergy, core-edge integration, confinement properties, etc.) of the steady-state operation will be illustrated in the content. In the future, EAST will aim at accessing more relevant dimensionless parameters to develop long-pulse high-performance plasma toward ITER and CFETR steady-state advanced operation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗