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Lithium Beam Emission Spectroscopy (Li-BES) diagnostic has been developed on the Experimental Advanced Superconducting Tokamak (EAST), aiming at providing the edge electron density profile and density fluctuation. This system has been upgraded to 32 × 4 (radial × poloidal) channels since the 2016 campaign with a radial observation range of about 30 cm at the midplane on the low field side. The spatial resolution of Li-BES diagnostic is about 1 cm. The whole optical system of Li-BES diagnostic has been shifted 9 cm away from the tokamak axis perpendicular to the flange at horizontal D-port on EAST since the 2017 campaign. It’s confirmed that transmissivities of Avalanche PhotoDiode (APD) channels in the edge region are improved by comparing the relative light intensity calibration factors of the same row of APD channels before and after the shift. Spatial calibration and relative light intensity calibration of this system have been performed. Based on Schweinzer’s algorithm [J. Schweinzer et al., Plasma Phys. Control. Fusion 34, 1173 (1992)], the edge electron density profile is reconstructed and shown to be consistent with those provided by other diagnostics on EAST. The electron density profile evolution during the plasma current ramp-down process is observed with Li-BES diagnostic in both SOL region and pedestal region. With an injected Li-beam under the high frequency chopping control, the temporal resolution of the reconstructed electron density profile can be up to 10 μ s , which reveals temporal behaviors of fast transient events on EAST, such as the L-H transition and ELM crashes.

A flush-mounted Langmuir probe system has been built on the lower graphitic divertor targets in the experimental advanced superconducting tokamak (EAST) in 2016, which is revised from the previous divertor Langmuir probes, aimed to reduce the erosion from high-energy particle and strong heat flux on the probe surfaces exposed in the plasma, and explore new structure applications. The theories of single and triple flush-mounted probes relevant to their dimensions and the plasma parameters in the EAST divertor region are reviewed. During the 2016 EAST campaign, the flush-mounted probe system measured the plasma parameters by using single and triple probes, respectively, to obtain plasma parameters. The results were compared with the previous measurements by the domed probe in the similar condition. The results showed a good agreement between measurements using different probe geometries and techniques. This demonstrated the reliability of the flush-mounted probe system as a diagnostic tool in the EAST divertor. Optimization of these Langmuir probe system for the next generation of EAST lower divertor, which will be upgraded to a full tungsten divertor with active water cooling, is also discussed.

Coronal heating is a big question for modern astronomy. Daily measurement of 985 solar spectral irradiances (SSIs) at the spectral intervals 1-39 nm and 116-2416 nm during March 1 2003 to October 28 2017 is utilized to investigate characteristics of solar rotation in the solar atmosphere by means of the Lomb \,-\, Scargle periodogram method to calculate their power spectra. The rotation period of coronal plasma is obtained to be 26.3 days, and that of the solar atmosphere at the bottom of the photosphere modulated by magnetic structures is 27.5 days. Here we report for the first time that unexpectedly the coronal atmosphere is found to rotate faster than the underlying photosphere. When time series of SSIs are divided into different cycles, and the ascending and descending periods of a solar cycle, rotation rate in the corona is also found to be larger than that in the photosphere, and this actually gives hidden evidence: it is small-scale magnetic activity that heats the corona.

Exploring the corresponding relation between structural and physical properties of materials at the atomic scale remains the fundamental problem in science. With the development of the aberration-corrected transmission electron microscopy (AC-TEM) and the ultrafast optical spectroscopy technique, sub-angstrom-scale spatial resolution and femtosecond-scale temporal resolution can be achieved, respectively. However, the attempt to combine both their advantages is still a great challenge. Here, we develop in situ optical spectroscopy with high temporal resolution in AC-TEM by utilizing a self-designed and manufactured TEM specimen holder, which has the capacity of sub-angstrom-scale spatial resolution and femtosecond-scale temporal resolution. The key and unique design of our apparatus is the use of the fiber bundle, which enables the delivery of focused pulse beams into TEM and collection of optical response simultaneously. The generated focused spot has a size less than 2 µm and can be scanned in plane with an area larger than 75 × 75 µm2. Most importantly, the positive group-velocity dispersion caused by glass fiber is compensated by a pair of diffraction gratings, thus resulting in the generation of pulse beams with a pulse width of about 300 fs (@ 3 mW) in TEM. The in situ experiment, observing the atomic structure of CdSe/ZnS quantum dots in AC-TEM and obtaining the photoluminescence lifetime (∼4.3 ns) in the meantime, has been realized. Further ultrafast optical spectroscopy with femtosecond-scale temporal resolution could be performed in TEM by utilizing this apparatus.

This study uses the diversity of materials at known locations in the Experimental Advanced Superconducting Tokamak (EAST) to extract, local information on which plasma-surface interaction processes are dominant during Ion Cyclotron Resonance Heating (ICRH) (near vs far field effects). Metallic impurity content is indicated by the intensity of impurity line emissions observed with a fast-time-response extreme ultraviolet (EUV) spectrometer, normalized to line-averaged plasma density, i.e. Iimp/ne. Parametric dependencies are explored over scans of ICRH and LH (Lower Hybrid) power and for different toroidal phasings between straps, strap power balance, and magnetic configurations. This diversity of behavior is interpreted as the signature of different physical processes. Before 2017, as only the upper divertor region contained tungsten (W), the W content in the core used to increase a lot when moving from lower (LSN) to upper single null (USN) configurations, and was correlated with the total injected power rather than the ICRH power. Molybdenum (Mo), covering the part of the inner wall facing one ICRF antenna appear sensitive to this antenna power and phasing benchmarked by modelling suggesting a probable interaction due to residual ICRF waves crossing the plasma. Materials close and magnetically-connected to an active antenna show better correlation with ICRF antenna electrical tuning than those which are far away, or not connected. This is particularly the case with W since 2018, because the limiter tiles of the LH launchers were changed from graphite to tungsten. In these latter conditions, it is shown that W sources at the mid-plane (equatorial plane) contribute to a significant fraction of the core contamination by tungsten (25% in ohmic regime, and more during ICRH).

EAST achieved 101.2 seconds H-mode discharge with total power injection up to 3MW in 2017. Consequently to the enhanced auxiliary heating power, the active divertor heat flux control is urgently needed in EAST. In 2018, the active divertor detachment feedback control was implemented successfully in EAST plasma control system (PCS) with divertor Langmuir probe measurements for evaluating the divertor particle flux. The control algorithm controlled the degree of detachment effectively during the 2018 EAST experiments through either D2 fueling in the low field side using SMBI or impurity seeding from the divertor volume in H-mode plasmas, without significant degradation of the core-plasma performance, i.e., exhibiting good core-edge-divertor integration. The algorithm implementation in PCS and experimental results will be reported in this paper. Further efforts will be made to extend active feedback control towards long-pulse H-mode detachment maintenance in the near future, which will benefit the high power, H-mode operation for ITER.

In order to achieve long-pulse H-mode plasma scenario over 400 s with high heating power in the Experimental Advanced Superconducting Tokamak (EAST) device, the lower graphite divertor will be upgraded into a tungsten (W) divertor with active water cooling, which consists of the W/Cu monoblock units and the W flat-tile units as the divertor plasma facing components. As a fundamental diagnostic tool, the divertor Langmuir probe (Div-LP) diagnostic system will be upgraded accordingly. This paper presents the design of two kinds of new Div-LP systems, which are planned to be utilized on the W/Cu monoblock units and the W flat-tile units for the upgraded lower tungsten divertor, respectively, including their structures and preliminary poloidal and toroidal layouts. The Div-LP diagnostic system can measure the plasma parameters with the schemes of triple-probe, double-probe, and single-probe, to obtain the spatial and temporal distribution of plasma behavior on the divertor targets, which is useful for the discharge control and operation in EAST. In addition, the thermal analysis of the two kinds of probe assemblies is also carried out by using the three-dimensional finite element code ANSYS, which is aimed to get the optimal designs to withstand the long-pulse and high-power operation in EAST future experiments.

Correlations between the edge fluctuations and the pedestal evolution during the relatively large edge localized mode (ELM) cycles at high pedestal normalized electron collisionality ( ν e , ped * > 1) on the EAST tokamak are investigated. Not only the edge electrostatic coherent mode (ECM, ∼50 kHz) and the low frequency magnetic coherent mode (MCM, ∼32 kHz) but also a high frequency electromagnetic mode (HFM, >150 kHz) are observed to be coexisting between ELMs. After the ELM crash, the pedestal electron temperature recovered faster than the pedestal electron density. It is found that the saturation of the ECM coincides more with the saturation of the pedestal electron density, while the saturation of the HFM and MCM coincides more with the saturation of the pedestal electron temperature. In addition, the characteristics of the electromagnetic fluctuations (the HFM and MCM) are studied in detail: the HFM propagates in the electron diamagnetic drift direction in the laboratory frame with an average poloidal wave number of k ¯ θ HFM ≈ 0.17 cm − 1, while the MCM propagates in the ion diamagnetic drift direction in the laboratory frame with k ¯ θ MCM ≈ 0.12 cm − 1 and the toroidal mode number of n = 1. Furthermore, both the HFM and MCM have inward average radial wave numbers of k ¯ R HFM ≈ 0.13 cm − 1 and k ¯ R MCM ≈ 4.64 cm − 1. The bispectral analysis shows that the HFM and MCM have strong nonlinear interactions. The HFM is clearly observed on both low and high field side Mirnov coils, which might suggest a feature beyond a ballooning type instability, e.g., the kinetic ballooning mode. These studies may contribute to a better understanding of the pedestal evolution.

The plasma current profile modification in the edge region is observed in LHCD (lower hybrid current drive) plasmas for the first time in EAST, correlated with an increased level of PI (parametric instability) activities with the decrease in LH (lower hybrid) source frequency or the increase in plasma density. With the increase in the PI strength, an increase in the edge current is observed despite of a reduction in current drive capability. In these plasmas, strike-point splitting behaviors are also observed, implying the modification of the magnetic geometry in the scrape-off-layer. Results show the effects of LH frequency and plasma density on power dissipation in the edge region, suggesting a role of anomalous wave power damping on the modification of current profile at the plasma edge. These novel results are significant in that they give insight for the first time into how nonlinear wave-plasma interactions such as PI may directly impact the edge current profile, the control of which is critical in order to achieve optimized modes of operation in a steady state fusion reactor. © 2018 IAEA, Vienna.

A novel bi-directional Retarding Field Analyzer (RFA) probe has been installed on a fast reciprocating drive system on the Experimental Advanced Superconducting Tokamak (EAST) to measure the ion temperature and fast electron fluxes. A Langmuir probe assembly was added on the top of the RFA head to control the RFA position relative to the last closed flux surface and to have a possibility to measure the electron density and temperature as well. Except the ion temperature, the fast electron fluxes from both ion and electron drift sides have been measured during lower hybrid current drive. The RFA probe has been also used to measure the fast electrons associated with edge localized modes (ELMs), indicating their substantial presence in the scrape-off-layer plasma of EAST.

Volume recombination plays an important role towards plasma detachment for magnetically confined fusion devices. High quantum number states of the Balmer series of deuterium are used to study recombination. On EAST (Experimental Advanced Superconducting Tokamak), two visible spectroscopic measurements are applied for the upper/lower divertor with 13 channels, respectively. Both systems are coupled with Princeton Instruments ProEM EMCCD 1024B camera: one is equipped on an Acton SP2750 spectrometer, which has a high spectral resolution ∼0.0049 nm with 2400 gr/mm grating to measure the Dα(Hα) spectral line and with 1200 gr/mm grating to measure deuterium molecular Fulcher band emissions and another is equipped on IsoPlane SCT320 using 600 gr/mm to measure high-n Balmer series emission lines, allowing us to study volume recombination on EAST and to obtain the related line averaged plasma parameters (Te, ne) during EAST detached phases. This paper will present the details of the measurements and the characteristics of deuterium Balmer series line emissions during density ramp-up L-mode USN plasma on EAST.

One of the major challenges for the design and operation of next-step high-power steady-state fusion devices is to develop and validate advanced divertor solutions for handling power exhaust, while maintaining acceptable divertor target plate erosion. This requires to access divertor detachment at relatively low main plasma densities compatible with current drive and high plasma confinement. Recently a new initiative has been launched on the EAST superconducting tokamak to develop a new divertor for evaluating boundary plasma solutions applicable to the next step fusion experiments beyond ITER. In the present work, four different divertor configurations with different degrees of closure are evaluated through detailed modeling with the SOLPS plasma boundary code. The modeling results show that increasing divertor closure can significantly trap more neutrals from to with the same upstream separatrix density and hence facilitate the onset of detachment decreasing from to Moreover, with increasing divertor closure the divertor radiated power is also increased from 200 to 450 kW and the peak heat flux density at the divertor target is reduced from 9.3 to 3.8 MW m−2. Therefore, increasing divertor closure can benefit divertor operation for EAST and may be used as one of the scientific metrics for the divertor design of future fusion devices.

A highly reproducible spontaneous non-inductive low recycling no-ELM regime has been achieved in the EAST superconducting tokamak with the water-cooled tungsten divertor and molybdenum first wall. The salient feature is that after the L-H transition, emission intensity, divertor neutral pressure and the separatrix electron density all decrease, and the amplitude of ELMs decreases simultaneously until they disappear completely. This scenario exhibits a distinct density threshold, which is dependent on plasma current and wall condition. ELITE/NIMROD simulations indicate that the density at the foot of pedestal and ion diamagnetic effect may play a key role in the achievement of no-ELM operation; the low pedestal foot density might have a strong ion diamagnetic stabilizing effect, which can stabilize the medium-n and high-n Peeling-Ballooning modes. In order to achieve this low pedestal foot density condition, a number of techniques have been employed in EAST, i.e. through extensive lithium wall conditioning and active control of plasma configuration and strike point position. The low recycling no-ELM regime can be extended into a small ELMs regime by increasing the pedestal foot density to facilitate impurity control for long pulse operation, which has been demonstrated in EAST with a pulse length exceeding 101 s. Such a small ELMs regime provide a possible approach toward long-pulse steady-state H-mode operation in future devices.

Divertor Langmuir probes (Div-LPs), embedded in the divertor target plates, are the important diagnostic tools to measure the plasma parameters in EAST divertor region. A series of measurement methods, i.e., single-probe, double-probe and triple-probe schemes, are applied and compared for the Div-LPs on EAST, to get the electron temperature Te and the electron density ne at the same poloidal position, respectively. It is found that the electron temperature Te and the electron density ne measured by the single-probe and the double-probe schemes are basically the same during the plasma discharge phase. Further analysis of the electron energy distribution function (EEDF) represented by the first derivative curve method shows that the electrons conform to a Maxwell distribution, which indicate that the three methods can be applied in the EAST divertor region. Besides, the domed and flush-mounted probe tips for measuring the plasma parameters are also compared, and the results show a good match. The sheath potential coefficient Λ is also calculated from the I-V characteristic curves by two ways, i.e. Λp=(Vplasma-Vf)/Te and ΛI= ln (|Ies/Iis|), and compared with the traditional value Λ=2.8, the results indicate that the ~1.5ΛI and Λ=2.8 are available to replace the Λp under the different strength of toroidal magnetic field in EAST tokamak.

The N-S asymmetry (the north-south hemispheric asymmetry) of sunspot areas for each of the cycles 7-24 have been investigated, and a trend of a long-term characteristic timescale of about eight cycles is inferred, which is confirmed again by studying the fitted lines of the yearly values of the N-S asymmetry of sunspot numbers and sunspot group numbers at solar cycle 24. Then, a periodic behavior of about 12 solar cycles is found in the cumulative counts of yearly sunspot areas for each of the cycles 7-24. Nevertheless, the cumulative counts of sunspot numbers and sunspot group numbers for cycle 24 have different behaviors. Moreover, the dominant hemispheres for cycles 7-23 show a trend of a long-term characteristic timescale of about 12 cycles. However, we cannot determine the dominant hemisphere of cycle 24, as these three parameters give different results for the dominant hemisphere. Cycle 24 is a particular solar activity cycle, as sunspot areas suggest a long characteristic timescale of about 12-cycle length, while sunspot numbers and sunspot group numbers support an eight-cycle period of the N-S asymmetry.

In order to withstand rapid increase in particle and power impact onto the divertor and demonstrate the feasibility of the ITER design under long pulse operation, the upper divertor of the EAST tokamak has been upgraded to actively water-cooled, ITER-like tungsten mono-block structure since the 2014 campaign, which is the first attempt for ITER on the tokamak devices. Therefore, a new divertor Langmuir probe diagnostic system (DivLP) was designed and successfully upgraded on the tungsten divertor to obtain the plasma parameters in the divertor region such as electron temperature, electron density, particle and heat fluxes. More specifically, two identical triple probe arrays have been installed at two ports of different toroidal positions (112.5-deg separated toroidally), which can provide fundamental data to study the toroidal asymmetry of divertor power deposition and related 3-dimension (3D) physics, as induced by resonant magnetic perturbations, lower hybrid wave, and so on. The shape of graphite tip and fixed structure of the probe are designed according to the structure of the upper tungsten divertor. The ceramic support, small graphite tip, and proper connector installed make it possible to be successfully installed in the very narrow interval between the cassette body and tungsten mono-block, i.e., 13.5 mm. It was demonstrated during the 2014 and 2015 commissioning campaigns that the newly upgraded divertor Langmuir probe diagnostic system is successful. Representative experimental data are given and discussed for the DivLP measurements, then proving its availability and reliability.

Hot spots induced by lower hybrid wave in experimental advanced superconducting tokamak tokamak have caused high performance experiment disruption and serious damages to the guard limiters. Experimental and theoretical analyses have been carried out to study its physical mechanism. Plasma density scan experiments indicate that the wall temperature within the hot spots enhanced by a factor of 5 and increases with the plasma density near the antenna. A lower hybrid current drive (LHCD)-only density climb experiment shows that the carbon impurity decreases to a minimum value at certain plasma density and then increases with the line averaged plasma density. A model has been developed to explain the mechanism of sputtering of graphite tiles due to hot spots as the plasma density near the LHCD antenna and the time increases. A theoretical scaling of the heat flux driven by LHCD is also presented and is consistent with the experimental scaling in the Tore Supra tokamak. The simulation results show that the total sputtering flux density has a minimum at a certain plasma density and gradually increases as the plasma density increases or decreases away from the minimum value, and the increase in parallel heat flux near the antenna would enhance the sputtering flux density. The sputtering flux density trend is qualitatively consistent with the density scan experiments. The simulated temporal evolution of sputtered flux implies that the chemical sputtering could be a candidate for the carbon impurity explosion.

In this paper, we will experimentally investigate the power threshold (PL-H) in upper single null plasmas with an ITER-like tungsten divertor under different ∇B drift directions on EAST [F. Ding et al., Commissioning and PSI Behavior of the ITER-Like W/Cu Divertor in EAST 22nd PSI, Rome (2016)]. The power threshold for the low (L) to high (H) confinement mode has a clear and positive toroidal magnetic field, BT, dependence when the ∇ B drift points toward the primary X-point (Bx∇B↑). A factor of 2-3 increase in PL-H is observed for the ∇B drift away from the primary X-point (Bx∇B↓). The edge and core impurities quantified by spectroscopy measurements show comparable levels for the transitions for both drift directions. On the other hand, it is found that the divertor Dα emission just prior to the L-H transition is lower for Bx∇B↑, compared with that for Bx∇B↓. The upper in-out divertor asymmetry, as manifested by particle fluxes measured by the divertor triple Langmuir probe, is most marked for Bx∇B↓, and with significantly more particle flux to the outer divertor. The reversing field increases the particle flux into the upper inner and lower outer divertor, reducing the in-out asymmetry. One important distinction between the two field directions has been observed, with respect to the amplitude of the scrape-off layer (SOL) parallel flow. A dedicated experiment under similar target plasma conditions shows a lower SOL density and thus a steeper density gradient slightly inside the separatrix, where a lower PL-H is found for the Bx∇B↑, compared to that for Bx∇B↓. We, therefore, conclude that the fielddependent SOL plasma conditions play an important role in the transition physics.

A comprehensive work of the effects of plasma current and heating schemes on divertor power footprint widths is carried out in the experimental advanced superconducting tokamak (EAST). The divertor power footprint widths, i.e., the scrape-off layer heat flux decay length λ q and the heat spreading S, are crucial physical and engineering parameters for fusion reactors. Strong inverse scaling of λ q and S with plasma current have been demonstrated for both neutral beam (NB) and lower hybrid wave (LHW) heated L-mode and H-mode plasmas at the inner divertor target. For plasmas heated by the combination of the two kinds of auxiliary heating schemes (NB and LHW), the divertor power widths tend to be larger in plasmas with higher ratio of LHW power. Comparison between experimental heat flux profiles at outer mid-plane (OMP) and divertor target for NB heated and LHW heated L-mode plasmas reveals that the magnetic topology changes induced by LHW may be the main reason to the wider divertor power widths in LHW heated discharges. The effect of heating schemes on divertor peak heat flux has also been investigated, and it is found that LHW heated discharges tend to have a lower divertor peak heat flux compared with NB heated discharges under similar input power. All these findings seem to suggest that plasmas with LHW auxiliary heating scheme are better heat exhaust scenarios for fusion reactors and should be the priorities for the design of next-step fusion reactors like China Fusion Engineering Test Reactor.

A new model for the edge harmonic oscillations (EHOs) in the quiescent H-mode regime has been developed, which successfully reproduces the recent observations in the DIII-D tokamak. In particular, at high E × B flow shear only a few low-n kink modes remain unstable at the plasma edge, consistent with the EHO behavior, while at low E × B flow shear, the unstable mode spectrum is significantly broadened, consistent with the low-n broadband electromagnetic turbulence behavior. The model is based on a new mechanism for destabilizing low-n kink/peeling modes by the E × B flow shear, which underlies the EHOs, separately from the previously found Kelvin–Helmholtz drive. We find that the differential advection of mode vorticity by sheared E × B flows modifies the 2D pattern of mode electrostatic potential perpendicular to the magnetic field lines, which in turn causes a radial expansion of the mode structure, an increase of field line bending away from the mode rational surface, and a reduction of inertial stabilization. This enhances the kink drive as the parallel wavenumber increases significantly away from the rational surface at the plasma edge where the magnetic shear is also strong. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low-n kink/peeling modes so destabilized in the linear regime.

Integrated studies of the scaling of divertor power footprint widths with plasma current in Experimental Advanced Superconducting Tokamak (EAST) L-mode plasmas are carried out through experiments and modeling. The divertor power widths, which consist of the scrape-off layer power decay length λq and the heat spreading S, are calculated from the measurements of divertor Langmuir probes (div-LPs) and scrape-off layer plasma simulation (SOLPS). A strong inverse scaling of both λq (mm) and S (mm) from the div-LP with plasma current Ip (MA) is demonstrated, with the regressions being λ q = 4.37 I p − 1.04 ± 0.075 and S = 2.31 I p − 0.997 ± 0.047. However, a much weaker inverse scaling of λq with Ip is shown by the measurement of outer mid-plane reciprocating probes, which gives λ q , R P = 6.56 I p − 0.31 ± 0.056. It indicates that the connection length may have played a stronger role in the negative scaling of λq with Ip than radial transport. A similar conclusion can also be drawn from a comparison of the si...

Based on continuous wavelet transformation analysis, the daily solar mean magnetic field (SMMF) from 1975 May 16 to 2014 July 31 is analyzed to reveal its rotational behavior. Both the recurrent plot in Bartels form and the continuous wavelet transformation analysis show the existence of rotational modulation in the variation of the daily SMMF. The dependence of the rotational cycle lengths on solar cycle phase is also studied, which indicates that the yearly mean rotational cycle lengths generally seem to be longer during the rising phase of solar cycles and shorter during the declining phase. The mean rotational cycle length for the rising phase of all of the solar cycles in the considered time is 28.28 +/- 0.67 days, while for the declining phase it is 27.32 +/- 0.64 days. The difference of the mean rotational cycle lengths between the rising phase and the declining phase is 0.96 days. The periodicity analysis, through the use of an auto-correlation function, indicates that the rotational cycle lengths have a significant period of about 10.1 years. Furthermore, the cross-correlation analysis indicates that there exists a phase difference between the rotational cycle lengths and solar activity.