HELIAS

A stellarator configuration in which the coils resemble distorted, non-planar toroidal field coils - no continuous helical coils or tokamak-like poloidal field coils are present. The Helias (HELIcal Advanced Stellarator) has been proposed as the most promising stellarator concept for a power plant, with a modular engineering design and optimised plasma, MHD and magnetic field properties. The WENDELSTEIN 7-X device (q.v.) is based on a five field-period Helias configuration.

CYLINDRICAL APPROXIMATION

An approximation to the true tokamak geometry in which the torus is cut and straightened, so that the toroidal direction becomes the cylinder axis. There are two directions of symmetry: along the axis (the ‘toroidal' direction) and about the axis (the ‘poloidal' direction).

COMPASS(-C)(-D)

Compact Assembly: the Culham conventional tokamak facility. COMPASS-C (with circular vacuum vessel) operated from 1989-91; COMPASS-D (with D-shaped vacuum vessel) operated until March 2001. COMPASS-D has a magnetic geometry similar to that of JET and therefore has played an important role in scaling experimental results through JET to ITER. It has been now been transferred to Prague, for experiments by the Czech Association.

E.C.C.D

Electron cyclotron current drive. Non-inductive current drive using ECRH.

DEUTERIUM

A stable isotope of hydrogen, whose nucleus contains one proton and one neutron. Deuterium plasmas are used routinely in present-day experiments; in a fusion power plant the plasma will consist of a mixture of deuterium and tritium which fuse more readily than two deuterium nuclei.