Magnetic Confinement Systems Research Articles

Collective CO2-Laser Scattering of Low Friquency Small-Scale Plasma Fluctuations

The scattering of electromagnetic waves is a primary importance of the short wave fluctuation studies in the fusion research plasmas. Among the scattering diagnostics the CO2-laser one is favorable for a number of reasons. It is insensitive to refraction distortions, is capable of easy coupling with a plasma machines and much more cheaply compared to far infrared scattering technique. The current status the diagnostics based on the light mixture detection principle is considered in the report. This kind of diagnostics for plasma micro-turbulence investigation is mostly employed in toroidal magnetic systems. However its application for the same purpose in mirror plasmas may be perspective as well. Two options of CO2-laser scattering diagnostics developed for FT-2 tokamak are presented. There are distinguished by a kind of laser probing sources and ω-K regions of density fluctuations. The diagnostics capabilities are exemplified by the recent results of CO2-laser scattering experiments in the FT-2 tokamak. The perspectives of the CO2-laser scattering are analyzed for small-scale fluctuation study in open magnetic confinement systems.

Quasi-two-dimensional waves in three-dimensional magnetic confinement systems

A reduced, scalar magnetohydrodynamic (MHD) description for linear perturbations of arbitrary aspect-ratio, fully three-dimensional plasma configurations is derived for perturbations with short scale-length perpendicular to the magnetic field. The application of the scalar wave equation to ballooning modes is presented. It is shown that coexistence of toroidally extended and toroidally localized unstable ideal hydromagnetic ballooning modes occurs in an interchange–unstable equilibrium case modelling the Large Helical Device (LHD) with a broad pressure profile. The toroidally extended modes can be understood on the basis of a ripple-averaged ballooning equation, whereas the toroidally localized branch corresponds to modes localized along a flux tube. A new three-dimensional ray phase space is introduced in which the periodicity properties are simplified.

Negative-energy perturbations in cylindrical equilibria with a radial electric field

The impact of an equilibrium radial electric field $E $ on negative-energy perturbations (NEPs) (which are potentially dangerous because they can lead to either linear or nonlinear explosive instabilities) in cylindrical equilibria of magnetically confined plasmas is investigated within the framework of Maxwell-drift kinetic theory. It turns out that for wave vectors with a non-vanishing component parallel to the magnetic field the conditions for the existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D. Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for the existence of perpendicular NEPs, which are found to be the most important perturbations, is modified. For $|e_i\phi|\approx T_i$ ($\phi$ is the electrostatic potential) and $T_i/T_e > \beta_c\approx P/(B^2/8\pi)$ ($P$ is the total plasma pressure), a case which is of operational interest in magnetic confinement systems, the existence of perpendicular NEPs depends on $e_\nu E$, where $e_\nu$ is the charge of the particle species $\nu$. In this case the electric field can reduce the NEPs activity in the edge region of tokamaklike and stellaratorlike equilibria with identical parabolic pressure profiles, the reduction of electron NEPs being more pronounced than that of ion NEPs.

Edge Plasma Turbulence Diagnosis by Langmuir Probes

A view of the experimental techniques used in the characterization of fluctuations in the plasma boundary region of magnetic confinement systems by Langmuir probes is given. In particular, recent experimental developments for the measurement of electron temperature fluctuations are discussed.

ASH Pumping from Mirror and Toroidal Magnetic Confinement Systems

Induced selective stochastical transversal diffusion coefficients for ions in axisymmetric open and closed magnetic systems are presented. Single particle dynamics in complex field is described. The possibility of setting the radial losses time level of 0.02 s is shown both for mirror trap and for tokamak. 9 refs., 1 fig.

Status of fusion reactor design and technology in Russia

Abstract This paper examines the four main directions of the Russian Fusion Program: ITER engineering design and research and development in its support including experiments on tokamak facilities; alternative magnetic confinement systems; inertial fusion; applied plasma processes.

Potential Formation at Plasma Edge due to Suprathermal Particle Losses

AbstractGeneration of the edge radial electric field and corresponding plasma rotation is studied for both uniform magnetic field and toroidal confinement systems with separatrix configuration of magnetic surfaces. The equations describing the edge plasma rotation due to suprathermal particle losses are derived. The solution on this equations is found for the simplest case of collisionless plasma flow to the neutralizing wall perpendicular to the magnetic field. It is shown that classical acceleration of plasma by ion orbital losses is enough to explain electric field and plasma rotation observed near walls.

An experimental study of magnetic islands as Hamiltonian systems

Magnetic islands play an important role in determining plasma transport in toroidal magnetic confinement systems. The magnetic error fields and the associated islands can be theoretically described by a Hamiltonian approach. Experiments have been conducted on the Compact Auburn Torsatron [Fusion Technol. 18, 281 (1990)] to test the applicability and limits of the first-order Hamiltonian theory to magnetic islands. A novel set of helical trim coils with the same spatial periodicity as an ι– = 1/2 magnetic island were used to create a perturbation field of variable magnitude and phase. Extensive experimental parametric studies of the magnetic island were conducted and compared with theory. It was found that the first-order Hamiltonian theory is applicable for the complete range of experimental error fields.

Requirements for accuracy of superconducting coils in the Large Helical Device

Irregular magnetic fields resonate with the rational surface of the magnetic confinement systems, form magnetic islands and ergodic layers, and destruct the plasma confinement. To avoid this confinement destruction the requirement of an accuracy of 10 −4 in the magnetic field is adopted as the magnetic-accuracy design criterion for the LHD machine. Following this criterion the width of the undesirable magnetic island is kept less than one tenth of the plasma radius. The irregular magnetic field from the superconducting (SC) helical and poloidal coils is produced by winding irregularity, installing irregularity, cooling-down deformations and electromagnetic deformations. The local irregularities such as feeders, layer connections, adjacent-conductor connections of the coils also produce an error field. The eddy currents on the supporting shell structure of SC coils, the cryostat, etc. are also evaluated. All irregular effects are analyzed using Fourier decomposition and field mapping methods for the LHD design, and it is confirmed that the present design of the superconducting coil system satisfies the design criterion for these field irregularities.

Open Confinement Systems and the D-3He Reaction

In this paper, the special synergisms between open-ended magnetic confinement systems and the D-{sup 3}He fuel cycle are discussed, both in general terms and through examples. Properties of open systems that make them especially suited for this fuel cycle include their ability to stably confine high-beta plasmas, their compatibility with electrostatic direct converters, and their linear geometry, which can greatly simplify the practical attainment of high magnetic fields. The example systems given include a linear collider and thermal barrier tandem mirror systems for both terrestrial and space travel applications. It is concluded that satisfying the demanding physics requirements posed by the D-{sup 3}He fuel cycle may be more readily possible through the use of open-ended magnetic systems than it will be through the use of closed systems of the tokamak genre.

The U.S. program for fusion nuclear technology development

The Fusion Nuclear Technology (FNT) research and development program in the United States is shaped by a hierarchy of documents and by the environment for nuclear energy existing in the United States. The fission nuclear industry in the United States has suffered problems with public perception of safety, waste disposal issues, and economics as influenced by safety and environmental issues. For fusion to be a viable energy alternative, it must offer significant improvements in these areas. The hierarchy of documents defining objectives, plans, and strategy of the U.S. FNT program consists of the Magnetic Fusion Program Plan (MFPP) (February 1985), The Technical Planning Activity Final Report (January 1987), the Finesse Program Report (January 1987), and the Blanket Comparison and Selection Study Final Report (September 1984). In addition, two other documents are also significant in shaping FNT policy. These are the IEA report on Material for Fusion (December 1986) and the Summary of the Report of the Senior Committee on Environmental, Safety, and Economic Aspects of Magnetic Fusion Energy (September 1987). The U.S. Magnetic Fusion Program Plan defines four key technical issues (magnetic confinement systems, properties of burning plasmas, fusion nuclear technology, and fusion materials). The goal of the plan is to establish the scientific and technological base required for economic and environmental assessment of fusion energy in the early post-2000 time period. The Technical Planning Activity (TPA) provides the program logic for accomplishing the MFPP goal. The Development and Technology Program of the Office of Fusion Energy contains the two key technical issues: Fusion Nuclear Technology and Materials. The FNT program seeks to develop safe and environmentally acceptable systems to ensure fuel (tritium) self-sufficiency, and energy conversion systems. The fuel self-sufficiency program consists of programs to breed tritium in blankets and for processing the tritium both from the blankets and the plasma exhaust. At present only a small amount of effort is devoted to the energy conversion systems, with most of the effort on tritium production and handling. The blanket program is focused on critical feasibility issues for both solid and liquid breeders, and the Tritium System Test Assembly is focused on safe handling and processing of tritium. Throughout the blanket program, emphasis is placed on low activation materials and safety. This talk will provide details of the FNT research and development program including its structure and budget for FY 1988.

Invariance principles and plasma confinement

If the equations that describe the observed anomalous transport in magnetic confinement systems are invariant under a scale transformation then any confinement time calculated from them must exhibit the same invariance, no matter how intractable the calculation. This principle places constraints on the form of the confinement time scaling which are characteristic of the plasma model represented by the equations. These constraints reduce the number of parameters which have to be investigated empirically and can serve to indicate which plasma models could describe the observed losses. By extending this argument to specific models of turbulent transport in which the magnetic configuration and the physical mechanism for transport are identified, one can closely define the form of local transport coefficients-in certain cases completely determining them. The paper provides a review of these ideas, shows how they provide a theoretical framework for discussing existing empirical confinement scalings and illustrates their use in classifying and determining the form of local transport coefficients.

STARPOWER: The U.S. and International Quest for Fusion Energy

"STARPOWER: The U.S. and International Quest for Fusion Energy." Fusion Technology, 13(4), pp. 662–663 Additional informationNotes on contributorsStephen O. DeanStephen O. Dean, president of Fusion Power Associates, has been an active fusion researcher and manager for 25 years. As president of Fusion Power Associates, which he cofounded in 1979, he actively explains and promotes fusion to a broad audience that includes congressional staff and science reporters. He sponsors symposia that bring together senior managers and researchers in both magnetic and inertial confinement fusion. As director of the Magnetic Confinement Systems Division at the U.S. Atomic Energy Commission/Energy Research and Development Administration/U.S. Department of Energy in the 1970s, he directed the growth of the major programs in tokamaks and magnetic mirrors at U.S. laboratories. In the late 1960s and early 1970s, he initiated and conducted experimental research in laser fusion at the Naval Research Laboratory.

Resistive ballooning modes in helical axis stellarators with longitudinal mass flow

The magnetohydrodynamic equilibrium equation for magnetic confinement systems with helical symmetry and longitudinal plasma flow is derived. The incompressible resistive ballooning mode equation for systems with a coordinate of symmetry and rigid longitudinal flow is also derived. A reduced equation is then obtained by expanding the ballooning mode equation for a system with a large field period length compared with the plasma cross section. An analytic solution is obtained for a model equilibrium with circular flux surfaces. In the limit of small longitudinal velocity, the static mode width and growth rate scaling as the resistivity to the one-third power are recovered. For small growth rates and large longitudinal velocity, these growth rates are driven by the interaction of the magnetic curvature and the centrifugal force with the radial pressure and mass density gradient, respectively, and scale linearly with the resistivity at a reduced level.

Considerations for design with cyclic softening materials in fusion reactor applications

Bainitic and martensitic steels have received considerable attention as structural materials in fusion reactor systems. Both magnetic and inertial confinement systems are expected to operate in a cyclic (pulsed) mode. While design stresses are usually low, certain physical or metallurgical stress concentrations can lead to changes in local materials properties inducing high local damage during cyclic loading. In particular, the bainitic and martensitic steels lose a considerable amount of their initial high strength when subjected to cyclic loading. Limitations in design with these cyclically softening materials are examined in this paper. The effects of strain range, fatigue cycles, hold times, strain rates, and environment on the elevated temperature fatigue behavior of bainitic 2.25Cr-lMo, modified 9Cr-lMo, and HT-9 are evaluated. These alloys are all found to cyclically soften, and these changes can also influence materials creep strength at elevated temperatures, leading to unacceptable strains and premature creep failure.

Electron temperature in field reversed configurations and theta pinches with closed magnetic field lines

Field-reversed configurations (FRC) and theta pinches with trapped reversed bias field are essentially the same magnetic confinement systems using closed magnetic field lines inside an open-ended magnetic flux tube. A simple model of joule heating and parallel electron thermal conduction along the open flux lines to an external heat sink gives the electron temperature as Te(eV) ≅ 0.05 B2/3(G) L1/3(cm), where B is the magnetic field and L is the coil length. This model appears to agree with measurements from present FRC experiments and past theta-pinch experiments which cover a range of 40–900 eV. The energy balance in the model is dominated by (a) parallel electron thermal conduction along the open field lines which has a steep temperature dependence, , and (b) the assumed rapid perpendicular transport in the plasma bulk which, in experiments to date, may be due to the small number of ion gyroradii across the plasma.

China's experimental efforts in fusion research

A historical survey is given of the experimental fusion-oriented research programme carried out in the People's Republic of China since 1958. China's research programme covers all major magnetic confinement systems, heating methods and diagnostics as well as laser development for inertial confinement. Experimental results obtained in the different plasma physics institutes in Hefei, Leshan, Beijing,and Shanghai are briefly described.

Parametric systems analysis of the modular stellarator reactor

The close coupling in the stellarator/torsatron/heliotron between coil design (winding law, peak field, current density, forces), magnetics topology (transform, shear, well depth) and plasma performance (equilibrium, stability, transport, beta) complicates reactor assessment more than for most magnetic confinement systems. In order to provide an additional degree of resolution of this problem for the Modular Stellarator Reactor (MSR), a parametric systems model has been developed and applied. This model reduces key issues associated with plasma performance, first-wall/blanket/shield and coil design to a simple relationship between beta, system geometry and a number of key indicators of overall plant performance. The results of this analysis can then be used to guide more detailed, multidimensional plasma, magnetics and coil design efforts towards technically and economically viable operating regimes. In general, it is shown that average beta values of ≤0.08 may be needed if the MSR approach is to be substantially competitive with other projected approaches to DT magnetic fusion in terms of system power density, mass utilization and cost for total thermal output power around 4.0 GW(th); lower powers will require even higher beta values.

The origin of fluctuations and cross-field transport in idealized magnetic confinement systems

The study of plasma fluctuations and confinement in idealized systems such as octupoles and levitrons has contributed to the understanding of cross-field transport processes. The linear theory of plasma instabilities that cause fluctuations is well developed and can predict growth rates γ and wavelengths θ x around lines of force. However, the theoretical prediction of cross-field transport coefficient D ± is restricted to quasilinear estimates of upper bounds (for example, D = 1 2 γ λ x 2 ) because of the complexity of the full nonlinear calculation. Such quasilinear estimates usually far exceed the measured values and are of limited worth. A general view of the results from octupole and levitron experiments shows that under collisional conditions ( λ ei / L < 0 ) the diffusion coefficient, D , scales in the same way as classical collisional diffusion ( D α n / T e 1 2 B 2 ). Agreement is closely approached in many cases, sometimes even in the presence of fluctuations. Under collisionless conditions ( D α n / T e 1 2 B 2 ), Bohm diffusion scaling ( D α T e / B ) is found in the few cases where the scaling law has been determined. This behaviour is consistent with the general scaling laws of Connor & Taylor (1977) but is not understood in detail. In addition there is evidence, both experimental and theoretical, that long-wavelength low-frequency electric fields (convection cells) can be generated nonlinearly from high-frequency fluctuations and can contribute to cross-field transport

Neutronics Shielding Analysis of the Last Mirror-Beam Duct System for a Laser Fusion Power Reactor

Three-dimensional Monte Carlo neutronics calculations for the last mirror-beam duct system for a laser-driven fusion power reactor conceptual design, where a three-section duct with focusing mirrors and right angle bends for the last two beam reflections is modeled. The estimate of neutron leakage flux after the second beam reflection is on the order of 10/sup 14/ n/(m/sup 2/ X s). Even though less in magnitude than the flux at the end point of neutral beam injectors in tokamak designs, reported in the range of 10/sup 17/ n/(m/sup 2/ X s), this still leads to a neutron dose rate of 10/sup 6/ rem/h after the second beam bend. Since space is not at a premium as in the case of magnet shields for magnetic confinement systems, minimum-cost lead mortar or concrete can be used as shielding materials instead of other minimum thickness costly materials. An energy leakage rate of 4.6 MW of 14-MeV neutrons per beam precludes the use of concrete behind the last mirror, suggesting the use of a secondary blanket composed of a lead acetate solution with immersed Boral (Al + B/sub 4/C) sheets. Boral as a penetration shielding material is found to reduce the thermal group flux aroundmore » the penetration by two to three orders of magnitude, compared to aluminum, and is recommended as a duct lining material for both inertial and magnetic fusion systems. Neutron heating rates and radiation damage parameters for the duct liner compare to those at the front face of the last mirror and first wall, and will require similar elaborate thermalhydraulic and mechanical designs.« less