Measurements of the tokamak safety factor profile by means of driven resonant Alfven waves

Alfven waves are launched in the TCA tokamak (R, a=0.61, 0.18 m, Bφ=0.78-1.51 T, Ip≤170kA and ne≤1.5x1020 m-3) by an external antenna structure. An Alfven resonance occurs wherever the local Alfven velocity matches the externally imposed wave velocity, ω/kparallel. In the large aspect ratio approximation the resonance condition can be written as, ω2ρ(0)=K[n+m/q(r)]2/[ρ(r)/ρ(0)], where (n,m) are the toroidal and poloidal mode numbers respectively, ρ(r) is the local mass density, and q(r) is the local safety factor. When the central line densities for which the resonance condition is satisfied at a given radius are known for two identical discharges, with, for example, (n,m)=(1,1) and (2,0) excitation, the local value of q can be obtained directly. (author) 3 refs., 4 figs