Experimental Advanced Superconducting Tokamak Research Articles

An Improved Voltage Control Method for EAST Fast Control Power Supply

The Experimental Advanced Superconducting Tokamak (EAST) fast control power supply (FCPS) is an important device for controlling the vertical displacement of plasma during the nuclear fusion power generation process, adopting a multiple H-bridge invertor branch parallel operation structure to output total current. At the beginning of each shot of plasma discharge, FCPS works in open-loop voltage control mode (VCM) or closed-loop current control mode (CCM) determined by the plasma control system to output current for exciting the load coil, to achieve plasma vertical displacement control. VCM has the characteristics of fast dynamic response speed but poor consistency of branch current and insufficient branch current control accuracy and stability because of open-loop control. CCM has the characteristics of high branch current control accuracy but poor dynamic response and robustness because of control delay and control parameters determined based on engineering experience. To achieve fast and robust control, an improved voltage control method (IVCM) is proposed by combining the advantages of VCM and CCM. In the beginning of establishing the output current, FCPS operates in VCM, and rapid establishment of the output current is ensured. After the output current rapidly increases to the critical value, closed-loop current control is added to VCM to ensure the accuracy of output current control. In closed-loop current control, linear super-twisting sliding mode control is designed to achieve fast and robust control, ensuring good consistency and fast dynamic response performance of each branch current. Simulations and experiments verify that the designed IVCM has better compatibility characteristics in output current stability, control accuracy, and consistency of each branch current compared to VCM.

Investigation of Cs27LiYCl6:Ce scintillator energy response for D-D fusion neutron spectrometer

During plasma experiments on EAST (Experimental Advanced Superconducting Tokamak), the discharges heated with neutral beam injection (NBI) for plasma results in the production of 2.45 MeV deuterium-deuterium (D-D) fusion neutrons. In order to measure the energy spectrum of D-D fusion neutrons, a new Cs27LiYCl6:Ce (CLYC-7) crystal with 7Li-enrichment has been developed and fabricated into a CLYC-7 scintillation detector. Before utilizing this detector for studying neutron energy spectra, it is crucial to explore the response function of the detector within a relevant neutron energy range. Therefore, the detector has been experimented using the 4.5 MeV electrostatic accelerator at Peking University to investigate its response to fast neutrons, energy resolution, and pulse discrimination capability in the neutron energy range 2.07 MeV–5.51 MeV. The neutron reactions occurring within the CLYC-7 scintillator were simulated using MCNPX, focusing on the reactions 35Cl(n,p) and 35Cl(n,α), as well as the energy response curve and the contributions of different particles (protons, alphas) to the neutron spectrum. The experimental results were successfully validated on EAST, where the 2.45 MeV fusion neutron energy spectrum was measured. That demonstrates the ability of the CLYC-7 scintillation detector to diagnose the fusion neutron energy spectrum for deuterium plasma discharge.

Design and operation of a load-tolerant ICRH system in Experimental Advanced Superconducting Tokamak

Ion Cyclotron Resonance Heating (ICRH) has been a dependable tool for sturdy plasma heating with high RF power of several megawatts. However, a sudden increase in the reflected power during ICRH heating experiments is a problem that should be solved for future fusion experimental devices. To solve this issue, a load tolerant matching network has been designed for the ICRH system in EAST. The matching network includes a 3-stub tuner impedance matching system with conjugate-T structure, 30 Ω to 50 Ω transmission line and center grounded antenna strap. By maintaining a low reflection ratio in the network for a wide range of resistance, this matching network can allow sturdy high-power operations without fast impedance matching in EAST. In our matching network, the two arms of a conjugate-T are designed to have a λ/2 length difference which could mitigate current imbalance and antenna poloidal phasing outside of the control problem. The T-point corresponds to the maximum point of the standing wave voltage, which could greatly improve the input impedance of the antenna.

Comparison of transport coefficients before and after density pump-out induced by resonant magnetic perturbation using a BOUT++ six-field model on the EAST tokamak

Many experiments have demonstrated that resonant magnetic perturbation (RMP) can affect the turbulent transport at the edge of the tokamak. Through the Experimental Advanced Superconducting Tokamak (EAST) density modulation experiment, the particle transport coefficients were calculated using the experimental data, and the result shows that the particle transport coefficients increase with RMP. In this study, the six-field two-fluid model in BOUT++ is used to simulate the transport before and after density pump-out induced by RMP, respectively referred as the case without RMP and the case with RMP. In the linear simulations, the instabilities generally decreases for cases with RMP. In the nonlinear simulation, ELM only appears in the case without RMP. Additionally, the particle transport coefficient was analyzed, and the result shows that the particle transport coefficient becomes larger for the case with RMP, which is consistent with the experimental conclusion. Moreover, its magnitude is comparable to the results calculated from experimental data.

Detection of ion cyclotron emission by using an ion cyclotron range of frequency antennas-based diagnostic system in experimental advanced superconducting tokamak

In the experimental advanced superconducting tokamak (EAST), a novel ion cyclotron range of frequency (ICRF) antenna-based diagnostic system is designed to measure ion cyclotron emission (ICE) driven by high-energy ions. The diagnostic system includes ICRF antenna straps, a three-tune impedance matching system, a coaxial switching system, a direct current block, and a data acquisition and storage system. Using the coaxial switching system, the ICRF antenna can be switched from the heating mode to the coupling mode between two discharges. In the 2023 EAST experiment campaign, core ICE was observed using the ICRF antenna-based diagnostic system during neutron beam injection heating, and the obtained results agreed well with the signal detected by the previous high-frequency B-dot probe-based diagnostic system.

Electron ITB formation in EAST high poloidal beta plasmas under dominant electron heating

Plasma confinement and transport in tokamaks play a crucial role in the development of high poloidal beta steady-state operation scenarios. Therefore, it is very important to study the relevant mechanism of internal transport barriers (ITBs), which can help plasmas to obtain better confinement in order to achieve higher fusion gain. This paper mainly introduces the analysis of the characteristics of electron heat transport of discharges with ITB in high βP operation regime in Experimental Advanced Superconducting Tokamak (EAST). Based on the statistical analysis of stable discharges with βP > 1.5, it is found that there is an obvious bifurcation of the normalised electron temperature gradient (ETG) ( R/LTe ) in the range of βP = 2–2.2. Then the discharges of lower βP ( βP < 2, where the value of βP is below the bifurcation threshold) and of higher βP ( βP > 2.2, where the value of βP is above the threshold) were selected for analysis. The diagnostic data provided by Thomson scattering, x-ray crystal spectrometry and charge exchange recombination spectroscopy are used to provide reliable parameter profiles and then combined with the data of external magnetic probe measurements and the polarisation interferometer diagnosis system to fully reconstruct the balance. A relevant plasma current calculation model is used to calculate and analyse the current density profiles and power deposition, and then the transport analysis is carried out. Interestingly, in the higher βP discharges, it is found that the turbulence intensity provided by the CO2 laser collective scattering system gradually decreases and the normalised ETG R/LTe gradually increases. It is also found that the electron heat transport coefficient decreases in the discharge with higher βP and the growth rate of the electron-scale turbulence calculated by transport gyro-Landau fluid (TGLF) is significantly reduced. Meanwhile, similar conclusions are also obtained in the discharges when the βP is further increased.

Safety factor diagnostic for tokamak core plasma from three-dimensional reconstruction of pellet ablation trail.

Using a stereo camera system, a new diagnostic for the safety factor of the core plasma based on the pellet ablation trail is applied on the Experimental Advanced Superconducting Tokamak (EAST). In EAST discharge No. 128 874, a shattered pellet injection system is applied to inject a shattered neon pellet into the EAST. Since the strong magnetic field in tokamaks binds the ablated pellet material, the orientation of the pellet ablation trail is the same as the local magnetic field direction. Thus, from the three-dimensional reconstruction result of the pellet ablation trail, the local safety factor q can be obtained. The motional Stark effect (MSE) diagnostic is applied to determine the safety factor q profile in this shot. The determined safety factor q results for this new diagnostic are in quantitative agreement with those from the MSE diagnostic with the mean relative difference of only 6.8%, confirming the effectiveness of this new diagnostic of the safety factor.

Progress of CO2 Dispersion Interferometer on EAST

A CO2 Dispersion Interferometer (DI) system on the Experimental Advanced Superconducting Tokamak (EAST) was successfully operated, providing plasma electron density measurements. The DI system utilizes a continuous-wave 9.3 μm CO2 laser source to measure line-averaged electron densities. This offers significant advantages, including the ability to minimize fringe jumps and insensitivity to mechanical vibrations. These characteristics are well-suited for future high-density, long-pulse plasma discharges. The DI system provides a real-time density feedback signal to the plasma control system for routine density control during long-pulse operation. Experiments with EAST demonstrated good agreement between the density obtained by the DI system and the preset densities. The DI system also exhibited stability during long-pulse discharge. Moreover, the DI system was stable during rapid density changes and high-density pellet injections. In shot No. 120594, the DI system exhibited stable density feedback during continuous projectile injection lasting over 50 seconds; the line-averaged electron density is approximately 4×1019 m-3. In contrast to the long-wavelength source interferometer, which may deflect light from the detector owing to excessive refraction angles in larger density-gradient discharges, the DI ensured accurate density measurements. The DI system on EAST is dependable for accurately measuring the electron density.

High-frequency fluctuation and EHO-like mode in the H-mode pedestal on the EAST tokamak

In the pedestal region of the Experimental Advanced Superconducting Tokamak (EAST) during high confinement mode plasma operations with radio-frequency heating, two distinct fluctuations are observed: high-frequency fluctuations (HFFs) and edge harmonic oscillation-like (EHO-like) modes. The HFFs are characterized by intermittent fluctuations with a broadband frequency range of 1−3 MHz and a poloidal wave number ( kθ ) greater than 0.9 cm−1 . On the other hand, the EHO-like mode exhibits characteristics similar to magnetohydrodynamics (MHD)-like modes with n = 1−5 and lower poloidal wave numbers ( kθ⩽0.12 cm−1 ). During the pedestal establishing phase following the L–H transition, a significant concurrent presence of HFF and EHO-like modes in high-density pedestal regions has been noted. In this phase, the EHO-like mode not only modulates the amplitude of the HFF but also engages in nonlinear interactions. The occurrence of EHO-like mode and HFF is associated with particle transport toward the divertor, though it is notably less than that caused by edge coherent modes. During the inter-edge localized mode (ELM) period, a significant decrease in the Dα baseline is observed whenever the low frequency fluctuation (LFF) weakens and the HFF grows, prior to each large ELM. One possible explanation is that the rapid increase of E×B shear stabilizes the LFF and destabilizes the HFF, which lowers the pedestal transport and enables the further growth of the pedestal until the onset of the ELM.

Conceptual design of a 3D printed liquid lithium divertor test modular for EAST

The utilization of Liquid Metal Divertor (LMD) stands as a promising prospect for the divertor component in DEMO. To explore the vapor shielding effect and provide technical accumulation for the development of DEMO LMD, the imperative development of a high-performance LMD test module has arisen. The Experimental Advanced Superconducting Tokamak (EAST) has amassed substantial expertise in LM first wall design and experimentation, rendering it suitably equipped for experimental pursuits. Therefore, this paper aims to design a test module running in the mid-plane of EAST to accumulate technical experience for the application of 3D printed capillary porous system (CPS) in LMD. Drawing upon prior experience, specific design requirements are articulated. Lithium is chosen as the operational LM due to its favorable balance between heat dissipation capacity and compatibility with the core plasma. The conceptual design encompasses active water cooling components, a CPS, and a lithium channel. Thermal analysis is conducted to ascertain the prevention of excessive evaporation or frozen during operation. The maximum power handling capacity of this design is projected, with practical solutions outlined for inter-component thermal management. The results affirm the viability of this design within the thermal load parameters of the EAST experiment, offering invaluable insights for designers exploring diverse LMD configurations.

Coupling between the Alfvén eigenmode and edge-coherent mode on the experimental advanced superconducting tokamak

High-frequency electromagnetic fluctuations and edge-coherent modes (ECMs) have been detected by Doppler reflectometry (DR) in the pedestal region of the Experimental Advanced Superconducting Tokamak. The frequency of the electromagnetic fluctuations was proportional to the Alfvén velocity and localized in the ellipticity-induced Alfvén eigenmodes (EAEs) gap in the Alfvén continuum. Therefore, the fluctuations are presumed to be EAE. The DR measurements of poloidal flow fluctuations show that EAEs and ECMs have amplitude envelopes that are localized near the bottom of the radial electric field well. Simultaneous EAE and ECM activity generates sidebands at fEAE±fECM , the strengths of the upper and lower sidebands are unequal, with the upper sideband being stronger. This is consistent with the theoretical prediction of Chen et al. Compared with ECM-only discharges, the inclusion of EAEs leads to an increase in Dα intensity, thus indicating enhanced outward particle transport.

First results of CO2 dispersion interferometer on EAST tokamak

A dispersion interferometer (DI) has been installed and operates on the Experimental Advanced Superconducting Tokamak (EAST). This DI system utilizes a continuous-wave 9.3 μm CO2 laser source to measure line-averaged electron densities accurately. In contrast to conventional interferometers, the DI does not require substantial vibration isolations or compensating systems to reduce the impact of vibrations in the optical path. It also employs a ratio of modulation amplitudes, ensuring it remains immune to the variations in detected intensities. Without a variation compensation system, the DI system on EAST reaches a density resolution of less than 1.8 × 10−2π rad and a temporal resolution of 20 μs. The measurements made by the POlarimeter-INTerferometer (POINT) system and the far-infrared hydrogen cyanide (HCN) interferometer are remarkably consistent with the DI’s results. The possibility of fringe jumps and the impact of refraction in high-density discharge can be significantly decreased using a shorter wavelength laser source. A rapid density change of 3 × 1019 m−3 during 0.15 s has been measured accurately in shot No. 114755 of EAST. Additionally, the DI system demonstrates dependability and stability under 305 s long-pulse discharges in shot No. 122054.

Observation of Doppler shift modulated by the internal kink mode using conventional reflectometry in the EAST tokamak

In this paper we present a new experimental observation using a conventional reflectometry technique, poloidal correlation reflectometry (PCR), in the Experimental Advanced Superconducting Tokamak (EAST). The turbulence spectrum detected by the PCR system exhibits an asymmetry and induced Doppler shift during the internal kink mode (IKM) rotation phase. This Doppler shift is the target measurement of Doppler reflectometry, but captured by conventional reflectometry. Results show that the Doppler shift is modulated by the periodic changes in the effective angle between the probing wave and cutoff layer normal, but not by plasma turbulence. The fishbone mode and saturated long-lived mode are typical IKMs, and this modulation phenomenon is observed in both cases. Moreover, the value of the Doppler shift is positively correlated with the amplitude of the IKM, even when the latter is small. However, the positive and negative frequency components of the Doppler shift can be asymmetric, which is related to the plasma configuration. A simulated analysis is performed by ray tracing to verify these observations. These results establish a clear link between and IKM rotation, and are helpful for studying the characteristics of IKM and related physical phenomena.

Load model of high power magnet power supply for EAST based on GMPSO-BP neural network

To provide an accurate dynamic load model for the stability analysis of Tokamak, a method of back propagation (BP) neural network employing particle swarm optimization(PSO) algorithm based on mutation of Gaussian white noise disturbance (GMPSO-BP) is recommended. This method performs high-precision fitting using the GMPSO-BP neural network on the measured data of the experimental advanced superconducting Tokamak (EAST) poloidal field magnet power supply, extracts network parameters to build a dynamic load model, and then compares the simulation results with the measured data to calculate the error coefficient. The model is a component of the EAST distribution network's digital simulation model. An analogous load model is employed instead of developing the poloidal field magnet power supply from the mechanism. The revised algorithm has quick convergence times, good initial value adaptability, and error function accuracy of 0.3 to 3 %. The simulation outcomes show that the approach has a greater training effect.

β-induced Alfvén eigenmodes and fishbone driven by energetic electrons in EAST electron heating dominant plasmas

β-induced Alfvén eigenmodes (e-BAE) and fishbone (e-fishbone) driven by the energetic electrons have been identified on the experimental advanced superconducting tokamak in electron cyclotron resonance heating (ECRH), low hybrid wave (LHW) together with neutral beam injection plasma and in pure radio frequency heating plasma, respectively. The e-BAE is predominantly located near the pedestal region, and its frequency typically displays a chirping characteristic. The frequency is notably associated with the count of energetic electrons with energy between 30 keV and 80 keV driven by LHW and undergoes three distinct phases. A direct correlation is established between the frequency of e-BAE and the global parameters, including electron temperature, Alfvén velocity and βp . The e-fishbone emerges in the core and becomes noticeable shortly after ECRH initiation, in an electron heated dominant and core confinement enhanced discharge. Experimental analyses suggest that the e-fishbone ties closely with both the population and energy distribution of energetic electrons. These observations can provide valuable insights into the behavior of energetic electrons, which play a crucial role in the formation and sustainability of transport barriers within hybrid plasma, both in the internal and pedestal regions.

Development of a real-time impedance matching system for ion cyclotron resonance heating in experimental advanced superconducting tokamak

To achieve stable operation of an ion cyclotron resonance heating (ICRH) system in the Experimental Advanced Superconducting Tokamak (EAST), a real-time impedance matching system needs to be established to respond to antenna load variation during long pulse discharges. A new impedance matching method based on capacitors was proposed in this study. By considering the reflected voltage of the transmission line as the feedback parameter, the real-time impedance-matching system can quickly control the motors based on a programmable logic controller to determine the minimum reflection voltage. A real-time impedance matching system was successfully used on the test platform in the laboratory and on the ICRH system in EAST. A significant result is that we can match the variable impedance within 1 s by suitably adjusting the motor controller to ensure high-power and long-pulse operation of the ICRH system to satisfy the requirements of the EAST experiment.

FP3D: A code for calculating 3D magnetic field and particle motion

An efficient numerical code FP3D has been developed to calculate particle orbits and evaluate particle confinement in 3D magnetic fields including stellarators and tokamaks with 3D fields. The magnetic field is either calculated from coils directly or obtained from equilibrium codes. FP3D has been verified with the 3D equilibrium code Variational Moments Equilibrium Code [Hirshman and Whitson, Phys. Fluids 26, 3553–3568 (1983)] for magnetic field calculation and with the drift-kinetic code Stellarator Fokker–Planck Iterative Neoclassical Conservative Solver [Landreman et al., Phys. Plasmas 21(4), 042503 (2014)] for neoclassical transport. The code has been applied successfully to the National Compact Stellarator Experiment stellarator [Nelson et al., Fusion Eng. Des. 66, 169–174 (2003)] for the calculation of neoclassical transport coefficient with the 3D magnetic field obtained directly from coils. FP3D is also used to calculate ripple losses in the tokamak Experimental Advanced Superconducting Tokamak [Y. Wan, Plasma Sci. Technol. 8(3) (2006)].

Line identification of extreme ultraviolet spectra from aluminum ions in EAST Tokamak plasmas

Extreme ultraviolet (EUV) spectra emitted from aluminum in the 5-340 Å wavelength range were observed in Experimental Advanced Superconducting Tokamak (EAST) discharges. Several spectral lines from aluminum ions with different degrees of ionization were successfully observed with sufficient spectral intensities and resolutions using three fast-time-response EUV spectrometers. The line identification uses three independent state-of-art computational codes for the atomic structure calculations, which provide the wavelengths and the collisional and radiative transition rate coefficients. These programs are hullac (Hebrew University—Lawrence Livermore Atomic Code), autostructure, and fac (Flexible Atomic Code). Using three different codes allows us to resolve some ambiguities in identifying certain spectral lines and assess the validity of the theoretical predictions.

Design of the CFC composite brazed HFS first wall on the NBI shine-through area of the EAST device

The high field side (HFS) first wall is the inner wall nearest to the vertical center axis in tokamak. To avoid high Z impurity sputtering due to plasma interaction and neutral beam injector (NBI) radiation, graphite is adopted as the plasma facing material (PFM) of the HFS first wall on the NBI shine-through area (NBISTA). In the experimental advanced superconducting tokamak (EAST), graphite tiles are bolted to the CuCrZr heat sinks by screw on the NBISTA, but cracks, fractures and ablations were observed on the graphite tiles after experimental campaigns because of insufficient heat removal capability. Thus, a new design of the HFS first wall on the NBISTA was proposed by adopting the carbon fiber composite (CFC) and brazing technology. In the new design, CFC tiles were brazed to the CuCrZr heat sink, and the oxygen-free copper (OFC) sheet was adopted between CFC tiles and CuCrZr heat sinks as stress-buffer layer. To avoid potential brazing failures or CFC tiles detachments, a modular pattern active cooling panels was proposed for the HFS first wall on the NBISTA. Steady heat transfer analysis of those panels was carried out and results show that the heat removal capacity satisfied the design requirements. Meanwhile, feasibility of the CFC brazing process was verified by nondestructive testing (NDT), mechanical property testing and high heat flux (HHF) testing, and testing results indicate that the CFC/OFC/CuCrZr bonding processed by one-step brazing had good mechanical property and heat removal capability.

Experimental observation of micro-tearing modes in the tokamak pedestal

A micro-tearing mode has been observed in electron temperature fluctuations and magnetic fluctuations with the frequency range of 80–120 kHz in the pedestal of the Experimental Advanced Superconducting Tokamak (EAST) using Electron Cyclotron Emission Imaging (ECEI) and Mirnov magnetic coil measurement. It appears in the type-I ELMs period after the L-H transition. The measured poloidal phase velocity of the electron temperature fluctuations is ∼40 km/s (f = 80–120 kHz) in the electron diamagnetic direction in the laboratory frame with the poloidal wave number around kΘ ∼0.15 /cm. The two-dimensional structure of MTMs is directly observed using two-dimensional Electron cyclotron emission imaging. The experiment confirmed that the electron temperature (ECEI) and radial electric field (Backward Doppler reflectometer) during MTM meet the pressure balance equation. Until now, the theory and simulation results showed that transport is in heat flux, small particle flux, while the experimental results of this paper indicate that the particle flux is small.