Design, Construction, and Operation of the Compact Toroidal Hybrid

Abstract

The Compact Toroidal Hybrid (CTH) is a low-aspect-ratio (), low-beta (%) torsatron with a major radius of . CTH is operable as a pure stellarator, but most research on this device is conducted with hybrid discharges in which a toroidal plasma current is driven in order to study magnetohydrodynamic instabilities and disruptions in current-carrying stellarator plasmas. The vacuum helical field of CTH is produced by a continuously wound helical coil with poloidal and toroidal periodicities of and , respectively. The maximum on-axis toroid al magnetic field is . The helical coil encloses a circular vacuum vessel of major radius = 0.75 m with a circular cross section of minor radius 0.29 m. A toroidal plasma current up to 80 kA is produced with an ohmic heating (OH) transformer. The average plasma radius is typically 0.20 m. Five independently controllable magnet coil sets produce the base stellarator magnetic field configuration. With 15-kW electro.n cyclotron heating at the fundamental frequency, densities of and electron temperatures of 20 eV are achieved. With the addition of OH, densities reach with temperatures of . Ten motor/generator power supplies provide up to 10 MW of power to energize the magnet set providing the equilibrium field, and a capacitor bank provides the pulsed current for the OH system. Design considerations, constraints, and construction techniques of the CTH magnet coils, vacuum vessel, and support structure are discussed, and an operational overview is given.

Keywords:

• Magnetic confinement
• stellarator
• torsatron

Acknowledgments

The authors thank T. Brown of the PPPL for designing the helical coil frame and T. Bigelow of Oak Ridge National Laboratory for his assistance with the installation of the ECRH systems and loan of related equipment. We also are grateful to the Massachusetts Institute of Technology and the University of Wisconsin for the donation of the ten flywheel motor generators to this project. The HSX group at the University of Wisconsin and the engineering staff at PPPL also generously provided useful advice on vacuum epoxy potting of our large coil sets and in numerous other areas. D. Anderson and S. Anderson with the HSX group at the University of Wisconsin have also provided valuable advice on stellarator construction. The authors also thank our current and previous engineering technicians, J. Dawson, C. Montgomery, and D. Forester, for their valuable assistance, as well as the many graduate and undergraduate students who participated in the construction and operation of the CTH device. This work is supported by U.S. Department of Fusion Energy Science, U.S. Department of Energy grant DE-FG-02-00ER54610.

Notes

^a The vacuum vessel was manufactured by Spincraft, Inc., North Billerica, Massachusetts; http://www.spincraft.net/.

^b The HF frame system was designed by T. Brown at the Princeton Plasma Physics Laboratory (PPPL).

^c Construction of the frame pieces was handled by J. P. Pattern, Inc., Milwaukee, Wisconsin; http://www.jppattern.com/.

^d The HF and TF conductors were manufactured by New England Wire Technologies, Lisbon, New Hampshire; http://www.newenglandwire.com/.

^e The OH coils were manufactured by Alpha Magnetics, Inc., Hayward, California; http://www.alphamag.com/.

^f The TVFD and SVFD coils were manufactured by New England Technicoil, Wolfeboro, New Hampshire; http://www.technicoil.com/.