Observations of mode frequency increase and the appearance of ITB during the m/n=1/1 kink mode in EAST high electron temperature long pulse operation

A new long-pulse high electron temperature(Te)regime has been achieved on experimental advanced superconducting tokamak by pure radio frequency heating.In this new scenario,there are mainly two confinement states involving two magneto-hydrodynamic(MHD)modes,one of which is identified as m/n=1/1 kink mode(where m and n are the poloidal and toroidal mode numbers,respectively).The frequency evolution of the kink mode is investigated through the three-dimensional,toroidal,and nonlinear Hall-MHD code CLT.We firstly find that the frequency of the m/n=1/1 kink mode significantly increases during each sawtooth crash and then confirmed it through the experimental data.The simulation results indicate that the increase of the mode frequency is mainly due to the significant increase of the electron diamagnetic frequency nearby the reconnection region.We have also observed the internal transport barrier(ITB)during the m/n=1/1 kink mode.To further investigate this m/n=1/1 kink mode in this new regime,the multi-scale interactions between the m/n=1/1 kink mode and turbulence are discussed.

Realization of T_(e0)>10 keV long pulse operation over 100 s on EAST

In 2021,EAST realized a steady-state long pulse with a duration over 100 s and a core electron temperature over 10 keV.This is an integrated operation that resolves several key issues,including active control of wall conditioning,long-lasting fully noninductive current and divertor heat/particle flux.The fully noninductive current is driven by pure radio frequency(RF)waves with a lower hybrid current drive power of 2.5 MW and electron cyclotron resonance heating of 1.4 MW.This is an excellent experimental platform on the timescale of hundreds of seconds for studying multiscale instabilities,electron-dominant transport and particle recycling(plasma-wall interactions)under weak collisionality.

Spatial localization of ECE measurement in EAST LHW-heated plasmas

In this work, electron cyclotron emission(ECE) is simulated by using the code SPECE to study the spatial localization of ECE measurement in EAST plasmas heated by lower hybrid wave(LHW).The results indicate that generally there are two emission layers for an individual frequency in plasmas with non-thermal electrons, and they are separately attributed to the thermal electrons and non-thermal electrons. The emission layer due to the thermal electrons is nearly identical to that for the case with Maxwellian distribution. The emission layer due to non-thermal electrons is well localized in the location of the non-thermal electrons. Even though the non-thermal emission layer is broader, the emission intensity is smaller than that from the thermal emission layer for the cases studied in this work. Localized electron temperature fluctuations can still be distinguished by ECE measurement as long as it does not coexist with the non-thermal electrons. Sawtooth inversion radii and tearing mode island location determined respectively by the ECE measurement and the soft x-ray measurement for a LHW-heated plasma show a good agreement, and this indicates that the ECE measurement in the plasma core region is not seriously polluted.

Neutronic analysis of ITER radial x-ray camera

The radial x-ray camera(RXC) is designed to measure the poloidal profile of plasma x-ray emission with high spatial and temporal resolution. The RXC diagnostic system consists of internal camera module and external camera module that view the core region and outer region through the vertical slots of the diagnostic first wall and diagnostics shield module of the equatorial port plug. To ensure the normal performance of the silicon photodiode array detectors of the cameras in the hard neutron irradiation environment in ITER tokamak, it is necessary to calculate neutron flux, radiation damage and the nuclear heating of the silicon photodiode array detectors and simulate the radiation maps of the range of RXC. This work estimated the nuclear environment of RXC based on Monte Carlo N-particle transport code, plasma scenarios of ITER tokamak and the RXC-integrated ITER CLITE model. The neutron flux of silicon photodiode array detectors and the lifetime of the silicon photodiode detector in the camera were calculated. The neutronic analysis results show that the shielding design has achieved the effect as expected and is able to guarantee the normal work of the detector during the ITER deuterium–deuterium phase without replacement, three detectors of the external camera can be operated during the whole deuterium–tritium phase without replacement.

Experimental study on fast electron generation during internal crash

Hard x-ray(HXR)burst is found during internal crash in the flat top current stage of experimental advanced superconducting tokamak(EAST)discharges and it is caused by fast electrons.The generated electrons during internal crashes may be an operational safety issue in advanced tokamaks.During an internal crash,locations of fast electron generation from HXR evolution agree with areas of magnetic reconnection from soft x-ray(SXR)tomographic reconstruction.Further statistical analyses show a 27μs time difference between SXR crashes and HXR bursts,and the agreement between time broadening of HXR bursts and estimated characteristic time of magnetic reconnection in EAST.The magnetic reconnections during internal crash are proved to generate fast electrons,by both spatial and temporal agreements.

Advances and development trends in eco-friendly pavements

The major contemporary in road pavement engineering is related to the creation of green and sustainable infrastructures,e.g.,reduction of environmental impacts,increase in traffic safety,and transportation efficiency,etc.This review presents the recent trends in research and the technical solutions developed so far to address these challenges.After the analysis of research status in the past decades,a novel technology system of eco-friendly pavements is proposed considering two solutions,materials modification and structure improvement.The construction of an eco-friendly pavement can be achieved thanks to several different technologies ensuring permeable,noise-reducing,self-luminous,and exhaust-decomposing properties as well as apporting lower heat absorbing and enhanced anti-/de-icing characteristics.A systematic review of these technologies is presented pivoting on four main aspects:technical principle,material and structural composition,performance evaluation,and engineering application.The current trend in road engineering is combining the pavement infrastructure with various eco-friendly functions,e.g.,water permeability,noise reduction,low heat absorption,exhaust gas decomposition,and anti-/de-icing.Finally,the review lists the drawbacks of the existing technologies,including high cost,single function,etc.,and depicts the future developing direction and architecture of the next generation of eco-friendly pavements in which the road infrastructure should have more environmentally friendly functions than the existing technology.

Highway constructions on the Qinghai-Tibet Plateau:Challenge,research and practice

Highway constructions on the Qinghai-Tibet Plateau(QTP)face great challenges induced by the unique local environmental,geological,and engineering conditions.The large area of permafrost,great temperature variability,strong UV rays,and complex geological conditions are the major factors that adversely influence the longterm performance of pavement systems.Since 1960s,Chinese engineers and researchers have started conducting research on the QTP to enhance the performance and durability of pavement systems.The present paper provide a comprehensive review of challenge,research and practice of highway constructions on the QTP including the special environmental and geological conditions,history of highway constructions on the QTP,major challenges and the state-of-the-art technology of subgrade constructions on permafrost,developments of the pavement structures and materials,performance prediction and maintenance methods of pavement surfaces,and applications of the research achievements on the first expressway on the QTP(i.e.,Gongyu Expressway).Based on the comprehensive literature review,it can be found that(1)frost heave and thaw weakening induced subgrade disease and longitudinal cracks on the pavement surface are complex coupled water-thermal-load problems.Engineering solutions are focusing on active cooling and thermal insulation methods,which can help to reduce temperature variations in the subgrade and thus improving its stability,(2)the harsh environmental and construction conditions may reduce the early strength and induce premature damage of cement-treated base materials.Some field validations showed that geocell-reinforced or asphalt-treated flexible base materials can provide better long-term performance,(3)the large temperature variability and strong UV rays can significantly accelerate aging of asphalt binders and greatly reduce the service life of asphalt mixtures.Various binder modification methods were developed for improving their viscoelasticity and enhance the low-temperature cracking resistance of pavement surface materials but are still lack of field validation data and comparisons of their life cycle costs.Therefore,it is recommended that a demonstration research project build test sections to examine a range of pavement structures and materials,and compare their long-term performance and life cycle costs,which can serve as important reference for future highway constructions on the QTP.

Simulations of scattered neutrons for the time-of-flight enhanced diagnostics(TOFED)neutron spectrometer on EAST

The time-of-flight enhanced diagnostics(TOFED)neutron spectrometer has been installed in TOFED house,which is a newly-built neutron diagnostic lab outside the EAST experimental hall.The line of sight(LOS)of TOFED is defined by the collimator going through the 150 cm biological shielding wall,which can reduce background neutrons very effectively for the neutron spectral measurements.The Monte Carlo code MCNP5 is used in the simulations to characterize collimation effects and the radiation safety of the new house.The collimator makes neutron flux almost fully perpendicular to S 1 detectors.In addition,the proportion of scattered neutrons in the LOS of the TOFED is obtained for the measured spectral data interpretation.The simulation results show that the TOFED house satisfies the requirement for the TOFED operations at EAST and gives a safe environment for personnel access during the EAST operation.

Saturation characteristics of low voltage ionization chamber filled with argon or xenon

Argon and xenon are both attractive working gas for low voltage ionization chamber(LVIC),which is a promising candidate for ITER X-ray detectors.In this work,the performances of Arfilling LVIC(Ar-LVIC)and Xe-filling LVIC(Xe-LVIC)as well as the impacts of operation parameters were investigated.Saturation curves of Ar-LVIC and Xe-LVIC with pressure from 0.4 to 1.2 bar were measured with a tungsten X-ray source.The minimum voltage of saturation region(V_(min))of Ar-LVIC and Xe-LVIC,the relationship between V_(min)and saturation current,the ideal operating voltage in ITER and impacts of pressure on saturation current were studied.It was found that Ar-LVIC had smaller V_(min)and saturation currents which decreased with the drop of pressure from 1.2 to 0.4 bar;Xe-LVIC had larger V_(min)and saturation currents which did not obviously decrease with the same pressure drop.It is envisaged that ITER can take advantage of the larger saturation current and lower pressure of Xe-LVIC in the non-nuclear operation phase,and flexibility of pressure and low sensitivity to neutron/gamma radiation of Ar-LVIC in the nuclear operation phase.

Spontaneous current relaxation in NBI heated plasmas on EAST

We report on current profile evolution in EAST NBI driven plasmas where two neutral beams are injected,one during the current ramp phase and the second during flattop.At the end of the current ramp phase,it is found that a flat q profile with q0-1 is achieved with low magnetic shear in the core.It is observed that plasma current and density both relax much faster than resistive time,even in the absence of sawtooth activity when H-L transition occurs.Density fluctuations associated with magnetic perturbations（3/2） as a precursor to the H-L transition are observed.It is likely that these modes play a role in fast current transport.

Gaussian process tomography based on Bayesian data analysis for soft x-ray and AXUV diagnostics on EAST

This work presents the Gaussian process tomography(GPT)based on Bayesian data analysis and its applications in soft x-ray(SXR)and absolute extreme ultraviolet spectroscopy(AXUV)diagnostics on experimental advanced superconducting tokamak(EAST).This is the first application of the GPT method in the AXUV diagnostic system in fusion devices.It is found that even if only horizontal detector arrays are used to reconstruct the two-dimensional(2D)distribution of SXR and AXUV emissivity fields,the GPT method performs robustly and extremely fast,which enables the GPT method to provide real-time feedback on impurity transport and fast magnetohydrodynamics(MHD)events.By reconstructing SXR emissivity in the poloidal cross section on EAST,an m/n=1/1 internal kink mode has been observed,and the plasma redistribution due to the kink mode is clearly visible in the reconstructions,where m is the poloidal mode number and n is the toroidal mode number.Sawtooth-like internal disruptions extended throughout the entire plasma core and mainly driven by the m/n=2/1 mode have been acquired.During the sawtooth-like internal disruption crash phase,the conversion from an m=2 mode to an m=1 mode is observed.Using the reconstructed AXUV emissivity field we were able to observe the process of impurity accumulated in the plasma core and the mitigation of core impurity due to neon injection in the plasma edge.The data from all other diagnostics involved in the analysis shows that the reconstructions from AXUV measurements are reliable.

Application of local Monte Carlo method in neutronics calculation of EAST radial neutron camera

The Local Monte Carlo(LMC)method is used to solve the problems of deep penetration and long time in the neutronics calculation of the radial neutron camera(RNC)diagnostic system on the experimental advanced superconducting tokamak(EAST),and the radiation distribution of the RNC and the neutron flux at the detector positions of each channel are obtained.Compared with the results calculated by the global variance reduction method,it is shown that the LMC calculation is reliable within the reasonable error range.The calculation process of LMC is analyzed in detail,and the transport process of radiation particles is simulated in two steps.In the first step,an integrated neutronics model considering the complex window environment and a neutron source model based on EAST plasma shape are used to support the calculation.The particle information on the equivalent surface is analyzed to evaluate the rationality of settings of equivalent surface source and boundary.Based on the characteristic that only a local geometric model is needed in the second step,it is shown that the LMC is an advantageous calculation method for the nuclear shielding design of tokamak diagnostic systems.

Excitation of RSAEs during Sawteeth-Like Oscillation in EAST

The excitation condition of reversed shear Alfven eigenmodes(RSAEs)has been investigated during sawtoothlike oscillation in the EAST tokamak.The sawtooth-like phenomena can be reproduced in the configuration of reversed magnetic shear,and the threshold gradient of electron temperature is formed accordingly,together with the increasing of the confinement of thermal particles.The distribution function of energetic ions density is altered dramatically when the neutral beam is switched from NBI1 L(tangent)to NBI1 R(perpendicular),which can be captured by the measurement of radial neutron camera.The RSAEs are excited easily in the vicinity of q_(min)(1.99 m≤R≤2.06 m)for the injection of neutral beam with perpendicular direction,which should be excited by the steep gradient of energetic ions density.Furthermore,the excitation of RSAEs and the formation of threshold gradient of electron temperature can take place concurrently,which means that the neutral beam with perpendicular injection is beneficial for the establishment of internal transport barrier.

Waring−Goldbach problem for one prime power and four prime cubes under Riemann Hypothesis

Let k≥1 be an integer.Assume that RH holds.In this paper we prove that a suitable asymptotic formula for the average number of representations of integers n=p^(k)_(1)+p^(3)_(2)+p^(3)_(3)+p^(3)_(4)+p^(3)_(5),where p_(1),p_(2),p_(3),p_(4),p_(5)are prime numbers.This expands the previous results.

Laboratory evaluation of cement treated aggregate containing crushed clay brick

The waste clay bricks from debris of buildings were evaluated through lab tests as environ- mental friendly materials for pavement sub-base in the research. Five sets of coarse aggregates which contained 0, 25%, 50%, 75% and 100% crushed bricks, respectively, were blended with sand and treated by 5 % cement. The test results indicated that cement treated aggregate which contains crushed clay brick aggregate had a lower maximum dry density （MDD） and a higher optimum moisture content （OMC）. Moreover, the unconfined compressive strength （UCS）, resilience modulus, splitting strength, and frost resistance performance of the specimens decreased with increase of the amount of crushed clay brick aggregate. On the other hand, it can be observed that the use of crushed clay brick in the mixture decreased the dry shrinkage strain of the specimens. Compared with the asphalt pave- ment design specifications of China, the results imply that the substitution rate of natural aggregate with crushed clay brick aggregate in the cement treated aggregate sub-base material should be less than 50% （5 % cement content in the mixture）. Furthermore, it needs to be noted that the cement treated aggre- gate which contains crushed clay bricks should be cautiously used in the cold region due to its insuffi- cient frost resistance performance.

Quadratic forms connected with Fourier coefficients of Maass cusp forms

For the normalized Fourier coefficients of Maass cusp forms λ（n） and the normalized Fourier coefficients of holomorphic cusp forms a（n）, we give the bound of