Abstract <p>The surface layer of highly oriented pyrolytic graphite after irradiation with argon ions with energies from 10 to 30 keV and fluences up to 10¹⁹ ion/cm² in the target temperature range from room temperature to 600°C has been experimentally studied. The regularities of the irradiated layer surface change are compared with the known regularities of changes in the morphology and dimensions of pyrolytic graphites under irradiation with fast reactor neutrons. It is found that above the critical fluence of ion irradiation of highly oriented pyrolytic graphite, a sharp increase in the roughness amplitude <i>R</i> of the surface with columnar-acicular morphology occurs, which is several orders of magnitude greater than the projective range <i>R</i>_p of ions. It is shown that the temperature range corresponding to the maximum values of the amplitude of the surface roughness is close to the temperature range of intense radiation-induced deformation of graphite under neutron irradiation, leading to its secondary swelling. An assessment of the critical fluence of the formation of columnar-acicular morphology at an argon ion irradiation energy of 10 to 30 keV is carried out. The measured levels of critical ion fluence, expressed as the number of radiation displacements, after their correction, taking into account the differences in the efficiency of radiation damage by neutrons and ions, can be used to assess the resistance of nuclear carbon materials using simulated ion irradiation.</p>