  In order to produce intrinsic rotation, bulk plasmas must be collectively
accelerated by the net force exerted on them, which results from both driving
and damping forces. So, to study the possible mechanisms of intrinsic rotation
generation, it is only needed to understand characteristics of driving and
damping terms because the toroidal driving and damping forces induce net
acceleration which generates intrinsic rotation. Experiments were performed on
EAST and J-TEXT for ohmic plasmas with net counter- and co-current toroidal
acceleration generated by density ramping up and ramping down. Additionally on
EAST, net co-current toroidal acceleration was also formed by LHCD or ICRF. For
the current experimental results, toroidal acceleration was between - 50 km/s^2
in counter-current direction and 70 km/s^2 in co-current direction. According
to toroidal momentum equation, toroidal electric field (E\-(\g(f))),
electron-ion toroidal friction, and toroidal viscous force etc. may play roles
in the evolution of toroidal rotation. To evaluate contribution of each term,
we first analyze characteristics of E\-(\g(f)). E\-(\g(f)) is one of the
co-current toroidal forces that acts on the plasma as a whole and persists for
the entire discharge period. It was shown to drive the co-current toroidal
acceleration at a magnitude of 10^3 km/s^2, which was much larger than the
experimental toroidal acceleration observed on EAST and J-TEXT. So E\-(\g(f))
is one of co-current forces producing cocurrent intrinsic toroidal acceleration
and rotation. Meanwhile, it indicates that there must be a strong
counter-current toroidal acceleration resulting from counter-current toroidal
forces. Electron-ion toroidal friction is one of the counter-current toroidal
forces because global electrons move in the counter-current direction in order
to produce a toroidal plasma current.
