Experimental study of core MHD behavior and a novel algorithm for rational surface detection based on profile reflectometry in EAST

Microwave reflectometry is a powerful diagnostic that can measure the density profile and localized turbulence with high spatial and temporal resolution and will be used in ITER,so understanding the influence of plasma perturbations on the reflect signal is important.The characteristics of the reflect signal from profile reflectometry,the time-of-flight(TOF)signal associated with the MHD instabilities,are investigated in EAST.Using a 1D full-wave simulation code by the Finite-DifferenceTime-Domain(FDTD)method,it is well validated that the local density flattening could induce the discontinuity of the simulated TOF signal and an obvious change of reflect amplitude.Experimental TOF signals under different types of MHD instabilities(sawtooth,sawtooth precursors and tearing mode)are studied in detail and show agreement with the simulation.Two new improved algorithms for detecting and localizing the radial positions of the low-order rational surface,the cross-correlation and gradient threshold(CGT)method and the 2D convolutional neural network approach(CNN)are presented for the first time.It is concluded that TOF signal analysis from profile reflectometry can provide a straightforward and localized measurement of the plasma perturbation from the edge to the core simultaneously and may be a complement or correction to the q-profile control,which will be beneficial for the advanced tokamak operation.

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.

Blob properties in I-mode and ELM-free H-mode compared to L-mode on EAST

The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak,including the blob detection rate Nb,sizeδb,lifetimeτb and radial velocity vr,b.The blob properties in L-mode and I-mode are similar,and those in ELM-free H-mode are different to them.The blob Nbis smaller whileτbis larger in H-mode.The experimental blob sizeδband velocity scalings vr,b-δb show a good agreement with the theoretical models.The variation in blob properties during the L-I and H-L transitions,and their relations to the scrape-off layer(SOL)density,edge and SOL turbulence,and SOL collisionality are discussed.The suppression of the edge(inside the last closed flux surface)turbulence is not reflected in the blob behavior,while the blob detection rate shows a correlation with the SOL density and its low-frequency(3–50 kH z)fluctuations.In addition,the blob detection rate is found to increase with the divertor collisionalityΛdiv,indicating a dependence of blob behavior onΛdiv.The differences in blob detection rates among the three operating regimes might be due to their different SOL densities and collisionalities.The investigation contributes to understanding the influences of edge and SOL plasma parameters on the blob behavior.

Feasibility of applying the lower cut-off frequency for the density radial coverage extension in EAST reflectometry measurement

The extraordinary mode(X-mode)lower cut-off frequency is proposed for use in the reflectometry diagnostic on ITER for the electron density profile measurement,which is a trade-off between extreme plasma parameters and the accessible probing frequency.In contemporary experiments,the lower cutoff frequency can be identified at the probing frequency below the electron cyclotron frequency(f_(ce)) under certain plasma conditions.We provide here,for the first time,the experimental validation of the use of the lower cut-off frequency for the density profiles via the reflectometry measurement on EAST.The corresponding group delay of the lower cut-off frequency evolves continuously with the upper one,revealing a reasonable radial coverage extension of reflectometry measurement toward the plasma core.It is concluded that the lower cut-off frequency can be used as a supplement to the upper one in the density profile inversion process,which is of particular interest in the high magnetic field and/or density discharge to extend the radial coverage of reflectometry measurement.

Experimental investigation of scrape-off layer blob high density transition in L-mode plasmas on EAST

Lithium Beam Emission Spectroscopy systems in the outer midplane and divertor Langmuir probe arrays embedded in the divertor target plates,are utilized to investigate the scrape-off layer(SOL)blob transition and its relation with divertor detachment on EAST.The blob transition in the near SOL is observed during the density ramp-up phase.When the plasma density,normalized to the Greenwald density limit,exceeds a threshold of f_(GW)~0.5,the blob size and lifetime increases by 2–3 times,while the blob detection rate decreases by about 2 times.In addition,a weak density shoulder is observed in the near SOL region at the same density threshold.Further analysis indicates that the divertor detachment is highly correlated with the blob transition,and the density threshold of blob transition is consistent with that of the access to the outer divertor detachment.The potential physical mechanisms are discussed.These results could be useful for the understanding of plasma-wall interaction issues in future devices that will operate under a detached divertor and high density conditions(over the blob transition threshold).

Experimental study of double tearing mode on EAST tokamak

The double tearing mode(DTM)in a high βN(βN>1.5)discharge with internal transport barrier on EAST was investigated.A 15 kHz tearing mode(TM)(m≥3,n=3)appears at outer q=2 surface at first,which is stable in the highβN phase.Then a 2 kHz TM(m=2,n=1)occurs at inner q=2 surface.Soon after,high βN collapsed with the crash of ELM,and DTM formed during the collapse of βN.The positions of the two islands of the DTM are consistent with the q=2 surface.The temperature fluctuations are the strongest between the two magnetic islands.A statistical analysis of high βN discharges operating with the reversed magnetic shear configuration in the EAST 2015-2018 campaign revealed the existence of the DTM in many discharges.During the DTM phase,all βN are reduced by 10%-30% within 0.1 s.However,there are two different βN behaviors thereafter-with and without βN recovery.Studying the physical mechanism of βN recovery during the DTM phase will benefit steady-state operation with reversed shear configurations in the future.

Experimental study of core and edge fluctuations by reflectometry on EAST tokamak

An eight-channel poloidal correlation reflectometer(PCR)with O-mode polarization has been installed in the EAST tokamak to measure the fluctuations from core to edge.The PCR launches eight different frequency microwaves(20.4,24.8,33,40,42.4,48,52.6,57.2 GHz)into the plasma from the low field side and two poloidally separated antennae are used to receive the reflected waves.As a result,the diagnostic can measure fluctuations in eight(radial)×two(poloidal)spatial positions.The diagnostic has been applied to study the core and edge pedestal fluctuations during an inter-ELM phase in H-mode plasma.This inter-ELM phase can be divided into two stages.In the first stage,a low frequency(<50 kHz)broadband fluctuation dominates in the pedestal gradient region.In the second stage,this fluctuation is strongly suppressed and quasi-coherent fluctuations(QCFs)appear.The QCF’s amplitude increases with the pedestal density gradient,implying density gradient driven instabilities.But the core fluctuations inside the pedestal show no evident changes during the inter-ELM phase.

Serum semaphorin 4C as a diagnostic biomarker in breast cancer:A multicenter retrospective study

Background:To date,there is no approved blood-based biomarker for breast cancer detection.Herein,we aimed to assess semaphorin 4C(SEMA4C),a pivotal protein involved in breast cancer progression,as a serum diagnostic biomarker.Methods:We included 6,213 consecutive inpatients from Tongji Hospital,Qilu Hospital,and Hubei Cancer Hospital.Training cohort and two validation cohorts were introduced for diagnostic exploration and validation.A pan-cancer cohort was used to independently explore the diagnostic potential of SEMA4C among solid tumors.Breast cancer patients who underwent mass excision prior to modified radical mastectomy were also analyzed.We hypothesized that increased pretreatment serum SEMA4C levels,measured using optimized in-house enzymelinked immunosorbent assay kits,could detect breast cancer.The endpoints were diagnostic performance,including area under the receiver operating characteristic curve(AUC),sensitivity,and specificity.Post-surgery pathological diagnosis was the reference standard and breast cancer staging followed the TNM classification.There was no restriction on disease stage for eligibilities.Results:We included 2667 inpatients with breast lesions,2378 patients with other solid tumors,and 1168 healthy participants.Specifically,118 patients with breast cancer were diagnosed with stage 0(5.71%),620 with stage I(30.00%),966 with stage II(46.73%),217 with stage III(10.50%),and 8 with stage IV(0.39%).Patients with breast cancer had significantly higher serum SEMA4C levels than benign breast tumor patients and normal controls(P<0.001).Elevated serum SEMA4C levels had AUC of 0.920(95%confidence interval[CI]:0.900–0.941)and 0.932(95%CI:0.911–0.953)for breast cancer detection in the two validation cohorts.The AUCs for detecting early-stage breast cancer(n=366)and ductal carcinoma in situ(n=85)were 0.931(95%CI:0.916–0.946)and 0.879(95%CI:0.832–0.925),respectively.Serum SEMA4C levels significantly decreased after surgery,and the reduction was more striking after modified radical mastectomy,compared with mass excision(P<0.001).The positive rate of enhanced serum SEMA4C levels was 84.77%for breast cancer and below 20.75%for the other 14 solid tumors.Conclusions:Serum SEMA4C demonstrated promising potential as a candidate biomarker for breast cancer diagnosis.However,validation in prospective settings and by other study groups is warranted.

NIR-Ⅱ fluorescence/photoacoustic imaging of ovarian cancer and peritoneal metastasis

Ovarian cancer is a global problem,and is typically diagnosed in the middle or late stages,with a mysterious abdominal mass or atypical abdominal metastases due to the lack of specific initial diagnostic methods.Dual-modal near-infrared Ⅱ(NIR-Ⅱ,1,000–1,700 nm)fluorescence/photoacoustic imaging has great potential in early ovarian cancer diagnosis and image-guided surgery due to its high sensitivity and deep penetration.Herein,we report a novel organic NIR-Ⅱ dye(H10)with excellent aggregation-induced-emission(AIE)characteristics(I/I0>1.6)utilizing a selenadiazolo-[3,4-f]benzo[c][1,2,5]thiadiazole(ST)-based building block.Then,water-soluble and biocompatible H10@follicle-stimulating hormone(H10@FSH)dots with superior optical/photoacoustic properties and a tenfold increase in ovarian-specific targeting ability were synthesized.Finally,for the first time,in vivo dual-mode NIR-Ⅱ fluorescent/photoacoustic(PA)imaging and image-guided surgery of patient-derived tumor xenograft(PDTX)and micro-metastatic abdominal ovarian cancer lesions were investigated.This novel strategy will establish a new method for early detection of ovarian cancer and significantly improve the prognosis of ovarian cancer patients.