The International Thermonuclear Experimental Reactor (ITER) neutron activation system (NAS) is an essential diagnostic system designed to measure the total neutron yield and the first-wall fluence in the ITER Tokamak. NAS principle is based on the neutron activation of small sample materials placed in the vicinity of the plasma using pneumatic transfer lines. The induced activity in the samples is subsequently measured using a gamma-ray counting station, enabling reconstruction of the total neutron yield. Accurate neutron transport modelling of both the NAS apparatus and the tokamak is essential for reliable measurements. This study systematically quantifies the primary sources of uncertainty in the NAS neutronic model, focusing on the geometric modelling of the NAS irradiation ends and tokamak environment, as well as uncertainties in nuclear data. Results indicate that the NAS can achieve a measurement accuracy of approximately 13% in deuterium-deuterium (DD) plasmas, with the largest uncertainty attributed to the detailed geometry of the diagnostic first-wall (DFW). To address this, in-situ calibration is paramount to identify unforeseen measurement errors and to mitigate the uncertainties in computational models. Utilizing a well-characterized neutron generator for NAS calibration could reduce the neutron yield measurement errors below 8%. These findings underscore the importance of precise modelling and calibration procedures for accurate neutron measurements during ITER's start of research operation (SRO).

The study is an analysis of the strength properties of a unique diagnostic system called Upper Vertical Neutron Camera (UVNC) under the loads of various nature. The UVNC includes a DN10 water cooling system, six detector units, electrical feedthroughs, and cables. Combinations of mechanical, thermal, seismic and electromagnetic loads were considered. The implementation of multiphysical processes is carried out in ANSYS Software, and the previously obtained data on electromagnetic and seismic loads, as well as thermal fields in Normal Operation and Baking modes are used in this study as initial data for mechanical formulations. The results of the structural analysis demonstrate a sufficient margin of safety of the main structural elements of the model while maintaining operational properties. In the article described and justified totally new design of developing system under extreme neutron fluxes, high thermal loads, and combined mechanical stresses, taking into account all the unique operational factors of the ITER facility.

The present study experimentally investigates non-flamelet behavior leading to extinction in a NonPremixed Flame (NPF) and a Partially Premixed Flame (PPF) in a turbulent counterflow configuration. Both flames at Re-t similar to 900 are indistinguishable in terms of the turbulence properties that are imposed at the cold boundaries and persist up to the mixing layer. For each extinction event, the perturbation that leads to the first breach of the OH layer is tracked back in time in a Lagrangian manner using high-speed stereoscopic PIV and OH-PLIF imaging techniques, allowing the reconstruction of the time sequence of strain rate and vorticity that leads to flame extinction. The NPF is found to be more prone to extinction than the PPF, which is at odds with the computed laminar extinction strain rate, which is 23 % larger in the NPF than in the PPF, implying a greater resistance to strain for the NPF. Extinction appears to be caused by a combination of relatively intense strain rate and/or vorticity pockets interacting with the flame and causing a tear of the OH layer. The maximum strain rate norm exceeds the computed extinction limit in >85 % of the cases for the PPF, whereas it does so in approximately 75 % of the cases for the NPF, revealing a more pronounced strain rate effect on the extinction process for the PPF. Vorticity plays multiple roles in extinction. It manifests itself as: i) a pair of counterrotating vortices approaching the flame from either or both sides, creating a region of high strain rate; ii) a single vortex interacting with the flame by diluting the reactants with inert, thereby, weakening the flame; and iii) a vortex penetrating the oxidizer layer, making it thicker and, possibly, disrupting the laminar flame structure. The last two scenarios may explain extinction without a history of remarkably high strain rates. A 35 % reduction in the overall strain rate of the flames resulted in nearly complete suppression of extinction events in both PPF and NPF.

The ITER Radial Gamma-Ray Spectrometer (RGRS) consists of three gamma-ray detectors observing the plasma through three collimated, coplanar, radial lines of sight (LoS). The system was initially designed to monitor the runaway electron emission and the alpha-particle density profile [Nocente et al., Nucl. Fusion 57, 076016 (2017)]. This work presents a novel technique for measuring the fusion power during D-T operation using the RGRS. This method is based on the absolute measurement of the 17 MeV fusion gamma-rays and a semi-analytical computation of their transport from the plasma source to the detectors. This approach was initially developed and tested at JET during the second D-T campaign (DTE2) on a single LoS diagnostic [Dal Molin et al., Phys. Rev. Lett. (submitted) (2024); Rebai et al., Phys. Rev. C (submitted) (2024); and Marcer et al., Nucl. Fusion (unpublished) (2024)]. This work exploits the multiple LoS of the RGRS to create a combined virtual diagnostic whose detected fraction of the total plasma emission is less affected by variations in the plasma emission profile, reducing systematic uncertainties on the estimated total emission, compared to the individual detectors.

The higher efficiency of superconducting radio-frequency (SRF) cavities compared to normal -conducting ones enables the development of high-energy continuous-wave linear accelerators (linacs). Recent progress in the development of high-quality Nb3Sn film coatings along with the availability of cryocoolers with high cooling capacity at 4 K makes it feasible to operate SRF cavities cooled by thermal conduction at relevant accelerating gradients for use in accelerators. A possible use of conduction-cooled SRF linacs is for environmental applications, requiring electron beams with energy of 1-10 MeV and 1 MW of power. We have designed a 915 MHz SRF linac for such an application and developed a prototype single-cell cavity to prove the proposed design by operating it with cryocoolers at the accelerating gradient required for 1 MeV energy gain. The cavity has a -3 mu m thick Nb3Sn film on the inner surface, deposited on a -4 mm thick bulk Nb substrate and a bulk -7 mm thick Cu outer shell with three Cu attachment tabs. The cavity was tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A horizontal test cryostat was designed and built to test the cavity cooled with three Gifford-McMahon cryocoolers. The rf tests of the conduction-cooled cavity, performed at General Atomics, achieved a peak surface magnetic field of 50 mT and stable operation was possible with up to 18.5 W of rf heat load. The peak frequency shift due to microphonics was 23 Hz. These results represent the highest peak surface magnetic field achieved in a conduction-cooled SRF cavity to date and meet the requirements for a 1 MeV energy gain.

The absolute calibration of the detection efficiency for the measurement of the total neutron yield in the whole plasma is one of the most important issues in neutron diagnostics. In ITER, a compact deuterium-tritium (D-T) neutron generator will be used as a neutron source for the neutron calibration prior to the D-T plasma experiments, where the neutron source will be moved in the vacuum vessel. Neutronic simulations of neutron diagnostic calibrations have been carried out for the strategy and scheduling of the calibration experiments. We have established a simplified 360 degrees ITER model for the simulation, which includes neutron flux monitors (NFMs) in an equatorial port (EQ), micro fission chambers, diverter neutron flux monitors, and a neutron activation system. At first, angular neutron spectra of the compact D-T neutron generator have been evaluated by MCNP calculations. We evaluate the discrepancies among the detection efficiencies to be obtained by the neutron calibration experiment, those by idealistic D-T ring source, and actual detection efficiencies for the plasma neutron source. Point efficiency measurement using the compact D-T neutron generator facing NFM in EQ#1 is an effective method for the NFM calibration.

Electron beam irradiation has been successfully implemented in industrial processes for many years and is now under consideration for mitigation of a variety of emerging issues. Of specific interest are energy and environmental applications such as flue gas treatment and wastewater reclamation [1]. Superconducting radio-frequency (SRF) accelerator technology is a novel approach to meet the ambitious electron beam power requirements for these applications [2], but significant development is required.

DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter- I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high- Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L–H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼ 8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co- I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.

Temperature measurements in environments that preclude the use of conventional methods are possible with remote sensing of thermal emission in the mm-wave to THz range of frequencies. A 300-GHz radiometer is demonstrated to be an effective linear temperature sensor. Measurements with a THz blackbody source corroborate the nominal emissivity value of the target to be close to unity. The temperature inferred from radiometry measurements of a target with unknown emissivity is consistent with the physical temperature of the target. Field testing of the radiometer at a nuclear fusion facility for reactor-wall measurements is planned.

power. Each of these developments has been individually proven and an effort is underway at the Illinois Accelerator Research Center at Fermilab to integrate them into the first prototype of an entirely new class of industrial SRF-based accelerators. These accelerators will enable robust, turn-key operation with very high electrical efficiency. The accelerator prototype under design will be capable of 10 MeV beam, CW operation, and 250 kW of electron beam power. These modular systems are small enough to be palletized and transported to the point of use. Their high electrical efficiency mean that portable power generation systems can be enable their use in mobile applications. The goal is a compact, cost-effective, high-power accelerator suitable for many of the applications covered by this conference. Fermilab is actively working to build the prototype. The end-product will be a commercially available, robust, turn-key system for applications requiring reliable electron beam or X-ray irradiation. Keywords: accelerator, applications, conduction-cooling, cryogen-free, industrial, super-conducting RF.

We present the technical and engineering design of a medium energy (10 MeV) and high average power (1000 kW) electron-beam accelerator intended for irradiation treatment of high-volume industrial and municipal wastewater. The accelerator uses a Nb3Sn superconducting radio-frequency (SRF) cavity for producing the high average beam power with >90% rf to beam efficiency. The design of the accelerator is tailored for industrial settings by adopting the cryocooler conduction-cooling technique for the SRF cavity instead of a conventional liquid helium bath cryosystem. The technical design is supplemented with a detailed analysis of capital and operating cost of the accelerator. The designed accelerator can treat up to 12 million gallons per day of wastewater, requires capital of ???$8 M for construction, and has ???13.5 ??/ton/kGy in material processing cost.

Helicon current drive (CD), also called fast wave CD in the lower hybrid range of frequencies, has long been regarded as a promising CD tool for reactor grade plasmas.A newly installed MW-level system at DIII-D will be the first test of this technology in reactor-relevant plasmas, in the sense that full single-pass absorption is expected.A 30-module traveling wave antenna has been installed and optimized in-vessel in early 2020.The linear electromagnetic characteristics of the unloaded module array have been extensively tested both on the bench and in the vessel at instrumentation power levels.Excellent performance has been achieved, ∼2% reflected power and ∼1.5% dissipated power per module in air, in a 10 MHz band around 476 MHz.Stripline feeds on both ends of the antenna allow either co or counter CD.The installation of a 1.2 MW klystron and associated high-power electronics was completed in Fall 2020.Commissioning of the antenna is ongoing.An important goal of this experiment is to validate the helicon CD physics basis using an extensive set of new and upgraded diagnostics.

Further theoretical and experimental studies have been performed on the magnetrons with external reactive loads either with a low-Q RF cavity or with a power combiner like the TM010 mode or Magic-tee type. The frequency pushing by a trimming magnetic field and pulling by the reflection between the magnetron and reactive load have been shown to improve the injection phase locking stability and enhance the locking bandwidth compared to the scheme to a matched load only. This principle has been further studied based on S.C. Chen’s model [1, 2], equivalent circuit simulation, analytical calculation and finally compared with experimental data from the magnetron test stands at 2450 MHz.

We present the technical and engineering design of a medium energy (10 MeV) and high average power (1 MW) electron beam accelerator intended for irradiation treatment of high volume industrial and municipal wastewater. The accelerator uses superconducting radiofrequency (SRF) cavity technology for producing the high average beam power with $>$90% RF to beam efficiency. The design of the accelerator is simplified and tailored for industrial settings by adopting the cryocooler conduction-cooling technique for the SRF cavity instead of a conventional liquid helium bath cryo-system. The technical design is supplemented with a detailed analysis of capital and operating cost of the accelerator. The designed accelerator can treat up to 12 million gallons per day of wastewater, requires capital of $\sim\$$8M for construction, and has $\sim$13.5 cents/ton/kGy in material processing cost.

Data assimilation techniques are investigated for integrating high-speed high-resolution experimental data into large-eddy simulations. To this end, an ensemble Kalman filter is employed to assimilate velocity measurements of a turbulent jet at a Reynolds number of 13,500 into simulations. The goal of the current work is to examine the behavior of the assimilation algorithm for state estimation of turbulent flows that are of relevance to engineering applications. This is accomplished by investigating the impact that localization, measurement uncertainties, assimilation frequency, data sparsity and ensemble size have on the estimated state vector. For the flow configuration and computational setup considered in this study an optimal value of the localization radius is identified, which minimizes the error between experimental data and state vector. The impact of experimental uncertainties on the state estimation is demonstrated to provide solution bounds on the assimilation algorithm. It is found that increasing the number of ensembles has a positive impact on the state estimation. In comparison, decreasing the assimilation frequency or reducing the experimental data available for assimilation is found to have a negative impact on the state estimation. These findings demonstrate the viability of assimilating measurements into numerical simulations to improve state estimates, to support parameter evaluations and to guide model assessments.

Data assimilation techniques are investigated to determine how high-speed experimental measurements can be infused into a combustion simulation with the goal of capturing transient combustion events and isolating model deficiencies. To this end, an ensemble Kalman filter (EnKF) is employed to assimilate simultaneous measurements from tomographic PIV and OH-PLIF into a combustion LES of a turbulent DME jet flame, taking into consideration experimental uncertainties and modeling errors. It is shown that by assimilating experimental data, EnKF improves the prediction of the extinction and reignition dynamics observed in this flame. Subsequently, the capability of the assimilation method in evaluating the model performance is examined by considering an assimilation sequence. It is shown that the combustion model investigated (namely a flamelet/progress variable model) exhibits a tendency to relax towards a more reactive state, indicating a deficiency in quantitatively predicting the extent of extinction and reignition with this particular model.

A series of turbulent, piloted dimethyl ether (DME)/air jet flames (Sandia DME flames D–G’), with Reynolds numbers ranging from 29,300 to 73,250, has been simulated using a sparse-Lagrangian multiple mapping conditioning (MMC) approach coupled to a large eddy simulation (LES) flow field solver. Mixing between the Monte-Carlo particles is modelled by a generalised form of MMC combined with a sparse distribution of particles leading to significant computational savings compared to what is required for conventional mixing models. This is achieved by pairwise mixing of particles that are selected dependent on their distance in an extended space comprised of a reference variable, given by the LES mixture fraction, and spatial location. The MMC-LES method successfully predicts the flame structure and composition field for the full flame series. Numerical results are compared against conditional statistics and spatially resolved experimental data acquired with Raman/Rayleigh scattering and laser-induced fluorescence measurements. They show good agreement even for flame DME-G’ where large turbulence-chemistry interactions lead to significant local extinction and large deviations from a flamelet structure. The influence of the mixing time on the predicted flame structure is investigated, and the systematic validation of the time scale models with the aid of measurements of the entire flame series has corroborated the findings of earlier DNS and single flame studies: a modified time scale model is needed to provide accurate predictions of conditional fluctuations and thus of possible deviations from a flamelet-like combustion regime.