Equilibrium reconstruction method for self-organized plasmas on reversed field pinches with polarimeter-interferometer

In the reversed field pinch(RFP),plasmas exhibit various self-organized states.Among these,the three-dimensional(3D)helical state known as the“quasi-single-helical”(QSH)state enhances RFP confinement.However,accurately describing the equilibrium is challenging due to the presence of 3D structures,magnetic islands,and chaotic regions.It is difficult to obtain a balance between the available diagnostic and the real equilibrium structure.To address this issue,we introduce KTX3DFit,a new 3D equilibrium reconstruction code specifically designed for the Keda Torus eXperiment(KTX)RFP.KTX3DFit utilizes the stepped-pressure equilibrium code(SPEC)to compute 3D equilibria and uses polarimetric interferometer signals from experiments.KTX3DFit is able to reconstruct equilibria in various states,including axisymmetric,doubleaxis helical(DAx),and single-helical-axis(SHAx)states.Notably,this study marks the first integration of the SPEC code with internal magnetic field data for equilibrium reconstruction and could be used for other 3D configurations.

Effects of vacuum magnetic field region on the compact torus trajectory in a tokamak plasma

The trajectory of the compact torus(CT)within a tokamak discharge is crucial to fueling.In this study,we developed a penetration model with a vacuum magnetic field region to accurately determine CT trajectories in tokamak discharges.This model was used to calculate the trajectory and penetration parameters of CT injections by applying both perpendicular and tangential injection schemes in both HL-2A and ITER tokamaks.For perpendicular injection along the tokamak's major radius direction from the outboard,CTs with the same injection parameters exhibited a 0.08 reduction in relative penetration depth when injected into HL-2A and a 0.13reduction when injected into ITER geometry when considering the vacuum magnetic field region compared with cases where this region was not considered.In addition,we proposed an optimization method for determining the CT's initial injection velocity to accurately calculate the initial injection velocity of CTs for central fueling in tokamaks.Furthermore,this paper discusses schemes for the tangential injection of CT into tokamak discharges.The optimal injection angle and CT magnetic moment direction for injection into both HL-2A and ITER were determined through numerical simulations.Finally,the kinetic energy loss occurring when the CT penetrated the vacuum magnetic field region in ITER was reduced byΔEk=975.08 J by optimizing the injection angle for the CT injected into ITER.These results provide valuable insights for optimizing injection angles in fusion experiments.Our model closely represents actual experimental scenarios and can assist the design of CT parameters.

Preliminary compact torus injection experiments on the Keda Torus eXperiment reversed field pinch

A new compact torus injector(KTX-CTI)has been built for injection experiments on the Keda Torus eXperiment(KTX)reversed field pinch(RFP).The aim is to study the fundamental physics governing the compact torus(CT)central fueling processes.In experiments conducted under the sole influence of a 0.1 T toroidal magnetic field,the injected CT successfully penetrated the entire toroidal magnetic field,reaching the inner wall of the KTX vacuum vessel.Upon reaching the inner wall,the CT diffused both radially outward and toroidally within the vessel at a discernible diffusion speed.Moreover,the inherent helicity within the CT induced a modest KTX plasma current of 200 A,consistent with predictions based on helicity conservation.CT injection demonstrated the capability to initiate KTX discharges at low loop voltages,suggesting its potential as a pre-ionization and current startup technique.During RFP discharges featuring CT injection,the central plasma density was found to exceed the Greenwald density limit,with more peaked density profiles,indicating the predominant confinement of CT plasma within the core region of the KTX bulk plasma.

The impact of toroidal mode coupling on high-density discharges in J-TEXT

Density limit has long been a widely studied issue influencing the operating range of tokamaks.The rapid growth of the m/n=2/1(where m and n are poloidal and toroidal mode numbers,respectively)tearing mode is generally regarded as a primary precursor to the density limit disruption.In this experiment,the coupling of the m/n=1/1 mode and the m/n=2/1 mode in highdensity plasma was observed.During a sawtooth cycle,the frequencies of the two modes gradually converge until they become equal.After that,toroidal coupling occurs between the 1/1 and 2/1 modes,resulting in a mutually fixed phase relationship.With the occurrence of toroidal coupling,the 2/1 mode is stabilized.Prior to the disruption,the cessation of the 1/1 and 2/1 mode coupling,along with the rapid growth in the amplitude of the 2/1 mode,can be observed.Additionally,under the same parameters,comparing discharges with or without the 1/1 mode,it is found that the presence of the 1/1 mode leads to higher plasma density and temperature parameters.

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.

Development of a compact torus injection system for the Keda Torus eXperiment

A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues associated with interaction between a compact torus(CT)and RFP.The key interests include fueling directly into the reactor center,confinement improvement,and the injection of momentum and helicity into the RFP discharges.The CT velocity and mass have been measured using a multichannel optical fiber interferometer,and for the first time the time evolution of the CT density profile during CT propagation is obtained.The effects of discharge parameters on the number of injected particles,CT velocity and CT density have been characterized:the maximum hydrogen CT plasma mass,m,CTis 50μg,corresponding to 30%of the mass in a typical KTX plasma;the CT velocity exceeds 120 km s-1.It is observed for the first time that multiple CTs can be produced and emitted during a very short period(<100μs)in one discharge,which is significant for the future study of repetitive CT injection,even with an ultra-high frequency.

Design of the poloidal field system for KTX

The design of the poloidal field （PF） system includes the ohmic heating field system and the equilibrium （EQ） field system, and is the basis for the design of a magnetic confinement fusion device. A coupling between the poloidal and plasma currents, especially the eddy current in the stabilizing shell, yields design difficulties. The effects of the eddy current in the stabilizing shell on the poloidal magnetic field also cannot be ignored. A new PF system design is thus proposed. By using a low-μ material （μ = 0.001, ε = 1） instead of a conductive shell, an electromagnetic model is established that can provide a continuous eddy current distribution on the conductive shell. In this model, a 3D time-domain problem with shells translates into a 2D magnetostatic problem, and the accuracy of the calculation is improved. Based on these current distributions, we design the PF system and analyze how the EQ coils and conductive shell affect the plasma EQ when the plasma ramps up. To meet the mainframe design requirements and achieve an efficient power-supply design, the position and connection of the poloidal coils are optimized further.

Construction of an Hα diagnostic system and its application to determine neutral hydrogen densities on the Keda Torus eXperiment

A 10-channel Hα diagnostic system has been designed with the rapid response rate of 300 kHz, spatial resolution of about 40 mm, and overlap between adjacent channels of about 3%, and it has been implemented successfully on Keda Torus eXperiment(KTX), a newly constructed, reversed field pinch(RFP) experimental device at the University of Science and Technology of China(USTC). This diagnostic system is a very important tool for the initial KTX operations. It is compact,with an aperture slit replacing the traditional optical lens system. A flexural interference filter is designed to prevent the center wavelength from shifting too much as the increase of angle from vertical incidence. To eliminate the stray light,the interior of the system is covered with the black aluminum foil having a very high absorptivity. Using the Hαemission data, together with the profiles of electron temperature and density obtained from the Langmuir probe, the neutral density profiles have been calculated for KTX plasmas. The rapid response rate and good spatial resolution of this Hαdiagnostic system will be beneficial for many studies in RFP plasma physics.

Fast radial scanning probe system on KTX

A fast radial scanning probe system was constructed for the Keda Torus eXperiment(KTX)to measure the profiles of boundary plasma parameters such as floating potential,electron density,temperature,transport fluxes,etc.The scanning probe system is driven by slow and fast motion mechanisms,corresponding to the stand-by movement of a stepping motor and the fast scanning movement of a high-torque servo-motor,respectively.In fast scanning,the scanner drives the probe radially up to 20 cm at a maximum velocity of 4.0 m s-1.A noncontact magnetic grating ruler with a high spatial resolution of 5μm is used for the displacement measurement.New scanning probe can reach the center of plasmas rapidly.The comparison of plasma floating potential profiles obtained by a fixed radial rake probe and the single scanning probe suggests that the high-speed scanning probe system is reliable for measuring edge plasma parameter profiles on the KTX device.

The theoretical study on intermittency and propagation of geodesic acoustic mode in L-mode discharge near tokamak edge

Through a systematically developed theory,we demonstrate that the motion of Instanton identified in Zhang et al(2017 Phys.Plasmas 24122304)is highly correlated to the intermittent excitation and propagation of geodesic acoustic mode(GAM)that is observed in tokamaks.While many numerical simulations have observed the phenomena,it is the first theory that reveals the physical mechanism behind GAM intermittent excitation and propagation.The preceding work is based on the micro-turbulence associated with toroidal ion temperature gradient mode,and slab-based phenomenological model of zonal flow.When full toroidal effect is introduced into the system,two branches of zonal flow emerge:the torus-modified low frequency zonal flow(TLFZF),and GAM,necessitating a unified exploration of GAM and TLFZF.Indeed,we observe that the transition from the Caviton to Instanton is triggered by a rapid zero-crossing of radial group velocity of drift wave and is found to be strongly correlated with the GAM onset.Many features peculiar to intermittent GAMs,observed in real machines,are thus identified in the numerical experiment.The results will be displayed in figures and in a movie;first for single central rational surface,and then with coupled multiple central rational surfaces.The periodic bursting first shown disappears as being replaced by irregular one,more similar to the intermittent characteristics observed in GAM experiments.

Investigations on the time evolution of the plasma density in argon electron-beam plasma at intermediate pressure

The time evolution of the argon electron-beam plasma at intermediate pressure and low electron beam intensily was presented.By applying the amplitude modulation with the frequency of 20 Hz on the stable beam current,the plasma evolution was studied.A Faraday cup was used for the measurement of the electron beam current and a single electrostatic probe was used for the measurement of the ion current.Experimental results indicated that the ion current was in phase with the electron beam current in the pressure range from 200 Pa to 3000 Pa and in the beam current range lower than 20 mA,the residual density increased approximately linearly with the maximum density in the log-log plot and the fitting coefficient was irrelative to the pressure.And then three kinds of kinetic models were developed and the simulated results given by the kinetic model,without the consideration of the excited atoms,mostly approached to the experimental results.This indicated that the effect of the excited atoms on the plasma density can be ignored at intermediate pressure and low electron beam current intensity,which can greatly simplify the kinetic model.In the end.the decrease of the plasma density when the beam current was suddenly off was studied based on the simplified model and it was found that the decease characteristic at intermediate pressure was approximate to the one at high pressure at low electron beam intensity,which was in good accordance with the experimental results.

The investigation of quasi coherent mode on EAST using Doppler reflectometry

An electrostatic Quasi coherent mode has been observed in density fluctuations and perpendicular velocity fluctuations with the frequency range of 3–80 k Hz on the Experimental Advanced Superconducting Tokamak using multi-channel Doppler reflectometry.It appears in the edge localized mode(ELM)-free period after L-H transition or in the inter-ELM period.The mode rotates almost together with the plasma with the poloidal wave number around 0.6cm-1 and its frequency chirps with plasma poloidal velocity.The mode can exist in a large radial coverage(ρ=0.75–0.98),and peaks near the top of pedestal,suggesting that it might be excited in the steep gradient pedestal region,and spread into the core area.

Zonal flow energy ratio evolution during L-H and H-L transitions in EAST plasmas

The essential role of zonal flow in the L-H transition and the suppression of turbulence have been studied with a long range correlation technique using Langmuir probe arrays in EAST tokamak.Two toroidally localized probe arrays are used to measure the zonal flow during L-H transition and H-L back transition.The energy ratio of the low frequency zonal flow to the total drift wave turbulence is calculated.During ELM-free H mode,the energy ratio is higher than that in L mode,which reveals the important role of zonal flows in regulating turbulence amplitude in L-H transition.

Nano-formulated delivery of active ingredients from traditional Chinese herbal medicines for cancer immunotherapy

Cancer immunotherapy has garnered promise in tumor progression, invasion, and metastasis through establishing durable and memorable immunological activity. However, low response rates, adverse side effects, and high costs compromise the additional benefits for patients treated with current chemical and biological agents. Chinese herbal medicines (CHMs) are a potential treasure trove of natural medicines and are gaining momentum in cancer immunomodulation with multi-component, multi-target, and multi-pathway characteristics. The active ingredient extracted from CHMs benefit generalized patients through modulating immune response mechanisms. Additionally, the introduction of nanotechnology has greatly improved the pharmacological qualities of active ingredients through increasing the hydrophilicity, stability, permeability, and targeting characteristics, further enhancing anti-cancer immunity. In this review, we summarize the mechanism of active ingredients for cancer immunomodulation, highlight nano-formulated deliveries of active ingredients for cancer immunotherapy, and provide insights into the future applications in the emerging field of nano-formulated active ingredients of CHMs.