The micreinstabilities driven by a pardel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyrekinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower, and the threshold temperature gradient q k is higher €or plasmas with negative magnetic shear compared to plasmas with p'ositive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insigdicant , does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed.
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