  A new synergy mechanism between Ohkawa current drive (OKCD) of electron
cyclotron (EC) waves and lower hybrid current drive (LHCD) is discovered and
discussed. And the methodology to achieve this synergy effect is also
introduced. Improvement of OKCD efficiency can be achieved up to a factor of ~
2.5 in far off-axis radial region (\r{ho} > 0.6) of tokamak plasmas. Making EC
wave heating the electrons of co-Ip direction and LH wave heating the electrons
of counter-Ip direction, the mechanism of this new synergy effect comes from
the results of electron trapping and detrapping processes. The OKCD makes the
low speed barely passing electrons to be trapped (trapping process), the LHCD
pulls some of the high speed barely trapped electrons out of the trapped region
in velocity space (detrapping process) and accelerates the detrapped electrons
to a higher speed.
