Radiation Heat Transfer and Vapor Shielding in a Two-Dimensional Model of an Electrothermal Plasma Source

Electrothermal (ET) plasma discharges are emerging as valuable mechanisms for pellet injection in magnetic confinement fusion reactors. They have been shown to be capable of achieving the required pellet velocities and pellet launch frequencies required for edge localized mode control. Another advantage of ET plasma discharges is their ability to simulate fusion disruption events by depositing large heat fluxes on exposed materials. A deeper understanding of the heat transfer processes occurring in ET plasma discharges will aid in this particular application. ET plasma discharges involve the passage of high currents (order of tens of kA) along the axis of a narrow, cylindrical channel. As the current passes through the channel, radiant heat is transferred from the plasma core to the capillary wall. Ablated particles eventually fill the plasma channel and the partially ionized plasma is ejected. It is well known that the ablated material separating the plasma core from the ablating surface can act as a vapor shield and limit the radiation heat flux reaching the ablating surface. In this work, the results from a two-dimensional simulation model for ET plasma discharges are presented. The simulation of the plasma in a two-dimensional domain combined with the diffusion approximation for radiation heat transfer is shown to successfully simulate the effects of the vapor shield layer that develops inside these devices.     

二维孔隙结构内单相流动阻力特性数值模拟

利用计算流体力学(CFD)商业软件CFX 10.0,采用标准k-ε、RNG k-ε以及SST模型3种不同的湍流模型,对矩形管内球形颗粒作2维有序排列所形成的孔隙流道的等温单相流动进行数值模拟,并与Ergun关系式预计值进行对比;探讨球形颗粒的排列方式、直径等对单相流动阻力的影响;研究矩形管内单位长度压降及阻力系数随孔隙雷诺数Re的变化规律(1.5≤Re≤1497)。     

Radial Profile of Plasma Flow Parameters Following Evolution of Electrothermal Polycarbonate Plasma into a Large Chamber Simulating Impurity Expansion in Fusion Reactor Vacuum Vessel

The 2-D evolution of the plasma as it expands outside the capillary source, which simulates ablation of plasma-facing materials due to high-heat flux deposition, is of importance to investigate the plasma flow scaling laws with inclusion of radial variations. The flow continues from the source exit through a converging–diverging transition region and expands into a large expansion volume that simulates the vacuum chamber of a tokamak fusion reactor. This 2-D modeling resolves the problem of the 1-D steady state analysis of the plasma bulk flow that assumes the flow parameters to vary only in the axial direction with a uniform radial distribution. As the plasma expands towards the sidewalls of the diverging section in the transition region, the bulk plasma has a finite chance to lose energy primarily in the form of heat loss, which might cause readjustment in the profile for plasma bulk temperature giving rise to a decreasing trend in the radial direction. This change in bulk plasma temperature triggers further changes in other bulk flow parameters along the radial directions, away from the axis of the flow. In this work, different mathematical models have been proposed for radial correction in the bulk flow parameter profiles within the system size as a simulation for expansion into the vacuum vessel of a magnetic fusion reactor. Symmetry of the radial profiles over a cross-sectional area has been assumed to facilitate ease of computation and analysis.     

Exchange Flow Characteristics in a Tokamak Vacuum Vessel of Fusion Reactor Under the Loss-of-Vacuum Conditions

When a Tokamak vacuum vessel of fusion reactor is broken, buoyancy-driven exchange flows will take place through breaches after the inside pressure of the vacuum vessel (VV) becomes equal to the outside pressure. The exchange flow may bring a mixture of activated dusts and tritium from the inside of the VV to the outside through the breaches. Moreover, the exchange flow may remove decay heat from the plasma-facing components. A preliminary LOVA (Loss Of VAcuum event) apparatus was constructed to investigate quantitative heat transfer characteristics of the exchange flows through the breaches under the LOVA conditions. The results of this study, the relationship between Froude numbers and breach locations in the VV was determined and empirical correlations for the average Froude numbers were derived.     

Characterization of Cable Gun Plasma with a Charge Collector Array

The density,drift velocity and reproducibility of the plasma produced by a cable plasma gun array have been measured with a charge collector array,The plasma is used to prefill a coaxial plasma-opening switch with a conducting time approaching 0.4us,The reproducibility of the plasma source in subsequent shots is better than 5%.Near the gun nozzle and the opposite electrode,the plasma density amounts to 10^15cm%-3,which is 2 times to 3 times that in the gap between the two coaxial electrodes.A plasma drift velocity of about 2.4cm/μs is observed from the time of flight of the charged particles.Both plasma density and drift velocity increase almost linearly with the rise in charge voltage.     

回旋加速器中的空间电荷效应和束晕(英文)

在考虑束团内粒子之间的空间电荷相互作用力的条件下,对日本理化研究所(RIKEN)现有的一台注入器(加速常数为K70的AVF型回旋加速器)中束团的演变过程进行了模拟计算。模拟结果表明,束团的形变、束晕现象同样发生在回旋加速器中,不过,其产生机制不同于直线加速器。它不是由共振和混沌引起,而是由于粒子的排斥运动和束团内粒子的涡流运动引起的。     

溶液堆台架模型热工水力数值分析

应用欧拉两相流最新CFD(computational fluid dynamics)模型,对某溶液堆台架模型堆芯内气-液两相流动传热进行数值分析.堆芯内气泡被考虑为不同直径的组分,摒弃了传统均一离散相的假设(即假设所有气泡为同一直径和形状),把应用群体平衡理论建立起来的MUSIG(Multiple-SIze-Group)模型考虑到CFD模拟中,MUSIG模型用于描述堆芯内气泡流动特性和尺度分布.同时,对采用MUSIG模型和传统两相流模型的模拟结果进行了比较分析.结果表明,采用MUSIG模型的模拟结果与台架实验结果吻合较好.     

Calculation of Electrical Potential and Dust Particle Charge in a Double Dusty Plasma Device

Dusty plasma consists of macroscopic particles of nanometer to micrometer size immersed in a gaseous plasma environment. It can be observed by introducing a flow of molecular impurity in a double plasma device. The impurity particles will be charged quickly, while keeping relatively in low temperature. The particles typically attain several hundred or thousand elementary charges due to the inflow of plasma electron and ions. The dust particles potential and electrical charge in plasma with two ions at different temperatures is calculated. Electrical charge of dust particles is self consistently determined by local plasma electron and ion currents. It is found out that the dust particle potential is strongly affected by the mass and temperature difference of plasma ions.     

Radiative Divertor Plasma Behavior in L- and H-Mode Discharges with Argon Injection in EAST

Introducing strong radiative impurities into divertor plasmas has been considered as an important way to mitigate the peak heat load at the divertor target plate for ITER, and will be employed in EAST for high power long pulse operations. To this end, radiative divertor experiments were explored under both low (L) and high (H)-mode confinement regimes, for the first time in EAST, with the injection of argon and its mixture (25% Ar in D 2 ). The Ar injection greatly reduced particle and heat fluxes to the divertor in L-mode discharges, achieving nearly complete detached divertor plasma regimes for both single null (SN) and double null (DN) configurations, without increasing the core impurity content. In particular, the peak heat flux was reduced by a factor of ～6, significantly reducing the intrinsic in-out divertor asymmetry for DN, as seen by both the new infra-red camera and the Langmuir probes at the divertor target. Promising results have also been obtained in the H-modes with argon seeding, demonstrating a significant increase in the frequency and decrease in the amplitude of the edge localized modes (ELMs), thus reducing both particle and heat loads caused by the ELMs. This will be further explored in the next experimental campaign with increasing heating power for long pulse operations.     

Electrical Characteristics of Pseudoglow Discharges in Helium under Atmospheric Pressure

A pseudoglow discharge behaviour is achieved at a 2.0-mm dielectric-dielectric electrode gap in pure helium under atmospheric pressure. An experimental study of the pseudoglow discharges is presented. The electrical characteristics and the discharge photos of the pseudoglow discharges are analyzed and discussed. The current-voltage parameters of the pseudoglow dis- charges are considered in regard to the influence on their behaviour.     

Electrical Characteristics of Dielectric-Barrier Discharges in Atmospheric Pressure Air Using a Power-Frequency Voltage Source

Dielectric-barrier discharges （DBDs） in atmospheric pressure air have been studied by using a power-frequency voltage source. In this paper the electrical characteristics of DBDs us- ing glass and alumina dielectrics have been investigated experimentally. According to the Lissajous figures of voltage-charges, it is discovered that the discharge power for an alumina dielectric is much higher than that for a glass dielectric at the same applied voltage. Also~ the voltage-current curves of the glass and alumina dielectrics confirm the fact that the dielectric barriers behave like semiconducting materials at certain applied voltages.     

Production of a High-Mach-Number Plasma Flow for an Advanced Plasma Space Thruster

A higher specific impulse and a larger thrust are required for a manned interplanetary space thruster. Prior to a realization of a fusion-plasma thruster, a magneto-plasma-dynamic arcjet (MPDA) powered by a fission reactor is one of the promising candidates for a manned Mars space thruster. The MPDA plasma is accelerated axially by a self-induced j × B force. Thrust performance of the MPDA is expected to increase by applying a magnetic nozzle instead of a solid nozzle. In order to get a much higher thruster performance, two methods have been investigated in the HITOP device, Tohoku University. One is to use a magnetic Laval nozzle in the vicinity of the MPDA muzzle for converting the high ion thermal energy to the axial flow energy. The other is to heat ions by use of an ICRF antenna in the divergent magnetic nozzle. It is found that by use of a small-sized Laval-type magnetic nozzle, the subsonic flow near the muzzle is converted to be supersonic through the magnetic Laval nozzle. A fast-flowing plasma     

Flow Shear Effects on the Resistive Wall Mode Stability in a Slab Model

The effects of flow shear on the resistive wall mode (RWM) are numerically studied in a slab geometry. The reversed shear in the plasma flow has a stable effect on the linear evolution of the RWM. On the other hand, the direction of the plasma flow has an effect on the stabilization of the RWM. The field-aligned flow exhibits the strongest suppressing effect. The RWM saturates in the nonlinear phase. The saturation level decreases with increasing of shear rate s. The saturation can be attributed to flux piling-up on the resistive wall.     

Production of Negative Helium Ions by Nearly-Resonant Charge Exchange in Potassium

The design criteria for a source of 5-10?A of He- ions suitable for tandem accelerator application have been investigated. The process used is a nearly-resonant charge exchange between He+ ions, from a duoplasmatron, and potassium vapor. In the He+ energy range of 5-25 keV, the He-/He+ yield has been measured as a function of He+ energy. Yields of ~2%/ have been observed. A He- beam emittance of 1.2 × 10-2 cm rad eV1/2 has been measured. The potassium flux into the system was found to be ~1016 particles/s.     

Charge and Mass Considerations for Plasma Velocity Measurements in Rotating Plasmas

Velocity of hydrogen plasmas rotating due to imposed E × B fields at the Maryland Centrifugal Experiment (MCX) (Ellis et al., Phys Plasmas 12:055704, 2005), where E is the electric field in the radial direction and B the magnetic field in the axial direction of a cylindrical configuration, has traditionally been measured using Doppler shifts of atomic spectra from impurity elements such as carbon. Ideally, the gyrocenter of trace particles rotates at the bulk plasma velocity, regardless of the charged state or trace particle mass. However, for sufficiently large applied |E/B| (or equivalently, a sufficiently large ratio of bulk plasma rotation frequency and particle gyrofrequency), charged particles may have gyroradii that depart significantly from quasi-circular orbits drifting about the B field axis. This effect is investigated numerically with a single particle code that includes scattering, as well as experimentally at MCX. Numerical findings are compared to experimentally measured Doppler shifts of singly inonized helium and oxygen, and doubly ionized carbon atoms.     

Effect of Wall Charge on Striation in Plasma Display Cells

Different configurations and driving voltages have been employed to investigate the effect of the wall charge on the striations in macroscopic plasma display panel （PDP） cells. The experimental results show that a discharge channel near the dielectric layer is indispensable to striation occurring in the anode area during a discharge, while the pre-accumulated charge on the dielectric layer and the surface state are not important. The origin of the striation is related only to the physical process in the cell. The dielectric layer acts as a charge collector during a PDP discharge.     

An Experimental Research to Study the Microwaves Transmission Characteristics of Ablating Material in Arc-Heated Plasma Flow

1. IntroductionThe main function of radome in high-speed missleflight is to retain the required pneumatic contour,endure the pneumatic heating and all kinds of loadsduring the missile flight in supersonic speed, and reduce the effects of flight environment on electronicdevices in radome. The radome is not only animportant structure on the top of a warhead, butalso a channel for transmitting and receiving various electromagnetic radiations. So the radome musthave an excellent high-temperature r…     

Effects of Alfvenic Poloidal Flow and External Vertical Field on Plasma Position in IR-T1 Tokamak

We analyzed dynamic equilibrium properties of a large aspect ratio and low Beta tokamaks, in particular deriving a modified relation for the Shafranov shift in the presence of poloidal flow and external vertical field, and demonstrate it experimentally on the IR-T1 tokamak. Poloidal flow can produce modifications in the equilibrium properties. By increasing Alfvenic Mach number from zero, flow produce outward force, and plasma shifted in outward direction. If the poloidal Alfvenic Mach number equal to one, singularity will observe in the solution of generalized Grad–Shafranov equation. Also inversion of Shafranov shift in the transition of flow speed between sub-Alfvenic to super-Alfvenic speeds can be observed due to inward force produced by flow.     

Flow Dynamics and Plasma Heating of Spheromaks in SSX

We report several new experimental results related to flow dynamics and heating from single dipole-trapped spheromaks and spheromak merging studies at SSX. Single spheromaks (stabilized with a pair of external coils, see Brown, Phys. Plasmas 13 102503 (2006)) and merged FRC-like configurations (see Brown, Phys. Plasmas 13, 056503 (2006)) are trapped in our prolate (R = 0.2 m, L = 0.6 m) copper flux conserver. Local spheromak flow is studied with two Mach probes (r ₁ ≤ ρ _i , r ₂ ≥ ρ _i ) calibrated by time-of-flight with a fast set of magnetic probes at the edge of the device. Both Mach probes feature six ion collectors housed in a boron nitride sheath. The larger Mach probe will ultimately be used in the MST reversed field pinch. Line averaged flow is measured by ion Doppler spectroscopy (IDS) at the midplane. The SSX IDS instrument measures with 1 μs or better time resolution the width and Doppler shift of the C _III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity (see Cothran, RSI 77, 063504 (2006)). We find axial flows up to 100 km/s during formation of the dipole trapped spheromak. Flow returns at the wall to form a large vortex. Recent high-resolution IDS velocity measurements during spheromak merging show bi-directional outflow jets at ±40 km/s (nearly the Alfvén speed). We also measure T _i ≥ 80 eV and T _e ≥ 20 eV during spheromak merging events after all plasma facing surfaces are cleaned with helium glow discharge conditioning. Transient electron heating is inferred from bursts on a four-channel soft x-ray array. The spheromaks are also characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), and interferometry for n _e . Finally, we are designing a new oblate, trapezoidal flux conserver for FRC studies. Equilibrium and dynamical simulations suggest that a tilt-stable, oblate FRC can be formed by spheromak merging in the new flux conserver.     

Numerical Investigation of Flow Field of a Dual-jet Plasma Generator

1. IntroductionThe dual-Jet plasma generator is a novel kind ofDC plasma generator developed in recent years [14]. Its positive and negative electrodes are placedin two plajsma torches, respectively. The outgoingjets from the two torches form a passage for electrical current flowing between the electrodes, with theplasma volume in the form of a y－shaped stream.The plasma generator with electrical current pathoutside the torch has some desirable advantages overother kinds, including even mul…