R.J. Thome

Magnet design for the international thermonuclear experimental reactor

The superconducting coil systems for ITER will consist of 24 toroidal field coils and a central solenoid operating at a field of 13 T as well as a set of 6 poloidal field coils. They will require about 1700 tonnes of Nb{sub 3}Sn strand in cable-in-conduit form, about 13,000 tonnes of steel structure, and a cryoplant providing for a heat load of 110 kW at 4.5 K. Selected features of the design, the manufacturing process envisioned and of the R&D program are described.

PQUENCH-A 3-D quench propagation code using a logical coordinate system

A computer program was developed to model the effects of normal region propagation in the longitudinal direction (along the conductor) and in the two transverse directions in a superconducting coil in a multicoil system. A simulation of 3-D quench propagation in real space was done using a logical coordinate system in which each magnet is transformed into a single long conductor which is divided into finite-length elements. Since an element can be associated with geometry-related information such as the element length, the local magnetic field influence coefficients, and the relationship to adjacent elements in 3-D, the quench propagation in any type of 3-D configuration can be simplified to a 1-D problem. As the growth of the normal region is determined, the transient current decay is calculated based on increases in conductor temperature and resistance. This calculation can be done for multiple, inductively coupled systems through the use of a circuit analysis subroutine. The code logic is described, and results are given for calculated versus measured quench times in a single-coil system.

Electrothermal evaluation of conductors for the Compact Ignition Tokamak (CIT) PF coils

The coils in the PF (poloidal field) system for CIT will be cooled to 80 K by liquid nitrogen between each machine pulse. During a pulse, the conductor temperature rises essentially adiabatically. Several conductors have been under consideration. These include an Alloy-718/copper/Alloy-718 laminate, alumina dispersion strengthened (ADS) copper, a laminate of copper and CuNb, and C107 copper. Electrothermal data on these materials are limited; hence, a test program was performed to determine resistivity as a function of temperature from 80 K to 300 K, and to determine the adiabatic characteristic sometimes referred to as the G function or action integral. This is, equivalently, the integral of current density squared over time for the sample or the integral of (density)*(specific heat)/(resistivity) over temperature for the material. The measurements naturally include the nonlinear character of the properties with temperature. The integral is a direct measure of the adiabatic thermal capacity of the material for a specified RMS (root-mean-square) current density over a time interval. Data have been taken on three grades of ADS copper, on laminates of copper and CuNb of two ratios, and on C107 copper. Functions have been computed for copper/Alloy 718 of different ratios. Results are given over the temperature interval from 80 K to 300 K.<<ETX>>

Mechanical evaluation of conductors and joints for the Compact Ignition Tokamak (CIT) central solenoid

The central solenoid for the CIT will be the largest bore diameter, 20/sup +/-Tesla, coil system ever constructed. The stringent design requirements necessitate an integrated conductor and structure. Toward this end, an explosively bonded laminate of Alloy 718/copper/Alloy 718 has been developed, and samples of advanced materials such as aluminum oxide dispersion-strengthened (ODS) copper and CuNb laminated with copper have been tested. Full-scale, explosively bonded Alloy 718/copper/Alloy 718 plates have been obtained from two vendors and tested. The plates consist of 4.76-mm-thick Alloy 718 sheets on each side of 9.53-mm-thick copper. The plate size is about 1778-mm/sup 2/. Results on fatigue lifetime under simulated operating stresses and temperatures have been obtained and are compared with similar data on ODS copper and laminated CuNb and copper. Ultrasonic testing methods and results for the laminate are given. Several joint options have been considered and evaluated for the different conductors. The types of mechanical joints, the initial selection process, the test results for components using 718/copper/718 laminates and results for bolted and pinned components using the same material are outlined.<<ETX>>

Poloidal field coil system optimization for the Compact Ignition Tokamak (CIT)

In the Compact Ignition Tokamak (CIT) design, the poloidal-field coil system (PF) is located symmetrically about the Z=0 plane. The system consists of seven pairs of coils external to the toroidal-field coil system, (TF), and two pairs of coils internal to the TF coils. The external PF coil system has three coils making up the central solenoid, and four ring coils. Previous designs for CIT called for a self-supporting central solenoid (called wedged design because the TF coil inner legs wedged under the radial inward loading) and a PF system capable of providing a flux swing and equilibrium and shaping fields for an 11 MA plasma. The current (bucked) design calls for a 12.3 MA plasma with a central solenoid that is partially supported by, and partially supports, the TF coil inner legs. A comparison of the two design options is made from the PF coil system standpoint. The operating points and structural and thermal requirements of the central solenoid lead to the selection of different conductors for the two cases.<<ETX>>

Evaluation of alumina dispersion strengthened (ODS) copper for possible use in the central solenoid & TF coils for the Compact Ignition Tokamak (CIT)

The tensile, fatigue, and electrical characteristics of small samples of ODS copper indicate that it is an attractive candidate for the conductor in the central solenoid and TF (toroidal-field) coils in the Compact Ignition Tokamak (CIT). It will, however, be necessary to obtain the material in substantially larger sizes than previously produced. The central solenoid requires plates which are about 1900*1900*22 mm (75*75*0.875 in) in size and the TF coils would need plates which are about 120*5300*22 mm (46*210*0.875 in). The status and results from R&D tasks which are underway to prove the feasibility of obtaining these materials and to evaluate the impact of scale-up on the mechanical properties is described. The materials has been obtained in three grades (of different fractional alumina content) in strip, bar, and plate form for initial evaluation. Yield strength, ultimate strength, and fatigue behavior are reported. Review of the results together with metallurgical examination of fractured specimens and the requirements for the tokamak have led to concentration on one grade (0.3-wt.% alumina). Subscale plates have been produced for one of the grades and scale-up to full size is presently underway.<<ETX>>

Bus design, development and test for the Superconducting Super Collider

The power bus to be used in the Superconducting Super Collider magnets must operate in supercritical helium at 4.35 K and about 4 atm. The bus is nominally 17 m in length, must accommodate large differential thermal contractions, and must be amenable to large-quantity, cost-effective production, installation, and joining to adjacent magnets. It must be stable with respect to the largest credible disturbance and be protected in the event of a propagating normal region. Stability and protection requirements are satisfied in the design presented with Super Collider cable for the conductor located between, and soldered to, two copper braids. Variations in the energy margin and in the protection characteristics of the bus as a function of the braid dimensions and channel cooling characteristics are discussed. A stability and quench test program for the bus is underway. Results to date are described, and the status of design and production of full length bus sections is given. >

Compact Ignition Tokamak (CIT) Central Solenoid Design and R&D for a “Bucked” and for a “Wedged” Machine

The CIT design has evolved recently from a system in which the central solenoid outer boundary interacts with the inner legs of the toroidal field coils for mutual radial support during operation, ...

Design and R&D for the central solenoid for the Compact Ignition Tokamak (CIT)

The CIT will require a liquid-nitrogen-cooled, pulsed poloidal field coil system for plasma heating, shaping, and control. The central solenoid will have a bore diameter of 0.8 m, a height of 4.8 m, and a central field of 23-256 T. Geometric restrictions are such that an aggressive structure concept is required. Two options are being considered for the machine. The first would require a self-supporting central solenoid consisting of a stack of explosively bonded copper/Alloy-718 plates with a copper/Alloy-718 ratio of 50/50. Each plate is cut into eight turns by a water-jet cutting process. Features of this design are presented along with selected results from an R&D program under way. Full-scale plates have been fabricated and cut, and prototypical mechanical and electrical joints have been tested. The other machine design option would allow the central solenoid to receive partial support from the TF (toroidal field) coil system. In this case the operating scenario and stresses are substantially different. R&D tasks have been started to evaluate conductor lifetime under simulated operating conditions for alumina dispersion strengthened (ADS) copper. Explosively bonded copper/Alloy-718 plates remain an option, but with a substantial increase in the ratio of copper to Alloy 718 to 70/30. The status of test results and plans for these materials is given.<<ETX>>

Engineering Status of the Fusion Ignition Research Experiment (FIRE)

FIRE is a compact, high field tokamak being studied as an option for the next step in the US magnetic fusion energy program. FIREs programmatic mission is to attain, explore, understand, and optimize alpha-dominated plasmas to provide the knowledge necessary for the design of attractive magnetic fusion energy systems. This study began in 1999 with broad participation of the US fusion community, including several industrial participants. The design under development has a major radius of 2 m, a minor radius of 0.525 m, a field on axis of 10T and capability to operate at 12T with upgrades to power supplies. Toroidal and poloidal field magnets are inertially cooled with liquid nitrogen. An important goal for FIRE is a total project cost in the