  A method is proposed to control the transverse motion and X-ray emission of
an electron beam in a laser driven wakefield by tuning the laser spatial chirp.
The dispersion of a transversely chirped laser pulse and the transverse
nonuniform refractive index of the plasma channel result in transverse laser
centroid oscillations, which leads to periodic transverse oscillations of the
laser-driven wake. Electrons accelerated inside the wake also undergo
transverse oscillations making wiggler like motion. Both the oscillation period
and amplitude can be controlled by tuning the laser chirp, the pulse duration
or the plasma channel width. As a result, the far field spectral distributions
of the X-ray emission can be flexibly manipulated.
