[en] For the investigation of the plasma density and potential in the TJ-1 tokamak, we applied the heavy ion beam probe (HIBP) diagnostics with the beam energy up to 100 keV. The geometry of the experiment allows us to observe the whole plasma cross section and to catch the primary beam for direct calibration. HIBP on TJ-1 operates in two modes: shot-by-shot measurements which allow us to obtain the time evolution of the plasma parameters at every desired point of the detector grid, and scanning along the detector line (generally passing through the center) in the single shot which allows us to get a few profiles of the plasma parameters. When scanning we varied the injection angle with a period less than 2 ms. The spatial resolution of measurements was 2 endash 5 mm. The bandwidth used (∼20 kHz) allows us to see the slow oscillations of the potential and density. The measurements were performed in the regimes with the magnetic field B=1.1 endash 1.4 T, current I=26 endash 32 kA, and the shot duration up to 25 ms. HIBP on TJ-1 enables us to measure simultaneously the time-spatial evolution of the potential and density; that makes HIBP a powerful tool for direct investigation of the transport processes in the plasma driven by the radial electric field. copyright 1997 American Institute of Physics