T.J. McManamy

Stability tests of the Westinghouse coil in the International Fusion Superconducting Magnet Test Facility

The Westinghouse coil is one of three forced-flow coils in the six-coil toroidal array of the International Fusion Superconducting Magnet Test Facility. A discussion is presented of results taken when the coil was tested both individually and in the six-coil array. The tests covered charging to full design current and field, when measuring the current-sharing threshold temperature using resistive heaters (installed to simulate nuclear heating), and when measuring the stability margin using pulsed inductive heaters (used to facilitate stability testing). It was found that at least one section of the conductor exhibits a very broad resistive transition (resistive transition index=4). The broad transition, though causing the appearance of voltage at relatively low temperatures, does not compromise the stability margin of the coil, which was greater than 1.1 J/cm/sup 3/ of strands. In another, nonresistive location, the stability margin was between 1.7 and 1.9 J/cm/sup 3/ of strands. This is from six to ten times larger than the value obtained by analyzing the current-sharing threshold. The cause of this discrepancy has been traced to failure of the conductor to obey the ideal critical-state theory. >

The IEA Large Coil Task test results in IFSMTF

The Large Coil Task (LCT) is an international collaboration under the auspices of the International Energy Agency (IEA) among the United States, EURATOM, Japan, and Switzerland to develop large superconducting toroidal field magnets for tokamak fusion reactors. Six 2.5-m*3.5-m bore coils capable of producing 8 T were fabricated, three by the US and one each by the other participants, and assembled in a toroidal array in the International Fusion Superconducting Magnet Test Facility (IFSMTF) at the Oak Ridge National Laboratory (ORNL). The coils were widely different in design with three cooled by pool-boiling helium at atmospheric pressure and three cooled for forced-flow helium at supercritical pressure (1.5 MPa). An overview is given of the various single-coil and six-coil array tests, to design point and beyond, and also the symmetric torus tests that were performed. All six coils exceeded the design goals, both as single coils and in six-coil toroidal tests. In the symmetric torus set, a maximum field of 9 T was reached in all coils simultaneously. Only brief summary is given of the specific thermal and mechanical experiments that were also conducted. >

First results of the full-array LCT coil tests

The international Large Coil Task (LCT) has designed, built, and is testing six different toroidal field coils. Each has a 2.5- × 3.5-m D-shaped bore, a current between 10 and 18 kA, and is designed for stable operation at 8 T. Three coils are bath-cooled; three are cooled by forced flow of helium at supercritical pressure. One uses Nb 3 Sn; the others NbTi. The test coils are equipped with voltage, temperature, magnetic field, flow pressure, strain, displacement, and acoustic emission sensors sufficient for penetrating analysis of performance field. Shakedown operation of the test facility and preliminary tests of the first three coils were accomplished in 1984. Tests of the full six-coil toroidal array began early in 1986 and have progressed to the stage of design-current, design-field stability tests. Results to date have elucidated complex structural and electrical interactions in a multicoil array and provide gratifying assurance of coil performance.

Preliminary results of the U.S. pool-boiling coils from the IFSMTF full-array tests

The Large Coil Task to develop superconducting magnets for fusion reactors, is now in the midst of full-array tests in the International Fusion Superconducting Magnet Test Facility at Oak Ridge National Laboratory. Included in the test array are two pool-boiling coils designed and fabricated by U.S. manufacturers, General Dynamics/Convair Division and General Electric/Union Carbide Corporation. So far, both coils have been energized to full design currents in the single-coil tests, and the General Dynamics coil has reached the design point in the first Standard-I full-array test. Both coils performed well in the charging experiments. Extensive heating tests and the heavy instrumentation of these coils have, however, revealed some generic limitations of large pool-boiling superconducting coils. Details of these results and their analyses are reported.

EXPERIENCE WITH COOLDOWN OF SUPERCONDUCTING MAGNET COILS IN THE LARGE COIL TASK

Six superconducting toroidal field coils have been tested in the Large Coil Task. In three coils, conductors are bath cooled. Three have conductors cooled by internal flow of helium. Coils provided by JAERI and EURATOM were cooled first in single-coil facilities at Naka and Karlsruhe. In the International Fusion Superconducting Magnet Test Facility (IFSMTF) at Oak Ridge, the 420,000-kg, six-coil array was successfully cooled to operating temperature early in 1986. Analysis of the IFSMTF data and comparison with cooldown of magnets in other facilities provided better understanding of massive, multicomponent arrays.

Test results of the US-LCT pool-boiling coils in the International Fusion Superconducting Magnet Test Facility (IFSMTF)

The international Large Coil Task (LCT) designed, built, and successfully tested six different toroidal-field coils. Included in the torus are two pool-boiling coils designed and fabricated by US firms, General Dynamics/Convair Division (GD) and General Electric/Oak Ridge National Laboratory (GE). Both coils were instrumented for studies of electromagnetic, mechanical and thermodynamic properties and performed well and met design specifications. The authors summarize the complete test results, including the extended-condition test in which both coils demonstrated capability for operation beyond design points. The highlights of all major experiments since April 1987 that involved the GD or GE coils are presented in tabular form. In the extended-condition tests, both coils operated stably at 100% design current and above 9 T, even with bath temperature higher than 4.3 K. The mechanical behavior of both coils was generally in good agreement with calculations. Both coils were also safely discharged several times in the extended-condition tests. All results indicate that the technology developed for these two pool-boiling LCT coils can be directly applied for future large-scale applications. >

Testing of the Euratom LCT coil in the toroidal arrangement of the International Fusion Superconducting Magnet Test Facility without external pulsed fields (standard-I) and with them (standard II) and an extended single-coil test

In this test, the coil reached (in stable operation) a field of 9 T at 140% of rated current. It reached the short-sample values of the strands used in the cable. The coil was operated up to 8 T with and without poloidal field transients in a toroidal configuration. The mass flow rate was reduced by a factor of 5 compared with the design value without any visible impact on stability. Averaged AC losses (winding, 14 W; case, 7 W) were measured under Large Coil Task (LCT)-specified poloidal field pulses, and the findings agreed with those of the short-sample measurements. The coils mechanical properties, which behaved as theoretically predicted, are also reported. All results obtained are thought to demonstrate that the applied technology has achieved reliable engineering standards. >

Single Magnet Test Results of the First EBT-P Development Magnet

The first development coil (D1) for the ELMO Bumpy Torus Proof-of-Principle (EBT-P) machine was successfully tested1 in a large “bucket” dewar — the “open dewar test”. Since then, it has been welded closed and installed in an individual dewar by a McDonnell Douglas/General Dynamics magnet development team. During the open dewar test, the bath contained 500 to 600 L of liquid helium surrounding the coil. In contrast, there is only a volume of about 15 L left for helium inside the individual dewar. This, plus the heat load introduced by the support structure, changed the cryogenic environment of the coil.

EBT-P Magnet Development Program summary

The ELMO Bumpy Torus Proof-of-Principle Magnet Development Program, which began in 1979, has fabricated and tested three NbTi superconducting magnets. The magnets are metastable with a maximum winding pack current density of 10,000 A/cm2at a peak field of 7.4 T. Each magnet has been installed in a close-fitting dewar with a warm bore. Previous publications have reported successful tests of the first two windings in a large dewar, tests of the first complete magnet in its own dewar, and construction details of the dewars. This paper gives procedures and results for the test of the third winding in an open dewar, the test of the second single magnet in its own dewar, and two tests in which two magnets were run in series to generate a 73,000-lb side load at 5 T. The last tests verified the mechanical integrity of the design and qualified two of the magnets for use in the National Radio Frequency Test Facility.