J.E.C. Williams

The ARIES-I Tokamak Reactor Study †

The ARIES research program is a multi-institutional effort to develop several visions of tokamak reactors with enhanced economic, safety, and environmental features. Three ARIES visions are currently planned for the ARIES program. The ARIES-I design is a DT-burning reactor based on modest extrapolation from the present tokamak physics data base; ARIES-II is a DT-burning reactor which will employ potential advances in physics; and ARIES-III is a conceptual D-3He reactor. The first design to be completed is ARIES-I, a 1000 MWe power reactor. The key features of ARIES-I are: (1) a passively safe and low environmental impact design because of choice of low activation material throughout the fusion power core, (2) an acceptable cost of electricity, (3) a plasma with performance as close as possible to present-day experimental achievements, (4) a high performance, low activation, SiC composite blanket cooled by He, and (5) an advanced Rankine power cycle as planned for near term coal-fired plants. The ARIES-I research has also identified key physics and technology areas with the highest leverage for achieving attractive fusion power system.

An overview of the 45-T hybrid magnet system for the new National High Magnetic Field Laboratory

The new National High Magnetic Field Laboratory (NHMFL) at Tallahassee, Florida is committed to putting into operation in 1995 a 45-T Hybrid Magnet System to support research in steady, high magnetic fields. This facility will be accessible by qualified users world-wide on the basis of proposal and review. The more prominent components of this system will be a 24-MW resistive insert and a 120-MJ superconducting outsert. But successful achievement of the performance goals for the 45-T Hybrid System will depend on a number of unique, state-of-the-art subsystems and components. This paper describes the requirements and specifications on the individual subsystems and components in the context of the overall performance gears and reviews the plan for putting the whole together. >

600 MHz spectrometer magnet

An NMR-grade superconducting magnet has been constructed which operates in persistent mode at 14.25 T at reduced temperature. The stored energy is 840 kJ. The magnet incorporates niobium-titanium and niobium-tin multifilamentary conductors. In the persistent mode all windings are in series with superconducting joints between sections. Six of the joints are hybrids, niobium-tin joined to niobium-titanium. The niobium-titanium windings reached short sample without training. The niobium-tin sections suffered two training quenches before reaching 14.25 T. >

Hybrid III: The system, test results, the next step

The authors describe the overall Hybrid III system, present test results, and indicate future plans. Hybrid III, completed in late 1991, has since undergone a sequence of tests in preparation for becoming a facility magnet. When first tested in December 1991, it generated a total central field of 33.5 T. The superconducting magnet (SCM), operating in a bath of superfluid helium at 1.65 K and with a current of 2200 A, contributed 12.7 T to the total. In subsequent runs it was shown that the SCM would reach a critical current of approximately 2230 A when operated at approximately 1.7 K. After the completion of improvements to the cryogenic components as described, two major goals were set: to reach 35 T in two steps and to operate Hybrid III as a facility magnet. Hybrid III is targeted to reach 35 T in the spring of 1993.<<ETX>>

A design for the superconducting outsert of a 45-T hybrid magnet system using cable-in-conduit conductors

A part of the mission of the new NHMFL is to have available for users in 1995 a hybrid magnet system capable of producing at least 45-T steady field on axis in a 33-mm working bore. Approximately 31 T of the combined field will be produced by a water-cooled insert. The superconducting outsert, which combines NbTi and Nb/sub 3/Sn conductor technologies, will provide more than 14 T. The authors describe an option for this superconducting outsert based on the cable-in-conduit-conductor (CICC) approach, where cabled strands of conductor are contained in intimate contact with helium coolant inside a strong steel sheath that also acts as distributed structure. A departure from the usual practice for CICC technology is in the application of static Hell cooling, which simultaneously provides higher conductor performance and nearly passive extraction of the rather modest heat loads during normal operation of the magnet system.<<ETX>>

The ARIES-III D-3He tokamak-reactor study

A description of the ARIES-III research effort is presented, and the general features of the ARIES-III reactor are described. The plasma engineering and fusion-power-core design are summarized, including the major results, the key technical issues, and the central conclusions. Analyses have shown that the plasma power-balance window for D-/sup 3/He tokamak reactors is small and requires a first wall (or coating) that is highly reflective to synchrotron radiation and small values of tau /sub ash// epsilon /sub e/ (the ratio of ash-particle to energy confinement times in the core plasma). Both first and second stability regimes of operation have been considered. The second stability regime is chosen for the ARIES-III design point because the reactor can operate at a higher value of tau /sub ash// tau /sub E// tau /sub E/ approximately=2 (twice that of a first stability version), and because it has a reduced plasma current (30 MA), magnetic field at the coil (14 T), mass, and cost (also compared to a first-stability D-/sup 3/He reactor). The major and minor radii are, respectively 7.5 and 2.5 m.<<ETX>>

Quenching in epoxy-impregnated superconducting solenoids: Prediction and verification

An experimentally verified model that predicts quenching characteristics of a multi-section, epoxy-impregnated superconducting solenoid is described. The model uses a semi-empirical relationship to correlate the turn-to-turn normal zone growth to the propagation along a single wire. Normal zone growth in a solenoid is modeled assuming that transverse propagation is dominant. The computer predictions are compared with experimental results from small multi-section solenoids. The coil currents and terminal voltages predicted by this model agree with the experiments at high currents. However, at low currents the agreement is less satisfactory. The reasons for the dissagreement are understood and explained.

Quenching in coupled adiabatic coils

The prediction of the effects of a quench on stress and temperature is an important aspect of the design of superconducting magnets. Of particular interest, and the exclusive topic of this study, is the prediction of the effects of quenching in coupled adiabatic coils, such as the multi-section windings of a high field NMR spectrometer magnet. The predictive methods used here are based on the measurement of the time of propagation of quench between turns. From this measurement an approximate algorithum for the propagation time is used in a code which solves the linear differential equations for the coil currents and calculates the movement of normal zone boundaries and hence the associated winding resistance.

A commercial tokamak reactor using super high field superconducting magnets

This paper explores the range of possibilities for producing super high fields with advanced superconducting magnets. Obtaining magnetic fields greater than about 18 T at the coil in a large superconducting magnet system will require advances in many areas of magnet technology. These needs are discussed and potential solutions (advanced superconductors, structural materials and design methods) evaluated. A point design for a commercial reactor with magnetic field at the coil of 24 T and fusion power of 1800 MW is presented. Critical issues and parameters for magnet design are identified. 20 refs., 9 figs., 4 tabs.

A 60 cm bore 2.0 tesla high homogeneity magnet for magnetic resonance imaging

A 60 cm warm bore imaging and spectroscopy magnet has been constructed and placed in operation at the Francis Bitter National Magnet Laboratory (FBNML). The magnet achieved its design central field of 2.0 T but is currently being operated at 1.5 T. It operates in the persistent mode with a measured decay rate of less than 0.03 ppm/hr. Employment of both 10 superconducting shims and small ferromagnetic shims located close to the warm bore has resulted in a homogencity of better than 3 ppm throughout the 25 cm diameter spherical volume (DSV). Room temperature shim coils have not been incorporated into the system. A novel form of compact shielded pulsed gradient coil system has been designed, constructed and tested. In such a system, appropriate configuration of an external shield coil results in cancellation of external flux without the introduction of impurity harmonics that degrade the linearity of the gradients. Six sets (X, Y, Z coils, and X, Y, Z shields) have been incorporated into a unit of 6 cm build. The all aluminum cryostat employs a 77 K nitrogen recondenser and a shield cooler operating at less than 20 K. Steady state helium consumption is about 50 ml/hour. The system is currently being used for both high resolution, in-vivo31P-NMR spectroscopy and a variety of MRI experiments including23Na imaging of eyes.