  Laser wakefield accelerators (LWFA) hold great potential to produce
high-quality high-energy electron beams (e beams) and simultaneously bright
x-ray sources via betatron radiation, which are very promising for pump-probe
study in ultrafast science. However, in order to obtain a high-quality e beam,
electron injection and acceleration should be carefully manipulated, where a
large oscillation amplitude has to be avoided and thus the emitted x-ray yield
is limited. Here, we report a new scheme to experimentally enhance betatron
radiation significantly both in photon yield and photon energy by separating
electron injection and acceleration from manipulation of the e-beam transverse
oscillation in the wake via introducing a slanted thin plasma refraction slab.
Particle-in-cell simulations indicate that the e-beam transverse oscillation
amplitude can be increased by more than 10 folds, after being steered into the
deflected laser-driven wakefield due to refraction at the slab's boundaries.
Spectral broadening of the x-rays can be suppressed owing to the small
variation in the peak energy of the low-energy-spread e beam in a plasma
wiggler regime. We demonstrate that the high-quality e-beam generation,
refracting and wiggling can act as a whole to realize the concurrence of
monoenergetic e beam and bright x-rays in a compact LWFA.
