Theta-pinch Reactor Research Articles

Transient neutral gas interactions with plasmas and walls

The use of neutral gas layers for confinement and/ or heat removal in controlled fusion reactors has been the subject of many investigations in recent years. Alfven and Smars [l] appear to be the first to propose the use of a “gas blanket” when they suggested that heat losses from a hot plasma can be reduced by a strong magnetic field in such a way as to allow a layer of high pressure neutral gas near the wall to surround the plasma and balance its pressure. Although it was later shown by Lehnert [2] that the plasma pressure cannot be balanced by the neutral gas pressure in steady state, the question of such balance in the case of fully ionized plasma cores bounded by a partially ionized layer, as well as the question of the penetration process of neutral gas into a plasma, were addressed at an early date also by Lehnert [3]. A mathematical model for the application of a neutral gas layer to the heat removal problem in a ThetaPinch reactor has been presented by Oliphant [4] in which estimates of the rate of heat flux from the plasma using a short-mean-free-path limit for thermal conduction, and a quasi-steady state assumption for the plasma and neutral gas profiles, were obtained. This paper represents an extension of the work cited in ref. 4. A time-dependent one-dimensional computer code is utilized to study the transient development of a neutral gas blanket by examining the effects of diatomic neutral gas streaming into a magnetized plasma. The interactions of the incoming diatomic gas and the resulting monatomic gas with the plasma ions, electrons and alphas are examined in

Nuclear Design Sensitivity Analysis for a Fusion Reactor

The final design of a nuclear reactor and any component thereof evolves through an iterative process that necessitates the evaluation of many alternative concepts. In particular, conceptual and preliminary reactor systems studies require many quick survey calculations to determine changes of certain important design parameters in response to changes of layout, material compositions, and other design features. Effective methods to perform such design sensitivity analyses are described and applied to the nuclear design of a fusion reactor. Generalized perturbation theory is used to calculate sensitivities of integral nuclear design parameters to certain design changes. The accuracy of this method is evaluated for specific cases where large ranges of design perturbations are considered. Specifically, the effects on tritium breeding, energy deposition, atom displacements and transmutations in the Reference Theta-Pinch Reactor design due to variations in the beryllium thickness, choices of molybdenum, vanadium, or niobium structural material, BeO versus beryllium neutron multiplier, graphite region thickness, and /sup 6/Li enrichment are investigated.

Recent Developments in the Design of Conceptual Fusion Reactors

Since the first round of conceptual fusion reactor designs in 1973 - 1974, there has been considerable progress in design improvement. Two recent tokamak designs of the Wisconsin and Culham groups, with increased plasma beta and wall loading (power density), lead to more compact reactors with easier maintenance. The Reference Theta-Pinch Reactor has undergone considerable upgrading in the design of the first wall insulator and blanket. In addition, a conceptual homopolar energy storage and transfer system has been designed. In the case of the mirror reactor, there are design changes toward improved modular construction and ease of handling, as well as improved direct converters. Conceptual designs of toroidal-multiple-mirror, liner-compression, and reverse-field pinch reactors are also discussed. A design is presented of a toroidal multiple-mirror reactor that combines the advantages of steady-state operation and high-aspect ratio. The liner-compression reactor eliminates a major problem of radiation damage by using a liquid-metal first wall that also serves as a neutron-thermalizing blanket. The reverse-field pinch reactor operates at higher beta, larger current density and larger aspect ratio than a tokamak reactor. These properties allow the possibility of ignition by ohmic heating alone and greater ease of maintenance.

First Wall Thermal-Mechanical Analyses of the Reference Theta-Pinch Reactor

The thermal-mechanical response of the Reference Theta-Pinch Reactor (RTPR) first wall was analyzed. The first wall problems anticipated for a pulsed, high-..beta.. fusion power plant can be ameliorated by either alterations in the physics operating point, materials reengineering, or blanket/first wall reconfiguration. Within the latter ''configuration'' scenario, a two-fold approach has been adopted for the thermal-mechanical portion of the RTPR first wall technology assessment. First, a number of new first wall configurations (bonded or unbonded laminated composites, all-ceramic structures, protective and/or sacrificial ''bumpers'') were considered. Second, a more quantitative failure criterion, based on the developing theories of fracture mechanics, was identified. For each first wall configuration, transient heat transfer and thermoelastic stress calculations have been made. Two-dimensional finite element structural analyses have been made for a variety of mechanical boundary conditions. Only the Al/sub 2/O/sub 3//Nb - 1 Zr system has been considered. The results of this study indicated a wide range of design solutions to the pulsed thermal stress problem anticipated for the RTPR.

First wall environment in the reference theta-pinch reactor (RTPR)

A review of the RTPR first-wall environment is given, with emphasis on the physical processes which determine the first wall insult. Recent results of calculations of the transient phenomena which occur when a neutral gas blanket is set up for first wall protection are given. New first-wall designs are described, and their responses to the first wall fluxes are discussed.

First wall environment in the reference theta-pinch reactor (RTPR)

A review of the RTPR first-wall environment is given, with emphasis on the physical processes which determine the first wall insult. Recent results of calculations of the transient phenomena which occur when a neutral gas blanket is set up for first wall protection are given. New first-wall designs are described, and their responses to the first wall fluxes are discussed. Une revue des problèmes posés par l'environnement de la première paroi du réacteur RTPR est présentée en insistant particulièrement sur les processus physiques responsables de la détérioration de la première paroi. Sont présentés les résultats récents concernant les calculs des phénomènes transitoires qui se produisent quand une protection par un gaz inerte est interposée pour protéger la première paroi. De nouveaux dispositifs pour réaliser cette première paroi sont décrits et leur réaction vis-à-vis des flux tombant sur la première paroi sont discutées. Es wird ein Überblick über die Umgebung der innersten Wand eines RTPR gegeben; der Schwerpunkt liegt bei den physikalischen Prozessen, die den Angriff der innersten Wand bestimmen. Es werden neue Ergebnisse zu Berechnungen der Einschaltvorgänge mitgeteilt, die auftreten, wenn ein Neutralgasbrutmantel zum Schutz der innersten Wand eingesetzt wird. Neue Konzepte für die innerste Wand werden beschrieben; ihr Verhalten auf den Fluss zur innersten Wand wird diskutiert.

Transient charge-exchange effects in a neutral-gas layer

The transient build-up of the neutral-gas blanket in a theta-pinch reactor has been investigated. A hydrodynamic fluid code was developed to account for charge-exchange, ionization and energy transport in the plasma-neutral-gas interaction region. An initially collisionless neutral gas is separated from the vacuum region by the first wall, and at time t = 0 the wall becomes transparent to these neutrals so that half of them move freely into the boundary layer where they react with a plasma whose parameters are those given in the RTPR (Reference Theta-Pinch Reactor) design after quench. Initial neutrals react with the low-density edge of the plasma, and succeeding neutrals therefore react with the edge of a cooler plasma, removing less energy from the plasma by charge exchange. Also less energetic charge-ex change neutrals hit the wall, causing less damage as time progresses. A steady-state profile is quickly established. Essentially all the energy reaching the wall arrives in the initial pulse (about 11 μs long), and this amount of energy is insufficient to cause wall damage.

Comparison of the Cross-Section Sensitivity of the Tritium Breeding Ratio in Various Fusion-Reactor Blankets

For several proposed fusion-reactor-blanket designs, the changes in the tritium breeding ratios due to estimated errors in nuclear cross-section data are presented and compared. The designs considered are those proposed at the Oak Ridge National Laboratory, the reference theta-pinch reactor design proposed at the Los Alamos Scientific Laboratory, and the reference fusion power plant design proposed at the Princeton Plasma Physics Laboratory. Results are presented for the changes in the breeding ratios due to estimated energy-dependent errors in various partial cross sections of 6Li, 7Li, C, Be, and F. The 7Li(n,n’) α,t cross section, the Be(n,2n’) cross section, and the fluorine cross sections are found to introduce changes of the order of a few percent in the breeding ratios for the various designs. Sensitivity profiles that show the changes in the breeding ratios due to changes in these cross sections in specific energy ranges are presented.

CTR applications of the high-density linear theta pinch

Some general scaling laws for the (idealized) linear theta pinch are derived with the magnetic field strength as the independent variable. These scaling laws are used to calculate machine parameters, such as length, confinement time, magnetic energy storage requirements, etc. for five potential linear theta-pinch applications of interest to CTR: (a) a confinement experiment to achieve the Lawson criterion; (2) a power-producing theta-pinch reactor; (3) a power-producing laser-heated reactor; (4) a radiation and materials test facility (FERF); and (5) a fusion/fission hybrid reactor. In each case the advantages of operating at large values of magnetic field strength are shown quantitatively. Some potential problem areas for the high-field (and therefore high-density) linear theta pinch are identified and discussed.

Superconducting magnetic energy storage

Abstract After a brief review of the reasons for and forms of secondary energy storage and of the elements and history of inductive or magnetic storage, we discuss the four distinct areas in which superconducting magnetic energy storage can be applied. Differences in energy transfer times place different requirements on the storage coil, on the switch or transfer element, and on the energy losses in the superconductor. We report on designs and experiments in one of these areas with 2 to 300 kJ units, and on the analysis and plans for an installation that is to provide 250 MJ of plasma compression energy for the theta-pinch controlled thermonuclear fusion test reactor. We point out those elements of inductive storage that need further development before a theta-pinch fusion reactor can become economically competitive. Finally, we compare the size and costs of the energy storage components of these systems with similar and with larger inductive storage systems that are to interact reversibly with electric utility networks.

Some Preliminary Considerations of A Molten-Salt Extraction Process to Remove Tritium from Liquid Lithium Fusion Reactor Blankets

AbstractA method is described for removing tritium from liquid lithium fusion reactor blankets by extraction with molten salt. Results of distribution coefficient measurements made with lithium-lithium halide mixtures have demonstrated that tritium is preferentially distributed in the salt phase by a factor >1.0 on a volumetric basis. Other considerations related to (a) mutual solubilities between the salt and metal, (b) phase separation, (c) blanket neutronics, (d) corrosion, (e) fabrication, and (f) recovery of tritium from the salt phase indicate that the extraction process should be feasible. Calculations based on the blanket processing requirements for the reference theta-pinch reactor (RTPR) show that the equipment and power needed to carry out a molten-salt extraction operation on the lithium blanket of the RTPR are reasonable.

Fusion reactor systems

In this review we consider deuterium-tritium (D-T) fusion reactors based on four different plasma-confinement and heating approaches: the tokamak, the theta-pinch, the magnetic-mirror, and the laser-pellet system. We begin with a discussion of the dynamics of reacting plasmas and basic considerations of reactor power balance. The essential plasma physical aspects of each system are summarized, and the main characteristics of the corresponding conceptual power plants are described. In tokamak reactors the plasma densities are about ${10}^{20}$ ${\mathrm{m}}^{\ensuremath{-}3}$, and the $\ensuremath{\beta}$ values (ratio of plasma pressure to confining magnetic pressure) are approximately 5%. Plasma burning times are of the order of 100-1000 sec. Large superconducting dc magnets furnish the toroidal magnetic field, and 2-m thick blankets and shields prevent heat deposition in the superconductor. Radially diffusing plasma is diverted away from the first wall by means of null singularities in the poloidal (or transverse) component of the confining magnetic field. The toroidal theta-pinch reactor has a much smaller minor diameter and a much larger major diameter, and operates on a 10-sec cycle with 0.1-sec burning pulses. It utilizes shock heating from high-voltage sources and adabatic-compression heating powered by low-voltage, pulsed cryogenic magnetic or inertial energy stores, outside the reactor core. The plasma has a density of about ${10}^{22}$ ${\mathrm{m}}^{\ensuremath{-}3}$ and $\ensuremath{\beta}$ values of nearly unity. In the power balance of the reactor, direct-conversion energy obtained by expansion of the burning high-$\ensuremath{\beta}$ plasma against the containing magnetic field is an important factor. No divertor is necessary since neutral-gas flow cools and replaces the spent plasma between pulses. The open-ended mirror reactor uses both thermal conversion of neutron energy and direct conversion of end-loss plasma energy to dc electrical power. A fraction of this direct-convertor power is then fed back to the ioninjection system to sustain the reaction and maintain the plasma. The average ion energy is 600 keV, plasma diameter 6 m, and the plasma beta 85%. The power levels of the three magnetic-confinement devices are in the 500-2000 MWe range, with the exception of the mirror reactor, for which the output is approximately 200 MWe. In Laser-Pellet reactors, frozen D-T pellets are ignited in a cavity which absorbs the electromagnetic, charged particle, and neutron energy from the fusion reaction. The confinement is inertial, since the fusion reaction occurs during the disassembly of the heated pellet. A pellet-cavity unit would produce about 200 MWt in pulses with a repetition rate of the order of 10 ${\mathrm{sec}}^{\ensuremath{-}1}$. Such units could be clustered to give power plants with outputs in the range of 1000 MWe.

Surface effects at the first wall of the Reference Theta-Pinch Reactor (RTPR)

The fundamental operating principles and parameters inherent to the Reference Theta-Pinch Reactor (RTPR) are described herein. An emphasis is placed on those engineering aspects of the RTPR design which bear directly on the thermal, hydraulic, and radiation response of the first wall. The major portion of the data presented is calculational, and further experimental and theoretical results are needed to assess accurately anticipated material problems and to forecast appropriate solutions. Material problems envisioned for the RTPR first wall are discussed briefly in the context of the particular RTPR design described.

Monte Carlo treatment of heat flow through a neutral gas layer

The flow of heat through a neutral gas layer under conditions of density and temperature relevant to the cooling layer used in a reference theta-pinch reactor (RTPR) has been investigated numerically by means of a Monte Carlo technique. The necessity for corrections to the fluid model has been indicated and assessed in an example calculation presented herein.