Patent Number: 046631097
Section: claims

1. A closed, curved, planar toroidal field coil for use on a stellarator having a helical axis, said coil having a radius r.sub.o, pitch kr.sub.o and period m, the curve of said coil being defined in .rho., .theta. coordinates by the relationship: EQU .rho.=a.sub.c +.delta..sub.2 cos 2.theta.+.delta..sub.3 cos 3.theta. where a.sub.c, .delta..sub.2, and .delta..sub.3 are constants and at least one of .sub.2 and .sub.3 is not equal to zero and wherein a.sub.c, .delta..sub.2, and .delta..sub.3 satisfy the relationship: ##EQU6## and .delta..sub.2 .noteq.0 and .delta..sub.3 .noteq.0. 2. The coil of claim 1 wherein the curve of said coil is substantially "D" shaped. 3. The coil of claim 1 wherein the curve of said coil is substantially "bean" shaped. 4. The coil of claim 1 wherein kr.sub.o =1, .delta..sub.2 /a.sub.c =-0.3, and .delta..sub.3 /a.sub.c =-0.1. 5. Apparatus for confining a plasma comprising: a closed endless tube; and  a plurality of closed, curved, planar coils spaced about said tube, the centers of said coils defining a helical axis, said helical axis having a radius r.sub.o, pitch kr.sub.o and period m and being substantially parallel to the axis of said tube, the plane of each coil being substantially perpendicular to said helical axis, the curve of each coil being defined in .rho., .theta. coordinates by the relationship: EQU .rho.=a.sub.c +.delta..sub.2 cos 2.theta.+.delta..sub.3 cos 3.theta., 6. The apparatus of claim 5 wherein the axis of said tube is coaxial with the helical axis of said coils. 7. The apparatus of claim 6 wherein kr.sub.o =1, .delta..sub.2 /a.sub.c =-0.3, and .delta..sub.3 /a.sub.c =-0.1.