Analysis of the Plasma Properties Affected by Magnetic Confinement with Special Emphasis on Helicon Discharges

A one-dimensional radial non-uniform fluid model is employed to study plasma behaviors with special emphasis laid on helicon discharges. The plasma density ne, electron temperature Te, electron azimuthal and radial drift velocities are investigated in terms of the plasma radius rp, magnetic field intensity B0 and gas pressure p0, by assuming radial ambipolar diffusion and negligible ion cyclotron movement. The results show that the magnetic confinement plays an important role in the discharge equilibrium, especially at low pressure, which significantly reduces Te compared with the case of a negligible magnetic field effect, and higher B0 leads to a greater average plasma density. Te shows little variations in the plasma density range of 1011 cm-3- 1013 cm-3 for p0 〈 3.0 mTorr. Comparison of the simulation results with experiments suggests that the model can make reasonable predictions of Te in low pressure helicon discharges.

Numerical simulation on magnetic confinement characteristics of internal vortex electrostatic cyclone precipitator under different working voltages

Aiming at improving the capture performance of internal vortex electrostatic cyclone precipitator(ECP),a theoretical model with mechanics-electric-magnetic coupling was established,the collection efficiency of magnetic confinement ECP under different working voltages was simulated,and the influence of magnetic flux intensity on the removal performance of submicron particles was explored.Results show that the number of particles escaped from the cyclone is greatly reduced after the introduction of magnetic field and electric field,indicating that charging effect and magnetic confinement are more conductive to trap submicron particles in the internal vortex ECP.The lower the working voltage is,the worse the charging lifting effect is,but the stronger the magnetic confinement characteristics are.Furthermore,the contributions of charging effect to collection efficiency and magnetic confinement characteristics are more obvious at a weaker magnetic flux density.The research results can provide a practical new idea for the innovative design of ECP.

Magnetic confinement fusion： a brief review

Fusion energy is considered to be the ultimate energy source, which does not contribute to climate change compared with conventional fossil fuel. It is massive compared with unconventional renewable energy and demonstrates fewer safety features compared with unconventional fission energy. During the past several decades, never-ceasing efforts have been made to peacefully utilize the fusion energy in various approaches, especially inertial confinement and magnetic confinement. In this paper, the main developments of magnetic confinement fusion with emphasis on confinement systems as well as challenges of materials related to superconducting magnet and plasmafacing components are reviewed. The scientific feasibility of magnetic confinement fusion has been demonstrated in JET, TFTR, JT-60, and EAST, which instigates the construction of the International Thermonuclear Experimental Reactor （ITER）. A fusion roadmap to DEMO and commercial fusion power plant has been established and steady progresses have been made to achieve the ultimate energy source.

The Enhanced Effect of Optical Emission from Laser Induced Breakdown Spectroscopy of an Al-Li Alloy in the Presence of Magnetic Field Confinement

In this paper, the influence of magnetic field strength on laser-induced breakdown spectroscopy （LIBS） has been investigated for various pressures. The plasma plume was produced by employing Q-switch Nd：YAG laser ablation of an A1-Li alloy operating at a 1064 nm wavelength. The results indicated that the LIBS intensity of the A1 and Li emission lines is boosted with an increase of magnetic strength. Typically, the intensity of the A11 and Li I spectral emissions can be magnified by 1.5-3 times in a steady magnetic field of 1.1 T compared with the field-free case. Also, in this investigation we recorded time-resolved images of the laser-produced plume by employing a fast ICCD camera. The results show that the luminance of the plasma is enhanced and the time of persistence is increased significantly, and the plasma plume splits into two lobes in the presence of a magnetic field. The probable reason for the enhancement is the magnetic confinement effect which increases the number density of excited atoms and the population of species in a high energy state. In addition, the electron temperature and density are also augmented by the magnetic field compared to the field-free case.

Implosion Plasma Driven Fusion Pellet of Inertial Confinement(A Short Memorandum)

The implosion plasma drive fusion pellet of inertial confinement is a concept related to nuclear fusion,a process in which atomic nuclei combine to form heavier nuclei,releasing a large amount of energy in the process.The implosion plasma drive fusion pellet is a potential fuel source for achieving controlled nuclear fusion.ICF(inertial confinement fusion)is a technique used to achieve fusion by compressing a small target containing fusion fuel to extremely high densities and temperatures using lasers or other methods.The implosion plasma drive fusion pellet concept involves using a small pellet of deuterium and tritium(two isotopes of hydrogen)as fusion fuel,and then rapidly heating and compressing it using a pulsed power system.The implosion process creates a high-pressure plasma that ignites the fusion reactions,releasing energy in the form of neutrons and charged particles.The resulting energy can be captured and used for power generation.This technology is still in the experimental stage,and significant research and development is required to make it commercially viable.However,it has the potential to provide a virtually limitless source of clean energy with no greenhouse gas emissions or long-term radioactive waste.Be that as it may,ICF has to get exact control of the implosion process,mitigate insecurities,and create modern materials and advances to resist the extraordinary conditions of the combined response.

Summary of the 10th Conference on Magnetically Confined Fusion Theory and Simulation(CMCFTS)

This paper gives a summary of the organization and the presentations delivered at the 10th Conference on Magnetically Confined Fusion Theory and Simulation(CMCFTS)held in Zhuhai,China,from 28th to 31st October 2022.The conference focused on the latest progress in the research of the magnetic confined fusion plasma theory and simulations,as well as the largescale numerical simulation techniques developed in recent years.This conference is held both online and offline,with about 110 domestic participants from 18 institutes participating in the live conference,and the statistical data from the live broadcast platform indicated that the online conference attracted over 20000 views per day.A summary of the conference is given,and the history of the CMCFTS is presented.A brief introduction to the poster section is also included in this paper.

Final results of the first phase of the PROTO-SPHERA experiment: obtainment of the full current stable screw pinch and first evidences of the jet + torus combined plasma configuration

In astrophysics, the boundary conditions for plasma phenomena are provided by nature and the astronomer faces the problem of understanding them from a variety of observations [Hester J J et al 1996 Astrophys. J. 456 225], on the other hand, in laboratory plasma experiments the electromagnetic boundary conditions become a major problem in the set-up of the machine that produces the plasma, an issue that has to be investigated step by step and to be modified and adapted with great patience, in particular in the case of an innovative plasma confinement experiment. The PROTO-SPHERA machine [Alladio F et al 2006 Nucl. Fusion 46 S613] is a magnetic confinement experiment, that emulates in the laboratory the jet + torus plasma configurations often observed in astrophysics: an inner magnetized jet of plasma centered on the(approximate) axis of symmetry and surrounded by a magnetized plasma torus orthogonal to this jet. The PROTO-SPHERA plasma is simply connected, i.e., no metal current conducting rod is linked to the plasma torus, while instead it is the inner magnetized plasma jet(in the following always called the plasma centerpost) that is linked to the torus. It is mandatory that no spurious plasma current path modifies the optimal shape of the plasma centerpost. Moreover, as the plasma torus is produced and sustained, in absence of any applied inductive electric field, by the inner plasma centerpost through magnetic reconnections [Taylor J B and Turner M F 1989 Nucl.Fusion 29 219], it is required as well that spurious current paths do not surround the torus on its outboard, in order not to lower the efficiency of the magnetic reconnections that maintain the plasma torus at the expense of the plasma centerpost. Boundary conditions have been corrected,up to the point that the first sustainment in steady state has been achieved for the combined plasma.

Spectral Enhancement of Laser-Induced Breakdown Spectroscopy in External Magnetic Field

In this paper the spectral enhancement of laser-induced breakdown spectroscopy （LIBS） for copper plasma in the presence of a magnetic field is investigated and the temporal- and spatial-resolved plasma emission spectra are analyzed. Experimental results show that the copper plasma atomic and ion spectra have been enhanced in the presence of the external magnetic field. In addition, the Cu I 521.82 nm spectral intensity evolution with delay time appears to have a double peak around the delay time of 2 μs, but that of Cu II 507.57 nm has a sharp decrease because of the electron-atom three body recombination process. The plasma temperature with magnetic confinement is lower than that of the case in the absence of magnetic fields. Finally, the spectral enhancement mechanisms of laser induced breakdown spectroscopy with magnetic confinement are analyzed.

The Effect of an External Magnetic Field on the Plume Expansion Dynamics of Laser-Induced Aluminum Plasma

In this work, we investigated the plasma morphology induced by a Nd：YAG laser with the aim of improving the understanding of the formation and dynamics of the plasma in two cases, with and without a magnetic field. Single laser pulse production of a plasma in the absence and presence of a magnetic field was performed with an aluminum target in air. A fast photography technique was employed to obtain information about the expansion dynamics and confinement of the aluminum plasma in each case. The generation of the laser plasma was allowed to expand at two locations with different magnetic field strengths, which correspond to the strength 0.58 T in the center of two magnetic poles and 0.83 T at a distance of 4 mm from the upper pole （N）. The plume showed lateral confinement at longer delays when the target was placed at the center of the two poles. When the target was placed at a distance of 4 mm from the upper pole it was observed that the plume was divided into two lobes at the initial stage and traveled towards the center of the magnetic field with further elapse of time.

Electromagnetic Calculation and Plasma Leakage Rate Analysis of the Magnetically Confined Plasma Rocket

An electromagnetic calculation and the parameters of the magnet system of the magnetically confined plasma rocket were established. By using ANSYS code, it was found that the leakage rate depends on the current intensity of the magnet and the change of the magnet position.

The Implementation of Magnetic Islands in Gyrokinetic Toroidal Code

The implementation of magnetic islands in gyrokinetic simulation has been verified in the gyrokinetic toroidal code（GTC）.The ion and electron density profiles become partially flattened inside the islands.The density profile at the low field side is less flattened than that at the high field side due to toroidally trapped particles in the low field side,which do not move along the perturbed magnetic field lines.When the fraction of trapped particles decreases,the density profile at the low field becomes more flattened.

Recent progress on deep learning-based disruption prediction algorithm in HL-2A tokamak

Disruption prediction and mitigation is a crucial topic,especially for future large-scale tokamaks,due to disruption’sconcomitant harmful effects on the devices.On this topic,disruption prediction algorithm takes the responsibility to giveaccurate trigger signal in advance of disruptions,therefore the disruption mitigation system can effectively alleviate theharmful effects.In the past 5 years,a deep learning-based algorithm is developed in HL-2A tokamak.It reaches a truepositive rate of 92.2%,a false positive rate of 2.5%and a total accuracy of 96.1%.Further research is implementedon the basis of this algorithm to solve three key problems,i.e.,the algorithm’s interpretability,real-time capability andtransferability.For the interpretability,HL-2A’s algorithm gives saliency maps indicating the correlation between thealgorithm’s input and output by perturbation analysis.The distribution of correlations shows good coherence with thedisruption causes.For the transferability,a preliminary disruption predictor is successfully developed in HL-2M,a newlybuilt tokamak in China.Although only 44 shots are used as the training set of this algorithm,it gives reasonable outputswith the help of data from HL-2A and J-TEXT.For the real-time capacity,the algorithm is accelerated to deal with an inputslice within 0.3 ms with the help of some adjustments on it and TFLite framework.It is also implemented into the plasmacontrol system and gets an accuracy of 89.0%during online test.This paper gives a global perspective on these results anddiscusses the possible pathways to make HL-2A’s algorithm a more comprehensive solution for future tokamaks.

The Design and Optimization of a Neutron Time-of-Flight Spectrometer with Double Scintillators for Neutron Diagnostics on EAST

Neutron energy spectrometry diagnosis plays an important role in magnetic con- finement fusion. A new neutron time-of-flight （TOF） spectrometer with double scintillators is designed and optimized for the EAST toknmak. A set of optimM parameters is obtained by Monte Carlo simulation, based on the GEANT4 and ROOT codes. The electronic setup of the measurement system is designed. The count rate capability is increased by introducing a flash ADC. The designed spectrometer with high resolution and efficiency is capable of being applied to fusion neutron diagnostics. Applications in mixed-energy and continuous energy neutron fields can also be considered.

Plasma Flows within the Context of Biasing Experiments

The understanding and reduction of turbulent transport in magneticconfinement devices is not only an academic task, but also the matter of practical interest, sincehigh confinement is chosen as the regime for ITER and possible future reactors it reduces both thesize and the cost. Since the pioneering work on CCT a lot of work has been devoted to the effect ofelectric field biasing carried out on many tokamaks, which in general leads to a strongly varyingradial electric fields as a function of radius and a resulting sheared E x B flow, giving rise toimproved confinement properties. The issue of plasma flows is utterly fundamental for understandingof tokamaks aimed at the achievement of fusion energy. This appears in the well known neoclassicaltheory as the most accomplished and self-consistent basis for understanding of fusion plasmas. Itpertains to the novel concept of 'zonal flows' emerging from the recent development of gyro-kinetictransport codes. The poloidal and toroidal flows are also crucial for the concept of the electricfield shear suppression of plasma turbulence in tokamaks. Yet, this timely and topical issue hasremained largely unaddressed experimentally because of great difficulties of measuring flows inplasmas. Recently, the team of scientists from all over the world developed innovative configurationof probes yielding the flow velocity locally. This timely and topical diagnostics has beensuccessfully applied on many tokamaks ranging from the huge JET through medium TEXTOR to a smallCASTOR due to the excellent collaboration and coordination between research teams. Results causedlarge interest of fusion community born out by numerous invited talks delivered at the majorinternational meetings.

Line identification of boron and nitrogen emissions in extreme-and vacuumultraviolet wavelength ranges in the impurity powder dropping experiments of the Large Helical Device and its application to spectroscopic diagnostics

An impurity powder dropper was installed in the 21 st campaign of the Large Helical Device experiment(Oct.2019–Feb.2020)under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control.In order to assess the effective injection of the impurity powders,spectroscopic diagnostics were applied to observe line emission from the injected impurity.Thus,extreme-ultraviolet(EUV)and vacuum-ultraviolet(VUV)emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection.Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300Ameasured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400Ameasured using three normal incidence 20 cm VUV spectrometers.BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection,respectively.Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows:BI(1825.89,1826.40)A(blended),BII 1362.46A,BIII(677.00,677.14,677.16)A(blended),BIV 60.31A,BV 48.59A,NIII(989.79,991.51,991.58)A(blended),NIV765.15A,NV(209.27,209.31)A(blended),NVI 1896.80A,and NVII 24.78A.Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated,such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.

Operation Control of a High-resolution Plasma Imaging System in KT5D Torus

This paper describes the control software together with the operational hardware, which successfully realizes the operation of a new fully programmable imaging system with high spatial and temporal resolutions on the KT5D magnetic torus, for observing the visible l ight emission from the plasma discharge.

Towards advanced divertor configurations on the J-TEXT tokamak

Developing advanced magnetic divertor configurations to address the coupling of heat and particle exhaust with impurity control is one of the major challenges currently constraining the further development of fusion research.It has therefore become the focus of extensive attention in recent years.In J-TEXT,several new divertor configurations,including the high-field-side single-null poloidal divertor and the island divertor,as well as their associated fundamental edge divertor plasma physics,have recently been investigated.The purpose of this paper is to briefly summarize the latest progress and achievements in this relevant research field on J-TEXT from the past few years.

Electric and magnetic screenings of gluons in a model with a dimension-2 gluon condensate

Electric and magnetic screenings of the thermal gluons are studied by using the background expansion method in a gluodynamic model with gauge invariant dimension-2 gluon condensate at zero momentum. At low temperature, the electric and magnetic gluons are degenerate. With the increase of temperature, it is found that the electric and magnetic gluons start to split at certain temperature T0. The electric screening mass changes rapidly with temperature when T 〉 T0, and the Polyakov loop expectation value rises sharply around T0 from zero in the vacuum to a value around 0.8 at high temperature. This suggests that the color electric deconfinement phase transition is driven by electric gluons. It is also observed that the magnetic screening mass keeps almost the same as its vacuum value, which manifests that the magnetic gluons remain confined. Both the screening masses and the Polyakov loop results are qualitatively in agreement with the Lattice calculations.

The Damage Spreading Method in Monte Carlo Simulations:A Brief Overview and Applications to Confined Magnetic Materials

The Damage Spreading(DS)method allows the investigation of the effect caused by tiny perturbations,in the initial conditions of physical systems,on their final stationary or equilibrium states.The damage(D(t))is determined during the dynamic evolution of a physical system and measures the time dependence of the difference between a reference(unperturbed)configuration and an initially perturbed one.In this paper we first give a brief overview of Monte Carlo simulation results obtained by applying the DS method.Different model systems under study often exhibit a transition between a state where the damage becomes healed(the frozen phase)and a regime where the damage spreads arriving at a finite(stationary)value(the damaged phase),when a control parameter is finely tuned.These kinds of transitions are actually true irreversible phase transitions themselves,and the issue of their universality class is also discussed.Subsequently,the attention is focused on the propagation of damage in magnetic systems placed in confined geometries.The influence of interfaces between magnetic domains of different orientation on the spreading of the perturbation is also discussed,showing that the presence of interfaces enhances the propagation of the damage.Furthermore,the critical transition between propagation and nonpropagation of the damage is discussed.In all cases,the determined critical exponents suggest that the DS transition does not belong to the universality class of Directed Percolation,unlike many other systems exhibiting irreversible phase transitions.This result reflects the dramatic influence of interfaces on the propagation of perturbations in magnetic systems.