Plasma Physics Model Research Articles

PLASMAKIN: A chemical kinetics library for plasma physics modeling

PLASMAKIN is a software library to handle physical and chemical data used in plasma physics modeling and to compute kinetics data from the reactions taking place in the gas or at the surfaces — particle generation and loss rates, photon emission rates and energy exchange rates. PLASMAKIN supports any number of chemical species and reactions, is independent of problem dimensions and can be used both in stationary and time-dependent problems. PLASMAKIN supports a large number of species properties and reaction types. Namely gas or electron temperature dependent collision rate coefficients, vibrational and cascade levels, evaluation of branching ratios, superelastic and other reverse processes, three-body collisions, radiation imprisonment and photoelectric emission. Non-standard rate coefficient functions can be handled by a user supplied routine. The interaction of the user with the library is limited to the preparation of an input file characterizing the interacting species and reactions, accessing the data or the chemical kinetics results through a reduced number of procedure calls with similar interfaces. PLASMAKIN allows the user to concentrate on the physical nature of the problems independently of the gas mixture properties and reactions model. As an example a program has been prepared to evaluate the maintenance field, equilibrium populations, relative contribution of each reaction, photon emission spectra and the energy losses rates on the positive column region of a discharge in electropositive gases. The program is applied to a discharge in neon. The library is written in Fortran 95 and has error support.

Co-dimension two bifurcation analysis for two-dimensional plasma convection

The plasma flow model of resistive interchange modes in a toroidally confined plasma is similar to the well known two-dimensional hydrodynamic Bénard–Rayleigh convection paradigm. A co-dimension two bifurcation analysis of the plasma problem is presented at a marginal point where two different wavelengths become simultaneously unstable. The weakly nonlinear interaction of convection cells is observed, and the hydrodynamic and plasma physics model systems are compared. With increasing magnetic shear, the dynamics of the resistive interchange model deviates significantly from the shearless hydrodynamic Bénard–Rayleigh convection predictions. The analytical results are confirmed by numerical simulations.

β scaling of confinement

Empirical scaling laws (Goldston, Kaye-Goldston, ITER89P and ITER93H) for the confinement time τE in tokamaks depend on dimensionless global plasma parameters in a way which is difficult to associate with some general plasma physics model. It is shown that such dependences can arise from artefacts in the database used to derive the scaling expression. The artefacts involve inner relationships, for example, collinearities between variables. For the ITER L mode and H mode databases, it is shown that subsets of the scaling expressions are approximately constant. An alternative description of L mode, ELM-free, small ELM and giant ELM H mode data is given. The alternative description does not include the dependences upon plasma β, elongation and safety factor which are present in the above scaling laws; extrapolations to ITER parameters by this alternative data description are virtually the same as those by ITER89P and ITER93H. The alternative description is based on a simple electrostatic physics model (plateau scaling) in which confinement is degraded by non-collisional processes. It can describe global confinement data for all four confinement regimes; the common scaling features a multiplier C which is assigned a different value for each regime. The complex physics associated with MHD instabilities (ELMs, sawteeth, outer modes) is hidden in the multiplier C, and attempts are made to uncover such physics. In these attempts global confinement is made to scale with physics models rather than physics variables.

Safety approach for plasma anomaly events in fusion reactor: Code development and assessments

A safety assessment method for plasma transients, including thermal response of in-vessel components, was provided. We developed a plasma physics model for safety analysis which has been implemented in a safety analysis code (SAFALY). The SAFALY code consists of a zero-dimensional plasma dynamics model and a 1.5-dimensional thermal behavior model of in-vessel components in the thickness direction. The code can treat hydraulic accidents using the results from a hydraulic code and analyze a passive plasma shutdown due to the impurity release from the wall. The abnormal events in the International Thermonuclear Experimental Reactor (ITER) calculated here are: (i) loss of plasma control, and (ii) large ex-vessel loss of coolant accident (LOCA) in the first wall and large ex-vessel LOCA in the divertor. The plasma transient and thermal response of in-vessel components in such events have been assessed using the code.

Development of Time Dependent Safety Analysis Code for Plasma Anomaly Events in Fusion Reactors

A safety analysis code SAFALY has been developed to analyze plasma anomaly events in fusion reactors, e.g., a loss of plasma control. The code is a hybrid code comprising a zero-dimensional plasma dynamics and a one-dimensional thermal analysis of in-vessel components. The code evaluates the time evolution of plasma parameters and temperature distributions of in-vessel components. As the plasma-safety interface model, we proposed a robust plasma physics model taking into account updated data for safety assessment. For example, physics safety guidelines for beta limit, density limit and H-L mode confinement transition threshold power, etc. are provided in the model. The model of the in-vessel components are divided into twenty temperature regions in the poloidal direction taking account of radiative heat transfer between each surface of each region. This code can also describe the coolant behavior under hydraulic accidents with the results by hydraulics code and treat vaporization (sublimation) from plasma facing components (PFCs). Furthermore, the code includes the model of impurity transport form PFCs by using a transport probability and a time delay. Quantitative analysis based on the model is possible for a scenario of plasma passive shutdown. We examined the possibility of the code as a safety analysis code for plasma anomaly events in fusion reactors and had a prospect that it would contribute to the safety analysis of the International Thermonuclear Experimental Reactor (ITER).

Development of Safety Assessment Method for Plasma Anomaly Events in Fusion Reactors

The objective of the study is to provide a safety assessment method for plasma transients including thermal response of in-vessel components. We developed a plasma physics model for safety analysis which has been implemented in a safety analysis code (SAFALY). The SAFALY code consists of a 0-D plasma dynamics model and a 1-D thermal behavior model of in-vessel components in the thickness direction. The code can treat hydraulic accidents using the results from a hydraulic code and analyze a passive plasma shutdown due to the impurity release from the wall. The overpower events in International Thermonuclear Experimental Reactor (ITER) were investigated, when the fueling rate and confinement improvement changes. The results show no significant damage to the confinement boundary of ITER is expected, as long as the cooling system works normally.

Development of Time Dependent Safety Analysis Code for Plasma Anomaly Events in Fusion Reactors.

A safety analysis code SAFALY has been developed to analyze plasma anomaly events in fusion reactors, e.g., a loss of plasma control. The code is a hybrid code comprising a zero-dimensional plasma dynamics and a one-dimensional thermal analysis of in-vessel components. The code evaluates the time evolution of plasma parameters and temperature distributions of in-vessel components. As the plasma-safety interface model, we proposed a robust plasma physics model taking into account updated data for safety assessment. For example, physics safety guidelines for beta limit, density limit and H-L mode confinement transition threshold power, etc. are provided in the model. The model of the in-vessel components are divided into twenty temperature regions in the poloidal direction taking account of radiative heat transfer between each surface of each region. This code can also describe the coolant behavior under hydraulic accidents with the results by hydraulics code and treat vaporization (sublimation) from plasma facing components (PFCs). Furthermore, the code includes the model of impurity transport form PFCs by using a transport probability and a time delay. Quantitative analysis based on the model is possible for a scenario of plasma passive shutdown. We examined the possibility of the code as a safety analysis code for plasma anomaly events in fusion reactors and had a prospect that it would contribute to the safety analysis of the International Thermonuclear Experimental Reactor (ITER).

Symmetries in hydrodynamic turbulence and MHD dynamo theory

The three-dimensional equations of ideal hydrodynamics and ideal MHD are expanded in eigenfunctions of the curl, and the resulting basic interactions of these nonlinear systems are analysed. As the equations are invariant under time and amplitude reversal, a criterion defining the arrow of time is introduced. A new parameter, the center of energy, serves to characterize a basic interaction. In the 3D Euler equations we find four different interactions and their mirror images, two of which can transport energy to smaller wavenumbers. This can lead to the appearance of structures in turbulent flow, and throws doubt on a derivation of Kolmogorov's law based on a cascading of energy to higher wavenumbers.In energy the corresponding two-dimensional equations, which are isomorphic to the guiding centre model in plasma physics, only one interaction exists, with a strong inverse cascade, which can lead to accumulation of energy in the spatially largest accessible modes. In MHD theory it is possible to separate magnetic from kinetic interactions. The former give again four basic interactions, two being regular and two being inverse cascades. One of these is quite strong, and can lead to the MHD dynamo effect. Kinetic energy can be transferred into magnetic energy. The dynamo effect is is accompanied by alignment of velocity and magnetic fields. We show that stationary velocity fields may lead to exponentially growing magnetic fields and we give an explicit criterion for this instability.

Transport coefficients of plasmas and disparate mass binary gases

Abstract We investigate the dynamics of an inhomogeneous disparate mass binary gas or plasma at various scales. The scaling of the cross collision terms follows that derived in [11] in the homogeneous case, and is combined with a scaling of the transport terms of the Boltzmann (or Fokker-Planck) equation which is not the same for the light and heavy particle. Then, a Chapman-Enskog procedure is applied. At the heavy particle (or ion) kinetic scale, this approach leads to a system consisting of a kinetic equation for the heavy particle coupled with massless compressible Navier-Stokes equations for the light particle. At the hydrodynamic/diffusion scale, it leads to a system of coupled compressible Navier-Stokes equations, in which the light particle mass has again being set to zero. In particular, the obtained model is very close to the conventional hydrodynamic model of plasma physics.

Surface and plasma simulation of deposition processes: CH4 plasmas for the growth of diamondlike carbon

A surface model was developed for diamondlike-carbon film deposition, and was connected in a self-consistent way with a one-dimensional plasma chemistry and physics model for a CH4 radio-frequency (rf) discharge. The surface model considers the adsorption of multiple species (CH3, CH2, and H), and solves for the surface coverage of each species. Comparison is also done with a one-adsorbed-species model. Deposition is assumed to take place via direct ion incorporation, and ion-induced stitching of adsorbed neutrals; film removal takes place via etching and sputtering. The effects of ion flux/energy and surface temperature are examined in detail: At high ion energies direct ion incorporation dominates, in spite of competition with sputtering; at intermediate energies stitching prevails, while for lower ion energies etching can become largest. Mass balances are written at the surface–gas interface, permitting the determination of the effective sticking coefficients of the reacting neutrals. The sticking coefficients calculated from the surface model are fed back into the gas-phase chemistry model to recalculate the neutral densities. The process is repeated until a self-consistent solution is obtained. It is shown that the effective sticking coefficient of a neutral changes drastically from a low value for the plasma-off (or low ion energy) state, to a high value for the plasma-on and high ion energy state, resulting in higher consumption at the surface. The results show that it is imperative for meaningful results to solve surface and gas-phase chemistry models in a self-consistent way, a fact demonstrated by successful comparison with experimental data for the deposition rate and the gas-phase densities.

Steady vortices in plasmas and geophysical flows.

A number of two-dimensional fluid models in geophysical fluid dynamics and plasma physics are examined to find out whether they have steady and localized monopole vortex solutions. A simple and general method that consists of two steps is used. First the dispersion relation is calculated, to find all possible values of the phase velocity of the linear waves. Then an integral relation that determines the center-of-mass velocity of localized structures must be found. The existence condition is that this velocity should be outside the region of linear phase velocities. After a presentation of the method, previous work on the plasma drift wave model and the shallow-water equations is reviewed. In both cases it is found that the center-of-mass velocity is larger than the maximum phase velocity of the linear waves if the amplitude is large enough, and steady localized vortices can therefore exist. New results are then obtained for a number of two-field models. For the coupled ion acoustic-drift modes in plasmas, it is found that the center-of-mass velocity depends on the ratio between the parallel ion velocity component and the electrostatic potential in the vortex. If this ratio is large enough, the vortex can be steady. For the drift-Alfven mode the "center-of-charge" velocity is proportional to the ratio between the parallel current and the total charge in the vortex. It can therefore be steady if this ratio satisfies the appropriate conditions. For the quasigeostrophic two-layer equations, describing stratified flow on a rotating planet, it is found that the center-of-mass velocity is determined by the ratio between the baroclinic and the barotropic components in the vortex. If a baroclinic component with an appropriate sign is added to a barotropic vortex, it propagates faster than the barotropic Rossby waves, and can be steady. Finally, the existence conditions for a vortex in an external zonal flow are examined. It is found that the center-of-mass velocity acquires an additional westward contribution in an anticyclonic shear zone in the framework of the shallow-water equations, and also that an easterly jet south of this shear zone partly shields a vortex situated in the shear zone from the dispersive influence of the fast Rossby waves on the equatorward side.

A “SuperCode” for Systems Analysis of Tokamak Experiments and Reactors

A new code, named SUPERCODE, has been developed to fill the gap between currently available zero dimensional systems codes and highly sophisticated, multidimensional plasma performance codes. The former are comprehensive in content, fast to execute, but rather simple in terms of the accuracy of their physics and engineering models. The latter contain state-of-the-art plasma physics modeling but are limited in engineering content and are time consuming to run. The SUPERCODE upgrades the reliability and accuracy of systems codes by calculating the self consistent 1 1/2-D plasma evolution in a realistic engineering environment. By a combination of variational techniques and careful formulation there is only a modest increase in CPU time over 0-D runs, thereby making the SUPERCODE suitable for use as a systems studies tool. In addition, we have expended considerable effort to make the code user- and programmer friendly, as well as operationally flexible, with the hope of encouraging wide usage throughout the fusion community.

The response of a microwave multipolar bucket plasma to a high voltage pulse

A collisional model that describes the response of a microwave multipolar bucket plasma to a high voltage pulse is developed for plasma source ion implantation (PSII). The primary purpose is to develop a theoretical model of PSII plasma physics to be used in conjunction with a model of ion-target interaction to optimize PSII processing. Measurements of the sheath position and target current in a 100 mtorr helium plasma are found to be consistent with the model. Sheath thicknesses predicted by the collisional model are significantly less than those predicted by similar noncollisional models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Halo plasma physics model for mirror machines with neutral beam injection

A model for halo plasmas in mirror machines sustained by neutral beam injection is described and applied to the conceptual tandem mirror test facilities TDF and TASKA-M. Halo source terms include alpha particle heating, radial transport, neutral beam attenuation, and reionization of charge exchanged neutrals. The primary sinks are end loss and charge exchange. The neutral beams are found to contribute substantially to first wall surface heat load, but little to halo density or temperature. Reference halo parameters for TDF and TASKA-M are exhibited.

Design of a Translating Field-Reversed Configuration Reactor

A compact fusion reactor design with magnetic confinement based on a field-reversed configuration is described. The reactor is linear and operates in a pulsed mode where the plasma moves as a translating ''plasmoid'' through the burn chamber. The plasma physics model incorporates recent theoretical and experimental results on confinement. The design is compact and its power output is limited by first-wall and blanket technology. A helium-cooled solid breeder blanket is used for tritium breeding and thermal energy removal. A graphite thermal shield is included to reduce the energy generation and resulting first-wall stresses during pulsed operation. These studies indicate that attractive designs in the range of 300 to 1000 MW(electric) are possible, provided that currently understood scaling laws extrapolate favorably into the reactor regime. Multidimensional neutronics analysis indicates tritium breeding ratios >1.0.

Poisson structure of the equations of ideal multispecies fluid electrodynamics

The equations of the two- (or multi-) fluid model of plasma physics are recast in Hamiltonian form, following general methods of symplectic geometry. The dynamical variables are the fields of physical interest, but are noncanonical, so that the Poisson bracket in the theory is not the standard one. However, it is a skew-symmetric bilinear form which, from the method of derivation, automatically satisfies the Jacobi identity; therefore, this noncanonical structure has all the essential properties of a canonical Poisson bracket.

A d-d Tandem Mirror Reactor with Central-Cell Potential Modification

A conceptual tandem-mirror reactor (TMR) configuration consists of a solenoidal central-cell with its ends plugged by a combination of electrostatic and magnetic fields. The magnetic fields in the end plug also provide MHD stability. The electrostatic plugs for ions and electrons are created by combining hot electron plasmas and neutral beams for fueling and pumping. A large negative potential may be formed in the end plug to contain central cell electrons, but the central cell floating potential /phi/ /SUB f/ is driven negative as charge neutrality is maintained. Cat-d TMR plasma performance is assessed with respect to standard (positive), neutral and negative central cell potential operating modes. It is determined that the plasma Q for a 2000 MW fusion power reactor is peaked for central cell potential /phi/ /SUB f/ near zero. This is because on one hand, the ion-loss cone is bigger for positive /phi/ /SUB f/ and the ion plug electrons must overcome larger /phi/ /SUB f/ + /phi/ /SUB c/ and hence more ECH is required to build the ion plug, and, on the other hand, the electron loss-cone is bigger for negative /phi/ /SUB f/ and synchrotron losses are severe. A zero-dimensional plasma physics model formore » the density and power balance of a Cat-d TMR has been developed from an existing code that models a d-t TMR operating with a positive central cell potential. The new Cat-d code models all potential operating modes and has been benchmarked.« less

The hard-sphere model in plasma and gas physics

Expressions are derived for the scattering cross sections and the macroscopic properties of gases and plasmas in a hard-sphere model in which the first two terms are retained in the expansion in the small parameter of the theory. These expressions are analyzed and compared with the results of the Maxwell model and also with numerical calculations for model interaction potentials.

Model' tverdoi sfery v fizike plazmy i gaza

Model' tverdoi sfery v fizike plazmy i gaza

Injection of tritium pellets into a two-component tokamak reactor

This paper gives the results of a numerical study of the plasma physics parameters of a tokamak reactor into which the fuel components are fed by various methods: tritium in the form of solid pellets and deuterium in the form of high-energy neutrals by means of an injector. The study was carried out with the use of a one-dimensional space-time plasma physics model describing the energy and particle balances in the tokamak plasma. The authors have determined the dependences of the reactor parameters (Q, βφ etc.) on the tritium fuelling rate.