Design, Construction, and Operation of the Compact Toroidal Hybrid

The Compact Toroidal Hybrid (CTH) is a low-aspect-ratio (A >= 3.5), low-beta (beta <= 0.1%) torsatron with a major radius of R-0 - 0.75 m. 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, - 2 and m - 5, respectively. The maximum on-axis toroid al magnetic field is B-0 - 0.7 T. The helical coil encloses a circular vacuum vessel of major radius R-0 = 0.75 m with a circular cross section of minor radius a - 0.29 m. A toroidal plasma current up to I-p - 80 kA is produced with an ohmic heating (OH) transformer. The average plasma radius is typically a(p) <= 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 ne <= 2.5 x 10(18) m(-3) and electron temperatures of T-e <= 20 eV are achieved. With the addition of OH, densities reach n(e) <= 5.0 x10(19) m(-3) with temperatures of T-e <= 200 eV. 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.