Plasma Confinement in Hybrid Stellarator with l=2 and l=3 Helical Field

Dependences of plasma transport on the rotational transform angle and the shear as well as the plasma parameters are studied using JIPP Ib stellarator which is equipped with both l =2 and l =3 helical windings. The properties of the resonant losses observed in the afterglow plasmas in the rational cases of the l =2 stellarator field are investigated and the shear effect on the resonant losses is examined by superposing the l =3 helical field. It is found that the plasma loss is due to the onset of dissipative drift instability. The observed properties of the fluctuations such as the frequency, the wave propagation etc. can be explained by the instability. The introduction of weak shear (shear length L s ∼300 cm) reduces the resonant loss in our experimental conditions.