AbstractThis paper reviews progress and unsolved fundamental problems in the turbulence study by the use of a heavy ion beam probe for the TEXT and JIPP TIIU tokamaks. The most serious problems are as follows. (1) The propagation velocity of the turbulence is faster than the fluid velocity. (2) Large fluctuation of the secondary beam energy up to several hundred electronvolts is observed. It is difficult to ascribe this to the plasma potential fluctuation. A probable mechanism is the resonant interaction of the beam with the tokamak turbulence. (3) The level of the magnetic fluctuation measured with a heavy ion beam probe is much greater than the level measured with the magnetic probe at the plasma boundary.