Analytical field results for stellerator/torsatron configurations
The simple winding law of constant pitch for the current density distribution in fully toroidal coordinates gives rise to particular magnetic field configurations. The quasi-separable solution for the scalar potential and fields in such coordinates is applied, using Green's function. The spectrum of scalar multipolar harmonics generated is derived analytically. This spectrum has contributions from the toroidal number (n) and from an infinity of poloidal numbers (m); however a truncation of the sum to low order (less than 10) is sufficient for m=1, 2, 3 stellarator/torsatron configurations. The resulting analytical fields produce closed magnetic surfaces for arbitrary m/n number and arbitrary low aspect ratios (R/a). The superposition of a vertical field produced from the n=0 limit of the same winding law allows edge rotational transform of unity, even at aspect ratios as low as 3. Magnetic or Boozer coordinates are easily evaluated on such configurations, exploiting the line field tracing and the analytical knowledge at the scalar potential. High energy and alpha particle containment on such low aspect ratio is studied in these magnetic coordinates. Examples of the vacuum magnetic surfaces are shown for a few low aspect ratio stellarator and torsatron configurations. The resilience of such magnetic configurations to helical and vertical field coils errors is explored, showing a remarkable solidity of the configuration. A preliminary assessment of the equilibrium properties is obtained using the VMEC code.
Bibliographic Reference: Report: RT/FUS/89/8 EN (1989) 13 pp.
Availability: Available from Servizio Studi e Documentazione, ENEA, Centro Ricerche Energia Frascati, C.P.65-00044 Frascati, Roma (IT)
Record Number: 199011305 / Last updated on: 1994-12-01
Original language: en
Available languages: en