查看更多>>摘要：In the plasma sheath,there is a significant gradient in ion velocity,resulting in strong stress on ions treated as a fluid.This aspect has often been neglected in previous sheath studies.This study is based on the Braginskii plasma transport theory and establishes a 1D3V sheath fluid model that takes into account the ion stress effect.Under the assumption that ions undergo both electric and diamagnetic drift in the presheath region,self-consistent boundary conditions,including the ion Bohm velocity,are derived based on the property of the Sagdeev pseudopotential.Furthermore,assuming that the electron velocity at the wall follows a truncated Maxwell distribution,the wall floating potential is calculated,leading to a more accurate sheath thickness estimation.The results show that ion stress significantly reduces the sheath thickness,enhances ion Bohm velocity,wall floating potential,and ion flux at the wall.It hinders the acceleration of ions within the sheath,leading to notable alterations in the particle density profiles within the sheath.Further research indicates that in ion stress,bulk viscous stress has the greatest impact on sheath properties.
查看更多>>摘要：Accurate measurement of the average plasma parameters in the edge region,including the temperature and density of electrons and ions,is critical for understanding the characteristics of the scrape-off layer(SOL)and divertor plasma transport in magnetically confined fusion research.On the J-TEXT tokamak,a multi-channel retarding field analyzer(RFA)probe has been developed to study average plasma parameters in the edge region under various poloidal divertor and island divertor configurations.The edge radial profile of the ion-to-electron temperature ratio,τi/e,has been determined,which gradually decreases as the SOL ion self-collisionality,v*SOL,increases.This is broadly consistent with what has been observed previously from various tokamak experiments.However,the comparison of experimental results under different configurations shows that in the poloidal divertor configuration,even under the same v*SOL,τi/e in the SOL region becomes smaller as the distance from the X-point to the target plate increases.In the island divertor configuration,ri/e near the O-point is higher than that near the X-point at the same v*SOL,and both are higher than those in the limiter configuration.These results suggest that the magnetic configuration plays a critical role in the energy distributions between electrons and ions at the plasma boundary.
查看更多>>摘要：In recent decades,tokamak discharges with zero total toroidal current have been reported in tokamak experiments,and this is one of the key problems in alternating current(AC)operations.An efficient free-boundary equilibrium code is developed to investigate such advanced tokamak discharges with current reversal equilibrium configuration.The calculation results show that the reversal current equilibrium can maintain finite pressure and also has considerable effects on the position of the X-point and the magnetic separatrix shape,and hence also on the position of the strike point on the divertor plates,which is extremely useful for magnetic design,MHD stability analysis,and experimental data analysis etc.for the AC plasma current operation on tokamaks.
Paolo MICOZZIFranco ALLADIOAlessandro MANCUSOVincenzo ZANZA...
31-43页
查看更多>>摘要：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.
查看更多>>摘要：To investigate the potential of utilizing visible spectral imaging for controlling the plasma boundary shape during stable operation of plasma in future tokamak,a Da band symmetric visible light diagnostic system was designed and implemented on the Experimental Advanced Superconducting Tokamak(EAST).This system leverages two symmetric optics for joint plasma imaging.The optical system exhibits a spatial resolution less than 2 mm at the poloidal cross-section,distortion within the field of view below 10％,and relative illumination of 91％.The high-quality images obtained enable clear observation of both the plasma boundary position and the characteristics of components within the vacuum vessel.Following system calibration and coordinate transformation,the image coordinate boundary features are mapped to the tokamak coordinate system.Utilizing this system,the plasma boundary was reconstructed,and the resulting representation showed alignment with the EFIT(Equilibrium Fitting)results.This underscores the system's superior performance in boundary reconstruction applications and provides a diagnostic foundation for boundary shape control based on visible spectral imaging.
查看更多>>摘要：This study investigates the single-pass absorption(SPA)of ion cyclotron range of frequency(1CRF)heating in hydrogen plasma of the EXL-50U spherical tokamak,which is an upgraded EXL-50 device with a central solenoid and a stronger magnetic field.The reliability of the kinetic dispersion equation is confirmed by the one-dimensional full-wave code,and the applicability of Porkolab's simplified theoretical SPA model is discussed based on the kinetic dispersion equation.Simulations are conducted to investigate the heating effects of the fundamental and second harmonic frequencies.The results indicate that with the design parameters of the EXL-50U device,the SPA for second harmonic heating is 63％,while the SPA for fundamental heating is 13％.Additionally,the optimal injection frequencies are 23 MHz at 0.9 T and 31 MHz at 1.2 T.The wave vector of the antenna parallel to the magnetic field,with a value of k‖=7.5 m-1,falls within the optimal heating region.Simulations reveal that the ICRF heating system can play an important role in the ion heating of the EXL-50U.
查看更多>>摘要：Giant electromagnetic pulses(EMPs)induced by high-power laser irradiating solid targets interfere with various experimental diagnoses and even damage equipment,so unveiling the evolution of EMPs inside the laser chamber is crucial for designing effective EMP shielding.In this work,the transmission characteristics of EMPs as a function of distances from the target chamber center(TCC)are studied using B-dot probes.The mean EMP amplitude generated by picosecond laser-target interaction reaches 561 kV m-1,357 kV m-1,395 kV m-1,and 341 kV m-1 at 0.32 m,0.53 m,0.76 m,and 1 m from TCC,which decreases dramatically from 0.32 m to 0.53 m.However,it shows a fluctuation from 0.53 m to 1 m.The temporal features of EMPs indicate that time-domain EMP signals near the target chamber wall have a wider full width at half maximum compared to that close to TCC,mainly due to the echo oscillation of electromagnetic waves inside the target chamber based on simulation and experimentation.The conclusions of this study will provide a new approach to mitigate strong electromagnetic pulses by decreasing the echo oscillation of electromagnetic waves inside the target chamber during laser coupling with targets.
查看更多>>摘要：Laser-accelerated high-flux-intensity heavy-ion beams are important for new types of accelerators.A particle-in-cell program(Smilei)is employed to simulate the entire process of Station of Extreme Light(SEL)100 PW laser-accelerated heavy particles using different nanoscale short targets with a thickness of 100 nm Cr,Fe,Ag,Ta,Au,Pb,Th and U,as well as 200 nm thick Al and Ca.An obvious stratification is observed in the simulation.The layering phenomenon is a hybrid acceleration mechanism reflecting target normal sheath acceleration and radiation pressure acceleration,and this phenomenon is understood from the simulated energy spectrum,ionization and spatial electric field distribution.According to the stratification,it is suggested that high-quality heavy-ion beams could be expected for fusion reactions to synthesize superheavy nuclei.Two plasma clusters in the stratification are observed simultaneously,which suggest new techniques for plasma experiments as well as thinner metal targets in the precision machining process.
查看更多>>摘要：The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes.The radio interference caused thereby is a key factor to be considered when designing transmission lines.To study the influence of altitude on negative corona characteristics,an experimental platform comprising a movable small corona cage was established:experiments were conducted at four altitudes in the range of 1120-4320 m,and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected.The experimental results show that the average amplitude,repetition frequency and average current of the corona current pulse increase with increasing altitude.The dispersion of pulse amplitude increases with increase in altitude,while the randomness of the pulse interval decreases continuously.Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained.The result of this research has some significance for understanding the corona discharge characteristics of ultra-high-voltage lines.
查看更多>>摘要：Rapid online analysis of liquid slag is essential for optimizing the quality and energy efficiency of steel production.To investigate the key factors that affect the online measurement of refined slag using laser-induced breakdown spectroscopy(LIBS),this study examined the effects of slag composition and temperature on the intensity and stability of the LIBS spectra.The experimental temperature was controlled at three levels:1350 ℃,1400 ℃,and 1450 ℃.The results showed that slag composition and temperature significantly affected the intensity and stability of the LIBS spectra.Increasing the Fe content and temperature in the slag reduces its viscosity,resulting in an enhanced intensity and stability of the LIBS spectra.Additionally,42 refined slag samples were quantitatively analyzed for Fe,Si,Ca,Mg,Al,and Mn at 1350 ℃,1400 ℃,and 1450 ℃.The normalized full spectrum combined with partial least squares(PLS)quantification modeling was used,using the Ca Ⅱ 317.91 nm spectral line as an internal standard.The results show that using the internal standard normalization method can significantly reduce the influence of spectral fluctuations.Meanwhile,a temperature of 1450 ℃ has been found to yield superior results compared to both 1350 ℃ and 1400 ℃,and it is advantageous to conduct a quantitative analysis of the slag when it is in a"water-like"state with low viscosity.
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