Numerical Analyses of Electromagnetic Forces on the ITER Blanket Module Shield Block During Major Disruptions

Electromagnetic（EM） load is one of the key design drivers for the blanket shield block（SB） and other in-vessel components. In this article, an EM analysis method was developed to address the EM force on the SB. The plasma currents, which vary spatially and temporally,are loaded as a filament at each time point. The standard blanket module No.04（BM04） under major disruption（MD） is selected to perform the analyses. The analyses results are validated by comparing currents on the passive structure. To better understand the effects of cooling channels and slits on the EM force, the case of SB without cooling channel and the case without slits are calculated to make comparisons. The results show that the slits play an important role in controlling the EM load on SB.     

A GPU-based general numerical framework for plasma simulations in terms of microscopic kinetic equations with full collision terms

We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms. Our numerical algorithm consistently deals with both long-range (classical forces in the Vlasov term) and short-range (quantum processes in the collision term) interactions. Providing the relevant particle masses, charges and types (classical, fermionic or bosonic), as well as the external forces and the matrix elements (in the collisional integral), the algorithm consistently solves the coupled multi-particle kinetic equations. Currently, the framework is being tested and applied in the field of relativistic heavy-ion collisions; extensions to other plasma systems are straightforward. Our framework is a potential and competitive numerical platform for consistent plasma simulations.     

Cross-focusing of two chirped Gaussian laser beams and THz wave generation in plasmas of multi-ion species under a weakly relativistic and ponderomotive regime

The generation of terahertz (THz) waves via the beating of two high-intensity chirped Gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive regime of interaction. The coupled differential equations for beamwidth parameters are extracted by introducing the dielectric function of such plasma and using WKB and paraxial ray approximations. The amplitude of THz radiation at beat frequency resulting from the nonlinear current density induced by the beat ponderomotive force of the cross-focusing of beams was obtained. The impacts of the chirp frequency parameter, initial laser intensity and initial ionic species density (specifically, the presence of singly and doubly charged ions) in the plasma on THz generation were discussed. Our numerical results reveal that THz radiation generation strongly depends on the chirp frequency parameter. A specific range of chirp frequencies exists for self-focusing as well as THz generation with a 'turning point', where the THz emission reaches its maximum value. The results show that the strength of self-focusing and consequently the generated THz radiation are reduced by increasing the density of doubly charged ionic species in the plasma due to the suppression of the nonlinear effects.     

Study of the O-mode in a relativistic degenerate electron plasma

Using the linearized relativistic Vlasov-Maxwell equations,a generalized expression for the plasma conductivity tensor is derived.The dispersion relation for the O-mode in a relativistic degenerate electron plasma is investigated by employing the Fermi-Dirac distribution function.The propagation characteristics of the O-mode (cut offs,resonances,propagation regimes,harmonic structure) are examined by using specific values of the density and the magnetic field that correspond to different relativistic dense environments.Further,it is observed that due to the relativistic effects the cut off and the resonance points are shifted to low frequency values,as a result the propagation regime is reduced.The dispersion relations for the non-relativistic and the ultra-relativistic limits are also presented.     

Enhanced Raman Scattering of Elliptical Laser Beam in a Collisionless Plasma

This paper presents the Enhanced Raman scattering of a elliptical laser beam in a collisionless plasma. The transverse intensity gradient of a pump beam generates a Ponderomotive force, which modifies the background plasma density profile in a direction transverse to pump beam axis. This modification in density effects the incident laser beam, plasma wave and back-scattered beam. Non-linear differential equations for the beam width parameters of pump laser beam, plasma wave and back-scattered beam are set up and solved numerically. The interplay between the self-focusing of the main beam and SRS has been studied in detail. The analysis clearly shows a coupling between the main beam and the plasma wave, therefore an increase in the self-focusing of the pump beam at lower intensities increases the self-focusing of the plasma wave which inturn leads to an increase in the back-reflectivity of the scattered wave. Further, it is also predicted that strong self-focusing of the pump beam at higher plasma density leads to strong self-focusing of the plasma wave and results in an increase in SRS reflectivity.     

Spin light identification in the presence of power synchrotron radiation

The relativistic radiation theory of the intrinsic magnetic moment of an electron (which is known as spin light) from the point of view of the correspondence principle of classical, semi-classical and quantum theory of radiation is discussed. It is shown that after separation of terms unbound with a spin in the power of the total radiation of electrons (with the example of the synchrotron radiation of an electron) the correspondence principle holds accurate within a second approximation by Plank’s constant. The formulas for the angular distribution, linear polarization and spectral structure of radiation obtainable here with an allowance for spin can find application for non-trivial problems of experimental identification of spin light.     

Numerical Simulation of Stall Flow Control Using a DBD Plasma Actuator in Pulse Mode

A numerical simulation method is employed to investigate the effects of the unsteady plasma body force over the stalled NACA 0015 airfoil at low Reynolds number flow conditions.The plasma body force created by a dielectric barrier discharge actuator is modeled with a phenomenological method for plasma simulation coupled with the compressible Navier-Stokes equations.The governing equations are solved using an efficient implicit finitevolume method.The responses of the separated flow field to the effects of an unsteady body force in various interpulses and duty cycles as well as different locations and magnitudes are studied.It is shown that the duty cycle and inter-pulse are key parameters for flow separation control.Additionally,it is concluded that the body force is able to attach the flow and can affect boundary layer grow that Mach number 0.1 and Reynolds number of 45000.     

Stimulated Brillouin Scattering of Gaussian Laser Beam in Relativistic Plasma

This paper presents an investigation of stimulated Brillouin scattering (SBS) of Gaussian laser beam in relativistic plasma. The pump beam interacts with a pre-excited ion-acoustic wave thereby generating a back-scattered wave. In the high intensity laser beam, electron oscillatory velocity becomes comparable to the velocity of light, which modifies the refractive index of plasma due to increase in the electron mass. This modification of refractive index affects the incident laser beam, ion-acoustic wave and back scattered beam. We have set up non-linear differential equations for the beam width parameters of the main beam, ion-acoustic wave, back-scattered wave and derived expression of SBS-reflectivity by taking full non-linear part of the dielectric constant of relativistic plasma with the help of moment theory approach. It is observed from the analysis that focusing of waves greatly affects the SBS reflectivity.     

Experiment on low-frequency electromagnetic waves propagating in shock-tube-generated magnetized cylindrical enveloping plasma

We propose a method of applying a static magnetic field to reduce the attenuation of the magnetic field component(S_H) of low-frequency electromagnetic(LF EM) waves in dense plasma. The principle of this method is to apply a static magnetic field to limit electron movement, thereby increasing the equivalent resistance and thus reducing the induced current and S_H. We consider the static magnetic field acting on the plasma of the entire induced current loop rather than on the local plasma, where the induced current is excited by the magnetic field component of LF EM waves. Analytical expressions of S_H suitable for magnetized cylindrical enveloping plasma are derived by adopting an equivalent circuit approach, by which S_His calculated with respect to various plasma parameter settings. The results show that S_H can be reduced under a static magnetic field and the maximum magnetic field strength that mitigates blackout is less than 0.1 T. Experiments in which LF EM waves propagate in a shock-tubegenerated magnetized cylindrical enveloping plasma are also conducted. S_H measured under the magnetic field(the magnetic field strength B0 acting on the magnetic field probe was about0.06 T) reduces at f=10 MHz and f=30 MHz when n_e≈1.9×10~(13) cm~(-3), which is consistent with theoretical results. The verification of the theory thus suggests that applying a static magnetic field with a weak magnetic field has the potential to improve the transmission capacity of LF EM waves in dense plasma.     

Numerical comparison between the ICF and the ICF-spherical pinch

The spherical pinch concept is an outgrowth of the inertial confinement model. The salient feature of the spherical pinch concept is the creation of a hot plasma in the center of a sphere.^(1,2) This plasma is then compressed by a strong shock wave launched from the periphery of the vessel by an imploded plasma acting as a driver. This scheme, reveals that convergence of the shock, which is the main feature of all inertial confinement schemes, is a component of the spherical pinch model. The reasons for classifying the spherical pinch as a particular ICF model and designating it as a ICF-SP are given here. The fluid mechanics and high-temperature hydrodynamics of the spherical pinch can be briefly described as an explosion within an implosion. The structure of the shock wave for such explosion within an implosion and for, an implosion alone is determined by solving numerically the governing equations of the phenomena. We present here a detailed computational comparison of the inertial confinement model and the spherical pinch in terms of density, pressure, temperature, confinement time, total accumulated number of neutrons, and time-resolved neutron flux from reactions in deuterium-tritium mixture. It is shown that temperature, confinement time, and total number of neutrons for the ICF-Spherical Pinch improve upon the classical ICF.     

Relativistic effect on synergy of electron cyclotron and lower hybrid waves on EAST

In recent experiments on EAST,the electron temperature at the center can be raised to 9.7 keV by injecting electron cyclotron(EC)and lower hybrid(LH)waves simultaneously.With such strong core electron heating,the relativistic effect could play an important role in the interactions between the plasma and waves.In order to explore the relativistic effect on synergy between the EC and LH waves on EAST,ray-tracing/Fokker-Planck simulations are conducted to investigate electron heating for a typical discharge with a center electron temperature of 9.7 keV.It is found that the relativistic effect can cause the EC wave to deposit its power deeper in the plasma core,where the synergy between the EC and LH waves occurs and enhances the absorption of the LH waves.As a result,a high center electron temperature can be achieved.     

The electromagnetic instability in electron flow with ion background

Electromagnetic (EM) behavior and instability resulting from the interaction between EM wave and plasma wave are analyzed based on linear perturbation theory. It is shown that the instability is caused by the the coupling between high frequency electromagnetic field and electron transverse oscillation derived from the deflection of electron longitudinal oscillation due to self-produced magnetic field. The influences of the self-produced magnetic field and plasma density on the instability are studied. In addition characteristics of EM wave propagation at different angles are investigated. The present results are of significance to new type plasma radiation source, ion accelerator and plasma diagnostic techniques.     

Preliminary Calculation of Electromagnetic Loads on Vacuum Vessel of HL-2M

For a robust design of vacuum vessel of HL-2M, the electromagnetic (EM) loads have to be understood clearly. In this paper, some crucial transient events, such as plasma major disruptions (MDs), vertical displacement events (VDEs), fast discharge of toroidal field (TF) coils, have been investigated to evaluate the eddy currents and EM forces on vacuum vessel and in-vessel components. The results show that the eddy currents depend strongly on the current decay time, and the maximum toroidal eddy current flowing in the whole vessel can reach up to 2.4 MA during MDs that is close to the plasma current. Large symmetric radial forces and a net vertical force on vessel shells could be caused by these transient events. Combination of eddy currents in in-vessel components and toroidal field could twist the copper plates and other internal parts, however, if these plates are supported and connected carefully, the twist moments will not have a big e®ect on the vessel shells and vessel support.     

Tangential force and heating rate of a neutral relativistic particle mediated by equilibrium background radiation

A relativistic theory of fluctuation-electromagnetic interaction of a small neutral polarizable particle moving with respect to the equilibrium background radiation is developed. It is assumed that the particle radius is smaller then the characteristic wave length of the background radiation. General relativistic relations for the particle heating rate and tangential force are obtained and compared with the nonrelativistic and relativistic expressions of other authors.     

Generation of Nonlinear Force Driven Blocks from Skin Layer Interaction of Petawatt-Picosecond Laser Pulses for ICF

The discovery of the essential difference of maximum ion energy for TW-ps laser plasma interaction compared with the 100 ns laser pulses led to the theory of a skin layer model where the control of prepulses suppressed the usual relativistic self-focusing.The subsequent generation of two nonlinear force driven blocks has been demonstrated experimentally and in extensive numerical studies where one block moves against the laser light and the other block into the irradiated target.These blocks of nearly solid state density DT plasma correspond to ion beam current densities exceeding 10^10 A/cm^2 where the ion velocity can be chosen up to highly relativistic values.Using the results of the expected ignition of DT fuel by light ion beams,a selfsustained fusion reaction front may be generated even into uncompressed solid DT fuel similar to the Nuckolls-Wood scheme where 10 kJ laser pulses produce 100 MJ fusion energy.This new and simplified scheme of laser-ICF needs and optimisation of the involved parameters.     

Mechanical Analysis for ITER Lower CC Feeder

ITER correction coils (CCs) feeder is the important component of ITER feeder systems to supply the cryogens and electrical power for CCs. They should withstand the huge electromagnetic (EM) force and high thermal shrinkage. Considering the EM and thermal loads, mechanical analysis is performed to qualify the structural strength of the lower CC feeder. Results show that containment duct and cryopipe can meet the static criteria but busbar jacket cannot meet. It is proposed that more supports should be added at the corners for the busbar. Basically, the lower CC feeder design is valid and feasible.     

Strong Dependency of Ion Acceleration on Ion Beam Divergency in Magnetized Collisionless Plasma Sheath

The ion acceleration inside the collisionless plasma sheath is investigated at the presence of external magnetic field. By using the fluid model, the number and momentum equations of the ions and the Boltzmann and Poisson equations are solved numerically in the case that the ion beam has a small divergency at the plasma sheath boundary. It is shown that the kinetic energy of the ions has a strong dependency to the magnitude of divergency when the magnetic field has a small component parallel to the sheath boundary.     

Investigation of the Plasma Behavior in Filippov-Type Plasma Focus Using the State Space of Sing Lee’s Model

The state space of Lee’s model (SSL model) is a model developed for plasma behavior in Filippov-type plasma focus facilities which has been described and used. This model is attractive because it provides a practical approach for analysis of a plasma focus device. In this article, we turn to an alternative method of system analysis using time-domain methods. We will reconsider the differential equations describing the Filippov-type plasma focus device and select a certain form of differential equations. We will use a set of variables that can be used to establish a set of first-order differential equations. Using matrix methods, we will be able to determine the transient response of the Filippov-type plasma focus device and examine the performance of this system. This model is a derivation of modified Lee’s model and is based on the so-called slug model. Using the SSL model, the discharged current and its derivative as a function of time, pinch time, and maximum discharge current; as functions of pressure, have been predicted. The experimental data obtained by using the UIPFF1 facility with a maximum energy of 20 kJ is compared with the simulated data obtained through SSL model. This investigation shows that the SSL model is capable of predicting the plasma behavior in the Filippov type plasma focus.     

Global computational models for analysis of electromagnetic transients to support ITER tokamak design and optimization

The International thermonuclear experimental reactor (ITER) concept implies a variety of operating modes, design complexity and demand for high reliability. A point of the major concern is the transient electromagnetic (EM) effects. Complex electromagnetic behaviour due to strong inductive coupling, the presence of numerous field sources, and a range of plasma burn scenarios requires careful predictive simulations. Different mathematical models applicable for the design and optimization studies are reviewed. Practical experience in developing detailed global models to investigate eddy currents, EM forces and other EM loads is summarized. Two numerical techniques implemented in the dedicated computer codes are compared, and the validity of relevant models is discussed.