We report the development and validation of a new neutron detector, the spherical moderator counter (SMC), which represents the next generation of long counter technology. Unlike conventional cylindrical designs, the SMC employs a spherical moderator geometry, optimized by Monte Carlo transport simulations to achieve a near isotropic angular response and a broad, flat energy sensitivity. The prototype detector has been extensively tested with a wide range of neutron energies, i.e., neutrons coming from d-D and d-T accelerators, Cf-252 spontaneous fission, Am-Be (alpha and n) reactions, fission reactors, and spallation sources, covering the entire energy range from thermal to several tens of MeV. The experimental results demonstrate that SMC achieves a uniform response over 4 pi steradians, with an angular deviation of less than 6% for fast neutrons, and maintains adequate sensitivity from 0.01 eV to 20 MeV. These findings confirm that SMC not only addresses the inherent limitations of traditional cylindrical long counters but also establishes a versatile and reliable platform for neutron metrology, with significant potential for applications in next-generation fusion and advanced nuclear technologies.

With the advancement of burning plasma operation goals, diagnostic systems in nuclear fusion reactors face a critical challenge: their key components will be continuously exposed to high-flux neutron and gamma radiation over long-term operation. The diagnostic Port Plug (PP), serving as the platform for installing diagnostic systems and other auxiliary devices, constitutes the first line of defense for the diagnostic systems against the nuclear environment. Based on the current Equatorial J Port Plug (JPP) design, this study employed Monte Carlo methods to perform a comprehensive neutronics analysis of the PP and its key components, covering neutron and gamma fluxes, nuclear heating, and displacement per atom (DPA).The results indicate that the flux distribution is mainly influenced by component layout and diagnostic openings. Nuclear heating analysis shows that gammainduced heating dominates in high-Z optical mirror assemblies, while the maximum DPA reaches 6.43 & times; 10-3, suggesting that plasma-facing key components may be subject to potential radiation-induced damage. This study provides a quantitative assessment of the neutron and gamma environment, nuclear heating, and radiation damage for the equatorial J-port diagnostic systems, offering fundamental data to guide the design optimization and reliability assurance of future diagnostic systems.

Preliminary results of soft X-ray (SXR) measurements on the Thailand Tokamak-1 (TT-1) have been successfully obtained using a newly developed silicon (Si)-based spectrometer system. This work presents the conceptual design, calibration, installation, and initial experimental results of the Si-based spectrometer implemented on TT-1. SXR emission during the plasma discharge phase was clearly observed.The results indicate that the TT-1 plasma emits SXR photons with energies approximately in the range of 3.6–4.8 keV. These initial results demonstrate significant progress in the development of advanced diagnostic capabilities on TT-1. The Si-based SXR diagnostic is expected to play an important role in improving the understanding of key plasma phenomena in future TT-1 experimental campaigns and to support the development of enhanced plasma performance.

To achieve high-accuracy in-situ calibration of the neutron flux monitor on the Experimental Advanced Superconducting Tokamak (EAST), a systematic comparison of continuous and multi-point calibration approaches is conducted using a full three-dimensional (3D) engineering model. 3D neutron transport simulations for 2.45 MeV neutrons in the complex structural environment of EAST are carried out using MCNP and PHITS. Calibration calculations are conducted for three different source configurations: a toroidal ring line source, 32 coplanar point sources, and a D-shaped volume source representing realistic plasma conditions. Neutron flux responses and energy spectrum at the spherical long counter (SLC) location are quantitatively analyzed. The results show that the differences in neutron flux between the ring source and point source calibration approaches remain within 2.2%. An operational calibration strategy for an upcoming in-situ experiment on EAST using a 1 × 109 n/s D-D accelerator neutron source is proposed. This work establishes quantitative criteria for relating volumetric and point-source models and provides a transferable framework for neutron calibration in EAST.

To advance impurity transport research in Experimental Advanced Superconducting Tokamak (EAST), this study develops a novel Laser Blow-Off (LBO) impurity injection system and presents the first experimental test results on EAST. The system employs a Nd:YAG laser to ablate a thin metal film coated on the quartz glass and inject a tracer amount of impurity atoms into the plasma. The optical system comprises four single-wavelength mirrors and a three-dimensional adjustable focusing lens, which enable control of the spot diameter and precise positioning of the laser spot. Experimental results demonstrate that the system is capable of controlling impurity injection time and quantity without perturbing plasma parameters. The measured temporal evolution of plasma radiation intensity clearly reveals the radial transport process after impurity injection, and the relaxation times at different radial positions are computed to estimate the impurity transport characteristics. The successful deployment of the LBO system provides an effective tool for investigating impurity transport behaviors in the EAST.

A high-performance neutron and gamma-ray collimator was developed to address the challenges of high-precision multi-particle diagnostics, such as deuterium-deuterium (D-D) neutron, deuterium-tritium (D-T) neutron, and gamma-ray, in the extreme radiation environment of fusion devices. The design integrates geometric shielding, material attenuation, and energy-selection optimization. Full-scale three-dimensional Monte Carlo radiation transport simulations were conducted to evaluate the collimator performance in a complex structural environment on the EAST device. After collimation, the peak contributions of 2.5 MeV and 14 MeV neutrons reach 57.47 % and 21.31 % of the total energy spectrum, respectively, demonstrating effective energy discrimination. Predicted neutron spectra under d-T operation in EAST show that the collimator significantly suppresses environmental scattering and enhances directional sensitivity. The results indicate strong potential for dual-mode neutron-gamma-ray diagnostics in future d-T fusion reactors and high applicability to ongoing d-D experiments such as EAST. The collimator has been fabricated and installed on EAST and will be deployed in the upcoming d-T experimental campaigns.

A dedicated real-time detection system (NTM-RTDS) has also been developed to determine the radial position of neoclassical tearing mode (NTM) magnetic islands. Built upon the LabVIEW real-time framework and PXIe architecture, it adopts a distributed upper-lower computer structure that enables high-speed acquisition and real-time processing of signals from magnetic probes and electron cyclotron emission diagnostics. By analyzing perturbation frequencies associated with magnetic island rotation and electron temperature profile variations, the system achieves island localization within a 10 ms cycle. Validation on experimentally advanced superconducting tokamak confirms a detection accuracy of 80.25% in identifying magnetic islands, verifying the system's robustness. The NTM-RTDS thus represents a critical instrument for enabling active, real-time NTM control via electron cyclotron resonant heating, and provides a foundational platform for real-time disruption mitigation strategies in future large-scale fusion experiments, including the international thermonuclear experimental reactor.

High plasma density operation is crucial for a tokamak to achieve energy breakeven and burning plasma. However, there is often an empirical upper limit of electron density in tokamak operation, namely, the Greenwald density limit [Formula: see text], above which tokamaks generally disrupt. Achieving high-density operation above the density limit has been a long-standing challenge in magnetic confinement fusion research. Here, we report experimental results on the Experimental Advanced Superconducting Tokamak (EAST) achieving line-averaged electron density in the range of (1.3 to 1.65) [Formula: see text], significantly above the typical EAST operational range of (0.8 to 1.0) [Formula: see text]. This is performed with electron cyclotron resonance heating (ECRH)-assisted ohmic start-up and sufficiently high initial neutral density. These experiments are shown to operate in the density-free regime first predicted by a recent plasma-wall self-organization theory. These results suggest a promising scheme for substantially increasing the density limit in tokamaks, a critical advancement toward achieving burning plasma.

An x-ray imaging diagnostic system using the Timepix3 detector has recently been developed and installed on the Experimental Advanced Superconducting Tokamak (EAST). The diagnostic system measures the temporal evolution, spatial distribution, and energy spectrum of x-ray signals during plasma discharge with a 16° diagonal field of view, spatial resolution of 4 mm, and broad spectral-energy response range (5–200 keV). Equipped with event-driven capability, the Timepix3 detector captures the coordinates, energy, and arrival time of each photon event with a temporal resolution of 1.56 ns. Herein, the energy resolution and spatial resolution performances of the detector were tested in counting and time-over-threshold modes. The energy resolution of the detector in both modes was within 5 keV. The temporal resolution of the detector and the temporal evolution of x-ray signals were analyzed during plasma discharge experiments on the EAST, harnessing the event-driven capability of the detector for latter analysis. Furthermore, the detector-measured signals were compared with conventional diagnostic signals, confirming the reliability of the Timepix3 detector. Overall, this paper presents the parameter testing results and preliminary experimental diagnostic outcomes.

A time-resolved deuterium-deuterium (D-D) fusion-born triton confinement study, aimed at understanding alpha particle confinement ability, was performed in Experimental Advanced Superconducting Tokamak (EAST) deuterium plasmas for the first time. A scintillating fiber detector was developed for measuring the secondary deuterium-tritium (D-T) neutrons, which provide evidence of triton slowdown, in EAST. The D-D fusion-born triton confinement experiment was performed by measuring secondary D-T neutrons in D-beam-heated D plasma with a plasma current of 400 kA. The secondary D-T neutron signal and its time evolution were obtained using pulse height discrimination analysis. The D-T neutron rate was calculated using the classical energetic ion confinement model to clarify the D-T neutron measurements. The secondary D-T neutron emission rate obtained from the numerical simulation closely agrees with the experimentally obtained results when considering the prompt loss of the tritons.

neutron activation system with two sets of activation terminals was developed in the experimental advanced superconducting tokamak (EAST), and it was implemented in the measurements of the time-integrated triton burnup for the deuterium plasma experiment in EAST. Indium and silicon samples with an energy threshold of 0.3 and 4.0 MeV were used to measure the DD and DT neutron, respectively. The shot-averaged triton burnup ratio was determined by simultaneously measuring the DD and DT neutron yields during plasma discharges. The triton burnup ratio of EAST was found to range from 0.035% to 0.65%, depending on plasma parameters. Due to a better confinement of fast triton, the triton burnup ratio increases with the plasma current and the magnetic field in the range of 400-600 kA and 1.74-2.57 T, respectively. Additionally, the triton burnup ratio initially increased and then decreased with electron density in the range of 3.8 x 10(19 )-6.0 x 10(19) m(-3), with a turning point observed at approximately 4.4 x 10(19) m(-3).

Innovation in neutron detection has supported basic science, the development of large-scale scientific facilities, and the development of clean nuclear energy. However, due to the uncharged nature of neutrons, accurately measuring neutron flux and spectrum simultaneously over a wide range of energies has always been challenging. A new type of neutron detector is designed based on PHITS-334, which utilizes a hydrogen-3He gas combination, combined with the nuclear recoil method and nuclear reaction method, to simultaneously measure neutron flux and spectrum in a broad energy region. Based on the isotope neutron sources of Am-B, Am-Be, Cf-252, and C-252 f -D2O given by ISO8529-1, the DD fusion neutron source of Experimental Advanced Superconducting Tokamak (EAST), and the theoretical fusion DT neutron source of International Thermonuclear Experimental Reactor (ITER), the energy spectrum measurement capability of the detector is evaluated. It has been demonstrated that the new detector can measure neutron flux over the entire energy range. The low limit of the conventional energy spectrum measurement is extended from 0.1 to 0.001 MeV through neutron spectrum analysis. The proposed method provides a new reference for developing neutron detectors. It should be noted that the new neutron detector can simultaneously measure neutron flux and spectrum information in a broad energy area, which will be the basis for integrating and miniaturizing neutron detection systems, such as fusion reactors.

Gamma-ray diagnosis can detect the energy and spatial distribution of fast ions, as well as identify disruption signs. The detector's response to the gamma-ray spectrum involves complex mappings, requiring a fast and accurate spectrum reconstruction method. The challenge lies in the ill-conditioned nature of spectrum inversion, where errors in measurement can significantly amplify the uncertainties of the inversion results. To solve this, additional information is needed, introducing non-linearity into the problem. Traditional approaches typically rely on iterative algorithms, such as linear regularization, maximum likelihood estimation method (ML-EM), and Gold deconvolution (Gold). Recently, neural networks have gained traction due to their strong capability in handling non-linear and highly ill-posed problems. In this paper, we present a method leveraging a master-secondary network structure that splits the spectrum inversion into two simpler sub-problems, improving outcomes beyond those of a single network. This network structure is verified suitable for solving highly ill-posed inversion problems and applying to gamma-ray spectrum reconstruction. Our method's accuracy is compared to ML-EM and Gold, demonstrating superior stability and effectiveness, particularly under high noise conditions, achieving a level suitable for practical applications. This method has been successfully applied to gamma-ray spectrum detection in the EAST tokamak facility.

High plasma density operation is crucial for a tokamak to achieve energy breakeven and a burning plasma. However, there is often an empirical upper limit of electron density in tokamak operation, namely the Greenwald density limit $n_G$, above which tokamaks generally disrupt. Achieving high-density operations above the density limit has been a long-standing challenge in magnetic confinement fusion research. Here, we report experimental results on EAST tokamak achieving the line-averaged electron density in the range of 1.3 $n_G$ to 1.65 $n_G$,while the usual range in EAST is (0.8-1.0)$n_G$. This is performed with ECRH-assisted Ohmic start-up and a sufficiently high initial neutral density. This is motivated by and consistent with predictions of a recent plasma-wall self-organization (PWSO) theory, that increasing ECRH power or pre-filled gas pressure leads to lower plasma temperatures around divertor target and higher density limits. In addition, the experiments are shown to operate in the density-free regime predicted by the PWSO model. These results suggest a promising scheme for substantially increasing the density limit in tokamaks, a critical advancement toward achieving the burning plasma.

Runaway electrons (REs) in experimental advanced superconducting tokamak (EAST) typically have an energy level of tens of MeV. Synchrotron radiation images of REs contain a wealth of information, making it crucial to handle this data properly to uncover hidden features. We observed distinct synchrotron radiation images emitted by the REs at different time points throughout the discharges and the focus of our study was an Ohmic discharge characterized by an evident synchrotron pattern and weaker background radiation. This paper aims to verify the feasibility of utilizing the green function and regularization method to obtain the distribution function information of synchrotron radiation images on EAST. We reconstruct the radial density profile of the REs beam by assuming the monoenergetic nature of REs at different time points. We employ the Tikhonov regularization method for this purpose. The results indicate that the radial density profile of the REs beam follows a roughly Gaussian distribution. Moreover, the peak density of the REs beam shifts inward to the magnetic axis as time progresses, a behavior also observed in the experimental image. However, a good fit between the simulated and experimental images is not achieved for all time points. This discrepancy is likely due to the intervention of q=2/1 magnetic islands and the increased complexity of the distribution function in both radial and momentum spaces.

Since the last IAEA-FEC in 2021, significant progress on the development of long pulse steady state scenario and its related key physics and technologies have been achieved, including the reproducible 403 s long-pulse steady-state H-mode plasma with pure radio frequency (RF) power heating. A thousand-second time scale (similar to 1056 s) fully non-inductive plasma with high injected energy up to 1.73 GJ has also been achieved. The EAST operational regime of high beta(P) has been significantly extended (H-98y2 > 1.3, beta(P) similar to 4.0, beta(N) similar to 2.4 and n(e)/n(GW) similar to 1.0) using RF and neutral beam injection (NBI). The full edge localized mode suppression using the n = 4 resonant magnetic perturbations has been achieved in ITER-like standard type-I ELMy H-mode plasmas with q(95) approximate to 3.1 on EAST, extrapolating favorably to the ITER baseline scenario. The sustained large ELM control and stable partial detachment have been achieved with Ne seeding. The underlying physics of plasma-beta effect for error field penetration, where toroidal effect dominates, is disclosed by comparing the results in cylindrical theory and MARS-Q simulation in EAST. Breakdown and plasma initiation at low toroidal electric fields (<0.3 V m(-1)) with EC pre-ionization is developed. A beneficial role on the lower hybrid wave injection to control the tungsten concentration in the NBI discharge is observed for the first time in EAST suggesting a potential way toward steady-state H-mode NBI operation.

[Background]In a tokamak,when fast electrons are deconfined by the tokamak magnetic field constraint and lost to the vacuum wall or limiter,the device may become damaged and the discharge may be affected.[Purpose]This study aims to explore the loss behavior of fast electrons during discharge using a diagnostic system based on a ZnS(Ag)scintillator probe for detecting the loss of fast electrons on the Experimental Advanced Superconducting Tokamak(EAST).[Methods]The Geant4 simulation program was employed to simulate the interaction between electrons in different initial states and the scintillator probe of the diagnostic system.Firstly,the probe model and the filling material model of stainless steel and ZnS(Ag)coating were established in Geant4.Then,the interaction between electron beam and scintillator probe under different incident conditions(incident energy,angle,scintillator thickness,magnetic field size,etc.)were simulated,and the physical processes were recorded.Finally,the recorded data were accessed by MATLAB programming for analysis.[Results]The results show that the contribution of secondary electrons and initial electrons to the luminescence intensity of scintillators occupies different dominant energy ranges.The luminescence intensity first increases and then decreases with the increase of incident electron energy,with a peak value around 12 MeV,and the number of emitted photons at oblique incidence is greater than that at vertical incidence.When the electron energy is lower than 4.3 MeV,secondary particles dominate the scintillation,and when the electron energy is higher than 4.3 MeV,primary particles dominate.The thickness of the scintillator has no significant effect on the peak position.After,the luminous intensity is considerably affected by the magnetic field angle and electron pitch angle after adding a magnetic field.[Conclusions]The results of this study contribute to the understanding of the fast electron loss signal detected by the scintillator probe in the EAST experiments,providing a basis for further study of fast electron loss.

Experimental research on the electron cyclotron wave (ECW) pre-ionization and assisted start-up was carried out systematically for the first time in EAST tokamak, which is a superconducting device with ITER-like full metal wall. Breakdown and plasma initiation at low toroidal electric fields (<0.3 V m(-1)) with ECW pre-ionization and startup assistance has been demonstrated. Also, the parameter domain of breakdown is significantly extended towards higher prefill gas pressure. The effect of ECW injection timing, power, toroidal injection angle on breakdown were also investigated. Injecting ECW earlier leads to an earlier breakdown and a higher plasma current ramp rate. The electron cyclotron heating (ECH) power threshold for breakdown in EAST is approximately 0.4 MW. In the range of ECH power tested in this work, higher ECH power is advantageous for achieving earlier and faster breakdown. Furthermore, the breakdown with radial ECW injection occurs earlier compared with oblique injections (co-current and counter-current). During the ECW-assisted startup, the process of burn-through is prolonged by the higher pre-filled gas pressure even though it enhances the ease of breakdown. In addition, compared to the low hybrid wave assistance, the ECW assistance has an effect in averting the generation of runaway electrons and improving the safety of device during startup. Moreover, the ECW assistance exhibits a high tolerance to the impurity and thus ensures a high ramp rate of plasma current even with a high impurity level.

We report in this paper the development of the single crystal diamond detector as a fast neutron spectroscopy in the EAST tokamak. The diamond detector is used to detect the fast neutron directly without any neutron converter during the deuterium-deuterium fusion experiment, then the neutron energy spectrum is reconstructed from the recorded continuous scattered spectrum by using a deconvolution algorithm. The results indicate the capability of the diamond spectroscopy which can be used directly to monitor the fast neutron flux and energy spectrum in the EAST tokamak.

A series of high-frequency ( 400 similar to 1000 kHz ) bursting core-localized Alfven instabilities have been observed during ohmic discharges in EAST tokamak. The instability trigger favours the discharge conditions of low toroidal magnetic field and low electron density. The toroidal mode numbers are mainly n=2 similar to 3 and they propagate in the ion diamagnetic drift (co-current) direction. These modes are radially localized in the range of rho tor=0.2 similar to 0.35 based on Doppler BackScatter measurement. They are identified as ellipticity-induced Alfven eigenmodes (EAEs) occurring at q=1 rational surfaces by magnetohydrodynamics simulations using the realistic geometry and plasma profiles. The EAEs show regular bursts with similar to 10 ms duration along with the mode frequency chirping downwards and upwards rapidly. It is also found that sawtooth events can interrupt the growth and evolution of the EAEs, causing the modes to disappear immediately. Passing energetic electrons (EEs) that move much faster than Alfven velocity are responsible for the destabilization of these EAEs, which attribute to the fact that the large poloidal and toroidal frequencies mostly cancel each other and satisfy the EAE resonance condition with primary energy exchange. These novel experimental results of the wave-particle interaction between EAEs and EEs are helpful for extrapolating alpha particle physics that are characterized by small orbit width with respect to machine size in future fusion reactors.